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can a jfet be placed in series with a mosfet's gate and swicthed on to turn off the mosfet? Answered

can a jfet be placed in series with a mosfet's gate and swicthed on to turn off the mosfet?
i'd like to know if this is possible because the mosfet's gate senses voltage instead of currnet.
I'm working on a schematic and its for a charge controller

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seandogue

7 years ago

Yes, of course it can be used that way, but you forgot one critical component, a drain resistor from the gate on Q1 to ground (assuming that's an N-channel FET).

As iceng pointed out, the gate on Q1 is capacitive and it will hold charge, so once enabled (as shown) it will remain enabled for a very very long time (without a drain resistor to drag all that charge to ground)

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seandogueseandogue

Answer 7 years ago

FTR, a resistor in the range of 25K -100K should do the job nicely, while keeping the drain current through the jeft gentle enough not to damage it.

You can find specifics by reviewing the data sheets for your devices.

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iceng

7 years ago

No.
A mosfet gate is a capacitor.
That  capacitor Gate must be charged to turn Q1 NFET ON !
And discharged to turn the fet Off !
How is your junction fet going to do that ??

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