# How to choose the optimal PWM frequency

#### ponas.jonas

Joined Feb 28, 2023
30
I have been playing around with a linear direct drive motor: SDLM-025-095-01-05. I use a driver that has the features listed below. I have made it work with a PWM frequency of 1kHz, and everything works well enough, but I want to understand how to get the optimal PWM frequency and duty cycle so I can give good reasoning. Can someone please help ;(

Driver features:
• Run DC and Voice Coil Motors with PWM and Direction Control Inputs
• 4 Amp Motor Output
• +6.5 VDC to +40 VDC Power Supply
• 0 ºC to 70 ºC Operating Temperature
• Light: 0.36 Oz (10 gm)
• PWM Frequency up to 50 KHz

#### crutschow

Joined Mar 14, 2008
32,849
Since the efficiency of a PWM driver generally goes down with frequency, you want to use as low a PWM frequency as possible, that still gives the desired results.
Driving an electro-mechanical device, the lower limit is generally determined by the needed frequency response of the device and/or minimizing mechanical noise and avoiding any mechanical resonances.

The PWM duty-cycle is determined by the average output voltage you want and is largely independent of the PWM frequency.

Joined Jul 18, 2013
27,605

#### ApacheKid

Joined Jan 12, 2015
1,265
I'm interested in this general question, surely the ideal frequency for a given RPM is a function of motor inductance, motor inertia and so on, I just don't see how it can be independent of the motor's physical characteristics.

#### crutschow

Joined Mar 14, 2008
32,849
I just don't see how it can be independent of the motor's physical characteristics.
It's not, obviously.
At some low frequency the motor will start exhibiting noise and/or oscillations that likely should be avoided.
It's also limited by how fast the motor needs to respond to a change in the PWM duty-cycle.