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About LED Driver dimming

Gary An
Intellectual 440 points

Hi all,

I have questions about current and PWM dimming.

1. Current dimming controls the output current. PWM dimming controls duty cycle, if the duty cycle is reduced, output current also will be reduced.

Both of dimming method controls actually output current, I cannot find the different. What are the different? 

2. Current dimming has low efficiency at low brightness(Low current), can you explain the reason?

3. PWM dimming has lower efficiency than current dimming at high brightness, can you explain the reason? 

4. Current dimming is not linearity, and PWM dimming is linearity, but I could not understand. Can you explain the reason?

 

Thank you

  • 0
    TI__Mastermind 22745 points

    Hi Gary,

        I guess your "current dimming" means the analog dimming mode. The different efficiency is due to the internal current sinks, for the current sink, it needs a headroom voltage to deliver the current. For analog dimming mode, the headroom voltage is linear to the current while for the PWM dimming mode, it needs to keep the headroom voltage to the maximum current.

        For both analog dimming mode and PWM mode, all should be linear.

    BR

    Sean