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UCC28951: UCC28951 PSFB with Full-Bridge SR

Benjamin Sprague
Prodigy 60 points
Part Number: UCC28951

Tool/software:

Posting for a colleague:

Project Specs:
Vout: 24VDC
Vin: 550V
P=500W
I am using UCC28951 (PSFB topology) IC for DC-DC isolated power supply project. I have a full bridge synchronous rectifier on the low voltage (secondary) side instead of a half bridge synchronous rectifier.
On the secondary side, PWM signals for E and F (SR FETS) coming from the UCC28951 ic are fed to diagonal switches of the bridge through a half-bridge gate driver ic (2EDL8124G3CXTMA1). Recently, I looked at the forum and found that PWM signals for E and F both could be high simultaneously during the free-wheeling duration. 
https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1400335/ucc28950-q1-centre-tapped-or-full-bridge-synchronous-rectifier?tisearch=e2e-sitesearch&keymatch=UCC28951%252525252525252520full-bridge#
In our project, under the same scenario the gate drive ic would not pass PWM signals to the switches when both the signals (E and F) are high simultaneously and hence it will avoid shoot through.  At the same time the anti-parallel diodes would be conducted during the free wheel time.
Do you see any issue in our design?Is it possible not to use PWM (E and F) signals instead just to use full bridge diode rectifier? Definitely efficiency will be compromised in that case.

  • 0
    TI__Guru* 85616 points

    Hello,

    Your inquiry is under review and I will get back to you shortly.

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 85616 points

    Hello,

    You do not have to use Out E and Out F.  I would still terminate the outputs to ground with 10 k ohm resistors to ground.

    There has been many designs of phase shifted full bridge using a rectifier output, so this can be done.  When using an SR bridge just make sure you get the timing correctly.  When QA and QD are on at the same time, you will need to drive two FETs in your bridge.  When QB and QC are on at the same time you will need the other two FETs on in the bridge.

    You could actaully use two half bridge drivers, OUT A , B, C and D with two and gates to feed to the H Bridge drivers.   Out A and Out D would need a resistor divider to drop the voltage down to 5 V max to feed the and gates.  Out A and Out D would be fed into one and gate, Out B and Out C would be fed to the other and gate.  You then would use the output of the and gates to control your FET driver.

    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,