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Why PWM generate circuit can not adjust the duty cycle to 10%?

Jason

I have a problem when I am debuging. My PWM generate circuit can not adjust the duty cycle to 10%! It just 46% when I modulate Rp_Potentiometer.SCH.jpg

 

But I have checked the circuit by a software called EWB and the follow images are test result.

 

1 R_potentiometer =100k Ohm  100%

   Duty cycle=10%

image

 

2 R_potentiometer =100k Ohm   50%

   Duty cycle=50%

image

 

3 R_potentiometer =100k Ohm      0%

   Duty cycle=90%

image

 

Why? Can anyone tell me why!

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  • I've had similar issues with op-amps of the like. I've experienced very spotty results with such circuits. It may just be an innate problem with these chips, but before categorizing it that way, let's try what we can with your setup.

     

    It could be a multitude of issues. For now we will look at a couple superficial ones.

     

    It looks like the input or microprocessor may be affecting you amp. Try adding a buffer transistor or op-amp to the output of your PWM signal between it and the input/microprocessor junction. What you'll be making is a voltage follower (unity gain amplifier) that will have no affect of the PWM signal, but will help it from being distorted.

     

    You might also want to check your resistors actual resistance, or use precision resistors. This check is often overlooked but has profound influence.

     

    Cabe

  • in reply to Catwell

    Hi, Cabe

    Thanks for sharing your experience in solving the AMP problem!

    I have cut the juncture of AMP output and the microprocessor, the problem is still being. So we can see microprocessor is not the cause. And I also checked my components, all of them are normal. Bythe way, my resisitor's tolerance is 1%.

     

    Jason

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  • in reply to Catwell

    Hi, Cabe

    Thanks for sharing your experience in solving the AMP problem!

    I have cut the juncture of AMP output and the microprocessor, the problem is still being. So we can see microprocessor is not the cause. And I also checked my components, all of them are normal. Bythe way, my resisitor's tolerance is 1%.

     

    Jason

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