Hi, I am trying to make a variable frequency supply unit using 555 timer, TLP250 driver, a mosfet P80NF55, and a flyback transformer 1V/250V. I need to drive a capacitive load (Plasma reactor) at 10 kV, 0.1 A, if the frequency is 3kHz. Circuit diagram is attached herewith. Before connecting the flyback transformer, I am getting variable frequency pulses across MOSFET (between drain and source). But when I connect the MOSFET (drain) through the primary of flyback transformer to the DC supply, I think MOSFET is burning. I have seen it not working later when I test it alone again removing flyback transformer.
I understood that there was a back emf problem due to inductive nature of the circuit. So, to reduce it, I need to connect diodes across coil and across MOSFET.
My applied voltage is 15 V at primary and maximum current is 25 A in primary side, when secondary gets 0.1 A.
So, what could be the rating of the diode that suits this application.
Thanks in advance.

 

You need a zener or transzorb across the MOSFET source to drain rated at about 75% of the MOSFET's voltage rating.

You do not need (or want) any flyback diodes across the coil as that will drastically reduce the output voltage.

Note that your diagram shows a P-MOSFET, not the N-MOSFET it is.

 

Same post here.....


https://forum.allaboutcircuits.com/...lyback-transformer.134011/page-2#post-1118199

 

One thread is enough, this thread will be locked.
The original one as below.
Need help to make variable frequency supply unit using 555, mosfet and flyback transformer.