Simple PWM Circuit for motor control

[[email protected]]

I need a simple PWM circuit to control a motor from my microprocessor,
I found this one:

http://home.cogeco.ca/~rpaisley4/LM555.html#17

Any comments? It looks cheap and simple to build so should fit my
requirements.

 

[Chris]

I need a simple PWM circuit to control a motor from my microprocessor,
I found this one:

http://home.cogeco.ca/~rpaisley4/LM555.html#17

Any comments? It looks cheap and simple to build so should fit my
requirements.

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

 

[James_sgp]

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.

 

[kell]

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.

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

 

[Charles Schuler]

I need a simple PWM circuit to control a motor from my microprocessor,
I found this one:

http://home.cogeco.ca/~rpaisley4/LM555.html#17

Any comments? It looks cheap and simple to build so should fit my
requirements.

Are you aware that many microprocessors have PWM firmware?

 

[John Fields]

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

 

[James_sgp]

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.

 

[Chris]

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.

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?"

http://groups.google.com/support/bin/answer.py?answer=12348&topic=250

Good luck
Chris

 

[kell]

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.

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.

 

[jasen]

On 21 Dec 2006 05:35:00 -0800, "kell" <[email protected]>
wrote:

Not if you want to reverse it!
indeed!

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

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

Bye.
Jasen