Using the 5V pin and a transistor to control a single very bright led

Other Hardware LEDs and Multiplexing
1

I want to create specific on/off blink patterns with a single extra bright led.

I bought a few different leds and started with the weakest: a Luxeon Rebel LXML-PWN1-0100.

The datasheet tells me that it wants 3V forward voltage and that the little thing will provide about 120lm with 350mA - if I interpret the specs correctly.

My arduino diecimila should be able to handle 300mA on the 5V output - and even 900mA if I power it using an external power supply.

I attached my little circuit. Could someone with a little experience have a look at it and tell me if I'm on the right path? Thanks!

circuit.jpg
circuit.jpg900×675 96.5 KB

2

Hi,

There can be problems with high-current leds like these. The problem is that they inevitably get warm, so need a heatsink, and as the temperature changes, so does that forward voltage. And if the forward voltage changes, the series resistor is the wrong value and could allow too much current to flow, leading to "thermal runaway" and... well, out comes the magic smoke!

Therefore it is usual to drive high current leds using a constant-current circuit. Watch out: many pre-made constant current modules don't allow PWM fading, which I assume you want.

Maybe take a look at this page.

Paul

4

646d64a7a1b8e5dd0eee6c099a72e4694b8ced1a.jpg
646d64a7a1b8e5dd0eee6c099a72e4694b8ced1a.jpg900×675 96.5 KB

Actually, the transistor version of the circuit PaulRB cites is this one:

You refer to "be able to handle 300mA on the 5V output". Using a constant current drive circuit like this, you power it from your main (not necessarily regulated) power supply so that the transistor (need one heavier than BC547 though) dissipates the power, not your Arduino regulator.

5

Thanks for all the answers. It amazes me how vibrant this forum is.
I will try to get my hands on those CAT4101 chips, Delta_G mentioned.

And I will have a look at the Meanwell drivers. There's a lot of interesting stuff out there. If anyone can recommend something, please do. The combination I'm looking for is a single, very bright led, which I can switch on and off according to specific rhythms. And the whole thing shouldn't burn down the house.

I'm also thinking about disassembling my 30 € bike light. The output is quite impressive for the small led and power supply (an usb charged battery).