Backlight unit and method of driving the same

1. A backlight unit, comprising:

at least one cold cathode fluorescent lamp having internal electrodes and arranged at a lower end of a bottom cover;

external electrode fluorescent lamps arranged on the bottom cover above the cold cathode fluorescent lamp; and

inverters disposed on a rear side of the bottom cover for driving the at least one cold cathode fluorescent lamp and the external electrode fluorescent lamps.

2. The backlight unit according to claim 1 , wherein the inverters include first and second transformers for driving the at least one cold cathode fluorescent lamp, and third and fourth transformers for driving the external electrode fluorescent lamps.

3. The backlight unit according to claim 1 , wherein the external electrode fluorescent lamps are connected in parallel.

4. The backlight unit according to claim 1 , further comprising first and second common electrodes at both ends of the external electrode fluorescent lamps that respectively contact first and second external electrodes of each external electrode fluorescent lamp.

5. A backlight unit, comprising:

a cold cathode fluorescent lamp at a lower end of a bottom cover and having first and second inner electrodes;

external electrode fluorescent lamps arranged on the bottom cover above the cold cathode fluorescent lamps, and each of which has first and second external electrodes; and

first and second common electrodes at both ends of the external electrode fluorescent lamps that respectively contact the first and second external electrodes of each external electrode fluorescent lamp.

6. The backlight unit according to claim 5 , further comprising:

first and second inverter printed circuit boards disposed on a rear side of the bottom cover;

first and second transformers provided on the first inverter printed circuit board to supply power to the first inner electrode of the cold cathode fluorescent lamp and to the first external electrode of each external electrode fluorescent lamp; and

third and fourth transformers provided to the second inverter printed circuit board to supply power to the second inner electrode of the cold cathode fluorescent lamp and to the second external electrode of each external electrode fluorescent lamp.

7. The backlight unit according to claim 6 , further comprising:

a first electric wire connected between the first common electrode and the first transformer; and

a second electric wire connected between the second common electrode and the third transformer.

8. The backlight unit according to claim 7 , further comprising a third electric wire connected between the first inner electrodes of the cold cathode fluorescent lamps and the second transformer, and a fourth electric wire connected between the second inner electrodes of the cold cathode fluorescent lamps and the fourth transformer.

9. The backlight unit according to claim 6 , further comprising a synchronization cable interconnecting the first and second inverter printed circuit boards.

10. The backlight unit according to claim 5 , wherein the first and second common electrodes are gripper type electrodes to secure the first and second external electrodes of each of the external electrode fluorescent lamps.

11. The backlight unit according to claim 5 , wherein each of the first and second common electrodes includes:

plural pairs of fastening members separated from each other while defining a slit in each pair of fastening members for holding the first or second external electrodes therein;

first or second common electrode line on both sides of the pairs of fastening members to connect the fastening members with each other; and

a stopper formed vertically at a distal end of the first and second common electrode lines such that a distal end of each external electrode fluorescent lamp is seated thereon.

12. The backlight unit according to claim 5 , further comprising upper structures on both ends of the cold cathode fluorescent lamps and the external electrode fluorescent lamps to cover the lamps.

13. The backlight unit according to claim 5 , further comprising lamp holders disposed at both ends of the cold cathode fluorescent lamps.

14. A method of driving a backlight unit, the backlight unit having a cold cathode fluorescent lamp having internal electrodes and arranged at a lower end of a bottom cover, and external electrode fluorescent lamps arranged on the bottom cover above the cold cathode fluorescent lamp, the method comprising:

applying alternating current to the cold cathode fluorescent lamps having internal electrodes and arranged at the lower end of the bottom cover; and

applying alternating current to the external electrode fluorescent lamps in a phase shifting manner after sequentially applying the alternating current to the one cold cathode fluorescent lamp.

15. A backlight unit, comprising:

a cold cathode fluorescent lamp at a lower end of a bottom cover and having first and second inner electrodes;

external electrode fluorescent lamps arranged on the bottom cover above the cold cathode fluorescent lamps, and each of which has first and second external electrodes;

plural pairs of fastening members separated from each other while defining a slit in each pair of fastening members for holding the first or second external electrodes therein; and

a first or second common electrode line on both sides of the pairs of fastening members to connect the fastening members with each other.

16. The backlight unit according to claim 15 , further comprising:

first and second inverter printed circuit boards disposed on a rear side of the bottom cover;

first and second transformers provided on the first inverter printed circuit board to supply power to the first inner electrode of the cold cathode fluorescent lamp and to the first external electrode of each external electrode fluorescent lamp; and

third and fourth transformers provided to the second inverter printed circuit board to supply power to the second inner electrode of the cold cathode fluorescent lamp and to the second external electrode of each external electrode fluorescent lamp.

17. The backlight unit according to claim 16 , further comprising:

a first electric wire connected between the first common electrode and the first transformer; and

a second electric wire connected between the second common electrode and the third transformer.

18. The backlight unit according to claim 17 , further comprising a third electric wire connected between the first inner electrodes of the cold cathode fluorescent lamps and the second transformer, and a fourth electric wire connected between the second inner electrodes of the cold cathode fluorescent lamps and the fourth transformer.

19. The backlight unit according to claim 16 , further comprising a synchronization cable interconnecting the first and second inverter printed circuit boards.

20. The backlight unit according to claim 15 , further comprising lamp holders disposed at both ends of the cold cathode fluorescent lamps.