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

Simple transistor problem

  1. Nov 5, 2005 #1
    Hey guys,

    Right now I have a circuit designed and seems to work fairly well. Now the output from my circuit is a negative output and I need it to drive a relay. The relay im using says it draws about 100mA and my chip will output 50mA max. I figured I would put a transistor on the output to drive my relay...the only problem is that the output is negative. In this case im not sure what to do. Do I need an PNP instead of an NPN?

    So far I figure the IC neg output goes to base, emitter to ground side of coil and collector to ground rail of circuit...but I dont think this will trigger because the base is negative.

    Thanks for your suggestions
  2. jcsd
  3. Nov 5, 2005 #2


    User Avatar

  4. Nov 6, 2005 #3


    User Avatar

    Staff: Mentor

    If your circuit pulls low, drive a PNP transistor in series with an NPN transistor, which pulls low again at a higher current.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook