The puropse of these diodes?

Discussion in 'General Electronics Chat' started by Yabba Rays, Oct 5, 2016.

  1. Yabba Rays

    Thread Starter New Member

    Oct 5, 2016
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    Not sure I can see the reason for the two series diodes. The bottom one is a DC clamp to earth for the gate, but the top one?

    Thanks,

    Jan part simple 60.jpg part simple 60.jpg
     
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,128
    266
    Looks like the two diodes center the average bias voltage on the cap right between the supply voltage rails.

    The upper one clamps the gate to the upper rail +0.6 V.
     
  3. Willen

    Member

    Nov 13, 2015
    138
    12
    Sometime to protect from high voltage spikes/surges/static charges, people use such back to back diode from gate to the Gnd and Vcc. If gate voltage goes less than Gnd then lower diode conducts, if gate voltage goes higher than Vcc then upper diode conducts. Thus it saves the gate of the FET.
     
  4. ci139

    Member

    Jul 11, 2016
    341
    38
  5. Yabba Rays

    Thread Starter New Member

    Oct 5, 2016
    6
    0
    Thanks for the replies. Very helpful.
     
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