@john

U are saying tht one can vary the brightness of a LED with a pot. I don't think this wud change much.
But a pot and transistor approach is better and will work for high lumen LEDs.

AAAAAAAH! Now I get why all the commotion with only PWM & Led Dimming...
Pish posh.....I did not think of the pot and transistor approach then...

 

Sure Bill,

Here are the RGB LEDs I'm using for my project. PDF on the page.
http://yesled.com/index.php?option=com_content&view=article&id=94:power-rgb-led&catid=2&Itemid=5

I'll have to look up Rheostats- not familiar with them.

 

Cool. Something all of us have overlook, and you will need to think of, is heat sinking for the LED itself. This is a high power LED, it will get hot enough without a heat sink to burn itself up. It doesn't need much, but you need something. You may need a fan for cooling.

Page 4 of the DataSheet...

*Notes:
[1] YL maintains a tolerance of ±10% on flux and power measurements
[2] CCT ±5% tester tolerance and λd ±1nm
[3] A tolerance of ±0.1V on forward voltage measurements
[4] Viewing Angle maintains a tolerance of ±20°

*Caution:
1. Please do not drive at rated current more than 5 sec. without proper heat sink.

Packing:
1. Package without heart sink LED（50pcs/tube）
2. Package with heart sink LED（50pcs/tray）

Red highlight inserted by me.

I also notice you mentioned these parts in plural. How many are you planning on lighting (it matters, a lot)? You need to decide on quantity before I make any real schematics, the power supply you choose is also critical.

These are SMT parts. This isn't a big deal, but those pins are going to be very hard to solder.

I've been thinking about the rheostats. This a very good reason I hate this design. You have said you don't care about linearity, but how would you feel if it is totally uncontrollable (which is nonlinear to the extreme), the difference between on and off is just a touch of the knob?

I'll make as simple a design using transistors as I can, but you are going to get a taste of electronics here. LEDs are electronic devices. The package style means you will have to make hardware, both for heatsinking and for electrical connections. The transistors will also need some minor heatsinking, probably shared with the LEDs. To most of the folks at this site it is doable, but you have picked one heck of a first time project.

How much do these units cost?

 

Thanks heaps Bill!
Sorry if I seem a little slow in grasping all of this- I tend to juggle too many priorities sometime, plus working heaps overtime doesn't help!

I just want to say thanks as well for pointing out the heat-sink, I was thinking maybe mounting it on a metal plate would suffice, but I will probably add mini heat-sinks and a fan as well now.

I also have other projects involving straight colours/white LEDs-- just on or off, (skin therapy, monitor backlight, etc.) the RGB is my more complex project

Thanks again for your time mate, I really appreciate your time in explaining things.
The LEDs ranged from about 1.50$ USD each up to 5$ each for the RGB ones I think. As the factory was in Hong Kong, it took a while to ship. (I'm in New Zealand btw)

Don't feel too much pressure to plan everything out for me- I realize I just have heaps more to learn and experiment with first.

 

That is all part of the fun. PWM tends to run a lot cooler, which is why it is popular even with the added complexity. You only need to worry about heatsinking the LEDs when it is used. Less heat is also less electricity, since that power (heat) comes from somewhere.

However, the transistor / pot method is a lot simpler, which is one of the reasons it is recommended. Fewer parts, and easier for a beginner to troubleshoot. With any electronics project there is almost always a step where you are following the wiring to see where the mistakes are.

So how many of these were you wanting to use?

 

Well I was thinking 3 or 4 for starters. I have 10 of these RGB leds ready to go.

 

Have you got one of these? If not you will probably need one to try some stuff out, then solder it to a board later. If you want to skip this step feel free, but I would recommend it. Like I said, you are going to get a dose of electronics.

You'll also need some 24 or 22 gauge solid copper wire. The board can be had from Radio Shack.

The other major component you will need is a power supply. We tend to recommend wall warts (transformer on a wall plug) due to their convenience and safety. Each LED is going to take just over an amp, and you want 10, so you may have to buy a beefier unit, with 12 amps or better. This is why I mentioned qty was important.

Looking at it, it might be better to get several smaller wall warts, and break it down a lot. You don't need all your power coming from one box. It will also let you experiment a bit with your design. Think 5V-12V around 3-5A. You propose, and I'll let you know the advantages and disadvantages.

 

The best I can figure out from the datasheet is that the LEDs have a common anode. It really is not very clear on that point. The only mention of it is that "The anode side of the device is denoted by a hole in the lead frame" - the "lead frame" being the plastic chip carrier that the LEDs are shipped in. Once removed from the lead frame, there does not seem to be an obvious way to tell what the proper orientation is, as the design is rather symmetrical. One of the wider leads should be the common.

