Push Pull

[bellx]

Why is the push pull topology not used in offline smps? I see mostly half bridge , full bridge and flyback. Can somebody explain ?

 

[bellx]

Nobody?

Surely somebody can answer?🙄

 

[subwo1]

One big reason is that it does not work well with ungapped transformers because of the tendency to apply magnetic offset to the trasformer core. Since the half bridge drives the transformer through a capacitor, any DC component in the pwm waveform is blocked.

 

[djk]

Push-pull also requires double the voltage ratings on the switch transistors.

For off line 240V the high voltage FETs have too much loss due to RDS.

IGBTs may be used with less loss, but they are not quite as fast.