transistor bias current

Discussion in 'General Electronics Chat' started by dcd528, Jul 28, 2011.

  1. dcd528

    Thread Starter Active Member

    Jul 28, 2011
    My apologies in advance for such a simple question. I have a circuit in which I am trying to bias a signal transistor to turn on a power transistor. If the bias current is 100mA is works fine, if the bias current is 20mA it doesn't work (both cases have a voltage of about 2 to 3 volts).
    Is there a ratio between base current and collector current that is critical? Is there a signal transistor that will respond to a 10mA bias current? Do I need to use a current amplifier? If there is an appropriate signal transistor please specify the model number same for the current amplifier.
    thanks so much
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    A schematic of what you are doing is essential for any sensible reply.
  3. debjit625

    Well-Known Member

    Apr 17, 2010
    Not sure but if you are talking about the (general purpose) signal transistor then its too much as normally their (Ic) collector current will be in that range 100mA to 500mA.But it also depends on which transistor you are using so as ErnieM said a schematic will be good.
    dcd528 likes this.
  4. SgtWookie


    Jul 17, 2007
    Very generally speaking, a current through the base controls a much larger current through the collector.

    As has already been said, we need to see a schematic of what your circuit looks like, and we also need the part numbers and values of other components in the circuit.
    dcd528 likes this.
  5. dcd528

    Thread Starter Active Member

    Jul 28, 2011
    thanks for the replies, I will hand sketch a schematic and post it on a new thread over the weekend.