WO2014013452A2

WO2014013452A2 - Lighting device comprising a monitoring circuit

Info

Publication number: WO2014013452A2
Application number: PCT/IB2013/055880
Authority: WO
Inventors: Jeroen Johannes Maria ZAAL; Franciska Elisabeth EVERTZ; Willem Dirk Van Driel
Original assignee: Koninklijke Philips N.V.
Priority date: 2012-07-19
Filing date: 2013-07-17
Publication date: 2014-01-23
Also published as: WO2014013452A3

Abstract

According to the present invention, a lighting device (100) and a method of indicating an incipient failure in a lighting device are provided. The lighting device comprises a light source (1), a constant current driver (2) configured to provide an output voltage for driving the light source and a monitoring circuit (4). The monitoring circuit is configured to monitor the output voltage, detect when the output voltage exceeds a threshold and actuate a failure indicator (8) based on the detection. The present invention is advantageous in that notification about an upcoming failure in the lighting device may be obtained before the failure is complete, thereby preventing the occurrence of an imminent light out.

Description

Lighting device comprising a monitoring circuit

FIELD OF THE INVENTION

The present invention generally relates to the field of lighting devices, in particular those comprising monitoring circuits for indicating imminent failure in the lighting devices.

BACKGROUND OF THE INVENTION

Solder connection failure is a plausible failure in electronics. Cracking of solder connections may cause an opening in the electrical circuit or a situation in which the solder connection is physically separated into two parts which are still in contact. Such solder connection failure is rather common in LED-based lighting device.

Regarding lighting devices comprising gas discharge light sources, changes in the gas mixture, such as sodium loss, normally occurs towards the end of the life of the gas discharge light source. Such change in the gas mixture will eventually cause a failure in the lighting device.

If failures of the above mentioned type are allowed to progress, the lighting device will be brought out of function, which may cause a sudden light out (i.e. the light output suddenly going to zero). In applications were sudden light out is highly undesirable, lighting devices have to be replaced after only around 50 % of the lighting device lifetime so as to reduce the risk of unintentional light out.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome, or at least alleviate, this problem, and to provide a lighting device having means for detecting an incipient failure in the lighting device. It is also an object of the present invention to provide a method of indicating an incipient failure in a lighting device. A further object of the present invention is to provide a lighting device for notifying about an upcoming failure in the lighting device before the failure is complete. These and other objects are achieved by means of a lighting device and a method as defined in the independent claims. Embodiments of the present invention are defined in the dependent claims.

According to a first aspect of the invention, a lighting device is provided. The lighting device comprises a light source, a constant current driver configured to provide an output voltage for driving the light source and a monitoring circuit. The monitoring circuit is configured to monitor the output voltage, detect when the output voltage exceeds a threshold and actuate a failure indicator based on the detection.

According to a second aspect of the present invention, a method of indicating imminent failure in a lighting device comprising a light source is provided. The method comprises the steps of monitoring an output voltage from a constant current driver configured to drive the light source, detecting when the output voltage exceeds a threshold, and actuating a failure indicator based on the detection.

Solder connection failure, such as cracking in the solder connection, introduces a resistance in the electrical circuit at the solder connection. This is for instance the case in a LED-based lighting device. Further, in gas discharge lighting devices, changes in the gas mixture introduce a resistance in the lighting device circuit. The inventors have realized that in both cases, the resistance often increases gradually when the failure is initiated and then progresses. Hence, the resistance in the lighting device circuit is slightly increased before the failure is complete.

Some lighting devices, such as LED-based lighting devices and gas discharge lamps, use a constant current driver for driving the light source in the device. The constant current driver continuously regulates its output voltage such that the light source is driven at a constant current (for a given light intensity). Hence, the constant current driver adjusts its output voltage until the desired current is reached or the constant current driver reaches its maximum or minimum output voltage. If a failure (e.g. of the above mentioned types) is initiated in the lighting device causing the circuit resistance in the device to rise, the constant current driver increases its output voltage to maintain a constant current. Further, large rises in output voltage may cause failure in other parts of the lighting device.

