Constant photon energy source

Claim 2

A constant photon energy source and circuit therefor comprising a light-emitting diode and a three-terminal active element device serially connected across a pair of power supply terminals and forming a conductive path for diode forward current, said active element device including a control electrode for receiving input control current for controlling the forward current through said diode, and temperature sensing means connected between said control electrode and one of said power supply terminals for providing said control current to said control electrode of said active element device in response to temperature changes within said circuit, whereby said temperature sensing means produces variations in current flowing in said series path to compensate for and offset temperaturE induced current variations in said diode, and thereby maintain a substantially constant forward current through and light output from said diode.

Claim 3

Source and circuit according to claim 1 wherein said temperature sensing means is a thermistor.

Claim 4

A circuit for generating a constant light output including, in combination: a light-emitting diode and a three-terminal active element device serially connected across a pair of power supply terminals and operative to conduct forward current through said diode when said terminals are connected to a power supply, said active element device having a control electrode for receiving a control current sufficient to maintain a substantially constant current through said active element device and through said light-emitting diode, and a control device connected between said control electrode of said active element device and one of said power supply terminals and operative to vary said control current as a function of the variations in temperature within said circuit, whereby said control current generates an offsetting current in the series path of said active element device and said diode for compensating for temperature induced current variations in said light-emitting diode as a result of the temperature coefficient of resistance of said diode, thereby maintaining a substantially constant light output from said light-emitting diode at all times.

Claim 5

A circuit for generating a constant light output including, in combination: a light-emitting diode and a three-terminal active element device serially connected across a pair of power supply terminals and operative to conduct forward current through said diode when said terminals are connected to a power supply, said active element device having a control electrode for receiving a control current sufficient to maintain a substantially constant current through said active element device and through said light-emitting diode, and a control device connected between said control electrode of said active element device and one of said power supply terminals and operative to vary said control current as a function of the variations in temperature within said circuit, whereby said control current generates an offsetting current in the series path of said active element device and said diode for compensating for temperature induced current variations in said light-emitting diode as a result of the temperature coefficient of resistance of said diode, thereby maintaining a substantially constant light output from said light-emitting diode at all times.

Claim 6

The circuit defined in claim 3 wherein said three-terminal active element device is a transistor having emitter, base, and collector electrodes, with said emitter and collector electrodes serially connected to said diode between said power supply terminals, and said control electrode connected to said control device.

Claim 7

The circuit defined in claim 3 wherein said control device is a thermistor connected between said base electrode of said transistor and the same power supply terminal to which said light-emitting diode is connected, said thermistor generating said control current at the base electrode of said transistor.

Claim 8

The circuit defined in claim 4 wherein said control device is a photodetector connected between said control electrode and one of said power supply terminals, said photodetector optically coupled to said light-emitting diode in an optical feedback arrangement, whereby temperature induced changes in the light output of said light-emitting diode are fed back to control the bias on said photodetector, and said photodetector in turn controls the level of said control current flowing to the control electrode of said active element device.

Claim 9

The circuit defined in claim 6 wherein said photodetector is a photodiode and wherein a current limiting resistor is connected in series with said photodiode and between said photodiode and one of said power supply terminals; the total current flowing through said current limiting resistor being divided between said photodiode and said active element device by an amount determined by the internal resistance of said photodiode, and said internal resistance of said photodiode being controlled by the light impinging thereon and received from said light-emitting diode, whereby said light-emitting diode provides self-stabilzation for the substantially constant forward current flowing therethrough.