Liquid crystal display device and method of driving the same

1. A liquid crystal display device comprising:

a liquid crystal display panel;

a timing controller configured to output a light-source controlling signal during a variable frequency mode comprising a plurality of frames with variable frame frequencies, the light-source controlling signal having a high level during a light-on period preset in an early period of a frame of the plurality of frames and a low level during a light-off period preset to a length according to a frame frequency in a latter period of the frame of the plurality of frames; and

a light source configured to emit light during the light-on period and not emit light during the light-off period in response to the light-source controlling signal,

wherein the timing controller is configured to output the light-source controlling signal having the high level throughout the frame of the plurality of frames when the length of the frame of the plurality of frames is shorter than the light-on period during the variable frequency mode.

2. The liquid crystal display device of claim 1 , wherein the timing controller comprises:

a frequency mode determiner configured to determine whether a frequency mode is the variable frequency mode using a synchronization signal; and

a light-source controlling signal generator configured to generate the light-source controlling signal when the frequency mode is the variable frequency mode.

3. The liquid crystal display device of claim 2 , wherein the frequency mode determiner is configured to determine the frequency mode using a counting value of the synchronization signal corresponding to a vertical blank period of the frame of the plurality of frames.

4. The liquid crystal display device of claim 1 , wherein the timing controller is configured to output a light-source controlling signal having the high level throughout the frame of the plurality of frames during a normal frequency mode comprising a plurality of frames with constant frame frequencies.

5. The liquid crystal display device of claim 1 , wherein the length of the light-on period corresponds to a frame length of 120 Hz.

6. The liquid crystal display device of claim 1 , wherein the length of the light-on period corresponds to a frame length of a highest frequency from among a variable frequency range in the variable frequency mode.

7. The liquid crystal display device of claim 1 , wherein the length of the light-on period corresponds to a frame length of a frequency higher than a highest frequency from among a variable frequency range in the variable frequency mode.

8. The liquid crystal display device of claim 1 , further comprising:

a light-source driver configured to generate a light-source driving signal having a pulse width modulation level corresponding to the high level of the light-source controlling signal and a low level corresponding to the low level of the light-source controlling signal.

9. A method of driving a liquid crystal display device, the method comprising:

outputting a light-source controlling signal during a variable frequency mode comprising a plurality of frames with variable frame frequencies, the light-source controlling signal having a high level during a light-on period preset in an early period of a frame of the plurality of frames and a low level during a light-off period preset to a length according to a frame frequency in a latter period of the frame of the plurality of frames;

lighting a liquid crystal display panel during the light-on period of the frame based on the light-source controlling signal during the variable frequency mode; and

not lighting the liquid crystal display panel during the light-off period of the frame based on the light-source controlling signal during the variable frequency mode,

wherein the method further comprises outputting the light-source controlling signal having the high level throughout the frame of the plurality of frames when the length of the frame of the plurality of frames is shorter than the light-on period in the variable frequency mode.

10. The method of claim 9 , further comprising:

determining whether a frequency mode is the variable frequency mode using a synchronization signal; and

generating the light-source controlling signal when the frequency mode is the variable frequency mode.

11. The method of claim 10 , wherein the frequency mode is determined using a counting value of the synchronization signal corresponding to a vertical blank period of the frame of the plurality of frames.

12. The method of claim 9 , further comprising:

outputting a light-source controlling signal having the high level throughout the frame of the plurality of frames during a normal frequency mode which includes a plurality of frames with constant frame frequencies.

13. The method of claim 9 , wherein the length of the light-on period corresponds to a frame length of 120 Hz.

14. The method of claim 9 , wherein the length of the light-on period corresponds to a frame length of a highest frequency from among a variable frequency range in the variable frequency mode.

15. The method of claim 9 , wherein the length of the light-on period corresponds to a frame length of a frequency higher than a highest frequency from among a variable frequency range in the variable frequency mode.

16. The method of claim 9 , further comprising:

generating a light-source driving signal having a pulse width modulation level corresponding to the high level of the light-source controlling signal and a low level corresponding to the low level of the light-source controlling signal; and

providing the light-source driving signal to a light source.