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Choosing LED PWM frequency


#1

Hey does anyone have any advice on choosing the frequency of PWM driving some RGB LEDs?

Originally I chose 200Hz because I read it was a good frequency to choose because it was the smallest that would likely not appear as pulses to viewers of any age.

Complications with noise led me to increasing it all the way to 20kHz. Now we have worked the noise issue out of the system. Idk if I should lower it again or not. At 20kHz I have a resolution of 400 values per channel which I believe is more than enough. What else should I be considering when choosing a frequency?


#2

You want a PWM frequency that is greater than the persistence of vision. If you look that up, you will find a wide variety of specifications for the rate.

From my experience in automotive electronics, we wanted a PWM frequency that was not a multiple of 60 Hz or 50 Hz so that we didn’t get beat frequencies with the overhead lighting on streets and highways. If my memory serves, we used 128 Hz, or something close to that.

That being said, here is a link to a DigiKey article on LED dimming which states that states:
“A key consideration is the PWM train’s frequency (or fDIM). The minimum value of fDIM is determined by the eye’s sensitivity to flicker. Recent guidelines on lighting design suggest fDIM should be greater than 80 to 100 Hz if no long-term health effects are to occur.”

The statement is followed by a link to an article addressing the recent guidelines on dimming: How New Flicker Recommendations Will Influence LED Lighting Design