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PWM generator using SG3524N

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Hendribs153

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i am using IC SG3524N to generate PWM signal. The problem is how to make duty cycle proportional to voltage input (pin 9 Voltage) ?

here is my circuit. In this circuit, the duty cycle isn't proportional to voltage input.

thanks
regards
Hendri Budi S

pwmcircuit.PNG
 

The PWM doesn't really care about PWM duty
proportionality because the error amp is there
to take that out by feedback.

If you want to use feedback (like an RC filter)
and the error amp in the loop then you should be
able to get decent(-ish) linearity. At the cost of
some lag.

I don't see an input here, so which voltage you
refer to is unclear.
 
Maybe you should limit the upper and lower limits of the input on pin 9, to correspond with the maximum and minimum levels of the waveform on pin 7.
 

The PWM doesn't really care about PWM duty
proportionality because the error amp is there
to take that out by feedback.

If you want to use feedback (like an RC filter)
and the error amp in the loop then you should be
able to get decent(-ish) linearity. At the cost of
some lag.

I don't see an input here, so which voltage you
refer to is unclear.




Thanks for the asnwer.
the input is on pin 9, my bad. I was try use error amp (pin 1) as feedback and pin 2 as input but the result is same as input on pin 9. If this IC can't give proportioniality, what IC I should use then?

This PWM generator is part of closed loop DC Motor Control system that i designed. So i really need to make sure that duty cycle is proportional to input voltage.

regards
Hendri Budi S
 

thanks for the answer.
Nice idea sir. But the problem is, when pin 9 is 0 V, the duty cycle isn't 0% or around 0%.
 

There are limitations to what duty cycle this chip can do.
 

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Well, you can trim or scale the limits into pin 9, but you are never going to get 100% duty cycle out. You will need to use a chip that can do 100% or design your own solution with discrete chips.
 
how to get 0-90% duty cycle?

hello everyone
right now i am designing a PWM generator using SG3524N. SG3524N has two outputs with 45% duty cycle each output. I am using pin 9 as input. How to get 0-90% duty cycle? thx before
 

How to get 0-90% duty cycle?
Easily by paralleling both outputs. Already done in post #1.

As shown, the LED is off when a PWM output is on. Intentionally?
 

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