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normally-on jfet

Discussion in 'General Electronics' started by sachin, Aug 19, 2003.

  1. sachin

    sachin Guest

    I am sachin.I am doing my research on jfets.

    I would like to know how to avoid the start up problems of an normally
    on jfet and the applications of jfets.

    Please reply me if any one has a answe for this.

    sachin.
     
  2. Robert Baer

    Robert Baer Guest

    What do you mean "start-up problem"?
    What circuit(s) are you having a problem with (describe)?
     
  3. sachin

    sachin Guest

    Thanks for your reply..

    start-up problem in my sense is the large transient current flowing
    through the jfet as it is connected to a voltage source..

    so i need a solution to avoid this large current in short how to avoid
    this short circuit behaviour of jfet.

    byee
     
  4. Robert Baer

    Robert Baer Guest

    Jfets, per se, do *not* act that way, unless you are looking at
    transients in the sub-nanosecond region, where capacitance is dominate.
    A jfet, with a reasonable Vgs bias (even zero bias) will "pinch off"
    above a certain drain to source voltage, making it act like an
    adjustable current source (or sink, depending on P or N channel jfet).
    A jfet with gate tied to source acts like a linear resistor without
    regard to polarity, over a fairly reasonable voltage range.
    Changing the Vgs will change that resistivity over orders of magnitude
    (down to leakage levels).
    Applying a positive bias to the gate will not only decrease that
    resistivity, but also may cause significant gate current.
    *That* is why i asked about the circuit(s), and i wish to repeat that
    question.
    Specifics, please....
     
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