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

    Distinguished Member

    Nov 20, 2008
    638
    108
    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

    Distinguished Member

    Aug 10, 2008
    764
    56
    The best way is to connect both grounds together.
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    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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