• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 64 subscribers
  • Views 124 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

Original question:

UCC29950: using PFC with different parameters

UCC29950: alternative simple buck boost controller

robin gangopadhya18
Mastermind 6050 points
Part Number: UCC29950

Hello:

I notice that using UCC29950 with requirement to have Vbulk at startup to be equal to peak AC will destroy one key feature of our system.

So is there a simple buck/ buckboost  or boost controller that we can use instead with TSSOP type pkg?

appreciate any suggestions..

\r

  • 0
    TI__Genius 10555 points

    Hi Robin,

    Please share some of your requirements so I can try to guide you to the best solution. Vin? Vout? Pout? Do you require PFC?

    Thank you,

    Ray

  • 0
    Mastermind 6050 points

    Vin: 85 min to 264 mx typ universal line voltage

    Vout: preferred: 325V

    Pout: min 50W max 500W

    Application: LLC follows the PFC, which drives high-power LEDs through current control in the load.

    No PFC actions are  required to be controlled by the controller.  The topology itself does it!

    But it cannot need to have Vout= Vinmax to start up!

    THAT kills the inrush control we have.

    Your help is very much appreciated.

    -r

  • 0 in reply to robin gangopadhya18
    TI__Genius 10555 points

    Hi Robin,

    Please clarify this statement: "...I notice that using UCC29950 with requirement to have Vbulk at startup to be equal to peak AC". 

    I don't believe the controller has such a requirement. Is this related to the soft start information in sec 7.3.12?

    Thank you,

    Ray

  • 0 in reply to Ray DiCecco
    Mastermind 6050 points

    Hello Ray:

    Pl see attached slides that I picked from the d/s of UCC29950. Hope this highlights issues we find in the documentation of the chip. It seems to be a very easy and powerful controller but these limits and confusing constraints appear to make it unsuitable. Bear in mind that SEPIC in DCM provides excellent PFC without all these and can give output far lower than 380. Lower values allow the use of GaN!

    • Any review will be highly appreciated.

    3312.ucc29950different_bulk.pdf

  • +1 in reply to robin gangopadhya18
    TI__Genius 10555 points

    Hi Robin,

    This controller was designed to provide a simple single-controller solution to an LLC preceded by PFC. I'm not saying the concept of using this as a SEPIC won't work, but we have no examples of it being used outside of this primary intended application. This controller was designed for universal input with the assumption it would be used in a traditional boost configuration where Vout > 264vac x sqrt(2) ~ 373Vdc

    That said, I will attempt to address your comments in the attached document:

    The use of a diode such as D1 is very common in boost designs. It is there to provide a path for the input voltage to charge the PFC bus cap without going through the PFC inductor, diode D3 or the MOSFET. This occurs during startup but also if there is a surge. It isn't necessary but recommended to protect your power stage.

    5.1.11: Yes, the 30mΩ and 73.3kΩ values are chosen for the intended application of Vout > 373Vdc. 

    Sec 7.3.2: At startup, Vout will be forward voltage drop of D1 below the peak input rectified voltage. Once the controller starts regulating, Vout will start rising and the diode will stop conducting and Q1, L2, D3 will take over. 

    Regards,

    Ray

  • 0 in reply to Ray DiCecco
    Mastermind 6050 points

    Understood. thnx for your review.

    You may checkout my simulation circuit of the SEPIC post  in this Forum ...for exploring all aspects of the circuit.

    There is nothing in the circuit per se that will prevent us from using it in our application!

    -r