Light-emitting device and method of driving light-emitting device

• US 8,786,209 B2
• Filed: 12/05/2012
• Issued: 07/22/2014
• Est. Priority Date: 12/09/2011
• Status: Expired due to Fees

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Takahashi, Kei
• Primary Examiner(s): PHILOGENE, HAISSA
• Application Number:
  US13/705,895
• Publication Number:
  US 20130147365A1
• Time in Patent Office: 594 Days
• Field of Search: 315/149, 315/151, 315/158, 315/250, 315/291, 315/294, 315/297, 315/307, 315/224, 315/247, 315/169.3, 315/312, 345/76, 345/77, 345/81, 345/84, 345/102, 345/204, 345/205, 345/207, 345/690
• US Class Current: 315/294
• CPC Class Codes: H05B 45/12 using optical feedback
• CPC Class Codes: H05B 47/10 Controlling the light source

Abstract

Reduction of luminance dispersion of a plurality of light-emitting panels combined into one light-emitting device is achieved by the use of a new light-emitting device which has a photosensor, a plurality of light-emitting panels, DC/DC converters connected to their respective light-emitting panels, and a control circuit configured to control output currents of the DC/DC converters in accordance with illuminance data acquired with the photosensor. The control circuit successively turns on the plurality of light-emitting panels, and controls the output currents of the DC/DC converters in accordance with differences of the illuminance data acquired with the photosensor when the light-emitting panels are turned on.

Claims

1. A light-emitting device comprising:

first to Nth light-emitting panels, wherein N is a natural number larger than 1;

first to Nth DC/DC converters, wherein the ith DC/DC converter is configured to supply an output current to the ith light-emitting panel, where i is a natural number arbitrarily selected from 1 to N;

a photosensor configured to estimate illuminances of the first to Nth light-emitting panels when the same output current is supplied to the first to Nth light-emitting panels; and

a power control circuit configured to acquire data of the illuminances and control output currents of the first to Nth DC/DC converters on the basis of the acquired data.

2. The light-emitting device according to claim 1, wherein the power control circuit is further configured to control the output currents so that the first to Nth light-emitting panels emit light with the same luminance.

3. The light-emitting device according to claim 1, further comprising a plurality of photosensors.

4. The light-emitting device according to claim 1, wherein the ith light-emitting panel comprises a plurality of light emitting elements.

5. The light-emitting device according to claim 1, wherein the photosensor is further configured to estimate external light illuminance.

6. The light-emitting device according to claim 1, wherein the photosensor is arranged so that a distance between the photosensor and each of the first to Nth light-emitting panels is equal.

7. A lighting device comprising the light-emitting device according to claim 1.

8. A light-emitting device comprising:

first to Nth light-emitting panels, wherein N is a natural number larger than 1;

first to Nth DC/DC converters, wherein the ith DC/DC converter is electrically connected to the ith light-emitting panel where i is a natural number arbitrarily selected from 1 to N;

a power control circuit electrically connected to the first to Nth DC/DC converters; and

a photosensor electrically connected to the power control circuit,

wherein the power control circuit is configured to control a current which is output from the ith DC/DC converter to the ith light-emitting panels.

9. The light-emitting device according to claim 8, wherein:

the power control circuit is configured to control the first to Nth DC/DC converters so that the first to Nth DC/DC converters supply the same output current to the first to Nth light-emitting panels,

the photosensor is configured to estimate illuminances of the first to Nth light-emitting panels at the same output current, and

the power control circuit is further configured to acquire data of the illuminances so that the control of the current output from the ith DC/DC converter to the ith light-emitting panel is performed on the basis of the acquired data to allow the first to Nth light-emitting panels to emit light with the same luminance.

10. The light-emitting device according to claim 8, further comprising a plurality of photosensors.

11. The light-emitting device according to claim 8, wherein the ith light-emitting panel comprises a light emitting element.

12. The light-emitting device according to claim 8, wherein the ith light-emitting panel comprises a plurality of light emitting elements.

13. The light-emitting device according to claim 8, wherein the photosensor is further configured to estimate external light illuminance.

14. The light-emitting device according to claim 8, wherein the photosensor is arranged so that a distance between the photosensor and each of the first to Nth light-emitting panels is equal.

15. A lighting device comprising the light-emitting device according to claim 8.

16. A method for driving a light-emitting device, the method comprising the steps of:

sequentially supplying a reference current to first to Nth light-emitting panels, wherein N is a natural number larger than 1;

sequentially measuring illuminances of the first to Nth light-emitting panels at the reference current; and

supplying each of the first to Nth light-emitting panels with a respective corrected current on the basis of the measured illuminances of the first to Nth light-emitting panels at the reference current.

17. The method according to claim 16, wherein the respective corrected current is determined so that the first to Nth light-emitting panels emit light with the same luminance.

18. The method according to claim 16, wherein the reference current is determined in accordance with external light illuminance.

19. The method according to claim 16, wherein the measurement of the illuminances of the first to Nth light-emitting panels is performed by a plurality of photosensors.

20. The method according to claim 16, wherein the ith light-emitting panel comprises a plurality of light emitting elements, where i is a natural number arbitrarily selected from 1 to N.