LED lamp with a fault-indicating impedance-changing circuit

• US 6,570,505 B1
• Filed: 12/30/1997
• Issued: 05/27/2003
• Est. Priority Date: 12/30/1997
• Status: Expired due to Term

• Current Assignee: Current Lighting Solutions, LLC (f/k/a GE Lighting Solutions, LLC) (American Industrial Partners), Intermec IP Corporation (Honeywell International Inc.)
• Original Assignee: Gelcore (General Electric Company)
• Inventors: Malenfant, Martin
• Primary Examiner(s): Lieu, Julie
• Application Number:
  US09/000,879
• Time in Patent Office: 1,974 Days
• Field of Search: 340/641, 340/642, 340/635, 340/912, 340/931, 340/907, 340/458, 738/656, 738/659, 738/664, 315/135, 315/136, 307/37, 307/10.8, 324/133, 361/58, 361/18, 361/92, 361/115
• US Class Current: 340/641
• CPC Class Codes: G08G 1/095 Traffic lights
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: H05B 45/58 involving end of life detection of LEDs

Abstract

In a light-emitting-diode lamp, there is provided an input impedance-changing circuit for establishing a low input impedance circuit when the light-emitting-diode lamp is missingline turned off. This input impedance-changing circuiting comprises Shunt circuit section, and a detector circuit section. The shunt circuit section includes a low impedance element and a controllable switching device connected in series. The detector circuit section detects turning off of the light-emitting-diode lamp and, in response to such detection, close the switching device to thereby cause electric current to flow through the shunt circuit section in order to simulate lower input impedance of the light-emitting-diode lamp. When the light-emitting-diode lamp replaces a conventional traffic signal incandescent lamp, the input impedance-changing circuitry prevents the conflict monitor of the already installed traffic-light lamp system to detect a high lamp impedance and accordingly a faulty lamp.

Claims

1. In a light-emitting-diode lamp, the improvement comprising an input impedance-changing circuitry for establishing a low input impedance circuit of the light-emitting-diode lamp when said light-emitting-diode lamp is turned off, said input impedance-changing circuitry comprising:

a shunt circuit section including a low impedance element and a controllable switching device connected in series; and

a detector circuit section comprising means for detecting turning off of the light-emitting-diode lamp and means for closing, in response to detection of turning off of the light-emitting diode lamp, the controllable switching device in order to establish a shunt circuit including the low impedance element and thereby establish said low input impedance circuit of the light-emitting-diode lamp.

2. An input impedance-changing circuitry as recited in claim 1, in which:

the light-emitting-diode lamp is supplied with electric power from an ac source;

the light-emitting-diode lamp further comprises (a) a set of light emitting diodes, (b) a rectifier circuit section supplied with ac voltage and current from the ac source and having an output for delivering rectified voltage and current, and (c) a power converter supplied with rectified voltage and current from the rectifier circuit section for producing dc voltage and current supplied to the set of light emitting diodes; and

the shunt circuit section is connected between the output of the rectifier circuit section and the ground and is therefore supplied with rectified voltage and current from the rectifier circuit section.

3. An input impedarce-changing circuit as recited in claim 2, in which the shunt circuit section comprises a resistor forming the low impedance element, a capacitor and the controllable switching device connected in series.

4. An input impedance-changing circuitry as recited in claim 3, in which the detector circuit section comprises means for detecting turning off of the light-emitting-diode lamp when the amplitude of a voltage across the capacitor is lower than a predetermined voltage threshold.

5. A input impedance-changing circuitry as recited in claim 3, in which the detector circuit section comprises a comparator having a first input supplied with a predetermined voltage threshold, a second input supplied with a voltage across the capacitor, and an output for delivering a given signal when the amplitude of the voltage across the capacitor is lower than the predetermined voltage threshold, said given signal being indicative of turning off of the light-emitting-diode lamp and being supplied to the controllable switching device to close said switching device.

6. An input impedance-changing circuitry as recited in claim 1, further comprising a set of light emitting diodes including a plurality of subsets of serially interconnected light emitting diodes, wherein the detector circuit section comprises means for detecting a dc current flowing through each subset of serially interconnected light emitting diodes and means for producing a fault signal when no do current is flowing through a predetermined number of said subsets of light emitting diodes.

