...put the 2 in series!
Choose the smaller one for whatever voltage you need and the second equal to
the difference of the smaller voltage and the higher one. Then you can short
out the second one with whatever means look good to you: you won't be able
to create a transient greater than the Zener voltage of the second Zener
diode. If you put an electrolytic cap of a few uF across the diodes
combination, you will also keep any possible spikes under control.
Alex 4Z5KS
"Jesus, come get your kids, they're tearing up my Mother's backyard!"
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Steve Flood
Sent: Tuesday, December 30, 2008 6:53 PM
To: amps@contesting.com; rfamplifiers@yahoogroups.com
Subject: [Amps] switchable zener cathode bias
Considering the common zener bias circuit (with the 2n3055 and resistor),
what precautions should be taken if I wanted two different zeners (and
associated bias voltages) selected by a switch or relay? Is there a danger
in the moment when the switch/relay throw is transferrring from one pole to
the other and neither zener is in the circuit? Likewise, if I used a
make-before-break setup, can the two zeners be in parallel for a moment
without causing trouble?
Thanks,
Steve KK7UV
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