I have a simple question. I am trying to drive a darlington transistor (TIP120) from an IR sensor (HC-SR501). See diagram. The load is a 300 LED strip using about 5 amps from a 12 v power supply. The circuit works, but the TIP120 gets pretty hot (I have it on a heat sink). I am just wondering why so much energy is being wasted in the heating. I've adjusted R1 selecting both 100 ohm and 150 ohm since I think that is the ballpark I want to be in for delivering 20mA to the transistor base and getting the transitor to act like a switch basically. The PIR puts out a 3.3v signal when detection occurs.