FLYBACK PRACTICAL DESIGN EXAMPLE

SWITCHING POWER SUPPLY SPECIFICATION

1. INPUT:

1.1 VOLTAGE: UNIVERSAL AC 90V-AC260V SINGLE PHASE. 1.2 FREQUENCY: 47Hz-63Hz. 1.3 RMS CURRENT: 2A Max.

1.4 INRUSH CURRENT: 30A Max. WHILE COLD START AT PEAK ON FULL LOAD, 25℃ AMBIENT. 1.5 EFFICIENCY: 70% Min. AT NOMINAL LINE INPUT, FULL LOAD.

2. OUTPUT:

2.1 DC OUTPUT: Voltage 15.0V MAX. Load 2.0A MIN. Load 0.1A Regulation +/- 5% Ripple & Noise 150mV NOTE: FOR RIPPLE & NOISE MEASUREMENT, USE A 20 MHz BANDWIDTH FREQUENCY OSCILLOSCOPE, AND ADD 0.1uF MULTILAYER CAPACITOR AND A 22uF ELECTROLYTIC CAPACITOR AT OUTPUT CONNETCTOR TERMINAL

3. TIME SEQUENCEE:

3.1 RISE TIME: 70mS Max. AT NOMINAL LINE VOLTAGE, FULL LOAD. 3.2 TURN-ON DELAY TIME: 1000mS Max. AT NOMINAL LINE VOLTAGE FULL LOAD.

3.3 HOLD-UP TIME: 20mS Min. AT 230Vac/50Hz INPUT, 16ms Min. AT 115Vac/60Hz INPUT. FOR OUTPUT, AT FULL LOAD 4. PROTECTION:

4.1 OVER VOLTAGE PROTECTION: OVP AT 110-140% 4.2 SHORT CIRCUIT PROTECTION:

THE OUTPUT WITHSTAND AN INDEFINITE SHORT CIRCUIT WITHOUT DAMAGE TO THE POWER SUPPLY 4.3 OVER POWER PROTECTION:

WHEN OUTPUT POWER EXCEEDS 110%-160% OF RATED LOAD, THE POWER SUPPLY WILL SHUT DOWN.

4.3 WHEN PROTECTION CIRCUIT IS WORKING, THE POWER SUPPLY WILL SHUT DOWN. ONCE THE ABNORMAL CONDITIONS ARE

REMOVED, THE POWER SUPPLY WILL RESTART AUTOMATICALLY.

5. SAFETY REQUIREMENT:

5.1 THIS POWER SUPPLY IS DESIGNED TO MEET FOLLOWING STANDARDS: 1) UL 1950.

2) CSA 22.2 NO. 0-M1982; BULLETIN 1402C. 3) IEC 950

5.2 DIELECTRIC WITHSTAND:

1) PRIMARY TO SECONDARY: 1500Vac FOR 1 MINUTEE. 2) PRIMARY TO SAFETY GROUND: 1500Vac FOR 1 MINUTE. 5.3 LEAKAGE CURRENT: 3.5mA Max. AT 245 Vac

6. CONDUCTED EMI REQUIREMENT:

1) FCC DOCKET 20780, PART 15, SUBPART J, CLASS B. 2) BZT Vfg 243/1991 CLASS B.

7. ENVIRONMENT:

7.1 OPERATING TEMPERATURE : 10℃TO 50℃.

7.2 OPERATING RELATIVE HUMIDITY: 20% TO 90%. 7.3 STORAGE TEMPERATURE : -20℃ TO 60℃. 7.4 STORAGE RELATIVE HUMIDITY: 10% TO 90%. 7.5 COOLING: SHOULD OPERATE WITHOUT FAN

FLYBACK DESIGN THEORY:

Considering Power MOSFET Vds stress is safe, and current level capacity is enough.

