Electronic – Ultra low ripple constant-current LED driver design

Basically you are putting a pot in parallel with Rsns in order to "allow" two current settings. Why don't you use a fixed resistor and a 0.1" jumper. Normally the jumper would be in place for the higher current thru the LED then you remove the jumper to activate the lower current feed. I also don't like pots much and would much rather use a resistor and jumper especially if the two settings are known and fixed.

If I understand your text you are asking how to control LEDs in the following scenarios:

• Continuous backlight dimmable.
• Strobed backlight where LEDs strobe in-synch with 3D lenses, also dimmable but at same average brightness as continuous mode.

You seem to think that you will have to use a different peak current for the two situations despite using PWM control. This is incorrect. What you do is set the max current of your system so that at, say, 40% PWM the LEDs are giving the required brightness. When you switch to 3D mode you pulse at 80% PWM but modulate the LEDs at the required strobe rate. Effectively you have a high-speed PWM controlling the average current to the LEDs and a low speed strobe synchronised with your camera.

Upper trace shows LED PWM current waveform during strobed mode. Note long on-time. Lower trace shows continuous LED lighting at half-current thus maintaining same average brightness on a longer time scale.