I'm trying to control a 7W 560MA 12-14V COB LED Strip using Arduino. When I connect the LED directly to a power supply at 14V (using 1 ohm limiting resistor) I have 0.56A / 12.3V on my LED. But if I connect it through TIP120 transistor to control it by Arduino (using 14V power supply) I have only 0.38A / 11.7V on my LED. So I have a significant drop of LED power. Did I choose the wrong transistor? If so, please help me to choose the right one.