(The free running frequency of U1 should be about 5-10% lower than the sync frequency for reliable synchronization.)
what do you want to say by 5-10% lower? how can i do that?

 

Hello cruts input 12VDC!

That's the Mod_In control voltage?
Whats the supply voltage?

does the values of resistors must be exactly like shown on your schematic? ex: 98k =100K

Should be within 5%.

 

Mod_In control voltage: 12VDC
supply voltage:12VDC

 

does the Rtot must be at 10K i have a 220K

 

Mod_In control voltage: 12VDC

Then the output should be 12Vdc.

does the Rtot must be at 10K i have a 220K

What's Rtot?
That's not on my schematic?

 

to test your circuit i have pur a 50k potentiometer to vary the pwm

 

to test your circuit i have pur a 50k potentiometer to vary the pwm

And how is the pot connected to the circuit?
You really need to post a schematic of your actual circuit, so it's not like pulling teeth having to play a game of 20 questions.

 

i have 50% dutcycle and the scope shows instability

 

Approaching 100 posts for a 555 PWM!
Could have done it with a 8 pin 12F628 in that time!
A couple of lines of code.
Max.

 

does the Rtot must be at 10K i have a 220K

If you're talking about the pot model, then right-click on its symbol and edit Rtot as you want.

 

Could have done it with a 6 pin 12F628 in that time!
LOL!!!!

 

i have 50% dutcycle and the scope shows instability

Where did the sync signal come from and why do you need that?
It's likely the sync signal that's messing it up.

Why do we keep getting the information in little bits and pieces?
You kept telling me you were using my circuit but you weren't.
I believe I'm through with this thread.

 

how can i test your circuit without a potentiometer!

 

how can i test your circuit without a potentiometer!

You apply a DC voltage.

 

thats rigth with a potentiometer in 12V

 

thats rigth with a potentiometer in 12V

We seem to be going in circles here.

 

Hi crutshow on your post 42 i have tried your circuit and it works from 6.6% to 99.9% duty cycle! On the other hand, the frequency varies from 408hz to 449hz! is it possible to have a fixed frequency?
thank you
regards

 

i have tried your circuit and it works from 6.6% to 99.9% duty cycle!

How do you figure that?
The simulation clearly shows 0% modulation (output low) at the left to 100% modulation (output high) at the right.

the frequency varies from 408hz to 449hz!

Your measurement is in error.
The oscillator on the left is not connected to the modulation input, and thus its frequency cannot be affected by that.

 

(How do you figure that? )
I varied the dc voltage(for testing) on (mod in ) of U2 !
(The oscillator on the left is not connected to the modulation input, and thus its frequency cannot be affected by that. )
can you give me an example with a potentiometer to test the result and compare with your?
regards

 

hi Matt.
I expect crutschow will get back to you on the frequency problem.
But I would check the resistive range of the potentiometer you are using, with a Ohm meter, many pots have high end resistance and also don't swing to zero or their maximum stated resistance

E