Decide turn ratio by Vds(stress)Vc(max)1.2(VoVf)N

The maximum duty D

Dmin(VoVf)NVin(max)Vds(on)(VoVf)NDmax(VoVf)NVin(min)Vds(on)(VoVf)N

Pout=1/2 Lp*Ipp2*f

Vinmin=Lp*Ipp*f/D

Ip=2*Pout/(Vinmin*Dmax)

Lp=VinminDmax/(Ipp*f)

DETERMINE DCM/CCM BOUNDARY IOB=Io(max)*(X% PERCENTAGE)

Vdc(BOUNDARY)=Vdc

DECIDE DUTY CYCLE AND CALCULATE TURN RATIO

NVdc(min)(VoVf)*Dmax1Dmax

WHERE N : TURN RATIO Np/Ns D(max) : MAX. DUTY CYCLE Vdc(min)=MIN. DC VOLTAGE Vo : OUTPUT VOLTAGE

Vf : DIODE FORWARD VOLTAGE DROP

IF N IS DECIDED, THEN RECKECK D(max)

DETERMINE SECONDARY PEAK CURRENT IN DCM/CCM

Dmax1DmaxN(VoVf)Vdc(min)

DECIDE SECONDARY WINDING INDUCTAANCE Ls

DECIDE PRIMARY WINDING INDUCTANCE Lp in CCM

For energy transfer,

And,

12Lp(IpIb)fs22

Ls(VoVf)(1Dmax)TsISB

Po

IbIpIIp(1Krp)

PoTherefore,

Lp2Ip(1Krp2*(1/Krp)

)fs

2

Lp = NLs

DETERMINE SECONDARY PEAK CURRENT IN CCM

Ip_avgPoVmin*Ip_avgN

Is_avg

IIpeak

Wave form factor Krp :

Peak current Ipeak (Ip):

Ripple current ΔI:

RMS current Irms:

IrmsIpDmax(Krp32Krp

IavgDmaxIavgDmax

Ipeak22Krp

I2(Ip)

Krp1)

Bac =Krp * Bmax

Io(max)Is(2IsIsB)*(1Dmax)2Io(max)IsB2IsB2IppIspN

1DmaxIo(max)1Dmax

IspIsBIsDETERMINE PRIMARY PEAK CURRENT IN CCM

Loss allocation factor Z

PoZ=0.5~0.7

PoZ(1)12LpIpk2

fs

CALCULATE APPARENT POWER

PtPo

DECIDE CORE SIZE

(1+K) Bmax + Br < Bsat

Ac*Ae=(25.32*Lp*Ipp*d*d)/Bmax

Set K=0.2; Bac=0.5*Bsat

ApWaAcPt*1042BmFsJKu

2

2

WHERE Wa : WINDOW AREA, cm

Ae : EFFECTIVE CROSS-SECTIONAL AREA, cm Ku : WINDING FACTOR, 0.2-0.5

2

J : CURRENT DENSITY, A/cm

Fs : OPERATING FREQUENCY, Hz

Bm : Magnetic flux density , T

Pt : total power including output and input power

CALCULATEE PRIMARY TURNS Np:

DETERMINE AIR GAP

LgLe1NpVminDmaxBacAefsLpIBAeLpIpeakBmaxAe

LgoNp2AeLp1Ler

effr

CALCULATTE SECONDARY TURNS Ns

NsNpN

CALCULATE AUXILIARY WINDING TURNS NA

VaVoVfNs(VOLTS/TURN)NA*VaVccVf1NAVccvF1Va

DETERMINE WINDING WIRE SIZE

AwIrmsJIrms14

2

2

WHERE Aw : WIRE AREA; cm

0.33DESIGN THEORY

CONSIDER DRAIN-SOURCE BREAKDOWN VOLTAGE BVDSS (COLLECTOR-EMITTER BREAKDOWN VOLTAGE BVceo)

BVDSS (BVceo) > Vdc(max) + N(Vo+Vf)

CONSIDER CONTINUOUS DRAIN CURRENT ID (D.C. COLLECTOR CURRENT Ic)

CONSIDER PULSED DRAIN CURRENT IDM(PEAK COLLECTOR CURRENT Ic(peak))

CONSIDER MOSFET STATIC DRAIN-SOURCE ON-STATE RESISTANCE RDS(ON) [TRANSISTORR COLLECTOR SATURATION VOLTAGE Vce(sat)]

IDM[Ic(peak)]IppIo(max)IOBN(1Dmax)

