30mA LED Dimmer
If you’ve ever tried dimming a LED with a simple potentiometer, you know that the approach does not work very well. Just as with ordinary diodes, the voltage-current characteristic of LEDs is far from linear. The result - depending on the potentiometer setting the LED brightness will hardly change most of the time as the pot is turned and a sudden variation at the end. The best method to tackle this problem is to power the LED from a current source with zero to 100% adjustment range. The circuit shown here is an example. A low-current LED (D1) is used to generate a reference voltage that’s first buffered by one half of an LM358. The actual current source that powers the LED(s) is built around the second opamp in the chip. Circuit diagram: 30-mA LED Dimmer Circuit Diagram The potentiometer allows the output current to be adjusted, with R2 acting as a current sense, the resistor dropping the same voltage as the one obtained from the pot. Using Ohm’s law we find that the maximum current t...