Re: gEDA-user: Dropping a few volts

[DJ Delorie <dj@xxxxxxxxxxx>]

> Yes, where the load is on the emitter.  You could also use one of
> those FETs.  I"d rather see the zener to common with a resistor
> above it drawing some reasonable current to give a less able to
> oscillate voltage to the base or gate...

Zener to input gives you a fixed drop, so the transistor doesn't have
to handle a wide range of conditions.  I suppose you could use a JFET
as a constant current source instead of the resistor.

If you used a FET instead of a BJT the zener/resistor would be
isolated from the load, add a bypass cap on the gate, should take care
of oscillations.

But keep in mind, this is driving a second regulator, so minor ripple
won't be as bad.

They do make high voltage zeners, though, if you want to do it the
"normal" way.


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