7. A traffic-light lamp system comprising:

a light-emitting-diode lamp comprising an input impedance-changing circuitry for establishing a low input impedance circuit of the light-emitting-diode lamp when said light-emitting-diode lamp is turned off, said input impedance-changing circuitry comprising;

a shunt circuit section including a first low impedance element and a first controllable switching device connected in series; and

a detector circuit section comprising means for detecting turning off of the light-emitting-diode lamp and means for closing, in response to detection of turning off of the light-emitting-diode lamp, the first controllable switching device in order to establish a shunt circuit including the first low impedance element and thereby establish the low input impedance circuit of the light-emitting-diode lamp; and

a second controllable switching device interposed between a source of electric power and the light-emitting-diode lamp for selectively turning on and turning off the light-emitting-diode lamp.

8. A traffic-light lamp system as defined in claim 7, wherein the second controllable switching device comprises:

a power switch for supplying, when said power switch is closed, the light-emitting-diode lamp with electric power from said source and thereby turning on said light-emitting-diode lamp; and

a second impedance element connected in parallel with the power switch.

9. A traffic-light lamp system as defined in claim 8, wherein:

the source of electric power is an ac source;

the light-emitting-diode lamp further comprises (a) a set of light emitting diodes, (b) a rectifier circuit section supplied with ac voltage and current from the ac source through the second controllable switching device and having an output for delivering rectified voltage and current, and (c) a power converter supplied with rectified voltage and current from the rectifier circuit section for producing dc voltage and current supplied to the set of light emitting diodes; and

the shunt circuit section is connected between the output of the rectifier circuit section and the ground and is therefore supplied with rectified voltage and current from the rectifier circuit section.

10. A traffic-light lamp system as defined in claim 9, wherein the shunt circuit section comprises a resistor forming the first low impedance element, a capacitor and the first controllable switching device connected in series.

11. A traffic-light lamp system as defined in claim 10, wherein the detector circuit section comprises means for detecting turning off of the light-emitting-diode lamp when the amplitude of a voltage across the capacitor is lower than a predetermined voltage threshold.

12. A traffic-light lamp system as defined in claim 10, in which the detector circuit section comprises a comparator having a first input supplied with a predetermined voltage threshold, a second input supplied with a voltage across the capacitor, and an output for delivering a first signal when the amplitude of the voltage across the capacitor is lower than the predetermined voltage threshold, said first signal being indicative of turning off of the light-emitting-diode lamp and being supplied to the first controllable switching device to close said first switching device.

13. A traffic-light lamp system as defined in claim 12, wherein:

the set of light emitting diodes comprises a plurality of subsets of serially interconnected light emitting diodes, said subsets of serially interconnected light emitting diodes being connected in parallel; and

the detector circuit section comprises means for detecting a dc current flowing through each subset of serially interconnected light emitting diodes and means for producing a second signal when no dc current is flowing through a predetermined number of said subsets.

14. A traffic-light lamp system as defined in claim 13, wherein the detector circuit section comprises:

means for detecting the amplitude of the dc current supplied to the set of light emitting diodes when the power switch is closed;

means for producing a third signal when the amplitude of the dc current supplied to the set of light emitting diodes when the power switch is closed is higher than a predetermined current threshold; and

means responsive to the second and third signal for preventing the first signal to reach the first controllable switching device to close said first switching device.

15. A traffic-light lamp system as defined in claim 12, wherein the detector circuit section comprises:

means for detecting the amplitude of the ac voltage supplied to the rectifier circuit section when the power switch is closed;

means for producing a second signal when the amplitude of the ac voltage supplied to the rectifier circuit when the power switch is closed is higher than a predetermined voltage threshold;

means for detecting the amplitude of the dc current supplied to the set of light emitting diodes when the power switch is closed;

means for producing a third signal when the amplitude of the dc current supplied to the set of light emitting diodes when the power switch is closed is higher than a predetermined current threshold; and

means responsive to the second and third signals for preventing the first signal to reach the controllable switching member to close said switching member.