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UCC28710DR: output voltage out of control

wu shaohui
Prodigy 30 points
Other Parts Discussed in Thread: UCC28710

Hi Team,

We use the UCC28710DR on our product, it is already mass production and no problem. But recently we found some issue during PWA function test. The output voltage out of control. The detailed please below.

Design specification:

Description Minimum  Typical  Maximum Unit
RMS Input Voltage 85 230 265 V
Output Voltage 28 30 32 V
Output Ripple Voltage     0.13 V
Output Load Step
10% to 60%, 60% to 10%		 28   32 V
Output Current     0.735 A
Switching Frequency     70000 Hz
Full Load Efficiency Typical 0.87     %

Schematic:

Phenomenon and questions:

1. During mass production some PWA's Vbus voltage out of control and up to 70Vdc (setting is 32Vdc) under 245Vac power supply, the 70Vdc Vbus will drop down after rated load (such as 20W)

2. The Vbus voltage is ok when power supply from 110Vac to 240Vac 

3. We check the components R33,R34 and R31 and all no problem  

4. We doubt the transformer's feedback winding with some problem, such as bigger variant on its parameters

 5. Could you please give some comments about this issue? Which component is potential risk for this?

Thanks

Shaohui Wu

  • 0
    TI__Mastermind 21835 points

    Hi Shaohui Wu,

    Thank you for the query on UCC28710.

    Before I can comment on the specific, could you please provide details of transformer (turns ratio and primary inductance) to verify the schematic and see what potentially could be triggering this issue? There could be number of issues like aux winding waveform (and how this is connected to Vs pin), snubber circuit etc. 

    Regards,

    Harish