Help: how to get a constant duty cycle output from comparator

[hltll]

Hi all, I am designing a comparator, the one input is dc voltage(ref voltage), and the other is square wave, what's worse, the low voltage of the square wave is varying. My problem is : how can I get a constant duty cycle output when the low voltage of the square wave is varying. Thanks for reply!

 

[zeyad.kassaby]

Hi all, I am designing a comparator, the one input is dc voltage(ref voltage), and the other is square wave, what's worse, the low voltage of the square wave is varying. My problem is : how can I get a constant duty cycle output when the low voltage of the square wave is varying. Thanks for reply!

try LM339N

 

[sankar.m8]

For a logic device, the output levels are independent of inputs. That means, if input<Vil(max), the device will output LOW (which is less than Volmax). If input>Vih(min), the device will output HIGH (which is greater than Vohmin).

What duty cycle are you looking at? if you need a adjustable duty cycle, you need a sawtooth waveform on the one input & the constant DC on the other input.so that by varying the DC input, you will get different duty cycle.

What you mean by low voltage of square wave varying?

 

[dick_freebird]

Your square wave can never be square, in an imperfect
universe. So the variation in low level moves one end of
a finite slew rate edge, and that is transformed to a time
variation across the slew-slope. Not to mention, if the
levels are small, timing sensitivity to overdrive with the
overdrive moving.

Sharper edges will help. Lower noise on the reference will
help. Question why the "square wave" levels move, maybe
you really have a ground / reference-ground integrity type
problem?