Connect with us

NPN and relay

Discussion in 'General Electronics Discussion' started by Chando, Feb 13, 2012.

Scroll to continue with content
  1. Chando

    Chando

    17
    0
    Nov 23, 2011
    Hi, i have a need to turn on a relay but because of where everything is sited/currently used the transistor needs to be before it (i.e. between the +ve and the relay coil). I have a 2N3904 NPN but it doesnt work. If i swop to a PNP will tht solve my problem. Also where would be best to connect the protection diode?

    Thanks
    Matt
     
  2. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    You'll need to tell us more about the circuit if we're to give good advice.
    For example if the relay supply has a higher voltage than the "logic" supply you can use a PNP but then the output driving the PNP has to be "open collector".
    You already know that the protective diode is supposed to go on the relay coil itself.
     
  3. Chando

    Chando

    17
    0
    Nov 23, 2011
    The input to the transistor is 1.2v which would then allow 12v to the relay coil.
     
  4. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Why can't the transistor be between the relay coil and ground? If the signal that you want to drive it is at 1.2V this is the better way to do it.

    Bob
     
  5. Chando

    Chando

    17
    0
    Nov 23, 2011
    the relay is part of a circuit and is tuck away in a awkward place and the circuit that feeds the 1.2v is by a switch that illuminates when 12v goes through it (which is needed to serve as a reminder its active!) hence the need for the awkward set up.
     
  6. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    So let me see if I have this right. You have access to the + power lead and the non-grounded lead of the relay coil, and the 1.2V signal, but no ground?

    Bob
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-