• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 435 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.

UCC28782: RDM resistor and the demagnetic time?

fleming fu
Prodigy 130 points
Part Number: UCC28782

But if the resistor is fixed, how can we estimate the demagnetic time?

in the application, the resitor is fixed, whether it means that the demagnetic time fixed too even in different load/input?

there's only the formula of the resistor as below. Also if the resistor is larger or smaller than the calculated value, what's the result?

  • 0
    TI__Mastermind 40120 points

    Hello Fleming,

    Thank you for your interest in the UCC28782 ACF controller.

    The RDM value calculated according to the equation will result in an emulation of the demagnetizing current slope based on the reflected output voltage sensed at the VS pin.  The UCC28782 incorporates an internal tuner circuit that can adjust the PWMH on-time to accommodate wide variations in many circuit parameter tolerances, including the magnetizing inductance.  

    The RDM resistance sets the nominal condition and the internal tuner makes the necessary adjustments to suit the actual operating condition.
    If the RDM resistance is set higher or lower than calculated, then some of the tuning range in one direction or another is used up. 
    In other words, it will not be able to tune adjust over the full range of tolerance in one direction and adjust too much in the other direction.

    Since the tuning range is wide, some minor deviation from the calculated value is okay, if necessary.  

    Regards,
    Ulrich