Maintaining a Stable PWM Frequency When Changing LED Brightness on STM32

[cedrick]

When using an STM32 timer to control LED brightness, is it generally better to keep the timer period fixed and adjust the compare value, rather than changing the timer period as well?

My understanding is that changing the compare value allows the duty cycle to vary while keeping the PWM frequency constant. Are there any practical considerations when selecting the timer prescaler and auto-reload value, particularly when aiming for smooth dimming across the full brightness range?

I’d appreciate any guidance on the timer configuration and potential trade-offs.

[Andrew Neil]

I guess this is a follow-on to your previous thread:

If that question is now answered, please mark the solution on the appropriate post in that thread.

 

is it generally better to keep the timer period fixed and adjust the compare value, rather than changing the timer period as well?

Again, that’s a general question - nothing specific to STM32.

“PWM” stands for Pulse Width Modulation - meaning that it’s the width of the pulses that changes.

The frequency is generally not changed.

What benefit would there be to changing the frequency?

As noted, the frequency is chosen for human perception - I don’t think that varies with brightness?

[Peter BENSCH]

​@cedrick

Basics on PWM can be found, for example, in the relevant Wikipedia article.

In-depth details on timers can be found, for example, in AN4013 and AN4776.

Regards
/Peter

[cedrick]

Thanks, Peter. I’ll go through AN4013 and AN4776 to better understand the timer configuration and its practical trade-offs.

[Andrew Neil]

And don’t forget to look at the examples provided by ST - there’s loads of them:

 

and videos: https://www.youtube.com/@stmicroelectronics/search?query=pwm

Not to mention 3rd-party stuff!

 

When your question is answered, please mark the solution on the post which provided the answer - not this one!

You still haven’t marked a solution in your previous thread - don’t just abandon it!