[SI-LIST] Re: Latching relays in optical switches
- From: "Steve Barton" <steve.barton@xxxxxxxxxxxxxxx>
- To: "Aubrey Sparkman" <asparkman@xxxxxxxxxxxxx>, "Kevin G. Rhoads" <kgrhoads@xxxxxxxxxxxx>, "Don Nelson" <dhwn@xxxxxxx>
- Date: Tue, 19 May 2009 13:13:05 -0700
Just curious - does your circuit have a diode across each relay coil?
With the cathode on the +5V supply and the anode going to the node that
has the low-side of the coil and the collector of the NPN.
And how much coil current are we talking here - 10's of mA, 100's of mA
or Amps?
Cheers,
Steve Barton
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Aubrey Sparkman
Sent: Tuesday, May 19, 2009 12:39 PM
To: 'Kevin G. Rhoads'; 'Don Nelson'
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Latching relays in optical switches
The question that occurs to me: Is there any other electronics inside
that you can't see? Are you sure you have only two coils wound on the
same core?
If there are some built in FETs, they could have a preference and be
causing some trouble...
Aubrey Sparkman
Aubrey.K.Sparkman@xxxxxxxx
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Kevin G. Rhoads
Sent: Tuesday, May 19, 2009 2:31 PM
To: Don Nelson
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Latching relays in optical switches
>The problem is, the manufacturer disagrees and insists our circuit
>needs to be redesigned to permanently tie one leg of the coils to GND
>and
switch the high side instead.
While that is more common, either should work. Particularly since you
have verified the +5 rail is not moving, which indicates it is a good
ground for all non-DC signals.
If you induce current in the other coil then the flux-linkage through
the magnetic circuit is kept minimal. That will interfere with
switching.
As for: 'They contend that having the 5V potential on the coil
permanently is "interfering with the magnetic field". I find this hard
to believe, but physics was a long time ago.'
That sounds like pseudo-scientific cruft. You should find it hard to
believe.
HTH
Kevin
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