Designing the Power Train of a 200W Power Supply with PFC

www.fairchildsemi.com Designing the Power Train of a 200W Power Supply with PFC Michael Weirich Global Power Resource Center, Europe 2 Design issues for 200W PSU System Specification • AC Input Voltage: 85 – 265 Vrms • Power-Factor: > 0.95 • Total Output Power: 200W • Three DC Outputs: • 5V/0.3A (standby) • 12V/6A, • 24V/5A • Height limit: 25mm Target application: LCD TV Design Issues • System partitioning • Low profile boost inductor • PFC MOSFET dissipation • Using single switch forward tools to design two-switch forward converters • Two-switch forward drive • Second post-regulated output for a forward converter • Auxiliary power supply • Layout 3 Control Component Overview • PFC/two switch forward circuit • FAN4800 combined CCM PFC and current mode controller • FAN7382 dual high and low side driver • Post regulation circuit • Low cost MC34063A controller with external MOSFET • Auxiliary power supply • FSD210 Fairchild Power Switch 4 PFC Stage Two Switch Forward Primary Side Rectifier ForwardTransformer Forward Output 85V – 265VAC input 24V, 6A Buck Post- regulation Flyback Auxiliary Primary Side Flyback Transformer Flyback Output 12V, 5A 5V, 0.3A System Partitioning Bias Power PFC/PWM Combo controller 24V,2.5A Isolation Boundary 5 Rectifier dimensioning and tips Output power Output power is 200W Efficiency assumptions: PFC stage: 90% Forward converter: 90% Maximum input current (rms) is 2.9A Bridge rectifier Rectifiers with larger current ratings typically have lower forward voltages We chose GBU6K (6A/800V): Vf=0.45V Estimate the equivalent resistance from the datasheet: RS=0.03 ohm Conclusion 4.7W dissipation 21ºC/W heatsink needed WWPIn 2479.09.0 200 =⋅= A V WI RMSIn 9.285 247 , == W I VI RIVIP RMSIn RMSIn DSDRMSDFDAVGBRLoss 7.4 )03.0 2 8.045.0(4 )(4 2 , , , 2 ,,,1, = Ω⋅⎟⎟⎠ ⎞ ⎜⎜⎝ ⎛+ ⋅⋅⋅= ⋅+⋅⋅= W WW P TT R BRLoss AJ BR C12 C0.75 7.4 C50-C150 1, max,max, 1, °≈ °−°°= −=Θ 6 PFC inductor dimensioning Pin = 247W, Input rms current = 2.9A Inductor inductance value FAN4800 PFC set to switch at 100kHz dI, the percentage current ripple is set to 20% Inductor peak current The peak value of the input rms current is added to half of the ripple current Conclusion 1mH inductor 4.5A peak current ( ) mH WkHzV VVV PdIfV VVV L InSOut InInOut 08.1 247%20100400 85)285400( 2 2 2 min,min, 1 = ⋅⋅⋅ ⋅⋅−= ⋅⋅⋅ ⋅⋅−= A I II III RMSIn RMSInRMSIn RippleRMSInLPeak 5.4 1.12 222.02 22 , ,, ,1, = ⋅⋅= ⋅⋅+⋅= +⋅= 7 PFC inductor design (1) Input rms current = 2.9A, peak = 4.5A Wire thickness Copper wire: 5A/mm2 for rms current 0.58mm2 copper wire area (ACu) Three or four strands required: skin effect Design used three strands of 0.5mm wire Core size Use the area product Ap to estimate core size from Ae (magnetic cross section) and Aw (winding cross section) Bpeak is 0.35 Tesla for standard ferrite core Conclusion Area product is 14914 mm4 σμμπδ ⋅⋅⋅⋅= rf 0 1 4 P mm14914A = Skin depth: Proximity effect: useful area of a conductor is reduced due to magnetic field generated by adjacent layers CuPeak CuPeak weP fB AILAAA ⋅ ⋅⋅=⋅= 8 PFC inductor design (2) Area product is 14914 mm4 General selection Normally Ae and Aw are equal, so as a starting point, select Ae as 122mm2 >> no 25mm height bobbins available Specific selection Look for cores meeting area product and size requirements: EER3542 core (Ae=107mm2,Aw=154mm2) Turns Aw is 154mm2, ACu is 0.58mm2 Assuming a fill factor of 50%, we can get 130 turns. . Gap A gap is needed to get the required Inductance. AL = 1mH/130^2 s is the gap size, AL,0 is the AL value for an ungapped core Adjust the turns to get a standard gap size Conclusion Gap is 2mm, 124 turns, 1mH inductance ⎟⎟⎠ ⎞ ⎜⎜⎝ ⎛ −⋅⋅π⋅≈ 0,LL e A 1 A 1A4.0s TAmHB 34.05.41 =⋅= mm107124 2max ⋅ 9 Low Profile Boost Inductor Specification PFC Choke Winding Details Name Pins (Start →End) Layers Strands x Wire ø Turns Construction Material W1 8 →16 6 3 x 0.5 mm 124 perfect solenoid CuLL Electrical Characteristics Parameter Pins Specification Conditions Inductance 8 → 16 1000 uH +/- 5% 10kHz, 100mV Core and Bobbin Core: EER3542 Material: PC40 (TDK) or equivalent Bobbin: EER3542 / 16 Pin / Horizontal e.g. Pin Shine P-3508 Gap in center leg:approx. 2.0 mm for an AL of 65 nH/Turns2 10 PFC MOSFET Selection Voltage and current ratings 500V MOSFET needs external surge protection 600V MOSFET preferred Peak current same as inductor (4.5A) Power dissipation and heatsink FCP16N60 chosen: RDSon=0.45ohm, Coss,eff=110pF Cext=150pF, (estimated parasitic capacitance) Conclusions Power dissipation: 9W 10ºC/W heatsink needed A V VA V V II Out MinIn RMSInQRMS 5.2 4003 852819.2 3 28 1 ,,1, = ⋅⋅ ⋅⋅−⋅= ⋅ ⋅⋅−⋅= π W RIP QDSONQRMS Cond QLoss 8.2 1, 2 1,1, max = ⋅= ( ) W. kHzns.VA.. ftVI.P W. kHzVpF. fVCC.P ScrossoverOutRMS,In Cross Q,Loss SOutexteff,OSS Cap Q,Loss 62 10050504009290 6 190 12 10040026050 50 1 2 2 1 = ⋅⋅⋅⋅⋅= ⋅⋅⋅⋅⋅≈ = ⋅⋅⋅= ⋅⋅+⋅≈ WPrr Q,Loss 21 ≈ 11 FAN4800 PFC Circuit - + ~ ~ BR1 GBU6K D15 FDLL4148 D1 ISL9R460P2 R8 10K D10 1N4148 D11 1N4148 C2 470nF D12 1N4148 Ieao 1 Iac2 Isense3 Vrms4 Ss5 Vdc 6 Ramp17 Ramp28 Ilim 9 GND 10 Vo2 11 Vo1 12 Vcc 13 Ref 14 Vfb 15 Veao 16 I C 1 F A N 4 8 0 0 C6 2.2nFR1c 390K R24 27k C16 680pF R3 110K R7b 1MR1a 390K D16 FDLL4148 C23 100nF R2a 620K R2b 620K + C5c 82uF 450V C12 470nF 50V C14 100nF 25V R12 47K C2 680nF 400V C13 470nF NTC1 2R 12A C248 1nF R7a 620K + C5b 82uF 450V R1b 390K R4 18K R11 820K C1 680nF X2 C7 220pF R23 4.7K LF1 10mH C15 22nF 1 2 R5 0.15 2W C8 100nF + C5a 82uF 450V R35 100 816 L1 1.0mH L3 FERRITE BEAD J1 GSF1.1001.31 C3 100nF C9 10nF R15 22 Q1 FCP16N60 Vcc Vbus 0 12 Two-switch forward design with PFC front-end • Use the forward design spreadsheet • Enter 284V to emulate PFC input • Use a very large DC link capacitor to account for the PFC stage • Set the maximum duty cycle to 0.45 to ensure demagnetisation • The ratio Np/Nr can be ignored as there is no need for a reset winding • A single switch forward would need 803V rating without any safety factor • two-switch forward designs need half of this For forward converter with reset winding Blue cell is the input parameters Red cell is the output parameters 1. Define specifications