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Is a driver circuit really necessary for power LEDs? Answered

I have heard that a constant current source or something like that is required to drive power LEDs such as the Luxeon. I want to power several Luxeon Rebels, and I have a 3.7v single cell 900mAh Li-Ion battery. The description I read for the Luxeon Rebel (cool white color) states that it can have a forward voltage anywhere from 3 to 4 volts. Can't I just connect it to the battery then? Or does it have to do with current?


The thing I understand is this: although your battery is producing the "correct" (i.e., within specifications) voltage for your LED, it is offering much more (in terms of amps) than your LED is designed for. Unlike a lot of other electrical components, high-power LEDs will attempt to take on all of the current you are able to offer them, even at low voltage, until they die. 900mA is a lot of current for most LEDs— the ones that will take that much current will burn brightly, but will die soon, often within hours. This is why you need to limit that current down to a rate that the LED can handle— a resistor can do this, though inefficiently (it will turn the extra current into heat, which means your battery gets used up much sooner than it should). What you really need is a driver that will hold the current down to something closer to 350mA of power (depending on what the specs of your LED are) and make sure the voltage doesn't drop out on you until the battery really is exhausted. Unfortunately, I do not know what driver that is, and none of the other posts given here seems to suggests one. But that is what I have come to understand about high-power LEDs and how they operate with regard to current.


8 years ago

With a 3.7V battery, you'd be fine with just a high-wattage resistor. Is it the most efficient way of driving the LED? No. But it's simple and effective, and if you calculate everything properly it's perfectly safe, too.

Is a steering wheel really necessary to drive a car? 

I mean assuming everything is balanced, you should be able to just point the car in the direction you want it to go, and then step on the gas. Right?

Try running your high powered LED's without a current regulator.  You'll see what happens.

I agree with Steve - A standard low power LED you will get away with just a suitable resistor but for high power leds you really need a driver. They cost so little anyway.

The thing is, the forward current characteristic of the diode means that the current it draws takes off exponentially, given a chance, and as the diode changes temperature, the "forward voltage" falls, causing it to draw more current. Without active limiting, by a resistor, regulator or switcher, you can't get the device to run safely, or you never get full brightness from it.