Electronics > Projects, Designs, and Technical Stuff

Control JFET using MCU

(1/4) > >>

gaminn:
Hi,
I want to control MMBFJ111 JFET using microcontroller (power supply = +3.3 V). JFET needs at least -3 V voltage to turn it off. There is also +5 V power supply available on the board.

How would you generate enough negative voltage and how would you turn off JFET using the negative voltage and microcontroller?

Thanks

Martin

jbb:
You may not need a negative rail at all... in some cases it’s possible to use a cascode circuit with an N Channel MOSFET.

Maybe you could post a little sketch of what you want to do?

Ian.M:
The  MMBFJ111's worst case Vgs(off) is -10V, not -3V, so to get guaranteed hard cut-off you'll need far more negative bias than you are expecting if either its (interchangable) drain or source are near 0V.  If you want a JFET that will actually cut-off with -3V on its gate,  try  MMBFJ113.

I echo Jbb's request for more information on your actual application, and we need the 'big picture' overview, not just the detail of what you think you need to do to solve your immediate problem.

gaminn:
I don't have any sketch at the moment. There is just an MCU (with 3V3 power supply) which turns off and on N-JFET. N-JFET's source is connected to ground and drain is connected to 5 V via some load.

I don't have to use MMBFJ111 - anything with approx 30 ohms on resistance is OK. But I guess the lower the on resistance I want the higher cut off voltage the transistor has.

Zero999:
Daft question: why are you using a JFET?

What are you switching?

Why not simply use a MOSFET? If you need a series resistance of 30R, simply add a resistor.

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod