At 06:32 PM 9/18/2007, David Kao wrote... >I never said it won't work. The record speaks for exactly what you've said. >Try two 3 watt LEDs with a resistor of single digit value. All of the examples I gave, which you said were wrong, used standard LEDs and resistors. I've also said that Luxeon type high power LEDs are properly driven with constant current sources, and the manufacturer agrees: "LEDs should be driven at a constant current" - Luxeon. A properly designed regulator would adapt if one of the LEDs shorted out. Here's a simple current source based on a cheap LM317: http://led.linear1.org/a-cheap-current-regulated-luxeon-star-driver-design/ I suspect that all but the cheapest Chinese high power LED flashlights use a similar circuit. If someone wants to try running them in series, it would be easy to see what happens in the very unlikely event one of the LEDs shorts out - try running a single one from 12V. Luxeon certainly recommends constant current sources for driving their LEDs. Driving LEDs in series is highly desirable for battery operated applications, since otherwise a lot of efficiency is wasted as heat when using low cost linear buck regulators. With a constant current source driving 3 LEDs in series vs. driving 3 LEDs in parallel, one uses only 1/3 of the power. They even sell a current regulator which can drive multiple LEDs in series ( http://www.luxeonstar.com/item.php?id=1747&link_str=240::241::1396&partno=2008B-700 ). As they say "The 2008 accepts a wide input voltage range and can power up to (6) High-Power LEDs in series." (but you can only do 3 in series from a 12V source, because the Luxeon modules have voltage drops of around 3.5V) I'd just build a cheap LM317 one, though. All of your arguments about voltage drop differences causing different output, and one LED failing causing others to fail is just plain incorrect. But, if you want to persist with your argument, I suggest you contact the manufacturer and tell them they're wrong to sell a product which allows using their products in a manner which you don't approve. Please forward their response. |
Please note - During the past 17 years of operation, several gigabytes of
Vanagon mail messages have been archived. Searching the entire collection
will take up to five minutes to complete. Please be patient!
Return to the archives @ gerry.vanagon.com
The vanagon mailing list archives are copyright (c) 1994-2011, and may not be reproduced without the express written permission of the list administrators. Posting messages to this mailing list grants a license to the mailing list administrators to reproduce the message in a compilation, either printed or electronic. All compilations will be not-for-profit, with any excess proceeds going to the Vanagon mailing list.
Any profits from list compilations go exclusively towards the management and operation of the Vanagon mailing list and vanagon mailing list web site.