PMP8787: half bridge and quasi resonant mode

Part Number: PMP8787
Other Parts Discussed in Thread: UCC28700

the file mentions this design sues high efficiency with the quasi-resonant mode, are all the plots in the test results using this mode?

We'd need to be able to have the input be a half-wave rectified input. Can the design accommodate this, and if so, what changes would need to be made?

  • Hi Nicholas,

    The UCC28700 operates with a control law that includes quasi resonant switching.  Essentially, the controller turns on the primary FET during the valleys of the quasi-resonant ring on the switch node.  The part is always switching on the valleys, so yes this is included in the test results.  Much more information about the control law is provided in the datasheet.

    For a half-wave rectified input, you will need much more capacitance on the input to hold up the input voltage between 1/2 cycles of the AC input voltage.  This does not affect the design of the UCC28700 circuit.