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

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AN1207EQUATION 72:------ ( VN DC– V Q,on)– V D, on– V OUTPI L() t = I L( 0)+ ---------------------------------------------------------------------------------tAt this point, the total current flowing into the primarycan be computed. It has two contributions: the magnetizingcurrent (see Equation 67) and the load currentreflected back into the primary, as shown inEquation 73.EQUATION 73:N SI P totalL O------ ( VV DC– V Q,onN SN DC– V Q,on)– V D, on– V OUT,I L( 0)------------------------------t ------ P= + + ---------------------------------------------------------------------------------tL MN PN SL OQ1 OFF [INTERVAL TON - (TON + TR)]Based on this configuration, the circuit is redrawn, asshown in Figure 19.FIGURE 19:FORWARD CONVERTER TOPOLOGY: INTERVAL TON - (TON + TR)D1VRNRVAAD2BVBLONPNSVSD3VLCOROVOUTVDCVPQ1DS01207B-page 20© 2009 <strong>Microchip</strong> Technology Inc.
AN1207Input Circuit BehaviorBefore the switch Q1 was opened, the magnetizingcurrent was flowing in NP. When the switch opens, itreverses all the voltages to continue the flow. The dotend of NR becomes negative in respect to the non-dotend, and a similar behavior is experienced by thewinding NP. Because of the polarity on NR, diode D1becomes forward-biased and keeps the voltage at thedot end of NR, one diode drop below ground.Magnetizing current can now flow through NR anddiode D1 into the power supply VDC, as shown inFigure 19. The voltage VR on NR is shown inEquation 74.EQUATION 74:The voltage on NP is shown in Equation 75.EQUATION 75:When t = TON, the current in the reset winding equalsthe magnetizing current IM multiplied by the windingsration, as shown in Equation 76.EQUATION 76:V R= –( V DC+ V D,on) < 0N PV P, off= ------N R– ( V DC+ V D,on) < 0Output Circuit BehaviorAs previously mentioned, the magnetizing currentreverses all voltages when the switch Q1 turns off. Asa result, the dot end of the secondary winding is morenegative than the non-dot end and diode D2 becomesreverse-biased.The secondary voltage is shown in Equation 77.EQUATION 77:To keep the current flowing into inductor LO, its voltagereverses so that the left end of the inductor is more negativethan the right end, and it would continuouslydecrease; however, the freewheeling diode D3,becoming forward-biased and sets VB to a diode voltagedrop below ground. The voltage on the inductor isnow equal to Equation 78.EQUATION 78:Consequently the inductor current will decreaseaccording to Equation 79:EQUATION 79:N SV S, off= ------N RV L– ( V DC+ V D,on)= – V OUT– V D,onI R=N PN R------I MV OUT+ V D,onI L() t = IT ( ON) – ---------------------------------- tL ODuring TR, this current has a down-slope and reacheszero when t = TON + TR.This current is the same current that is flowing into thefree-wheeling diode D3.© 2009 <strong>Microchip</strong> Technology Inc. DS01207B-page 21
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: AN1207Q1 ON (INTERVAL 0 - TON)For t
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 and 44: AN1207FIGURE 39:HALF-BRIDGE CONVERT
Page 45 and 46: AN1207Design Equations and Componen
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 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 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
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AN1207PROBLEMSAs seen in Figure 71,
Page 85 and 86:
AN1207Other Current Mode Techniques
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AN1207Control TheoryUp to this poin
Page 89 and 90:
AN1207The GM(s) transfer function i
Page 91 and 92:
AN1207bus and the address generatin
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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
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AN1207TABLE 5:FrequencyFIGURE 90:FR
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AN1207FIGURE 91:PROGRAM FLOWMAINIni
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AN1207ADC Interrupt Service Routine
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AN1207APPENDIX A:SOURCE CODESoftwar
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Note the following details of the c
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Switch Mode Power Supply (SMPS) Topologies (Part II) - Microchip

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