the LED backlight driving circuit comprises a plurality of LED strings, a channel control switch device, a constant current module, a channel switching control module, a signal control unit, and a serial peripheral interface (SPI) interface unit;

each of the LED strings has a high-potential-end directly connected to an LED driving voltage V_LED and a low-potential-end connected to the channel control switch device; a plurality of the LED strings form a group of LED strings, each group of LED strings shares one constant current module, and a plurality of channel control switch devices in each group of LED strings are connected to one channel switching control module; and the channel switching control module is used to control turn-on of the LED strings in the group; and

the channel switching control module is connected to the signal control unit, and the signal control unit is connected to the SPI interface unit; the SPI interface unit receives an external display signal and transmits the external display signal to the signal control unit, and the signal control unit determines an on-state duty cycle of each LED string in each group of LED strings according to required display brightness, and transmits on-state duty cycle data to the corresponding channel switching control module for controlling the on-state duty cycle of each LED string in each group of LED strings;

wherein the LED backlight driving method comprises:

in each group of LED strings, determining required brightness duty cycles of LED strings and an upper limit of an evenly shared duty cycle;

calculating differences between the required brightness duty cycles and the upper limit of the evenly shared duty cycle of each LED string to obtain duty cycle margins;

compensating the duty cycle margins to the LED string of which the required brightness duty cycle exceeds the upper limit of the evenly shared duty cycle, thereby improving display brightness of the LED string;

when a sum of the duty cycle margins and the upper limit of the evenly shared duty cycle is greater than the required brightness duty cycle of the LED string of which the required brightness duty cycle exceeds the upper limit of the evenly shared duty cycle, setting an actual on-state duty cycle of the LED string to the required brightness duty cycle of the LED string; and

when the sum of the duty cycle margins and the upper limit of the evenly shared duty cycle is less than the required brightness duty cycle of the LED string of which the required brightness duty cycle exceeds the upper limit of the evenly shared duty cycle, setting the actual on-state duty cycle of the LED string to a sum of the duty cycle margin and the upper limit of the evenly shared duty cycle.