Please read my license notice before copying my photos.
A little LED controller circuit I built. At the center of the board is a Micrel 2145 boost mode converter chip. It works by rapidly cycling the supply voltage across an inductor. This is normally a voltage regulator but I'm using it with a sense resistor for constant current operation.
The circuit operates from almost any input voltage from about two to twenty volts, making it suitable for operation from batteries, surplus cellphone chargers, etc. The constant current output means you can put any number of LEDs on the output, up to the output voltage and power rating of the chip. So for example you can vary the light output by simply varying the number of LEDs without having to make any other adjustments.
The only light source for the photo on the right is the one watt white LED at the left side of the frame.
Total parts cost $3.91 of which $2.72 is for the chip. Much cheaper in quantity.
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