Backlight Driving Circuit, LCD Device, and Method for Driving the Backlight Driving Circuit

1. A backlight driving circuit, comprising: a light emitting diode (LED) lightbar, a power supply driving the LED lightbar; a constant current driving chip controlling the power supply and the LED lightbar; and a control unit monitoring voltage of a cathode of the LED lightbar; wherein the constant current driving chip comprises a main control unit that drives the power supply, and an adjusting unit that adjusts brightness of the LED lightbar; an input end of the adjusting unit is coupled to the cathode of the LED lightbar, and an output end of the adjusting unit is coupled to a load unit, a resistance value of the load unit is adjustable; when the voltage of the cathode of the LED lightbar is greater than or equal to a preset threshold, the control unit controls the load unit to reduce the resistance value of the load unit.

2. The backlight driving circuit of claim 1 , wherein the control unit comprises a first comparator and a monitor unit; a first reference voltage is input to a first input end of the first comparator, a second input end of the first comparator is coupled to the cathode of the LED lightbar, and an output end of the first comparator is coupled to the monitor unit; when the voltage of the cathode of the LED lightbar is greater than or equal to a preset threshold, the first comparator outputs a reserved voltage, and the monitor unit controls the load unit to reduce the resistance value of the load unit; the first reference voltage is less than or equal to the preset threshold.

3. The backlight driving circuit of claim 2 , wherein the monitor unit comprises an adjusting assembly that adjusts a duty cycle of a pulse-width modulation (PWM) dimming signal, and the adjusting assembly is coupled to the adjusting unit; when the voltage of the cathode of the LED lightbar is greater than or equal to the preset threshold, the adjusting assembly reduces the duty cycle of the PWM dimming signal.

4. The backlight driving circuit of claim 3 , wherein the adjusting unit comprises a second controllable switch and a second comparator coupled to the second controllable switch; the second controllable switch is connected in series between the cathode of the LED lightbar and the load unit; an output end of the adjusting assembly is coupled to a control end of the second controllable switch.

5. The backlight driving circuit of claim 1 , wherein the load unit comprises N resistors connected in parallel, and (N−1) resistors are connected with the controllable switches in series; when the voltage of the cathode of the LED lightbar is greater than or equal to the preset threshold, the control unit controls at least one controllable switch to turn on; wherein N is a natural number that is greater than or equal to 2.

6. The backlight driving circuit of claim 5 , wherein the control unit comprises a first comparator and a monitor unit; a first reference voltage is input to a first input end of the first comparator, a second input end of the first comparator is coupled to the cathode of the LED lightbar, and an output end of the first comparator is coupled to the monitor unit; when the voltage of the cathode of the LED lightbars is greater than or equal to the preset threshold, the first comparator outputs a reserved voltage, and the monitor unit controls the load unit to reduce the resistance value of the load unit; the first reference voltage is less than or equal to the preset threshold; wherein the monitor unit comprises an adjusting assembly that adjusts a duty cycle of a pulse-width modulation (PWM) dimming signal; and the adjusting assembly is coupled to the adjusting unit; when the voltage of the cathode of the LED lightbar is greater than or equal to the preset threshold, the adjusting assembly reduces the duty cycle of the PWM dimming signal; wherein the adjusting unit comprises a second controllable switch and a second comparator coupled to the second controllable switch; the second controllable switch is connected in series between the cathode of the LED lightbar and the load unit; an output end of the adjusting assembly is coupled to a control end of the second controllable switch.

7. The backlight driving circuit of claim 1 , the load unit comprises a first resistor and a second resistor that are connected in parallel; the second resistor is connected with a first controllable switch in series; when the voltage of the cathode of the LED lightbar is greater than or equal to the preset threshold, the control unit controls the first controllable switch to turn on.

8. The backlight driving circuit of claim 7 , wherein the control unit comprises a first comparator and a monitor unit; a first reference voltage is input to a first input end of the first comparator, a second input end of the first comparator is coupled to the cathode of the LED lightbar, and an output end of the first comparator is coupled to the monitor unit; when the voltage of the cathode of the LED lightbar is greater than or equal to the preset threshold, the first comparator outputs a reserved voltage, and the monitor unit controls the load unit to reduce the resistance value of the load unit; the first reference voltage is less than or equal to the preset threshold; wherein the monitor unit comprises an adjusting assembly that adjusts a duty cycle of a pulse-width modulation (PWM) dimming signal, and the adjusting assembly is coupled to the adjusting unit; when the voltage of the cathode of the LED lightbar is greater than or equal to the preset threshold, the adjusting assembly reduces the duty cycle of the PWM dimming signal; wherein the adjusting unit comprises a second controllable switch and a second comparator coupled to the second controllable switch; the second controllable switch is connected in series between the cathode of the LED lightbar and the load unit; an output end of the adjusting assembly is coupled to a control end of the second controllable switch.

