ucc28061 operate in the same phase

I  desire using ucc28061 to design a 2000w PFC,but sometimes the DRA and DRB output the same phase driving signal,this is very dangerous,especially in high power situation.dozens of MOSFETs  I have already destoryed,when i pull up the power at 1700W.would you please give me some suggestion,especially the POWER BOARD layout.

  • Can look in the schematic diagram and parameters.Last year I did a 2000 w out the products in the United States.
  • I'm new to this device and have noted the some behavior under various conditions.

    I'm led to believe (from this forum) that GDA and GDB are held 180 degrees out of phase by a PLL. This takes some time to settle so for a few cycles after commencing operation they start in phase and then drift to the correct 180 degrees out of phase. So as my prototype stands now I only see this at power up. However this was not always the case.

    In my application the internal soft-start was not sufficiently slow and the start up current was excessive. I think this caused saturation in the inductors and the Zcd input lost a sensible signal. Hence the UCC28061 would shut down multiple times during start up and up and restart. Each time the GDA/B would be in phase again.

    Also I initially had insufficient turns on the current sense windings that drive the ZCD inputs. Hence near the zero crossings of the mains the sense winding voltage was too low and the UCC28061 would not detect the zero current point. Hence several restarts would at every mains zero crossing. Note my ZCD resistor was the correct value for the low turns I still had aprox 2mA maximum current.

    Problems related to the Zcd input seem easy to spot as the UCC28061 will stop switching for 200us then restart. After the restart the GDA and GDB will be in phase for several cycles and then drift to 180. This is discussed in the datasheet in one of the notes to the main table:

    (4) An output on-time is generated at both GDA and GDB if both ZCDA and ZCDB negative-going edges are not detected for the restart
    time. In single-phase mode, the restart time applies for the ZCDA input and the GDA output.
  • In reply to DEP:

    Hello Dep

    You are correct - the UCC28061 uses a PLL to force the 180 degree interleaving. The PLL takes some time to capture the correct phase and will always start with the two phases at 0 degrees to each other.
    Getting the ZCD circuit to work at peak of line is also not always easy -

    It seems to me that you have made substantial progress and are on the right track but do please post again if you have any more problems.

    Regards
    Colin