SWITCHMODE™ Power Supply Reference Manual

SMPSRM/DRev. 3, Jul-2002SWITCHMODE PowerSupply Reference Manual

SWITCHMODE Power SuppliesReference Manual and Design GuideSMPSRM/DRev. 3, July–2002© SCILLC, 2002Previous Edition © 2000“All Rights Reserved’’

SMPSRMON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to makechanges without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for anyparticular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and allliability, including without limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/orspecifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must bevalidated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others.SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applicationsintended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or deathmay occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLCand its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney feesarising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges thatSCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer.PUBLICATION ORDERING INFORMATIONLiterature Fulfillment:Literature Distribution Center for ON SemiconductorP.O. Box 5163, Denver, Colorado 80217 USAPhone: 303–675–2175 or 800–344–3860 Toll Free USA/CanadaFax: 303–675–2176 or 800–344–3867 Toll Free USA/CanadaEmail: ONlit@hibbertco.comN. American Technical Support: 800–282–9855 Toll Free USA/CanadaJAPAN: ON Semiconductor, Japan Customer Focus Center4–32–1 Nishi–Gotanda, Shinagawa–ku, Tokyo, Japan 141–0031Phone: 81–3–5740–2700Email: r14525@onsemi.comON Semiconductor Website: http://onsemi.comFor additional information, please contact your localSales Representative.http://onsemi.com2

ForwardSMPSRMEvery new electronic product, except those that are battery powered, requires converting off–line115 Vac or 230 Vac power to some dc voltage for powering the electronics. The availability of designand application information and highly integrated semiconductor control ICs for switching powersupplies allows the designer to complete this portion of the system design quickly and easily.Whether you are an experienced power supply designer, designing your first switching powersupply or responsible for a make or buy decision for power supplies, the variety of informationin the SWITCHMODE Power Supplies Reference Manual and Design Guide should proveuseful.ON Semiconductor has been a key supplier of semiconductor products for switching power suppliessince we introduced bipolar power transistors and rectifiers designed specifically for switchingpower supplies in the mid–70’s. We identified these as SWITCHMODE products. A switchingpower supply designed using ON Semiconductor components can rightfully be called aSWITCHMODE power supply or SMPS.This brochure contains useful background information on switching power supplies for those whowant to have more meaningful discussions and are not necessarily experts on power supplies. It alsoprovides real SMPS examples, and identifies several application notes and additional designresources available from ON Semiconductor, as well as helpful books available from variouspublishers and useful web sites for those who are experts and want to increase their expertise. Anextensive list and brief description of analog ICs, power transistors, rectifiers and other discretecomponents available from ON Semiconductor for designing a SMPS are also provided. Thisincludes our newest GreenLine, Easy Switcher and very high voltage ICs (VHVICs), as well ashigh efficiency HDTMOS® and HVTMOS® power FETs, and a wide choice of discrete productsin surface mount packages.For the latest updates and additional information on analog and discrete products for power supply andpower management applications, please visit our website: (http://onsemi.com).MEGAHERTZ, POWERTAP, SENSEFET, SWITCHMODE, and TMOS are trademarks of Semiconductor Components Industries,LLC. HDTMOS and HVTMOS are registered trademarks of Semiconductor Components Industries, LLC.GreenLine, SMARTMOS and Motorola are trademarks of Motorola Inc.http://onsemi.com3

SMPSRMIntroductionThe never–ending drive towards smaller and lighterproducts poses severe challenges for the power supplydesigner. In particular, disposing of excess heatgenerated by power semiconductors is becoming moreand more difficult. Consequently it is important that thepower supply be as small and as efficient as possible, andover the years power supply engineers have responded tothese challenges by steadily reducing the size andimproving the efficiency of their designs.Switching power supplies offer not only higherefficiencies but also greater flexibility to the designer.Recent advances in semiconductor, magnetic and passivetechnologies make the switching power supply an evermore popular choice in the power conversion arena.This guide is designed to give the prospective designeran overview of the issues involved in designingswitchmode power supplies. It describes the basicoperation of the more popular topologies of switchingpower supplies, their relevant parameters, providescircuit design tips, and information on how to select themost appropriate semiconductor and passivecomponents. The guide also lists the ON Semiconductorcomponents expressly built for use in switching powersupplies.Linear versus SwitchingPower SuppliesSwitching and linear regulators use fundamentallydifferent techniques to produce a regulated outputvoltage from an unregulated input. Each technique hasadvantages and disadvantages, so the application willdetermine the most suitable choice.Linear power supplies can only step–down an inputvoltage to produce a lower output voltage. This is doneby operating a bipolar transistor or MOSFET pass unit inits linear operating mode; that is, the drive to the pass unitis proportionally changed to maintain the required outputvoltage. Operating in this mode means that there isalways a headroom voltage, Vdrop, between the inputand the output. Consequently the regulator dissipates aconsiderable amount of power, given by (Vdrop Iload).This headroom loss causes the linear regulator to onlybe 35 to 65 percent efficient. For example, if a 5.0 Vregulator has a 12 V input and is supplying 100 mA, itmust dissipate 700 mW in the regulator in order to deliver500 mW to the load , an efficiency of only 42 percent.The cost of the heatsink actually makes the linearregulator uneconomical above 10 watts for smallapplications. Below that point, however, linearregulators are cost–effective in step–down applications.A low drop–out (LDO) regulator uses an improvedoutput stage that can reduce Vdrop to considerably lessthan 1.0 V. This increases the efficiency and allows thelinear regulator to be used in higher power applications.Designing with a linear regulator is simple and cheap,requiring few external components. A linear design isconsiderably quieter than a switcher since there is nohigh–frequency switching noise.Switching power supplies operate by rapidly switchingthe pass units between two efficient operating states:cutoff, where there is a high voltage across the pass unitbut no current flow; and saturation, where there is a highcurrent through the pass unit but at a very small voltagedrop. Essentially, the semiconductor power switchcreates an AC voltage from the input DC voltage. ThisAC voltage can then be stepped–up or down bytransformers and then finally filtered back to DC at itsoutput. Switching power supplies are much moreefficient, ranging from 65 to 95 percent.The downside of a switching design is that it isconsiderably more complex. In addition, the outputvoltage contains switching noise, which must beremoved for many applications.Although there are clear differences between linearand switching regulators, many applications require bothtypes to be used. For example, a switching regulator mayprovide the initial regulation, then a linear regulator mayprovide post–regulation for a noise–sensitive part of thedesign, such as a sensor interface circuit.Switching Power SupplyFundamentalsThere are two basic types of pulse–width modulated(PWM) switching power supplies, forward–mode andboost–mode. They differ in the way the magneticelements are operated. Each basic type has its advantagesand disadvantages.The Forward–Mode ConverterThe forward–mode converter can be recognized by thepresence of an L–C filter on its output. The L–C filtercreates a DC output voltage, which is essentially thevolt–time average of the L–C filter’s input ACrectangular waveform. This can be expressed as:Vout Vin duty cycle (eq. 1)The switching power supply controller varies the dutycycle of the input rectangular voltage waveform and thuscontrols the signal’s volt–time average.The buck or step–down converter is the simplestforward–mode converter, which is shown in Figure 1.http://onsemi.com5

SMPSRMSWL OV inI onDI offC outR loadDIODE VOLTAGE(VOLTS)PowerSwitchONV satPowerSwitchOFFPowerSwitchONPowerSwitchOFFTIMEINDUCTOR CURRENT(AMPS)I pkI minV fwdI loadPower SW Diode Power SW DiodeTIMEFigure 1. A Basic Forward–Mode Converter and Waveforms (Buck Converter Shown)Its operation can be better understood when it is brokeninto two time periods: when the power switch is turnedon and turned off. When the power switch is turned on,the input voltage is directly connected to the input of theL–C filter. Assuming that the converter is in asteady–state, there is the output voltage on the filter’soutput. The inductor current begins a linear ramp from aninitial current dictated by the remaining flux in theinductor. The inductor current is given by:iL(on) (V in Vout ) t Liinit 0 t ton (eq. 2)During this period, energy is stored as magnetic fluxwithin the core of the inductor. When the power switchis turned off, the core contains enough energy to supplythe load during the following off period plus somereserve energy.When the power switch turns off, the voltage on theinput side of the inductor tries to fly below ground, but isclamped when the catch diode D becomes forwardbiased. The stored energy then continues flowing to theoutput through the catch diode and the inductor. Theinductor current decreases from an initial value i pk and isgiven by:iL(off) ipk V outt0 t Ltoff (eq. 3)The off period continues until the controller turns thepower switch back on and the cycle repeats itself.The buck converter is capable of over one kilowatt ofoutput power, but is typically used for on–board regulatorapplications whose output powers are less than 100 watts.Compared to the flyback–mode converter, the forwardconverter exhibits lower output peak–to–peak ripplevoltage. The disadvantage is that it is a step–downtopology only. Since it is not an isolated topology, forsafety reasons the forward converter cannot be used forinput voltages greater than 42.5 VDC.http://onsemi.com6

SMPSRMThe Flyback–Mode ConverterThe basic flyback–mode converter uses the samecomponents as the basic forward–mode converter, but ina different configuration. Consequently, it operates in adifferent fashion from the forward–mode converter. Themost elementary flyback–mode converter, the boost orstep–up converter, is shown in Figure 2.LDC outV inIonSWI offI loadR loadV inSWITCH VOLTAGE(VOLTS)PowerSwitchONV satDiodeONV flbk(V out )PowerSwitchONDiodeONPowerSwitchONTIMEINDUCTOR CURRENT(AMPS)I pkI loadTIMEFigure 2. A Basic Boost–Mode Converter and Waveforms (Boost Converter Shown)Again, its operation is best understood by considering the“on” and “off” periods separately. When the powerswitch is turned on, the inductor is connected directlyacross the input voltage source. The inductor current thenrises from zero and is given by:iL(on) V int t L0on (eq. 4)Energy is stored within the flux in the core of the inductor.The peak current, i pk , occurs at the instant the powerswitch is turned off and is given by:ipk V in ton(eq. 5)LWhen the power switch turns off, the switched side ofthe inductor wants to fly–up in voltage, but is clamped bythe output rectifier when its voltage exceeds the outputvoltage. The energy within the core of the inductor is thenpassed to the output capacitor. The inductor currentduring the off period has a negative ramp whose slope isgiven by:iL(off) (V in Vout)L(eq. 6)The energy is then completely emptied into the outputcapacitor and the switched terminal of the inductor fallsback to the level of the input voltage. Some ringing isevident during this time due to residual energy flowingthrough parasitic elements such as the stray inductancesand capacitances in the circuit.http://onsemi.com7

SMPSRMWhen there is some residual energy permitted toremain within the inductor core, the operation is calledcontinuous– mode. This can be seen in Figure 3.Energy for the entire on and off time periods must bestored within the inductor. The stored energy is definedby:EL 0.5L ipk 2 (eq. 7)The boost–mode inductor must store enough energy tosupply the output load for the entire switching period (t on+ t off ). Also, boost–mode converters are typically limitedto a 50 percent duty cycle. There must be a time periodwhen the inductor is permitted to empty itself of itsenergy.The boost converter is used for board–level (i.e.,non–isolated) step–up applications and is limited to lessthan 100–150 watts due to high peak currents. Being anon–isolated converter, it is limited to input voltages ofless than 42.5 VDC. Replacing the inductor with atransformer results in a flyback converter, which may bestep–up or step–down. The transformer also providesdielectric isolation from input to output.SWITCH VOLTAGE(VOLTS)V inPowerSwitchONDiodeONV flbk(V out )PowerSwitchONDiodeONTIMEINDUCTOR CURRENT(AMPS)V satI pkTIMEFigure 3. Waveforms for a Continuous–Mode Boost ConverterCommon SwitchingPower Supply TopologiesA topology is the arrangement of the power devicesand their magnetic elements. Each topology has its ownmerits within certain applications. There are five majorfactors to consider when selecting a topology for aparticular application. These are:1. Is input–to–output dielectric isolation required forthe application? This is typically dictated by thesafety regulatory bodies in effect in the region.2. Are multiple outputs required?3. Does the prospective topology place a reasonablevoltage stress across the power semiconductors?4. Does the prospective topology place a reasonablecurrent stress upon the power semiconductors?5. How much of the input voltage is placed acrossthe primary transformer winding or inductor?Factor 1 is a safety–related issue. Input voltages above42.5 VDC are considered hazardous by the safetyregulatory agencies throughout the world. Therefore,only transformer–isolated topologies must be used abovethis voltage. These are the off–line applications where thepower supply is plugged into an AC source such as a wallsocket.Multiple outputs require a transformer–basedtopology. The input and output grounds may beconnected together if the input voltage is below42.5 VDC. Otherwise full dielectric isolation is required.http://onsemi.com8

