Is the 1n5817 being used for reverse protection or what. I would have thought it would have been a zener. Thanks

 

Clamp the - transient from L feed back thru miller C ? Even though
there is one on drain to ground. Or stray L - Cgate ringing from
driving the Gate ?

Or back thru Cg-d....


Regards, Dana.

 

During the time that the pass transistor inside the IC is off, the voltage reverses on that pin and the diode catches the voltage at just below ground so the current can continue to flow through the inductor.

 

Thank you both.

 

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Is the 1n5817 being used for reverse protection or what. I would have thought it would have been a zener. Thanks

They were not uncommon on flyback direct off line converters, the SB diode has a reverse breakdown voltage close to Vgs max and fail hard. They have been known to save the driver chip (sometimes) when the MOSFET punches through. The circuit dynamic is different there - it may be a clamp for ringing in stray inductance.

 

They were not uncommon on flyback direct off line converters, the SB diode has a reverse breakdown voltage close to Vgs max and fail hard. They have been known to save the driver chip (sometimes) when the MOSFET punches through. The circuit dynamic is different there - it may be a clamp for ringing in stray inductance.

Got a good picture of what it is for now, thanks all.