ID(Ic)DmaxIo(max)N(1Dmax)

DESIGN THEORY

CONSIDER REPETITIVE PEAK REVERSE VOLTAGE VRRM

CONSIDER AVERAGE OUTPUT RECTIFIED CURRENT Io(avg)

Io(avg) > Io(max)

CONSIDER NON-REPETITIVE PEAK SURGE CURRENT IFSM

IFSMIspIo(max)IOB1Dmax

Vdc(max)VRRMVoN

DESIGN THEORY

CALCULATE OUTPUT CAPACITANC

CHOOSE CAPACITOR RATED VOLTAGE W.V. > 1.2*Vo CALCULATE R.M.S. RIPPLE CURRENT

CALCULATE E.S.R. OF CAPACITOR

ESR(max)VoIspVo(1Dmax)Io(MIN)IOBVoDmaxTsVoRL(min)Io(max)DmaxTsVo

Co

Iripple(rms)VoRL(min)Dmax1DmaxRL(min)Ts1Dmax12LsDmax2

FLYBACK DESIGN EXAMPLE

[DESIGN ENVIROMENT RATING]

CONDITION: Po=30W, EFF=0.7,P.F.=0.6, Vac(min)=90V Vin: Bmax Iin: D: Pout: Circuit Topology Transformer Electrical Diagram Minimum Working AC input Voltage VACMIN Volts Minimum Working DC input Voltage VDCMIN Volts Maximum Working AC input Voltage VACMAX Volts Maximum Working DC input Voltage VDCMAX Volts AC Mains Frequency Range FAC Hertz Bridge Rectifier Conduction Time Estimate TC mSeconds Input Bulk Filter Capacitor CIN uFarads PWM Switching Frequency Range FS Hertz Permit Maximum Operation Duty D % Voltage Regulation VR % Output Voltage VO(n) Volts Output Rectifier Diode Forward Voltage Drop VD Volts Output Current Io(n) Amperes Output Power Po(n) Watts Switch on-state Drain to Source Voltage VDS Volts Efficiency Estimate EFF % Loss Allocation Factor LAF Safety Class CLASS

[FUSE DESIGN SECTION]

Max. INPUT CURRENT

I(max)3090*0.7*0.61A0.794A

CHOOSEFUSE

BECAUSE THEE ADAPTOR IS UNIVERSAL INPUT

CHOOSE 250V VOLTAGE RATING FUSEE

IF THE MAX INRUSH CURRENT IS 12A, TIME DURATION IS 10mS,

THEN

22-3

[Iit] = (12) * (10 * 10) =1.44

IF WE CHOOSE 1A FUSE OF \"2AG FAST-ACTING\" TYPE, THEN FROM CURRENT-TIME CHART WE CAN GET THE CURRENT ABOUT 8A IN THE 10mS CONDITION. THEREFORE, THE ENERGY IS

22-3

[Iit] = (9) * (10 * 10) =0.81 BECAUSE [It] < [Iit], SO WE CAN NOT USE THIS TYPE FUSE.

CHOOSE ANOTHER 1A FUSE OF \"2AG SLOW-BLOW\" TYPE, THEN WE CAN GET THE CURRENT ABOUT 23A IN TTHE 10mS CONDITION. THEREFORE, THE ENERGY IS

22-3

[Iit] = (23) * (10 * 10) =5.29

2

2

IF THE THERMAL AGEING COEFFICIENT \"A\" IS 0.3, THEN

2

A[It] = 0.3 * 5.29 = 1.59 SO

22

A[It] > [Iit] WE CAN CHOOSE THIS TYPE FUSE.

[NTC DESIGN SECTION]

CONDITION : Po=30W, η=0.7, PF=0.6, Vac(spec) = 230V, Vac(min)=90V

ZERO POWER RESISTANCE RT

RT230V30A3090*0.7*0.67.7(OHM)

MAXIMUM PERMISSIBLE CURRENT IT

IT0.794A

THEREFORE, WE CHOOSE \"UEI\" NTC THERMISTORR \"N10SP010\ RT=10 (OHM) IT=3.0A

[RECTIFIER DESIGN SECTION]

MAX. DC BLOCKING VOLTAGE

V PIV2*2374MAX. AVERAGE FORWARD RECTIFIED OUTPUT CURRENT

IdiodePo12830128*0.7

0.334A

CHOOSE RS105 BRIDGE DIODE 1A/600V

[BULK CAPACITOR DESIGN SECTION]

CAP.VALUE

Cub(min)WinV2pkVmin2(30/0.7*60)(90*2)(75)22=67.6μF

RIPPLE CURRENT

Icin(rms)300.7*900.476A

WORKING VOLTAGE

W.Vcin(max)2*2373.3V

CHOOSE 68uF/400V RUBYCON USP SERIES

[VARISTOR DESIGN SECTION]

[X’FM DESIGN SECTION]

PRACTICAL DESIGN

WINDING AREA ALLOCATION FACTOR 1:3 Core Type Core Bobbin Type Bobbin Core Saturated Flux Density 100℃ BS Tesla Core Rest Flux Density 100℃ BR Tesla Core Effective Cross Sectional Area AE cm^2 Core Effective Path Length LE cm Core Volumn/Weight VC cm^3 Core Loss Density Pb Watts/cm^3 Ungapped Core Effective Inductance AL nH/T^2 Bobbin Effective Widing Area AC mm^2 Bobbin Physical Winding Width BW mm Safety Margin Width MW mm Frenquency Range F Hz ui He A/m

CHOOSE CORE MATERIAL

FERRITE----------Mn-Zn

EFFECTIVE SATURATION MAGNETIC FLUX DENSITY Bsat 5000 Gauss CHOOSE CORE MANUFACTORY AND FERRITE MATERIAL 1. TDK------PC30, PC40 2. THOMSON------B50 3. TOMITA------2E6 4. FUJI------H45

5. TOKIN------2500B, 2500B2 6. SIEMENS------N27, N67, N87

7. MAGNETICS------R, P, F MATERRIAL 8. FERROXCUBE------3B7, 3C8 9. SATCKPOLE------24B 10. INDIANA GENERAL------

11. NIPPON FERRITE------SB-5S, GP-5, GP-7 12. 川鐵------MB-3

13. HITACHI------SB7C, SB9C 14. PHILIPS------3C80, 3C85, 3F3

15. NIPPON CERAMIC------NC-1M, NC-2M 16. MITSUBISHI------NZ, NK, NA, NX 17. SAM HWA------SB-5S, GP-5, GP-7

CHOOSE CORE TYPE

1. EI TYPE 5. LP (FQK) TYPE 2. EE TYPE 6. RM TYPE 3. EER TYPEE 7. EPC TYPE

4. PQ TYPE 8 .ETD (EC) TYPE

CONDITION : Po=30W, Fs=40KHz,η=0.7,Vo=15V,Io=2A

DCM/CCM BOUNDARY

IOB = Io(min) = 65%*Io(max)

= 0.65*2 =1.3A

Vdc(BOUNDARY)=100Vdc

MAX. DUTY CYCLE AND TURN RATIO

ASSUME Dmax = 0.45

NVdc(min)(VoVf)*Dmax1Dmax100151*0.4510.455.11

CHOOSEN5

RECHECK D(max)

Dmax

1Dmax5*(151)100

Dmax0.44

IN DCM / CCM △IsB SECONDARY PEAK CURRENT

IsB2IOB1Dmax5*(151)100

Dmax0.44

Ip=2*Pout/Vinmin*Dmax Lp=Vinmin*Dmax/(Ipp*f) DECIDE Ls

LsVo15Vf1DmaxTsISB4.

