PWM - What is it, How does it work and how to detect it.


Newly Enlightened
Apr 13, 2020
can you help explain the difference between PWM and Ripple, in practical terms?

1. does ripple create banding in photos, the way PWM does

2. does ripple cause visual trailing dots, when moving ones head... as happens with LED tail lights?

Ripple is due to simple architectures for the driver and trade-offs on capacitor size. By typical regulation in North America, the ripple depth is <30%. As your eye responds to a power law, this is not really noticeable, except when you have some significant motion. It can create banding in photos, but the dark spots are just not a bright, not black. Trailing dots would not really happen, especially since you are not looking directly at the light source like say tail lights. Fixed light sources, don't move either.

With PWM, you have intentional on/off with 100% and then 0%. In a flashlight you have a moving source which makes the impact far worse.


Newly Enlightened
Feb 26, 2020
PWM is also used in radio controlled receivers e.g airplanes and such as this full range translates to a range of 1194μs which when applied to a PWM servo signal equals 903μs to 2097μs, PWM_OUT - the pulse length that is output to the servo or motor in μs.
same concept as PWM in flash lights, just different application