LED's have replaced the good old lightbulb in many applications. For a simple control LED a simple resistor should be enough, but modern high power LEDs need specific driver circuits to operate at optimum performance and to achieve maximum lifetime. In many cases StepUp Voltage converters are used to operate LEDSs from a single battery cell.
Here are some Links to LED Driver Schematics

Here you may find Circuit, Basics, Schematic Diagram and components for LED Driver

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