You need to first know the maximum and minimum current that your circuit
will draw, then you can design the zener part. While this is over
simplified, it should give you a start in the right direction:

The zener is sort of a current buffer in that it will absorb the current NOT
taken by the load when the load is drawing its minimum current. Start
thinking like this:

When the ckt being regulated is drawing maximum current, the series resistor
in the zener leg is sized to provide a low zener current. When the ckt is
drawing minimum current, all that extra current (the difference between the
maximum and minimum current) goes through the zener. If it is too much you
either need to get a higher dissipation zener, go to an amplified zener or
some other regulator type.

--
Steve N, K,9;d, c. i My email has no u's.

"The Eternal Squire" wrote in message
...
Hi,

I'm going fast and furious into building things, which is the reason I am
posting
so much. Latest project is a variable power supply.

Situation: Radio Shack wall transformer with 11 VDC unregulated output is
going into an LM371. I want to shunt with a pair of 5.1 V , 1A Zeners in
series
so that my adjustable output voltage is repeatable. Presently my Zener
series resistor is 180 ohms.

Problem.. I'm frying my zeners!!

What should I be doing differently?

Thanks in advance,

The Eternal Squire


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