How would I manually dim an LED TV backlight?

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  • ohren
    Senior Member
    • Mar 2015
    • 119
    • Sweden
    #1

    How would I manually dim an LED TV backlight?

    Hello! I thought I'd repurpose a 55" 4k Philips led tv backlight for something else (7 strips, ~45 V), and thought I'd get the dimming working without the logic board.

    Measuring the PSU "dim" pin upon startup (I assume 100% brightness here) gives 3.3 V, and after it's dimmed down a bit I get less voltage. Giving that pin a constant 1.8 V seems to result in full brightness, so I'm assuming it uses PWM.

    1. Is this a reasonable assumption?
    2. If yes, what are reasonable values for frequency and duty cycle? Does it matter what I use, or can I experiment freely without causing damage?

    I don't have an oscilloscope so I'm just looking for some guidelines if anyone is willing to share their intuition — don't know exactly how logic boards usually communicate backlight levels nor exactly what the power board does with that signal, so I didn't want to assume too much. Is the signal generally interpreted or used raw?
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