TEMPERATURE COMPENSATED LIGHT SOURCE USING A LIGHT EMITTING DIODE

• US 3,705,316 A
• Filed: 12/27/1971
• Issued: 12/05/1972
• Est. Priority Date: 12/27/1971
• Status: Expired due to Term

• Current Assignee: Clifford N. Burrous, Gordon J. Deboo
• Original Assignee: Clifford N. Burrous, Gordon J. Deboo
• Inventors: Burrous, Clifford N., Deboo, Gordon J.
• Application Number:
  US05/212,028
• Time in Patent Office: 344 Days
• US Class Current: 327/513
• CPC Class Codes: H03F 1/30 Modifications of amplifiers to reduce influence of variations of temperature or supply voltage or other physical parameters in differential amplifiers H03F3/45479
• CPC Class Codes: H03F 3/087 with IC amplifier blocks H03F3/085 takes precedence
• CPC Class Codes: H04B 10/502 LED transmitters
• CPC Class Codes: H05B 45/18 using temperature feedback
• CPC Class Codes: H05B 45/395 Linear regulators
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]
• CPC Class Codes: Y10S 323/907 Temperature compensation of semiconductor

Abstract

A temperature compensated light source including a thermistor, several resistors, an operational amplifier and a light emitting diode combined in such a manner that the non-linear characteristics of the thermistor cause the operational amplifier to vary the energizing current supplied to the light emitting diode to compensate for the non-linear temperature characteristics of the diode. The radiant energy output of the light source is constant if a fixed input voltage is applied to its input terminal, or will vary in direct proportion to a variable input voltage applied to its input terminal.

Claims

1. A temperature compensated light source, comprising:

a light emitting diode for developing radiant energy in response to a first current applied thereto, said diode having a nonlinear radiant energy output vs. temperature characteristic;

means for developing a second current which changes with ambient temperature in a manner commensurate with said nonlinear characteristic; and

means responsive to said second current and operative to supply a temperature compensated first current to said light emitting diode whereby the radiant energy output of said light emitting diode is maintained constant independent of ambient temperature.

2. A temperature compensated light source as recited in claim 1 wherein said means for developing a second current includes a first source of potential, a second source of potential, and a series circuit coupling said first source of potential to said second source of potential, said series circuit being comprised of a resistance means having a resistance which varies with temperature, and a first resistor.

3. A temperature compensated light source as recited in claim 1 wherein said means responsive to said second current includes a current regulating means for causing said first current to have a predetermined relationship to said second current.

4. A temperature compensated light source as recited in claim 3 wherein said means responsive to said second current further includes an operational amplifier for comparing said first and second currents and developing a control signal commensurate with the difference therebetween for driving said current regulating means.

5. A temperature compensated light source, comprising:

a light emitting diode for developing a radiant energy output in response to a first current caused to flow therethrough, said radiant energy output being constant when said first current varies with the ambient temperature in a predetermined non-linear fashion;

means for developing a second current which varies with the ambient temperature in a manner proportional to said predetermined non-linear fashion; and

means responsive to said second current and operative to supply a first current to said light emitting diode such that the ratio between said first and second currents is fixed.

6. A temperature compensation circuit for a light emitting diode, comprising:

a first source of potential, a second source of potential, and a third source of potential;

a first series circuit coupling said first source of potential to said second source of potEntial and including, a resistance means having a resistance which varies nonlinearly with temperature, and a first resistor;

a second series circuit coupling said third source of potential to said second source of potential and including, a current regulating means, the light emitting diode, and a second resistor, said current regulating means being responsive to any difference in the potential drops across said first and second resistors and operative to cause the current flowing through said second series circuit to bear a predetermined relationship to the current flowing through said first series circuit whereby the radiant energy output of said light emitting diode is proportional to the magnitude of the potential of said first source.

7. A temperature compensation circuit for a light emitting diode, comprising:

a first series circuit including a temperature responsive resistance means and a first resistor, said resistance means having a resistance which varies non-linearly with temperature;

a second series circuit including, a current regulating means, the light emitting diode, and a second resistor;

first means for causing a first current to flow through said first series circuit; and

second means for causing a second current to flow through said second series circuit, said current regulating means being responsive to the different in the IR drops across said first and second resistors and operative to cause said first and second currents to have a predetermined ration whereby the radiant energy output of said light emitting diode remains constant independent of temperature.

8. A temperature compensation circuit as recited in claim 7 wherein said current regulating means includes an operational amplifier for comparing the IR drop across said first resistor to the IR drop across said second resistor.

9. A temperature compensation circuit as recited in claim 7 wherein said resistance means is comprised of a third resistor and a thermistor connected in parallel.

10. A temperature compensation circuit as recited in claim 7 wherein said current regulating means includes, an operational amplifier having a first input terminal coupled to the circuit junction of said resistance means to said first resistor, a second input terminal coupled to the circuit junction of said diode to said second resistor, an output terminal, and a transistor having a base electrode coupled to said output terminal, a collector electrode coupled to said second means, and an emitter coupled to said light emitting diode.

11. A temperature compensation circuit as recited in claim 10 wherein said second current (iout) is defined by the expression iout R1ein/R2 ( (RThR3/(RTh +R3)) + R1) where R1 is the resistance of said first resistor, ein is the potential applied across said first series circuit, R2 is the resistance of said second resistor, RTh is the resistance of said thermistor, and R3 is the resistance of said third resistor.

12. A circuit for maintaining the radiant energy output of a light emitting diode constant over a selected operating temperature range, comprising:

a first source of potential and a second source of potential;

a resistance means having a resistance which varies non-linearly with temperature;

a first resistor connected in series with said resistance means to form a first series circuit between said first and second sources of potential;

a second resistor connected in series with said light emitting diode to form a second series circuit; and

an operational amplifier responsive to any difference in the potential drops across said first and second resistors and operative to develop an electrical current in said second series circuit which is commensurate with said difference, said electrIcal current maintaining the radiant energy output of said light emitting diode constant independent of ambient temperature.