Control of the luminous intensity of power LEDs by using the photoelectric effect characteristics of said power LEDs

• US 20080121761A1
• Filed: 10/12/2006
• Published: 05/29/2008
• Est. Priority Date: 10/27/2005
• Status: Active Grant

• Current Assignee: Alcatel SA (Nokia Corporation)
• Original Assignee: Alcatel SA (Nokia Corporation)
• Inventors: Telefont, Heinz
• Granted Patent: US 7,508,317 B2
• Time in Patent Office: Days
• US Class Current: 246/473.3
• CPC Class Codes: B61L 2207/02 using light-emitting diodes [LEDs]
• CPC Class Codes: B61L 5/1881 Wiring diagrams for power supply, control or testing
• CPC Class Codes: H05B 45/12 using optical feedback
• CPC Class Codes: H05B 45/39 Circuits containing inverter bridges

Abstract

A method for operating a signal lamp (1), in particular a railway signal lamp, wherein the signal lamp (1) comprises as its illuminant at least one light emitting diode (=LED) (2), and wherein the luminous intensity of the signal lamp (1) is adapted to the brightness of the surrounding, is characterized in that the at least one LED (2) is operated during first time intervals as the illuminant of the signal lamp (1), and during second time intervals, the at least one LED (2) is operated as a photo diode, that first and second time intervals alternate over time, in particular periodically, and that the output voltage of the LED (2) during the second time intervals is used to control the operating current of the at least one LED (2) during first time intervals. The inventive method does without a separate sensor, thus allowing the use of a corresponding signal lamp arrangement which is simple and inexpensive.

Claims

1. Method for operating a signal lamp, in particular a railway signal lamp, wherein the signal lamp comprises as its illuminant at least one light emitting diode (=LED),

and wherein the luminous intensity of the signal lamp is adapted to the brightness of the surrounding,

wherein

at least one LED is operated during first time intervals as the illuminant of the signal lamp,

and during second time intervals, the at least one LED is operated as a photo diode,

that first and second time intervals alternate over time, in particular periodically,

and that the output voltage of the LED during the second time intervals is used to control the operating current of the at least one LED during first time intervals.

2. Method according to claim 1, wherein a low output voltage of the LED during the second time intervals, i.e. a dark surrounding, is used to establish a low operating current of the at least one LED during first time intervals, i.e. a low luminous intensity of the signal lamp, and that a high output voltage of the LED during the second time intervals, i.e. a bright surrounding, is used to establish a high operating current of the at least one LED during first time intervals, i.e. a high luminous intensity of the signal lamp.

3. Method according to claim 1, wherein the distribution of first and second time intervals is chosen such that for a human observer, the signal lamp appears to be constantly operating,

in particular wherein the first time intervals are at least 1.0 seconds long, and the second time intervals are at maximum 0.001 seconds long.

4. Signal lamp arrangement, in particular railway signal lamp arrangement, with a signal lamp comprising at least one light emitting diode (=LED) as its illuminant,

and with an electronic circuit for operating the signal lamp,

wherein

that the electronic circuit comprises

a supply means for supplying the at least one LED with operating current,

a tapping means for tapping the LED voltage of the at least one LED,

a comparison means for comparing the LED voltage to a reference voltage,

wherein the comparison means is connected to the supply means for controlling the supply means,

and a switching means for switching the electronic circuit from a first state into a second state and vice versa,

wherein in the first state, the supply means is connected to the at least one LED, and the comparison means is disconnected form the at least one LED, in particular wherein the tapping means is disconnected from the comparison means,

and wherein in the second state, the supply means is disconnected from the at least one LED, and the comparison means is connected to the at least one LED, in particular wherein the tapping means is connected to the comparison means.

5. Signal lamp arrangement according to claim 4, wherein the tapping means comprises a measuring resistance and an operational amplifier tapping the voltage of the measuring resistance.

6. Signal lamp arrangement according to claim 4, wherein the input of the comparison means is connected to a capacitor for smoothing the LED voltage during a switching cycle of the switching means.

7. Signal lamp arrangement according to claim 4, wherein the comparison means comprises an operational amplifier, in particular a summing amplifier, connected to the voltage input of a voltage controlled current supply.

8. Signal lamp arrangement according to claim 4, wherein the supply means is connected to a DC voltage supply, and that the supply means comprises a control input and a voltage output, wherein the voltage at the control input controls the voltage at the voltage output, in particular wherein the supply means comprises a push-pullup-controller with a voltage converter.

9. Signal lamp arrangement according to claim 4, wherein the switching means comprises an impulse generator and a plurality of switches, wherein the impulse generator controls the positions of the switches.

10. Signal lamp arrangement according to claim 4, wherein the signal lamp comprises a plurality of LEDs connected in series.