PW driving LEDs

[MikeEvans]

I've built a color changing circuit to cycle 3 colors (red green and blue) of LEDs. I have cycling pulse width circuits for each color. I watched on a scope as the pulse duty cycle shortens and the LEDs don't noticeably dim until the pulses drop to 10-15%. For the short times when one LED is driven under 15% the color changing is pretty cool! I guess I could adjust the circuit to PW at 15% to 0% to 15% rather than 100% to 0% to 100%

Mike

 

[Doug Owen]

If I follow you, yes, that will 'solve' the saturation issue, but at the expense of dynamic range (you'll only have 15 one percent steps, not 100). Another way is to modify the driver so it takes 100% (or nearly so) to make 'full blast'.

Doug Owen

 

[MikeEvans]

15% would be too low, I think 30% max is what I'll try. Steps aren't an issue, it's an analog circuit. I still lack driver section yet so I've only tested at lower current but other than the cycling speed/pattern I like the results. I was going to use 1/3 amp constant current sources to drive the luxeons but by keeping pulses so short I should be OK using 1/2 amp source. Drivers will be on/off switching only to avoid heating so no adjustment there.

Mike