The present invention makes use of the output voltage adjustment function inherent in the constant current driver for detecting an upcoming failure (or an incipient failure) causing the circuit resistance in the lighting device to increase. Such a failure makes the constant current driver to increase its output voltage for compensating for the voltage drop caused by the increased resistance in the circuit and thereby maintain the current at a constant level. The monitoring circuit monitors the output voltage from the constant current driver and detects if the output voltage exceeds a threshold, which may indicate that a failure is initiated and that a complete failure may soon occur. When the output voltage exceeds the threshold, the monitoring circuit actuates the failure indicator, which enables a user to be notified about the incipient failure. A failure (or incipient failure) causing the circuit resistance to raise may, e.g., be an incipient or complete crack in a solder connection between the constant current driver and the light source, a change in the gas mixture in a gas discharge light source or any other failure causing the resistance in the lighting device to increase.

The present invention is advantageous in that notification about an upcoming failure in the lighting device may be obtained before the failure is complete, thereby preventing the occurrence of an imminent light out (i.e. the light output suddenly going to zero, which also may be referred to as catastrophic failure). A user, or a control unit receiving the notification, may then take action, such as repair or replace the lighting device before it is out of function or adapt the control of the lighting system, in which the lighting device is arranged, consequently. In particular in applications wherein light out is not acceptable, the present invention is advantageous in that the lighting device may be used for almost its full lifetime instead of being replaced at e.g. 50 % of its possible lifetime for reducing the risk of unintentional light out. Further, other parts in the lighting device may be better protected from large voltages, which may occur when the constant current driver adjusts its output voltage to compensate for the increased circuit resistance caused by a failure.

According to an embodiment of the present invention, the light source may be in electrical connection to the driver via a solder connection, whereby the monitoring circuit in the lighting device may be used for revealing (or detecting) solder connection failure, such as cracking in the solder connection. When cracking is initiated in the solder connection, the resistance in the solder connection increases, which in turn causes the constant current driver to increase its output voltage. The monitoring circuit detects when the output voltage exceeds the threshold and then actuates the failure indicator. For example, the light source may be soldered to a printed circuit board (PCB), which in turn may be connected to the driver via a cable. Solder connections in the electrical connection between the driver and the light source are common e.g. in LED-based lighting devices.

According to an embodiment of the present invention, the light source may be a gas discharge light source, whereby the monitoring circuit in the lighting device may be used for revealing change in the gas mixture (such as sodium loss), which may occur towards the end of the life of the gas discharge light source. When change in the gas mixture is initiated, the resistance in the light source increases, which in turn causes the constant current driver to increase its output voltage. The monitoring circuit detects when the output voltage exceeds the threshold and then actuates the failure indicator. The gas is typically part of the electrical circuit of the lighting device, as it is forced into a plasma-like state and carries the current. If certain elements in the gas mixture are present in reduced amounts (or even lost) there is not enough base material to make good conducting plasma, which results in a higher resistance of the gas (in plasma form) and eventually failure in the lighting device.

In an embodiment, the constant current driver may be configured to, preferably continuously, regulate (or adjust) the output voltage such that the light source is driven at (at least almost) constant current for a given light intensity of the light source. Hence, the constant current driver may adjust its output voltage until the desired current is reached or the constant current driver reaches its maximum or minimum output voltage. It will be appreciated that the output voltage in addition may be manually adjusted by a user for adjusting the light intensity of the lighting device. The light intensity may also be adjusted by adjusting a duty cycle of the output voltage, which may be modulated by a pulse wide modulation (PWM) signal.

According to embodiments of the present invention, the monitoring circuit may comprise a comparator configured to compare the monitored output voltage with a reference voltage for detecting if the output voltage exceeds the threshold. For example, the reference voltage and the output voltage may be received as inputs to the comparator, which in turn outputs a voltage indicative of which of the reference and the output voltages is the largest. The monitoring circuit may be configured such that the voltage (or signal) outputted from the comparator may actuate the failure indicator. Further, the threshold may be weighted in relation to the reference voltage, such as a certain (predetermined) percentage of the reference voltage. As an example, the threshold may be 120 % of the reference voltage, wherein the comparator may compare the output voltage with the reference voltage and actuate the failure indicator when the output voltage is larger than 120 % of the reference voltage.

