Topband: Detuning Relay Flyback Diode

[David Cutter]

The back emf diode slows the relay a lot and you can improve that with a 
resistor in series, fudge as required.
Here's another method:
in the drive transistor circuit, fit a small capacitor between collector and 
base.  As the back emf builds up, a current will be fed back to the base 
which will tend to keep the transistor on.  This results in a slower rise 
time and this can be controlled with the value of capacitor used.  A 
resistor in series with the capacitor provides even more control.  Fudge as 
required.

David
G3UNA



----- Original Message ----- 
From: "Brad Denison" <brad.denison at gmail.com>
To: <topband at contesting.com>
Sent: Saturday, December 23, 2017 3:51 PM
Subject: Topband: Detuning Relay Flyback Diode


>I have a couple of 6ms 12V Kilovac relays wired up as a detuning circuit
> during RX.  One question comes up before implementation regarding flyback
> diodes - would they be needed?  Seeking opinions on this question.  The
> relays are powered during TX and not powered for RX direct keyed by the
> radio with no sequencer.
>
> Thanks,
>
> Brad W1NT <http://w1nt.com>
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband