uc2526: not getting PWM output from UC2526 IC

Hello Anand,

From the voltage readings, I can say that the SHUTDOWN pin is pulled low which is preventing the PWM from generating any gate drive signal. Now, if you look at the block diagram from the datasheet the CS+, CS- feeds the Shutdown pin. You will have to make sure that these pins are connected as recommended in the datasheet.

I am concerned if you might have damaged the PWM controller by shorting pin 6,7. I will suggest checking if the oscillator of the controller is still operation before making any changes. This can be done by looking at the voltage at Ct (Pin 10), you should be expecting to see a sawtooth waveform. If the oscillator is not working I would suggest replacing the controller with a new one.

Can I also suggest to remove the cap parallel to the switch to SHUTDOWN because it will result in extensive switching at the cap as the voltage is fed from the comparator internally.

I hope this helps.

Thank you,

Sonal

Hello Anand,

What I understand from this question is that you are trying to change the duty cycle of the PWM signal. Please correct me if I am wrong, but if this is the case then I would point you to the Electrical characteristics of the UC2526A datasheet.

The duty cycle of the PWM signal can be altered by regulating the voltage at the COMP (pin3).

I hope this will answer your question.

Thanks,

Ms. Sonal Singh

Hello Anand,

I don't see any problem with these values, the PWM is operating as one would have expected. I would like you to see the voltage at COMP pin @ No load and Full Load condition. The reason why I say so is because I would like to see if the controller is entering in burst mode @ No load, If not you are probably fine.

Thank you

Ms. Sonal Singh