9. The backlight driving circuit of claim 1 , wherein the load unit comprises a first resistor and a second resistor that are connected in parallel; the second resistor is connected with a first controllable switch in series; wherein the control unit comprises a first comparator and a monitor unit; a first reference voltage is input to a first input end of the first comparator, a second input end of the first comparator is coupled to the cathode of the LED lightbar, and an output end of the first comparator is coupled to the monitor unit; the first reference voltage is less than or equal to the preset threshold; wherein the monitor unit comprises an adjusting assembly that adjusts a duty cycle of a pulse-width modulation (PWM) dimming signal, and the adjusting assembly is coupled to the adjusting unit; wherein the adjusting unit comprises a second controllable switch and a second comparator coupled to the second controllable switch; the second controllable switch is connected in series between the cathode of the LED lightbar and the load unit; an output end of the adjusting assembly is coupled to a control end of the second controllable switch; when the voltage of the cathode of the LED lightbar is greater than or equal to the first reference voltage, the first comparator outputs a reserved voltage, the control unit controls the first controllable switch to turn on, and simultaneously, the adjusting assembly reduces the duty cycle of the PWM dimming signal.

10. A light crystal display (LCD) device, comprising: a backlight driving circuit; wherein the backlight driving circuit comprises a light emitting diode (LED) lightbar, a power supply driving the LED lightbar, a constant current driving chip controlling the power supply and the LED lightbar, and a control unit monitoring a voltage of a cathode of the LED lightbar; wherein constant current driving chip comprises a main control unit that drives the power supply, and an adjusting unit that adjusts brightness of the LED lightbar; an input end of the adjusting unit is coupled to the cathode of the LED lightbar, and an output end of the adjusting unit is coupled to a load unit, a resistance value of the load unit is adjusted; when the voltage of the cathode of the LED lightbar is greater than or equal to a preset threshold, the control unit controls the load unit to reduce the resistance value of the load unit.

11. The LCD device of claim 10 , wherein the control unit comprises a first comparator and a monitor unit; a first reference voltage is input to a first input end of the first comparator, a second input end of the first comparator is coupled to the cathode of the LED lightbar, and an output end of the first comparator is coupled to the monitor unit; when the voltage of the cathode of the LED lightbar is greater than or equal to the preset threshold, the first comparator outputs a reserved voltage, and the monitor unit controls the load unit to reduce the resistance value of the load unit; the first reference voltage is less than or equal to the preset threshold.

12. The LCD device of claim 10 , wherein the monitor unit comprises an adjusting assembly that adjusts a duty cycle of a pulse-width modulation (PWM) dimming signal; and the adjusting assembly is coupled to the adjusting unit; when the voltage of the cathode of the LED lightbar is greater than or equal to the preset threshold, the adjusting assembly reduces the duty cycle of the PWM dimming signal.

13. The LCD device of claim 12 , wherein the adjusting unit comprises a second controllable switch and a second comparator coupled to the second controllable switch; the second controllable switch is connected in series between the cathode of the LED lightbar and the load unit; an output end of the adjusting assembly is coupled to a control end of the second controllable switch.

14. The LCD device of claim 10 , wherein the load unit comprises N resistors connected in parallel, and (N−1) resistors are connected with the controllable switches in series; when the voltage of the cathode of the LED lightbars is greater than or equal to the preset threshold, the control unit controls at least one controllable switch to turn on; wherein N is a natural number that is greater than or equal to 2.

