Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Transistor that *Stops* current when base is powered

  1. Mar 16, 2015 #1
    Hello, in a small scale project I need a way to get 7 outputs from 3 inputs, I have an idea how to do that using transistors but the cost adds up due to the high amount of transistors, it would simplify things space wise, and cost wise if I could eliminate the NOT gates, is there such a thing that blocks power from emitter to collector when base is on instead of the contrary? Any help appreciated.
  2. jcsd
  3. Mar 16, 2015 #2


    User Avatar

    Staff: Mentor

    Electronics can achieve anything. Perhaps if you explain in detail what you are wanting, we can suggest a solution.
  4. Mar 16, 2015 #3
    Why don't you use a specialized BCD decoder ?
  5. Mar 16, 2015 #4


    User Avatar
    Science Advisor

    You need to define "on". If "on" is "close to the supply voltage", a PNP will turn off.
  6. Mar 16, 2015 #5
    A JFET is a depletion-mode device. When the gate to source voltage is zero, the device is ON. In order to turn it OFF, the base must be driven negative, for an n-channel part.

  7. Mar 17, 2015 #6


    User Avatar
    Science Advisor

  8. Mar 17, 2015 #7


    User Avatar
    Gold Member

    As others have said you should look into decoders.
    To answer your question, you want a depletion mode MOSFET. The device acts as a 'closed switch' with an open gate or low gate voltage. you need to pass above the gate threshold to 'turn the switch off.' 1-4 VGS_on typically depending on the device
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook