next topic »

[on:]

This seems like the type of question a that could have been answered by a simple google search, however I must be searching wrong, because I've spent a lot of time looking with no luck.

I'm trying to figure out what sort of cheap and simple driver I can use to drive 3 or more Cree XML T6 LED's.  They have a max current of 3000ma, and I believe a maximum voltage of around 3.35 volts.  So if I'm not mistaken, that means that I am to wire the led's in series (I hear this is the best way), that would need a driver that can deliver 3000ma at 10.05 volts.  I'm thinking I'd likely use a 3 cell lipo battery to power it, which are around 12 volts.  Where could I find a driver for this application?

And how about if I wanted to wire say 6 of the LED's in series.  I'd need 3000ma at 20.1 volts.  How could I find a driver to step up the 12 volts into 20.1 and 300ma?

[Reply #1 on:]

This seems like the type of question a that could have been answered by a simple google search, however I must be searching wrong, because I've spent a lot of time looking with no luck.

I'm trying to figure out what sort of cheap and simple driver I can use to drive 3 or more Cree XML T6 LED's.  They have a max current of 3000ma, and I believe a maximum voltage of around 3.35 volts.  So if I'm not mistaken, that means that I am to wire the led's in series (I hear this is the best way), that would need a driver that can deliver 3000ma at 10.05 volts.  I'm thinking I'd likely use a 3 cell lipo battery to power it, which are around 12 volts.  Where could I find a driver for this application?

And how about if I wanted to wire say 6 of the LED's in series.  I'd need 3000ma at 20.1 volts.  How could I find a driver to step up the 12 volts into 20.1 and 300ma?

You need a CURRENT LIMITED power source. You can buy nice inexpensive switching current regulators, or you can make your own with an ordinary 3 terminal regulator (like a 7805). Or you can be fancy and use a MOSFET and some feedback (analog or a microcontroller) and make your own switcher.

A really good, simple and useful current regulator is a simply incandescent light bulb. You can use something like an 1156 backup light bulb. Put a few of those in parallel, and setup your power supply so that you only drop 3 or 4 volts across the bulb. It will give you decent current regulation (i.e. protect your LED modules) and at such a low voltage they will barely get warm and they'll last forever.

Keep it simple. Simple is best.

[Reply #2 on:]

barely get warm?.. if those cree led's are not producing enough heat to to burn you without a heatsink.... you'll barely hit 100 lumens output!


you need a good heatsink and a switching regulator....

[Reply #3 on:]

barely get warm?.. if those cree led's are not producing enough heat to to burn you without a heatsink.... you'll barely hit 100 lumens output!


you need a good heatsink and a switching regulator....

I said using incandescent lamps as current limiters will work without them getting terribly warm.

The OP wants 3000 ma (3 amps). 3 amps times 3 to 4 volts drop across an incandescent lamp is only 9 to 12 watts. A single christmas tree bulb (the old fashioned large kind) is 7 watts. Those run cool enough to hold by hand when they are on.

(fixed typo)

[Reply #4 on:]

A really good, simple and useful current regulator is a simply incandescent light bulb. You can use something like an 1156 backup light bulb. Put a few of those in parallel, and setup your power supply so that you only drop 3 or 4 volts across the bulb. It will give you decent current regulation (i.e. protect your LED modules) and at such a low voltage they will barely get warm and they'll last forever.

I would be very careful about using an incandescent bulb as a current regulator unless I knew that the power supply voltage rises only slowly when switched on. The reason is that an incandescent bulb has a resistance when cold much lower than its resistance when running at normal power - about 10 to 14 times lower for a standard bulb, more for a halogen one. If you are running the incandescent bulb at much less than its rated voltage, the resistance change will be lower, but there will still be a surge of excess current to some degree when you power the system up.

[Reply #5 on:]

I would be very careful about using an incandescent bulb as a current regulator unless I knew that the power supply voltage rises only slowly when switched on. The reason is that an incandescent bulb has a resistance when cold much lower than its resistance when running at normal power - about 10 to 14 times lower for a standard bulb, more for a halogen one. If you are running the incandescent bulb at much less than its rated voltage, the resistance change will be lower, but there will still be a surge of excess current to some degree when you power the system up.

Very true. However, I've found that this isn't a problem for power LED's. An LED is destroyed by excessive heat (power dissipation). Using incandescent bulbs as current regulators DOES put a momentary overcurrent surge into the LED, but it never lasts long enough to overheat the LED.

Think of the technique of running 7 segment displays directly from uP ports without resistors. Each LED segment is turned on only for a percentage of the total time (i.e. PWM) so that even though the INSTANTANEOUS current is way too high, the AVERAGE current is correct.

Look at "flash" lamps in camera phones. Those use a white LED which is "flashed" with a very high current for a very short time. The LED makes a LOT of light (and would burn out almost immediately if run that way constantly), but it works because the duty cycle is so low the LED never even gets warm.

[Reply #6 on:]

I'm a little confused about the incandescent bulb idea. Seems to defeat the purpose of the LED's being small and efficient.  Putting an ugly old incandescent bulb in there.  And also confused why use an incandescent bulb rather than a resistor of the same value?  Afterall, isn't a incandescent bulb just a resistor?

I know they make single led drivers.  There is a abundant supply of cheap and compact drivers, that are about the size of a nickel, and cost $10 or less, to drive single XML-T6 leds.  Looking for something similar, but to be able to drive 3 or more of them.  Can't find this anywhere.

[Reply #7 on:]

The incandescent bulb is just a low-cost alternative to a power resistor.

[Reply #8 on:]

for my project i used 3 of this constant corrent regulated driver to power an RGB 3 watt led
with minor mod