[time-nuts] Totally unrelated, but..

David davidwhess at gmail.com
Thu Dec 8 18:52:41 EST 2016

I am pretty sure that I ran across this once as well with the
7800/LM340 series in the early 1980s with parts from a major
manufacturer like Motorola, National, or Texas Instruments; the
regulators ran hot and the output voltages were slightly low no matter
what decoupling arrangements were made at the input and output.  The
stability was poor as if the parts were oscillating but no oscillation
was apparent.

There is some discussion here about different designs for these
regulators although the photographs are broken:


On Wed, 7 Dec 2016 15:56:55 -0500, you wrote:

>I don't think so.  I first ran into a batch of LM340-5's
>that were excellent oscillators back in the 1970's... long
>before counterfeiting was even remotely possible.
>The symptom is the regulator puts out only 4.5 out of 5V.
>LM309's were, however, totally immune.
>Usually, I had to be really bad to make it happen, things
>like using clip leads between the power supply and load
>with the LM340-5 dangling in between.
>The answer is as simple as a couple of 0.1uf ceramic caps
>soldered right at the input and ground, and the output
>and ground pins.
>LDO (low dropout) regulators are very susceptible to
>oscillation.  They need to have a couple of hundred uf
>of good quality capacitance right on the input and output
>leads.  Where people usually get in trouble, is in not
>knowing that electrolytic capacitors lose most of their
>capacitance as the temperature starts hovering around 0C.
>The circuit works great on the bench, but fails when out
>hanging on a light pole...
>-Chuck Harris

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