Power LED, 1 W and 3 W
A high-power LED on a 20 mm aluminum star: rated 350 mA (1 W) or 700 mA (3 W), so it needs a MOSFET and a current limit.
Aliases: high power LED, 1 W LED, 3 W LED, star LED, power LED, flashlight LED. It is the same junction as the 5 mm LED, with a power die's numbers, and it burns out the same way when nothing limits its current.
Pins
| Pin | What it does |
|---|---|
+ |
The anode pad on the star. |
- |
The cathode pad. |
Wiring it to an Arduino
A pin gives 20 mA, and a 3 W LED wants 700 mA, so the pin drives a logic-level MOSFET (an IRLZ44N or a D4184 module) and the LED runs off a supply of its own. Something has to set the current:
- a resistor: from 12 V to a 3 W white, (12 - 3.4) / 0.7 = 12 ohm, burning 6 W, so a 10 W part. From 5 V to a 1 W white, (5 - 3.2) / 0.35 = 5.1 ohm, 0.6 W.
- a constant-current driver (a PT4115 or LM3414 buck board): it wastes far less and holds the current as the LED warms. Mokxi has no such driver yet, so the resistor is the way here.
Models
| Model | Drop | Rated | Most |
|---|---|---|---|
1W white |
3.2 V at 350 mA | 350 mA | 500 mA |
3W white, 3W warm white |
3.4 V at 700 mA | 700 mA | 1 A |
3W red |
2.3 V at 700 mA | 700 mA | 1 A |
3W green |
3.5 V at 700 mA | 700 mA | 1 A |
3W blue |
3.4 V at 700 mA | 700 mA | 1 A |
The drops are the middle of the bands the star listings give. custom is a
3 W white with the vf, rated and max settings yours.
While it runs
The dome glows with the current over the rated current, averaged as an eye sees PWM.
It burns out
It survives its most current held for ever, which assumes a heatsink, and past that it heats over a couple of seconds and fails: open and dark until the next Run. A 3 W LED straight across 5 V with no resistor takes amps and is gone in about a second.
What it does not model
Heat: a star with no heatsink at its rated current dims and dies over minutes, and its drop falls as it warms, which is why a resistor is a poor limit for one. The color shift and reverse breakdown are not modeled either.
Common mistakes
No resistor. The drop is not a limit: a little more voltage is a lot more current.
A quarter-watt resistor. The one above burns 6 W.
See it in action
Workbench light flashes a 3 W spot through a 12 ohm resistor. Open it at /templates.