[Simetrix] UC3848 Duty Cycle

[guitarnoob123]

Hello, I want to produce a PWM/pulse train with 125 kHz frequency and a 35% Duty.
This is my simple schematic and I followed the formula 1.72/RC from the appnote of UC3848.

I can vary my output's frequency but I can't seem to find a way to obtain my desired duty cycle.
I can't find any formula for the Duty and its the weekend so I can't consult my professors.
How should my R and C values be chosen?

 

[FvM]

Which controller are you asking about? UC3848 has dedicated duty cycle clamp, UC3843 hasn't.

 

[BradtheRad]

You might be able to adapt a technique used to alter duty cycle on a 555 pulse generator.

Diodes change the charge/discharge rates on the capacitor.

 

[guitarnoob123]

My bad. I meant UC3843, the one in the picture. What do you mean about a dedicated duty cycle clamp?

You might be able to adapt a technique used to alter duty cycle on a 555 pulse generator.


Diodes change the charge/discharge rates on the capacitor.

In your case, do replace UC3843 with the 555 completely as a PWM generator or do I connect it somewhere to control the UC3843?

 

[aqildad]

My bad. I meant UC3843, the one in the picture. What do you mean about a dedicated duty cycle clamp?



In your case, do replace UC3843 with the 555 completely as a PWM generator or do I connect it somewhere to control the UC3843?

i think you can control using I-sense pin