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Need help with understanding a clamping diode in a circuit

Discussion in 'Electronic Basics' started by [email protected], May 9, 2005.

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  1. Guest

    Can someone show me in the most generic form how a clamping diode
    works? I have some cicuit anaylsis background from years ago, but I
    cant seem to remember coming across this item. I've read the theory but
    I still don't see it in a real circuit and how it "clamps". Are there
    different ratings on clamping diodes? Basically I have a problem with a
    transient spike that jumps from nominal 20V dc up to 30V dc and down to
    -10V dc in about 1ms time. I'm was told a clamping diode will work.

  2. There are two distinct ways to clamp voltage peaks with diodes. one
    involves a diode from the signal line to a supply voltage or ground
    that becomes forward biased when the signal voltage gets one diode
    drop (about .3 volts for silicon Schottky diodes and about .6 volts
    for silicon junction diodes) past the particular supply voltage. This
    provides a low impedance path for current that tends to load the
    signal voltage down if it tries to go further.

    The second method involved putting a device between the signal and
    ground that has a high impedance up to some breakdown voltage, and
    switches to a low impedance for higher voltages. A zener diode is the
    classic example of this sort of clamp but there are lots of
    variations, including Metal Oxide Varistors for higher voltages and
    bidirectional high surge current zeners. These devices turn the
    energy that would have produced an over voltage into heat.
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