This is old post. Original post dated 2008.03. You can visit it at original page in Lithuanian blog. Also try to read comments to this blog post.
The old post is about LED light torch using lots of typical small LEDs to create light. But there are better LED diodes- high power ones. One of these diodes I bought in local shop. But seller could not tell me exact properties of the device- typical for our shops and for noname China products. The only thing I know about this device, that max current of the diode is 700mA (some other sources state something about 800mA).
Diode is mouted on a small heatsink, but this is only to spread heat to big real heatsink.
As it was quite expensive diode, I decided to use real LED driver chip for it. I decided to use TexasInstruments TPS61058/TPS61059 (SYNCHRONOUS BOOST CONVERTER WITH DOWN MODE HIGH POWER WHITE LED DRIVER). This chip, as stated in datasheet is usable with Liion battery and has all protections buil in.
Chip is very small, there is blog article in my web pages. Original Lithuaniain one and there is breef translation to English version.
Finished device looks like this:
After power up everything works very fine, but heat sink is too small. I am using only 570mA current (and the voltage drop on the diode is 3.37V. So it give us only 2W of power).
There was some problems in the design of this PCB. I did not managed to get higher current. There is quite complicated working current and voltage setting system using 5 resistors! I’ve set 0.7A current, but even using fancy startup schematics it didn’t start in full power. Maybe I used bad L component- it is critical.
Also, I’ve mae experiments with TPS61059 and it looks like that this chip is 0.5A max current… 🙂
Finished device is quite small and compact. As I used single side home made PCB it is a bit bigger. If I used double sided, everthing could be much better. (Check Lithuanian version and more recent articles- I am using professionally mande double side PCB and many of mu projects are rebuild using “real” PCBs)
Biggest devices are electrolitic capacitors (3x22uF) and inductor. Inductor is only 4.7uH but it must handle quite big currents. So it is not very small. I used thantalum and maybe alluminum polymer capacitors, few ceramic chips. Almoust all components are recycled.
LED is quite bright, but the light is not focused. The best way to get good torchlight is to used some optics to focus light to single spot.
Such focused light is way much better than older constructions.