Relay design - ok to skip flyback diode, if controlling with mechanical switch?

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leigh

Well-known member
Joined
Jun 4, 2004
Messages
394
Location
Portland, OR
I ordered a couple of these pre-assembled boards to drop into a monitor controller project:

Balanced Four Stereo Audio Signal Input Selector

Was reviewing their design, and noticed that flyback diodes are not included in the circuit. The relays are switched with a simple rotary mechanical switch, so there's no "relay driver" per-se to protect from the high-voltage pulse at coil shutoff. Wondering if it was an OK call for the designers of this circuit to skip the flyback diodes, or if I should retrofit some for the long-term health of the components (the contacts of the mechanical switch, specifically, yes?).

The schematic, for quick ref:
A-140SCH-800x600.jpg


Thanks!
 
Rob Flinn said:
It's better to have the diodes there.  The back E.M.F is big enough to potentially arc across switch contacts possibly damaging the switch.

Thanks for the confirmation! I had actually just finished soldering the last diode on there when a notification email chimed with your reply. (I was thinking, I hope that's not someone saying "don't bother"...)

I had thought about it further, that the monitor controller will live in a quiet studio environment, so it seemed best to avoid turning the switch into a spark gap transmitter and thereby adding more RF noise to the environment. So I went ahead with it, figuring it couldn't hurt, and it would be a pain to dig the board out of the box later to add them.


 

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