Three topologies and transformer calculation of switching power supply

Switching power supply Three topologies: Buck,boost,buck-boost. The topology diagram is as follows:

Buck

Boostδ

Buck-boost

Transformer calculation:

One, Buck circuit transformer calculation

The buck Circuit is the most severe inductor operating condition at the highest input voltage;

1, first set the following parameters: Input voltage vin, Output voltage iout, operating frequency F;

2, because the circuit works in the critical mode, so the inductor peak current of 2Iout;

3, duty ratio d=vout/vin;

4, by the Volt-second balance v*ton=l*i, can get L= (V*DT)/di = (V*DT)/ipk, of which ton=d*t=d/f;

5, determine the number of primary winding turns: n1= (l*di)/(Δb*ae) = (L*IPK)/(ΔB*AE);

6, determine the number of secondary winding turns: n2= (VCC*N1)/(Vin-vout).

Second, flyback transformer calculation

Buck-boost circuit, the lowest voltage is the worst case

If the circuit is in CCM mode, take frequency to F .

Note: 1, NP is the primary winding turn number, NS is the secondary winding turns; 2, VMOs for MOS maximum withstand voltage, 1 for rectifier tube pressure drop, Vl for leakage, Vl=100v,vmos selection follows the principle: switch off the moment, add on the MoS voltage value of VMOs 25% (or 30V), should leave a 50V margin.

1. Determine the primary/secondary turns ratio

∵vmos=vinmax+ (vo+1) +VL

∴ primary/secondary turns ratio n=np/ns= (vmos-vinmax-80-100)/(vo+1);

2, ensure the core is not saturated and always work in CCM mode

By the Volt-second balance (Vinmin-1) ton= (vo+1) *toff---① (set MOS, Rectifier is the forward-guide voltage drop of 1V)

To ensure that the circuit works in DCM mode, the ton+toff=t should be-----------②

So ①② tonmax={(vo+1) * (np/ns) *t}/{(Vinmin-1) + (vo+1) * (Np/ns)};

3, primary inductance determination

∵pout= pin,pout=vo*icps* (toff/t), pin=vinmin*icpr* (tonmax/t);

(ICPR: Primary current rise ramp middle value, Icps: secondary current descent ramp median)

∴icpr= (po*t)/(Η*vinmin*tonmax)

∵icpr=dip/2

∴lp= = (Vinmin-1) *tonmax/dip= (Vinmin-1) *tonmax/(2*ICPR)

4. Initial/secondary turns determined

np= (LP*IP)/(Δb*ae)

ns=np/n

5, initial/secondary current RMS value determination

Irms (Beginner) = (ip/√3) * (√ (ton/t))

Irms (secondary) =ip* (np/ns) * (√ (toff/t))/(√3)

If the circuit is in CDM mode,

(not to be continued)

Three topologies and transformer calculation of switching power supply