Opto-Coupler Resistor Value

Author	Message
Mixtel90 Guru Joined: 05/10/2019 Location: United Kingdom Posts: 9125	Posted: 08:49am 10 May 2022       You usually only need a couple of mA through the LED to get good enough current transfer. With a 24v input, that's 22.2v / .002 = 11.1k. Try 10k as the series resistor. It'll dissipate about 0.05W. The exact output current depends on the LED current, but it hardly matters here.