what's the purpose of the zener, mosfet

Discussion in 'Homework Help' started by bug13, Aug 16, 2012.

  1. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Hi

    I am just wondering what's the purpose of the zener between the s and g of the mosfet, a 2kHz signal is fed to the G.

    thanks

    Zhuhua

    [​IMG]
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The zener diode is there to protect the mosfet.
    It will probably be a 12 Volts zener, as a gate voltage higher as 15 Volts will damage the mosfet.

    Bertus
     
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  3. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
    1,208
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    so what would be the cause of the higher voltage? the signal fed to the mosfet should be 12v as swell, the whole circuit is power by 12v (other part of the circuit is not in the pic)

    Zhuhua
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    As bertus said, it's just an additional (maybe unnecessary protection (under normal circumstances)).

    VGSmax for this transistor is +-30V.
     
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  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
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  6. ramancini8

    Member

    Jul 18, 2012
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    Speakers are inductive loads and they can cause transiets that can destroy FETs.
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    Say what?!? Uh, No. While they have inductive properties it is very small compared to the total resistance. These are not relays, which do have substantial inductance.
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Especially with a resistor in series, as in the schematic.
     
  9. steveb

    Senior Member

    Jul 3, 2008
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    Static discharge would be a concern. Also transients can happen.
     
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