simulate this circuit – Schematic created using CircuitLab
That's my circuit, although it's an RGB LED strip that I'm driving, rather than three individual LEDs. It works. I can PWM each channel and fade between colours as I need.
You may have noticed that the resistor value on the base of the transistor (you can find the data-sheet here) driving the red channel is lower than the others; a lot lower. This is the value I need to make each channel appear the same brightness.
My issue is that the transistor on the red channel is getting quite hot, too hot to touch for more than a few seconds.
I've put my multimeter in series with the collector of the transistor and the cathode of the LED to measure the current draw and it's reading 150 mA. I'm just a hobbyist, but from what I can tell, the transistor should be able to handle 600 mA from collector to emitter (at least that's how I've interpreted the data-sheet).
I suppose I have three questions:
- Is the way that I've designed the circuitry reasonable/correct?
- Is it normal/OK for transistors to get hot when operating within their limits?
- As I've just read the transistor part number from the side of the component and then searched for the datasheet, is it possible that I've got a different spec'd device?