Zener Purpose?

Thread Starter

deluxeray

Joined Aug 18, 2020
3
D2 aids in ending the snub current by converting it to heat and dissipating it.
Hm, to me it seems kind of pointless to have a Zener on just for heat dissipation, especially when it's only on a 12V circuit. If that's all it's for I could get rid of it without causing harm, correct?
 

BobTPH

Joined Jun 5, 2013
3,316
The Zener raises the voltage when the the flyback diode is conducting, which speeds the collapse of the field. This is normally done on a relay or solenoid to speed up the turn off time. Not sure why it would be used in this circuit, or why any flyback is needed at all, since the load on the other side of the transformer will absorb the energy.

Bob
 

crutschow

Joined Mar 14, 2008
27,229
This normally done in a flyback circuit with one Zener from the MOSFET drain (Zener cathode) to ground, to absorb the high voltage spike if the flyback output has no load.
In that case the Zener has a voltage rating of perhaps 75% of the MOSFET maximum Vds.

The circuit shown seems to be overly complex for what it apparently does.
If it's trying to provide some regulation for the output voltage, that's a poor-efficiency way to do it.
 
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