Help.. switching 24V to PLC sinking input using 5 V signal

Thread Starter


Joined Apr 7, 2009
I want to switch to 24V DC to PLC sinking input by using 5 V DC signal - small current (approximately 10mA). 5V signal is extracted out from NI-USB Daq digital output.

I tried using PNP transistor, but it is not working, 5V signal does not have any effect on the circuit..

Any suggestion how I should do it? Switching circuit suggestion, not necessary using transistor..

Thank you in advance


Joined Mar 6, 2009
Try using an opto-coupler instead. You can drive the input LED with your 5V in series with a limiting resistor. Your opto-coupler output transistor can switch the 24V to the sinking PLC input.