I purchased several IXYS CPC1017NTR SS relays from Mouser.

I have 1.2v and .5mA of current running over the control input of this relay and the load side isn't connecting.

Here's a diagram of what I'm trying to do roughly (I missed connecting the positive to the load side of the relay in this drawing though)

enter image description here

I've confirmed with my multimeter the 1.2v/.5mA, so I must have read the datasheet wrong.

Any help would be appreciated. Thanks!


  • 1
    \$\begingroup\$ Have you tried reducing R1 to 10K ohm? \$\endgroup\$ – Autistic Dec 20 '15 at 19:50

You need at least 1 mA to turn o the optoisolatorn. Your 20k on its own would limit the current to 12/20000 = 0.6 mA which isn't enough. R2 is shunting some of the current that does make it through and stealing it from the SSR.

Try this (and note convention of + rail at top with current flowing from top to bottom of circuit for readability).


simulate this circuit – Schematic created using CircuitLab


The datasheet says the relay is guaranteed operate with at least 1 mA, and can tolerate up to 50 mA through the LED. The voltage across the LED when the relay operates may be as much as 1.4 volts.

LEDs are current-operated devices - they will decide what the forward voltage is. You should always apply a current to an LED, not a fixed voltage.

I would remove R2, and change R1 to 5K1 or less. That will give the LED about 2 mA, which should reliably operate the relay.

  • \$\begingroup\$ The also say in a footnote "For applications requiring high temperature operation (greater than 60ºC) a minimum LED drive current of 3mA is recommended." \$\endgroup\$ – Fizz Dec 20 '15 at 19:53
  • \$\begingroup\$ I went with a 3.6k resistor since i already had a bunch and it worked perfectly. Thanks everyone \$\endgroup\$ – Matt McElroy Dec 21 '15 at 2:22

0.4mA and 1.2V are the typical values to turn it on. There will be devices for which these do not suffice. Consider exceeding the extreme values instead.

  • \$\begingroup\$ Max being 1mA and 1.4V. \$\endgroup\$ – Fizz Dec 20 '15 at 19:48
  • \$\begingroup\$ Thanks. So am I reading this right that I can put up to 50mA on the control input? It just says that typically you'd need .4mA and in all cases 1mA will work? I can probably just drop the resistor values and easily make that happen. \$\endgroup\$ – Matt McElroy Dec 20 '15 at 19:48
  • \$\begingroup\$ @MattMcElroy: Correct. I wouldn't put more than 5mA though, which gives more than enough wiggle room. \$\endgroup\$ – Ignacio Vazquez-Abrams Dec 20 '15 at 19:51

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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