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!
Cheers

 

PNP transistor, not NPN.

 

PNP transistor, not NPN.

But using an NPN to convert the 0-5V input up to the +24V contactor supply.

 

But using an NPN to convert the 0-5V input up to the +24V contactor supply.

Hi AlbertHall and MaxHeadRoom,
thanks for your suggestion. Do you mean a circuit like this?
Thanks for your help!

 

Do you mean a circuit like this?

Yes, except for this to work, V4 would have go up to 24V to turn off the transistor. The circuit I was thinking of wouldn't do as it would invert the function.
A circuit as below would do the job (Q2 could be a junction transistor if you wanted).