Using +4V output, to trigger an npn transistor operating on +12V

Question

In a +12V circuit, I am trying to use a proximity sensor, which works on +5V and its output is +4V, and goes 0V when triggered. Using a L7805, I get the +5V for the sensor supply. However, I try to use its output to trigger a transistor operating from the +12V reference voltage. I thought of using a 5V or 6V relay, but I would prefer a “pure” electronic method..... How can the sensor’s output be used to trigger a transistor operating from the +12V reference voltage?

Answer 1

An NPN transistor can do a great job of translating the 0-4V output of the sensor to 0-12V swing. See the circuit below:

Note that when your sensor activates and goes low on the output the output of this circuit will pull to +12V through the R3 resistor.

Component values shown in the circuit are a nominal starting place for you to work with. You may have to adjust the resistors R1 & R2 some based upon what the sensor output swing is once it has this circuit connected. R3 may require adjustment in the case the load you are driving is low impedance.