Autopsy on the body of a voltage regulator

Jul 07, 2006 4 Replies
N

Well sort of as still functioned and no downstream damge, but replaced of course anyway. USA kit 120V, powered up in UK at 240 V this LM317T set for 15V out survived 40 or 50V instead of 25V at its input. Clamped to heat sink with a thick Ali bar pulled against the body so sandwiched between 2 bits of ali. The grey PTFE/Teflon or whatever it is insulator was "welded" to the metal of the V Reg and all lettering disappeared from the other face. Anyone else seen this before, no explosive eruptions from the body at all.


-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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T

hmmm, the 317 data sheet from national doesn't list an absolute V max input but does list a input output max differential V of 40V so for a

15V output you should be good to a 55V input. Still if it were me I'd try to knock down the input DC somehow. If you go thru the numbers for heat/thermal transfer you're probably right at the limit. That maybe the reason you've "welded" the insulator and "cooked" off the lettering. Try to get a sense of the temperature of the device, I suspect you will find it's a bit on the toasty side.

tomh

n cook wrote:

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N

of

explosive

I just cracked it open and it looks or rather looked perfectly healthy

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D

You must have a lot of free time on your hands! :-)

Dave

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N

So I can take it on good authority that the Lincoln Lab does no research.

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