Patent ID: 7480463

Claim:
A light-emitting diode (LED) drive circuit including a circuit that drives a light-emitting diode with a common connected cathode, said drive circuit comprising: a first resistor having a first terminal connected to an anode of said light-emitting diode; a first NPN-type transistor that has an emitter connected to a second terminal of said first resistor and that approximately determines a control current for emission of light in cooperation with said first resistor; a second NPN-type transistor positioned parallel with said first resistor element that has an emitter connected to said anode of said light-emitting diode; and a current supply, a level shifter, and a switch for selectively changing a voltage between a base-emitter of said second NPN-type transistor, that are positioned between a base of said second NPN-type transistor and said second terminal of said first resistor.