This simple circuit allows you to drive a 1W LED with a car battery. The IC MC34063 is used here as a buck converter. It is a monolithic switching regulator subsystem that can be used as a DC-DC converter. The device includes an internal temperature compensation reference, a comparator, an oscillator with an active-controlled duty cycle, a current limiting circuit, a driver and a high-current output switch. These functions are contained in an 8-pin dual in-line package.