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Control JFET using MCU
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janoc:

--- Quote from: Zero999 on August 20, 2019, 07:36:09 pm ---Why?

--- End quote ---

Smaller ON resistance and easier to control thanks to the isolated gate?
Kleinstein:
The BSS139 depletion mode MOSFET and  NSVJ3910SB3 JFET behave quite similar if used in the normal drain to source polarity.
The advantage of the BSS139 is the likely lower price and usually tighter specs on the threshold voltage. The maximum DS voltage is also much higher. The JFET as the advantage of also working in the reverse direction (no body diode) - the input is nearly as high in impedance and the gate capacitance is considerably smaller.

Just for switching for one direction they should both work and could use the same circuit.
SiliconWizard:
Of course it's much more common to use MOSFETs especially for power switching. I don't think there are many (if any?) JFETs around that can handle several Amps of current. Now for low-power stuff, they can have their uses. The absence of body diode Kleinstein mentioned is a good point and could be a distinct advantage depending on your particular application.

Now if it's for a switch controlled by an MCU's IO, and if the only reason you considered a JFET is that you needed a "normally ON" device, a depletion mode MOSFET seems more adequate here.

Also consider cost and availability to make a choice.
Kleinstein:
There are powerful JFETs available, especially SiC and GaN versions. There are / were even a few enhancement mode JFETs with a high bandgap material.
Ian.M:
Why is it a requirement that it be on with no power applied?
Unless you are driving something like a high sensitivity moving coil galvanometer (which absolutely do require the coil to be shorted to damp their motion for transport),  why  should it matter whether the FET is on or off when the 5V rail is off?

IMHO an ordinary low Vgs threshold enhancement N-MOSFET, with its gate pulled up to +5V can be used.   *IF* its a requirement that it be on when the MCU is off, drive it from another MOSFET (with a gate pulldown) or a NPN BJT,  to get a true open drain or collector drive that wont be pulled low via the I/O pin ESD diodes when the MCU's Vcc is not present.
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