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Substituting a transistor for a MOSFET in a flyback driver

Apocaloptigon

Jun 23, 2018
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Jun 23, 2018
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Here's the classic circuit im using:
schematic1.gif
It's made to create high voltage AC from DC.
I've killed a few transistors with overvoltage using this circuit and because of that im considering using a mosfet to take the higher power and maybe get better performance. Before i go out and buy a mosfet, would this even work?
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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With no load on the feedback coil the risk is that the voltage would rise high enough to destroy the gate of the mosfet.

Another risk is that it may not rise high enough to turn the mosfet completely on (it is most likely design to deliver current to switch a bjt rather than voltage to switch a mosfet).

These two risks are not independent!

Protecting the gate from excessive voltage is pretty simple (series resistor and back to back zeners) but the second issue may require rewinding the feedback winding.
 

Apocaloptigon

Jun 23, 2018
15
Joined
Jun 23, 2018
Messages
15
Ahh, that clears up quite a bit. I don't have enough time right now to experiment with either risk, but i have taken advice from the powerlabs.org website and increased the number of turns on both the primary and feedback coils to potentially save the transistor. Since i haven't seen anybody else using mosfets on this driver, it probably is based on current. But in the future i'll get to testing out mosfets, resisters, and coil turns (or maybe just use a different circuit).
Thanks!
 
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