relay surge suppression options

Discussion in 'General Electronics Chat' started by minkey01, Dec 7, 2015.

  1. minkey01

    Thread Starter Member

    Jul 23, 2014
    Good day. I'd like to hear some thoughts from people familiar with relays about this issue below.

    I have an old relay circuit on a pcb that I will be adding a new control path to. The old design had only a capacitor across the relay. I've read that this is a bad design and makes the back emf surge worse. I would like to update it and protect my controls from the back emf surge that is often seen when relay coils discharge. I was thinking of leaving the parallel capacitor and adding a diode also parallel to the coil. Would this be ok? They may have had that capacitor there for timing. Not sure. Or would it be better to completely remove the capacitor and only have the diode?

    See this webpage for the relay best practice circuits:

    relay :

    Here is what I'm planning :

    omron relay.jpg

    Thank you!
  2. JohnInTX


    Jun 26, 2012
    For a DC coil a diode is usually used like you've shown without the cap. An improvement to the diode is described in the attached apnote.
    Good luck!