hi! i want to drive a Dc Motor with TL494 and i can t found how to fix duty cycle can someone help me??

 

By fix, do your mean 'set' or vary?
Max.

 

i mean to vary

 

Duty cycle varies according to the voltage on pin 3.

 

thanks..but how to choose the right value of the resistance to vary the duty cycle in pin 3 ???

 

I'd suggest:
Connect one end of a potentiometer (say, 25k or 50k...the value isn't critical) to ground, connect the other end of the pot to Vcc (positive supply) via a resistor whose value is ~10% of the pot value, and connect the pot wiper to pin 3.