Clip my large gate voltage?

Discussion in 'General Electronics Chat' started by kenw232, May 3, 2015.

  1. kenw232

    Thread Starter Active Member

    May 18, 2009
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    1
    Due to backemf I seem to be getting a large voltage oscillation as shown in the scope view with channel 2 in blue. It seems to clear 64V there.
    without_diode-1N5338BG.png

    This is the circuit.
    Zener Test 2.png

    As shown I tried to put a zener diode 1N5338BG across the resistor going to the gate. The zener has a zener voltage of 5.1V. All it did is clip it down to about 20V as shown in the scope view.
    with_diode-1N5338BG.png

    Should it not have clipped it all the way down to 5.1V? Why is this happening?

    Does anyone know what the easiest way would be to completely clip all negative voltage, and anything over +3 to 5V? Would a TVS diode work better?
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    To act as a clamp, the Zener would have to be between B and A.
     
  3. kenw232

    Thread Starter Active Member

    May 18, 2009
    54
    1
    I tried this, same thing, it only clamps it to ~12V. Shouldn't it clamp it to its zener voltage of 5.XV?
    a-b.png
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
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    Where are you putting your scope ground clip?
     
  5. kenw232

    Thread Starter Active Member

    May 18, 2009
    54
    1
    Point A in the schematic.
     
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