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Old 5th October 2009, 03:52 AM   #11
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Default some differences between IRF540 and IRF540N FETs

Guys,

I was reading this thread with interest and thought I'd look over the datasheets for these two FETs. Comparing the International Rectifier datasheet for the IRF540N and the Phillips Semiconductor datacheet for the IRF540, I noticed that the input capacitance of the "N" suffix part is more than twice as high as the IRF540. I'd imagine that for a given gate drive circuit the turn-on and turn-off would be correspondingly slower with the larger input capacitance. If these were used in the power supply I could see how they'd possibly cause cross conduction if the deadtime wasn't long enough.

Perry,

In the audio output circuits do you suppose the larger input capacitance might also explain the oscillation you experienced? It'd be interesting to cut the value of the gate resistors in half to see if the oscilation goes away. I'm not sure if the circuitry driving the gate resistors would be OK with the larger load though.
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Old 14th October 2009, 03:01 AM   #12
spooney is offline spooney  United States
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ok so after using this amplifier in my car for a couple days to power a pair of tens another issue has presented itself. The amplifier plays cleanly and loudly but it is cutting out at higher volume. I get to almost maximum volume and it is fine but a couple clicks higher on the volume knob and the amp will cut out and in. It cuts out on the louder bass notes and comes right back in. I haven't watched the power light to see if it completely powers off or not but it happens so fast I don't think i'd really be able to tell. is there perhaps a damaged op amp that would cause this? The amplifier doesn't seem overly hot at all when this is happening and it will do it whether it has been playing for 15 seconds or an hour. I hooked up another subwoofer to see if that was the issue but the problem remains.
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Old 14th October 2009, 06:33 AM   #13
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Did the amp burn any of the 0.1 ohm source resistors?

If so, did you check ALL of the SMD resistors for the protection circuit (connected across the source resistors)?

Did you check all of the source resistors carefully to confirm that all were within tolerance?
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Old 15th October 2009, 12:25 AM   #14
spooney is offline spooney  United States
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None of the source resistors were burnt however i did replace them anyways with some 1% source resistors that i saw you had recommended for the repair of a punch 200x2(boards appear to be identical) . I also checked those smd resistors as you had recommended in that same thread. They all appeared to be within tolerance. I will recheck them all once i get the amp back on my bench and maybe take a look at the other channel as well. Perhaps there is some problems over there even though it never failed
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Old 15th October 2009, 04:51 PM   #15
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Desolder one leg of the 0.1 ohm source resistors when checking the SMD resistors in the protection circuit so that the 0.1 ohm resistors don't skew the readings.
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Old 17th October 2009, 03:34 AM   #16
damage is offline damage  United States
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Quote:
Originally Posted by 17DoubleE View Post
I'd imagine that for a given gate drive circuit the turn-on and turn-off would be correspondingly slower with the larger input capacitance. If these were used in the power supply I could see how they'd possibly cause cross conduction if the deadtime wasn't long enough.
My one experience with cross conduction results in excessive noise on the outputs and a significant current drain.
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Old 17th October 2009, 03:46 AM   #17
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This is a class AB amp.
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