Re: [CAD_CAM_EDM_DRO] Re: cap question

On Mon Apr 1 21:35:05 2002, JanRwl@..., <JanRwl@...> wrote:

>In a message dated 01-Apr-02 21:55:50 Central Standard Time,
>pbweber@... writes:
>
>
>> I'm thinking a zener diode to ground rated a little
>> above the rated voltage of the cap?
>
>
>Paul: This first must assume the zener you'd USE for that has a sufficient
>WATTAGE to accept the over-voltage, and the current through it that would
>result therefrom. This can cause WORSE "explosions", not to mention damage
>to the power-supply bridge-rectifier, or VR, if used.
>
>One way to "protect" the zener is to insert a low-R (0.1 ohm, etc.) of how
>many, fifty watts?, in series with the zener. And, use a 50 W zener. Ever
>price those???
>
>This is simply one of those "good ideas on paper which are not practical".
>Best engineering is to design with a CAP rated for the "worst case" voltage!
>It doesn't have to be "close", just "over"! MUCH cheaper alternative to
>"engineering a fix for an imagined, not-yet-experienced problem!!!!! Jan
>Rowland

Couldn't you use a transistor to drop it? Consider: One of the ways zeners are
used to regulate voltage, is to put a potentiometer between it and ground. Now
if at that zener/pot juncture, you connect the base of an NPN transistor with
the emitter going to ground, and the collector connected above the zener, the
transistor would drop the voltage everytime the zener reached it's limit. An
extra pot might be needed between the juncture and the transistor base, in order
to adjust the transistor properly, but you could get away with using a
lightweight zener that way.

Bill

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