Patent ID: 8368322

Claim:
A driving circuit for a light-emitting diode (LED) lamp comprising no more than 4 strings each having an input and an output terminals and comprising a plurality of LEDs coupled in series between the input and the output terminals, the driving circuit for receiving an on-off control signal and a dimming control signal and outputting a direct-current (DC) voltage of no more than 70 volts to the input terminals of the strings, the driving circuit comprising: a plurality of diodes, each having an anode terminal coupled to the output terminal of a corresponding string and a cathode terminal; an overvoltage protection circuit, coupled to the cathode terminals of the diodes, for outputting an overvoltage control signal when a voltage at the output terminal of one of the strings is greater than a threshold voltage; a plurality of constant current circuits, each coupled between the output terminal of a corresponding string and ground, the on-off control signal for controlling whether the constant current circuits work or not so as to control whether the LED lamp works or not, the dimming control signal for controlling a duty cycle of working of the constant current circuits so as to control a brightness of the LED lamp; and a switch for forcing the on-off control signal to control the constant current circuits not to work when receiving the overvoltage control signal.