controlling led with transistor question

So i’m back on my project, and yes i’m a rookie
Object To control a 3w, 3.2V 700MA LED with a 2N2222 transistor.

When connected in the circuit attached it will only pull 100ma. If I connect the LED to my power bus i will 250ma. Why do i have a loss of 150ma thru the transistor.

led 1.png

Transistor has voltage drop across it, 0.5V to 0.7V. Thus you are not getting full 3.2V across the LED with a 3.2V source, you need more like 4V.
That design also has issues in that there is no current limiting.
A part like this would be better
http://www.digikey.com/product-detail/en/infineon-technologies/ILD6070XUMA1/ILD6070XUMA1CT-ND/4897539
There are others that are similar, they keep the current thru the LED constant even as the LED heats up trys to dissipate more current.

You can make use of the 5V pin: the voltage drop in the transistor won't be so critical and you will also be able to put a resistor in series with the LED to limit the current.

Moreover, you can tweak the resistor value to obtain the exact current you need in the LED (because, in case you are powering the arduino with a USB attached to a computer, the 5V will have a quite high variability).

Listen to Crossroads. Unfortunately, Jusep does not know what he is talking about (no offence intended, Jusep, but you have more learning to do. You can’t treat a high current led the same as other leds. And USB can normally only supply 500mA).

5fc53b43d4dacb1040e8425ceab2613415e5491c.png