99 LEDs....

Are the LED's carrefully factory matched? If not, you do not have a prayer.

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Many thanks,

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You've had bad advice, as you will be albe to see from the voltage versus current curves in the data sheet.

The worst case forward votlage at room temperature at 20mA is 2,5V.

2.25V is typical, so a 12V power pack probably can't drive a string of more than 5V diodes.

You could probably set up a current mirror to put a well-defined 10mA through a string of four LEDs running from a 12V supply, but this is a long way short of 99, which you'd have to manange with 25 parallel strings, controlled by 25 current mirrors.

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Bill Sloman, Nijmegen

Here's what I would do, not knowing exactly what your requirements are. These are red, so about 1.7V forward voltage drop. Connect 6 or 7 in series, along with a resistor 20-80 ohms. I'm just making wild guesses; you'd have to measure the current draw to get the appropriate value. Yeah, it could be calculated but it's easier to experiment.

You'll end up with about 15 of these strings. Just connect them all to your battery. One string will have a different amount of LEDs, just use a different value resistor.

It's not precise, you could use about 15 current regulators, but it's quick and dirty and all you probably need.

You can make a current regulator from a 2N2222 transistor with a single resistor to the base. For 12V you need between 100k and 200k for 20mA, but you have to choose it for each transistor individually. This regulator only takes 0.4V forward voltage, so you can wire 6 LEDs in a row. Usually when they get warm, the forward voltage also lowers and they will pull much more current, which might shorten lifetime. This is prevented with the transistor, which driven in this way will limit the increase to 10% or so.

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ciao Ban
Apricale, Italy

Crank up the voltage to at least 18. You can probably get one at 24 volds DC also.

greg

That's true but the informant failed to mention that means a Royer Converter. Now some nut is going to come on here and rage about Peter Baxandall, but it is the Royer that you really want.

Assuming some kind of hobby project, this makes the most sense. Although 6 in a row might be pushing it. L-53HD does not come up at the Kingsbright web site; so, no way to tell for sure what the forward drop is. Also, it makes a difference based on what kind of "12 Volt" supply there is. They tend to come 12.0, 12.6, and 13.8 V. A car battery with the engine running will be at least 13.8. Depending on how the car is wired, the cigarette lighter socket could go as high as 15V.

If you want to do something fancier, build a DC/DC converter with an output of about 180(?)V, and set the current limit to 20 ma. All LEDs in series. Tam

This used to be true. However, the resistive component of many high efficiency LEDs is large enough, and their matching is often good enough 'right out of the bag', that parallel combinations work out just fine, particularly if you don't really need brightness matching. It's as if they're self-ballasted to a degree. If the battery pack has some significant amount of source impedance, you can sometimes get away without any resistors. Try it. Paul Mathews

The 1 watt and 5 watt Phillips Luxeons are very well matched out of the bag. A group of American Bright I used were very well matched.

greg