I am running a small DC car motor with PWM and I am using 20 kHz. This requires special op-amps with fast v/us times to get a proper square wave out to drive the MOSFETs even with drivers. I am trying to keep the costs down. I want to be able to reduce this frequency for the PWM braking circuit. I'm just pulsing a MOSFET directly across the motor using the direct short duty cycle to control the amount of braking. It will only brake for a fraction of a second every second or so. Can the braking circuit be pulsed at 100-1000 Hz without worrying about any of the issues for using 20 kHz on the drive side.
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1\$\begingroup\$ Why are you using op-amps to drive MOSFETs? This sounds like underlying issues (that may deserve their own questions / research). \$\endgroup\$– Tim WilliamsCommented Aug 3, 2023 at 5:15
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\$\begingroup\$ I'm trying to make this a simple and inexpensive PWM circuit. I'm using Op-amps to create the PWM signal. With low frequencies the losses in the FET would not be much, especially with just a braking circuit. I have redesigned using a Driver due to the lower current output of the TL084. I have been using the same circuit to develop the drive circuit for the same small motor. At a few hundred HZ the control was really good. When I increased to 17kHZ the motor just hummed. It needed about 80-90% duty cycle to move. I've been trying to figure out if these small motors just won't work at high freq. \$\endgroup\$– JerryCommented Aug 5, 2023 at 5:08
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. Can the braking circuit be pulsed at 100-1000HZ without worrying about any of the issues for using 20KHz on the drive side.
Yes, as described.
There may be other issues which are not obvious from your description, but it should be acceptable.
You may produce audible noise due to the low frequency - probably not a significant issue in this context.
Lower than 20 kHz PWM should work for motor drive unless audible effects or special considerations are relevant.
answered Aug 3, 2023 at 4:09