UCC28C42: Open-loop Gain

Hi,

If I understand your post correctly your power supply is generating audible noise and the root cause is most likely an instability in the control loop.

Do you have a bode plot (gain phase plot) for the control loop in you system ?

Please also post your schematic and images of the switching waveform and output voltage ripple so we can get a better understanding of the problem.

Are you using voltage mode or current Please also refer to TI app note SNVA555 for a better understand on current mode control.

Also in the post it shows Resr as 43 , is that Ohms or millohms.

Regards

Peter

Dear Peter,

yes. There will be a small number productor of generating audible noise in power supply in production. I want to learn the design technology of loop control. In the process of learning, the equations in datasheet are calculated, but the results I calculate are different from those in the Datasheets. I don't know what's wrong , So I'm ask for advice Or provide relevant information about loop control design for in-depth study.

I don't have a BODE diagram. I want to draw a BODE diagram with a EXCEL table.

Also in the post it shows Resr as 43 , is that  millohms.

Thanks!

Hi,

As shown in the above figure. The gain given in the book is -19.55dB and the phase at fBW is equal to -58°. And I Caculated the gain is -7 and phase is -155.

From the BODE I drew, it was also -7.23 and -155.24 As shown in the following figure.

I Checked the equation carefully and found no mistake. Where did I go wrong?

Thanks!

Hi

It will take me a couple of days to create the calculations in Excel and figure out the differences.

In the meantime I have attached some links on control loop design that you may find of use.

Regards

Peter

Dear Peter,

thank you very much for your reply!

I am very moved to spend two days of your time for me! You have worked hard! Thank you!

The information you provided is very useful to me, I vill study hard, in order to master the theoretical knowledge of loop control, for the desgin of stable power supply services.Thanks again!

Hi

I am working through the calculations in Excel and the D value I get for Vout 12V and NPS of 10 with Vbulkmin of 75 is 0.615, not 0.627?

It will take me a while to generate the plots the excel I should have an update by the end of the week.

Regards

Peter

Hi 

 yes, if the duty cycle at VOUT 12V is 0.615, but from the transformer point of view, the voltage drop of diod is 0.6V. Datasheet is also added.

As describe in Datasheet:

Thany you! Hope to continue!

Xia chime

Hi Xia,

I have put the calculations in Excel but there is a error somewhere as the plots do not match the curves in the datasheet.

I am traveling next week and it will be Thursday before I can look at this again.

I can send you the Excel file if you are interested in trying to modify it and use it.

Regards

Peter

Dear,Peter

Good, please provide your EXCEL documentation for my reference, in order to find my mistakes.

I am also traveling these days. I went to Guilin and just came back today.

I wish you a pleasant journey! Welcome you to travel to Guilin!

Hi Xia,

Your pictures look great!UCC28C42 Calculator CCM Flyback.xlsx

I have attached the Excel file but there is a problem with the plotting of the power stage gain phase as it is incorrect and there must be an error in it.

You are welcome to look through it and I will try and fix it soon.

Regards

Peter

Hi Peter,

EXCEL I have downloaded, I am learning. I admire your serious attitude very much!

These two days I am doing a project, with UCC2897A to do, encountered burning SR MOSFET, is under study.I may finish UCC2897A first these days.And then come back and learn about loop design.

Thank you very much for your answer!

Xia Chime