Non-linear light-emitting load current control

• US 6,285,139 B1
• Filed: 12/23/1999
• Issued: 09/04/2001
• Est. Priority Date: 12/23/1999
• Status: Expired due to Term

• Current Assignee: Current Lighting Solutions, LLC (f/k/a GE Lighting Solutions, LLC) (American Industrial Partners)
• Original Assignee: Gelcore (General Electric Company)
• Inventors: Ghanem, Mohamed Sherif
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): TRAN, THUY V
• Application Number:
  US09/471,372
• Time in Patent Office: 621 Days
• Field of Search: 315/291, 315/219, 315/209 R, 315/224, 315/247, 315/272, 315/307, 315/311, 363/20, 363/21, 363/89, 307/52, 307/60
• US Class Current: 315/291
• CPC Class Codes: G01R 31/2653 using electron beams
• CPC Class Codes: H05B 45/14 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/18 using temperature feedback
• CPC Class Codes: H05B 45/385 using flyback topology

Abstract

A sensor circuit detects a current supplied to a set of light-emitting diodes and produces a current reading dependent on the temperature of operation of these light-emitting diodes. The sensor circuit comprises first and second serially interconnected resistors also connected in series with the set of light-emitting diodes. The sensor circuit also comprises a temperature-dependent impedance connected in parallel with one of the first and second resistors. At least a portion of the current through the set of light-emitting diodes flows through the sensor circuit to enable the first and second serially interconnected resistors and the temperature-dependent impedance to produce a variable voltage signal representative of the current through the set of light-emitting diodes, this variable voltage signal being dependent upon temperature. The above sensor circuit finds application in a substantially constant intensity light source.

Claims

1. A substantially constant intensity light source comprising:

a) a controllable dc voltage and current source having first and second terminals;

b) a non-linear light-emitting load connected between the first and second terminals and supplied with dc voltage and current from the controllable dc voltage and current source;

c) a current sensor circuit connected in series with the non-linear light-emitting load between said first and second terminals, the current sensor circuit having an impedance varying with a condition of operation of the light-emitting load and being supplied with at least a portion of the current through said non-linear light-emitting load, whereby the variable impedance produces a variable current-representative signal; and

d) a voltage and current control feedback circuit connected between said current sensor circuit and said controllable dc voltage and current source and through which the dc voltage and current source is controlled in relation to the variable current-representative signal to adjust the dc voltage and current to amplitudes that keep the light intensity produced by the light source substantially constant.

2. A substantially constant intensity light source as defined in claim 1, wherein said current sensor circuit comprises an output for delivering said variable current-representative signal, and one of said first and second terminals comprises a lower voltage terminal, and wherein said voltage and current control feedback circuit comprises an input for receiving the variable current-representative signal, said light source further comprising a linearizing filter circuit having a resistor connected between said current sensor circuit output and said control feedback circuit input, and a capacitor connected between said control feedback circuit input and said lower voltage terminal.

3. A substantially constant intensity light source as defined in claim 1, wherein said feedback control circuit comprises:

a) a comparator having a first input for receiving said variable current-representative signal, a second input for receiving a fixed current-representative reference signal, and an output for producing a signal representative of a comparison between the variable current-representative signal and the fixed current-representative reference signal; and

b) a controller through which the dc voltage and current source is controlled in relation to said comparison representative signal to adjust the dc voltage and current to amplitudes that keep the light intensity produced by the light source substantially constant.

4. A substantially constant intensity light source as defined in claim 1, wherein said variable impedance comprises a temperature-dependent impedance whereby said light source intensity is kept substantially constant within a given temperature range.

5. A substantially constant intensity light source as defined in claim 4, wherein said variable impedance further comprises a first fixed resistor connected in series with said temperature-dependent impedance.

6. A substantially constant intensity light source as defined in claim 5, wherein said variable impedance further comprises a second fixed resistor connected in parallel with said temperature-dependent impedance.

7. A substantially constant intensity light source as defined in claim 1, wherein said non-linear light-emitting load comprises at least one light-emitting diode.

8. A substantially constant intensity light source as defined in claim 7, wherein said at least one light-emitting diode comprises a plurality of sets of light-emitting diodes connected in parallel.

9. A substantially constant intensity light source as defined in claim 8, wherein each of said sets of light-emitting diodes connected in parallel comprises at least two light-emitting diodes connected in series.

10. A method for keeping the intensity of a light source substantially constant, comprising:

a) supplying from a controllable dc voltage and current source a dc voltage and current to a non-linear light-emitting load;

b) supplying at least a portion of the current through said non-linear light-emitting load to a current sensor circuit having an impedance varying with a condition of operation of the light-emitting load, whereby the variable impedance produces a variable current-representative signal; and

c) feedback controlling said dc voltage and current in relation to the variable current-representative signal to adjust the dc voltage and current to amplitudes that keep the light intensity produced by the light source substantially constant.

11. A method for keeping the intensity of a light source substantially constant as defined in claim 10, further comprising low-pass filtering the variable current-representative signal.

12. A method for keeping the intensity of a light source substantially constant as defined in claim 10, wherein feedback controlling comprises;

a) comparing said variable current-representative signal and a fixed current-representative reference signal to produce a signal representative of a comparison between the variable current-representative signal and the fixed current-representative reference signal; and

b) controlling the dc voltage and current source in relation to said comparison representative signal to adjust the dc voltage and current to amplitudes that keep the light intensity produced by the light source substantially constant.

13. A method for keeping the intensity of a light source substantially constant as defined in claim 10, wherein said variable impedance comprises a temperature-dependent impedance whereby said light source intensity is kept substantially constant within a given temperature range.

14. A method for keeping the intensity of a light source substantially constant as defined in claim 10, wherein said non-linear light-emitting load comprises at least one light-emitting diode.

15. A method for keeping the intensity of a light source substantially constant as defined in claim 14, wherein said at least one light-emitting diode comprises a plurality of sets of light-emitting diodes connected in parallel.

16. A substantially constant intensity light source as defined in claim 15, wherein each of said sets of light-emitting diodes connected in parallel comprises at least two light-emitting diodes connected in series.

17. A substantially constant intensity light source comprising:

a) a non-linear light-emitting load;

b) a controllable dc voltage and current source for supplying the non-linear light-emitting load with dc voltage and current;

c) a current sensor circuit connected in series with the non-linear light-emitting load and the controllable dc voltage and current source, the current sensor circuit having an impedance varying with a condition of operation of the light-emitting load and being supplied with at least a portion of the current through said non-linear light-emitting load, whereby the variable impedance produces a variable current-representative signal; and

d) a voltage and current control feedback circuit connected between said current sensor circuit and said controllable dc voltage and current source for controlling the dc voltage and current source in relation to the variable current-representative signal to thereby adjust the dc voltage and current to amplitudes that keep the light intensity produced by the light source substantially constant.