Circuit and method for driving LED string for backlight, and backlight and display device using the circuit

摘要

An LED driving circuit drives a display backlight LED string including multiple LEDs connected in series. A power supply supplies a driving voltage from an output terminal thereof to a first end of the LED string. A detection resistor is arranged between a second end of the LED string and a fixed voltage terminal. The LED driving circuit receives a pulse modulation signal having a duty ratio that corresponds to the luminance. In the on period, in which the PDIM signal is the first level, the LED driving circuit controls the power supply such that the voltage drop across the detection resistor approaches a predetermined target value. In the off period, in which the PDIM signal is the second level, the LED driving circuit stops the control operation for the power supply.