freewheeling diode

Discussion in 'General Electronics Chat' started by TAKYMOUNIR, Sep 4, 2011.

  1. TAKYMOUNIR

    Thread Starter Active Member

    Jun 23, 2008
    351
    1
    what is the freewheeling diode
     
  2. mbxs3

    Active Member

    Oct 14, 2009
    141
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  3. JDT

    Well-Known Member

    Feb 12, 2009
    658
    85
    The current in an inductor (a relay coil, for example) is a bit like the motion of a heavy flywheel. Hard to get it going but once it's going it doesn't want to stop.

    In an electronic circuit, the free-wheel diode gives this current somewhere to flow when the thing that controls the current switches off. While the current is slowly reducing.
     
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  4. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    There are various functional reasons for having free-wheel diodes, but one of the most basic is avoiding excessive rise of voltage or heating when a controlling or switch device turns off abruptly.

    The tendency of a coil to maintain current flow results in an induced voltage proportional to the rate of change of current (e = -Ldi/dt), so attempting to reduce the current very quickly could give rise to a large and possibly damaging voltage. Even if the voltage were not great enough to be destructive in itself, a large proportion of the energy stored in the coil's magnetic field could be dissipated in the switching device, leading to excessive heating.

    A free-wheel diode can let the coil current decay at a reasonable rate without excessive voltage being developed, while allowing the coil energy to be dissipated elsewhere than in the switch.
     
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