Normally, I think, an NPN transistor conducts (between C and E) when current is applied to the base and opens when it isn't. I want the opposite. I don't think an PNP transistor works for this situation because it requires current to flow from the base whilst what I want is for the circuit to close/conduct when there is no current flowing either to or from the base. Is there some arrangement of components which does this?

 

Does it have to be solid state?
There is a DIP N.C. relay that will do it.
Max.

 

I think a depletion mode mosfet is the nearest thing I can think of that is similar to what you want. The difference is the input to a mosfet is a voltage not a current. (Other than the current required to charge and discharge the gate to source capacitance.)

Les.

 

Applying positive to the base of transistor 1 will turn off transistor 2.

 

A junction N-FET conducts with zero gate voltage and turns off when a negative gate voltage is applied.

 

You question gives us no clue about what you are trying to accomplish. You have assumed a solution, i.e. a transistor that works the opposite of an NPN. There have been several suggestions of such things, but do they solve your actual problem?

Please tell us what you are trying to do.

For example, you might say:

I have a signal that is ether 0V or 3V. I want to turn on a 20mA red LED when the signal is 0V and turn it off when the signal is 3V.

Bob