The world record for worst use of a Zener has to go to the Triumph Motorcycle Company. Instead of putting in a proper voltage regulator, the alternator output had a large (75W?) Zener diode stuck across it to limit the voltage when the headlamp wasn’t on and the battery was fully charged. They were stuck on a small heatsink under the headlamp.
Of course, if you happened to be in, say, London traffic with a charged battery and frequent stop start, the engine was often turning over quite fast and the airflow was negligible, so they burnt out on a regular basis.
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Jesus H. Christ. I wouldn’t resort to such a hack on a prototype board.
I would. Sticking a 3W 5.1V Zener across a 3-AA supply is a good way to protect against polarity reversal if someone else is using the board. But for a voltage regulator…never.
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Never say never. It may be an expedient solution in a given situation, the least available evil.
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Yeah, OK.
I once failed a job interview because I was asked (by the chief scientist who was interviewing) to explain what a piece of circuit did. (…and it was a software job, go figure). I didn’t know, and he told me it was a voltage regulator. To which I replied that I didn’t see how because there was no compensation for load current, no temperature compensation and the Hfe of the transistors would slowly drift with time, thus affecting the output.
Then he told me had had designed it and, as they say, I made my excuses and left.
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If you did that to me, I’d hire you on the spot.
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See, that sounds perfectly reasonable to me in a pinch. I mean yeah, just because it’s parameters allow for it to be used as a crude voltage regulator doesn’t mean it’s a good idea.
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