Will this circuit work?

Discussion in 'General Electronics Chat' started by ScorpFire, Dec 30, 2009.

  1. ScorpFire

    Thread Starter Member

    Jun 4, 2009
    13
    0
    I have this certain setup. I have very a very limited time with trainer boards at school so i need to confirm this before i try it out physically.

    i used just 1 BC547 transitor before but it was not enough to turn on the relay. Will this now turn on the relay?

    [​IMG]
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    Is the -12 Volts ground level?
    As drawn the power supply is 24 Volts.
    The relays is most times connected at the collector side of the transistor.
    There should also be a diode accross the relayls coil to prevent back EMF to destroy the transistor.
    This diode has the cathode to the plus-side of the relays.

    Greetings,
    Bertus
     
  3. ScorpFire

    Thread Starter Member

    Jun 4, 2009
    13
    0
    How can i determine if the -12v is ground level?. The 12v is coming from an external relay module board which has a +12 -12v.

    WIll the current be a bit too high for the base of the BD139?
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    What is the voltage difference between the - 12 Volts and the input base connection (2.8 Volts)?
    That is why I asked if the -12 volts is your ground reference.

    Greetings,
    Bertus
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    The drop on the transistors Collector-Emitter will be 1.2V. It is basically a Darlington Pair configuration.

    You didn't tell use the voltage of the relay, it matters.

    If you want to reduce this CE drop you can use a Sziklia Pair.
     
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