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UCC28950 600-W, Phase-Shifted, Full-Bridge

Harrison 2011
Expert 2085 points
Other Parts Discussed in Thread: UCC28950, TAS5630

Hello,

 

in slua560c,UCC28950 600-W, Phase-Shifted, Full-Bridge

Application Report

 

on page 3, it says "Select transformer turns based on 70% duty cycle (D

 

MAX) at minimum specified input voltage. This will give some room for dropout if a PFC front end is used."

does this mean that D could go higher such as 0.85 when PFC input even drops lower than the minimu 370v?

I thought Dmax is already calculated using the minimum input voltage, could you please explain it a bit?

Thank you,

 

  • 0
    TI__Guru 74095 points

    The datasheet (page 3) specifies Dmax can be as high as 95%. So it is ok to use a maximum duty cycle of 85%.

    If PFC front end is the input of the converter, usually the requirement of hold-up time from one line cycle missing exists. In such a case, the converter input volage may drop to a value lower than 370V. But exact number can be designed, usually maybe about 350V or so. So a larger Dmax is needed in such a case.

    Besides, even if there is no front end PFC, the requirements such as load regulation from power losses, and load transient response, etc,  the Dmax should be designed with these factors into account in addtion to the minimum input voltage.    

  • 0 in reply to Hong Huang
    Expert 2085 points

    Hi Hong,

     

    Appreciate it a lot for your answer, it greatly helps.

     

     

  • 0 in reply to Hong Huang
    Expert 2085 points

    Hi Hong,

     

    if I set the maximum duty cycle to 50% instead of 70% , ie.50% at minimum input voltage,370v, how will this affect the performance or so?any problems?

    I am trying to use an off-the -shelf planar transformer which is specified at this duty cycle to have the voltage I want.

     

    thank you very much,

  • 0 in reply to Harrison 2011
    TI__Guru 74095 points

    The transformer turns ratio should be reviewed with 50% maximum duty cycle at 370V input to make sure the output voltage is still in regulation. If the transformer turns ratio has to be changed to adapt the maximum duty cycle 50%, then the secondary side MOSFET voltage rating may need to review too to make sure their rating is still sufficient.

    These would be main checks.

  • 0 in reply to Hong Huang
    Prodigy 30 points

    Hi Hong,

    I received an evaluation version of the TAS5630 design from our local TI representative, but he was unable to locate a version of the SLOU293A 600W power supply design in manufactured form. I really would like to test the TAS5630EVM with the 600W power supply. Is there an evaluation version of the power supply that I can obtain? If not, the SLOU293A.pdf file mentions Gerber files; could I get a copy of those so I can try getting the design made to test?

    Thanks for your time.

     

    HK