Importance

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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.

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First Claim