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UCC256304: about multiple output on LLC topology

ACGUY
Guru 11170 points
Part Number: UCC256304
Other Parts Discussed in Thread: UCC28180, , UCC28056

Hello E2E,

Our customer is planning to design a 550-W AC/DC power supply unit.
I suggested the UCC256304 and UCC28056 or UCC28180 for primary side devices.
That power supply has 5-output, they are no-isolateed.
Customer's request is "5-output from 1-transformer".
Is it possible on LLC?

Regards,
ACGUY

  • 0
    TI__Guru 73495 points
    How do you want to achieve the five outputs from 1 transformer? Are you going to do one output with four post regulators such as buck? If so, it is ok to get 5 outputs from 1 transformer on LLC. If you want to use 5 windings and use cross regulation, each Vout regulation is loose. I recommend you use 1 winding on the secondary and add four post regulators of buck for this application, particularly, no isolation is needed between these 5 outputs.
  • 0 in reply to Hong Huang
    Guru 11170 points
    Hello Hong,

    Output voltages are 32V, 5V,12V x 2-line and 24V.
    I suggested that 1-transformer and 4-DC/DCs. However, our customer is worried to efficiency descend.
    What if, efficiency 90% for LLC-converter, 90% for DC/DCs, total efficiency to be 0.9*0.9=81%.
    That design spec is 85% over.
    If possible, we want to delete DC/DCs.

    Thanks,
    ACGUY
  • 0 in reply to ACGUY
    TI__Guru 73495 points

    Here is my experience on efficiency estimation.

    LLC stage should be at about 93%. The DC-DC should be > 94%. So the total efficiency should be around 88%.

    Both LLC stage and DC-DC are possible fine tuned up to close to 95%.

  • 0 in reply to Hong Huang
    TI__Guru 73495 points
    As no further info from you, I assume this is resolved. If additional support is needed, please open a new thread. I am closing this thread.