15. The LCD device of claim 14 , wherein the control unit comprises a first comparator and a monitor unit; a first reference voltage is input to a first input end of the first comparator, a second input end of the first comparator is coupled to the cathode of the LED lightbar, and an output end of the first comparator is coupled to the monitor unit; when the voltage of the cathode of the LED lightbars is greater than or equal to the preset threshold, the first comparator outputs a reserved voltage, and the monitor unit controls the load unit to reduce the resistance value of the load unit; the first reference voltage is less than or equal to the preset threshold; wherein the monitor unit comprises an adjusting assembly that adjusts a duty cycle of a pulse-width modulation (PWM) dimming signal; and the adjusting assembly is coupled to the adjusting unit; when the voltage of the cathode of the LED lightbar is greater than or equal to the preset threshold, the adjusting assembly reduces the duty cycle of the PWM dimming signal; wherein the adjusting unit comprises a second controllable switch and a second comparator coupled to the second controllable switch; the second controllable switch is connected in series between the cathode of the LED lightbar and the load unit; an output end of the adjusting assembly is coupled to a control end of the second controllable switch.

16. The LCD device of claim 10 , wherein the load unit comprises a first resistor and a second resistor that are connected in parallel; the second resistor is connected with a first controllable switch in series; when the voltage of the cathode of the LED lightbar is greater than or equal to the preset threshold, the control unit controls the first controllable switch to turn on.

17. The LCD device of claim 16 , wherein the control unit comprises a first comparator and a monitor unit; a first reference voltage is input to a first input end of the first comparator, a second input end of the first comparator is coupled to the cathode of the LED lightbar, and an output end of the first comparator is coupled to the monitor unit; when the voltage of the cathode of the LED lightbar is greater than or equal to the preset threshold, the first comparator outputs a reserved voltage, and the monitor unit controls the load unit to reduce the resistance value of the load unit; the first reference voltage is less than or equal to the preset threshold; wherein the monitor unit comprises an adjusting assembly that adjusts a duty cycle of a pulse-width modulation (PWM) dimming signal, and the adjusting assembly is coupled to the adjusting unit; when the voltage of the cathode of the LED lightbar is greater than or equal to the preset threshold, the adjusting assembly reduces the duty cycle of the PWM dimming signal; wherein the adjusting unit comprises a second controllable switch and a second comparator coupled to the second controllable switch; the second controllable switch is connected in series between the cathode of the LED lightbar and the load unit; an output end of the adjusting assembly is coupled to a control end of the second controllable switch.

18. The LCD device of claim 10 , wherein the load unit comprises a first resistor and a second resistor that are connected in parallel; the second resistor is connected with a first controllable switch in series; wherein the control unit comprises a first comparator and a monitor unit; a first reference voltage is input to a first input end of the first comparator, a second input end of the first comparator is coupled to the cathode of the LED lightbar, and an output end of the first comparator is coupled to the monitor unit; the first reference voltage is less than or equal to the preset threshold; wherein the monitor unit comprises an adjusting assembly that adjusts a duty cycle of a pulse-width modulation (PWM) dimming signal, and the adjusting assembly is coupled to the adjusting unit; wherein the adjusting unit comprises a second controllable switch and a second comparator coupled to the second controllable switch; the second controllable switch is connected in series between the cathode of the LED lightbar and the load unit; an output end of the adjusting assembly is coupled to a control end of the second controllable switch; when the voltage of the cathode of the LED lightbar is greater than or equal to the first reference voltage, the first comparator outputs a reserved voltage, the control unit controls the first controllable switch to turn on, and simultaneously, the adjusting assembly reduces the duty cycle of the PWM dimming signal.

19. A method for driving a backlight driving circuit, the backlight driving circuit comprising a light emitting diode (LED) lightbar, a power supply driving the LED lightbar, and a constant current driving chip controlling the power supply and the LED lightbar; the constant current driving chip comprising a main control unit that drives the power supply, and an adjusting unit that adjusts brightness of the LED lightbar; an input end of the adjusting unit being coupled to a cathode of the LED lightbar, an output end of the adjusting unit being coupled to a load unit, and a resistance value of the load unit being adjusted; the method comprising: A: setting a preset threshold; and B: monitoring a voltage of the cathode of the LED lightbar, if the voltage of the cathode of the LED lightbar is greater than or equal to the preset threshold, reducing the resistance value of the load unit; if the voltage of the cathode of the LED lightbar is less than the preset threshold, maintaining the resistance value of the load unit.

20. The method for driving the backlight driving circuit of claim 19 , wherein the step B comprises: when reducing the resistance value of the load unit, reducing a duty cycle of a driving signal of the adjusting unit, which allows effective current flowing through the LED lightbar that is short-circuited to be consistent with current flowing through the LED lightbars that are not short-circuited.