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

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AN1207TWO-SWITCH FORWARDCONVERTERClearly derived from the single-ended topology(Forward Converter), this circuit has significantadvantages over single-ended forward converters. Aschematic of this topology is shown in Figure 25.FIGURE 25:TWO-SWITCH FORWARD CONVERTER TOPOLOGYQ1D3VBVLVDCD2D1NPNSVSD4LOCOVOUTQ2Topology EquationsReferring to the section on Two-Switch ForwardConverters in AN1114 (see “Introduction”), the basicequations are reviewed first followed by the selection ofcircuit components.Both switches, Q1 and Q2, are simultaneously drivenby a square wave signal with a duty cycle less than 0.5,as shown in Figure 26.FIGURE 26:SIGNAL DRIVING SWITCHES Q1 AND Q2TRQ1 CommandQ2 CommandTONTDS01207B-page 30© 2009 Microchip Technology Inc.
AN1207Q1 ON, Q2 ON (INTERVAL 0 - TON)In this configuration, the circuit is redrawn, as shown inFigure 27.FIGURE 27:TWO-SWITCH FORWARD CONVERTER TOPOLOGY: INTERVAL 0 - TONIPRIMARYQ1D3VBVLVDCD2D1NPNSVSD4LOCOVOUTQ2Input Circuit BehaviorThe transformer is connected between VDC andground; the dot end is more positive than the non-dotend and the magnetizing current is flowing through it.Both diodes at the primary are reverse-biased and donot contribute to the operation.The voltage on the primary is equal to Equation 104.EQUATION 104:The secondary voltage is equal to Equation 106.EQUATION 106:V SN S= ------ ( V DC– 2V Q,on)N PEquation 107 shows the voltage on the inductor.EQUATION 107:V P= V DC– 2V Q,onV L=N S------ ( V DC– 2V Q,on) VN P– D, on– V OUTThe magnetizing current in the transformer has apositive slope increase as shown in Figure 30(C):EQUATION 105:I M() t( )= -------------------------------------- tV DC– 2V Q,onL MThe total current in the primary is this magnetizingcurrent plus the secondary current reflected by thetransformer back to the primary.Output Circuit BehaviorSimilar to the primary, the secondary winding experiencesa voltage that is higher at the dot end comparedto the non-dot end. Therefore, diode D3 is forwardbiasedand conducting the current to the inductor, whilediode D4 is reversed-biased.As shown in Equation 108, the current in the inductorhas a linearly growing behavior (see alsoFigure 31(E)).EQUATION 108:N S------ ( VN DC– 2V Q,on)– V D, on– V OUTPI L() t = I L( 0)+ ----------------------------------------------------------------------------------tAt this point, the total current in the primary windingscan be computed as the sum of the magnetizing currentand the secondary current reflected back into theprimary (see Figure 30(F)), as shown in Equation 109.L OEQUATION 109:I P, total() t = I L( 0)------ ( V( ) N-------------------------------------- ------ SN DC– 2V Q,on)– V D, on– V OUTP+ + ----------------------------------------------------------------------------------tV DC– 2V Q,onL MN PN SL O© 2009 Microchip Technology Inc. DS01207B-page 31
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: AN1207FIGURE 24:FORWARD CONVERTER W
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
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AN1207The GM(s) transfer function i
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AN1207bus and the address generatin
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AN1207The block diagram now is as s
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AN1207Behavior of the PIDAs can be
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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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