of the SMPS Minimum Line voltage (V_line.min) 284 V.rms Maximum Line voltage (V_line.max) 284 V.rms Line frequency (fL) 50 Hz Vo Io Po KL 1st output for feedback 24 V 8.5 A 203 W 100 2nd output 0 V 0 A 0 W 0 3rd output 0 V 0 A 0 W 0 4th output 0 V 0 A 0 W 0 Maximum output power (Po) = 202.8 W Estimated efficiency (Eff) 90 % Maximum input power (Pin) = 225.3 W 2. Determine DC link capacitor and the DC voltage range DC link capacitor 1000 uF DC link voltage ripple = 4 V Minimum DC link voltage = 397 V Maximum DC link voltage = 402 V 3. Determine the maximum duty ratio (Dmax) Maximum duty ratio 0.45 Turns ratio (Np/Nr) 1 > Maximum nominal MOSFET voltage = 803 V 0.82 13 Two Switch Forward Output Inductor Output Inductor Design • Current ripple should be small as possible to reduce the RMS and peak values of the primary and secondary currents. • Small current ripple results in large inductors • Design compromise: • Current ripple is set to 42% (Note KRF used in spreadsheet is half of the current ripple) • Output inductance 40uH • The calculated windings will fill an EER2828 core completely. Choke 40uH / 9A (L5) Winding Details Name Pins (Start →End) Layers Strands x Wire ø Turns Construction Material W1 1,2,3,4,5 →8,9,10,11,12 6 5 x 0.71 mm 15 perfect solenoid CuL Electrical Characteristics Parameter Pins Specification Conditions Inductance 1 → 5 40 uH +/- 5% 10kHz, 100mV 14 Two Switch Forward Transformer Main Transformer Specification Winding Details Name Pins (Start →End) Layers Strands x Wire ø Turns Construction Material W1a 6 →3 1 1 x 0.5 mm 39 perfect solenoid CuLL W3 10,11,12 →7 ,8,9 2 3 x 0.7 mm 11 perfect solenoid Triple insulated W1b 3 →1 1 1 x 0.5 mm 38 perfect solenoid CuLL 6 1 Layers not to scale ! 3 W1a W2 W1b 6 3 1 = 3 Layers of Tape e.g. 3M 1350 W1b W1a 3 10,11,12 7,8,9 10 11 12 7 8 9 Schematic Construction Electrical Characteristics Parameter Pins Specification Conditions Primary Inductance 1 → 6 13 mH +/- 30% 10kHz, 100mV, all secondaries open Leakage Inductance 1 → 3 500 uH maximum 10kHz, 100mV, all secondaries short Core and Bobbin Core: EER2834 Material: PC40 (TDK) or equivalent Bobbin: EER2834 / 12 Pin / Horizontal e.g. Pin Shine P-2809 Gap in center leg: 0 mm 15 Two-switch forward MOSFETs From forward calculation spreadsheet: Peak current is 1.6A RMS current is 0.9A Voltage and current ratings 600V MOSFET preferred Peak current same as inductor (1.6A) Power dissipation and heatsink FCP7N60 chosen: Rdson=1.1ohm, 100ºC Coss,eff=60pF Cext=60pF, (estimated) As tr=120ns and tf=75ns in datasheet are measured at 7A scale by 1.6A/7A Conclusions Power dissipation: 3.7W 20ºC/W heatsink needed ( ) WP W kHznsVA f tt VIP W kHzVpF fVCCP W A RIP Tot QLoss S fr OutQPeak Cross QLoss SOutexteffOSS Cap QLoss SwDSONSwRMS Cond SwLoss 7.3 4.1 100 7 6.1 2 751204006.1 2 2.1 1004001205.0 5.0 9.0 1.19.0 205, 205,205, 2 2 ,205, 2 , 2 1,, max ≈ = ⋅⋅+⋅⋅= +⋅⋅≈ = ⋅⋅⋅= ⋅⋅+⋅≈ = Ω⋅= ⋅= 16 FAN4800 Two Switch Forward Converter 24V R242 n.a. C249 1nF R246 33 Q211 FCP7N60 1 2 CONN5 B2P-VH R225 22 R205 13k R202 10k C235 100nF R245 1.5K C15 22nF TR1 Main