AN4134

AN4134 FAIRCHILD | Alldatasheet

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forward converter employing FPS (Fairchild Power Switch). with a large number of design variables. described in this paper, is also provided. MOSFET and PWM controller solution. example using the software tool is provided. Figure 1. Basic Off-line Forward Converter Using FPS

winding and reset winding, respectively. voltage on the MOSFET can be reduced by decreasing Dmax. is widely used for many cost-sensitive SMPS. Figure 4. RCD Reset Forward Converter in reduced voltage stress on the secondary side. design, it is reasonable to set KRF=0.1~ 0.2. Figure 5. Output Inductor Current and Ripple Factor below the pulse-by-pulse current limit level of the FPS (Ilim).

equation as a starting point. Figure 6. Window Area and Cross Sectional Area the feedback controlled secondary side as a reference. AL is the AL-value with no gap in nH/turns2. forward voltage drop of the n-th output. differently according to the reset method. voltage protection during the normal operation. proper to set Vcc* to be 2-3 V higher than Vcc start voltage. transformer winding based on the rms current. Io(n) is the maximum current of n-th output.

11.1 Pin×

rent of the reset winding is as follows. multiple strands of thinner wire to minimize skin effect. Ac is the actual conductor area and KF is the fill factor. Typically the fill factor is 0.2-0.3 when a bobbin is used. winding their separate coils on a single, common core. Figure 7. Coupled Output Inductors transformer turns ratio of the two outputs as follows. inductor winding based on the rms current. multiple strands of thinner wire to minimize skin effect. based on the voltage and current ratings. considering the voltage and current ripple.

©2003 Fairchild Semiconductor Corporation where VOP is opto-diode forward voltage drop, which is typically 1V and IFB is the feedback current of FPS, which is typically 1mA. For example, Rbias<1kΩ and RD <1.5kΩ for Vo1=5V . Vo VOP– 2.5– RD VOP Rbias

©2002 Fairchild Semiconductor Corporation - Summary of symbols - Aw : Window area of the core in mm2 Ae : Cross sectional area of the core in mm2 Bsat : Saturation flux density in tesla. ∆B : Maximum flux density swing in tesla in normal operation Co : Capacitance of the output capacitor. Dmax : Maximum duty cycle ratio Eff : Estimated efficiency fL : Line frequency fs : Switching frequency Ids peak : Maximum peak current of MOSFET Ids rms : RMS current of MOSFET Ilim : FPS current limit level. Isec(n) rms : RMS current of the n-th secondary winding ID(n) rms : Maximum rms current of the rectifier diode for the n-th output Ic(n) rms : RMS Ripple current of the n-th output capacitor IO : Output load current KL(n) : Load occupying factor for n-th output KRF : Current ripple factor Lm : Transformer primary side inductance Losssn : Power loss of the snubber network in normal operation Np min : The minimum number of turns for the transformer primary side to avoid saturation Np : Number of turns for primary side Nr : Number of turns for reset winding Ns1 : Number of turns for the reference output Po : Maximum output power Pin : Maximum input power Rc : Effective series resistance (ESR) of the output capacitor. Rsn : Snubber resistor RL : Output load resistor Vline min : Minimum line voltage Vline max : Maximum line voltage VDC min : Minimum DC link voltage VDC max : Maximum DC line voltage Vds nom : Maximum nominal MOSFET voltage Vo1 : Output voltage of the reference output. VF1* : Diode forward voltage drop of the reference output. Vcc* : Nominal voltage for Vcc VFa : Diode forward voltage drop of Vcc winding ∆VDC max : Maximum DC link voltage ripple VD(n) : Maximum voltage of the rectifier diode for the n-th output ∆Vo(n) : Output voltage ripple of the n-th output Vsn : Snubber capacitor voltage in normal operation ∆Vsn : Snubber capacitor voltage ripple Vsn max : Maximum snubber capacitor voltage during transient or over load situation Vds max : Maximum voltage stress of MOSFET

