Buck converter with SG3524 and IR2117, problem with duty cyc

[AbhimanyuSingh]

I have to build a buck converter, with variable input from 10 V - !5 V. Use a PI controller to maintain the output at 5 V. I have used SG3524. Now, it is clear that I should be able to attain a pulse width of duty ratio 33% to 50%, exactly speaking. And wider range of duty ratio will be even better. Also I am getting duty ratio of 20% to 70% from SG3524. But the problem comes after that. The output of gate driver IR2117 which is supposed to follow its input, does not follow it for a pulse of duty ratio more than 30%. Why is it so? If i decrease the duty ratio below 30 % the output of IR2117 follows input, but not for more than 30%. There is nothing mentioned so on the datasheet. The frequency i m using is 100 khz. is there any other option for me, like change the gate driver. Can anyone suggest me a gate driver which wont be having this problem. Or else can anyone tell why is this happening.
Ask if have missed some information to provide.

 

[AbhimanyuSingh]

Re: Buck converter with SG3524 and IR2117, problem with duty

It was this bootstrap problem and I dealt with it.
But there is a new prob now.
I have to connect a PI controller in my circuit to keep the output voltage equal to 5 volts. I have passed the output (of the buck converter, which is supposed to be 5 Volts, after scaling it down) to the positive output of the comparator of SG3524. The negative input of comparator is output of PI controller and PI controller's input is the output of comparator. I know this sounds confusing. If you ppl need the schematic, I will upload it next time. I have used LM324N for PI controller. The prob that I see is, "P" controller works alone fine. "I" controller works alone fine. I.e. if they are broken in to parts and connect them , they individually work fine. But when I short the input and output of "P" and "I" controller, the output no more remains as expected. Why dont the "P" and "I" work together properly?
Also when I use "P" and "I", I use the same IC for both.

Thanks in advance.

 

[farjad]

Re: Buck converter with SG3524 and IR2117, problem with duty

It was this bootstrap problem and I dealt with it.

What was the problem and how did you resolve it? (I am also having problems with giving varying duty-cycle PWM to this driver IC.)