Patent ID: 9241377
Filing Date: 2016-01-19
CPC Classification: G09G,H05B

Claim Text:
1. A light emitting diode (LED) backlight driving circuit, comprising: a power supply; an LED light bar; and a constant current driving chip that adjusts brightness of the LED light bar; wherein the constant current driving chip receives a pulse-width modulation (PWM) dimming signal; N boost units are connected in series between the power supply and the LED light bar, and the N boost units are connected in parallel with each other; comparing units are correspondingly coupled to control ends of one or more of (N−1) boost units; when a duty ratio of the PWM dimming signal is less than a preset threshold, the comparing unit drives a corresponding boost unit to turn off; N is an integer greater than or equal to 2, wherein the comparing unit comprises a comparator, a non-inverting end of the comparator receives a reference voltage, a converting unit is coupled to an inverting end of the comparator, and the converting unit converts the PWM dimming signal to an equivalent voltage; a changing-over controllable switch is connected in series between the control end of the boost unit and a ground terminal of the LED backlight driving circuit; the reference voltage is less than or equal to the equivalent voltage of the PWM dimming signal corresponding to the preset threshold; when the equivalent voltage outputted by the converting unit is less than the reference voltage, the comparator drives the changing-over controllable switch to turn off, wherein the converting unit comprises a filter resistor and a filter capacitor, the inverting end of the comparator receives the PWM dimming signal through the filter resistor, and the filter capacitor is connected in series between the inverting end of the comparator and the ground terminal of the LED backlight driving circuit.