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Need help with 555 PWM with current limiter

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Yes, I mean R4, R6 hardly carries any current and can be 1/4W
 
Super,

I have a lot to learn about mosfets & igbts. Also, I am a bit rusty on my electronics theory. But, if you trying to control a highly inductive load such as a transformer primary, it is not a simple matter. I strongly suspect your problem is not the failure of your output devices due to excessive current, but drain-source breakdown from excessive voltage which occurs when your hexfets (that's what they are) turn off. You might try a voltage clamp across your load. I would send you a schematic of what I am talking about if I could.
 
Super,

Going a bit futher, note the internal drain-source zeners shown on the data sheet of the hexfets you are using.
 
Super,

You might do a bit of reading on crowbar circuits to get an idea of how to design your protective circuit. Best wishes.
 
Hi Ian,

It is 6 am here in Georgia in the US...barely awake and just killing some time, reading some of this stuff. Didn't realize that until after responding, but that's ok. Thanks & best wishes to you good folks in the UK.
 
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