# US 2012/0074856 A1 · Light-emitting element driving device

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- Number: US 2012/0074856 A1
- Document ID: US20120074856A1
- Status: Published application
- Kind: A1
- Application number: 13/314,597
- Filed: 2011-12-08
- Published: 2012-03-29
- Earliest claimed: 2009-06-09
- Assignees: Panasonic Corporation
- Inventors: Go TAKATA; Shinichiro Kataoka; Yasunori Yamamoto; Tsukasa Kawahara; Ryuji Ueda; Daisuke Itou
- Web page: https://patentgrep.com/patent/US20120074856A1

## CPC

- H05B 45/46: having LEDs disposed in parallel lines
- G09G 3/3406: {Control of illumination source (illumination devices structurally associated with liquid crystal cells G02F1/1336)}
- H05B 45/347: Dynamic headroom control [DHC]
- H05B 45/38: using boost topology
- H05B 45/48: having LEDs organised in strings and incorporating parallel shunting devices
- H05B 45/52: in a parallel array of LEDs
- G09G 2320/0233: Improving the luminance or brightness uniformity across the screen
- H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- G09G: ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION (arrangements for transferring data between digital computers and displays G06F3/14; static indicating arrangements comprising an association of a number of separate sources or light control cells G09F9/00; static indicating arrangements comprising integral associations of a number of light sources H01J, H01K, H10H, H05B33/12; scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission, details thereof H04N1/00)

## Abstract

Short circuit failures and open circuit failures of light-emitting elements used for the backlight in an LCD panel can be reliably and easily detected. The voltage at the node between each series-connected light-emitting element array and a drive circuit is detected as a monitored voltage. A maximum detector detects the highest and a minimum detector detects the lowest of these monitored voltages. Short circuit or open circuit failure of a light-emitting element is detected by comparing the voltage difference between the maximum detector output and the minimum detector output with a specific reference voltage.

## Claims

### Claim 1

A light-emitting element driving device comprising:
a light-emitting element load group having a plurality of parallel-connected light-emitting element arrays each having more than one light-emitting elements connected in series;
a supply voltage converter that converts a supply voltage and supplies a specific output voltage to the light-emitting element load group;
a drive circuit that supplies a load current for driving a light-emitting element connected in series in the light-emitting element array;
a power controller that generates a control signal for the supply voltage converter; and
a failure detector that detects failure of the light-emitting element,
wherein the failure detector monitors the potential of a node between the light-emitting element array and the drive circuit, or a voltage based on this node potential, as a monitored voltage, and detects failure of a light-emitting element based on the monitored voltages of at least two light-emitting element arrays.

### Claim 2 (depends on 1)

The light-emitting element driving device described in claim 1, wherein:
the failure detector detects short circuiting of the light-emitting element.

### Claim 3 (depends on 1)

The light-emitting element driving device described in claim 1, wherein:
the failure detector detects if the light-emitting element is open.

### Claim 4 (depends on 1)

The light-emitting element driving device described in claim 1, wherein:
the power controller also controls the supply voltage converter so that the lowest monitored voltage of the plural monitored voltages becomes equal to a specific first reference voltage.

### Claim 5 (depends on 1)

The light-emitting element driving device described in claim 1, wherein:
the failure detector detects failure of a light-emitting element based on the difference between two monitored voltages.

### Claim 6 (depends on 5)

The light-emitting element driving device described in claim 5, wherein:
of the two monitored voltages, one is the highest or based on the highest of the plural monitored voltages.

### Claim 7 (depends on 5)

The light-emitting element driving device described in claim 5, wherein:
of the two monitored voltages, the other is the lowest or based on the lowest of the plural monitored voltages.

### Claim 8 (depends on 5)

The light-emitting element driving device described in claim 5, wherein:
the failure detector detects light-emitting element failure by comparing the difference of two monitored voltages with a second reference voltage,
the second reference voltage being higher than the variation between the forward voltages of the plural light-emitting element arrays.

### Claim 9 (depends on 8)

The light-emitting element driving device described in claim 8, wherein:
the second reference voltage is also less than the forward voltage of N (where N>=1) light-emitting elements.

### Claim 10 (depends on 8)

The light-emitting element driving device described in claim 8, wherein:
the failure detector has a timer function and detects light-emitting element failure based on whether the difference between the two monitored voltages and the second reference voltage remains the same for a specified time.

### Claim 11

A light-emitting element driving device that can drive N (where N is an integer of 2 or more) light-emitting element arrays each having more than one serially connected light-emitting elements, the light-emitting element driving device comprising:
a drive voltage generator that can generate and supply a drive voltage to the light-emitting element arrays;
a drive current generator that can generate and supply a drive current based on the drive voltage through a monitored path to the light-emitting element arrays; and
a failure detector that detects device failure in the light-emitting element arrays based on the monitored voltage of at least two monitored paths;
wherein each monitored voltage is the voltage of a monitored path,
there are N monitored voltage paths corresponding to the N light-emitting element arrays, and
the drive voltage generator adjusts the drive voltage based on the monitored voltage.

### Claim 12 (depends on 11)

The light-emitting element driving device described in claim 11, wherein:
the failure detector detects short circuiting of the light-emitting element array.

### Claim 13 (depends on 11)

The light-emitting element driving device described in claim 11, wherein:
the failure detector detects if the light-emitting element array is open.

### Claim 14 (depends on 11)

The light-emitting element driving device described in claim 11, wherein:
the drive voltage generator adjusts the drive voltage so that the lowest of the N monitored voltages is equal to a specific first reference voltage.

### Claim 15 (depends on 11)

The light-emitting element driving device described in claim 11, wherein:
the failure detector detects a failure by comparing the monitored voltages of two paths.

### Claim 16 (depends on 15)

The light-emitting element driving device described in claim 15, wherein:
the failure detector detects a device failure based on the difference between the monitored voltages from two paths.

### Claim 17 (depends on 15)

The light-emitting element driving device described in claim 15, wherein:
one of the two monitored voltages is a voltage that is higher than the lowest of the N monitored voltages.

### Claim 18 (depends on 17)

The light-emitting element driving device described in claim 17, wherein:
one of the two monitored voltages is the highest of the N monitored voltages.

### Claim 19 (depends on 15)

The light-emitting element driving device described in claim 15, wherein:
the other of the two monitored voltages is a voltage that is less than the highest of the N monitored voltages.

### Claim 20 (depends on 19)

The light-emitting element driving device described in claim 19, wherein:
the other of the two monitored voltages is the lowest of the N monitored voltages.

### Claim 21 (depends on 15)

The light-emitting element driving device described in claim 15, wherein:
the failure detector detects a light-emitting element failure by determining if the difference between two monitored voltages is higher than or equal to a specified second reference voltage.

### Claim 22 (depends on 21)

The light-emitting element driving device described in claim 21, wherein:
the second reference voltage is higher than the variation between the forward voltages of the N light-emitting element arrays.

### Claim 23 (depends on 21)

The light-emitting element driving device described in claim 21, wherein:
the second reference voltage is less than the forward voltage of M (M>=1) light-emitting elements.

### Claim 24 (depends on 21)

The light-emitting element driving device described in claim 21, wherein:
the failure detector detects a light-emitting element failure by determining if the difference between two monitored voltages is higher than or equal to the second reference voltage for a specified time.

### Claim 25 (depends on 11)

The light-emitting element driving device described in claim 11, wherein:
the drive voltage generator includes a power controller and a supply voltage converter;
the power controller generates a control signal based on the monitored voltage; and
the supply voltage converter converts a specific supply voltage to a drive voltage, supplies the drive voltage to light-emitting element array, and adjusts the drive voltage based on the control signal.

### Claim 26 (depends on 5)

The light-emitting element driving device described in claim 5, wherein:
the failure detector detects light-emitting element failure by comparing the difference of two monitored voltages with a second reference voltage.