Further, the reference voltage may be equal to or higher than an output voltage of the constant current driver required for driving the light source (at a certain, preferably full, light intensity) at an originally designed electrical resistance between the light source and the constant current driver and/or in the light source. The originally electrical designed resistance is the resistance in the circuit, in which the driver and the light source are comprised, as designed, before any failure (such as solder cracking or change in gas mixture) has been initiated. For example, the reference voltage may represent (or be equal to) the threshold, such that the monitoring circuit detects that the output voltage exceeds the threshold when it exceeds the reference voltage (as may be determined by the comparator). In this case, the reference voltage may e.g. be equal to or higher than a normal operation voltage (i.e. the voltage required for operation at the originally designed resistance without any failure). Alternatively, the reference voltage may be lower than the threshold, e.g.

representing a normal operation voltage, wherein the monitoring circuit detects that the output voltage exceeds the threshold when it deviates by a certain amount from the reference voltage (which deviation may be determined by the comparator).

The threshold (and the reference voltage) may be selected based on how early the actuation of the failure indicator is desired to occur, i.e. how long time margin is desired for taking action before complete failure occurs in the lighting device. For example, in applications wherein unintentional light out is highly undesirable, such as in an emergency corridor without any window, the threshold may be selected to be a voltage close (or almost equal) to normal operation voltage.

According to an embodiment, the lighting device may be configured to be set (or settable) in a calibration mode, in which the monitoring circuit may be configured to measure the output voltage and set (or determine) the reference voltage based on the measured output voltage. For example, the reference voltage may be set to be equal to or (slightly) higher than the measured output voltage. The present embodiment is advantageous in that the monitoring circuit may be calibrated (or adapted) to the actual normal (preferably failure-free) operation resistance in the circuit (comprising the constant current driver and the light source). The calibration mode may e.g. be actuated by a calibration actuating means, such as a button at (or at least connected or connectable to) the lighting device. Further, the calibration mode may preferably be used in the beginning of the life (or usage) of the lighting device, such as upon installation of the lighting device. It will be appreciated that the calibration mode may be actuated centrally for a lighting system (or device) comprising many light sources.

According to another embodiment, the reference voltage may be predetermined, such as set during manufacturing of the lighting device. With the present embodiment, the technical complexity of the lighting device is reduced, as a calibration function is not required.

According to an embodiment of the present invention, the lighting device may further comprise a memory or other storage means for storing the reference voltage. The memory may be comprised in the constant current driver and/or the monitoring circuit. For example, the reference voltage may be stored in the memory during calibration (wherein e.g. the measured output voltage may be stored in the memory as the reference voltage) or during manufacturing of the lighting device.

According to an embodiment, the monitoring circuit may be configured to measure the output voltage continuously or at predetermined time intervals, thereby reducing the delay from failure initiation to actuation of the failure indicator.

According to another embodiment, the lighting device may be configured to be set (or settable) in a test mode, in which the monitoring circuit may be configured to perform the monitoring of the output voltage. Actuation of the test mode may for instance be manually initiated by means of a test actuating means, such as a button, or remotely via a control unit of a lighting system in which the lighting device is arranged. With the present embodiment, a user may manually test the lighting device for revealing failure (or incipient failure) in the lighting device. If the test mode is actuated centrally by the control unit of a lighting system, the control unit may better determine how to control the various lighting devices of the lighting system.

