# LED Drivers?

Discussion in 'LEDs and Optoelectronics' started by Y2KEDDIE, Mar 15, 2013.

1. ### Y2KEDDIE

259
15
Sep 23, 2012
Typically I see a LED circuit consistng of the LED and a current limiting resistor in series with a power supply.

Why, and when are current limiting regulator circuitry used? In these new LED flashlites, is it just a LED, resistor and (4) AAA cells, or is there some active components required?

Thanks,

2. ### GreenGiant

842
6
Feb 9, 2012
if you pump too much current through an LED (sometimes thats as little as 50mA) you will destroy it, now there are some LED's that will work fine at higher current, because they have internal limiters, but if you let the voltage get too high they will blow.

The resistors are there tolimit everything, in the new flashlights you have a set max voltage (in the 4AA one you have listed) of 6V so the LED's are probably internally limited to the right current, but if you up it to 9V they might fry, or at least die quicker

3. ### BobK

7,682
1,688
Jan 5, 2010
Low power LEDs tend to use a resitors only. High power LEDs tend to use a constant current source. Some flashlights actually use a boost converter and can provide full power even as the batteries run down.

Bob

4. ### Y2KEDDIE

259
15
Sep 23, 2012
LED circuitry

I was thinking: with a battery, supply the current would decrease as the battery discharged so why not just a series limiting resistor. Added circuitry would just discharge the battery faster?

If voltage decreases, the current has to decrease as well. What am I missing?

5. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,839
Jan 21, 2010
The magic of the added circuitry is essentially to maintain the current through the LED at the same value as the battery voltage falls.

This can be done in one of 2 ways.

1) effectively adjusting a resistance so that the it is always "just right" for the current required and the battery voltage at that point in time.

2) Using the magic of inductors to trade voltage for current so that the power drawn from the battery remains constant as the voltage falls (and thus current is inversely related to voltage).

The second method is the most efficient, but also required the most components and fairly advanced design.

The former is a simple linear current regulator and these are described here:

https://www.electronicspoint.com/got-question-driving-leds-t256849.html