why not depletion type fets

Discussion in 'General Electronics Chat' started by acelectr, Apr 10, 2011.

  1. acelectr

    Thread Starter Member

    Aug 28, 2010
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    Hi, I've started to study on mosfets and I'm wondering why not using depletion type mosfets instead of encahncement types?:confused:

    thnx;)
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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  3. acelectr

    Thread Starter Member

    Aug 28, 2010
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    I dont know at first glance I think the depletion type looked better because it is simpler and you do not need to worry about the threshold voltage that is required at the enhancement types. It looks like if you can do with depletion type why not using it
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    That doesn´t make sense. Why would you use a transistor if you wanted it on all the time? The threshold voltage matters in the depletion type as well, but it is the voltage required to turn it off.
     
  5. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Depletion type MOSFETS do exist, but they have relatively limited applications. One of these is as a current limiter, where it is useful to have a device which can conduct with zero gate bias. They can also be used as small-signal amplifiers, but are not so convenient for power amplifiers or switching circuits.

    In conventional switching or large-signal amplifying circuits, depletion MOSFETs would typically require gate voltages beyond the main supplies to switch them off, which is inconvenient. Alternatively, the MOSFET drain could be held at some voltage within the span of the main supply, but this would not be efficient for large signal swings.
     
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