SMPSRMFactors 3, 4 and 5 have a direct affect upon thereliability of the system. Switching power suppliesdeliver constant power to the output load. This power isthen reflected back to the input, so at low input voltages,the input current must be high to maintain the outputpower. Conversely, the higher the input voltage, thelower the input current. The design goal is to place asmuch as possible of the input voltage across thetransformer or inductor so as to minimize the inputcurrent.Boost–mode topologies have peak currents that areabout twice those found in forward–mode topologies.This makes them unusable at output powers greater than100–150 watts.Cost is a major factor that enters into the topologydecision. There are large overlaps in the performanceboundaries between the topologies. Sometimes the mostcost–effective choice is to purposely design one topologyto operate in a region that usually is performed byanother. This, though, may affect the reliability of thedesired topology.Figure 4 shows where the common topologies are usedfor a given level of DC input voltage and required outputpower. Figures 5 through 12 show the commontopologies. There are more topologies than shown, suchas the Sepic and the Cuk, but they are not commonlyused.1000Half–BridgeDC INPUT VOLTAGE (V)10042.510FlybackNon–IsolatedBuckFull–BridgeFull–BridgeVery HighPeak Currents10100OUTPUT POWER (W)1000Figure 4. Where Various Topologies Are Usedhttp://onsemi.com9

SMPSRM+V in–C inPower SwitchControlLDVC in in+Control SW +C out V outV DI LOAD IMINLV FWD+0V inD+ V outC outI LFeedback–0Figure 5. The Buck (Step–Down) ConverterV FLBKDV SWV SAT ONSW ON–I LV inI PKFigure 6. The Boost (Step–Up) Converter00I PKI SWI DDONTIMETIMETIMETIME+Control SWDV in C in–+L C out V out–+FeedbackV LI L00I SWI DV inI PK–V outTIMETIMEFigure 7. The Buck–Boost (Inverting) ConverterV FLBK+N1 N2CinV inControlSWDC out++V out–V SW0I PRI0V inV SATI PKSWONTIMETIME–FeedbackI SEC0TIMEFigure 8. The Flyback Converterhttp://onsemi.com10

SMPSRM+N1 N2C inV inControlTSWDL OC out++V out––FeedbackSWV SWON02VV in SATI PRI0I MIN I PKTIMETIMEFigure 9. The One–Transistor Forward Converter (Half Forward Converter)SW1TD1L O++V inC inControlSW2D2C out+V out––Feedback2V inV inSW 2V SW0SW 1TIMEV SATI PKI PRI0TIMEI MINFigure 10. The Push–Pull Converterhttp://onsemi.com11

SMPSRML ODs++C outV out+C inControlXFMRSW1SW2N2N1TCC–V in0–FeedbackV inSW 1V in2V SW2SW 2TIMEV SATI PRII MINI PK0TIMEFigure 11. The Half–Bridge ConverterL ODsC out++V out+V inC inControlXFMRSW1SW2N2N1TSW3CSW4XFMR––SWV in2V SW2 0V SATSW2-31-4TIMEI SW2I MINV inI PK0TIMEFigure 12. The Full–Bridge Converterhttp://onsemi.com12

SMPSRMInterleaved Multiphase ConvertersOne method of increasing the output power of anytopology and reducing the stresses upon thesemiconductors, is a technique called interleaving. Anytopology can be interleaved. An interleaved multiphaseconverter has two or more identical converters placed inparallel which share key components. For an n–phaseconverter, each converter is driven at a phase differenceof 360/n degrees from the next. The output current fromall the phases sum together at the output, requiring onlyI out /n amperes from each phase.The input and output capacitors are shared among thephases. The input capacitor sees less RMS ripple currentbecause the peak currents are less and the combined dutycycle of the phases is greater than it would experiencewith a single phase converter. The output capacitor canbe made smaller because the frequency of currentwaveform is n–times higher and its combined duty cycleis greater. The semiconductors also see less currentstress.A block diagram of an interleaved multiphase buckconverter is shown in Figure 13. This is a 2–phasetopology that is useful in providing power to a highperformance microprocessor.++–V FDBKControlGNDC FAV IN C IN+S A1L AGATEA1GATEA2GATEB2GATEB1S A2S B1L B+C OUT V OUT–C FBCS5308S B2Voltage FeedbackCurrent Feedback ACurrent Feedback BFigure 13. Example of a Two–Phase Buck Converter with Voltage and Current Feedbackhttp://onsemi.com13

SMPSRMSelecting the Method of ControlThere are three major methods of controlling aswitching power supply. There are also variations ofthese control methods that provide additional protectionfeatures. One should review these methods carefully andthen carefully review the controller IC data sheets toselect the one that is wanted.Table 1 summarizes the features of each of the popularmethods of control. Certain methods are better adapted tocertain topologies due to reasons of stability or transientresponse.Table 1. Common Control Methods Used in ICsControl Method OC Protection Response Time Preferred TopologiesAverage OC Slow Forward–ModeVoltage–ModePulse–by–Pulse OC Slow Forward–ModeIntrinsic Rapid Boost–ModeCurrent–ModeHysteretic Rapid Boost & Forward–ModeHysteric Voltage Average Slow Boost & Forward–ModeVoltage–mode control (see Figure 14) is typically usedfor forward–mode topologies. In voltage–mode control,only the output voltage is monitored. A voltage errorsignal is calculated by forming the difference betweenVout (actual) and Vout(desired). This error signal is thenfed into a comparator that compares it to the ramp voltagegenerated by the internal oscillator section of the controlIC. The comparator thus converts the voltage error signalinto the PWM drive signal to the power switch. Since theonly control parameter is the output voltage, and there isinherent delay through the power circuit, voltage–modecontrol tends to respond slowly to input variations.Overcurrent protection for a voltage–mode controlledconverter can either be based on the average outputcurrent or use a pulse–by–pulse method. In averageovercurrent protection, the DC output current ismonitored, and if a threshold is exceeded, the pulse widthof the power switch is reduced. In pulse–by–pulseovercurrent protection, the peak current of each powerswitch “on” cycle is monitored and the power switch isinstantly cutoff if its limits are exceeded. This offersbetter protection to the power switch.Current–mode control (see Figure 15) is typically usedwith boost–mode converters. Current–mode controlmonitors not only the output voltage, but also the outputcurrent. Here the voltage error signal is used to controlthe peak current within the magnetic elements duringeach power switch on–time. Current–mode control has avery rapid input and output response time, and has aninherent overcurrent protection. It is not commonly usedfor forward–mode converters; their current waveformshave much lower slopes in their current waveformswhich can create jitter within comparators.Hysteretic control is a method of control which tries tokeep a monitored parameter between two limits. Thereare hysteretic current and voltage control methods, butthey are not commonly used.The designer should be very careful when reviewing aprospective control IC data sheet. The method of controland any variations are usually not clearly described onthe first page of the data sheet.http://onsemi.com14

SMPSRMV CCOSCChargeClock RampV errorCtDischargeV FBVoltComp.+–V error Amp.V ref–+Steering+–PulsewidthComparatorOutputGatingLogicI out (lavOC)orI SW (P–POC)R CSCur.Comp.+–Current Amp.V OC–+V SSAverageOvercurrentProtectionPulse–by–PulseOvercurrentProtectionFigure 14. Voltage–Mode ControlV CCOSC–+CtDischargeOutputGatingLogicVoltComp.V error Amp.SQOutput+–V ref–+V FBI SWI pkV errorV errorCurrentComparatorRS R S–+I SWR CSV SSFigure 15. Turn–On with Clock Current–Mode Controlhttp://onsemi.com15

SMPSRMThe Choice of SemiconductorsPower SwitchesThe choice of which semiconductor technology to usefor the power switch function is influenced by manyfactors such as cost, peak voltage and current, frequencyof operation, and heatsinking. Each technology has itsown peculiarities that must be addressed during thedesign phase.There are three major power switch choices: thebipolar junction transistor (BJT), the power MOSFET,and the integrated gate bipolar transistor (IGBT). TheBJT was the first power switch to be used in this field andstill offers many cost advantages over the others. It is alsostill used for very low cost or in high power switchingconverters. The maximum frequency of operation ofbipolar transistors is less than 80–100 kHz because ofsome of their switching characteristics. The IGBT is usedfor high power switching converters, displacing many ofthe BJT applications. They too, though, have a slowerswitching characteristic which limits their frequency ofoperation to below 30 kHz typically although some canreach 100 kHz. IGBTs have smaller die areas than powerMOSFETs of the same ratings, which typically means alower cost. Power MOSFETs are used in the majority ofapplications due to their ease of use and their higherfrequency capabilities. Each of the technologies will bereviewed.The Bipolar Power TransistorThe BJT is a current driven device. That means that thebase current is in proportion to the current drawn throughthe collector. So one must provide:IB IC hFE (eq. 8)In power transistors, the average gain (h FE ) exhibited atthe higher collector currents is between 5 and 20. Thiscould create a large base drive loss if the base drive circuitis not properly designed.One should generate a gate drive voltage that is as closeto 0.7 volts as possible. This is to minimize any losscreated by dropping the base drive voltage at the requiredbase current to the level exhibited by the base.A second consideration is the storage time exhibited bythe collector during its turn–off transition. When the baseis overdriven, or where the base current is more thanneeded to sustain the collector current, the collectorexhibits a 0.3–2 s delay in its turn–off which isproportional to the base overdrive. Although the storagetime is not a major source of loss, it does significantlylimit the maximum switching frequency of abipolar–based switching power supply. There are twomethods of reducing the storage time and increasing itsswitching time. The first is to use a base speed–upcapacitor whose value, typically around 100 pF, is placedin parallel with the base current limiting resistor(Figure 16a). The second is to use proportional base drive(Figure 16b). Here, only the amount of needed basecurrent is provided by the drive circuit by bleeding theexcess around the base into the collector.The last consideration with BJTs is the risk ofexcessive second breakdown. This phenomenon iscaused by the resistance of the base across the die,permitting the furthest portions of the collector to turn offlater. This forces the current being forced through thecollector by an inductive load, to concentrate at theopposite ends of the die, thus causing an excessivelocalized heating on the die. This can result in ashort–circuit failure of the BJT which can happeninstantaneously if the amount of current crowding isgreat, or it can happen later if the amount of heating isless. Current crowding is always present when aninductive load is attached to the collector. By switchingthe BJT faster, with the circuits in Figure 15, one cangreatly reduce the effects of second breakdown on thereliability of the device.V BBV BB100 pFControl IC100 pF+V BE–+V CE–Control ICPower GroundPower Ground(a) Fixed Base Drive Circuit(b) Proportional Base Drive Circuit (Baker Clamp)Figure 16. Driving a Bipolar Junction Transistorhttp://onsemi.com16