These LEDs absolutely must be mounted on a board before being powered on, or they will quickly be fried from the heat dissipation. The heat must be carried away from the slug (round metal item on the bottom of the LED) by a rather large area of copper on a PCB that you will have to make; either that, or you will need to use copper sheet stock to make heat sinks for them.

It appears that each color is rated for up to 350mA current, or roughly 1A total for the whole LED. That will be up to 3.6 Watts power dissipation, which is not trivial to remove.

Obligatory Safety Warning:
When operating at maximum intensity, these LEDs will be extremely bright, plenty bright enough to burn holes in your retinas if you look directly at them without protection.

You would really be much better off to start experimenting with low-power LEDs. They are much less expensive, you can power them with simple circuits, the mounting requirements are simple, you can have a lot of fun with them, and learn plenty.

However, even the low-power super-bright LEDs can cause blind spots (burned retinas) if you stare at them for a period of time, so you must keep that in mind. A simple sheet of white copier/typewriter/printer paper about halfway between the LEDs and your eyes can save your vision from damage, as it will diffuse the light. You only get one set of eyes; protect your vision.

 

You would really be much better off to start experimenting with low-power LEDs. They are much less expensive, you can power them with simple circuits, the mounting requirements are simple, you can have a lot of fun with them, and learn plenty.

I couldn't agree more, with this advice and Bill's advice on breadboarding. Jumping straight to a finished project will almost certainly be frustrating (doesn't work, components fried) and possibly dangerous as Sarge notes.

Anyone attempting such a project should have LED basics down pat and should be highly confident of all aspects of the design. Power source, working circuit, heat dissipation, etc. Many of these things can be worked out at the breadboard level. And even a pro would start with minimal currents and brightness, to make sure things are working (no hot spots, for instance), before going to full power. The final build rarely behaves exactly as the breadboard did, even if you built it right, which is not guaranteed either!

 

Actually the first thing I was going to suggest is to identify the leads. LEDs can be burned out if too much voltage is used backwards. Frankly this datasheet sucks, it does not identify any real layout or even the internal schematic.

Use a 6V battery (you can buy a AA battery pack from Radio Shack), solder a 1KΩ ¼W resistor (also from Radio Shack) to it and make a couple of wire leads. Then try various combination of connections to map out the internal LED wiring. Take good notes. I would appreciate it very much if you would post the LED connections on this thread after doing so. I'm using a very low voltage source to try not to damage the LED when you make backward connections, the odds of which are extremely high.

Using the low voltage/low current approach above you can ignore the heat sink requirements for the moment. Once you know how this LED is laid out then you can proceed to the next steps. Don't forget, we need the layout of this LED.

At this point you need to think about heat sinking and how to mount the LED. I've used #6/32 screws and washers, and drilled and tapped holes in a heat sink (ie, a chunk of metal, mine was a very old computer heat sink) to hold the edges of the LED down. It can not short the leads to the LEDs, and it doesn't need to be extra tight, just enough to hold them down securely.

If you come up with another method feel free, but it needs to be mechanically secure (not adhesive). This was how I handled the situation on my LEDs.

You will need to have the LEDs mounted to experiment with them. However, after working out how you are going to do this remove the LED from the heatsink. Solder fine wire (#28 or #26 gauge wire) to the leads. Personally I would color code the wires to the LED colors (Red, Green, Blue), and white for the positive lead, or black for the negative (whichever is the common lead). If you try to solder wires to the LED while it is on the heatsink it won't work. Solder needs to get hot, and the heat will be sucked away from the LED as fast as you can inject it if it is still attached.

I've given you a couple hours of work, when you've got the details worked out let me know the LED layout and we'll move on from there.

 

I suggest that instead of 6v/4 batteries, you use three 1.5v batteries in series with a resistor, as that way you cannot exceed the 5v maximum reverse breakdown voltage of the LEDs.

 

Agreed. The results will be very dim, but better than burning out the LED. Do not use Lithium or rechargeable batteries, since their voltage is lower than standard alkalines.

 

Thanks heaps for all the advice!
I have other similar high-powered LEDs, without the RGB complication factor. Probably best to put this project on hold until I'm more comfortable with the basics. It doesn't help that I'm 12,000 km away from from dad's garage and all his tools... will have to beg/borrow/buy what I need to put it together.

I appreciate your time so much, and I ask that you don't spend more time on my RGB project- as it'll have to hold for now as I get a better understanding and more experience wiring these guys together!

First on my list is to wire together a few solid white LEDs that take 350 mA each. All the LEDs do come with hexagonal heatsinks- so I figure maybe I'll use thermal paste to attach those to little heat sinks.

 

Don't use past, it is to conduct heat. It isn't a glue. You need something mechanical to hold it in place.

 

True, of course. I'll work it out as I get there.