According to an embodiment of the present invention, the failure indicator may be provided by one or more of: an indicator LED (e.g. arranged at the lighting device), a failure indication signal to a communication network (such as the Internet or a network based system for controlling lighting e.g. in buildings), an adjustment of the light output of the light source and an audible signal. The indicator LED may e.g. be configured to be switched on, flash and/or change color upon actuation by the monitoring circuit. The failure indication signal may e.g. be transmitted via the communication network to a display (or any other indicating means) for notifying a user, or a control unit in a lighting system, that a failure may have been initiated, which in particular is advantageous for use in lighting systems, wherein the failure indication may be arranged centrally for several lighting devices. The failure indication signal may e.g. be generated by a sensor, such as a temperature sensor configured to sense the increased temperature in the circuit caused by the increased resistance, or a light sensor configured to sense a change in the light output of the lighting device, which change may be caused by the previously described adjustment in the light output. The adjustment of the light output of the light source may include dimming and/or flashing the light source for attracting the attention of a user and/or trigger the light sensor for generating the failure indicating signal. It will be appreciated that the failure indicator may include any appropriate means for notifying a user and/or a control unit. According to an embodiment, the light source may comprise at least one light emitting diode, LED. For example, the LED may be connected to the driver via a solder connection.

It is noted that the invention relates to all possible combinations of features recited in the claims. Further, it will be appreciated that the various embodiments described for the lighting device are all combinable with the method as defined in accordance with the second aspect of the present invention.

Further objectives of, features of, and advantages with, the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described in the following.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawing showing embodiments of the invention.

Figure 1 shows a lighting device according to an embodiment of the present invention.

Figure 2 shows a method of indicating failure in a lighting device according to an embodiment of the present invention.

The figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the invention, wherein other parts may be omitted or merely suggested.

DETAILED DESCRIPTION

With reference to Figure 1, a lighting device according to an embodiment of the present invention will be described.

Figure 1 shows a lighting device 100 comprising a light source 1 connected to a constant current driver 2 configured to drive the light source 1 at a constant current. The light source 1 may e.g. comprise one or more light emitting diodes (LEDs) 9 or a gas discharge light source (not shown). The constant current driver 2 is connected to a voltage source 3, e.g. provided by the mains or a battery, providing the constant current driver 2 with an input voltage (denoted as Ui_n in Figure 1). For driving the light source 1 at a constant current, the constant current driver 2 is configured to continuously adapt its output voltage (denoted as U_out in Figure 1) for compensating for any change in the circuit resistance in the lighting device 100 and thereby maintain a constant current for the light source 1. For example, if the circuit resistance increases, the constant current driver 2 will increase the output voltage until the desired current is reached or until it reaches its maximum output voltage. Light sources, such as LEDs or gas discharge light sources, are normally driven by constant current drivers, as they require a certain minimum current (and voltage) for emitting light. Typically, the light intensity of the lighting device is adjusted by adjusting a duty cycle of the output voltage, which may be modulated by a PWM signal.

Failure may occur in the electrical circuit (including the driver 2 and the light source 1) of the lighting device 100, causing the circuit resistance to increase. Such a failure may e.g. be a crack in a solder connection in the circuit (such as in a solder connection between the light source 1 and the driver 2), which is a plausible failure in LED-based lighting devices. Another failure causing the circuit resistance to increase may be changes in the gas mixture (such as sodium loss) in gas discharge light sources. If such a failure is initiated in the lighting device 100, the constant current driver 2 will increase its output voltage to compensate for the voltage drop caused by the increase circuit resistance.

For detecting such a failure, the lighting device 100 comprises a monitoring circuit 4 configured to monitor the output voltage of the constant current driver 2 and connected to (or in communication with) a failure indicator 8. For monitoring the output voltage, the monitoring circuit 4 may comprise a voltmeter 5 arranged to measure the output voltage of the constant current driver 2. The monitoring circuit 4 may further comprise a comparator 7 connected to the voltmeter 5 and configured to compare the output voltage measured by the voltmeter 5 with a reference voltage for determining if the output voltage exceeds a certain threshold. The comparator 7 may further be connected to (or be in communication with) the failure indicator 8 and configured to actuate the failure indicator 8 when the output voltage exceeds the threshold.

