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how to flip a relay by digital signal

Discussion in 'Electronic Basics' started by saurabh9, Jul 10, 2008.

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  1. saurabh9

    saurabh9 Guest

    What would be an easy way to turn on a relay by a digital signal. The
    relay would be hooked to a 220 V AC device.
  2. neon


    Oct 21, 2006
    flip flop changes states but for relay to change states all you need is remove power and re-apply power like a switch douple pole double throw 240v humm are you sure your relay is rated for that voltage and current i say that because of your question.
  3. Rich Grise

    Rich Grise Guest

    Drive the coil with a suitable transistor. Don't forget the catch diode!

  4. Bill Bowden

    Bill Bowden Guest

    Actually, the catch diode might not be needed. There's lots of
    capacitance in the windings of the relay coil which charges up when
    the transistor switches off and limits the voltage to whatever the
    capacitance is combined with the energy put into it. A 1 millihenry
    coil at 12 volts and 120 ohms will store 1/2 L* I^2 = 5 microjoules.
    If the winding capacitance is say 2000pF, the voltage will be 1/2
    CE^2= .000005 = 70 volts.

    Did I do that right?

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