Is MOSFET signal as it should be?

Thread Starter

stevenmahoney

Joined Jan 25, 2013
10
I have a power supply that I am repairing and I wanted to know if signals are as they suppose to be. here is the schematics:



And here is what I got:



Do signals look OK to you?

Steven
 

Dodgydave

Joined Jun 22, 2012
11,285
Does the psu work, the signals look ok to me, the main signals to look for are B ,E they look like they are working, C will be near enough at Zero as its a current monitor signal, D will be at the supply of the IC as its a DC take over winding from the pulse transformer, A,B should be nearly the same square wave pulses, and the signal on pin 1 will be the shut down signal from the opto coupler.
 

Thread Starter

stevenmahoney

Joined Jan 25, 2013
10
Yes, the power supply works, I was just thrown off by that ringing... I expected a square signal at E. Can you tell me how that ringing comes to be? Especially little one on the top of the signal graph and larger one after that?

Steven
 

Jony130

Joined Feb 17, 2009
5,487
This high frequency ringing (little one on the top of the signal graph ) are caused by primary winding leaking inductance and MOSFET parasitic capacitance.
The low frequency ringing are caused by primary winding inductance and MOSFET parasitic capacitance. But this is quite normal, so no worries.
 
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