LED lighting device and LCD device using the same

• US 20070210722A1
• Filed: 01/18/2007
• Published: 09/13/2007
• Est. Priority Date: 03/09/2006
• Status: Active Grant

• Current Assignee: Panasonic Intellectual Property Corporation of America (Panasonic Holdings Corporation)
• Original Assignee: Hitachi Displays Limited (Japan Display Incorporated)
• Inventors: Yamamoto, Tsunenori, Konno, Akitoyo, Inuzuka, Tatsuki
• Granted Patent: US 7,518,319 B2
• Time in Patent Office: Days
• US Class Current: 315/185.S
• CPC Class Codes: H05B 45/00 Circuit arrangements for operating light-emitting diodes [LED]
• CPC Class Codes: H05B 45/14 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/24 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/44 with an active control inside an LED matrix
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

An LED lighting device can compensate a brightness change and a color change caused by a temperature change and exhibit an in-plane uniform luminance and color. A lighting device includes: at least one line connected in parallel, a constant voltage source for applying a constant voltage to the line, an ON/OFF controller, and a current detector for measuring a value of current flowing in the line. The line is formed by one or more light-emitting diodes and a switch for turning ON/OFF the current flowing in the light emitting diodes connected in series. According to the current value of each of the lines measured by the current detector, the ON/OFF controller controls the ON/OFF period of the switch of each of the lines.

Claims

1. A lighting device comprising:

at least one line connected in parallel,

a constant voltage source for applying a constant voltage to the line,

an ON/OFF controller, and

a current detector for measuring a value of current flowing in the line,

wherein

the line is formed by one or more light-emitting diodes and a switch for turning ON/OFF the current flowing in the light emitting diodes connected in series, and

according to the current value of each of the lines measured by the current detector, the ON/OFF controller controls the ON/OFF period of the switch of each of the lines.

2. The lighting device as claimed in claim 1, wherein the device further comprises a condition table for deciding the ON/OFF period ratio according to the current value of the line and the ON/OFF controller controls the ON/OFF period according to the condition table.

3. The lighting device as claimed in claim 1, wherein the current detector measures a voltage drop of a resistor when current flows in the resistor.

4. The lighting device as claimed in claim 3, wherein

a bypass switch is connected in parallel to the current detector, and

a light emission period of the light-emitting diodes to turn ON the bypass switch is distinguished from a current measurement period by the current detector to turn OFF the bypass switch.

5. The lighting device as claimed in claim 4, wherein a cycle of the light emission period and the current measurement period is set to 16.6 milliseconds or below.

6. The lighting device as claimed in claim 5, wherein during the current detection period, the switch of each of the lines is turned on by time division.

7. The lighting device as claimed in claim 6, wherein the current measurement period is set to 100 microseconds or below.

8. The lighting device as claimed in claim 1, wherein

the at least one line comprises lines of two or more primary colors among:

a red line formed by connecting a red light-emitting diode and a switch in series,

a green line formed by connecting a green light-emitting diode and a switch in series, and

a blue line formed by connecting a blue light-emitting diode and a switch in series, and

a single constant voltage source is used for lines of the two or more primary colors.

9. The lighting device as claimed in claim 8, wherein

the at least one line comprises the red line, the green line, and the blue line, and

a single constant voltage source is used for the green line and the blue line.

10. The lighting device as claimed in claim 1, wherein

the at least one line comprises lines all commonly connected at a low potential point, and

the current detector is arranged between the low potential point of the common connection and a circuit lowest potential point.

13. The lighting device as claimed in claim 1, further comprising:

temperature measuring means and

a condition table for deciding the ON/OFF period ratio according to a signal from the temperature measuring means and the current detector,

wherein the ON/OFF controller controls the ON/OFF period according to the condition table.

14. The lighting device as claimed in claim 13, wherein the temperature measuring means measures an ambient temperature of the lighting device or a temperature of a metal plate connected to the light-emitting diode.

17. The lighting device as claimed in claim 1, further comprising one or more air cooling fans,

wherein the one or more cooling fans are driven separately according to the current value of each line measured by the current detector.

19. A liquid crystal display device comprising:

a liquid crystal panel having a pair of glass substrates, a pair of polarizing plates, and a liquid crystal layer sandwiched by the substrates, and

the lighting device disclosed in claim 1 for supplying light to the liquid crystal panel.

11. A lighting device comprising:

at least one line connected in parallel,

a constant current source for applying a constant current to the line,

an ON/OFF controller, and

a voltage detector for measuring a value of voltage flowing in the line,

wherein

the line is formed by one or more light-emitting diodes and a switch for turning ON/OFF the current flowing in the light emitting diodes connected in series, and

according to the voltage value of each of the lines measured by the voltage detector, the ON/OFF controller controls the ON/OFF period of the switch of each of the lines.

12. The lighting device as claimed in claim 11, further comprising a selector for selectively outputting a voltage value of each line to the voltage detector.

15. The lighting device as claimed in claim 11, further comprising:

temperature measuring means, and

a condition table for deciding the ON/OFF period ratio according to a signal from the temperature measuring means and the voltage detector,

wherein the ON/OFF controller controls the ON/OFF period according to the condition table.

16. The lighting device as claimed in claim 15, wherein the temperature measuring means measures a temperature of the air in a vicinity of the lighting device or a temperature of the metal plate connected to the light emitting diode.

18. The lighting device as claimed in claim 11, further comprising one or more air cooling fans,

wherein the one or more cooling fans are driven separately according to the voltage value of each line measured by the voltage detector.

20. A liquid crystal display device comprising:

a liquid crystal panel having a pair of glass substrates, a pair of polarizing plates, and a liquid crystal layer sandwiched by the substrates, and

the lighting device disclosed in claim 11 for supplying light to the liquid crystal panel.