• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 255 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.

UCC28740: reducing transformer windings, want to power multiple branches off Vdd power source.

Steve j
Prodigy 10 points
Part Number: UCC28740

Tool/software:

I have a system with several secondary windings, I'd like to reduce these 4 windings down to 2. We have one 24V rail which is the regulated rail. Then the other windings I would like to combine and tap off to produce my needed base voltages for post regulation. 

With the UCC28740 I understand the need for the VS pin to monitor a secondary winding voltage directly. 

I often see flybacks with designated aux windings for their own power supply. I cannot find a reason that this is mandatory. I would like to combine this aux winding into the tapped winding system and place the valley switching detection node on that winding. This won't affect the valley switching functionality at all will it? I can't see that it would, but didn't know if there was a relationship between Vdd & VS that I'm not realizing. 

Primary : regulated secondary

Primary : unregulated multitap winding feeding flyback IC, gate drive & processor

  • 0
    TI__Genius 15546 points

    Hi Steve,

    I will be back to you tomorrow.

    Thank you

  • +1 in reply to Manuel Alva Hernandez
    TI__Genius 15546 points

    Steve,

    -You can bias UCC28740 controller with a aux winding regardless if this winding is biasing another components (gate driver, processor). 

    -Sensing of Input Voltage and secondary voltage needs to happen across VS pin and this can be done using the same aux winding. See examples below from DS.

    -Keep in mind that vias through VDD and sensing through VS is recommended to be through an aux winding at the primary side. If not, you need to go through isolation to go from secondary to primary and that might complicate the BOM (extra components needed) and increase standby losses.

    Thank you 

  • 0 in reply to Manuel Alva Hernandez
    Prodigy 10 points

    Thanks for the reply. This confirms my thoughts. 

    We have 2 main power networks, an isolated 24V secondary and the DC- referenced control and gate drive. The DC- is the same reference the primary uses so no need for isolated VS measurement.

    Just wanted confirmation hanging other systems off the VS monitored winding wouldn't upset the control.