MOSFET properties

  • Thread starter Kerso1991
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  • #1
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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
 

Answers and Replies

  • #2
rbelli1
Gold Member
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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
 
  • #3
Svein
Science Advisor
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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
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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