# FET drain voltage spike in push-pull converter

I have returned to my 150W inverter simulation and have a new problem I can't decipher. This is the design:

It runs, it allegedly has good efficiency, and it creates a stable 180V output voltage. I've included a leakage inductance of 198nH on each primary winding to simulate stored energy in the transformer windings. I'm getting ringing on the drains which I expect, and I've added an RC snubber to reduce them. However, at the point of turn-off for the mosfets there is an enormous drain voltage spike up to 100V. It might be higher, but the Vds breakdown is 100V and I suspect the spike is even higher but the models are simply clamping it there.

I have experimented with diodes across drain-source, freewheeling diodes across drain-Vin, but the former does nothing and the latter severely distorts the switching waveform. When I check the primary input waveform of the transformer after the leakage it does not have these spikes:

I'm not sure how else to dissipate this stored leakage energy without interfering with operation. Since it happens at turn-off I wonder if there is a better drive scheme I can be doing? The whole idea of simulation was to identify issues that could destroy components but I'm not sure how to reduce this spike. Any help is appreciated.

• the Rdson is 23 mΩ and the R/L=T values matter ! 1 uOhm? dead-time is important Mar 19 at 1:38
• What is the pulse voltage across the snubber resistor, R1. Is it constant with the magnetizing current at turn-off? There would also be some self-capacitance of the transformer that would reduce the pulse. The avalanche energy rating for the MOSFET is probably large enough so no damage would result in real-life. There is a diode, D1, not connected to anything. Unconnected components sometimes mess up SPICE. Mar 19 at 1:45
• Why do you have 2 trafos? What coupling do they have? Why the 1u resistors, they can't be realistic. And why waste a full bridge when you could have had only two diodes? Also, do yourself, and others, a favour and use the already existent symbols for diode and MOSFET, it'll make for a much clearer schematic. As you probably know, if they're subcircuits instead of models, you need to change the prefix to X, in rest it works just like a .model. Mar 19 at 7:34