# Stacked flyback transformer

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##### Junior Member level 3
My DCM flyback has specs:

Vin,min =21.6V
Pout,total = 11W
Vo1 = 3.3V (regulated) 1.98W
Vo2 = 20V 4W
Vo3 = 24V 4.8W
Vo4 = 7V 0.210W

I have calculated transformer primary and secondary windings as:

Np = 16
Ns1 = 2
Ns2 = 11
Ns3 = 13
Ns4 = 4

I am going to use stacked windings for first three outputs. So the stacked windings would be Ns1 = 2, Ns2 = 9 (2+9 = 11) and Ns3 = 2 (2+9+2 = 13). Now when calculating peak currents for stacked secondary windings, i am not sure is my calculations right? Pout, total = 11W gives me Ton = 2.18us and primary peak current Ip = 2.9196A ( Lm = 16.128uH ) and currents for stacked windings:

Is1 = Ip*$\frac{ Np}{Ns1 }$*$\frac{Po1+Po2+Po3 }{ Po,total}$ = 2.9196A*$\frac{ 16}{2 }$*$\frac{1.98W+4W+4.8W }{11W }$=22.89A
Is2 = Ip*$\frac{ Np}{Ns2 }$*$\frac{Po2+Po3 }{ Po,total}$ = 2.9196A*$\frac{ 16}{11 }$*$\frac{4W+4.8W }{11W }$=3.397A
Is3= Ip*$\frac{ Np}{Ns3 }$*$\frac{Po3 }{ Po,total}$ = 2.9196A*$\frac{ 16}{13 }$*$\frac{4.8W }{11W }$=1.568A

Hi
Goldsmith

#### grizedale

also worth remebering that even of you do stacked windings, its still best to give each secondary "section" its own full layer....this improves cross regulation further.

##### Junior Member level 3
Goldsmith, Switching frequency is fs = 200kHz

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