Cree MX6 XLamp build

Building a light source for a Stanton Instruments, Ltd. B15 balance.

A quick project for anoth­er big­ger project.
I am in the mid­dle of restor­ing a Stanton Instruments, Ltd. B15 ape­ri­od­ic auto-load­ing ana­lyt­i­cal bal­ance. The orig­i­nal light source for the dis­play optics con­sist­ed of a high inten­si­ty 6 volt AC light bulb pow­ered by a large 240 volt to 6 volt 50 Hertz AC transformer.

I want­ed a small­er light source with less heat pro­duced, so I designed a small cir­cuit board to hold a Cree MX6 XLamp sur­face mount LED chip.

The cir­cuit is very sim­ple, con­sist­ing of the foot­print for the Cree MX6, two pads for con­nect­ing the wires, and a ceram­ic capac­i­tor. I tried to max­i­mize the sur­face areas con­nect­ed to the LED pads for heat dis­si­pa­tion.
I had some Carclo 20mm LED lens­es #10138 sal­vaged from a large flood­lamp that had failed, that would focus the wide angle light dis­per­sion of the XLamp chip into a more focused beam need­ed for the bal­ance. The inner set of four holes are for mount­ing the #10737 lens holder.

The Cree MX6 chip has an iso­lat­ed ther­mal pad which trans­fers heat to the back side of the board thru vias includ­ed in the foot print and addi­tion­al vias I added on both sides of the chip. I also removed all sol­der mask from the back side of the board for max­i­mum ther­mal cou­pling to the ther­mal pad and heatsink.

I did get a lit­tle (a lot) car­ried away with the heat sink. I had a spare CPU cool­er with a nice cop­per but­ton and alu­minum fins that matched up with board very well, but is much larg­er than need­ed for this 1 watt LED. At least it will stay nice and cool.
The typ­i­cal cur­rent for this LED is 300 mA at 3.16 volts DC, with a max­i­mum of 1,000 mA cur­rent with prop­er cool­ing. I will most like­ly be oper­at­ing this at 300 mA or less from an exter­nal wall mount­ed 3.3 volt supply.

Below 300 mA the board by itself with no heatsink stays below 38 degrees C at room tem­per­a­ture with only con­vec­tion cooling.

Eagle CAD V7.7 Schematic and Board files for Cree XLED V1.1 ZIP file

OSH Park project page for board fabrication.