It works, and it works quite great, in fact. Well, it did work anyway :) I smoked 3 XM-Ls, but it was my fault - not the electronics. Everything was working great, and 6 XM-Ls were burning away at 1.5Amps each - looking good...
So I started cranking up the input voltage to see how the DSP handled the larger Delta-V from input to output.. Got to 60V and it was doing great - The DSP kept backing off the Buck converter keeping a nice steady 1.5 Amps going to the emitters.. Here's me, wanting to look at the signals - Output of MOSFET Gate Driver - beautiful. FAST rise and fall times. Output of Current-Sense Op-Amp - Really Nice.. Clean.. And then.. Slip, and I shorted the high side input of the op-amp to ground with the scope probe... The output of the op-amp went low (as it should), The DSP's internal comparator went low (as it should), the DSP instantly ramped the buck-converter up to 100% duty cycle (as it should), and the XML-s (near) instantly saw 60V accross the group of 3.. 20V each.. BAM, POP, Smoke, and I'm still seeing spots. For about 1 micro-second, XML-s are REALLY bright at 20V :) .. The perils of poking around with an oscilloscope..
So, I've got a perfectly functioning board! All tests out perfectly. I placed the order for 24 brand-new XM-L emitters (going Neutral White T6 instead of Cool White U2) and they should be here Friday. I'm also going to swap out the 15uH inductors for 22uH since they're back in stock - 22uH is really what I wanted to begin with, but CoilCraft was out of stock on them, so I went with the 15s. For this load 15uH is just not quite enough - the current rises and falls a bit too quickly. It doesn't take more than 10 minutes to swap out the 8 inductors, so I'm going to get the ones I really want on there..
Other than the little mishap, I couldn't be happier. If I can keep my grubby little scope probe out of places it doesn't belong, this board will be making more than 20,000 lumens by the weekend.
Now on the the control software in the DSP. All it does right now is turn the LEDs on or off - time to starting coding up the communications routines (Bluetooth) and the dimming routines. Luckily, now that the DSP is properly controlling current (the hard part), there's nothing I can really do to "blow things up".
I really can't explain how bright those three emitters were for a fraction of a second - it was like someone cut off a small piece of the sun and dropped it on the desk in my lab. I wasn't looking anywhere near the emitters and I was still absolutely blinded. I don't recommend feeding XM-L LEDs 20V - it's truly dangerous to the eyes.
PPtk