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MOSFET properties

  1. Jan 25, 2015 #1
    Hiya, I've been mucking around with a 2n7000 MOSFET and I can successfully turn it on and off, but to turn it off I either have to put the gate at 0v and wait a few seconds and it turns off itself or apply negative voltage to the gate and it'll stay off when I return it to 0v. Is this normal for MOSFETs or for even just FETs? Or is this just a dodgy MOSFET? Because as far as I know the MOSFET should turn off at 0v at the gate
    Any help would be great
     
  2. jcsd
  3. Jan 25, 2015 #2

    rbelli1

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    Gold Member

    How are you changing the voltage on the gate? Does the 0V reference point (GND) of the controlling circuit have a DC connection to the source of the FET? The switching of the FET requires charging and discharging of some capacitance inside the device.

    I had a similar experience debugging a circuit I put together. I forgot to wire all of my grounds together. As I recall, the FET was a 2N7000.

    BoB
     
  4. Jan 26, 2015 #3

    Svein

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    Science Advisor

    You have connected the source to 0V, a large resistor between the gate and the source and a 1k resistor from the drain to +5V? Your problems seem to me as if the gate is floating...

    Check the pinout and your wiring again. Possible problem: Because of the extremely high input impedance at the gate, it is very easy to destroy a MOSFET just by handling it.
     
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