Simple PWM Circuit for motor control

Hi, James. Yep, it'll work pretty well. I'd assume you're driving a transistor or MOSFET with the comparator output, right

6mA sinking output is pretty much the most you can ask of an LM393. You should probably expect somewhere around 0.3V output for a logic low. Unless there's a good reason, I'd replace the 2.2K with a 10K resistor. That'll pretty much ensure that your logic low will be less than 0.1V.

Now you really should run the PWM of the motor at more than 37Hz, which is the frequency shown on the link. You can do this by replacing the .05uF cap on the 555 with an .01uF cap, and replacing the 1 meg resistor with a 180K. Circuit operation will remain almost exactly the same, except the output frequency will be multiplied by 30 or so. This will give you a roughly 1KHz PWM output.

Make sure not to replace the LM393 with another comparator, or use a lower output voltage, without looking things over carefully.

Good luck Chris

Chris,

Thanks for a quick, concise response. I`ll make the changes as you suggested, yes it will be powering an H-bridge IC to run my motor. I now feel much more confident, with a second opinion.

Thanks again.

Chris wrote:

And don't forget to put a diode across the motor.

Are you aware that many microprocessors have PWM firmware?

--- Not if you want to reverse it!

In which case you could use TVSs or Zeners in series opposition across the motor.

-- JF

Charles,

Yes I am, but as I`m using firmware in the micro that was written by someone else; using the PWM function isn`t currently possible.

Charles Schuler wrote:

Hi, James. You might have a bit of a problem with range of your control signal. The 555 oscillator goes from 1/3 Vcc to 2/3 Vcc, and your output has to be within that range to be effective.

Also, since you're a Google Grouper, you should know that it's considered good form to bottom post. On Google, click "show options", then "reply". Put your response to the post below the previous post -- that gives greater continuity, and makes it easier to answer the previous post with minimum scolling. Also, it helps for continuity -- most newsreaders don't act like Google Groups. Please check out Google Groups Help Topic "What's good 'netiquette' when posting to Usenet?"

Good luck Chris

of your

the circuit has the voltae at the positive input of the comparator ramping up and down between 1/3 Vcc and 2/3 Vcc. The control voltage to the comparator's negative input adjusts in the same range, 1/3 Vcc to 2/3 Vcc. So far I don't see any problem.

indeed!

what about bridge rectifier, AC side to the motor, DC side to the supply rails?

Bye. Jasen