Switch Mode Power Supply (SMPS) Topologies (Part II) - Microchip

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AN1207FIGURE 40:HALF-BRIDGE CONVERTER WAVEFORMS: SECONDARY SIDEQ1 Commandt(A)Q2 Commandt(B)NP/NS VDC/2VS-NS/NP VDC/2NS/NP VDCVD3tt(C)(D)ID3t(E)VD4t(F)ID4t(G)VLt(H)IO, av, nomILt(I)(A) = Command signal on Q1 MOSFET gate(B) = Command signal on Q2 MOSFET gate(C) = Voltage V S on secondary winding NS(D) = Voltage on diode D3(E) = Current flowing in diode D3(F) = Voltage on diode D4(G) = Current flowing in diode D4(H) = Voltage on inductor LO(I) = Current in inductor LODS01207B-page 44© 2009 <strong>Microchip</strong> Technology Inc.
AN1207Design Equations and ComponentSelectionINPUT/OUTPUT RELATIONSHIP AND DUTYCYCLEAt the Steady state, the increase in inductor currentduring TON must equal its decrease during TR (neglectingthe forward drop on the diode), as shown inEquation 144.EQUATION 144:Equation 147 shows the input power.EQUATION 147:Equation 148 shows the output power.EQUATION 148:P I=V--------- DCI2 P, mr2DP O= ηP IV OUT=N S------V DCDN Pwhere η is the efficiencywhere DT ON= --------- , and ( TTON+ T R)=T--2Operating on these two equations results inEquation 149.Consequently, knowing that there are two pulses in thePWM period, the maximum theoretical duty cycle isDmax, theoretical = 0.5. Of course, to avoid the shootthroughin the two switches, the maximum duty cyclecorresponding to the minimum input voltage, will beless.TRANSFORMER: PRIMARYAs soon as the transformer core has been defined, theprimary turns number can be computed from Faraday’slaw as shown in Equation 145, resulting inEquation 146.EQUATION 149:P OI P, mr= -------------------------------------ηV DC, minD maxEquation 150 shows the rms value.EQUATION 150:I P, rms= I P, mrD maxEQUATION 145:TRANSFORMER: SECONDARY, NUMBER OFTURNS, WIRE SIZEΔBV PT ON= -------------------N PA coreThe secondary turns number shown in Equation 151,can be obtained from Equation 144 and Equation 146.EQUATION 146:EQUATION 151:N P=V DC, minD max---------------------------------------2F PWMA coreΔBN S=V OUT---------------------------------------2F PWMA coreΔBTRANSFORMER: PRIMARY, WIRE SIZECurrent flowing in the primary windings is plotted inFigure 39(E and G). It is the sum of the magnetizingcurrent flowing into the primary windings and the secondaryload current reflected back by the transformerturn ratio.To make computations simpler, the real current waveformscan be replaced with the mid-ramp value (IP, mr)and determine its value considering the input (PI) andoutput (PO) power.The average output current, shown as IO, av, nom inFigure 40(I), is the average output current the converteris designed for. The rms secondary current (IS)results in Equation 152.EQUATION 152:I Srms ,= I O, av,nomD max© 2009 <strong>Microchip</strong> Technology Inc. DS01207B-page 45
Page 1 and 2: AN1207Switch Mode Power Supply (SMP
Page 3 and 4: AN1207FIGURE 4:VLINDUCTOR BEHAVIORI
Page 5: AN1207Supposing the output load RO
Page 8: AN1207OUTPUT CAPACITORThe current r
Page 13 and 14: AN1207MOSFET selectionThe key param
Page 15 and 16: AN1207EQUATION 50:V OUTwhere D is t
Page 19 and 20: AN1207Q1 ON (INTERVAL 0 - TON)For t
Page 21 and 22: AN1207Input Circuit BehaviorBefore
Page 23 and 24: AN1207TRANSFORMER: PRIMARYThe core
Page 25 and 26: AN1207FIGURE 22:FORWARD CONVERTER W
Page 27 and 28: AN1207EQUATION 96:( - )------------
Page 29 and 30: AN1207FIGURE 24:FORWARD CONVERTER W
Page 31 and 32: AN1207Q1 ON, Q2 ON (INTERVAL 0 - TO
Page 33 and 34: AN1207Q1 OFF Q2 OFF (INTERVAL (TON
Page 35 and 36: AN1207FIGURE 30:TWO-SWITCH FORWARD
Page 37 and 38: AN1207DIODESTable 2 provides calcul
Page 39 and 40: AN1207HALF-BRIDGE CONVERTERDesign E
Page 41 and 42: AN1207Q1 OFF, Q2 ONIn this configur
Page 43: AN1207FIGURE 39:HALF-BRIDGE CONVERT
Page 47 and 48: AN1207PUSH-PULL CONVERTERThe Push-P
Page 49 and 50: AN1207Q1 OFF, Q2 ONIn this configur
Page 51 and 52: AN1207TRANSFORMER: PRIMARY, NUMBER
Page 53 and 54: AN1207TRANSFORMER: SECONDARY, NUMBE
Page 55 and 56: AN1207Switching LossesFigure 48 plo
Page 57 and 58: AN1207FULL-BRIDGE CONVERTERA Full-B
Page 59 and 60: AN1207Q1 ON, Q4 ON; Q2 OFF, Q3 OFF(
Page 61 and 62: AN1207Design Equations and Componen
Page 63 and 64: AN1207TRANSFORMER: SECONDARY, NUMBE
Page 65 and 66: AN1207OUTPUT INDUCTORThe minimum in
Page 67 and 68: AN1207Q1 ON (INTERVAL 0 - TON)Figur
Page 69 and 70: AN1207Design Equations and Componen
Page 71 and 72: AN1207FIGURE 61:FLYBACK CONVERTER T
Page 73 and 74: AN1207Topology Equations - Continuo
Page 75 and 76: AN1207TRANSFORMER WINDINGS TURN RAT
Page 77 and 78: AN1207FIGURE 64:BUCK CONVERTER - BA
Page 79 and 80: AN1207FIGURE 67:VOLTAGE MODE CONTRO
Page 81 and 82: AN1207ADVANTAGES AND DISADVANTAGES
Page 83 and 84: AN1207PROBLEMSAs seen in Figure 71,
Page 85 and 86: AN1207Other Current Mode Techniques
Page 87 and 88: AN1207Control TheoryUp to this poin
Page 89 and 90: AN1207The GM(s) transfer function i
Page 91 and 92: AN1207bus and the address generatin
Page 93 and 94: AN1207The block diagram now is as s
Page 95 and 96:
AN1207Behavior of the PIDAs can be
Page 97 and 98:
AN1207The voltage from the ADC is s
Page 99 and 100:
AN1207TABLE 5:FrequencyFIGURE 90:FR
Page 101 and 102:
AN1207FIGURE 91:PROGRAM FLOWMAINIni
Page 103 and 104:
AN1207ADC Interrupt Service Routine
Page 105 and 106:
AN1207APPENDIX A:SOURCE CODESoftwar
Page 107 and 108:
Note the following details of the c
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