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UCC28950: VBAIS power supply and Vsense isolation

Florian Wallaert
Prodigy 50 points
Part Number: UCC28950
Other Parts Discussed in Thread: LM5160, UCC28701

Tool/software:

Hello, 

I'm designing a phase-shifted full bridge DC/DC converter (18-50V to 28V @ 10A) controlled by the UCC28950. The schematic is based on the one we find in the datasheet of the controller ( UCC28950 Green Phase-Shifted Full-Bridge Controller With Synchronous Rectification datasheet (Rev. D)) but I have 2 questions : 

 - There's no explanations on how we can provide the 12V bias supply for powering the controller. Can I use the LM5160 controller in a buck converter, in order to get the 12V ?

 - In the feedback loop, the output voltage seems to be directly connected to the controller (in the EA- for example). Is that normal given the fact that we are designing an isolated converter ? Or shall I add an isolated ampliop to achieve the isolation ?

Thanks in advance,

Regards,

Florian Wallaert

  • 0
    TI__Guru* 86266 points

    Hello,

    Your inquiry has been received and is under review.

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 86266 points

    Hello,

    If you require isolation you might want to power the UCC28950 with a flyback converter.  You could use the UCC28701 in a primary side regulated flyback converter.  The following link will get you to the UCC280701 product folder where you can find the data sheet application note and design tools.

    https://www.ti.com/product/UCC28700?

    The UCC28950 was designed to operate on the secondary and take use of the on board amplifier for feedback.  So it is common to find the resistor divider to EA +.   If you power the UCC28950 with a flyback you will not need opto feedback.

    I have had customers do opto feedback with following circuit using a type II amplifier so it is possible. 

    If you find an opto isolator with a CTR of 1 you can the compensation information in the application note to compensate the voltage loop.  The following link will bring you to the application note for designing with the UCC28950 in a phase shifted full bridge converter.  There is a section on compensating the voltage loop. 

    https://www.ti.com/lit/pdf/slua560

    Thank you for interest in Texas Instruments (TI) products.  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.

    Regards,