I am using a TIP120 Transistor with pwm from my Arduino to fade an led strip. The RGB led strip requires 12 volts and 1.6 amps of current. I bought a 12 V / 2.5 Amp power supply from Radio Shack and I'm using it to power my TIP120. Here's how I have the set up:
[0-5v] PWM from arduino - > base of tip120
emitter of tip120 - > ground
ground of led strip - > collector
hot of led strip - > +12 v power supply
I have connected the GND from Arduino with the GND from the power supply to keep a common reference for ground. Now here's my problem, the setup works fine in terms of function, but my led strip doesn't light up at all. When I switch it out for a small led with a resistor and change the power supply to 6V, the small led fades in and out as expected but when I switch back to my original setup, the led strip doesn't budge. So I hooked up my multimeter and checked the current, it read 12.8 on the 200mA range. I assume that's 12.8 milli amps, which is weird because it should also show up on the 20mA range on my multimeter but it maxes it out.
So anyway, I figured I wasn't getting enough current out to the led strip. But I know that the TIP120 can handle up to 5 amps. My power supply can supply 2.5 amps, so what am I doing wrong? How can I get the current up to 1.6 amps?