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AC-DC 5V-15W POWER Using UCC28740D issue

Hoang Manh
Intellectual 380 points
Other Parts Discussed in Thread: UCC28740

Hi all,

We are using UCC28740D from TI for designing our AC-DC module with output 5V@3A.

The design is based on one reference design for UCC28740D.

But our module can not supply output 5V like expected...

Attached are our design, UCC28740 reference design, Output waveform from our module and Transformer datasheet.

Please help take a look at the output waveform and give us any idea. Also let me know if you need any information.

Thanks and Best Regards,

Hoang Manh

1. Our Design:6036.AC-DC 5V-3A.pdf

2. UCC28740 reference design

UCC28740D_REF_5V_3A.pdf

3. Output waveform from our module:

4. Transformer datasheet:

BCK2001-247 最新资料.pdf

  • 0
    TI__Guru* 86266 points

    It looks like your power converter is coming up into a fault.  This device during power up looks for input under voltage, over voltage and over current.

    I am not sure which one of these faults your are activating.

    To see if this is the case study VDD, DRV, CS and the auxiliary winding voltage. If VDD is transitioning between VVDD(off) and VVDD(on) you have a fault condition.  You should be able to tell which fault based on these signals as well.

    There are some instructions in regards the aux signal that should be observed as well.  Page 14 goes into detail of what the auxiliary winding's signal should be to prevent false OVP or regulation issues.

    Regards,

    Mike

     

  • 0 in reply to Mike O'
    Intellectual 380 points

    Hi Mike,

    Thanks for the response.

    We will capture some waveform at VDD, DRV, CS and the auxiliary winding voltage.

    Besides, right now we have 3 modules of AC-DC boards, on others 2 boards, the waveform is different:

    You can see the output is more stable, but it just can reach ~4V (not 5V like expected).

    Please let me know if you have any idea.

    Thanks,

    Hoang

  • 0 in reply to Hoang Manh
    TI__Guru* 86266 points
    Hello Hoang,

    Your transformers might be different. If there is excessive ringing on the transformer or the deration of the leakage spike is too long it could cause the supply to activate a fault. I would study the previously suggested test points on both the good unit and failed unit. There is most likely a substantial difference between the two.

    The auxiliary winding needs be clean and within the guidelines specified on page 14 of the data sheet.

    Regards,

    Mike