What happens when I drive a signal into the center tap of a center tapped transformer?

Question

I am trying to drive both a high-side and a low-side MOSFET as part of an H-Bridge circuit and had the idea to gang both MOSFETs with the same input. My idea was if I drive one side of a center-tapped transformer the other side being magnetically coupled to the first half of the primary would act like a step-up transformer and the other side would be in phase and have a magnitude of 2x the input single.

the signal represents a pulsed DC square wave generated by a digital pin of a microcontroller. Are center-tapped transformers supposed to work like this? Is this a valid method to drive a MOSFET H-Bridge? am I risking sending too much voltage into the gate pins? is this even a good idea?

Answer 1

Center tapped transformers (or any transformers (or any components)) don't care about single pins. What matters is the voltage across each coil (which has two pins) and the current through each coil. A center-tapped coil is the same as two coils connected together in the middle.

The way you're using the center-tapped coil makes an autotransformer configuration. It saves wire compared to a two-coil transformer, but doesn't provide isolation. Image from Wikipedia:

It works just how you'd expect a transformer to work - the voltage ratio is the turns ratio. At least, it does for sine-wave AC. Passing a square wave through a transformer distorts the wave, but you probably already know that and don't care.

You're using the transformer for two transformations at once - the left side as an autotransformer and the right side as a normal transformer. If this works for you, then great. You found a trick to do something with less parts. Congratulations.