? Zener diodes safely/effectively used in series?

Discussion in 'General Electronics Chat' started by mjdx9, Dec 17, 2003.

  1. mjdx9

    Thread Starter New Member

    Dec 17, 2003
    Hi All,
    Excuse my etiquette, this is my first post.

    I have a relay coil flyback problem. Relay response timing is critical and an RC circuit delays relay response to unacceptable limits.

    The circuit is 270VDC, and I can only find Zener diodes to 200VDC.

    Can I stack zener diodes in series to achieve the required voltage?

    Any suggestions, experiences or comments welcome.

    Thanks in advance.

  2. Battousai

    Senior Member

    Nov 14, 2003
    Maybe you could just use a transformer?
  3. Dave

    Retired Moderator

    Nov 17, 2003
    If you can only find Zener diodes that operate up to 200V and you are operating at 270V, it would be very dangerous to use them due to the problems of voltage breakdown and runaway current. A zener will operate happily as a voltage regulator at the specified voltage and within the tolerance stated; usually between 5% and 10%.

    Like Battousai says why not just look at a transformer.
  4. mjdx9

    Thread Starter New Member

    Dec 17, 2003
    I am not trying to create a power supply, I am trying to limit a voltage spike that occurs from a collapsing electrical field from a coil on a relay.
    the contacts which open the circuit running the 270VDC relay arc badly when opened since an approx. 1400V spike is generated from the inductive power of the coil. The intention is to quickly short this current without delaying the contact opening. An RC circuit works, but slows the relay close-to-open (make to break) time beyond a critical acceptable limit. A zener would essentially look like an open circuit until the spike exceeds the zener voltage, then would conduct to eliminate the arcing and dissipate the stored energy in the coil...

    Sorry I wasn't more clear in the first post...
  5. hatvmt

    New Member

    Dec 25, 2003
    Perhaps I'm reading your question incorrectly! In the trade we fit a diode across the coil of the relay, so that the collapsing (field) B.E.M.F. will be bypassing the coil via the diode back into the supply rail, therefore only the level of the supply rail should(!) be the max!