White LED Drive Circuit

A minimum number of parts yields a compact switching converter that can provide sufficient voltage to drive white LEDs. The resulting lamp is much more efficient, in terms of lumen hours per pound of battery, than incandescent bulbs, and because the color of the light is determined by fluorescence of phosphors within the LED assembly, the color of the lamp does not change perceptibly as the battery runs down. As a result, very long battery life is achievable. This circuit is suitable for powering flashlights, emergency lighting, and other applications in which it is desirable to power white LEDs from one or two primary cell batteries using a low cost circuit.

The circuit could not be simpler than this. The transistor, 1K resistor and the tapped inductor form a blocking oscillator. When the power button is pressed, the transistor is biased on through the 1 k resistor. Voltage that appears from the tap on the in

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