©2003 Fairchild Semiconductor Corporation Appendix. Design Example using FPS design Assistant Target System : PC Power Supply - Input : universal input (90V-265Vrms) with voltage doubler - Output : 5V/15A, 3.3V/10A, 12V/6A By Choi For forward converter with reset winding Blue cell is the input parameters Red cellRed cellRed cellRed cell is th e output param eters 1. Define specifications of th e SMPS1. Define specifications of th e SMPS1. Define specifications of th e SMPS1. Define specifications of th e SMPS Minimum Lin e voltage (V_line.min) 180 V.rms Maximum Line voltage (V_line.max) 265 V.rms Line frequency (fL) 60 Hz VoVoVoVo Io IoIoIo Po PoPoPo KL KLKLKL 1st output for f eedback 5 V 15 A 75757575 WWWW4 2 424242 %%%% 2nd output 3.3 V1 0 A 33333333 WWWW1 8 181818 %%%% 3rd output 12 V6 A 72727272 WWWW4 0 404040 %%%% 4th output 0 V 0 A 0000WWWW0 000%%%% Maximum output po wer (Po) =Maximum output po wer (Po) =Maximum output po wer (Po) =Maximum output po wer (Po) = 180.0 180.0180.0180.0 WWWW Estimated efficiency (Eff) 70 % Maximum input po wer (Pin) =Maximum input po wer (Pin) =Maximum input po wer (Pin) =Maximum input po wer (Pin) = 257.1 257.1257.1257.1 WWWW 2. Determine DC link capacitor and th e DC voltag e range2. Determine DC link capacitor and th e DC voltag e range2. Determine DC link capacitor and th e DC voltag e range2. Determine DC link capacitor and th e DC voltag e range DC link capacitor 235 uF DC link voltag e ripple =DC link voltag e ripple =DC link voltag e ripple =DC link voltag e ripple =2 9 292929 VVVV Minimum DC link voltag e =Minimum DC link voltag e =Minimum DC link voltag e =Minimum DC link voltag e =2 2 6 226226226 VVVV Maximum DC link voltag e =Maximum DC link voltag e =Maximum DC link voltag e =Maximum DC link voltag e =3 7 5 375375375 VVVV 3. Determine the maximum duty ratio (Dmax)3. Determine the maximum duty ratio (Dmax)3. Determine the maximum duty ratio (Dmax)3. Determine the maximum duty ratio (Dmax) Maximum duty ratio 0.4 Turns ratio (Np/Nr) 1 > Maximum nominal MOSFET voltag e =Maximum nominal MOSFET voltag e =Maximum nominal MOSFET voltag e =Maximum nominal MOSFET voltag e =7 5 0 750750750 VVVV 4. Determine the ripple factor of th e output inductor curr ent4. Determine the ripple factor of th e output inductor curr ent4. Determine the ripple factor of th e output inductor curr ent4. Determine the ripple factor of th e output inductor curr ent Output Inductor curr ent ripple factor 0.15 Maximum p eak drain curr ent =Maximum p eak drain curr ent =Maximum p eak drain curr ent =Maximum p eak drain curr ent = 3.27 3.273.273.27 AAAA RMS drain curr ent =RMS drain curr ent =RMS drain curr ent =RMS drain curr ent = 1.81 1.811.811.81 AAAA Current limit of FPS 4 A 5. Determine proper core and minimum primary turns for transform er5. Determine proper core and minimum primary turns for transform er5. Determine proper core and minimum primary turns for transform er5. Determine proper core and minimum primary turns for transform er Switching frequency of FPS (kHz) 67 kHz Maximum flux d ensity swing 0.32 T -->-->-->-->EER2834EER2834EER2834EER2834 Estimated AP value of core = Estimated AP value of core = Estimated AP value of core = Estimated AP value of core = 9275 927592759275 mmmmmmmm4444 AP=12470AP=12470AP=12470AP=12470 Cross sectional area of core (Ae)8 6 m m 2 Ae=86Ae=86Ae=86Ae=86 Minimum primary turns =Minimum primary turns =Minimum primary turns =Minimum primary turns = 49.0 49.049.049.0 TTTT Aw=145Aw=145Aw=145Aw=145 FPS Design Assistant ver.1.0 0.670.670.670.67 I∆ oI o RF I IK Ts DTs