Transformer R241 n.a. C16 680pF + C247 n.a. 1 2 R233 0.47 R24 27k R240 n.a. D216 RS1K + C246 680uF OC1 FOD2741BTV R23 4.7K Ieao 1 Iac 2 Isense 3 Vrms 4 Ss 5 Vdc 6 Ramp1 7 Ramp2 8 Ilim 9 GND 10 Vo2 11 Vo1 12 Vcc 13 Ref 14 Vfb 15 Veao 16 IC1 ML4800IS R247 33 D220 FYP2010DN R226 22 D14 FDLL4148 C231 15nF L5 40uH 9A D224 n.a. C238 470pF C239 220nF C250 1nF + C245 680uFQ212 FCP7N60 D217 UF5407 Q210 n.a. +C244 680uF D218 UF5407 D219 FYP2010DN C12 470nF 50V D13 FDLL4148 VCC 1 HIN 2 LIN 3 COM 4 LO 5 VS 6 HO 7 VB 8 IC4 FAN7382N R204 180K R234 220 C230 n.a. Vbus Vcc Vcc 17 Waveforms for low side switch and output diode Low side switch voltage and current Output diode voltage and current 18 Detail of High Voltage Driver Circuit Q211 FCP7N60R225 22C235 100nF TR1 Main Transformer 1 2 R233 0.47 D216 RS1K R226 22 D14 FDLL4148 C238 470pF C239 220nF Q212 FCP7N60 D217 UF5407 D218 UF5407 D13 FDLL4148 VCC 1 HIN2 LIN 3 COM 4 LO 5 VS 6 HO 7 VB 8 IC4 FAN7382N R234 220 Vbus Vcc 19 Rectifier diodes From forward calculation spreadsheet: Diode reverse output voltage is 57V Output current is 8.5A Rs=0.04ohm (from datasheet curves) Vf=0.25V Snubber network Schottky diodes switch fast causing oscillations RC snubber network needed to damp these Conclusions Power dissipation: 2.5W 20ºC/W heatsink needed Snubber network needed Voltage and current ratings 100V Schottky diode used: FYP2010DN Average current: 4.7A Power dissipation and heatsink A A DII OutrectAvg 7.4 55.05.8 )1( max, = ⋅= −⋅= W AVA RIVIP ctSrectRMSctFrectAvgrectLoss 5.2 04.07.525.07.4 2 Re, 2 ,Re,,, = Ω⋅+⋅= ⋅+⋅≈ 20 MC34063A Post-regulation Circuit R26 680 C252 100nF R32 Q212 BC858C Q211 BC848B 1 2 CONN4 B2P-VH 1 2 3 45 6 7 8 SWc SWe Ct GndFB Vcc Ipk DRc IC5 KA34063AD + C18 680uF R22 1.5K C19 100pF L6 100uH 6A 1 2 3 Q209 FQP47P06 R25 13K R29 D223 MBR745 R21 680 R33 0.12R + C251 470uF 35V 12V/6A 12V 24V 0 Hysteretic buck control (or ripple regulator) 21 Inductor for Post Regulated Output Choke 100uH / 6A (L6) Winding Details Name Pins (Start →End) Layers Strands x Wire ø Turns Construction Material W1 1,2,3,4,5 →8,9,10,11,12 5 x 0.56mm 25 perfect solenoid CuL Electrical Characteristics Parameter Pins Specification Conditions Inductance 1 → 5 100 uH +/- 5% 10kHz, 100mV Core and Bobbin Core: EER2828 Material: PC40 (TDK) or equivalent Bobbin: EER2828 / 12 Pin / Horizontal e.g. Pin Shine P-2816 Gap in center leg:approx. 0.45 mm for an AL of 205nH/Turns2 22 Auxiliary Power Supply using FSD210 D208 SB380 C236 220nF OC3 FOD2711BTV R235 75 + C21 4.7uF 1 23 4 OC2 H11A817A.W D6 1N4148 R229 1K 1 3 4 5 6 8 TR2 Stdby Transf ormer C22 22nF R31 47 R230 1.5K D225 18V 0.5W C237 220nF + C232 100uF R227 1K C20 2.2nF 1 2 CONN6 D5 U F 4 0 0 7 R30 75k R228 3.3K C253 4.7nF V C C 5 D R A I N 7 V S T R 8 G N D 1 G N D 2 G N D 3 V F B 4 IC6 FSD210BM 1 2 CONN1 + C233 100uF L4 22uH Standby ON/OFF 5V Vbus 0 Vcc 23 Flyback Transformer for Auxiliary Output Standby Transformer Specification Winding Details Name Pins (Start →End) # of Layers Strands x Wire ø Turns Construction Material W1a 3 →2 2 1 x 0.15 mm 91 spaced winding CuLL W3 8 →6 1 1 x 