Hello again, I'm in lockdown and have gone flyback mad!What TVS reverse stand off and breakdown voltage would you guys select for a 400v transistor?I've gotten myself confused when it comes to TVS datasheets. I'm running a TV flyback transformer like in the pic at 12v, it's actually quite efficient with nothing getting that warm drawing about 2 amps from the 12v supply and a 2 inch arc (still working on 24v mode). Frequency is about 15khz.as the capacitor is selected to limit the peak voltage to something sensible (about 170v peak right now when the output is unloaded), the TVS is just added protection for unloaded flyback output and capacitor charging situations.However by reducing the capacitor value and allowing the primary voltage to peak higher I can get more hv on the output without needing to increase the supply voltage, so I want to select a TVS which protects the transistor but doesn't conduct under normal operation.But here's where I'm stuck, I've currently got a 200v TVS in there and when I retuned the capacitor to allow for more peak primary voltage the TVS clamps much harder than I expected. I'm looking at the datasheet for the P6KE200 and was expecting maximum peaks of 274v, but reality it clamps pretty close to the 200v breakdown rating rather than shooting up that large exponential curve.I'm guessing the energy in the circuit isn't enough to push the TVS to such a high clamping level? And if that's the case what TVS voltage can I safely go up to for protecting my 400v NPN transistor (MJE)? Maybe the 300-350v standoff versions would be best suited, they're pretty expensive so I wanted check before ordering something which might not be a good choice, then there's the whole transistor safe operating area to further complicate things.which TVS diode breakdown would be a good choice for protecting a 400v transistor switching 15khz tv flyback at 2 amps average primary current?Thanks.
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