Patent ID: 9439259
Filing Date: 2016-09-06
CPC Classification: G02F,G05F,H05B,Y02B

Claim Text:
1. A drive circuit, for driving a light-emitting diode (LED) string, comprising: an output transistor, being a PNP bipolar transistor, wherein an emitter of the output transistor is connected to a cathode of the LED string; a current control resistor, disposed between a collector of the output transistor and a fixed voltage terminal that is stabilized at a specific potential; a first error amplifier, wherein an output terminal of the first error amplifier is connected to a base of the output transistor, a first input terminal of the first error amplifier is connected to a connection point of the output transistor and the current control resistor, and a first reference voltage is applied to a second input terminal of the first error amplifier, and the first error amplifier enables a sink current sunk from the output terminal to flow to the current control resistor; a switch power supply, providing an output voltage to an anode of the LED string and inputting a feedback voltage based on the output voltage to a feedback terminal; a second error amplifier, amplifying an error between a base voltage of the output transistor and a second reference voltage and generating an error voltage according to the error; a transistor, wherein a first terminal of the transistor is connected to the error voltage; and a feedback voltage control resistor having a first end connected to a second terminal of the transistor and a second end connected to the feedback terminal, and the error voltage being output through the transistor and the feedback voltage control resistor and being input to the feedback terminal.