Transister gets really hot in RGB LED circuit.

Hey guys, I am working on a project were i control 2 meters of RGB LED strip cut into 5 pieces, each consist of 21 LED'S
My setup is based on the picture below but I only use all three colors, on two of my strips. On the other three strips i only use one color on each.


So that means that I'm using 9 TIP 120 transisters, with 5 strips(21 leds on each).
My setup have worked flawless until today where one of my tip120 tranisters started to make noise, and heat up alot! The LED connected to that TIP120 also started to be unstable. The other LED'S worked perfectly and the other transisters was cool. I control the lights via loadcells through the PMW pins.

I'm using the same 9.5V power supply for all the LED strips, and that have worked the last two weeks, but they are recommended 12V. Could that be the problem or do any one what could have caused this over heating tip120? ?

A common 12volt LED strip has three LEDs of one colour, plus a current limiting resistor in series.
The blue and green LEDs have a forward voltage of ~3.3volt.
3x 3.3volt = 9.9volt.

A properly REGULATED 9.5volt supply wouldn't have worked. Or the LEDs would have been very dim.
Use a regulated (switching) 12volt supply if you want maximum/constant brightness.

A TIP120 is a bad choice for a 12volt LED strip. Too much dropout/saturation voltage (dimmer LEDs).
You could compensate for that by using a regulated 13.5volt supply.
Or use a 12volt supply and logic fets.

The TIP120 could have failed from a short between the 12volt pin of the strip and one of the colour pins.
A short there puts the full supply across the transistor.
Leo..

Use a better part, such as AOI-514, really low Rds, logic level, N-channel MOSFET

This board I offer has 32 of them, driven by 74HC595 MOSFETs with on/off data shifted in from an Arduino.
http://www.crossroadsfencing.com/BobuinoRev17/


CrossRoads:
This board I offer has 32 of them, driven by 74HC595 MOSFETs with on/off data shifted in from an Arduino.

Another shameless free plug. :smiley:

Is your circuit on crap solder less bread board? Note, all solder less bread board is crap.

That's the only kind of plug I do!