SMPSRMThe Power MOSFETPower MOSFETs are the popular choices used aspower switches and synchronous rectifiers. They are, onthe surface, simpler to use than BJTs, but they have somehidden complexities.A simplified model for a MOSFET can be seen inFigure 17. The capacitances seen in the model arespecified within the MOSFET data sheets, but can benonlinear and vary with their applied voltages.C DGC GSC ossFigure 17. The MOSFET ModelFrom the gate terminal, there are two capacitances thedesigner encounters, the gate input capacitance (C iss ) andthe drain–gate reverse capacitance (C rss ). The gate inputcapacitance is a fixed value caused by the capacitanceformed between the gate metalization and the substrate.Its value usually falls in the range of 800–3200 pF,depending upon the physical construction of theMOSFET. The C rss is the capacitance between the drainand the gate, and has values in the range of 60–150 pF.Although the C rss is smaller, it has a much morepronounced effect upon the gate drive. It couples thedrain voltage to the gate, thus dumping its stored chargeinto the gate input capacitance. The typical gate drivewaveforms can be seen in Figure 18. Time period t1 isonly the C iss being charged or discharged by theimpedance of the external gate drive circuit. Period t2shows the effect of the changing drain voltage beingcoupled into the gate through C rss . One can readilyobserve the “flattening” of the gate drive voltage duringthis period, both during the turn–on and turn–off of theMOSFET. Time period t3 is the amount of overdrivevoltage provided by the drive circuit but not reallyneeded by the MOSFET.TURN–ONt3V DRTURN–OFFt1 t2t2 t1t3V GS0V thV plV DSI G0+0–Figure 18. Typical MOSFET Drive Waveforms (Top: V GS , Middle: V DG , Bottom: I G )http://onsemi.com17

SMPSRMThe time needed to switch the MOSFET between onand off states is dependent upon the impedance of thegate drive circuit. It is very important that the drive circuitbe bypassed with a capacitor that will keep the drivevoltage constant over the drive period. A 0.1 F capacitoris more than sufficient.Driving MOSFETs in SwitchingPower Supply ApplicationsThere are three things that are very important in thehigh frequency driving of MOSFETs: there must be atotem–pole driver; the drive voltage source must be wellbypassed; and the drive devices must be able to sourcehigh levels of current in very short periods of time (lowcompliance). The optimal drive circuit is shown inFigure 19.V GLOADV GLOADR onR offa. Passive Turn–ONb. Passive Turn–OFFV GLOADV GLOADc. Bipolar Totem–poled. MOS Totem–poleFigure 19. Bipolar and FET–Based Drive Circuits (a. Bipolar Drivers, b. MOSFET Drivers)http://onsemi.com18

SMPSRMThe Magnetic ComponentsThe magnetic elements within a switching powersupply are used either for stepping–up or down aswitched AC voltage, or for energy storage. Inforward–mode topologies, the transformer is only usedfor stepping–up or down the AC voltage generated by thepower switches. The output filter (the output inductorand capacitor) in forward–mode topologies is used forenergy storage. In boost–mode topologies, thetransformer is used both for energy storage and to providea step–up or step–down function.Many design engineers consider the magneticelements of switching power supplies counter–intuitiveor too complicated to design. Fortunately, help is at hand;the suppliers of magnetic components have applicationsengineers who are quite capable of performing thetransformer design and discussing the tradeoffs neededfor success. For those who are more experienced or moreadventuresome, please refer to Reference 2 in theBibliography for transformer design guidelines.The general procedure in the design of any magneticcomponent is as follows (Reference 2, p 42):1. Select an appropriate core material for theapplication and the frequency of operation.2. Select a core form factor that is appropriate forthe application and that satisfies applicableregulatory requirements.3. Determine the core cross–sectional areanecessary to handle the required power4. Determine whether an airgap is needed andcalculate the number of turns needed for eachwinding. Then determine whether the accuracyof the output voltages meets the requirementsand whether the windings will fit into theselected core size.5. Wind the magnetic component using properwinding techniques.6. During the prototype stage, verify thecomponent’s operation with respect to the levelof voltage spikes, cross–regulation, outputaccuracy and ripple, RFI, etc., and makecorrections were necessary.The design of any magnetic component is a “calculatedestimate.” There are methods of “stretching” the designlimits for smaller size or lower losses, but these tend tobe diametrically opposed to one another. One should becautious when doing this.Some useful sources for magnetics components are:CoilCraft, Inc.1102 Silver Lake Rd.Cary, IL (USA) 60013website: http://www.coilcraft.com/email: info@coilcraft.comTelephone: 847–639–6400Coiltronics, Division of Cooper ElectronicsTechnology6000 Park of Commerce BlvdBoca Raton, FL (USA) 33487website: http://www.coiltronics.comTelephone: 561–241–7876Cramer Coil, Inc.401 Progress Dr.Saukville, WI (USA) 53080website: http://www.cramerco.comemail: techsales@cramercoil.comTelephone: 262–268–2150Pulse, Inc.San Diego, CAwebsite: http://www.pulseeng.comTelephone: 858–674–8100TDK1600 Feehanville DriveMount Prospect, IL 60056website: http://www.component.talk.comTelephone: 847–803–6100Laying Out the Printed Circuit BoardThe printed circuit board (PCB) layout is the thirdcritical portion of every switching power supply designin addition to the basic design and the magnetics design.Improper layout can adversely affect RFI radiation,component reliability, efficiency and stability. EveryPCB layout will be different, but if the designerappreciates the common factors present in all switchingpower supplies, the process will be simplified.All PCB traces exhibit inductance and resistance.These can cause high voltage transitions whenever thereis a high rate of change in current flowing through thetrace. For operational amplifiers sharing a trace withpower signals, it means that the supply would beimpossible to stabilize. For traces that are too narrow forthe current flowing through them, it means a voltage dropfrom one end of the trace to the other which potentiallycan be an antenna for RFI. In addition, capacitivecoupling between adjacent traces can interfere withproper circuit operation.There are two rules of thumb for PCB layouts: “shortand fat” for all power–carrying traces and “one pointgrounding” for the various ground systems within aswitching power supply. Traces that are short and fatminimize the inductive and resistive aspects of the trace,thus reducing noise within the circuits and RFI.Single–point grounding keeps the noise sourcesseparated from the sensitive control circuits.http://onsemi.com21

SMPSRMWithin all switching power supplies, there are fourmajor current loops. Two of the loops conduct thehigh–level AC currents needed by the supply. These arethe power switch AC current loop and the output rectifierAC current loop. The currents are the typical trapezoidalcurrent pulses with very high peak currents and veryrapid di/dts. The other two current loops are the inputsource and the output load current loops, which carry lowfrequency current being supplied from the voltage sourceand to the load respectively.For the power switch AC current loop, current flowsfrom the input filter capacitor through the inductor ortransformer winding, through the power switch and backto the negative pin of the input capacitor. Similarly, theoutput rectifier current loop’s current flows from theinductor or secondary transformer winding, through theInput CurrentLoop+V in–C inPower SwitchCurrent LoopSWControlAnalogrectifier to the output filter capacitor and back to theinductor or winding. The filter capacitors are the onlycomponents that can source and sink the large levels ofAC current in the time needed by the switching powersupply. The PCB traces should be made as wide and asshort as possible, to minimize resistive and inductiveeffects. These traces should be the first to be laid out.Turning to the input source and output load currentloops, both of these loops must be connected directly totheir respective filter capacitor’s terminals, otherwiseswitching noise could bypass the filtering action of thecapacitor and escape into the environment. This noise iscalled conducted interference. These loops can be seenin Figure 21 for the two major forms of switchingpower supplies, non–isolated (Figure 21a) andtransformer–isolated (Figure 21b).LGNDOutput RectifierCurrent LoopV FBCC outV outOutput LoadCurrent LoopInput SourceGroundAJoinPowerSwitch GroundJoinOutput RectifierGround(a) The Non–Isolated DC/DC ConverterBJoinOutput LoadGroundInput CurrentLoopPower SwitchCurrent LoopOutput RectifierCurrent LoopOutput LoadCurrent LoopV outV FB+SWC outV in–C inFBControlAnalogGNDCR CSOutput Rectifier BGroundJoinJoinOutput LoadGroundInput Source AGroundJoinPower Switch Ground(b) The Transformer–Isolated ConverterFigure 21. The Current Loops and Grounds for the Major Converter Topologieshttp://onsemi.com22

ÉÉ ÂÂÂÂÂÂÂÂÂÂÂÉÉÉÉÉÉÉÉSMPSRMThe grounds are extremely important to the properoperation of the switching power supply, since they formthe reference connections for the entire supply; eachground has its own unique set of signals which canadversely affect the operation of the supply if connectedimproperly.There are five distinct grounds within the typicalswitching power supply. Four of them form the returnpaths for the current loops described above. Theremaining ground is the low–level analog control groundwhich is critical for the proper operation of the supply.The grounds which are part of the major current loopsmust be connected together exactly as shown inFigure 21. Here again, the connecting point between thehigh–level AC grounds and the input or output groundsis at the negative terminal of the appropriate filtercapacitor (points A and B in Figures 21a and 21b). Noiseon the AC grounds can very easily escape into theenvironment if the grounds are not directly connected tothe negative terminal of the filter capacitor(s). Theanalog control ground must be connected to the pointwhere the control IC and associated circuitry mustmeasure key power parameters, such as AC or DCcurrent and the output voltage (point C in Figures 21a and21b). Here any noise introduced by large AC signalswithin the AC grounds will sum directly onto thelow–level control parameters and greatly affect theoperation of the supply. The purpose of connecting thecontrol ground to the lower side of the current sensingresistor or the output voltage resistor divider is to form a“Kelvin contact” where any common mode noise is notsensed by the control circuit. In short, follow the examplegiven by Figure 21 exactly as shown for best results.The last important factor in the PCB design is thelayout surrounding the AC voltage nodes. These are thedrain of the power MOSFET (or collector of a BJT) andthe anode of the output rectifier(s). These nodes cancapacitively couple into any trace on different layers ofthe PCB that run underneath the AC pad. In surfacemount designs, these nodes also need to be large enoughto provide heatsinking for the power switch or rectifier.This is at odds with the desire to keep the pad as small aspossible to discourage capacitive coupling to othertraces. One good compromise is to make all layers belowthe AC node identical to the AC node and connect themwith many vias (plated–through holes). This greatlyincreases the thermal mass of the pad for improvedheatsinking and locates any surrounding traces offlaterally where the coupling capacitance is much smaller.An example of this can be seen in Figure 22.Many times it is necessary to parallel filter capacitorsto reduce the amount of RMS ripple current eachcapacitor experiences. Close attention should be paid tothis layout. If the paralleled capacitors are in a line, thecapacitor closest to the source of the ripple current willoperate hotter than the others, shortening its operatinglife; the others will not see this level of AC current. Toensure that they will evenly share the ripple current,ideally, any paralleled capacitors should be laid out in aradially–symmetric manner around the current source,typically a rectifier or power switch.The PCB layout, if not done properly, can ruin a goodpaper design. It is important to follow these basicguidelines and monitor the layout every step of theprocess.Power DeviceViaPCB TopÉÉÉÉPlated–Thru HolePCB BottomÂÂÂÂÂÂÂÂÂÂÂ ÉÉFigure 22. Method for Minimizing AC Capacitive Coupling and Enhancing Heatsinkinghttp://onsemi.com23

SMPSRMLosses and Stresses in SwitchingPower SuppliesMuch of the designer’s time during a switching powersupply design is spent in identifying and minimizing thelosses within the supply. Most of the losses occur in thepower components within the switching power supply.Some of these losses can also present stresses to thepower semiconductors which may affect the long termreliability of the power supply, so knowing where theyarise and how to control them is important.Whenever there is a simultaneous voltage drop acrossa component with a current flowing through, there is aloss. Some of these losses are controllable by modifyingthe circuitry, and some are controlled by simply selectinga different part. Identifying the major sources for loss canbe as easy as placing a finger on each of the componentsin search of heat, or measuring the currents and voltagesassociated with each power component using anoscilloscope, AC current probe and voltage probe.Semiconductor losses fall into two categories:conduction losses and switching losses. The conductionloss is the product of the terminal voltage and currentduring the power device’s on period. Examples ofconduction losses are the saturation voltage of a bipolarpower transistor and the “on” loss of a power MOSFETshown in Figure 23 and Figure 24 respectively.COLLECTOR-TO-EMITTER(VOLTS)RISETIMEDYNAMICSATURATIONSATURATIONVOLTAGEV PEAKSTORAGETIMEFALLTIMEDRAIN-TO-SOURCE VOLTAGE(VOLTS)RISETIMEON VOLTAGEV PEAKFALLTIMECOLLECTOR CURRENT(AMPS)PINCHING OFF INDUCTIVECHARACTERISTICS OF THETRANSFORMERTURN-ONCURRENTCLEARINGRECTIFIERSSATURATIONCURRENTTURN-OFFCURRENTI PEAKCURRENTTAILDRAIN CURRENT(AMPS)TURN-ONCURRENTCLEARINGRECTIFIERSPINCHING OFF INDUCTIVECHARACTERISTICS OF THETRANSFORMERON CURRENTI PEAKTURN-OFFCURRENTINSTANTANEOUS ENERGYLOSS (JOULES)TURN-ONLOSSSECONDBREAKDOWNPERIODSATURATIONLOSSTURN-OFF LOSSSWITCHING LOSSCURRENTCROWDINGPERIODINSTANTANEOUS ENERGYLOSS (JOULES)TURN-ONLOSSON LOSSTURN-OFF LOSSSWITCHING LOSSFigure 23. Stresses and Losseswithin a Bipolar Power TransistorFigure 24. Stresses and Losseswithin a Power MOSFEThttp://onsemi.com24

