| Adam M. |
It was no fault of the chip, it did its job, I messed up. I put the output wires down to pick up a speaker while the thing was on, they shorted, and in a couple seconds I had a lm3886 minus the power supply pins and a nice lightshow. Now I gotta go order another chip!
How do I protect against this besides the very obvious of don't do it? |
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| Vikash |
I can't see why you would want to look past the obvious? ;)
I know the LM's have built in protection but it appears it won't þrotect against a short circuit on the output if you say there was a light show... |
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| Adam M. |
I think what I would like is for a fuse to act as a fuse, instead of the power pins acting like a fuse. would fuses on the rails blow a fuse instead of a chip if this happens again?
I got to protect the amp from myself. :-) its defensless.
THe light show was actually pretty cool, if it were safer and I wouldn't lose another chip, I'd do it again. (well, probably not...) |
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| johnnyx |
I'm surprised - they seem rugged to me. I was looking at the numbers on a chip amp in a commercial unit, and had to remove a metal plate that held the chip to the heatsink. When I re-fitted the metal plate, it slipped through my fingers and shorted several pins. There were sparks and crackling sounds, :ashamed: The amp was still switched on:ashamed:
Well, I thought I'd killed it. But no,:boggled: it worked perfectly afterwards.
I have found to my cost that shorts between output and ground are protected, but shorts between output and supply rails are destructive.
Maybe the output short was not your only problem. |
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| Adam M. |
| The amp actually worked before I shorted the outputs, I had it hooked up with alligator clips to a junk speaker before i went to get wire to hook it up to the junk speaker when I crossed the outputs. It was prolonged, probably shorted for 3 or 4 seconds before I pulled the plug |
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| Franz G |
This chips are safe for a short circuit between the output and the ground: they heat up quickly and then the thermal protection begins to work (periodically shutting down the chip).
Must be another short circuit.
One way out of the dilemma: no alligator clips, use a pcb or an experimental board.
Dont use fuses on the rail :( (better regulate the psu with LM338 a la Carlos FM, then you get some current limiting)
Franz |
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| Adam M. |
| Interesting on the output protection... Do you have any idea what could have been shorted? There were only 2 clips in the circuit, they were cipped to binding posts on the back of the chassis bevause I didn't have plain wire right next to me when I was testing it. I have found a second problem, I have a 60Hz hum, which I can't figure out, but that'll be another thread. |
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| ir |
i've shorted outputs weith no worries. also shorted the power supply pins wihtout worries (64V at 6 amps is nothing). i even mangaed to short something to ground that really shouldn't have been shoted to ground.
i was using a razor blade to remove excess thermal compound from around the chip mounted to the heatisnk, of course the insulated packages actually havea few exposed points on the sides ot the case. anyweays, i didn't realise the amp was powered on, slide the razor up the side. BZZZZZZT flash, pop, click. then a few minutes later, it was all working fine again
National chips are pretty indestructable really |
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| Franz G |
I did the same: cut some mica with a swiss knife, while the amp was playing.
This is the result, some erosion :D (chip still working O.K.):
Franz |
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| Vikash |
A 750 pixel wide 160kb image to show a tip of a blade. :smash:
;) |
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| JojoD818 |
| well i guess the lesson to this story is switch off your amps before doing any electronics. :clown: |
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| Franz G |
I reduced the size of the picture.
Sorry! |
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| Nuuk |
| quote: | | well i guess the lesson to this story is switch off your amps before doing any electronics. |
Amen! ;) |
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| morfeas |
Sort of the output to the + supply for about 5 minutes didn’t do the job for me either. The loudspeaker died of course.
Good job National engineers!
:) |
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