Patent ID: 8896214

Claim:
A LED driving system for driving multi-string LEDs, comprising: an input port configured to receive an input signal; a switch node configured to provide a switching signal; an energy storage component coupled between the input port and the switch node; a main switch coupled between the switch node and a reference ground; n output lines coupled in parallel, wherein n is a natural number, and each output line having a first terminal and a second terminal, wherein each output line having an output switch, a diode and a LED string coupled in series between the first and second terminals, and wherein each output line having a capacitor coupled in parallel with the LED string, and wherein all the first terminals are coupled together to the switch node, and all the second terminals are coupled together to the reference ground via a current sense resistor, the current sense resistor configured to provide a current sense signal indicative of the current flowing through the LED string when a corresponding output switch of the LED string is on; and a controller configured to provide a control signal to the main switch and to provide corresponding n control signals to the corresponding n output switches in the corresponding n output lines; and wherein the controller further comprises: a transconductance amplifier having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the current sense resistor to receive the current sense signal, the second input terminal is coupled to the reference ground, wherein based on the current sense signal, the transconductance amplifier generates an amplified signal; an integrated capacitor coupled to the output terminal of the transconductance amplifier to receive the amplified signal, to generate an integrated signal; a reset switch coupled in parallel with the integrated capacitor to reset the integrated signal to be zero when the integrated signal reaches a current reference signal; a comparator having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is coupled to integrated capacitor to receive the integrated signal, the second terminal is configured to receive the current reference signal, wherein based on the integrated signal and the current reference signal, the comparator generates a comparison signal; and a logical circuit coupled to the comparator to receive the comparison signal, and wherein based on the comparison signal, the logical circuit generates control signals to the reset switch, the main switch, and the output switch.