# US 7,741,790 B2 · Backlight system having a lamp current balance and feedback mechanism and related method thereof

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- Number: US 7,741,790 B2
- Document ID: US7741790B2
- Status: Granted
- Kind: B2
- Application number: 12/053,624
- Filed: 2008-03-24
- Published: 2009-07-23
- Granted: 2010-06-22
- Earliest claimed: 2008-01-21
- Assignees: Au Optronics Corporation
- Inventors: Yen-Chen Huang; Chia-Hung Sun; Huang-Ti Lin; Yuan-Pin Cho
- Web page: https://patentgrep.com/patent/US7741790B2

## CPC

- H05B 41/2855: {against abnormal lamp operating conditions}
- H05B 41/282: with semiconductor devices ({H05B41/2806}, H05B41/288, H05B41/295 take precedence)
- Y02B 20/00: Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
- H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS

## Abstract

A lamp current balance and feedback system and related method are disclosed for balancing the input and output currents of a lamp by making use of a lamp current balance and feedback mechanism. The operation of the lamp current balance and feedback mechanism includes coupling the input current of the lamp for generating a first balance current by a first transformer, coupling the output current of the lamp for generating a second balance current by a second transformer, coupling the first and second transformers for substantially equalizing the first and second balance currents, generating a feedback signal based on the first or second balance current by a feedback circuit, generating a pulse width modulation signal based on the feedback signal by a pulse width modulation signal generation circuit, and driving the input and output currents of the lamp based on the pulse width modulation signal by a driving circuit.

## Claims

### Claim 1

A backlight system comprising:
a first lamp comprising a first end and a second end;
a first transformer comprising a first winding and a second winding, a first end of the first winding of the first transformer being coupled to the first end of the first lamp;
a second transformer comprising a first winding and a second winding, a first end of the first winding of the second transformer being coupled to the second end of the first lamp, a first end of the second winding of the second transformer being coupled to a first end of the second winding of the first transformer, a second end of the second winding of the second transformer being coupled to a second end of the second winding of the first transformer;
a third transformer comprising a first winding and a second winding, a first end of the second winding of the third transformer being coupled to a second end of the first winding of the first transformer, a second end of the second winding of the third transformer being coupled to a ground;
a fourth transformer comprising a first winding and a second winding, a first end of the second winding of the fourth transformer being coupled to a second end of the first winding of the second transformer, a second end of the second winding of the fourth transformer being coupled to the ground; and
a driving circuit, coupled to the first winding of the third transformer and the first winding of the fourth transformer, for generating a first driving voltage and a second driving voltage having opposite phase with each other;
wherein the first driving voltage is furnished to the first winding of the third transformer and the second driving voltage is furnished to the first winding of the fourth transformer.

### Claim 2 (depends on 1)

The backlight system of claim 1, further comprising:
a first capacitor coupled between the first end of the second winding of the third transformer and the ground; and
a second capacitor coupled between the first end of the second winding of the fourth transformer and the ground.

### Claim 3 (depends on 1)

The backlight system of claim 1, further comprising:
a feedback circuit coupled between the second end of the second winding of the first transformer and the second end of the second winding of the second transformer for receiving a feedback current and generating a feedback signal based on the feedback current; and
a pulse width modulation (PWM) signal generator coupled between the feedback circuit and the driving circuit for receiving the feedback signal and generating a PWM signal based on the feedback signal, the PWM signal being furnished to the driving circuit;
wherein the driving circuit generates the first and second driving voltages based on the PWM signal.

### Claim 4 (depends on 3)

The backlight system of claim 3, further comprising:
a first balance circuit coupled between the first end of the first winding of the first transformer and the first end of the first lamp;
a second balance circuit coupled between the first end of the first winding of the second transformer and the second end of the first lamp; and
a second lamp coupled between the first balance circuit and the second balance circuit.

### Claim 5 (depends on 1)

The backlight system of claim 1, wherein the first transformer further comprises a third winding, the second transformer further comprises a third winding, and a first end of the third winding of the first transformer is coupled to a first end of the third winding of the second transformer.

### Claim 6 (depends on 5)

The backlight system of claim 5, further comprising:
a feedback circuit coupled between a second end of the third winding of the first transformer and a second end of the third winding of the second transformer for receiving a feedback current and generating a feedback signal based on the feedback current; and
a pulse width modulation signal generator coupled between the feedback circuit and the driving circuit for receiving the feedback signal and generating a PWM signal based on the feedback signal, the PWM signal being furnished to the driving circuit;
wherein the driving circuit generates the first and second driving voltages based on the PWM signal.

### Claim 7 (depends on 6)

The backlight system of claim 6, further comprising:
a first balance circuit coupled between the first end of the first winding of the first transformer and the first end of the first lamp;
a second balance circuit coupled between the first end of the first winding of the second transformer and the second end of the first lamp; and
a second lamp coupled between the first balance circuit and the second balance circuit.

### Claim 8 (depends on 1)

The backlight system of claim 1, wherein the first transformer further comprises a third winding, and the second transformer further comprises a third winding.

### Claim 9 (depends on 8)

The backlight system of claim 8, further comprising:
a feedback circuit coupled to a first end and a second end of the third winding of the first transformer for receiving a first feedback current, further coupled to a first end and a second end of the third winding of the second transformer for receiving a second feedback current, and generating a first feedback signal and a second feedback signal based on the first feedback current and the second feedback current respectively; and
a pulse width modulation signal generator coupled between the feedback circuit and the driving circuit for receiving the first and second feedback signals and generating a first PWM signal and a second PWM signal based on the first and second feedback signals respectively, the first and second PWM signals being furnished to the driving circuit;
wherein the driving circuit generates the first and second driving voltages based on the first and second PWM signals respectively.

### Claim 10 (depends on 9)

The backlight system of claim 9, further comprising:
a first balance circuit coupled between the first end of the first winding of the first transformer and the first end of the first lamp;
a second balance circuit coupled between the first end of the first winding of the second transformer and the second end of the first lamp; and
a second lamp coupled between the first balance circuit and the second balance circuit.