White led driver

  
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After I smashed about 5 mobile phones and collected some white LEDs, I decided to build some some LED searchlight. There are two ways to solve this problem: first, Chinese version, just connect some white LED`s to battery and use some ballast resistor. And watch you spotlight fading while the battery is loosing it`s power. Ante the second, hi-tech
White led driver - schematic

, way. To build special LED driver. almost all recent white LEDs are in fact blue LEDs with special coating to emit missing wavelengths and the result is white color. To use LED and full efficiency, you must supply constant working current to LED. It is possible to connect LED in daisy chain way using only one current ballast, but the voltage must be quite high (~3V per LED) or connect them in parallel. But in parallel mode you must use separate ballast for each LED. Chip manufacturers make special chips- LED drivers. This chip lets you to connect LEDs in daisy chain and is working from single cell. I received sample from Linear Technologies. It is LT3486, dual channel white LED driver from single Li-ion cell. It is generic step-up converter with feedback from current shunt resistor and over-voltage protection. In sample circuit there are 2G—8 white LEDs connected to chip. But other example is with 2G—16! I thing the limit is only max power on the chip, max voltage on the output (35V) and max current (~25mA typical) per channel. And the number of diodes are not very significant value. The circuit is very simple. All component are easy to get. As I love using second hand components, I had some difficulties collecting very small 10G H inductors. Thanks to Samsung digital cameras, I removed inductor from camera`s PCBs. Other component was fast schottky diode- recommended one was ZHCS400 (40V, 400mA), but I placed IR1F4...



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