'fraid so. My understanding is that the dimming is strictly by varying duty cycle in a pulsed constant current source. That's how Huw's circuit works as I recall. The spec sheets for the Luxeons seem to require a constant current somewhere between 750ma and 1000ma for operation. I'm left wondering if his inability to get a harder contrast than 4.5 comes from some sort of intermittency effect. Would raising the frequency help. I have an old book by Zakia suggesting that intermittency effects go away as the pulse frequency goes above a certain point. Is low MHz sufficient? Any phys chem dudes out there?
Originally Posted by argentic