can a power supply hooked up to a lm3409 fry an led?

I have a psu (meanwell ms-250-36) connected to an lm3409 (http://store3.sure-electronics.com/ps-sp12153) which i tried to hook up to a string of leds. However one of my 9w leds (cree xpl) turned blue and fried, which I did not expect because I thought the voltage would be regulated and it's possible to drive a single 1w 300ma led. Was I wrong? or was there another reason for the led frying?

Insufficient cooling, ESD while soldering/connecting, reverse polarity? In my experience, blue LEDs are very sensitive to ESD. 36volt in for 3.3volt out (single LED) is a lot of difference. Don't know if the CC driver will be happy with that. Leo..

Hmmm you might be right. My leds are white but some went blue when I connected them and I read they do that when overheating. Does this sound like they were overdriven with too many volts or not attached to the heatsink properly?

You can't use a 1watt (~300mA) LED without heatsink. It will fry the LED within seconds. 1watt only needs a small heatsink. A 5cm x 5cm piece of aluminium will do.

The constant current controller you linked to does NOT control voltage. It controls current. You should connect a string of 8-10 LEDs to it if you use a 36volt supply. 8-string or 10-string COB (chip-on-board) LEDs are common, and easier to use than single unmounted LEDs.

http://www.ebay.com/itm/5-20-50W-COB-LED-Square-Strip-Light-Lamp-Bead-Chip-diy-DC-12-24-36V-Long-Life-/262324885095?var=&hash=item3d13c81667:m:maloyXqq9_2zffTB7ewPcOw Leo..

I understand the need for a heatsink. I was just using poor quality cement and it came undone.

However can you elaborate on how the lm3409 regulates current? I thought that was how bucks did it - by regulating voltage.

skreech: However can you elaborate on how the lm3409 regulates current? I thought that was how bucks did it - by regulating voltage.

"Buck" simply means "step-down". The module's input (supply) voltage must be higher than the output (LED) voltage.

The module measures current across a (user selectable) current sense resistor. And adjusts output voltage, so the current stays constant (e.g. 300mA). The output voltage depends on the nr of LEDs connected and LED temperature/age. Leo..

If that’s the case then if I supplied a 3v led with 36v, it would just step the output voltage down to 3v and I would not fry the led right?

Yes. The voltage on the output of the driver board will increase untill the set current is achieved.

If that is a short, there will be running 300mA through that wire. If it's a single LED, the voltage will rise to Vf of the LED @300mA (~3.3volt for a white LED). If that's 10 LEDs in series, the voltage will rise to ~33volt, untill there flows 300mA.

The regulator needs ~3volt more to do so, so the limit is 10 LEDs on a 36volt supply. A LED will instantly fry on that voltage if you connect it with the wrong polarity. Leo..

Wawa: The constant current controller you linked to does NOT control voltage. It controls current.

So just to be clear, the lm3409 does actually control the voltage.

skreech:
So just to be clear, the lm3409 does actually control the voltage.

That makes it sound like a voltage regulator.

There is no current without voltage.
So yes, it adjusts the output voltage to keep the current constant.
Leo…