This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC28950: Control Loop for Dual Output Power Supply

Part Number: UCC28950
Other Parts Discussed in Thread: PMP8606

Hello, 

I am designing a 3kW power supply with dual output voltage (+-125V) using UCC28950 for the dc-dc stage, and I'd appreciate if you answer my questions. 

According to TI Switch-mode power converter compensation made easy, I am trying to implement a peak current mode control with a type II compensator. 

What considerations are required for a dual output voltage power supply compared to a single output voltage one?  Is there any TI reference designs with dual output voltage so that I can get some idea how I should close the feedback loop?

Also, could you advise if the compensation network has to be isolated for this application? 

It seems to me that PMP8606 is the only reference design for UCC28950 with an optocoupler feedback. Is there any other UCC28950 reference designs with an optocoupler feedback?

Thank you very much,

Best

  • Hello,

    There is an application note that you can use to compensate feed back loop and design a peak current PSFB converter using the UCC28950.   This does use type II compensation as well.

    This does go with an excel design tool that you can find at the following link.  

    If you you use the UCC28950 as the application note suggests on the secondary you will not need an opto isolator in the feedback loop.  The application shows how to compensate the loop with out an opto isolator.

    If you do need an opto isolator feedback you can use the PMP8606 as a reference on how to set it up.

    Regards,

  • Thank you very much Mike. 

    Could you also please comment on implementing the control loop on the dual output voltage (+Vo, -Vo , and G) applications. In a regular single output voltage application (like the 600-W that you sent), on the secondary side, the ground of the power (-Vo) is connected to the ground of UCC28950, since the voltage divider (formed by resistor RC and RI) are connected to the +Vo and ground. But what should be the connection of voltage divider and the ground of the IC and feedback in the dual output voltage (+Vo, -Vo , and G) system?

    Is there any TI reference design with a dual output voltage?

    Thank you once again for your help.

    Best,

    Mehdi

  • Hi, Mehdi,

    Mike is out of the office. He will get back with you early next week.

  • Hello,

    I don't believe that Texas Instruments has done a dual output design using the in a phase shifted full bridge.  So there is no information or application notes available on how to do this as far as I know.  Generally in these high power applications it is one single output.  If multiple high output are needed the UCC28950 PSFB power stages are paralleled.  You could consider doing this.

    The other option might be to regulate the positive output and depend on the transformer turns ratio to regulate the negative output.   You might be able to get +/- 10 % by doing this.

    If +/- 10% regulation is not good enough you could consider a buck converter on negative output that is not well regulated.

    Regards,

     

  • Thank you very much Mike. 

    Do you think Multiple/weighted feedback approach suggested in Multiple Output Flybacks: How to Improve Cross Regulation works in my application with UCC28950? If so, do you think this approach would be better than only regulating the positive output with +/- 10 % regulation? 

    Thank you once again for your help. 

    Best,

    Mehdi

  • Hello,

    Weight feedback has been used for multiple outputs and I believe will still be +/- 10%.

    Most references that are used for control have a tolerance of +/- 3% and with 1 % resistors you tolerance is +/- 4%.

    Regards,

  • Thank you very much Mike.