Re: Adjustable 10A linear constant current driver
Below is an excerpt from an e-mail sent to 350xfire regarding questions he had about using the LDO10C with the IS1006:
Someone needs to teach those idiots how to write a data sheet. In order to use the device, you need three documents - the data sheet, the longform datasheet, and the application note. The latter two I found on the "certificates, TRN's & documents" link from the LDO10C web site.
After looking at the thermal data in the longform datasheet, I'm a little alarmed at the possibility of the LDO10C overheating. It says it's designed to use forced air (fan) cooling. They don't give any information about running in still air (as you would have in a flashlight). At 5A, you are probably okay, as long as you don't have high input voltage and high ambient temp around the module. 9V and 40degrees C should be fine. At 8A, you may have a problem, but it's really hard to tell. At 10A you might be screwed.
It's best if the input voltage is as low as possible. The IS1006 needs 0.3V above the LED voltage, and the LDO10C probably needs another 0.5V, so the minimum input voltage is Vled+0.8V. 5S or 6S NiMH or 2S Li-Ion packs should provide sufficient input voltage (but if you're going NiMH, I'd recommend 4S packs and eliminate the LDO10C). From here on I'll assume you are using 2S Li-Ion packs.
A single resistor sets the output voltage of the LDO10C. The equation is
R (K ohms) = 1.182/(Vout-0.591V).
For 5A output, I would recommend Vout = Vled + 0.4V. This would maximize overall system efficiency. If Vled is 3.9V, then R= 0.319 K ohms, or 319 ohms. The nearest standard value would be 316 ohms.
For 8A output, you could run the same way if you had good cooling, but I worry the LDO would overheat. In a closed container with no real cooling for the LDO10, I would recommend sacrificing some overall efficiency to protect the LDO10. I would raise the LDO10's output voltage to 5V using a 267 ohm resistor. Explaination: the heat generated in the LDO10 increases as the output current increases, and also as the ratio of input to output voltage increases. Keeping the ratio of input to output voltage low helps keep the LDO10 from overheating.
Packhorse has more experience keeping electronics cool in a light than I do. Perhaps he can add some suggestions.
D