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diff between FET, JFET and MOSFET

Discussion in 'Electronic Basics' started by anonymous, Sep 25, 2004.

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  1. anonymous

    anonymous Guest

    I get the naming difference - what are the different uses for each? IE why
    would one use one vs another?
     
  2. Fet is field effect transistor, the generic name for a gain device
    based on the electrostatic modulation of conductivity in the channel
    between source and drain.

    JFET is a junction fet. The isolation between gate and channel is a
    reverse biased PN junction. These are depletion only devices
    (normally on, turned off by gate bias voltage). They make good low
    noise small signal amplifiers, though there is nothing in principle
    that prevents them from being scaled up to power devices. They are
    functionally similar to triode vacuum tubes at low drain voltage and
    more like pentodes at higher drain voltage, if you happen to be
    familiar with this older technology.

    MOSFET is metal gate isolated from the channel by semiconductor
    oxide. They can be made as normally on (depletion mode) devices like
    JFETs but are most often made as enhancement types (normally off but
    turned on by gate voltage. They can even be made about half way on and
    gate bias can turn them on more or turn them off. These are made in a
    wide range od device sizes, for small signal through high power
    devices, but, by far, the greatest numbers are used for high density
    logic devices like microprocessors and gates. I think that MOSFETS
    are often noisier than otherwise similar JFETS.
     
  3. Usually, but not only. There are a few exceptions:)

    Kevin Aylward

    http://www.anasoft.co.uk
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
     
  4. Aren't there always? :)
     
  5. No:)

    Kevin Aylward

    http://www.anasoft.co.uk
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
     
  6. Damn. Another rule with an exception.
     
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