Patent ID: 8552660
Filing Date: 2013-10-08
Classification: H05B

Abstract:
1. A drive circuit configured to drive a parallel array of light emitting diodes (LEDs), the drive circuit comprising: a plurality of switches, each configured to be coupled to a respective LED in the parallel array of LEDs; a plurality of sampling resistors, each coupled to a respective switch in the plurality of switches and configured to receive a drive current when the respective switch is in a closed state; a plurality of chopper operational amplifiers, each chopper operational amplifier configured to receive a reference voltage at a positive feedback input terminal, a voltage taken across one of the plurality of sampling resistors at a negative feedback input terminal, and a switching control signal at a switching control signal terminal and generate an input offset voltage configured to control a respective switch in the plurality of switches using the reference voltage, the voltage taken across one of the plurality of sampling resistors, and the switching control signal, wherein each chopper operational amplifier includes a differential amplifier including an input transistor pair, a current mirror transistor pair, and a Miller compensation capacitor; wherein the input transistor pair and current mirror transistor pair are mismatched, such that when the switching control signal is switched between a first state and a second state, electrical positions of the input transistor pair switch and electrical positions of the current mirror transistor pair switch to thereby cause a reversing of polarity of the input offset voltage of the chopper operational amplifier; and wherein: when the switching signal is in the first state: when the switching signal is in the second state: