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Normally On switch

Discussion in 'Electronic Design' started by Jens Gydesen, Nov 28, 2006.

  1. Jens Gydesen

    Jens Gydesen Guest

    Hi,

    I need a switch or some kind of FET etc. that has a low impedans (10 Ohm)
    when no supply is present.

    There is no room for some kind of relay, the housing max hight is 1.1mm

    Thanks,

    regards Jens
     
  2. Jim Thompson

    Jim Thompson Guest

    Isn't that a JFET? But 10 ohms might be hard to find.

    What other conditions apply?

    ...Jim Thompson
     
  3. J.A. Legris

    J.A. Legris Guest

    Supertex makes several depletion-mode mosfets, but even they will be a
    tight fit in 1.1 mm of headroom. They require a negative gate voltage
    to switch them off.

    http://www.supertex.com/products/datasheets/102
     
  4. PeteS

    PeteS Guest

    What is the specific application? (Schematics appreciated to a.b.s.e. if
    possible).

    It's possible an enhancement mode P-channel device with gate pulled low
    might do what is required, a depletion mode device, a JFET or even a
    diode - depends on what is required.

    Cheers

    PeteS
     
  5. Jens Gydesen

    Jens Gydesen Guest

    Hi,

    the job for the FET is to shortend a 13MHz RFID receiver, and open for it
    when required.

    The RFID receiver must be shortend when the battery is discharged.

    Regards Jens
     
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