Re: [SI-LIST] : Fw: Relay switching spike

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From: Doug McKean ([email protected])
Date: Tue Jun 20 2000 - 11:28:37 PDT

Srajudheen wrote:
> >
> >I am switching a relay between 21v and Read signal of
> >microprocessor for programming an EPROM. But while
> >switching from 21v to read a 21 v spike is coming to
> >the read signel. Can I know the reason, and how can
> >I solve this problem.

Probably two things going on here.

#1: Your contacts may need a snubber. There's several ways
to do this as already mentioned. Best to put a cap (I'm
guessing now but try a standard 0.01uF cap) and low ohmage
resistor (like about 10 or 20 ohms) in series with each
other, then put this little assembly across the contacts
and experiment with different values. Most likely you'll
find more significant changes by varying the resistor than
the cap. The resistor is what's used to dissipate the energy.
There's a whole science to snubbers with quite a wide array
of types. And there are rules of thumb for constructing
them for different purposes. But unfortunately, it's been
a long time since I did anything with them. Snubbers are
used more to protect contacts.

#2: The current in the coil when switched is probably
causing an inductive kick. Put a simple 1N4003 type
diode reversed biased in relation to the applied coil
voltage across the coil.

Try #2 first.

- Doug McKean

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