110.441/40*103

48.28uHDECIDE Lp

Lp = NLs = (5)*48.28

=1.207mH

IN CCM △Isp SECONDARY PEAK CURRENT

22

IspIo(max)1Dmax210.44ISB24.2

5.AIN CCM △Ipp PRIMARY PEAK CURRENT

IppIspN5.51.178A



APPARENT POWER Pt

PtPoPo300.730

72.86W

CORE SIZE Ku =0.6

Ac*Ae=6.33*Lp*Ipp*d*d/Bmax/Ku

ApWaAcPt*104

2BmFsJKu72.86*1034

0.456cm420.240105000.2

PRIMARY TURNS Np

NpCHOOSE EER-28 JPP-4 FERRITE CORE, CORE DATA AS FOLLOWING : Ae: 85.4mm2 Ac:141.25mm2 Ve=6353.8mm3

Ac*Ae=1.206cm4

Lp*IppBmAc1.207*103*1.17840.2*1.18*10TURNS

60SECONDARY TURNS Ns

NsNpN60512TURNS

AUX. WINDING TURNS NA

VaNAVoVfNsVa151121.333VOLTS/TURNSVccVf11611.33312.75

CHOOSENA13TURNS

WINDING WIRE SIZE

AW(Np)IpJ(30/0.7)10025000.5500*15000.86*103cm2

AWG#22CHOOSEAW(Ns)Io(Ns)JIo(NA)JAWG#294*101*103cmcm2CHOOSECHOOSE

AW(NA)

32AWG#27[POWER MOSFET DESIGN SECTION]

DRAIN-SORCE BREAKDOWN VOLTAGEE BVDSS

BVDSS > Vdc(max) + N(Vo+Vf)=360+5*(15+1)=435V

CONTINUOUS DRAIN CURRENT ID

PULSED DRAIN CURRENT IDM

IDDmaxIo(max)N(1Dmax)0.44*25*(10.44)0.314A

IDMIppIo(max)IOBN(1Dmax)

21.35*(10.44)

1.18A

CHOOSE 2SK118 MOSFET (TOSHIBA), THE RATING ARE : BVDSS (VDSS) = 600V ID=6A

IDM (IDP) = 24A RDS(ON)=0.95(OHM)

[OUTPUT DIODE DESIGN SECTION]

REPETITIVE PEAK REVERSE VOLTAGE VRRM

AVERAGE OUTPUT REECTIFIED CURRENT Io(avg)

Io(avg) > Io(max) = 2A

NON-REPETITIVE PEAK SURGE CURRENT IFSM

IFSMIspIo(max)IOB1Dmax21.310.445.A

Vdc(max)VRRMVoN(3605)1587V



CHOOSE BYQ28-100 ULTRA FAST-RECOVERY DIODE (PHILIPS)

VRRM=100V Io(avg)=10A (TWO DIODE) IFSM=50A VFM=0.85V

[OUTPUT CAPACITOR DESIGN SECTION]

OUTPUT CAPACITANCE

CoIo(max)DmaxTsVo2*0.44*(1/40*10)0.153

147uF CHOOSE 2200uF

CAPACITOR RATED VOLTAGEE

W.V. > Vo = 15V

CHOOSE RATED VOLTAGE 25V

R.M.S. RIPPLE CURRENT

Iripple(rms)VoRL(min)157.50.44Dmax1DmaxRL(min)Ts1Dmax12LsDmax2

30.4410.44*7.5*1/40*10610.441248.28*102

2A

CHOOSE RUBYCON YXB SERIES CAPACITOR 2200uF/25V,

THE RIPPLE CURRENT IS

Iripple(rms)=1.6A (AT 105℃ ,100KHZ)

BUT IN 85℃ , 50KHZ, THE R.M.S. RIPPLE CURRENT IS

Iripple(rms)=1.6*1.7*0.=2.74A

WHICH CAN SATISFY THE ABOVE REQUIREMENT

E.S.R. OFF CAPACITOR

ESR(max)Vo(1Dmax)2Io(max)IOB0.15*(10.44)213

25.452200uF/16 ESR=29m (OHM)

CAN NOT SATISFY THE REQUIREMENT, MUST ADD ANOTHER LC FILTER

DECIDE Lc FILTER

ASSUME

12LfCf110Fs

IF CHOOSE Lf = 10uH, THEN

1

210*106*Cf110*40*103

Cf158.5uF

CHOOSE Cf = 1000uF / 16V

[OUTPUT REGULATION DESIGN SECTION] [OUTPUT PROTECTION DESIGN SECTION] [PWM CONTROLER IC DESIGN SECTION] [FEEDBACK LOOP GAIN DESIGN SECTION] [THERMAL DESIGN SECTION] [EMC FILTER DESIGN SECTION]