SMPSRMThe forward conduction loss of a rectifier is shown inFigure 25. During turn–off, the rectifier exhibits a reverserecovery loss where minority carriers trapped within theP–N junction must reverse their direction and exit thejunction after a reverse voltage is applied. This results inwhat appears to be a current flowing in reverse throughthe diode with a high reverse terminal voltage.The switching loss is the instantaneous product of theterminal voltage and current of a power device when it istransitioning between operating states (on–to–off andoff–to–on). Here, voltages are transitional betweenfull–on and cutoff states while simultaneously the currentis transitional between full–on and cut–off states. Thiscreates a very large V–I product which is as significant asthe conduction losses. Switching losses are also the majorfrequency dependent loss within every PWM switchingpower supply.The loss–induced heat generation causes stress withinthe power component. This can be minimized by aneffective thermal design. For bipolar power transistors,however, excessive switching losses can also provide alethal stress to the transistor in the form of secondbreakdown and current crowding failures. Care should betaken in the careful analysis of each transistor’s ForwardBiased–Safe Operating Area (FBSOA) and ReverseBiased–Safe Operating Area (RBSOA) operation.DIODE VOLTAGE(VOLTS)FORWARD VOLTAGEREVERSE VOLTAGEDIODE CURRENT(AMPS)FORWARDRECOVERYTIME (T fr )FORWARD CONDUCTION CURRENTDEGREE OF DIODERECOVERYABRUPTNESSI PKREVERSERECOVERYTIME (T rr )INSTANTANEOUS ENERGYLOSS (JOULES)FORWARD CONDUCTION LOSSSWITCHINGLOSSFigure 25. Stresses and Losses within RectifiersTechniques to Improve Efficiency inSwitching Power SuppliesThe reduction of losses is important to the efficientoperation of a switching power supply, and a great dealof time is spent during the design phase to minimize theselosses. Some common techniques are described below.The Synchronous RectifierAs output voltages decrease, the losses due to theoutput rectifier become increasingly significant. ForV out = 3.3 V, a typical Schottky diode forward voltage of0.4 V leads to a 12% loss of efficiency. Synchronousrectification is a technique to reduce this conduction lossby using a switch in place of the diode. The synchronousrectifier switch is open when the power switch is closed,and closed when the power switch is open, and istypically a MOSFET inserted in place of the outputrectifier. To prevent ”crowbar” current that would flow ifboth switches were closed at the same time, the switchingscheme must be break–before–make. Because of this, adiode is still required to conduct the initial current duringthe interval between the opening of the main switch andthe closing of the synchronous rectifier switch. ASchottky rectifier with a current rating of 30 percent ofhttp://onsemi.com25

SMPSRMthe MOSFET should be placed in parallel with thesynchronous MOSFET. The MOSFET does contain aparasitic body diode that could conduct current, but it islossy, slow to turn off, and can lower efficiency by 1% to2%. The lower turn–on voltage of the Schottky preventsthe parasitic diode from ever conducting and exhibitingits poor reverse recovery characteristic.Using synchronous rectification, the conductionvoltage can be reduced from 400 mV to 100 mV or less.An improvement of 1–5 percent can be expected for thetypical switching power supply.The synchronous rectifier can be driven either actively,that is directly controlled from the control IC, orpassively, driven from other signals within the powercircuit. It is very important to provide a non–overlappingdrive between the power switch(es) and the synchronousrectifier(s) to prevent any shoot–through currents. Thisdead time is usually between 50 to 100 ns. Some typicalcircuits can be seen in Figure 26.V in+V out–SWDriveGNDDirectSRV GCR GCD1 k1:1C > 10 C issTransformer–Isolated(a) Actively Driven Synchronous RectifiersL O+V outPrimary–(b) Passively Driven Synchronous RectifiersFigure 26. Synchronous Rectifier Circuitshttp://onsemi.com26

SMPSRMSnubbers and ClampsSnubbers and clamps are used for two very differentpurposes. When misapplied, the reliability of thesemiconductors within the power supply is greatlyjeopardized.A snubber is used to reduce the level of a voltage spikeand decrease the rate of change of a voltage waveform.This then reduces the amount of overlap of the voltageand current waveforms during a transition, thus reducingthe switching loss. This has its benefits in the SafeOperating Area (SOA) of the semiconductors, and itreduces emissions by lowering the spectral content of anyRFI.A clamp is used only for reducing the level of a voltagespike. It has no affect on the dV/dt of the transition.Therefore it is not very useful for reducing RFI. It isuseful for preventing components such assemiconductors and capacitors from entering avalanchebreakdown.Bipolar power transistors suffer from current crowdingwhich is an instantaneous failure mode. If a voltage spikeoccurs during the turn–off voltage transition of greaterthan 75 percent of its VCEO rating, it may have too muchcurrent crowding stress. Here both the rate of change ofthe voltage and the peak voltage of the spike must becontrolled. A snubber is needed to bring the transistorwithin its RBSOA (Reverse Bias Safe Operating Area)rating. Typical snubber and clamp circuits are shown inFigure 27. The effects that these have on a representativeswitching waveform are shown in Figure 28.ZENERCLAMPSOFTCLAMPSNUBBERSNUBBERSOFTCLAMPZENERCLAMPFigure 27. Common Methods for Controlling Voltage Spikes and/or RFIVOLTAGE (VOLTS)CLAMPORIGINALWAVEFORMSNUBBERt, TIME (µsec)Figure 28. The Effects of a Snubber versus a Clamphttp://onsemi.com27

SMPSRMThe Lossless SnubberA lossless snubber is a snubber whose trapped energyis recovered by the power circuit. The lossless snubber isdesigned to absorb a fixed amount of energy from thetransition of a switched AC voltage node. This energy isstored in a capacitor whose size dictates how muchenergy the snubber can absorb. A typical implementationof a lossless snubber can be seen in Figure 29.The design for a lossless snubber varies from topologyto topology and for each desired transition. Someadaptation may be necessary for each circuit. Theimportant factors in the design of a lossless snubber are:1. The snubber must have initial conditions thatallow it to operate during the desired transitionand at the desired voltages. Lossless snubbersshould be emptied of their energy prior to thedesired transition. The voltage to which it isreset dictates where the snubber will begin tooperate. So if the snubber is reset to the inputvoltage, then it will act as a lossless clamp whichwill remove any spikes above the input voltage.2. When the lossless snubber is “reset,” theenergy should be returned to the inputcapacitor or back into the output power path.Study the supply carefully. Returning theenergy to the input capacitor allows the supplyto use the energy again on the next cycle.Returning the energy to ground in a boost–mode supply does not return the energy forreuse, but acts as a shunt current path aroundthe power switch. Sometimes additionaltransformer windings are used.3. The reset current waveform should be bandlimited with a series inductor to preventadditional EMI from being generated. Use of a2 to 3 turn spiral PCB inductor is sufficient togreatly lower the di/dt of the energy exiting thelossless snubber.Unsnubbed V SW+Snubbed V SWV SW I D–Drain Current (I D )Figure 29. Lossless Snubber for a One Transistor Forward or Flyback Converterhttp://onsemi.com28

SMPSRMThe Active ClampAn active clamp is a gated MOSFET circuit that allowsthe controller IC to activate a clamp or a snubber circuitat a particular moment in a switching power supply’scycle of operation. An active clamp for a flybackconverter is shown in Figure 30.In Figure 30, the active clamp is reset (or emptied of itsstored energy) just prior to the turn–off transition. It isthen disabled during the negative transition.Obviously, the implementation of an active clamp ismore expensive than other approaches, and is usuallyreserved for very compact power supplies where heat isa critical issue.UnclampedSwitch Voltage(V SW )Clamped SwitchVoltage (V SW )V inSwitchCurrent (I SW )+V DR–I CL+GNDI SWV SW–DriveVoltage (V DR )DischargeChargeClampCurrent (I CL )Figure 30. An Active Clamp Used in a One Transistor Forward or a Flyback Converterhttp://onsemi.com29

SMPSRMQuasi–Resonant TopologiesA quasi–resonant topology is designed to reduce oreliminate the frequency–dependent switching losseswithin the power switches and rectifiers. Switchinglosses account for about 40% of the total loss within aPWM power supply and are proportional to the switchingfrequency. Eliminating these losses allows the designerto increase the operating frequency of the switchingpower supply and so use smaller inductors andcapacitors, reducing size and weight. In addition, RFIlevels are reduced due to the controlled rate of change ofcurrent or voltage.The downside to quasi–resonant designs is that theyare more complex than non–resonant topologies due toparasitic RF effects that must be considered whenswitching frequencies are in the 100’s of kHz.Schematically, quasi–resonant topologies are minormodifications of the standard PWM topologies. Aresonant tank circuit is added to the power switch sectionto make either the current or the voltage “ring” througha half a sinusoid waveform. Since the sinusoid starts atzero and ends at zero, the product of the voltage andcurrent at the starting and ending points is zero, thus hasno switching loss.There are two quasi–resonant methods: zero currentswitching (ZCS) or zero voltage switching (ZVS). ZCSis a fixed on–time, variable off–time method of control.ZCS starts from an initial condition where the powerswitch is off and no current is flowing through theresonant inductor. The ZCS quasi–resonant buckconverter is shown in Figure 31.I LRL RL OC RV in V SWC in CONTROLDFEEDBACKC outV outA ZCS Quasi–Resonant Buck ConverterSWITCHTURN-OFFV SWV inPOWER SWITCHONI PKV DI LRFigure 31. Schematic and Waveforms for a ZCS Quasi-Resonant Buck Converterhttp://onsemi.com30

SMPSRMIn this design, both the power switch and the catchdiode operate in a zero current switching mode. Power ispassed to the output during the resonant periods. So toincrease the power delivered to the load, the frequencywould increase, and vice versa for decreasing loads. Intypical designs the frequency can change 10:1 over theZCS supply’s operating range.The ZVS is a fixed off–time, variable on–time methodcontrol. Here the initial condition occurs when the powerswitch is on, and the familiar current ramp is flowingthrough the filter inductor. The ZVS quasi–resonant buckconverter is shown in Figure 32. Here, to control thepower delivered to the load, the amount of “resonant offtimes” are varied. For light loads, the frequency is high.When the load is heavy, the frequency drops. In a typicalZVS power supply, the frequency typically varies 4:1over the entire operating range of the supply.There are other variations on the resonant theme thatpromote zero switching losses, such as full resonantPWM, full and half–bridge topologies for higher powerand resonant transition topologies. For a more detailedtreatment, see Chapter 4 in the “Power SupplyCookbook” (Bibliography reference 2).L RL OC RDV inC inCONTROLV I/PFEEDBACKC outV outA ZVS Quasi–Resonant Buck ConverterV inV I/P0POWER SWITCHTURNS ONV in V outI PKL R L OI SWV in0I LOADI DL RFigure 32. Schematic and Waveforms for aZVS Quasi-Resonant Buck Converterhttp://onsemi.com31

