How to pick an LED driver?

Say I have 3 LEDs in series that have a Max Forward Voltage of 6v and an operating current of 1000mA. I could get a driver like a buck puck, say the 3021-D-E-1000mA BuckPuck. It has an input voltage of 5 - 32v, and let's say I give it the full 32v, so how does that not end up burning out my LEDs?

My actual goal is to have 3 strings of 6 Cree XP-e LEDs connected to 3 Drivers. But I can't quite figure out how to properly size the driver. I know it puts out a constant current, and the voltage fluctuates -- what is there to determine which one to get so I don't end up pushing too much voltage? Or am I misunderstanding something about how the voltage will fluctuate?

Sorry for the noobishness, this is my first real electronics project.

frollard4 years ago
The ONLY reasonable way to drive a high power led -- or ledS...is with a constant current driver.

Super-simplification:
Leds ...Diodes...are semiconductors. (read: sometimes conduct, sometimes do not conduct) They need their forward voltage requirements met in order to conduct (and light) - but once they are at that voltage, they are no longer semi-conductors, they are essentially just conductors, and offer relatively little extra resistance, so they are completely willing to take any additional current allowed by the current source. This current number is EXPONENTIAL based on the overvoltage and will QUICKLY destroy any led if not controlled. Controlling the voltage simply won't work, because the 'equivalent' resistance changes with voltage and temperature.

Enter the constant current driver.
It starts by ramping up the voltage until current flows - and it measures ONLY the current - often by monitoring the voltage drop across a known small value resistor, and using that to drop to calculate the amount of current flowing, from there it can alter its voltage output. Closed loop feedback that stops the voltage from destroying the led.
It won't work, until you have slightly more than 18V available - it can't magic volts to drive the LEDs in series, since its a "buck" not "boost" driver. Then, unlike any PSU you've ever seen, it will control the output CURRENT not the voltage to some set level.

Steve
iceng4 years ago
The puck electronics is designed to deliver a constant current output !
No matter if you have one led or three in series,
that is what constant current means.

The puck is designed to accept a widely fluctuating input voltage !

A