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

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From: Ingraham, Andrew (Andrew.Ingraham@compaq.com)
Date: Tue Jun 20 2000 - 08:28:29 PDT


>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.
 
I think you are saying that the relay contact toggles between 21V and a Read
signal, and that the coil is on a completely different circuit.

If the relay's contacts are make-before-break, then there is a brief moment
when 21V is directly connected to the Read signal. Get a different relay
that is guaranteed to be break-before-make.

If it already is break-before-make, then I think the relay contact (and
whatever circuit it is hard-wired to) holds the 21V charge briefly, which
must discharge into the Read signal line. Minimize the capacitance of that
part of the circuit, so that it can discharge more quickly. Also add
capacitance to the Read signal line if you can, making a two-cap
voltage-divider. Adding a zener from the Read line to ground might also
help, as well as a series resistor between the Read line and the relay
contact.

Regards,
Andy

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