SMPSRMPower Factor CorrectionPower Factor (PF) is defined as the ratio of real powerto apparent power. In a typical AC power supplyapplication where both the voltage and current aresinusoidal, the PF is given by the cosine of the phaseangle between the input current and the input voltage andis a measure of how much of the current contributes toreal power in the load. A power factor of unity indicatesthat 100% of the current is contributing to power in theload while a power factor of zero indicates that none ofthe current contributes to power in the load. Purelyresistive loads have a power factor of unity; the currentthrough them is directly proportional to the appliedvoltage.The current in an ac line can be thought of as consistingof two components: real and imaginary. The real partresults in power absorbed by the load while the imaginarypart is power being reflected back into the source, suchas is the case when current and voltage are of oppositepolarity and their product, power, is negative.It is important to have a power factor as close aspossible to unity so that none of the delivered power isreflected back to the source. Reflected power isundesirable for three reasons:1. The transmission lines or power cord willgenerate heat according to the total currentbeing carried, the real part plus the reflectedpart. This causes problems for the electricutilities and has prompted various regulationsrequiring all electrical equipment connected toa low voltage distribution system to minimizecurrent harmonics and maximize power factor.2. The reflected power not wasted in theresistance of the power cord may generateunnecessary heat in the source (the localstep–down transformer), contributing topremature failure and constituting a fire hazard.3. Since the ac mains are limited to a finite currentby their circuit breakers, it is desirable to getthe most power possible from the given currentavailable. This can only happen when thepower factor is close to or equal to unity.The typical AC input rectification circuit is a diodebridge followed by a large input filter capacitor. Duringthe time that the bridge diodes conduct, the AC line isdriving an electrolytic capacitor, a nearly reactive load.This circuit will only draw current from the input lineswhen the input’s voltage exceeds the voltage of the filtercapacitor. This leads to very high currents near the peaksof the input AC voltage waveform as seen in Figure 33.Since the conduction periods of the rectifiers are small,the peak value of the current can be 3–5 times the averageinput current needed by the equipment. A circuit breakeronly senses average current, so it will not trip when thepeak current becomes unsafe, as found in many officeareas. This can present a fire hazard. In three–phasedistribution systems, these current peaks sum onto theneutral line, not meant to carry this kind of current, whichagain presents a fire hazard.Powernot usedCURRENTVOLTAGEPower usedI110/220+AC VOLTS INDC To PowerC large Supply–I AVFigure 33. The Waveforms of a Capacitive Input Filterhttp://onsemi.com32

SMPSRMA Power Factor Correction (PFC) circuit is a switchingpower converter, essentially a boost converter with a verywide input range, that precisely controls its input currenton an instantaneous basis to match the waveshape andphase of the input voltage. This represents a zero degreesor 100 percent power factor and mimics a purely resistiveload. The amplitude of the input current waveform isvaried over longer time frames to maintain a constantvoltage at the converter’s output filter capacitor. Thismimics a resistor which slowly changes value to absorbthe correct amount of power to meet the demand of theload. Short term energy excesses and deficits caused bysudden changes in the load are supplemented by a ”bulkenergy storage capacitor”, the boost converter’s outputfilter device. The PFC input filter capacitor is reduced toa few microfarads, thus placing a half–wave haversinewaveshape into the PFC converter.The PFC boost converter can operate down to about30 V before there is insufficient voltage to draw any moresignificant power from its input. The converter then canbegin again when the input haversine reaches 30 V on thenext half–wave haversine. This greatly increases theconduction angle of the input rectifiers. The drop–outregion of the PFC converter is then filtered (smoothed)by the input EMI filter.A PFC circuit not only ensures that no power isreflected back to the source, it also eliminates thehigh current pulses associated with conventionalrectifier–filter input circuits. Because heat lost in thetransmission line and adjacent circuits is proportional tothe square of the current in the line, short strong currentpulses generate more heat than a purely resistive load ofthe same power. The active power factor correctioncircuit is placed just following the AC rectifier bridge. Anexample can be seen in Figure 34.Depending upon how much power is drawn by the unit,there is a choice of three different common controlmodes. All of the schematics for the power sections arethe same, but the value of the PFC inductor and thecontrol method are different. For input currents of lessthan 150 watts, a discontinuous–mode control scheme istypically used, in which the PFC core is completelyemptied prior to the next power switch conduction cycle.For powers between 150 and 250 watts, the criticalconduction mode is recommended. This is a method ofcontrol where the control IC senses just when the PFCcore is emptied of its energy and the next power switchconduction cycle is immediately begun; this eliminatesany dead time exhibited in the discontinuous–mode ofcontrol. For an input power greater than 250 watts, thecontinuous–mode of control is recommended. Here thepeak currents can be lowered by the use of a largerinductor, but a troublesome reverse recoverycharacteristic of the output rectifier is encountered,which can add an additional 20–40 percent in losses to thePFC circuit.Many countries cooperate in the coordination of theirpower factor requirements. The most appropriatedocument is IEC61000–3–2, which encompasses theperformance of generalized electronic products. Thereare more detailed specifications for particular productsmade for special markets.Switch CurrentInput VoltageConduction AngleC smallIControlV senseC largeV out+To PowerSupply–Figure 34. Power Factor Correction CircuitVoltageCurrentI AVGFigure 35. Waveform of Corrected Inputhttp://onsemi.com33

SMPSRMBibliography1. Ben–Yaakov Sam, Gregory Ivensky, “Passive Lossless Snubbers for High Frequency PWM Converters,”Seminar 12, APEC 99.2. Brown, Marty, Power Supply Cookbook, Butterworth–Heinemann, 1994, 2001.3. Brown, Marty, “Laying Out PC Boards for Embedded Switching Supplies,” Electronic Design, Dec. 1999.4. Martin, Robert F., “Harmonic Currents,” Compliance Engineering – 1999 Annual Resources Guide, CannonCommunications, LLC, pp. 103–107.5. ON Semiconductor, Rectifier Applications Handbook, HB214/D, Rev. 2, Nov. 2001.http://onsemi.com34

SWITCHMODE Power Supply ExamplesSMPSRMThis section provides both initial and detailed information to simplify the selection and design of a variety ofSWITCHMODE power supplies. The ICs for Switching Power Supplies figure identifies control, reference voltage,output protection and switching regulator ICs for various topologies.ICs for Switching Power Supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36Integrated circuits identified for various sections of a switching power supply.Suggested Components for Specific Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37A list of suggested control ICs, power transistors and rectifiers for SWITCHMODE power supplies by application.• CRT Display System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38• AC/DC Power Supply for CRT Displays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39• AC/DC Power Supply for Storage, Imaging & Entertainment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39• DC–DC Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40• Typical PC Forward–Mode SMPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Real SMPS Applications80 W Power Factor Correction Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Compact Power Factor Correction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43Monitor Pulsed–Mode SMPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4470 W Wide Mains TV SMPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46100 W Wide Mains TV SMPS with 1.3 W Stand–by . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Low–Cost Off–line IGBT Battery Charger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50110 W Output Flyback SMPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51Efficient Safety Circuit for Electronic Ballast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53AC–DC Battery Charger – Constant Current with Voltage Limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Some of these circuits may have a more complete application note, spice model information or even an evaluation boardavailable. Consult ON Semiconductor’s website (http://onsemi.com) or local sales office for more information.Pagehttp://onsemi.com35

POWER FACTORCORRECTIONMC33260MC33262MC33368MC34262NCP1650NCP1651POWER MOSDRIVERSPOWER MOSDRIVERSMC33151MC33152MC33153SNUBBER/CLAMP1N62xxA1N63xxAMUR160MUR260MURS160MURS260P6KExxxAP6SMB1xxAOUTPUT FILTERSMBR1100MBR3100MBR360MBRD360MBRS1100MBRS240LMBRS360MURHF860CTMURS360OUTPUT PROTECTIONMAX707 MC33161MAX708 MC33164MAX809 MC3423MAX810 NCP30xMC33064 NCP803DC–DC CONVERSIONCS51031 MC34063ACS51033 MC34163CS51411 MC34166CS51412 MC34167CS51413 NCP1400ACS51414 NCP1402CS5171 NCP1410CS5172 NCP1411CS5173 NCP1417CS5174 NCP1450AMC33463 NCP1550MC33466Figure 36. . Intergrated Ciruitsfor Switching Power SuppliesSMPSRMhttp://onsemi.com36MC33362MC33363MC33365NCP100xNCP105xHV SWITCHINGREGULATORSPOWER FACTORCORRECTIONPOWERSWITCHSTARTUPMMBZ52xxMMSZ52xxMMSZ46xxSTARTUPSNUBBER/ TRANS–OUTPUTOUTPUTVOLTAGECLAMP FORMERSFILTERSPROTECTION REGULATIONPWMOSCREFCONTROLCS3843CS51021CS51022CS51023CS51024CS5106CS51220CS51221CS51227CS5124MC33023MC33025MC33065MC33067MC33364MC44603ACONTROLMC44604MC44605MC44608NCP1200NCP1205UC384xVOLTAGEFEEDBACKCS5101NCP100TL431/A/BTLV431AVOLTAGEFEEDBACKDC–DCCONVERSIONL4949LM2931LM2935LM317LM317LLM317MLM337LM350LP2950LP2951MC33263MC33269MC33275MC33761MC34268MC78xxMC78BxxMC78FxxMC78LxxMC78MxxMC78PCxxMC78TxxMC7905MC7905.2VOLTAGE REGULATIONV refMC7905AMC7906MC7908MC7908AMC7912MC7915MC7918MC7924MC79MxxNCP1117NCP50xNCP51xFigure 30. Integrated Circuits for Switching Power Supplies

V_SyncH_SyncMonitorMCUSYNC PROCESSOR1280x1024RWM10101100101I 2 C BUSV_SyncH_SyncOn Screen DisplayGeneratorRGBFigure 37.. 15”MonitorPowerSuppliesOverlayedRGBRGBVideoDriverRGBCRThttp://onsemi.com37DOWNUPMEMORYUSB HUBUSB & Auxiliary StandbyAC/DCPower SupplyLineA.C.HC05CPUCOREPWMor I 2 CRGBMC33363A/BNCP100xNCP105xNCP1200V_SyncH_SyncRBGGeometry CorrectionIRF630 / 640 / 730 /740 / 830 / 840Timebase ProcessorDC TO DCCONTROLLERVerticalDriverH–DriverLine DriverH–Output TRH–Driver TRMTD6N10/15Damper DiodeMUR8100EMUR4100EMUR460PFC DevicesNCP1650NCP1651MC34262MC33368MC33260S.M.P.SController600V 8AN–ChMOSFETUC3842/3MTP6P20EUC384xMC44603/5MC44608NCP1200NCP1205SyncSignalMUR420MUR440MUR460Figure 31. 15” Monitor Power SuppliesSMPSRM

SMPSRMACLineRectifier+Start–upSwitchBulkStorageCapacitorPWMControlICPWM SwitcherUltrafastRectifierMOSFET+Prog.Prec.RefLoadn–outputsFigure 38. AC/DC Power Supply for CRT DisplaysTable 1.Part # Description Key Parameters Samples/Prod.MC33262 PFC Control IC Critical Conduction PFC Controller Now/NowMC33368 PFC Control IC Critical Conduction PFC Controller + Internal Start–up Now/NowMC33260 PFC Control IC Low System Cost, PFC with SynchronizationCapability, Follower Boost Mode, or Normal ModeNow/NowMC33365 PWM Control IC Fixed Frequency Controller + 700 V Start–up, 1 APower SwitchNow/NowMC33364 PWM Control IC Variable Frequency Controller + 700 V Start–up Switch Now/NowMC44603A/604 PWM Control IC GreenLine, Sync. Facility with Low Standby Mode Now/NowMC44605 PWM Control IC GreenLine, Sync. Facility, Current–mode Now/NowMC44608 PWM Control IC GreenLine, Fixed Frequency (40 kHz, 75 kHz and 100kHz options), Controller + Internal Start–up, 8–pinNow/NowMSR860 Ultrasoft Rectifier 600 V, 8 A, trr = 55 ns, Ir max = 1 uA Now/NowMUR440 Ultrafast Rectifier 400 V, 4 A, trr = 50 ns, Ir max = 10 uA Now/NowMRA4006T3 Fast Recovery Rectifier 800 V, 1 A, Vf = 1.1 V @ 1.0 A Now/NowMR856 Fast Recovery Rectifier 600 V, 3 A, Vf = 1.25 V @ 3.0 A Now/NowNCP1200 PWM Current–Mode Controller 110 mA Source/Sink, O/P Protection, 40/60/110 kHz Now/NowNCP1205 Single–Ended PWM Controller Quasi–resonant Operation, 250 mA Source/Sink,8–36 V OperationNow/NowUC3842/3/4/5High Performance Current–ModeControllers500 kHz Freq., Totem Pole O/P, Cycle–by–CycleCurrent Limiting, UV LockoutNow/Nowhttp://onsemi.com38

SMPSRMACLineRectifier+Start–upSwitchBulkStorageCapacitorPWMControlICPWM SwitcherUltrafastRectifierMOSFETFigure 39. AC/DC Power Supply for Storage,Imaging & Entertainment+Prog.Prec.RefLoadn–outputsTable 2.Part # Description Key Parameters Samples/Prod.MC33363A/B/65 PWM Control IC Controller + 700 V Start–up & Power Switch, < 15 W Now/NowMC33364 PWM Control IC Critical Conduction Mode, SMPS Controller Now/NowTL431B Program Precision Reference 0.4% Tolerance, Prog. Output up to 36 V, TemperatureCompensatedNow/NowMSRD620CT Ultrasoft Rectifier 200 V, 6 A, trr = 55 ns, Ir max = 1 uA Now/NowMR856 Fast Recovery Rectifier 600 V, 3 A, Vf = 1.25 V @ 3.0 A Now/NowNCP1200 PWM Current–Mode Controller 110 mA Source/Sink, O/P Protection, 40/60/110 kHz Now/NowNCP1205 Single–Ended PWM Controller Quasi–resonant Operation, 250 mA Source/Sink,8–36 V OperationNow/NowUC3842/3/4/5High Performance Current–ModeControllers500 kHz Freq., Totem Pole O/P, Cycle–by–CycleCurrent Limiting, UV LockoutNow/Nowhttp://onsemi.com39

SMPSRM+V in–Control ICLoCoVoltageRegulation+V out–LoadLo++V in Co VControl ICout––LoadBuck RegulatorSynchronous Buck RegulatorFigure 40. DC – DC ConversionTable 3.Part # Description Key Parameters Samples/Prod.MC33263Low Noise, Low DropoutRegulator IC150 mA; 8 Outputs 2.8 V – 5 V; SOT 23L 6 LeadPackageNow/NowMC33269 Medium Dropout Regulator IC 0.8 A; 3.3; 5, 12 V out; 1 V diff; 1% Tolerance Now/NowMC33275/375 Low Dropout Regulator 300 mA; 2.5, 3, 3.3, 5 V out Now/NowLP2950/51 Low Dropout, Fixed Voltage IC 0.1 A; 3, 3.3, 5 V out; 0.38 V diff; 0.5% Tolerance Now/NowMC78PCCMOS LDO Linear VoltageRegulatorI out = 150 mA, Available in 2.8 V, 3 V, 3.3 V, 5 V; SOT23 – 5 LeadsNow/NowMC33470 Synchronous Buck Regulator IC Digital Controlled; V cc = 7 V; Fast Response Now/NowNTMSD2P102LR2 P–Ch FET w/Schottky in SO–8 20 V, 2 A, 160 m FET/1 A, Vf = 0.46 V Schottky Now/NowNTMSD3P102R2 P–Ch FET w/Schottky in SO–8 20 V, 3 A, 160 m FET/1 A, Vf = 0.46 V Schottky Now/NowMMDFS6N303R2 N–Ch FET w/Schottky in SO–8 30 V, 6 A, 35 m FET/3 A, Vf = 0.42 V Schottky Now/NowNTMSD3P303R2 P–Ch FET w/Schottky in SO–8 30 V, 3 A, 100 m FET/3 A, Vf = 0.42 V Schottky Now/NowMBRM140T31A Schottky in POWERMITE®Package40 V, 1 A, Vf = 0.43 @ 1 A; Ir = 0.4 mA @ 40 V Now/NowMBRA130LT3 1A Schottky in SMA Package 40 V, 1 A, Vf = 0.395 @ 1 A; Ir = 1 mA @ 40 V Now/NowMBRS2040LT3 2A Schottky in SMB Package 40 V, 2 A, Vf = 0.43 @ 2 A; Ir = 0.8 mA @ 40 V Now/NowMMSF3300 Single N–Ch MOSFET in SO–8 30 V, 11.5 A (1) , 12.5 m @ 10 V Now/NowNTD4302 Single N–Ch MOSFET in DPAK 30 V, 18.3 A (1) , 10 m @ 10 V Now/NowNTTS2P03R2MGSF3454X/VNTGS3441T1Single P–Ch MOSFET inMicro8 PackageSingle N–Ch MOSFET inTSOP–6Single P–Ch MOSFET inTSOP–630 V, 2.7 A, 90 m @ 10 V Now/Now30 V, 4.2 A, 65 m @ 10 V Now/Now20 V, 3.3 A, 100 m @ 4.5 V Now/NowNCP1500Dual Mode PWM Linear BuckConverterProg. O/P Voltage 1.0, 1.3, 1.5, 1.8 VNow/NowNCP1570Low Voltage Synchronous BuckConverterUV Lockout, 200 kHz Osc. Freq., 200 ns ResponseNow/NowNCP1571Low Voltage Synchronous BuckConverterUV Lockout, 200 kHz Osc. Freq., 200 ns ResponseNow/NowCS5422Dual Synchronous BuckConverter150 kHz–600 kHz Prog. Freq., UV Lockout, 150 nsTransient ResponseNow/Now(1) Continuous at T A = 25° C, Mounted on 1” square FR–4 or G10, V GS = 10 V t 10 secondshttp://onsemi.com40

http://onsemi.com41Part No. VRRM(V) Io(A) Package1N5404RL 400 1000 3 Axial1N5406RL 400 1000 3 Axial1N5408RL 400 10003 AxialPart No.U384X SeriesMC34060TL494TL594MC34023MC44608MC44603MC44603AVoltageStand–byMains230 Vac5 V 0.1 APackageDIP8/SO–8/SO–14DIP14/SO–14DIP16/SO–16DIP16/SO–16DIP16/SO–16DIP8DIP16/SO–16DIP16/SO–16Part No.MBR160+PWMICV (V)RRMI (A)o60 1PackageAxial+++++MATRIX+3.3 V 14 A+5 V 22 A+12 V 6 A–5 V 0.5 A–12 V 0.8 APart No.MBR2535CTLPart No. VRRM(V) Io(A) PackageMBR2535CTL 35 25 TO–220MBR2545CT 45 25 TO–220MBR3045ST 45 30 TO–220MBRF2545CT 45 25 TO–220MBR3045PT 45 30 TO–218MBR3045WT 45 30 TO–247Part No. VRRM(V) Io(A) PackageMBR2060CT 60 20 TO–220MBR20100CT 100 20 TO–220MBR20200CT 200 20 TO–220MUR1620CT 200 16 TO–220MUR1620CTR 200 16 TO–220MURF1620CT 200 16 TO–220Part No. VRRM(V) Io(A) PackageMBRS340T3MBRD340404033SMCDPAK1N5821 30 3 Axial1N5822 40 3 AxialMBR340 40 3 AxialPart No.MBR3100V (V)RRMV (V)RRMI (A)o100 3I (A)o35 25PackageAxialPackageTO–220Part No.VRRM(V)MUR180E, MUR1100E 600 1000MUR480E, MUR4100E 600 1000MR756RL, MR760RL 600 10001N4937 600Io(A)1461PackageAxialAxialAxialAxialFigure 35. Typical 200 W ATX Forward Mode SMPSFigure 41. . Typical 200 WATX Forward Mode SMPSPart No.TL431PackageTO–92SMPSRM

SMPSRMApplication: 80 W Power Factor Controller92 to138 VacRFIFILTERD 2D 11D 4D 3C 5MC33262ZERO CURRENTDETECTOR2.5 VREFERENCE++1.2 V1.6 V/1.4 V36 V6.7 V+ 13 V/8.0 V100 kR 685+1N4934D 6100C 422 kR 4TMUR130D 5V O0.01C 2TIMER R 16 V230 V/10500 V/8 A70.35 ADRIVEN–ChDELAYMOSFET +OUTPUT 220RS10Q 1 C 3LATCH2.2 M1.0 MR 20 k 45 R 21.5 V OVERVOLTAGE0.110 pFR 7CURRENTCOMPARATORSENSECOMPARATOR+ 1.08 VrefERROR AMP10 A +Vref7.5 kR 33QUICKSTART111 kR 16 20.68C 1Figure 42. 80 W Power Factor ControllerFeatures:Reduced part count, low–cost solution.ON Semiconductor Advantages:Complete semiconductor solution based around highly integrated MC33262.Devices:Part NumberDescriptionMC33262Power Factor ControllerMUR130 Axial Lead Ultrafast Recovery Rectifier (300 V)TransformerCoilcraft N2881–APrimary: 62 turns of #22 AWGSecondary: 5 turns of #22 AWGCore: Coilcraft PT2510Gap: 0.072” total for a primary inductance (Lp) of 320 Hhttp://onsemi.com42

SMPSRMApplication: Compact Power Factor CorrectionVccFUSE 0.33 µFAC LINE100 nFMAINSFILTER1N540410 µF/16 V+L1MUR460Vout+100 µF/450 V100 nF123MC3326087610 500 V/8 AN–ChMOSFET12 k451 M120 pF0.5 /3 W45 k 1 MFigure 43. Compact Power Factor CorrectionFeatures :Low–cost system solution for boost mode follower.Meets IEC1000–3–2 standard.Critical conduction, voltage mode.Follower boost mode for system cost reduction – smaller inductor and MOSFET can be used.Inrush current detection.Protection against overcurrent, overvoltage and undervoltage.ON Semiconductor advantages:Very low component count.No Auxiliary winding required.High reliability.Complete semiconductor solution.Significant system cost reduction.Devices:Part NumberDescriptionMC33260Power Factor ControllerMUR460 Ultrafast Recovery Rectifier (600 V)1N5404 General Purpose Rectifier (400 V)http://onsemi.com43

SMPSRMApplication: Monitor Pulsed–Mode SMPS90 Vac to270 VacRFIFILTER1 nF/500 V1 nF/1 kV4.7 MMR85647 µF22 µH90 V/0.1 A+ +47 µF1 D1 – D41N5404 150 µF400 V1 nF/500 V2WSYNC22 k47 µF +25 V3.3 k1.2 k10 pF 47 k982.2 nF1074.7 µF 2.2 k470 pF+1168.2 k12522 4704.7 µF+nF1N4148 560 kk10 V134V in2.2 nF56 k14310 152270 16156 k10 k1.8 MMC44605PNote 1: 500 V/8 A N–Channel MOSFETV in1N49343.9 k/6 W1 µH4.7 µF+10 V150 k1 k470 2.7 k1N4934100 nFMR8560.1 SMT31L p470 pFNote 1MOC81071N4742A12 V1 kMR856MR8521000 µFMR852MBR3604700 µFTL4314.7 k1000 µF220 µF120 pF1N4934 MCR22–6100 ++++10 k100 nF100 nF1N414845 V/1 A15 V/0.8 A–10 V/0.3 A8 V/1.5 A96.8 k2.7 kBC237BV PFROM P0: STAND–BY1: NORMAL MODEFigure 44. Monitor Pulsed–Mode SMPShttp://onsemi.com44

SMPSRMFeatures:Off power consumption: 40 mA drawn from the 8 V output in Burst mode.Vac (110 V) about 1 wattVac (240 V) about 3 wattsEfficiency (pout = 85 watts)Around 77% @ Vac (110 V)Around 80% @ Vac (240 V)Maximum Power limitation.Over–temperature detection.Winding short circuit detection.ON Semiconductor Advantages:Designed around high performance current mode controller.Built–in latched disabling mode.Complete semiconductor solution.Devices:Part NumberDescriptionMC44605PHigh Safety Latched Mode GreenLine ControllerFor (Multi) Synchronized ApplicationsTL431Programmable Precision ReferenceMR856 Fast Recovery Rectifier (600 V)MR852 Fast Recovery Rectifier (200 V)MBR360 Axial Lead Schottky Rectifier (60 V)BC237BNPN Bipolar Transistor1N5404 General–Purpose Rectifier (400 V)1N4742A Zener Regulator (12 V, 1 W)TransformerG6351–00 (SMT31M) from Thomson OregaPrimary inductance = 207 HArea = 190 nH/turns2Primary turns = 33Turns (90 V) = 31http://onsemi.com45

