I'm running 14 ~3W (700mA) LEDs in series on a constant current LED Driver that handles between 36-65V output. The driver runs the LEDs at 600mA.

The heatsinks I've attached are pretty small, and if I put my fingers on one, it heats up in about 2 minutes or so, and then takes about 20 seconds to get cold again.

I'd like to use an Arduino to turn on and off the circuit, for roughly these periods.

I wrote a basic sketch to handle the Arduino part to keep a relay on for this period...

  s_l = millis() % 120000;
  on = (s_l < 100000) ;
  digitalWrite(relayPin, on);

I have relay modules, and transistors lying around... but I'm not sure how well they will play with a constant current circuit. The LEDs don't care if I am PWM'ing, but maybe the driver will get some weird feedback loop if I mess with it?

I'd prefer to use transistors, because the relays clicking will probably drive me crazy - but I will take any solution. What is my best option?

Just a relay on the AC side? I'd prefer not to work with AC, as it is a lot more dangerous.

Thanks in advance...

Edit: picture of constant current LED driver guts: enter image description here

enter image description here

  • \$\begingroup\$ What LED driver are you using? There may be numerous methods that cold be used, but it will depend on the details of the driver. \$\endgroup\$ Jan 7, 2016 at 15:06
  • \$\begingroup\$ Unfortunately it's a mysterious Chinese driver... bit.ly/1PSbctI ... I can take a picture of its guts if that will help? \$\endgroup\$
    – djb
    Jan 8, 2016 at 8:23
  • \$\begingroup\$ a picture may be helpful. I would be very wary of interrupting the current path (as Ross suggests) unless the thing is known to have open LED sensing (the output voltage can rise to dangerous levels if not). \$\endgroup\$ Jan 9, 2016 at 15:52

1 Answer 1


I would probably use an N type mosfet on the low side of your LED string and switch the earth end. Being on the low side will mean that you can drive it on/off directly from an Arduino output.

edit. Yes your diagram is fine, except... be sure to connect the Arduino's ground to the N-Mosfet's S terminal.

edit2. That mosfet's Vgs is a bit high, so you may find the Arduino struggles to turn the mosfet on hard enough to avoid heating. What other n-mosfets do you have?


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.