©2002 Fairchild Semiconductor Corporation 6. Determine the numner of turns for each outputs6. Determine the numner of turns for each outputs6. Determine the numner of turns for each outputs6. Determine the numner of turns for each outputs VoVoVoVo VF VFVFVF # of turns # of turns# of turns# of turns 1st output for f eedback1st output for f eedback1st output for f eedback1st output for f eedback 5V 0 . 4V 3 => 3333TTTT 4th output4th output4th output4th output 0V 0V 0000 => 0000TTTT VF : Forward voltag e drop of rectifier diode Reset winding = Reset winding = Reset winding = Reset winding = 50 505050 TTTT Primary turns = Primary turns = Primary turns = Primary turns = 50505050 TTTT ->enough turns->enough turns->enough turns->enough turns AL value (no gap) 2490 nH/T2 Transform er magn etizing inductanc e =Transform er magn etizing inductanc e =Transform er magn etizing inductanc e =Transform er magn etizing inductanc e = 6.274996.274996.274996.27499 mHmHmHmH -->EER2834EER2834EER2834EER2834 7. Determine the wire diameter for each transform er winding7. Determine the wire diameter for each transform er winding7. Determine the wire diameter for each transform er winding7. Determine the wire diameter for each transform er winding DiameterDiameterDiameterDiameter Parall elParall elParall elParall el Irms Irms Irms Irms (A/mm(A/mm(A/mm(A/mm2222)))) 4th output winding4th output winding4th output winding4th output winding 0m m 0 T 0.00.00.00.0 AAAA Copper area =Copper area =Copper area =Copper area = 33.9262 33.926233.926233.9262 mmmmmmmm2222 Fill factor 0.25 Required windo w areaRequired windo w areaRequired windo w areaRequired windo w area 135.705 135.705135.705135.705 mmmmmmmm2222 --> EER2834EER2834EER2834EER2834 ( Aw=145)(Aw=145)(Aw=145)(Aw=145) 8. Determine proper core and numb er of turns for inductor (coupl ed inductor)8. Determine proper core and numb er of turns for inductor (coupl ed inductor)8. Determine proper core and numb er of turns for inductor (coupl ed inductor)8. Determine proper core and numb er of turns for inductor (coupl ed inductor) Cross sectional ar ea of Inductor cor e (A 86 mm2 --> EER2834EER2834EER2834EER2834 Saturation flux d ensity 0.42 T Inductanc e of 1st output (L1) =Inductanc e of 1st output (L1) =Inductanc e of 1st output (L1) =Inductanc e of 1st output (L1) = 5.7 5.75.75.7 uHuHuHuH Minimum turns of L1 =Minimum turns of L1 =Minimum turns of L1 =Minimum turns of L1 = 6.5 6.56.56.5 TTTT Actual numb er of turns for L1 6 => 6666TTTT Number of turns for L2 =Number of turns for L2 =Number of turns for L2 =Number of turns for L2 = 4444 => 4444TTTT Number of turns for L3 =Number of turns for L3 =Number of turns for L3 =Number of turns for L3 = 14 141414 => 14141414 TTTT Number of turns for L4 =Number of turns for L4 =Number of turns for L4 =Number of turns for L4 = 0 000 => 0000TTTT 9. Determine the wire diameter for each inductor winding9. Determine the wire diameter for each inductor winding9. Determine the wire diameter for each inductor winding9. Determine the wire diameter for each inductor winding DiameterDiameterDiameterDiameter Parall elParall elParall elParall el Irms Irms Irms Irms (A/mm(A/mm(A/mm(A/mm2222)))) Winding for L4Winding for L4Winding for L4Winding for L4 0m m 0 T 0.00.00.00.0 AAAA Copper area =Copper area =Copper area =Copper area = 25.408925.408925.408925.4089 mmmmmmmm2222 Fill factor 0.25 Required windo w areaRequired windo w areaRequired windo w areaRequired windo w area 101.636101.636101.636101.636 mmmmmmmm2222 --> EER2834( Aw=145)EER2834(Aw=145)EER2834(Aw=145)EER2834(Aw=145) 10. Determine the rectifier diodes in the secondary sid e10. Determine the rectifier diodes in the secondary sid e10. Determine the rectifier diodes in the secondary sid e10. Determine the rectifier diodes in the secondary sid e Reverse voltageReverse voltageReverse voltageReverse voltage Rms CurrentRms CurrentRms CurrentRms Current Vcc diod eVcc diod eVcc diod eVcc diod e 55555555 V VVV0 . 1 0 0.100.100.10 AAAA -->UF4003-->UF4003-->UF4003-->UF4003 1st output diod e1st output diod e1st output diod e1st output diod e 22222222 VVVV9 . 5 9.59.59.5 AAAA -->MBR3060PT-->MBR3060PT-->MBR3060PT-->MBR3060PT 2nd output diod e2nd output diod e2nd output diod e2nd output diod e 15151515 VVVV6 . 3 6.36.36.3 AAAA -->MBR3045PT-->MBR3045PT-->MBR3045PT-->MBR3045PT 3rd output diod e3rd output diod e3rd output diod e3rd output diod e 52525252 V VVV3 . 8 1 3.813.813.81 AAAA -->MBR20H100CT-->MBR20H100CT-->MBR20H100CT-->MBR20H100CT 4th output diod e4th output diod e4th output diod e4th output diod e 0000V VVV0 . 0 0 0.000.000.00 AAAA 8.308.308.308.30 9.229.229.229.22 8.308.308.308.30 5.835.835.835.83 5.255.255.255.25 4.984.984.984.98 1.041.041.041.04 1.331.331.331.33 6.566.566.566.56

