#### kender

##### Advanced Member level 4

I'm making calculations for a push-pull transformer and following equations in Microchip application note AN1207 (pp.51ff).

\[{\Delta} B = \frac{V_P T_{ON}}{N_P A_{core}}\] eq.175

\[N_P=\frac{V_{DC,min}-V_{Q,on}}{A_{core}f_{PWM} {\Delta} B}D_{max}\] eq.176

where

\[V_{DC}\] is the input voltage

\[D_{max}\] is the max PWM duty cycle (between 0 and 0.5 for push-pull topology)

Why do they use \[V_{DC,min}\] and not \[V_{DC,max}\] in this calculation?

I though that higher voltage across the primary will cause higher magnetic flux. Higher magnetic flux can saturate the core.

Any suggestion, insight or reference is really appreciated!

Cheers,

- Nick