Constant current driving device, backlight light source device, and color liquid crystal display device

• US 20050231459A1
• Filed: 04/15/2005
• Published: 10/20/2005
• 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 7,425,943 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• 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 2330/08 Fault-tolerant or redundant circuits, or circuits in which repair of defects is prepared
• CPC Class Codes: G09G 2330/12 Test circuits or failure detection circuits included in a display system, as permanent part thereof
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• 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 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices
• CPC Class Codes: H05B 45/54 in a series array of LEDs

Abstract

A constant current driving device for constant current driving of a plurality of elements connected in series with each other by a pulse width modulation constant current driving circuit includes: switching elements respectively connected in parallel with the plurality of elements connected in series with each other; a control circuit for performing control to bypass a driving current flowing through the other elements than an arbitrary element to be measured via the respective switching elements and pass a measuring driving current through only the element to be measured; and a detecting circuit for identifying an element at a faulty position by detecting the driving current flowing through the plurality of elements connected in series with each other.

Claims

1. A constant current driving device for constant current driving of a plurality of elements connected in series with each other by a pulse width modulation constant current driving circuit, said constant current driving device comprising:

switching elements respectively connected in parallel with said plurality of elements connected in series with each other;

a control circuit for performing control to bypass a driving current flowing through the other elements than an arbitrary element to be measured via the respective switching elements and pass a measuring driving current through only the element to be measured; and

a detecting circuit for identifying an element at a faulty position by detecting the driving current flowing through said plurality of elements connected in series with each other.

2. A constant current driving device as claimed in claim 1,

wherein a main constant current circuit for constant current driving of said plurality of elements connected in series with each other by the pulse width modulation constant current driving circuit and a measuring reference constant current circuit are selectively connectable to said plurality of elements connected in series with each other via a switching unit.

3. A constant current driving device as claimed in claim 2,

wherein said switching elements are each formed of a transistor;

and

said control circuit performs control to bypass a driving current flowing through said plurality of elements connected in series with each other via switching elements formed of said transistor individually.

4. A constant current driving device as claimed in claim 3,

wherein said switching elements each include a diode connected between a base and an emitter of said transistor and a capacitor connected to the base of said transistor;

and

said control circuit performs the control to bypass the driving current flowing through said plurality of elements connected in series with each other via the switching elements formed of said transistor individually by supplying a switching control signal to the base of said transistor via said capacitor.

5. A constant current driving device as claimed in claim 3,

wherein said control circuit performs control to bypass the driving current flowing to the element at the faulty position at all times by operating a switching element formed by said transistor connected in parallel with the element at the faulty position, the element at the faulty position being identified by said detecting circuit, in synchronism with pulse width modulation driving by said pulse width modulation constant current driving circuit.

6. A constant current driving device as claimed in claim 1,

wherein said plurality of elements connected in series with each other are light emitting diodes.

7. A backlight light source device for lighting a display panel from a back side of the display panel, said backlight light source device comprising:

a plurality of light emitting diodes connected in series with each other;

switching elements respectively connected in parallel with said plurality of light emitting diodes connected in series with each other;

a control circuit for performing control to bypass a driving current flowing through the other light emitting diodes than an arbitrary light emitting diode to be measured via the respective switching elements and pass a measuring driving current through only the light emitting diode to be measured; and

a detecting circuit for identifying a light emitting diode at a faulty position by detecting the driving current flowing through said plurality of light emitting diodes connected in series with each other.

8. A backlight light source device as claimed in claim 7,

wherein a main constant current circuit for constant current driving of said plurality of light emitting diodes connected in series with each other by a pulse width modulation constant current driving circuit and a measuring reference constant current circuit are selectively connectable to said plurality of light emitting diodes connected in series with each other via a switching unit.

9. A backlight light source device as claimed in claim 8,

wherein said switching elements are each formed of a transistor;

and

said control circuit performs control to bypass a driving current flowing through said plurality of light emitting diodes connected in series with each other via switching elements formed of said transistor individually.

10. A backlight light source device as claimed in claim 9,

wherein said switching elements each include a diode connected between a base and an emitter of said transistor and a capacitor connected to the base of said transistor;

and

said control circuit performs the control to bypass the driving current flowing through said plurality of light emitting diodes connected in series with each other via the switching elements formed of said transistor individually by supplying a switching control signal to the base of said transistor via said capacitor.

11. A backlight light source device as claimed in claim 9,

wherein said control circuit performs control to bypass the driving current flowing to the light emitting diode at the faulty position at all times by operating a switching element formed by said transistor connected in parallel with the light emitting diode at the faulty position, the light emitting diode at the faulty position being identified by said detecting circuit, in synchronism with pulse width modulation driving by said pulse width modulation constant current driving circuit.

12. A color liquid crystal display device comprising:

a transmissive type color liquid crystal display panel having a color filter; and

a backlight light source device for lighting the color liquid crystal display panel from a back side of the color liquid crystal display panel;

wherein said backlight light source device includes;

a plurality of light emitting diodes connected in series with each other;

switching elements respectively connected in parallel with said plurality of light emitting diodes connected in series with each other;

a control circuit for performing control to bypass a driving current flowing through the other light emitting diodes than an arbitrary light emitting diode to be measured via the respective switching elements and pass a measuring driving current through only the light emitting diode to be measured; and

a detecting circuit for identifying a light emitting diode at a faulty position by detecting the driving current flowing through said plurality of light emitting diodes connected in series with each other.

13. A color liquid crystal display device as claimed in claim 12,

wherein a main constant current circuit for constant current driving of said plurality of light emitting diodes connected in series with each other by a pulse width modulation constant current driving circuit and a measuring reference constant current circuit are selectively connectable to said plurality of light emitting diodes connected in series with each other via a switching unit.

14. A color liquid crystal display device as claimed in claim 13,

wherein said switching elements are each formed of a transistor;

and

said control circuit performs control to bypass a driving current flowing through said plurality of light emitting diodes connected in series with each other via switching elements formed of said transistor individually.

15. A color liquid crystal display device as claimed in claim 14,

wherein said switching elements each include a diode connected between a base and an emitter of said transistor and a capacitor connected to the base of said transistor;

and

said control circuit performs the control to bypass the driving current flowing through said plurality of light emitting diodes connected in series with each other via the switching elements formed of said transistor individually by supplying a switching control signal to the base of said transistor via said capacitor.

16. A color liquid crystal display device as claimed in claim 14,

wherein said control circuit performs control to bypass the driving current flowing to the light emitting diode at the faulty position at all times by operating a switching element formed by said transistor connected in parallel with the light emitting diode at the faulty position, the light emitting diode at the faulty position being identified by said detecting circuit, in synchronism with pulse width modulation driving by said pulse width modulation constant current driving circuit.