Need help with 555 PWM with current limiter

Thanks hero I'll give it a shot.
I appreciate your help with this.

Hero999 said:

For R6 5m will do use two 10m resistors in parallel on a huge heatsink:

Click to expand...

Hero don't you mean R4 not R6?

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.

This is a three and a half year old thread... The OP hasn't posted since then... I doubt you'll get a response.

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.