For my project i have to build a pwm generator. I use opamp, capacitor, pot and resistors as seen in the attachment. However while potantiometer value changes, frequency also changes. I mean there is a big difference in %90 & %10 duty cycle but this is detrimental for me. I must build it in nearly constant frequency values. What can i do to handle this problem? I am waiting your suggestions.

 

I mean there is a big difference in %90 & %10 duty cycle but this is detrimental for me.

how big of a "big" difference is it? how much of a difference can you tolerate?

in that design, the key is to use a low voltage diode, like shottcky or germanium diode.

I must build it in nearly constant frequency values.

how constant is "nearly constant"?

What can i do to handle this problem?

a ramp + a comparator.

 

The above circuit is from the Electronic Design website http://electronicdesign.com/analog/independently-vary-multivibrators-duty-cycle-and-frequency

 

The above circuit is from the Electronic Design

the first opamp is a ramp generator and the 2nd opamp is a comparator.

use opamps / comparators with push-pull OPS will save you two resistors.

 

Thank you very much for your responses.