Single cell lights any LED


Posted on Jul 15, 2012

The circuit in Figure 1 allows you to light any type of LED from a single cell whose voltage ranges from 1 to 1.5V. This range accommodates alkaline, carbon-zinc, NiCd, or NiMH single cells. The circuit`s principal application is in LED-based flashlights, such as a red LED in an astronomer`s flashlight, which doesn`t interfere with night vision. White LEDs make handy general-purpose flashlights. You can use the circuit in Figure 1 with LEDs ranging from infrared (1.2V) to blue or white (3.5V). The circuit is tolerant of the varying LED voltage requirements and delivers relatively constant power. It provides compensation for varying battery voltage. The circuit is an open-loop, discontinuous, flyback boost converter. Q2 is the main switch, which charges L1 with the energy to deliver to the LED. When Q2 turns off, it allows L1 to dump the stored energy into the LED during flyback.






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