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LED current control in Pattern Sequence

Aaron Gong
Prodigy 85 points
Other Parts Discussed in Thread: DLPC300

Hello,

I have a few questions about LED current controls in Pattern Sequence mode.

1) As it is right now, the current on the 530nm needs to be at least (1) in order for any of the LEDs to turn on during pattern sequence mode. In fact, if the 530nm channel is set to (1) and the other channels are set to (0), those other channels will still output light at their minimum (1) output settings. Is there a solution available that would shut off the LEDs if their channel was set to (0)?

2) Also, in general, the lowest output I can achieve from the LEDs is about 30% of the maximum output value. Is it possible to achieve output power less than 30%?

Thanks,

Aaron

  • 0
    TI__Mastermind 30875 points

    Hello Aaron,

    #1.
    Very interesting finding. Thank you for bringing it out the behavior in the E2E forum. I appreciate your keen observation.

    The reason, in the pattern sequence mode, actually the the LED_Enable signal coming from the DLPC300 is ALWAYS on the GREEN (LED_ENABLE) channel. Now the FPGA does the functionality of providing the user selected color by appropriately sending the incoming GREEN channel enable signal into RED or GREEN or BLUE enable channel going to the LED Driver circuit.

    Now, when you set the GREEN LED current = 0 inside the DLPC300 we are disabling the GREEN channel output (GREEN_LED_EN) signal going into the FPGA. This would cause FPGA not to generate the signal for driving the user selected color. Hence you are not seeing output unless setting Green LED current = 0. This is a minor bug in the software, we will correct it in next release.

    Use the the bellow logic till then -

    A). To turn-on user selected LED_Color, set the LED current of the color + set Green LED color = 1.

    For example:
    To use Red LED, then set RED LED current + Green LED current = 1
    Similarly, for Blue LED, set Blue LED current + Green LED current = 1
    Green LED can be used as it is.

    B). To disable or set the LED current = 0, do the following,
    Set Red LED = 0 and also Green LED = 0.
    Similarly for Blue LED, set the Blue LED current = 0, and then Green LED = 0
    Green LED can be used as it is.

    #2.
    Along with reducing the LED current, the lower intensities can be achieved by reducing the RATIO of PE(Pattern Exposure):TP(Pattern Trigger Period).You can use this approach only if your design allows reducing the pattern exposure time.

    For example: Lets say you are running 1bpp pattern with Pattern Exposure = 250us and Trigger Period = 250us.

    From LED driver circuit, setting current = 1 goes to list value.

    From here, just start reducing the Pattern Exposure time = 200, 150, 100, 50 ,10 etc..

    This will reduce the intensity.

    Regards,
    Sanjeev