7805 light load benaviour

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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.



Re: 7805 light load benaviour


We'll be holding our breath.
Fred



Re: 7805 light load benaviour


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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 !



--
Regards
Mike
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Re: 7805 light load benaviour



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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.



Re: 7805 light load benaviour


wrote:
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regulator to the board?
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a large whitegoods
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boards. It eventuated
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wires between the pins
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board until another solution
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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

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