JFET switch question

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ajhoward

Joined Nov 16, 2011
46
I am working on a project that uses a reed switch . I need a electronic switch that will go low and connect the reset pin of a 555 timer to earth when the reed switch is open and go high when the reed switch is closed. I am thinking a jfet may do the trick, but no very little of fets in general.
 

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DickCappels

Joined Aug 21, 2008
6,579
Change that to a MOSFET (and add ESD protection, and it will work!

The problem with using a JFET this way that the vast majority of JFETs are depletion mode, meaning that in this circuit, it would act like a normally closed relay, not turning off until a voltage high enough to turn off the FET (more properly to "pinch off"). In the case of an N-channel JFET, the voltage would be negative with respect to the source.

You might want to try an NPN transistor such as the 2N2222. Connect similarly to your JFET, but put the resistor in series with the base.
 
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