1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
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.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Simple transistor problem