JFET switch question

Discussion in 'The Projects Forum' started by ajhoward, Nov 22, 2011.

  1. ajhoward

    Thread Starter Member

    Nov 16, 2011
    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.
    Last edited: Nov 22, 2011
  2. DickCappels


    Aug 21, 2008
    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.