Why are the PWM pulses distorted when I set the duty cycle of the pulse cycle 1% -3% and 98% -99%?

[Adam_K]

Hi, I configured PWM 25 kHz on Nucleo-767ZI to control the PWM fan.

When I set up Duty Cycle 1% -3% and 98% -99% the PWM signal is deformed.

When the Duty Cycle is 4% to 97% PWM signal is good.

Can it be improved or is it normal?

Regards

[waclawek.jan]

That's your oscilloscope's inability to trigger on short pulses, or maybe it's set so (search for "HF rejection, noise rejection" in Trigger settings).

JW

[RMcCa]

This is normal for pwm. Designers often use 5%-95%.​