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Old 26th June 2003, 04:47 AM   #1
CH2 is offline CH2
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Unhappy Bosoz PSU problem

Hi all

I am working on my BOSOZ PSU, and have some problem with my PSU. when I am not loading the PSU, all the voltage is at +/- 54 (as according to my zener). But once I start loading the circuit, drawing 0.03A, the voltage drops to +/- 14. Initially I though I short the mosfet, so I switched the fet, but it still yield the same result. Did I short the fet again?

Seems kind of strange.


Hope for some enlightenment.
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Old 26th June 2003, 06:10 AM   #2
CH2 is offline CH2
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I just did some measurement.

The Gate to source voltage is less than 50mv. I think I blew it again.



Will try again.

CH2
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Old 27th June 2003, 04:33 PM   #3
eLarson is offline eLarson  United States
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Some idle speculation while I am home today enjoying some nice Chicago weather...

Would it be worthwhile to keep a 20V (or less... maybe a 9V?) zener directly across the gate-source pins of the MOSFET?

I'm wondering if the max VGS isn't getting exceeded (briefly) as the gate goes whoosh! towards 54 volts. That is, could the source voltage lag behind ever so slightly?

An equally, or more likely scenario is that the MOSFET blew you took it out of the packet and prepared to solder it.

I always try to short all three pins together until I have the mosfet situated in the circuit. A hemostat seems to work decently enough and I don't have to remember to desolder a resistor lead from across the pins later.

Erik
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Old 28th June 2003, 04:08 PM   #4
CH2 is offline CH2
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Quote:
Originally posted by eLarson
Some idle speculation while I am home today enjoying some nice Chicago weather...

Would it be worthwhile to keep a 20V (or less... maybe a 9V?) zener directly across the gate-source pins of the MOSFET?

I'm wondering if the max VGS isn't getting exceeded (briefly) as the gate goes whoosh! towards 54 volts. That is, could the source voltage lag behind ever so slightly?

An equally, or more likely scenario is that the MOSFET blew you took it out of the packet and prepared to solder it.

I always try to short all three pins together until I have the mosfet situated in the circuit. A hemostat seems to work decently enough and I don't have to remember to desolder a resistor lead from across the pins later.

Erik
Hi Erik

You are right on the cause. I had the zener blowed in my first try. It took me another 3 sets of fet before I realised my blowed zener. I went throught the circuit again and again, but just could not understand what gone wrong. I even try testing the mosfet before I mound them. After testing the caps, resistor and mosfet, I finally test the zener. Even thought wasted 8 fet, but well I finally get it working.

Hope I have lesser problem with the main circuit.

Cheers
CH2
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