High powered RGB LED - where to buy

Hi all,

I am in the UK - wondering about where to get a nice high powered RGB LED for a mood lamp etc

James

i recommend this, it’s where i got mine!
http://www.dealextreme.com/details.dx/sku.4530

and it is really high power!! just watch out, the polarity is different than what’s printed on the pcb. read the discussions on the site itself.

takes about 2-3 weeks to ship, but definitely worth it.

Can someone tell me why they are this strange star shape? Just intrigued...

The star shaped piece is the heat sink. I imagine the shape allows better heat exchange...

Thanks mexduino - I have ordered a couple from there.

James

Can someone tell me why they are this strange star shape?

The cut-out bits are bolt holes so you can mount them on an even bigger lump of metal. Usually the backing is a lump of sheet aluminium, with a thin shim of FP-4 and copper bonded on the front. I can only guess they're hexagonal to get packing density. Seems to go back to the Luxeon LEDs.

Finally got my LEDs - can someone point me in the direction of a good schematic?

They are common anode - so take a +5V - then you feed each R, G and B in to the Arduino PWM... and set those pins as output.

(I know this is by way of transistors etc)

Which way are you using to power them?

I'm interested in LED lighting too and there are two different schools, the ones who just use a MOSFET or a transistor like ULN2003 (useful for RGB models) and the ones with constant current drivers, which seems to preserve LED's life but also more complex.

I'm using a powerful transistor (sadly I can't tell you the type right now, just ask for one that can switch up to 1A) and driving its base from the PWM output. Then one of the color channels is attached to the collector, in series with a 4.7 or 6.8[ch937] 1W resistor. Emitter is grounded. Repeat the same circuit three times and there you go! :)

You can use a ULN2003 - you can double up if you need more than 500mA per channel

http://fightpc.blogspot.com/2008/03/arduino-mood-light.html

Is there any full schematic somewhere that explain how to use this RGB led with arduino? The 5V pin and a uln2003 are enough to drive this led or there is something else? Thank you

Is this the Mexduino schematic? And is it correct?

These lights from BlinkM are insanely bright

http://www.coolcomponents.co.uk/catalog/product_info.php?cPath=45_69&products_id=244

how about my schematic? Please? :D

how about my schematic? Please?

It all depends on what kind of LED’s you are using. What is the current required per color, what are each colors forward voltage drop? Typically not all of the colors will have the same current limiting resistor because their Vf’s are different. You also need to know the voltage drop of your transistor.

(FYI the best way to drive high powered led’s (>20mA) is through a constant current circuit. Not just using a current limiting resistor. Although it will work. Make sure you have sufficient heat sinks ive heard 10in2 per LED Watt, couldn’t tell you if this is true without doing a lot of math)

To calculate the required resistors take (Vsup-SUM(Vf of each component))/I

thanks for your reply. The led is this http://www.dealextreme.com/details.dx/sku.4530 Specifics are : * Red: 2.5V ~ 3.0V, 350mA * Green: 3.2V ~ 3.8V, 350mA * Blue: 3.2V ~ 3.8V, 350mA

And there are the specifics for the BC639:

Code BC639 Structure NPN Case style TO92A IC max. 1A VCE max. 80V hFE min. 40 Ptot max. 800mW

Im not great at reading Transistor data sheets, so I could guess that that transistor would work however im not 100% sure. You will also need to find its forward voltage drop. Then plug everything into that formula i posted earlier to find the necessary resistor values. It is going to be a range because you won't know the exact Vf's of your LED's. This is one reason to use a constant current circuit instead.

I actually have some of those LED's on order and have been looking for a suitable circuit to drive them. I stumbled apon the TL4242 today that looks promising. Only downfall ive found so far is it is surface mount.