Backlight unit, method of operating the same and liquid crystal display device having the same

1. A backlight unit comprising:

a light source;

an inverter which provides the light source with an input voltage; and

a printed circuit board connected to the light source,

wherein the printed circuit board includes a protection circuit which detects an open-lamp-protection voltage which varies according to a change of the input voltage, and changes a reference voltage according to the change of the input voltage, and

wherein the protection circuit turns off the inverter when the detected open-lamp-protection voltage is higher than the changed reference voltage by comparing the detected open-lamp-protection voltage with the changed reference voltage, and

wherein the protection circuit includes;

a voltage detection part which distributes the input voltage applied to the light source by using a capacitor to detect the open-lamp-protection voltage;

a reference voltage changing part which distributes the input voltage by using the capacitor to change the reference voltage according to the change of the input voltage; and

a protection-control signal generation part which compares the open-lamp-protection voltage with the reference voltage and generates a protection-control signal Which controls the operation of the inverter.

2. The backlight unit of claim 1 , wherein the input voltage is a local dimming voltage.

3. The backlight unit of claim 1 , wherein the capacitor is a pattern capacitor comprising patterns disposed on at least one of an upper surface and a lower surface of the printed circuit board.

4. The backlight unit of claim 1 , wherein the protection-control signal generation part includes a comparator which compares the open-lamp-protection voltage with the reference voltage.

5. The backlight unit of claim 1 , wherein a difference between the open-lamp-protection voltage and the reference voltage is in a range of about 2 Volts to about 11 Volts.

6. The backlight unit of claim 1 , wherein the printed circuit board further includes a plurality of balance capacitors which control the input voltage to substantially uniformly maintain a balance of electrical currents applied to the light source.

7. The backlight unit of claim 1 , wherein the printed circuit board further includes a plurality of balance inductors which control the input voltage to substantially uniformly maintain a balance of electrical currents applied to the light source.

8. The backlight unit of claim 1 , further comprising a feedback control part which generates a feedback signal which controls the voltage level of the input voltage according to whether the light source is turned on normally.

9. The backlight unit of claim 1 , wherein the light source is one of a plurality of light-emitting diodes and at least one cold cathode fluorescent lamp.

10. A method of operating a backlight unit, the method comprising:

applying an input voltage to a light source;

detecting an open-lamp-protection voltage using a capacitor to distribute the input voltage;

changing a reference voltage according to the change of the input voltage using the capacitor to distribute the input voltage;

comparing the detected open-lamp-protection voltage with the changed reference voltage; and

turning off the input voltage applied to the light source when the detected open-lamp-protection voltage is higher than the changed reference voltage by comparing the detected open-lamp-protection voltage with the changed reference voltage.

11. The method of claim 10 , wherein turning off the input voltage includes:

changing the reference voltage according to a change of the input voltage;

comparing the open-lamp-protection voltage with the changed reference voltage; and

turning off the input voltage applied to the light source when the detected open-lamp-protection voltage is higher than the changed reference voltage, or maintaining the input voltage applied to the light source when the detected open-lamp-protection voltage is substantially the same as or lower than the changed reference voltage.

12. The method of claim 11 , wherein the input voltage is turned off when the detected open-lamp-protection voltage is higher than the changed reference voltage for about 2 seconds or longer.

13. The method of claim 11 , wherein a difference between the open-lamp-protection voltage and the reference voltage is in a range of about 2 Volts to about 11 volts.

14. A liquid crystal display device comprising:

an liquid crystal display panel which displays an image; and

a backlight unit providing the liquid crystal display panel with light, the backlight unit including:

a light source;

an inverter which provides the light source with an input voltage; and

a printed circuit board connected to the light source, the printed circuit board including a protection circuit which detects an open-lamp-protection voltage which varies according to a change of the input voltage and changes a reference voltage according to the change of the input voltage, and the protection circuit turns off the inverter when the detected open-lamp-protection voltage is higher than the changed reference voltage by comparing the detected open-lamp-protection voltage with the changed reference voltage, and

wherein the protection circuit includes:

a voltage detection part which distributes the input voltage applied to the light source by using a capacitor to detect the open-lamp-protection voltage;

a reference voltage changing part which distributes the input voltage by using the capacitor to change the reference voltage according to the change of the input voltage; and

a protection-control signal generation part which compares the open-lamp-protection voltage with the reference voltage and generates a protection-control signal which controls the operation of the inverter.

15. The liquid crystal display device of claim 14 , wherein the input voltage is a local dimming voltage.

16. The liquid crystal display device of claim 14 , wherein the capacitor is a pattern capacitor comprising patterns disposed on at least one of an upper surface and a lower surface of the printed circuit board.

17. The liquid crystal display device of claim 14 , wherein the printed circuit board further includes a plurality of balance capacitors which control the input voltage to uniformly maintain a balance of electrical currents applied to the light source.

18. The liquid crystal display device of claim 14 , wherein the printed circuit board further includes a plurality of balance inductors which control the input voltage to substantially uniformly maintain a balance of electrical currents applied to the light source.

19. The liquid crystal display device of claim 14 , further comprising a feedback control part which generates a feedback signal which controls the voltage level of the input voltage according to whether the light source is turned on normally.

20. The liquid crystal display device of claim 14 , wherein the light source is one of a plurality of light-emitting diodes and at least one cold cathode fluorescent lamp.