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

• US 7,538,497 B2
• Filed: 03/24/2005
• Issued: 05/26/2009
• Est. Priority Date: 04/20/2004
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Furukawa, Norimasa
• Primary Examiner(s): Philogene; Haissa
• Application Number:
  US10/560,444
• Publication Number:
  US 20060176411A1
• Time in Patent Office: 1,524 Days
• Field of Search: 315/291, 315/307, 315/310, 315/312, 315/315, 315/169.1, 315/169.3, 345/39, 345/40, 345/44, 345/46, 345/82, 345/83, 345/102, 345/104, 345/204, 345/690, 349/1, 349/33, 349/65, 349/69, 349/149, 362/227, 362/251, 362/800
• US Class Current: 315/291
• 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 light emitting devices by a pulse width modulating constant current driving circuit, comprising:

a bypass circuit including (a) a plurality of thyristors, each of which is connected in parallel with a respective one of said series connected light emitting diodes, and (b) a gate potential setting circuit;

a switching device for pulse width modulation; and

a resistor connected in parallel with said switching device for pulse width modulation,

wherein,

said gate potential setting circuit provides to said thyristors a gate potential value such that, when said light emitting devices are operating normally, said thyristors are in the off state,

said gate potential setting circuit provides to said thyristors another gate potential value such that, when said light emitting devices are in the open state, said thyristors are on, and

said resistor is coupled to said pulse width modulating constant current driving circuit via a transistor such that current for maintaining the on state of a turned-on thyristor flows through said resistor when said transistor is off.

2. A bypass circuit comprising:

a plurality of thyristors;

a plurality of voltage dividers each of which is coupled in parallel with a respective one of said thyristors;

voltage dividers comprising operatively coupled resistors; and

a plurality of series connected light emitting diodes,

wherein,

each voltage divider is connected to the gate terminal of its respective thyristor and supplies a gate potential value to the thyristor such that the thyristor is turned off during normal operation of said series-connected light emitting diodes and turned on when said series-connected light emitting diodes are open-circuited.

3. A gate potential setting circuit for a backlight light source comprising:

a plurality of thyristors;

a plurality of voltage dividers each of which is coupled in parallel with a respective one of said thyristors;

voltage dividers comprising operatively coupled resistors; and

a plurality of series connected light emitting diodes,

wherein,

each voltage divider is connected to the gate terminal of its respective thyristor and supplies a gate potential value to the thyristor such that the thyristor is turned off during normal operation of said series-connected light emitting diodes and turned on when said series-connected light emitting diodes are open-circuited.

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;

a plurality of thyristors, each of which is connected in parallel with a respective one of said series connected light emitting diodes;

a bypass circuit including said thyristors and a gate potential setting circuit;

a switching device for pulse width modulation; and

and a resistor connected in parallel with said switching device for pulse width modulation,

wherein,

said gate potential setting circuit provides to said thyristors a gate potential value such that, when the series connected light emitting diodes are operating normally, said thyristors are off

said gate potential setting circuit provides to said thyristors another gate potential value such that, when said series connected light emitting diodes are in the open state, said thyristors are on and,

said resistor is coupled to said pulse width modulating constant current driving circuit via a transistor such that current for maintaining the on state of a turned on thyristor flows through said resistor when the transistor is off.

5. A gate potential setting circuit for a backlight light source comprising:

a plurality of thyristors;

a plurality of voltage dividers each of which is coupled in parallel with a respective one of said thyristors;

voltage dividers comprising operatively coupled resistors; and

a plurality of series connected light emitting diodes,

wherein,

each voltage divider is connected to the gate terminal of its respective thyristor and supplies a gate potential value to the thyristor such that the thyristor is turned off during normal operation of said series-connected light emitting diodes and turned on when said series-connected light emitting diodes are open-circuited.

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;

a plurality of light emitting diodes connected in series;

a bypass circuit including (a) a plurality of thyristors, each of which is connected in parallel with a respective one of said series connected light emitting diodes, and (b) a gate potential setting circuit;

a switching device for pulse width modulation;

and a resistor connected in parallel with said switching device for pulse width modulation,

wherein,

said gate potential setting circuit provides to said thyristors a gate potential value such that, when the series connected light emitting diodes are operating normally, said thyristors are off

said gate potential setting circuit provides to said thyristors another gate potential value such that, when said series connected light emitting diodes are in the open-circuited, said thyristors are turned on, and

said resistor is coupled to said pulse width modulating constant current driving circuit via a transistor such that current for maintaining the on state of a turned on thyristor flows through said resistor when the transistor is off.