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UCC28951-Q1: Circuit design recommendation

KIM Andy
Expert 2530 points
Part Number: UCC28951-Q1
Other Parts Discussed in Thread: UCC28070-Q1, , UCC28180, UCC28700-Q1, PMP8787, UCC27424-Q1

HI

Currently, my client is planning to develop the specification of AC 220V Input / 2.5V, 450A Output.

I think the circuit should be composed of UCC28070-Q1 + UCC28951-Q1.

Is it possible to configure the circuit to satisfy the SPEC with this configuration?

Or do you have an IC that you can recommend separately?

  • 0
    TI__Mastermind 25570 points
    Hi Andy

    This is a 1.1kW application so an interleaved boost PFC is a good choice and the UCC28070-Q1 would be the best controller for the application. If the automotive qual were not needed then they could consider the UCC28180 single phase CCM PFC controller.

    The PSFB is also a good choice for the dc/dc stage. The transformer should have a single turn on its secondary - this is needed to minimise its resistance. The choice is then between a current doubler output or a full bridge rectified output with a tradeoff between number of rectifier switches (4 in the bridge rectifier) and number of output inductors (2 in the current doubler circuit)

    The UCC28951-Q1 needs a VCC supply of about 12V and this can be supplied by a small isolated flyback circuit using a UCC28700-Q1 for example (PMP8787). The controller should be on the secondary side of the isolation barrier rather than the primary. There are two reasons for this. if the controller is on the secondary - then you don't need an optocoupler to transfer the feedback signal across the isolation barrier and you can get a faster transient response as a result. The second reason is that 2.5V is not enough to drive a FB signal through a optocoupler - and you would need an aux rail in any case.

    The MOSFET gate drive signals can be transferred across the isolation barrier from the controller on the secondary side to the MOSFETs on the primary side through a ISO7740F-Q1 isolator or through the isolator/driver device UCC21521-Q1

    At this low output voltage you will have to use Synchronous rectifiers - and again a bias rail for their gate on/off signals and the UCC27424-Q1 may be used to drive the SR MOSFETS.

    Hope this helps - let me know if you need any more information.

    Regards
    Colin
  • 0 in reply to Colin Gillmor
    Expert 2530 points

    HI Colin

    Thank you very much for your quick reply.
    I would like to ask you one more thing.
    If using UCC28951-Q1, I want to remove the PFC circuit in front.
    Is it possible to use it from 250Vdc ~ 375Vdc (bridge next to AC220V design)?
    How do I configure the flyback circuit for the 12V input stage
  • 0 in reply to KIM Andy
    TI__Mastermind 25570 points

    Hello Andy

    Yes, the PFC stage is not necessary. The UCC28951-Q1 will operate from a DC voltage generated at the output of an AC bridge rectifier. The Excel calculator for this device allows you to set the DC input voltage range and it will then run through the other calculations needed for your design. The duty cycle range (Dmin to Dmax) increases as the input voltage range increases, but 250Vdc to 375Vdc is achievable without difficulty.

    Regards

    Colin

  • 0 in reply to Colin Gillmor
    Expert 2530 points

    HI Colin

    Thank you very much for your quick reply.

     I would like to ask you one more thing.

    Can you get the excel file you mentioned ??

  • 0 in reply to KIM Andy
    TI__Mastermind 25570 points

    Hi Andy

    It's on the product web page at http://www.ti.com/product/UCC28950/toolssoftware

    Scroll down the page to 'Software 2' and select the Excel or Mathcad design tools.

    Be careful with the transformer turns ratio - which is displayed rounded to nearest integer. Use copy and paste to bring the unrounded value from cell C25 into cell C26 (both cells display the rounded value)

    Secondary voltage stresses on SRs are  twice those calculated

    Regards

    Colin