BUCK CONVERTER for HIGH-POWER LED 210mA

This circuit will drive 1 high-power white LED from a 12v supply and is capable of delivering 210mA. The driver transistor is BD 139 and the details of the inductor are shown above. The voltage across the LED is approx 3.3v - 3.5v The driver transistor will need a small heatsink. The 2R2 can be increased if a lower drive-current is required.