0.5 mm 8 spaced winding Triple insulated W1b 2 →1 2 1 x 0.15 mm 91 spaced winding CuLL W2 4 →5 1 1 x 0.15 mm 24 spaced winding CuLL W2 5 4 3 1 8 W3 2 W1b W1a 6 = 3 Layers of Tape e.g. 3 M 1350 = 1 Layer Tape e.g. 3 M 1350 Layers not to scale ! W1a W3 W1b W2 3 2 1 4 5 8 2 6 Schematic Construction Electrical Characteristics Parameter Pins Specification Conditions Primary Inductance 1 → 3 5.85 mH +/- 5% 10kHz, 100mV, all secondaries open Leakage inductance 1 → 3 290 uH maximum 10kHz, 100mV, all secondaries short Core and Bobbin Core: EF 20 Material: FI325 (Vogt) or equivalent Bobbin: EF20 / 10 Pin / Horizontal / Increased creepage Gap in center leg: approx. 0.2 mm for AL of 177 nH/Turns2 24 Layout and Heatsink • General Power Supply Layout Rules • the enclosed area of loops with high di/dt must be as small as possible • the copper area of nodes with high dv/dt must be as small as possible. • avoid common impedance coupling by using star connections to ground • These rules conflict with other requirements • Heatsink construction at the edge of a board • Star connection of all ground lines would enlarge the PCB • Low cost solutions require single sided PCB’s which result in longer traces • Compromise • Critical signals are routed to the shortest path • Less critical signals give way to the large ground plane which emulates star-like connection • Heatsink • All devices except Q1 are connected to a simple heatsink made of 2mm aluminium bent into the form of a U • Q1 dissipates more power so needs an additional heatsink 25 Layout and photo of finished board Dimensions: 170mm x 156mm x 25mm (L x W x H) 26 Standby power and efficiency Less than 0.5W standby power for 195V-265V Overall efficiency target of 81% (90%x90%) met 0.0 0.1 0.2 0.3 0.4 0.5 0.6 85 110 135 160 185 210 235 260 Input Voltage [Vrms] S t a n d b y P o w e r [ W ] 75.0 77.0 79.0 81.0 83.0 85.0 87.0 89.0 85 110 135 160 185 210 235 260 Input Voltage [Vrms] E f f i c i e n c y [ % ] 27 Summary Design Issues • System partitioning • Low profile boost inductor • PFC MOSFET dissipation • Using single switch forward tools to design two-switch forward converters • Two-switch forward drive • Second output for a forward converter • Auxiliary power supply • Layout • Performance Designing the Power Train of a� 200W Power Supply with PFC Design issues for 200W PSU Control Component Overview System Partitioning Rectifier dimensioning and tips PFC inductor dimensioning PFC inductor design (1) PFC inductor design (2) Low Profile Boost Inductor Specification PFC MOSFET Selection FAN4800 PFC Circuit Two-switch forward design with PFC front-end Two Switch Forward Output Inductor Two Switch Forward Transformer Two-switch forward MOSFETs FAN4800 Two Switch Forward Converter Waveforms for low side switch and output diode Detail of High Voltage Driver Circuit Rectifier diodes MC34063A Post-regulation Circuit Inductor for Post Regulated Output Auxiliary Power Supply using FSD210 Flyback Transformer for Auxiliary Output Layout and Heatsink Layout and photo of finished board Standby power and efficiency Summary