SMPSRMApplication: 70 W Wide Mains TV SMPS95 Vac to265 VacC30100 nF250 VacLF1RFIFILTERF1FUSE 1.6 AC191 nF/1 kVR322 kC4–C51 nF/1 kVC9100 nFR151 MR43.9 kR52.2 kR1447 kD151N4148D1–D41N40079C8 560 pF10C10 1 µF11R185.6 kC710 nF1213141516R1310 kR768 k/1 WMC44603AP3.8 M87654321C121 nFC16100 µFR1927 kC11100 pF R2215 k180 kR20 47R9 1501 kC1220 FD131N4148L11 µHR1668 k/2 W C15 220 pF L322 µH 115 V/0.45 AR81 kR330.31 C264.7 nFD71N4937Q1600 V/4 AN–ChMOSFETR214.7 MC14220 pFD12MR856 C2047 µFD5MR854D8MR854D2347 µF15 V/1.5 AC211000 µF11 V/0.5 AC221000 µFOREGA TRANSFORMERG6191–00THOMSON TV COMPONENTSFigure 45. 70 W Wide Mains TV SMPShttp://onsemi.com46

SMPSRMFeatures:70 W output power from 95 to 265 Vac.Efficiency@ 230 Vac = 86%@ 110 Vac = 84%Load regulation (115 Vac) = 0.8 V.Cross regulation (115 Vac) = 0.2 V.Frequency 20 kHz fully stable.ON Semiconductor Advantages:DIP16 or SO16 packaging options for controller.Meets IEC emi radiation standards.A narrow supply voltage design (80 W) is also available.Devices:Part NumberDescriptionMC44603APEnhanced Mixed Frequency ModeGreenLine PWM ControllerMR856 Fast Recovery Rectifier (600 V)MR854 Fast Recovery Rectifier (400 V)1N4007 General Purpose Rectifier (1000 V)1N4937 General Purpose Rectifier (600 V)TransformerThomson Orega SMT18http://onsemi.com47

SMPSRMApplication: Wide Mains 100 W TV SMPS with 1.3 W TV Stand–byC31100 nF47283900 R F6RFIFILTERF1C192N2F–YC31 nFR16 4.7 M/4 kVIsense1234C41 nFD51N4007R5 100 kMC44608P75R4 3.9 kD1–D41N54048765C8100 nFVccR210 +C5220 F400 VD6MR856D71N4148+ C722 F16 V600 V/6 AN–CHMOSFETR122 k5WC647 nF630 V67C9470 pF630 VD14MR856R172.2 k5 W121412111089C11220 pF/500 VD18 MR856C1247 µF/250 V+R7 47 kΩ C17 120 pFD9 MR852C14 +1000 µF/35 VC16100 pFD121N4934D10+MR852C151000 µF/16 VR1918 kC13100 nFDZ1MCR22–6R121 k112 V/0.45 A16 V/1.5 A8 V/1 AD131N4148C18100 nF123123J3J4R30.27 R21 47 R9100 kONOFFR1147 kOPT1DZ310 V1N4740ADZ2TL431CLPC1933 nFR1010 kR82.4 kON = Normal modeOFF = Pulsed modeFigure 46. Wide Mains 100 W TV SMPS with SecondaryReconfiguration for 1.3 W TV Stand–byhttp://onsemi.com48

SMPSRMFeatures:Off power consumption: 300mW drawn from the 8V output in pulsed mode.P in = 1.3W independent of the mains.Efficiency: 83%Maximum power limitation.Over–temperature detection.Demagnetization detection.Protection against open loop.ON Semiconductor Advantages:Very low component count controller.Fail safe open feedback loop.Programmable pulsed–mode power transfer for efficient system stand–by mode.Stand–by losses independent of the mains value.Complete semiconductor solution.Devices:Part NumberDescriptionMC44608P75GreenLine Very High Voltage PWM ControllerTL431Programmable Precision ReferenceMR856 Fast Recovery Rectifier (600 V)MR852 Fast Recovery Rectifier (200 V)1N5404 General Purpose Rectifier (400 V)1N4740A Zener Regulator (10 V, 1 W)TransformerSMT19 40346–29 (9 slots coil former)Primary inductance: 181 mHNprimary: 40 turnsN 112 V: 40 turnsN 16 V: 6 turnsN 8 V: 3 turnshttp://onsemi.com49

SMPSRMApplication: Low–Cost Offline IGBT Battery Charger130 to 350 V DC+R3220 kR1150R13100 kD11N4148C101 nFD4C3220 F/10 VD3MBRS240LT3D5 R2++C2220 F/10 V8 V at 400 mA–+C310 F/350 VR1120 kM1MMG05N60DR51 kMC14093R51N49371N4148IC1MOC8103150R11113 k0 VC710 FD212 V+C51 nF1.2 kQ1MBT3946DWR9470C91 nFR23.98 7 6 5MC33341R9100 Q5R10+C81 F1 2 3 4 D4C412 V47 nFR1220 kFigure 47. Low–Cost Offline IGBT Battery ChargerFeatures:Universal ac input.3 Watt capability for charging portable equipment.Light weight.Space saving surface mount design.ON Semiconductor Advantages:Special–process IGBT (Normal IGBTs will not function properly in this application).Off the shelf components.SPICE model available for MC33341.Devices:Part NumberDescriptionMMG05N60DInsulated Gate Bipolar Transistor in SOT–223 PackageMC33341Power Supply Battery Charger Regulator Control CircuitMBT3946DWDual General Purpose (Bipolar) TransistorsMBRS240LT3Surface Mount Schottky Power RectifierMC14093Quad 2–Input “NAND” Schmitt Trigger1N4937 General–Purpose Rectifier (600 V)http://onsemi.com50

SMPSRMApplication: 110 W Output Flyback SMPS180 VAC TO 280 VAC C31 nF / 1 KVRFIFILTERR11 / 5 WC4–C71 nF / 1000 VR34.7 kC32220 pFD1–D41N4007C2220 FC1100 FD51N4934C1747 nFR2022 k5 WD8MR856C30100 F120 V / 0.5 AC310.1 FC9C10R1510 kC111 nFR1610 k820 pF1 FR268 k / 2 W9101112131415MC44603P8765432C151 nFR427 kC16100 pFR7180 kR815 kR1010 R91 kL11 HD61N4148C144.7 nFD7MR856R51.2 kR6180 R261 kLauxLPNote 1C29220 pFD9MR852C271000 FC26220 pFD10MR852C251000 F28 V / 1 AC280.1 F15 V / 1 AC240.1 F161C23220 pFR1827 kR1910 kC13100 nFR142 X 0.56 //D11MR852C211000 F8 V / 1 AC220.1 FR1710 kR24270 R23117.5 kR2110 kC19100 nFD141N4733R251 kC126.8 nFNote 1: 600 V/ 6 A N–Channel MOSFETTL431C2033 nFR222.5 kFigure 48. 110 W Output Flyback SMPShttp://onsemi.com51

SMPSRMFeatures:Off–line operation from 180 V to 280 Vac mains.Fixed frquency and stand–by mode.Automatically changes operating mode based on load requirements.Precise limiting of maximum power in fixed frequency mode.ON Semiconductor Advantages:Built–in protection circuitry for current limitation, overvoltage detection, foldback, demagnetization and softstart.Reduced frequency in stand–by mode.Devices:Part NumberDescriptionMC44603PEnhanced Mixed Frequency Mode GreenLine PWM ControllerMR856 Fast Recovery Rectifier (600 V)MR852 Fast Recovery Rectifier (200 V)TL431Programmable Precision Reference1N4733A Zener Voltage Regulator Diode (5.1 V)1N4007 General Purpose Rectifier (1000 V)http://onsemi.com52

SMPSRMApplication: Efficient Safety Circuit for Electronic BallastC13 100 nF250 V R18 PTCC12 22 nFC14 100 nF250 VAGNDC11 4.7 nF1200 VPTUBE =55 WL1 1.6 mHQ2MJE18004D2R132.2 RT1AFT063 Q3MJE18004D2R142.2 RC92.2 nFR114.7 RC82.2 nFR124.7 RC6 10 nFT1BD3 1N4007DIACD4R1010 RC7 10 nFT1CNOTES: * All resistors are ± 5%, 0.25 Wunless otherwise noted* All capacitors are Polycarbonate, 63 V,± 10%, unless otherwise notedR9330 kR7 1.8 MD2 MUR180ET2D1MUR120R4 22 k+R3100 k/1.0 WR2 1.2 MC4 47 F+Q1500 V/4 A N–ChMOSFET3 182AGNDC2330 F25 V5 7U1MC342623450 V4261C1 10 nFC5 0.22 FP1 20 kR6 1.0 RR5 1.0 RC3 1.0 FR1 12 k1N5407D8D71N5407FUSEC15 100 nFC1647 nFC17 47 nF630 VLINE220 V1N5407D9630 V1N5407D6FILTERFigure 49. Efficient Safety Circuit for Electronic Ballasthttp://onsemi.com53

SMPSRMFeatures:Easy to implement circuit to avoid thermal runaway when fluorescent lamp does not strike.ON Semiconductor Advantages:Power devices do not have to be oversized – lower cost solution.Includes power factor correction.Devices:Part NumberDescriptionMC34262Power Factor ControllerMUR120 Ultrafast Rectifier (200 V)MJE18004D2 High Voltage Planar Bipolar Power Transistor (100 V)1N4007 General Purpose Diode (1000 V)1N5240B Zener Voltage Regulator Diode (10 V)1N5407 Rectifier (3 A, 800 V)*Other Lamp Ballast Options:1, 2 Lamps 3, 4 Lamps825 V BUL642D2 BUL642D2100 V MJD18002D2 MJB18004D21200 V MJD18202D2 MJB18204D2MJE18204D2ON Semiconductor’s H2BIP process integrates a diode and bipolar transistor for a single package solution.http://onsemi.com54

SMPSRMApplication: AC–DC Battery Charger – Constant Current withVoltage LimitJ11T0.2xF1D1250R5U1C3100 nF2+LINE10 F/350 VC110 V R12201N4140D3+R2D2 C2 20 F 4 kD4BZX84/18V1N4140R38Line7V CCMC33364GNDC3V ref FL4 31ICD6222 k1N4140R4330D5R647 kD6R547 kC41 nFMURS160T3R72.7MOC01025432R8100T16Q1600 V/1 AN–Ch MOSFET1SO1542171N4140D8 C5 + 4 kD91 FBZX84/5 V100 F +D7MURS320T3C5U2R10100 RR48 7 6 5MC333411 2 3 4C733 nFR110.255 VDOV CCCSIVSICSICTACMPGNDR1422 kR1312 kR1210 kJ212Figure 50. AC–DC Battery Charger – Constant Current with Voltage LimitFeatures:Universal ac input.9.5 Watt capability for charging portable equipment.Light weight.Space saving surface mount design.ON Semiconductor Advantages:Off the shelf componentsSPICE model available for MC33341Devices:Part NumberDescriptionMC33341Power Supply Battery Charger Regulator Control CircuitMC33364Critical Conduction SMPS ControllerMURS160T3 Surface Mount Ultrafast Rectifier (600 V)MURS320T3 Surface Mount Ultrafast Rectifier (200 V)BZX84C5V1LT1 Zener Voltage Regulator Diode (5.1 V)BZX84/18VZener Voltage Regulator Diode (MMSZ18T1)TransformerFor details consult AN1600http://onsemi.com55

