High-power motor driver 18v15 behavior

Hi there,

I’m testing out a 18v15 high-power driver, and each time I change the PWM duty cycle (increments as low as 0.1 % via function generator) the motor reacts with a pronounced jerk. It appears to briefly stop or otherwise jump. I’ve tested it with a biggish 12 V wiper motor and a tiny DC motor (unknown specs, but probably around 3-9 V, next to no current). PWM frequency has no influence.

Is this expected behavior? I hope not. Any suggestions for smoothing this out?


Hi, Wolfgang.

I have not heard of a problem like this before. It sounds like this might be caused by something happening in the signal from the function generator when you change the duty cycle. Do you have access to an oscilloscope that you could use to view the output from the function generator when it adjusts the duty cycle?


Hi Claire, I’ve already looked at it on a scope, and it appears to be fine.
Today I’ll replace the function generator with a microcontroller and let it sweep the duty cycle to see if it makes a difference.
I’ll report back then.

Ok, issue resolved. It’s the function generator. Can’t see anything on the scope, but it’s got to be there.

You might not have seen anything on your scope because it happened too fast. To catch it you would probably have to put your scope into single capture mode and set it up so that it triggers when the function generator changes duty cycle, which would probably be really difficult. The function generator might behave the same way when changing other parameters like amplitude. So you might try setting up your scope to trigger on a voltage that is above your initial amplitude setting and seeing if there is any strange behavior when it switches to a larger amplitude.