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# Ho do I pick an LED driver? Answered

I bought a few cree XP-E LEDs and I'm very confused as to what drivers I should buy. This is my first electronic project so I'm a bit confused. I do know that for high powered LEDs, constant current is the only way to go but I have no idea how much I need. These are the LEDs I bought: http://www.ebay.com/itm/CREE-XP-E-XPE2-12W-4-Leds-Colorful-Red-White-Green-Blue-LED-Light-20MM-6V-12V-/221887486794?var=520780573872

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Make sure you put a heat sink on that LED.

You want an LED driver like this one.

My interpretation of the scribbles in the, uh, parameter sheet, you have attached to this question is as follows:

There are broadly 2 kinds of LED modules in this category, namely: 6V modules and 12V modules.

The maximum allowable current for the 6V modules is 2A = 2000 mA of current.

The maximum allowable current for the 12V modules is 1A = 1000 mA of current.

So, maybe the first step is to discover what kind of module you've got. Is it a 6V one? Or is it a 12V one?

The module shown in the picture you have attached has a "6V" printed on it, suggesting it is one of the 6V variety.

Sort of generalizing from there, I might expect the 12V modules to have the word "12V" printed on them.

By the way, it turns out the brightness of an LED is roughly proportional to the current flowing through it. So the answer to "How much current do I need?", depends on how much light you want.

If you want the brightness turned up to 100%, then for a 12V module, the answer is 1 A =1000 mA of current.

If you want the brightness turned up to 100%, then for a 6V module, the answer is 2 A =2000 mA of current.

Final note: part of the parameter sheet is suggesting a minimum value for current, namely 0.350 A = 350 mA. This lower limit seems nonsensical to me. You should be able push arbitrarily small amounts of forward current through these modules, as low as 1 mA, or 0.1 mA, or even 0 mA, without harm to the module.

The upper limit is the one you should take seriously.

That was the data sheet on the seller's page so that was the only thing I could find. Thanks! That helped a lot! I'm assuming input voltage doesn't matter as much then?

A constant current driver uses feedback to keep the current at its output constant.

The voltage at its output will be that which is necessary to push current through the given load. The constant current driver does not really care about the voltage at its output, except in one respect: there is an upper limit for output voltage. I mean the constant current driver will supply as much voltage as is needed, within the range it is capable of, typically a range from 0 to Vmax.

For example, if you have constant current driver, with its current set to 500 mA, and with output voltage range of 0 to 20 V, and you connect it to one of those LED modules that has "12V" printed on it, then I expect the voltage at its output would be close to 12 volts, and the current to be very close to 500 mA.

As an example of something that might not work, suppose you put two 12V modules in series, so the total forward voltage of both modules in series is going to be like 24 volts. A constant current driver with a maximum voltage of only 20 V, might not work with that arrangement.

By the way, the mathematical product of voltage (in volts) and current (in amperes) is power (in watts). Or saying that another way: the power dissipated by a LED module, or resistor, or any two terminal device, is the voltage across it, multiplied by the current flowing through it.

I mean, this is sort of provides a physical explanation for why constant current drivers have a upper limit for the voltage they can supply. (Similarly, real constant voltage sources have an upper limit for current.) The reason why is because there are real physical limits on the amount of power a practical black brick gizmo can supply.

You keep saying that you are new to this electronics stuff. Maybe you could do some homework,
http://www.electronics-tutorials.ws/dccircuits/dcp...

and try to get up to speed on the this topic.

I forgot. I'll only have 1 plate. 4 LEDs mounted in series. I am completely new to electronics so I have very little knowledge on what those values mean and how they go together.