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
dcd

 

A schematic of what you are doing is essential for any sensible reply.

 

If the bias current is 100mA is works fine

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.

 

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.

 

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