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UC1825A: Please refer to description

Bob Aivati28
Prodigy 70 points
Part Number: UC1825A
Other Parts Discussed in Thread: TL431, UC1825

DC DC converter-- interleaved fly back converter:

Vin= 28-23v

Vout= 5v (Master output @17A)

Two 75W flyback interleaved and working 180 degree out of phase using UC1825A.  Feed back loop is closed non isolated. works and regulates fine.

Question:

Having trouble to close the loop in isolated config using opto and TL431.

Has anybody tried this? Any app note / software that can help?

thx 

  • 0
    TI__Expert 7445 points
    Hi Bob,

    Can you elaborate what trouble you are having. Can you share your schematic.
  • 0 in reply to Ramesh Khanna
    Prodigy 70 points

    Hi Ramesh,

    I do not think the copy and paste the schematic is needed.  This is a question of how to properly bias the TL431 and the opto in an isolated 5V (main) flyback--come up with the compensation values around the error amp when using UC1825. there are a few ways to do this:

    1)Opto is fed from the output.  In this mode TL431 will be a automatic type 2, but the resistor setting the LED current also effects the gain-- Opto configuration: common emitter   

    2)Opto is fed from the output.  In this mode TL431 will be a automatic type 2, but the resistor setting the LED current also effects the gain-- Opto configuration: common collector which then requires another inversion which the internal error amp of 1825 can be used

    3)Dedicated Opto supply, TL431 WILL BE DESIGNED as type 2. The gain can be adjusted without effecting the LED bias current.

    Thanks

    Bob

  • 0 in reply to Bob Aivati28
    TI__Expert 7445 points
    Bob,

    You can use the following reference, it is a good article and will help you address your concerns.

    cbasso.pagesperso-orange.fr/.../TL431addedRC.pdf