u/Last-Effective-6758 — reddlx

This is an H-bridge based induction heater. The tank circuit is drive by a coupling transformer which is driven by an h-bridge.

Square wave -> Gate drivers -> coupling -> hbridge -> coupling -> LC tank

Yellow trace is LC.Purple is the coupling transformer/h-bridge. Ideally purple trace should be square wave.

When it is not loaded - coil empty - the purple trace is more or less ok.

When it is loaded - insert large iron rod - the purple trace is severely distorted and power consumption decreases a lot.

Can anyone tell what is wrong here?

PS - I didn't follow the same design - these are MOSFETs with MOSFET drivers.

Edit: forgot images