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UCC28810EVM-003 - short circuit behaviour and variable output lines

1) The circuit board only works, if all 4 outputs are used. As soon as only 1, 2 or 3 output lines are used for lighting LEDs, it does not work. How do we have to modify the electronic circuit board that it also works if only 1, 2 or 3 output lines are connected?

2) Short circuit behaviour: If one SINGLE output  is on short circuit THREE LED-output lines fail.  This is valid for each output to be on short circuit. The final electrical parts heat up massively and will most likely burn. We need to have the electronic circuit board modified, that each of the four output lines can be independent and permanent on short circuit, without harm to the board.

I am very grateful for a response on how to achieve this.
  • Georg:
    UCC28810EVM-03 uses DC transformers to drive LED strings. The secondary of the DC transformer is full wave rectified to drive two LED strings. In this configuration, each transfomer needs two strings of LEDs to work. You can change the full wave rectify to bridge rectify and one transfomer will drive one LED string. In that case, you need 4 transformers to drive 4 LED strings.
    There is no easy way to implement short circuit protection for DC transformers. If you really have concern about short circuit over heating, try to use buck converter instead of DC transformers for the second stage. But that is going to be a big change of the eval board.
    David Zhang
  • Dear David,

    thank you for your prompt and detailed response. We understand the problem, but isn't it possible to use a Smart FET


    with short circuit prevention which opens the string to avoid this behavior?

    How would the open string protection work?
    Will it be the same behavior like short circuit?

    Thank you and best regards,

  • Georg:
    The smart FET can provide over voltage protection which works as open LED string protection. When the LED string is open, the output voltage is higher than normal operation. It does not work for the LED short protection. When the LED string is short, the output current does not increase beacuse the LED driver is a constant current source. The smart FET can only do over current protection.
    David Zhang
  • Hello David Zhang,

    Thank you for your advice.
    How can we redesign the circuit with 4 transformers?
    Can you provide us with a design example?
    Will the efficency decrease? (We excepcted about 90%)

    We have a 100VDC supply and want to drive 4 LED strings, each of them with short and open circuit and it has to be isolated!
    Is there a better switcher concept? Only a isolated flyback and 4 deticated buck LED driver?

    Thank you for your support, we hope you can help us,

    kind regards