Firstly, it is not allowed to use 555 or something like that. allowed to use opamps etc..

From this and other posts it is clear that this is homework (of some type).

Secondly, if you have a answer ,do you mind send with a photo or schematic pls? Thanks

And from this it is clear that what you really want is someone to just do your homework for you.

You are expected to show YOUR best attempt to work YOUR homework! We will help guide you along the way, but you've got to do the work.

 

MOD NOTE: Moved to Homework Help.

 

let me prove myself in order to show i have done other parts,

LM35 out connected to +in for NON inverting amplifier (for amplify the mV out of LM35).

Then i need a Duty cyle adjustment which i did not make it .!!!

Then i need a RC filter to convert DUty cycle signals into DC in order to compare desired Temperature and environment Temp.!!!

and lastly i have connected these 2 outputs into 2 different opamp in order to compare which one higher or lower so that turn it on FAN or STONE RESISTOR (Of course i have used transistors to drive fan ,stone resistor BD135)

NOW, ARE YOU GUYS HAPPY FOR BLAMING ME INSTEAD OF HELPING????
IS THAT YOUR WAY HOW YOU HELP PEOPLE? !!!!!!!!!

 

We are still waiting to see some indication that you are even making an attempt to use what you are being told to solve your problem (the problem in this thread, namely getting an adjustable duty cycle PWM circuit working). You keep asking people to tell you what component values to use but won't even make any effort to try to figure that out for yourself. People keep asking you what frequency you want to use and you won't provide it. Even if some one was willing to give you component values, you won't provide the most basic information they would need in order to do so.

 

Basicly i need PWM generator.

 

Basicly i need PWM generator.

Basically, you need to show an attempt at designing a PWM generator.

 

We are still waiting to see some indication that you are even making an attempt to use what you are being told to solve your problem (the problem in this thread, namely getting an adjustable duty cycle PWM circuit working). You keep asking people to tell you what component values to use but won't even make any effort to try to figure that out for yourself. People keep asking you what frequency you want to use and you won't provide it. Even if some one was willing to give you component values, you won't provide the most basic information they would need in order to do so.

The point is frequency not important!!!! Thats what i tried to tell . I just need to change duty cycle anytime i want . When i change the duty cyle that will give me (after RC FILTER) DC signal.SO i can compare this DC signal and enviroment signal that comes from LM35 multiplied by noninverting amp. So why people asking what freq. you need? Does it matter?

 

The point is frequency not important!!!!

Pick one and design your circuit.

 

If you use a triangle wave generator (ie opamp generated triangle wave), feed that into the input of a comparator and then feed a variable voltage into the other input of the comparator that will give you an adjustable pulse width at the output of the comparator without affecting the frequency. It's a very well know and simple technique.

This method has been discussed in the last week or so on this very site, have a search for PWM, you'll find it.

And BTW it would have taken far less time to answer the question regarding frequency rather than arguing as to why it's relevant.

Is it something like that ? sorry for bad scratch