• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 83 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: Secondary side resonant circuit

Kaji@PAN
Mastermind 7805 points
Part Number: UCC28782

Tool/software:

Hello,

I previously asked a question about secondary side resonant circuits in the following thread.
I would like to ask two additional questions about this.
(Question 1)
There are two configurations for secondary-side resonant circuits: primary resonance and secondary resonance.
At present, primary resonance seems sufficient for my circuit.
However, I am not sure which configuration is better to adopt.
Are there any criteria for deciding which configuration to use?
(Question 2)
You said that because ACF relies on the resonance between the transformer leakage inductance and the resonant capacitor, changing one element usually affects multiple other elements.
However, even when I look at equations (9), (10), and (11) on the datasheet, I don't understand whether they have any effect on the CO1 and Cclamp settings.
For reference, could you please tell me how (9), (10), and (11) affect the results?

Best regards,

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1521840/ucc28782-unstable-operation

  • +1
    TI__Mastermind 40580 points

    Hello Kaji-san, 

    For Q1: 
    With UCC28782 ACF design, the two configurations for secondary-side resonant circuits: primary-side resonance and secondary-side resonance.
    In general, primary-side resonance is simpler to implement and can typically achieve ~94% conversion efficiency (in most cases).  
    Secondary-side resonance can typically improve efficiency by another +1% at the cost of more complexity and fine-tuning effort.  
    (Efficiencies are typical expectations with good design practice, but not guaranteed.)

    For Q2: 
    Leakage inductance and resonant capacitance do not directly affect the parameters of (9), (10), and (11), but can have an indirect affect on them.
    My statement was intended to be more generalized because the original post involved adding 470pF to the high-side GaN Fet. 
    Changing the total switched-node capacitance will affect the optimal value for RTZ.   
    Changing Llk only will change the resonance time which affects minimum frequency.  If f(min) cannot change then Lm must change which affects RDM. 
    Changing from primary-resonance to secondary-resonance (or vice-versa) may or may not lead to additional changes depending on whether certain design targets must be held firm or can be flexible. 

    My main point is that it is best to go through the entire Excel calculator tool each time some parameter is changed to see how it may affect other parameters. 
    It is not always obvious what effects a single change can have on the system.  Sometimes it is obvious, like changing the OVP set point, but where resonance is concerned it is better to be thorough. 

    Regards,
    Ulrich