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LT3518 Open LED protection

Hi,

My customers are considering LT 3518.
So I got a question.

#1  Although there is description "open LED protection" in the feature portion of the data sheet, How do you protect

      Open LED?
      The method of protection is not described in the data sheet and I do not know how to use it.

Best regards,

Yuya

  • When the load is removed, or the LED string has an open, current no longer flows into the output.
    Once this happens in an LED driver, the current sense resistor sees no voltage (no current * R = no voltage).

    So, the loop tries to push harder, for more current. However, the result is that the output voltage climbs, but the LED current remains zero.


    To protect against this, the output voltage is set at a limited voltage with the feedback pin (FB). Most simply, two resistors set the over voltage protection point, as seen in most schematics. This is easy to do and one can follow the rules for OVP and setting FB in the datasheet.

    For 20V LEDs string, set OVP to about 24V as an example by setting the regulation point of FB with resistors to match 24V output. When the LED current is in regulation, the LED string voltage will remain below 24V and the circuit will run well. When the LEDs are removed or open, the current goes to zero and the output climbs, and stops, at 24V.

    That is how open LED protection works.

    Thanks,

    KSz