7805 light load benaviour

Just to let people know that I'm working through the problem with low load benaviour of 7805 regs thoroughly, and will post the outcome. Given the nature of the problem, it'll probably be at least a few weeks before I have anything to report.

Thus far, it looks like a bad batch is the most likely cause.

Input from posters is appreciated.

Reply to
bruce varley
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We'll be holding our breath. Fred

Reply to
Fred Bear

Tell me you do have bypassing caps on the device, the barest minimum in my experience is 0.1uf on input *and* output very close to device. I have seen a 60MHz +- 10MHz oscillation if the devices are not properly bypassed.

Some electros dont provide good bypassing by themselves.

I prefer to use 100uF on input with a 1uf monolithic close to input of 7805 and a 0.1uF minimum monolithic close to output.

Never seen a bad batch of these devices, which manufacturer have you had troubles with - have only ever seen a batch of 74C14 from SGS that refused to work at 5v, like 30% out of 2000 units !

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Regards
Mike
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Reply to
Mike

How are you mounting the regulator? Are you pop rivetting the tab of the regulator to the board? Around '88 or '89 I was working for the research and development department of a large whitegoods manufacturer, and we had similar problems with the 7805s on the controller boards. It eventuated that the shock of pop rivetting the regulator to the board broke the bonding wires between the pins of the regulator and the die. As I remember, we bolted the regulator to the board until another solution was found.

Reply to
dmm

regulator to the board?

a large whitegoods

boards. It eventuated

wires between the pins

board until another solution

when I went to the US, I got lumbered with an OEM UPS for terabyte raid arrays (to flush the 128Gb ram cache). We had a 30% failure rate (out of perhaps 300 units) on Motorola 7805s - "motorola make shitty 7805s" was the excuse. yeah right. So I got the contract manufacturer to not pop-rivet them, and we built 19,000 units without a single 7805 failure. Duh, motorola AN1040.....

the really funny bit was the contract manufacturer using a nylok nut on the battery charger smps FET. Which heated the nylon up to 100C, whereupon it all oozed out the back of the nut which then came loose, causing thermal runaway and kaboom. Of course the nylon then solidified, locking the nut in the "extremely sloppy" position. LOL.

Cheers Terry

Reply to
Terry Given

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