Re: Looking for pulse-rated zener.



Hello - (hope this is the right place .. pardon the cross-post)...

I was recently asked to come up with a circuit for rapidly turning off a
modest magnetic field (about 100 gauss) in a microsecond or less.  Did a
little math, some thinking, and came up with a Helmholtz coil pair that
seems to do the right thing.  Approximate inductance of the coil pair is
8 uH.

Turning the field off in under a microsecond was the difficult part..
but a hint in a reference suggested placing a zener across the
inductors.  This was tried with a much lower current (and a much lower
field) and indications are that this will work.  However...

Generating a 100 gauss field requires about 15 amperes.  Turning off
that field by circulating the current through a zener means the zener
must (a) handle a pulse of 15 amps and (b) dissipate nearly 1 mJ in less
than a microsecond.  The repetition rate is once every 5 seconds, maybe
a little faster if the research turns the frequency up.

I have found only one maker of pulse-rated zener diodes.. and while I
was able to get a few as samples, now a small quantity is needed (<100)
and these things are only sold in bulk.  I don't need 12,000 or 25,000
diodes, not for a research effort.

Questions:
1. Anyone know a house selling small quantities of BZW03D100 diodes?
2. Anyone know a maker of suitable zeners?
3. Do I really need a high-power zener for this?

Your time is appreciated.

Mark

P.S. Postings to the newsgroup preferred.. however, if you e-mail a
response to this note, the e-mailer at stowetel will challenge.  Please
ack the challenge.. it slows down the spammers.  Thanks.

Failing availability of the pulse-rated zener, you can always use the more common TVS variety by reverse biasing to just below minimum withstanding voltage.

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