The solid state relay board functions normally by shorting + to input, but latches closed on device side of the relay until load is turned off or is disconnected. Is this normal for solid state relays with inductor type devices?


1 Answer 1


SSRs use triacs as switching elements, and those are for AC, not DC. A triac is like two transistors so arranged that, once ignited, they keep each other switched on. The only way to switch it off is to reduce the current to below the hold current. AC devices do this 100 or 120 times per second, at zero crossings of the mains, but at DC it will not switch off.

Instead of interrupting the circuit you can also briefly short-circuit the triac's terminals to switch it off.

  • \$\begingroup\$ So that means SSRs are not suitable for switching DC devices? I just now got AQH2223 and tried to turn LED ON and off by connecting it between output pins 6 and 8. I had driven pin 2 of this SSR through my micro controller. I observed that even if micro controller port pin is driven LOW (after making high once), LED remains ON. \$\endgroup\$
    – Rajesh
    Commented Sep 23, 2019 at 7:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.