Hi All

I have simulated a PWM circuit, which published by EFY magazine. The problem is that circuit is not oscillating. From the reference. The circuit has to produce 250Hz square wave signal. Any one please help me to get the proper output from this simulation. I have attached the EFY reference document and the TINA-TI circuit diagram also.​

 

I've tried to get TINA to oscillate on a couple of occasions, but she's just not that kind of girl. One time she generated exponentially increasing voltage (beyond GV in about 15 seconds) rather than oscillating. This is one reason I don't trust simulators.

 

Your oscillator does not work because one of your diodes is connected backwards,
Tina is a nice girl. It is not her fault.

 

As audioguru has pointed out, you need to reverse the direction of either D1 or D2. If you look at the article you will see it calls for the diodes in the feedback path to be reversed from each other.

hgmjr

 

Along with reversing either D1 or D2, R3 and R4 should be a single potentiometer.

If Tina-TI does not have a potentiometer available, then you will need to manually decrease one of those two resistors the same amount as you increase the other, and vice versa.

 

After modification (D2 connected reverse). I am getting the following wave forms. I am surprising what wave form i am getting. Its completely incorrect. plese help me to solve this problem.​

 

The delay is most likely while C1 charges to the average that it oscillates about. Not sure why you aren't getting nice squarewaves, could be that you're trying to make it go too fast for one of the component models' maximum slew rates. I'll have try simulating it & let you know what's wrong in a few hours if nobody else beats me to it. Need to sleep now.

 

You don't have enough base drive to your transistor to ensure saturation. You need at least 2mA, and 5mA would be better. I would put all unused sections of the 40106 in parallel with U1, and change R1 to 1k.
EDIT: That still does not explain why you are getting oscillations.

 

Like RonH said, if you parallel the other 5 inverters, you can get up to around 21mA current out of the 40106 when Vdd is 5v. You could go even lower than 1k; try 470 Ohms.