• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 64 subscribers
  • Views 648 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.

UCC28910 auxiliary power at primary side

K.Hamamoto
Guru 12155 points
Other Parts Discussed in Thread: UCC28740

Hi

Our customer are considering to use the primary auxiliary power for VDD and other IC. 

(Please see following image)

Is it possible to use by the following configuration?

Vdd_out is for other IC's supply voltage. 

The condition is Vdd_out=15~20V, Iout=0.3A (peak max 0.8A).

Please let me know if you have any question.

Regards,

Koji Hamamoto

  • 0
    TI__Mastermind 31580 points
    Hi Koji-san,

    The problem with this circuit is that when the main output load is reduced to light load and down to no-load the Vdd voltage will collapse as there will no be enough energy delivered to the Vdd winding to maintain its voltage within regulation.

    Regards

    Peter
  • 0
    TI__Expert 7395 points
    Koji-san,
    With PSR(Primary -side regulated = No optocoupler feedback), it's not recommended to use the aux winding for additional bias circuitry. Peter's comments are right on, but even with load at the main output, this heavy current and potential transient load on the aux winding would affect the output regulation because that signal is monitored to control the output. Even if you did a separate aux winding with PSR for biasing this additional circuitry of yours, you would still see the effect Peter describes.
    It's probably best to use a SSR (Secondary side regulated= uses opto feedback) solution like UCC28740 where you the cross regulation is better because of direct output feedback. that way, you could use an aux winding to bias your other circuit. it would also be recommended to use preloads on the outputs or zener diodes+preload resistors to maintain the cross regulation over all conditions.
    Regards,
    John
  • 0 in reply to John Stevens
    Guru 12155 points

    Hi Peter-san, John-san

    Thank you for your comment.

    I understand your comment.

    On the other hand, is it possible if the secondary output ( main output) is not used?

    Our customer would like to use this device only for the auxiliary power if this way affect to the output regulation.

    Regards,

    Koji Hamamoto