Constant current driver, back light source and color liquid crystal display

• US 20060176411A1
• Filed: 03/24/2005
• Published: 08/10/2006
• Est. Priority Date: 04/20/2004
• Status: Active Grant

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Furukawa, Norimasa
• Granted Patent: US 7,538,497 B2
• Time in Patent Office: Days
• US Class Current: 349/33
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G09G 2300/0452 Details of colour pixel setup, e.g. pixel composed of a red, a blue and two green components
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/37 Converter circuits
• CPC Class Codes: H05B 45/54 in a series array of LEDs

Abstract

Disclosed is a constant current driving unit for constant current driving a plural number of series connected light emitting diodes by a pulse-width modulating constant current driving circuit. Bypass circuits (80A) to 80(E), made up by a plural number of thyristors (81A) to (81E), each connected in parallel with each of series-connected light emitting diodes (41A) to (41E), are provided with gate potential setting circuits (83A) to (83E). These gate potential setting circuits afford to the thyristors a gate potential value such that, when the series-connected light emitting diodes (41A) to (41E) are operating as normally, the thyristors (81A) to (81E) are in the off-state. The gate potential setting circuit affords to the thyristors another gate potential value such that, when the light emitting diodes (41A) to (41E) are in the open state, the thyristors connected in parallel with the light emitting diodes (41A) to (41E) in the opened state will be in a turned-on state.

Claims

1. A constant current driving unit for constant current driving a plurality of series-connected devices by a pulse width modulating constant current driving circuit, comprising:

a bypass circuit including a plurality of thyristors each connected in parallel with each of said series-connected devices;

said bypass circuit including a gate potential setting circuit for affording to said thyristors a gate potential value such that, when the series-connected devices are operating as normally, the thyristors are in the off-state, said gate potential setting circuit affording to said thyristors another gate potential value such that, when the devices are in the open state, the thyristors will be in a turned-on state.

2. The constant current driving unit according to claim 1 wherein a resistor is connected in parallel with a switching device for pulse width modulation provided to said pulse width modulating constant current driving circuit so that the current for maintaining the turn-on state of a turned-on thyristor in the turned-on state will be caused to flow through said resistor.

3. The constant current driving unit according to claim 1 wherein said plural series-connected devices are light emitting diodes.

4. A backlight light source unit for illuminating a display panel from a back side thereof, comprising

a plurality of light-emitting diodes connected in series with one another;

and

a bypass circuit including a plurality of thyristors each connected in parallel with each of said series-connected light emitting diodes;

said bypass circuit including a gate potential setting circuit for affording to said thyristors a gate potential value such that, when the series-connected light emitting diodes are operating as normally, the thyristors are in the off-state, said gate potential setting circuit affording to said thyristors another gate potential value such that, when the light emitting diodes are in the open state, the thyristors will be in a turned-on state.

5. The backlight light source unit according to claim 4 wherein a resistor is connected in parallel with said switching device for pulse width modulation provided to said pulse width modulating constant current driving circuit so that the current for maintaining the turn-on state of a turned-on thyristor in the turned-on state will be caused to flow through said resistor.

6. A color liquid crystal display apparatus comprising

a light transmitting color liquid crystal display panel including a color filter and a backlight light source unit for illuminating said light transmitting color liquid crystal display panel from the back side thereof, wherein

said backlight light source unit includes

a plurality of light-emitting diodes connected in series with one another;

and

a bypass circuits each being a thyristor and each being connected in parallel with each of said series-connected light emitting diodes;

said bypass circuit including a gate potential setting circuit for affording to said thyristors a gate potential value such that, when the series-connected light emitting diodes are operating as normally, the thyristors are in the off-state, said gate potential setting circuit affording to said thyristors another gate potential value such that, when the light emitting diodes are in the open state, the thyristors will be in a turned-on state.

7. The color liquid crystal display apparatus according to claim 6 wherein a resistor is connected in parallel with a switching device for pulse width modulation provided to said pulse width modulating constant current driving circuit so that the current for maintaining the turn-on state of a turned-on thyristor in the turned-on state will be caused to flow through said resistor.