Constant output light emitting device

• US 4,182,977 A
• Filed: 06/01/1978
• Issued: 01/08/1980
• Est. Priority Date: 06/01/1978
• Status: Expired due to Term

• Current Assignee: Optron, Inc.
• Original Assignee: TRW Inc. (Northrop Grumman Corporation)
• Inventors: Stricklin, Robert S. Jr.
• Primary Examiner(s): LaRoche, Eugene R.
• Application Number:
  US05/911,431
• Time in Patent Office: 586 Days
• Field of Search: 315/151, 315/156, 315/158, 315/307, 307/311, 250/205, 250/552, 250/239
• US Class Current: 315/158
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48137 the bodies being arranged next to each other, e.g. on a common substrate
• CPC Class Codes: H01L 25/167 comprising optoelectronic devices, e.g. LED, photodiodes
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H05B 45/12 using optical feedback
• CPC Class Codes: H05B 45/395 Linear regulators
• CPC Class Codes: H05B 45/40 Details of LED load circuits
• CPC Class Codes: H05B 47/10 Controlling the light source
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A light emitting device which provides substantially constant output power is disclosed. The light emitting device includes a light emitter and a compensating circuit for supplying current to the light emitter so that at any given time an increase in electric current produces a corresponding increase in light intensity. The compensating circuit includes a following circuit for supplying current to the light emitter, a differential isolation amplifier for driving the following circuit and a light sensor and its related circuitry. The light sensor is in proximity to and substantially to the side of the light emitter and is connected in a feedback relationship to the differential isolation amplifier. In one arrangement, the compensating circuit is an integrated circuit, and the light emitter and compensating circuit are mounted on a header. The header forms a recess, and the light emitter is mounted on the header in the recess. In one arrangement, a substantially clear overcoat substantially covers both the light sensor and the light emitting surface of the light emitter in such a way that substantially all of the light emitted from the light emitter is transmitted through the overcoat, but some of the light is reflected to the light sensor. In one arrangement, the integrated circuit also includes circuitry to limit the current supplied to the light emitter to a predetermined maximum level.

Claims

1. A light emitting device to be used in conjunction with a power supply, comprising in combination:

a light emitter for emitting light when supplied with electric current, wherein an increase in electric current supplied to the light emitter increases the output light intensity;

a compensating circuit comprising an integrated circuit powered by the power supply, electrically connected to the light emitter for supplying current to the light emitter, the compensating circuit including a light sensor in proximity to and substantially to the side of the light emitter wherein the compensating circuit is responsive to the light intensity sensed by the light sensor, increasing the current supplied to the light emitter as the intensity of the light sensed decreases;

means for electrically connecting the compensating circuit to the power supply;

a substantially clear overcoat substantially covering the light emitting surface of the light emitter wherein part of the light emitted from the light emitter is transmitted through the overcoat and part of the light emitted is reflected by the overcoat to the light sensor, whereby the intensity of light transmitted through the overcoat when the light emitting device is on remains substantially constant over the useful life of the light emitter; and

a header for mounting electrical components, wherein the light emitter and the compensating circuit are mounted on the header;

wherein the header forms a recess for mounting the light emitter, and the light emitter is mounted on the header in the recess, and wherein the substantially clear overcoat substantially covers both the light sensor and the light emitting surface of the light emitter.

2. A light emitting device according to claim 1 wherein substantially all of the light emitted from the light emitter is transmitted through the overcoat.

3. A light emitting device to be used in conjunction with a power supply, comprising in combination:

a light emitter consisting of a light emitting diode for emitting light when supplied with electric current, wherein an increase in electric current supplied to the light emitter increases the output light intensity;

a compensating circuit comprising an integrated circuit powered by the power supply, electrically connected to the light emitter for supplying current to the light emitter, the compensating circuit including in combination;

a light sensor in proximity to and substantially to the side of the light emitter wherein the compensating circuit is responsive to the light intensity sensed by the light sensor, increasing the current supplied to the light emitter as the intensity of the light sensed decreases;

a following circuit for supplying current to the light emitter;

a differential isolation amplifier for driving the following circuit, having a first input and a second input; and

a circuit for driving the light sensor, wherein the circuit for driving the light sensor is connected in a feedback relationship to the first input of the differential isolation amplifier whereby the integrated circuit is responsive to the light sensed by the light sensor when the second input to the differential isolation amplifier is at a predetermined voltage level;

means for electrically connecting the compensating circuit to the power supply; and

a substantially clear overcoat substantially covering the light emitting surface of the light emitter wherein substantially all of the light emitted from the light emitter is transmitted through the overcoat and part of the light emitted is reflected by the overcoat to the light sensor, whereby the intensity of light transmitted through the overcoat when the light emitting device is on remains substantially constant over the useful life of the light emitter; and

a header for mounting electrical components, wherein the light emitter and the compensating circuit are mounted on the header;

wherein the header forms a recess for mounting the light emitter, and the light emitter is mounted on the header in the recess, and wherein the substantially clear overcoat substantially covers both the light sensor and the light emitting surface of the light emitter.

4. A light emitting device according to claim 3 wherein the integrated circuit further comprises means for limiting the current supplied to the light emitter to a predetermined maximum level.

5. A light emitting device according to claim 3 to be used in conjunction with a logic gate wherein the predetermined voltage level of the second input corresponds to a first output voltage level of the logic gate and wherein the light emitting device is switched off when the second input of the differential isolation amplifier is at a second predetermined voltage level, the second predetermined voltage level corresponding to a second output voltage level of the logic gate whereby the logic gate can switch the light emitting device on and off when the output of the logic gate controls the second input to the differential isolation amplifier.

6. A light emitting device to be used in conjunction with a power supply, comprising in combination:

a light emitter for emitting light when supplied with electric current, wherein an increase in electric current supplied to the light emitter increases the output light intensity;

a compensating circuit powered by the power supply, electrically connected to the light emitter for supplying current to the light emitter, the compensating circuit including in combination;

a light sensor in proximity to and substantially to the side of the light emitter wherein the compensating circuit is responsive to the light intensity sensed by the light sensor, increasing the current supplied to the light emitter as the intensity of the light sensed decreases;

a following circuit for supplying current to the light emitter;

a differential isolation amplifier for driving the following circuit, having a first input and a second input; and

a circuit for driving the light sensor, wherein the circuit for driving the light sensor is connected in a feedback relationship to the first input of the differential isolation amplifier whereby the compensating circuit is responsive to the light sensed by the light sensor when the second input to the differential isolation amplifier is at a predetermined voltage level;

means for electrically connecting the compensating circuit to the power supply; and

a substantially clear overcoat substantially covering the light emitting surface of the light emitter wherein substantially all of the light emitted from the light emitter is transmitted through the overcoat and part of the light emitted is reflected by the overcoat to the light sensor, whereby the intensity of light transmitted through the overcoat when the light emitting device is on remains substantially constant over the useful life of the light emitter.

7. A light emitting device according to claim 6 wherein the compensating circuit further comprises means for limiting the current supplied to the light emitter to a predetermined maximum level.

8. A light emitting device according to claim 6 to be used in conjunction with a logic gate wherein the predetermined voltage level of the second input corresponds to a first output voltage level of the logic gate and wherein the light emitting device is switched off when the second input of the differential isolation amplifier is at a second predetermined voltage level, the second predetermined voltage level corresponding to a second output voltage level of the logic gate whereby the logic gate can switch the light emitting device on and off when the output of the logic gate controls the second input to the differential isolation amplifier.