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UCC3895: Swapping Leg OUTA + OUTB with OUTC + OUTD

Part Number: UCC3895

Dear TI team,

I have a curiosity question.

Can I use UCC3895 in a PSFB converter to drive the passive to active (P->A) leg by the IC's outputs OUTC and OUTD?

The (P->A) leg should be driven by the OUTA and OUTB as according to the datasheet. The clock rise edge is sync to the OUTA and OUTB states directly, which probably indicates that 

these outputs are somewhat unique and non-interchangeable.

What are the implications for low load and high load lossess in the full bridge switches if OUTC and OUTD instead is used to drive the P->A leg?

Thank you in advance!

Best regards,


  • Hello RW

    The PSFB is a symmetrical topology - if you swap the OUTA/OUTB and OUTC/OUTD pairs then the voltage waveform seen across the transformer is unchanged. If diode rectification is used for the secondary then there is no need to make any changes to the secondary. If SRs are used for the secondary then their drive signals would have to be changed too - OUTE/OUTF below.

    There are some second order effects regarding the placement of any shim inductor and their clamp diodes. Usually the shim inductor is placed in the PA leg. Swapping OUTA/OUTB with OUTC/OUTD turns the PA (Passive-Active) leg into the AP (Active-Passive) leg but it is also possible to place the shim inductor in the AP leg.

    There are no control law implications.

    Hope this helps