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UCC24624: Is it available to apply ucc24624 to all converter using a center-tapped rectifier (PSFB)?

sunho lee1
Prodigy 100 points
Part Number: UCC24624
Other Parts Discussed in Thread: UCC28950, UCC28951, UCC27324

Hi, i want to ask that if it is possible to ucc24624 to PSFB converter operates in DCM or CCM

which has a center tapped rectifier .

The target topology of PSFB converter is shown in the figure below.

Unlike LLC, it has an inductor on the secondary side, so i wonder is it possible to apply ucc24624 in this structure.

If possible, the converter operates in either  DCM  or CCM  according to the value of the output current

, similar to the converter of the ucc28950.  

In summary, I am wondering if ucc24624 is applicable to PSFB converters with DCM / CCM operation.

  • 0
    TI__Mastermind 25570 points

    Hello Sunho

    The short answer is that it is possible to use the UCC24624 to control the SRs of a PSFB but it's not a good solution. The UCC28951 PSFB controller has two outputs (OUTE and OUTF) specially dedicated to controlling the SRs. You can use the UCC27324 gate driver for the SRs

    If you use the UCC28951 then you get SR control 'for free' and you will get better light load performance because the controller disables the SR drives at light loads. Ideally this is done at the point where the SR gate drive losses become equal to the body diode conduction losses - in any case the user can control the load at which this happens,

    Finally - The UCC28951 device is an enhanced version of the UCC28950. It is a fully compatible drop-in replacement for the UCC28950. Refer to application note SLUA853 at http://www.ti.com/lit/an/slua853/slua853.pdf for more details.

    Regards

    Colin

  • 0 in reply to Colin Gillmor
    Prodigy 100 points

    Thanks for the answer. It seems that my curiosity is almost resolved. But one more.

    I wonder whats the reason of  'UCC24624, but it's not a good solution for PSFB '. 

    I think that drain-source sensed SR controller (UCC24624) is a little sensitive than UCC28950 or UCC28951 in heavy load condition. is that right?

    Thanks for considering.

  • 0 in reply to sunho lee1
    TI__Mastermind 25570 points

    Hello Sunho

    That's a fair question - here are three reasons for not using the UCC24624 in your application.

    1/  As you correctly point out, the UCC24624 monitors the Vds of the SR to decide when to turn it on and off. This method works well but requires very careful PCB layout so that the SR controller is not affected by noise - this is especially true at light loads.

    2/ The UCC28951(0) provides dedicated SR drives which do everything that the UCC24624 does but with fewer problems with noise. The UCC28951(0) DCM mode function disables the SR drives at light loads for better efficiency.

    3/ In general I prefer the simplest solution that will do the job and using the UCC24624 is an unnecessary complication.

    BTW: The LLC topology operates in a completely different manner and for that topology a dedicated SR controller is needed - like the UCC24624.

    Regards

    Colin