SMPSRMLiterature Available from ON SemiconductorApplication NotesThese older Application Notes may contain part numbers that are no longer available, but the applications informationmay still be helpful in designing an SMPS. They are available through the Literature Distribution Center forON Semiconductor at 800–344–3860 or 303–675–2175 or by email at ONlit@hibbertco.com.AN873 – Understanding Power Transistor Dynamic Behavior: dv/dt Effects on Switching RBSOAAN875 – Power Transistor Safe Operating Area: Special Consideration for Switching Power SuppliesAN913 – Designing with TMOS Power MOSFETsAN915 – Characterizing Collector–to–Emitter and Drain–to–Source Diodes for Switchmode ApplicationsAN918 – Paralleling Power MOSFETs in Switching ApplicationsAN920 – Theory and Applications of the MC34063 and A78S40 Switching Regulator Control CircuitsAN929 – Insuring Reliable Performance from Power MOSFETsAN952 – Ultrafast Recovery Rectifiers Extend Power Transistor SOAAN1040 – Mounting Considerations for Power SemiconductorsAN1043 – SPICE Model for TMOS Power MOSFETsAN1080 – External–Sync Power Supply with Universal Input Voltage Range for MonitorsAN1083 – Basic Thermal Management of Power SemiconductorsAN1090 – Understanding and Predicting Power MOSFET Switching BehaviorAN1320 – 300 Watt, 100 kHz Converter Utilizes Economical Bipolar Planar Power TransistorsThe following Application Notes are available directly from the ON Semiconductor website(http://onsemi.com).AN1327 – Very Wide Input Voltage Range, Off–line Flyback Switching Power SupplyAN1520 – HDTMOS Power MOSFETs Excel in Synchronous Rectifier ApplicationsAN1541 – Introduction to Insulated Gate Bipolar TransistorAN1542 – Active Inrush Current Limiting Using MOSFETsAN1543 – Electronic Lamp Ballast DesignAN1547 – A DC to DC Converter for Notebook Computers Using HDTMOS and Synchronous RectificationAN1570 – Basic Semiconductor Thermal MeasurementAN1576 – Reduce Compact Fluorescent Cost with Motorola’s (ON Semiconductor) IGBTs for LightingAN1577 – Motorola’s (ON Semiconductor) D2 Series Transistors for Fluorescent ConvertersAN1593 – Low Cost 1.0 A Current Source for Battery ChargersAN1594 – Critical Conduction Mode, Flyback Switching Power Supply Using the MC33364AN1600 – AC–DC Battery Charger – Constant Current with Voltage Limithttp://onsemi.com56

SMPSRMLiterature Available from ON Semiconductor (continued)AN1601 – Efficient Safety Circuit for Electronic BallastAN1628 – Understanding Power Transistors Breakdown ParametersAN1631 – Using PSPICE to Analyze Performance of Power MOSFETs in Step–Down, Switching RegulatorsEmploying Synchronous RectificationAN1669 – MC44603 in a 110 W Output SMPS ApplicationAN1679 – How to Deal with Leakage Elements in Flyback ConvertersAN1680 – Design Considerations for Clamping Networks for Very High Voltage Monolithic Off–Line PWMControllersAN1681 – How to Keep a Flyback Switch Mode Supply stable with a Critical–Mode ControllerBrochures and Data BooksThermal Modeling & Management of Discrete Surface Mount PackagesAnalog/Interface ICs DeviceBipolar Device DataThyristor Device DataPower MOSFETsTVS/Zener Device DataRectifier Device DataMaster Components Selector GuideBR1487/DDL128/DDL111/DDL137/DDL135/DDL150/DDL151/DSG388/DDevice ModelsDevice models for SMPS circuits (MC33363 and MC33365), power transistors, rectifiers and other discrete productsare available through ON Semiconductor’s website or by contacting your local sales office.http://onsemi.com57

SMPSRMReference Books Relating to Switching Power Supply DesignBaliga, B. Jayant,Power Semiconductor Devices, PWS Publishing Co., Boston, 1996. 624 pages.Brown, Marty,Practical Switching Power Supply Design, Academic Press, Harcourt Brace Jovanovich, 1990. 240 pages.Brown, MartyPower Supply Cookbook, EDN Series for Design Engineers, ON Semiconductor Series in Solid State Electronics,Butterworth–Heinmann, MA, 1994. 238 pagesChrysiss, G. C.,High Frequency Switching Power Supplies: Theory and Design, Second Edition, McGraw–Hill, 1989. 287 pagesGottlieb, Irving M.,Power Supplies, Switching Regulators, Inverters, and Converters, 2nd Edition, TAB Books, 1994. 479 pages.Kassakian, John G., Martin F. Schlect, and George C. Verghese,Principles of Power Electronics, Addison–Wesley, 1991. 738 pages.Lee, Yim–Shu,Computer–Aided Analysis and Design of Switch–Mode Power Supplies, Marcel Dekker, Inc., NY, 1993Lenk, John D.,Simplified Design of Switching Power Supplies, EDN Series for Design Engineers, Butterworth–Heinmann, MA,1994. 221 pages.McLyman, C. W. T.,Designing Magnetic Components for High Frequency DC–DC Converters, KG Magnetics, San Marino, CA, 1993.433 pages, 146 figures, 32 tablesMitchell, Daniel,Small–Signal MathCAD Design Aids, e/j Bloom Associates, 115 Duran Drive, San Rafael, Ca 94903–2317,415–492–8443, 1992. Computer disk included.Mohan, Ned, Tore M. Undeland, William P. Robbins,Power Electronics: Converter, Applications and Design, 2nd Edition, Wiley, 1995. 802 pagesPaice, Derek A.,Power Electronic Converter Harmonics, Multipulse Methods for Clean Power, IEEE Press, 1995. 224 pages.Whittington, H. W.,Switched Mode Power Supplies: Design and Construction, 2nd Edition, Wiley, 1996 224 pages.Basso, Christophe,Switch–Mode Power Supply SPICE Cookbook, McGraw–Hill, 2001. CD–ROM included. 255 pages.http://onsemi.com58

SMPSRMWeb Locations for Switching–Mode Power Supply InformationArdem Associates (Dr. R. David Middlebrook)http://www.ardem.com/Applied Power Electronics Conference (APEC)The power electronics conference for the practical aspects of power supplies.http://www.apec–conf.org/Dr. Vincent G. Bello’s Home PageSPICE simulation for switching–mode power supplies.http://www.SpiceSim.com/e/j BLOOM Associates(Ed Bloom) Educational Materials & Services for Power Electronics.http://www.ejbloom.com/The Darnell Group(Jeff Shepard) Contains an excellent list of power electronics websites, an extensive list of manufacturer’s contactinformation and more.http://www.darnell.com/Switching–Mode Power Supply Design by Jerrold FoutzAn excellent location for switching mode power supply information and links to other sources.http://www.smpstech.com/Institute of Electrical and Electronics Engineers (IEEE)http://www.ieee.org/IEEE Power Electronics Societyhttp://www.pels.org/pels.htmlPower Control and Intelligent Motion (PCIM)Articles from present and past issues.http://www.pcim.com/Power CornerFrank Greenhalgh’s Power Corner in EDTNhttp://fgl.com/power1.htmPower Designershttp://www.powerdesigners.com/Power Quality Assurance MagazineArticles from present and past issues.http://powerquality.com/Power Sources Manufacturers AssociationA trade organization for the power sources industry.http://www.psma.com/Quantum Power LabsAn excellent hypertext–linked glossary of power electronics terms.http://www.quantumpower.com/Ridley Engineering, Inc.Dr. Ray Ridleyhttp://www.ridleyengineering.com/http://onsemi.com59

SMPSRMWeb Locations for Switching–Mode Power Supply Information(continued)Springtime Enterprises – Rudy SevernsRudy Severns has over 40 years of experience in switching–mode power supply design and static power conversionfor design engineers.http://www.rudyseverns.com/TESLAcoDr. Slobodan Cuk is both chairman of TESLAco and head of the Caltech Power Electronics Group.http://www.teslaco.com/Venable Industrieshttp://www.venableind.com/http://onsemi.com60

Analog ICs for SWITCHMODE Power SuppliesSMPSRMA number of different analog circuits that can be used for designing switchmode power supplies can be found in ourAnalog IC Family Tree and Selector Guide (SGD504/D) available on our website at www.onsemi.com or through ourLiterature Distribution Center, 800–344–3860 or (+1) 303–675–2175 or by email at ONlit@hibbertco.com. Thesecircuits are the same as those in the Power Management and System Management sections of the ON SemiconductorMaster Components Selector Guide, also available as SG388/D. Circuits used specifically for the off–line controllersand power factor controllers are in the Power Management section. Additional circuits that are frequently used with aSMPS design (dc–dc converters, voltage references, voltage regulators, MOSFET/IGBT drivers and dedicated powermanagement controllers) are included for reference purposes. Undervoltage and overvoltage supervisory circuits are inthe System Management section.Information about the discrete semiconductors that are shown in this brochure and other discrete products that maybe required for a switching power supply can also be found in the ON Semiconductor Master Components Selector Guide(SG388/D).http://onsemi.com61

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SMPSRMON SEMICONDUCTOR STANDARD DOCUMENT TYPE DEFINITIONSDATA SHEET CLASSIFICATIONSA Data Sheet is the fundamental publication for each individual product/device, or series of products/devices, containing detailedparametric information and any other key information needed in using, designing–in or purchasing of the product(s)/device(s) itdescribes. Below are the three classifications of Data Sheet: Product Preview; Advance Information; and Fully Released Technical Data.PRODUCT PREVIEWA Product Preview is a summary document for a product/device under consideration or in the early stages of development.The Product Preview exists only until an “Advance Information” document is published that replaces it. The Product Previewis often used as the first section or chapter in a corresponding reference manual. The Product Preview displays the followingdisclaimer at the bottom of the first page: “This document contains information on a product under development.ON Semiconductor reserves the right to change or discontinue this product without notice.”ADVANCE INFORMATIONThe Advance Information document is for a device that is NOT fully qualified, but is in the final stages of the releaseprocess, and for which production is eminent. While the commitment has been made to produce the device, finalcharacterization and qualification may not be complete. The Advance Information document is replaced with the “FullyReleased Technical Data” document once the device/part becomes fully qualified. The Advance Information documentdisplays the following disclaimer at the bottom of the first page: “This document contains information on a new product.Specifications and information herein are subject to change without notice.”FULLY RELEASED TECHNICAL DATAThe Fully Released Technical Data document is for a product/device that is in full production (i.e., fully released). Itreplaces the Advance Information document and represents a part that is fully qualified. The Fully Released Technical Datadocument is virtually the same document as the Product Preview and the Advance Information document with the exceptionthat it provides information that is unavailable for a product in the early phases of development, such as complete parametriccharacterization data. The Fully Released Technical Data document is also a more comprehensive document than either ofits earlier incarnations. This document displays no disclaimer, and while it may be informally referred to as a “data sheet,”it is not labeled as such.DATA BOOKA Data Book is a publication that contains primarily a collection of Data Sheets, general family and/or parametric information,Application Notes and any other information needed as reference or support material for the Data Sheets. It may also contain crossreference or selector guide information, detailed quality and reliability information, packaging and case outline information, etc.APPLICATION NOTEAn Application Note is a document that contains real–world application information about how a specific ON Semiconductordevice/product is used, or information that is pertinent to its use. It is designed to address a particular technical issue. Parts and/orsoftware must already exist and be available.SELECTOR GUIDEA Selector Guide is a document published, generally at set intervals, that contains key line–item, device–specific information forparticular products or families. The Selector Guide is designed to be a quick reference tool that will assist a customer in determiningthe availability of a particular device, along with its key parameters and available packaging options. In essence, it allows a customerto quickly “select” a device. For detailed design and parametric information, the customer would then refer to the device’s Data Sheet.The Master Components Selector Guide (SG388/D) is a listing of ALL currently available ON Semiconductor devices.REFERENCE MANUALA Reference Manual is a publication that contains a comprehensive system or device–specific descriptions of the structure andfunction (operation) of a particular part/system; used overwhelmingly to describe the functionality or application of a device, seriesof devices or device category. Procedural information in a Reference Manual is limited to less than 40 percent (usually much less).HANDBOOKA Handbook is a publication that contains a collection of information on almost any give subject which does not fall into theReference Manual definition. The subject matter can consist of information ranging from a device specific design information, tosystem design, to quality and reliability information.ADDENDUMA documentation Addendum is a supplemental publication that contains missing information or replaces preliminary informationin the primary publication it supports. Individual addendum items are published cumulatively. The Addendum is destroyed upon thenext revision of the primary document.http://onsemi.com63

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