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UCC28950 - can it be used on the primary side?

farhan alam12004
Prodigy 130 points
Other Parts Discussed in Thread: UCC28950, TL431

hi 

i want to build a DC DC full bridge converter for 3kw power level with 400v input and approximately 400v out put .and for this application i have planed t use ucc28950.but i want to place this controller on the primary side of the full bridge but the application note and the excel design tool gives the calculation for placing this controller on secondary side .i want to know is it possible to place it on primary side or not and using optocoupler for vsense but then hoe to calculate the resistance and capacitor for vsense circuitry will it be same as in excel sheet or will it be different because it looks to me that it will be change.

please help me  thank you very much

Best Regards

Muhammad Farhan Alam

  • 0
    TI__Guru* 86266 points

    Yes you can use the UCC28950 for primary side control withan opto coupler.  You will just need to setup the voltage amplfier as a voltage follower by tying the COMP pin th EA-.  You would then tie EA+ with a pull up resistor greater than 1K to Vref.  Then you would tie the EA+ pin to the collector of the optocoupler and use the standard opto feedback network.  Figure 1-1 of the UCC289500 EVM shows a standard opto coupler/TL431 feedback configuration.  http://www.ti.com/lit/pdf/sluu068

    There is not an excel tool setup to compensate the voltage loop in this configuration. There is a Math-CAD file that you could add and opto block too and compensate the loop theoretically.  However, the easy method since you are using an opto coupler is by using a network analyzer.  I have attached an article that explains how to compensate the loop with a network analyzer.

    Regards,

    Mike

    H2PToday1004_design_TexasInstruments_for_review.pdf
  • 0 in reply to Mike O'
    Prodigy 125 points

    Mike 1414007 said:

    Yes you can use the UCC28950 for primary side control withan opto coupler.  You will just need to setup the voltage amplfier as a voltage follower by tying the COMP pin th EA-.  You would then tie EA+ with a pull up resistor greater than 1K to Vref.  Then you would tie the EA+ pin to the collector of the optocoupler and use the standard opto feedback network.  Figure 1-1 of the UCC289500 EVM shows a standard opto coupler/TL431 feedback configuration.  http://www.ti.com/lit/pdf/sluu068

    There is not an excel tool setup to compensate the voltage loop in this configuration. There is a Math-CAD file that you could add and opto block too and compensate the loop theoretically.  However, the easy method since you are using an opto coupler is by using a network analyzer.  I have attached an article that explains how to compensate the loop with a network analyzer.

    Regards,

    Mike

    Hi Mike,

    I have gone through your article and is very helpful in feedback design. I am presently struggling to compensate the feedback loop.I have placed the UCC28950 IC in primary side and taking feedback using TL431 and Opto. Can you please help share me the MathCAD file with TL431 and opto feedback. 

    Regards,

    Ashok

  • 0 in reply to Mike O'
    Prodigy 125 points
    Hi Muhammad Farhan Alam,

    Have you completed your design. How you calculated your loop components. Can you post any reference.

    Regards,
    Ashok