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Please help with flyback current protection

Discussion in 'General Electronics Discussion' started by hpfiend, Jul 9, 2013.

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  1. hpfiend

    hpfiend

    31
    0
    Feb 20, 2013
    Hello there!

    I have a circuit that drives a solenoid. From my limited understanding it is sort of like the braking mode of an h-bridge. There are two wires, one sends a negative current and one a positive current to result in a net direction of movement and amplitude. IE one wire provides -14 volts and the other 10 for a -4 net volts. I am wanting to replace the 15 mH solenoid with an inductor for testing purposes. I am concerned about flyback EM current when the power is turned off. Should I use an optoisolater on each wire or will diodes work? A large capacitor across the two in parallel?

    The circuit solenoid uses 14 volts and 4 amps.

    As the current goes both directions I do not understand how a schottky diode on either would work unless I ran each to a separate ground?

    Thank you for your help!
     
  2. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    A flyback diode is placed across the winding with the opposite polarity that it is driven, i.e. the cathode goes to the positive side and anode to the negative side of coil.

    If you are indeed using a H-bridge to drive the solenoid both directions you cannot use that configuration. In this case, the diodes are across each of the 4 transistors with opposite of the polarity that they are when conducting.

    Show us the circuit you are talking about.


    Bob
     
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