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#1
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Mosfet noise - Clicking and Screetching
I have a custom power supply that has an input rating of 120vac and an=20
ouput rating of 24vdc @ 6amps (apx 140watts working). The main switching=20 MOSFET is making an audible noise... clicking when first turned on and=20 then it screetches and voltage drops to 0 then clicking and slowly back=20 up to 24=B1 vdc then screetching and back down to 0. What could be causing= =20 this? - could this be a bad rectifier in the AC/DC wave form conversion=20 or do you think it could be a bad capacitor that is leaving the circuit=20 out of ballance... I have tested everything and it seems to check out.=20 All resistors are within spec. MOSFET has been replaced (no change). The=20 capacitors under 100uf test out ok (I have no way to test the 2 caps=20 that are 200v 330uf). Thanks, kj |
#2
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Sounds like the unit is trying to drive into a dead short
Paul |
#3
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#4
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The clue is warming up
do you have pre driver transistors for the MOSFETS? the other way to find out is to let it warm up and hit it with freezer spray, various components, probably driver transistors and caps Paul |
#5
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loedown wrote:
The clue is warming up do you have pre driver transistors for the MOSFETS? There is a small 8 pin IC that looks like it is driving the gate on the MOSFET... would heat cause this IC to work? - I will try the freeze test as soon as I can get the board back out - we were forced to put it back in use temporarly... I would imagine diode test on the IC when removed should let me know if there is a short or too much resistance... the other way to find out is to let it warm up and hit it with freezer spray, various components, probably driver transistors and caps Paul Thanks for the tip on the spray freeze... I was thinking about using canned air to freeze the components... -kj |
#6
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The IC could be very much the culprit
Paul |
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