Simple transistor circuit help...

Discussion in 'General Electronics Chat' started by jester, Feb 17, 2010.

  1. jester

    Thread Starter New Member

    Feb 17, 2010
    1
    0
    Okay I'm making a very simple transistor circuit. The problem I'm having is that the 5v control is separate from the 12v supply for the load (there two entirely separate sources with separate grounds). I need to be able to control and supply the transistor with two separate circuits.thanks in advance for help.
     
  2. ifixit

    AAC Fanatic!

    Nov 20, 2008
    650
    117
    Welcome,

    Can you connect the grounds of the two supplies together?

    If yes, do it.
    If no, use an opto-isolator on the +5V source control to the base. That will maintain the circuit isolation. Google: 'opto-isolator' if required.

    Good Luck
     
  3. hobbyist

    AAC Fanatic!

    Aug 10, 2008
    885
    85
    The best way is to connect both grounds together.
     
  4. Audioguru

    Expert

    Dec 20, 2007
    10,606
    1,182
    The transistor is connected as an emitter follower. When the base is at +5.0V then the emitter and load are only +4.3V, not +12V.
     
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