Transistor Contactor coil command: contactor OFF when voltage on base

Thread Starter


Joined Feb 9, 2018
Dear All,
I am trying to design a circuit in order to command the coil of a contactor. The coil is 78 Ohms, 24 Vdc.
I would like to command a transistor with a signal of 5Vdc peak (0 to 5V).
I would like the following behavior:

- when Voltage on Base is 0, the contact is closed --> current in the coil
- when Voltage on Base is 5V, the contact is open --> no current in the coil

I tried a circuit like the one attached, but without success: R2 and R3 are only to measure Current, they are not real resistors.

Thanks a lot for your help!