transistor switch


Joined Jan 28, 2005
Two volts should work pretty much with all standard bipolar junction transistors (BJTs). This is not sufficient voltage to operate a field effect transistor. A darlington BJT transistor would probably not be a good choice.



Joined Apr 19, 2007
If you are trying to switch 2 volts with a transistor, remember that the forward voltage drop accross the device is about 0.7 volts.....2 volts will switch a transistor on without a problem, through a resistor (about 2K2) into the base........ Daniel.


Joined Aug 8, 2005
Is 2V your source voltage (Vcc), or your drive voltage? In either case, the general answer is, yes.

As noted above, a general bipolar transistor (2N3904 / 2N3906) only requires ~0.7V on the base-emitter. Some FET's can be used with a lower drive voltage, for example the NTD3055 FET requires a gate voltage of only 2V.


Joined May 7, 2007
If you are going to drive a relay with a bjt you should not forget that you need to have enough current available to go into the base.

Roughly I_C = I_B * beta
I usually use beta = 50 for relay drive ckts (for margin) and look at the coil resistance and voltage of the relay to get my I_C. Then calculate the I_B. From this I can size the base resistor accordingly.

R = (2V-0.7)/I_B

Using R = 2K2 you can easily drive 30mA of coil current.