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DLP4500: Controlling DLP4500 LEDs with a constant current

Part Number: DLP4500
Other Parts Discussed in Thread: DLPC350

I have tried to find the answer for this question in the DLP forum but only found a similar thread https://e2e.ti.com/support/dlp/f/94/t/378732

I'm using the DLP in pattern sequence mode to display one bit images with a fixed exposure time from an HDMI source. From what I understand the LED control is done using a PWM method. This means that, during one pattern exposure, the LED blinks very fast. This is causing big problems with my experiment.

So, I want to set the LED to a fixed current in order to avoid the blinking effect. I believe that putting the PWM value to the maximum using USB command (USB: CMD2: 0x0B, CMD3: 0x01) should put the current to a constant value. However I don't want to use the maximum current.

Is it a way to define a constant current (not maximum) for the LEDs using software or hardware? I'm following the DLPC350 Programmer’s Guide (http://www.ti.com/lit/ug/dlpu010g/dlpu010g.pdf) and using commands (USB: CMD2: 0x0B, CMD3: 0x01) and (USB: CMD2: 0x1A, CMD3: 0x07).

Best regards,

  • Hello Pedro,

    You should be able to use LED Enable Output command (see programmer's guide section 2.3.7.1) to keep the LEDs always enabled. The LED pwm output from the DLPC350 controller is then used to control the LED brightness. However, this signal does not actually PWM the LED itself. It is used to set the LED at a constant current. See the schematic below for the red LED driver (a similar driver exists for the blue and green LEDs):

    Thanks,
    Kyle