• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 507 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

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.

UCC28722: Reliability

Gerardo Tadeo de la Garza Mora
Prodigy 380 points
Part Number: UCC28722

Hi,

How can we guarantee that the device will always switch at the valley at the right time under any condition?

 I looked at a couple of designs we have with this device trying to find specifically load jump conditions, but I had no luck. Could you help me out with this question?

thanks!

Tadeo

  • 0
    TI__Guru* 86286 points

    Hello Gerado,

    The UCC28722 controller controls the converter’s duty cycle of the converter with peak current modulation (AM) and frequency modulation (FM).  This converter always is operating in the DCM range.  This control methodology is known as control law.

    To achieve valley switching the UCC28722 controller will determine which valley to turn on the BJT to maintain the appropriate duty cycle. This is based on the converters control law represented in the data sheet in figure 15. Depending the on the required duty cycle the converter could turn on during the first valley, second valley, third valley, etc…

    The UCC28722 monitor’s the transformer current through the auxiliary to secondary transformer turns ratio and looks for zero current/zero voltage transitions. If the controller has determined it should turn on the switch it will look for a zero voltage transition on the aux winding beforehand and delay the turn-on of the switch by roughly 500 ns. This will ensure the BJT turns on when the BJT’s collector is ringing towards the valley.  

    Regards,

    Mike