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UCC28711: ucc28711

Part Number: UCC28711

Tool/software:

Hi,

I am Having issue with the controller that the output is going to some protection but as soon as i turn off AC input, after i second like that the output comes before discharging to zero. I am getting Square wave kind of pulses in NTC pin. What might be the reasons.

It would be very helpful if you help me solve it.

Thanking You.

  • Hi Cs power,

    Thank you for reaching out.

    Please probe if there is any output overvoltage is occuring. Page 12 of the datasheet shows potential reasons for shutdown. For OVP I would recommend checking AUX winding instead of the Vs pin.

    Regards,

    Harish

  • Thank you for the response

    At AUX waveform I observed that there is a negative spike of 70 V. The transformer turns are Primary 18 ,secondary 5, aux 4 turns. and the output is 24V . Does this effect the VS pin because after some time the Vs pin impedance become 106 Ohms and the R1 of divider of Vs is 110K ohms.

  • And The ouput going to protection. Like this we have changed to a new one ,That also same thing Happened and the both ic got damaged

  • Hi cs power,

    Definitely if the spike on Vs pin is above the abs max rating then it will damage the IC. Since OVP is also being triggered, I would suspect if the transformer has excessive leakage potentially leading to this effect.

    Regards,

    Harish