APPENDIX AWG Size 12 AWG 13 AWG 14 AWG 15 AWG 16 AWG 17 AWG 18 AWG 19 AWG 20 AWG 21 AWG 22 AWG 23 AWG 24 AWG 25 AWG 26 AWG 27 AWG 28 AWG 29 AWG 30 AWG 31 AWG 32 AWG 33 AWG 34 AWG 35 AWG 36 AWG 37 AWG 38 AWG 39 AWG 40 AWG mm mm Area A mps Amps Amps Amps Amps Amps Amps Amps (mm2) 3A/mm2 4A/mm2 5A/mm2 6A/mm2 7A/mm2 8A/mm2 9A/mm2 10A/mm2 2.052 2.052 3.3071 9.921 13.228 16.535 19.842 23.150 26.457 29.7 33.071 1.829 1.829 2.6273 7.882 10.509 13.137 15.7 18.391 21.019 23.6 26.273 1.928 1.928 2.9195 8.758 11.678 14.597 17.517 20.436 23.356 26.275 29.195 1.450 1.450 1.6513 4.954 6.605 8.256 9.908 11.559 13.210 14.862 16.513 1.291 1.291 1.3090 3.927 5.236 6.545 7.854 9.163 10.472 11.781 13.090 1.150 1.150 1.0387 3.116 4.155 5.193 6.232 7.271 8.310 9.348 10.387 1.024 1.024 0.8235 2.471 3.294 4.118 4.941 5.765 6.588 7.412 8.235 0.912 0.912 0.6533 1.960 2.613 3.266 3.920 4.573 5.226 5.879 6.533 0.813 0.813 0.5191 1.557 2.076 2.596 3.115 3.634 4.153 4.672 5.191 0.724 0.724 0.4117 1.235 1.7 2.058 2.470 2.882 3.293 3.705 4.117 0.3 0.3 0.3247 0.974 1.299 1.624 1.948 2.273 2.598 2.922 3.247 0.574 0.574 0.2588 0.776 1.035 1.294 1.553 1.811 2.070 2.329 2.588 0.511 0.511 0.2051 0.615 0.820 1.025 1.231 1.436 1.1 1.846 2.051 0.455 0.455 0.1626 0.488 0.650 0.813 0.976 1.138 1.301 1.463 1.626 0.404 0.404 0.1282 0.385 0.513 0.1 0.769 0.7 1.026 1.154 1.282 0.361 0.361 0.1024 0.307 0.409 0.512 0.614 0.716 0.819 0.921 1.024 0.320 0.320 0.0804 0.241 0.322 0.402 0.483 0.563 0.3 0.724 0.804 0.287 0.287 0.07 0.194 0.259 0.323 0.388 0.453 0.518 0.582 0.7 0.254 0.254 0.0507 0.152 0.203 0.253 0.304 0.355 0.405 0.456 0.507 0.226 0.226 0.0401 0.120 0.160 0.201 0.241 0.281 0.321 0.361 0.401 0.203 0.203 0.0324 0.097 0.129 0.162 0.194 0.227 0.259 0.291 0.324 0.180 0.180 0.0254 0.076 0.102 0.127 0.153 0.178 0.204 0.229 0.254 0.160 0.160 0.0201 0.060 0.080 0.101 0.121 0.141 0.161 0.181 0.201 0.142 0.142 0.0158 0.048 0.063 0.079 0.095 0.111 0.127 0.143 0.158 0.127 0.127 0.0127 0.038 0.051 0.063 0.076 0.0 0.101 0.114 0.127 0.114 0.114 0.0102 0.031 0.041 0.051 0.061 0.071 0.082 0.092 0.102 0.102 0.102 0.0082 0.025 0.033 0.041 0.049 0.057 0.065 0.074 0.082 0.0 0.0 0.0062 0.019 0.025 0.031 0.037 0.044 0.050 0.056 0.062 0.079 0.079 0.0049 0.015 0.020 0.025 0.029 0.034 0.039 0.044 0.049 附件1

附件2