voltagetransferratioDV.N2(10-7)VaN, 1- DThe voltage conversion ratio of Flyback convertersoperating in CCM (incomplete demagnetization mode)depends on D, but is independent of the output load. If theoutput load decreases to the extent that im becomesdiscontinuous (DCM) (completedemagnetization mode)the relationship (10-7) is no longer valid
voltage transfer ratio The voltage conversion ratio of Flyback converters operating in CCM (incomplete demagnetization mode ) depends on D, but is independent of the output load. If the output load decreases to the extent that im becomes discontinuous (DCM) (complete demagnetization mode) , the relationship (10-7) is no longer valid. (10 −7) Vo = N2 D Vd N1 1− D
4PSpiceModelingC:IFirstCourse PE Book03lflyback.sch8TX1C1100uF7.0R2IC=4.15VCOUPLING=0.99331megL1_VALUE=30uHL2VALUE=1.875uHR1B100pwm_saw1V1S132V1mTC21n=院V2fs=200kHz0.4VE-mail
E-mail 13 : xjhuang@bjtu.edu.cn C:\FirstCourse_PE_Book03\flyback.sch 4 PSpice Modeling
Simulation Results102227455u2s450us460us465us470us475us480a5485us490u5495us500us口I(31)I (DL)
Simulation Results i1 i2
Example 10-A Assume you are asked to design aphotovoltaic (PV) based power supply to power on 12VDC loads. The power supply shall be able to out constant12V when PV's voltage is changing between 2V to 44.4VIfaflybackconverterisused,(a)What is the transformer turns ratio, N,:N2, to make theminimum duty ratio of switch to be 0.2?(b)Take the turns ratio from (a), what is the maximum dutyratio?(c)Take the turns ratio from (a), having V。=12V(constant)and R=2 ohm, based on the T-equivalent of the circuitcalculate the minimum mutual inductance thatguarantees continuous mutual inductance current,assuming 10kHz switching
Example 10-A Assume you are asked to design a photovoltaic (PV) based power supply to power on 12V DC loads. The power supply shall be able to out constant 12V when PV’s voltage is changing between 2V to 44.4V. If a flyback converter is used, (a)What is the transformer turns ratio, N1 :N2 , to make the minimum duty ratio of switch to be 0.2? (b)Take the turns ratio from (a), what is the maximum duty ratio? (c)Take the turns ratio from (a), having Vo=12V(constant) and R=2 ohm, based on the T-equivalent of the circuit, calculate the minimum mutual inductance that guarantees continuous mutual inductance current, assuming 10 kHz switching
V。_N2 DSolutionVaN, 1-D(a) When V=Vdmax,D=Dmin, hence,D.NiVamax44.4×0.20.925minN2V。12(1-0.2)1- D.minSoN1:Nzis0.925(b) When V=Vdmin, D=DmaxNiVN20.925×12D=0.847maxN0.925×12+2dminN2
Solution Vo = N2 D Vd N1 1− D 2 2 1 = 0.847 0.92512+ 2 0.92512 = o dmin o +V 1 V N V N N Dmax = N (b) When Vd=Vdmin, D=Dmax 12(1−0.2) N1 = 44.40.2 = = 0.925 Vd max Dmin (a) When Vd=Vdmax, D=Dmin, hence, N2 Vo 1− Dmin So N1 :N2 is 0.925