:) First signs of life. I had a little spare time tonight, so I started putting components on the circuit board and doing some basic testing. So far, all good news. The op-amp based current sense circuit works perfectly - I'm only using a 0.01 OHM Current Sense resistor (to mitigate power loss in the sense circuit), and the 50 to 1 op-amp works beautifully. At 3 amps, I'm seeing 1.5143V out of the sense circuit - well within the 1% component tolerances - and it's stable and quiet.
The DSP is soldered down - always fun soldering a fine pitch QFN by hand with an iron. 3 XM-L's are in place, and the first lumens have been emitted. I ran it up to 3 Amps for just long enough to measure the current sense output, but with the paper-thin circuit board not being attached to a heat-sink of any kind, it gets HOT in a hurry. 1.5 amps is about the most I can run for more than 5 seconds without risking damage.
All in all though - a successful beginning.
Pictures of the process:
This is the 64 pin QFN part drowning in water soluble flux. The tip of the soldering iron is in the picture for size comparison. 3 XM-L U2 Parts are also visible. Those are a real pain to solder by hand - the only real way to do it is with two irons. They look good though - nice and centered. At the far right of the picture, you can also catch a glimpse of the 50:1 Op-Amp. I love these TI parts - very stable, and very tiny.
Side view of the pads of the QFN. Soldered up nicely, considering it was done by hand rather than reflow. You can also see a few 0603 caps and one 0805 cap.
A picture of the emitters through the TIR optic. These Cute-3-XML optics from LEDIL are very well made, I have to say.
You can see how perfectly centered the emitters are in the optic though.
The emitters lighting up for the first time. This is insanely low current - 0.001 Amps (1 milliamp).
Emitters fired at 50mA with TIR Optic in place.
Emitters at 1.5 Amp With TIR Optic :)
Overall, I'm very satisfied with the results thus far. The THIN (0.3mm) circuit board was a good move - it allows heat to move from the emitters to the back side of the board (and into the enclosure) through the vias with incredible efficiency. There is no doubt that a THIN board like this with heavy copper and LOTS of via's will perform better than an aluminum star board. At 1.5 Amps, Its less than a second before the back side of the board is WARM - which is good - it means the heat is moving away from the emitters rather than staying trapped in them.
More tomorrow, I hope.
PPtk