©2003 Fairchild Semiconductor Corporation 11. Determine the output capacitor 11. Determine the output capacitor 11. Determine the output capacitor 11. Determine the output capacitor ESRESRESRESR CurrentCurrentCurrentCurrent VoltageVoltageVoltageVoltage rippleripplerippleripple RippleRippleRippleRipple 4th output capacitor4th output capacitor4th output capacitor4th output capacitor 0u F 0m Ω 0.00.00.00.0 VVVV ################ VVVV 12. Design th e Reset Circuit12. Design th e Reset Circuit12. Design th e Reset Circuit12. Design th e Reset Circuit Reset diode rms curr entReset diode rms curr entReset diode rms curr entReset diode rms curr ent 0.080.080.080.08 AAAA Maximum voltag e of reset diodeMaximum voltag e of reset diodeMaximum voltag e of reset diodeMaximum voltag e of reset diode 750750750750 VVVV -->UF4007-->UF4007-->UF4007-->UF4007 13. Design Feedback control loop13. Design Feedback control loop13. Design Feedback control loop13. Design Feedback control loop Control-to-output DC gain =Control-to-output DC gain =Control-to-output DC gain =Control-to-output DC gain = 3333 Control-to-output z ero =Control-to-output z ero =Control-to-output z ero =Control-to-output z ero = 1,809 1,8091,8091,809 HzHzHzHz Control-to-output pol e =Control-to-output pol e =Control-to-output pol e =Control-to-output pol e = 261 261261261 HzHzHzHz Voltage divider resistor (R1) 5 ㏀ Voltage divider resistor (R2) 5 ㏀ Opto coupler diode resistor (RD) 1 ㏀ 431 Bias r esistor (Rbias) 1.2 ㏀ Feeback pin capacitor (CB) = 10 nF Feedback Capacitor (CF) = 100 nF Feedback resistor (RF) = 1 ㏀ Feedback int egrator gain (fi) =Feedback int egrator gain (fi) =Feedback int egrator gain (fi) =Feedback int egrator gain (fi) = 955 955955955 HzHzHzHz Feedback zero (fz) =Feedback zero (fz) =Feedback zero (fz) =Feedback zero (fz) = 265.393 265.393265.393265.393 HzHzHzHz Feedback pol e (fp) =Feedback pol e (fp) =Feedback pol e (fp) =Feedback pol e (fp) = 5307.865307.865307.865307.86 HzHzHzHz 16 9.80783 36 45 16 # -86.7 # 25 9.78487 32 41 25 # -84.9 # 40 9.7248 28 37 40 # -81.9 # 63 9.58236 24 33 63 # -77.3 # 100 9.24037 20 29 100 # -70.4 # 160 8.46816 17 25 160 # -60.6 # 250 7.07174 14 21 250 # -49.4 # 400 4.77208 13 17 400 # -37.8 # 630 1.96652 12 14 630 # -29.6 # 1000 -0.9856 11 10 1000 # -25.5 # 1600 -3.5451 11 7.3 1600 # -26.2 # 2500 -5.2263 10 5.1 2500 # -31.3 # 4000 -6.2187 9.2 3 4000 # -40.8 # 6300 -6.6721 7.3 0.6 6300 # -52.3 # Capacitanc eCapacitanc eCapacitanc eCapacitanc e vo RD iD Rbia s B ibias CB vFB 1: 1 FPS vo CF RF 43 1 -40 -20 10 100 1000 10000 100000 Gain (dB) Contorl-to-output Compensator T -120 -90 -60 -30 10 100 1000 10000 100000 Phase (degree)

3/24/04 0.0m 002  2003 Fairchild Semiconductor Corporation DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. LIFE SUPPORT POLICY FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPROATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, or (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. www.fairchildsemi.com by Hang-Seok Choi / Ph. D Phone : +82-32-680-1383 Facsimile : +82-32-680-1317 E-mail : hschoi@fairchildsemi.co.kr