This design describes how to light a string of LEDs of any color from a 1.5-V cell using just a few inexpensive components. The circuit (see figure) forms a self-oscillating, unregulated step-up converter that can deliver an average output power of about 230 mW to a load when the nominal input voltage is 1.5 V, with power-conversion efficiency of approximately 65%. The driver has been tested with a string of three standard white LEDs (see table)...
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