Hi!!! i've been working on a stair lighting proyect for a few days and got it working with de PWM channels of my arduino one like a charm, the leds go fade on one after the other and then off after a delay.
I use a TIP31 transistor to use a strip of SMD 12volts single color LEDs with an external power supply.
now i need to have more channels so i got a TLC5940 to extend my PWM channels to 16 or more, when i use a regular LED directly on any of the TLC's channels the LED works perfectly but when i conect the transistor circuit insted, nothing happens. i used this link from the arduino TLC5940 library page http://sonicrobots.com/2012/04/24/the-pwm-controller-tlc-5940-the-arduino-and-a-high-current-output-circuit/
before using the TLC my arduino PWM channel was conected at the base of the TIP31, the colector to my LED and the emiter to the ground
i use the same circuit on the TLC and doesn't work i tried also using TIP122 like on the link and same result