I am trying to use two APEX PA12A to control two groups of IR LEDs. I have this circuit:


PA12A to take the PWM 0-5 V control signal to limit the power supply to LEDs. The thing is even when the PWM gives 0 V signal at pin 4, the LEDs still get full 48 V power, which by design should be 0 V.

The connections on the datasheet is enter image description here

  • 1
    \$\begingroup\$ The answer is on the first page of the datasheet, in the lower right corner. \$\endgroup\$
    – bobflux
    Aug 3 at 17:19
  • 1
    \$\begingroup\$ I hope you only left out components on the above schematic and not in your working circuit. \$\endgroup\$
    – Rudy
    Aug 3 at 17:22
  • \$\begingroup\$ @bobflux the first page lower right corner is the external connections picture, but is there any connection I did wrong? Thanks. \$\endgroup\$
    – seraph333
    Aug 3 at 18:16
  • \$\begingroup\$ You have to add the two resistors. It's explained in the datasheet. But why are you using an expensive power opamp to apply PWM to LEDs when a 50c MOSFET would do the job just fine? \$\endgroup\$
    – bobflux
    Aug 3 at 19:14
  • \$\begingroup\$ @bobflux If the LED is connect with pin1, it seems does not need the resistors. I tried the MOSFET, the LED I am using is to heat a material and the temperature uniformity has to be within 1 degree C, was not able to achieve it, that is the reason to go with power amp. \$\endgroup\$
    – seraph333
    Aug 3 at 19:24


Your Answer

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

Browse other questions tagged or ask your own question.