The failure indicator 8 may be comprised in the lighting device 1 or arranged separately. For example, the failure indicator may be provided by an indicator LED, a failure indication signal to a communication network or an adjustment of the light output of the light source 1. The purpose of the failure indicator 8 is to notify a user or a control unit of a lighting system, in which the lighting device is arranged, that a failure has been detected, such that the user may take action, such as replacing or repairing the lighting device 100, or the control unit may adapt the control of the lighting system, such as adjusting the light output of neighboring lighting devices or in any other way changing the control parameters in the system to prevent sudden darkness. Preferably, the threshold is selected such that a rather small increase in the circuit resistance is detected by the monitoring circuit 4, thereby allowing replacement/repair of the lighting device 100 before it is completely out of function. For example, the threshold may be selected such that the increased resistance caused by an incipient (but not yet full) crack in a solder connection or a slight change in the gas mixture in a gas discharge light source is detected.

For storing the reference voltage, which the monitored output voltage is compared with, the monitoring circuit 4 may comprise a memory 6 connected to the comparator 7 and, preferably also to the voltmeter 5.

In an embodiment, the monitoring circuit 4 may be configured to be set in a calibration mode, e.g. upon actuation by a user. In the calibration mode, the voltmeter 5 measures the output voltage and the memory 6 stores the measured output voltage, wherein the reference voltage is set based on the measured output voltage. For example, the reference voltage may be set to the measured output voltage or, alternatively, to the measured voltage with an offset voltage added. Preferably, the lighting device 100 may be calibrated in the beginning of its lifetime, such as upon installation, whereby the reference voltage will represent (or be based on) the output voltage required to drive the light source 1 at the originally designed circuit resistance, i.e., the output voltage required for driving the lighting device 100 in a healthy (unbroken) state (only depending on the manufacturing process and not the usage of the lighting device).

In an embodiment, the lighting device 100 may be configured to be set in a test mode, in which the monitoring circuit 4 is activated. Alternatively, the monitoring circuit 4 may be configured to continuously, or at predetermined time intervals, monitor the output voltage, thereby reducing the effort for a user who wants to check the lighting device 100 for failure and reducing a potential delay from a failure occurring to failure indication actuation. In the following, an illustrative example of the operation of the lighting device 100 will be described.

When the lighting device 100 is installed, the installer switches on the lighting device and activates the calibration mode, e.g. by pushing a button, wherein the voltmeter 5 measures the output voltage from the constant current driver 2 and the memory 6 stores the measured output voltage, whereby the reference voltage is set to the measured output voltage. When the calibration is completed, the calibration mode is deactivated and the lighting device 100 is set to a normal operation mode, wherein the monitoring circuit 4 is active. When the lighting device 100 is switched on, the monitoring circuit 4, preferably continuously, monitors the output voltage from the constant current driver 2. During the monitoring, the voltmeter 5 measures the output voltage and the comparator 7 compares the measured output voltage with the reference voltage (provided by the memory 6). If the output voltage increases and e.g. becomes larger than the reference voltage, and thereby exceeds the threshold, the comparator actuates the failure indicator 8, whereby a user may be notified that a failure may have occurred.

With reference to Figure 2, an embodiment of a method according to the second aspect of the present invention will be described.

Figure 2 shows a method 200 of indicating failure in a lighting device (such as the lighting device 100 described with reference to Figure 1) comprising a light source. The method 200 comprises the steps of monitoring 201 an output voltage from a constant current driver configured to drive the light source, e.g. by measuring the output voltage continuously or at predetermined time intervals, detecting 202 when the output voltage exceeds a threshold, and actuating 203 a failure indicator based on the detection. In an embodiment, the method may comprise a step of comparing the monitored output voltage with a reference voltage. Further, the method may comprise a step of calibrating the lighting device by measuring the output voltage and setting the reference voltage based on the measured output voltage.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

Claims

CLAIMS:

1. A lighting device (100) comprising:

a light source (1),

a constant current driver (2) configured to provide an output voltage for driving the light source, and

a monitoring circuit (4) configured to monitor said output voltage, detect when the output voltage exceeds a threshold and actuate a failure indicator (8) based on said detection.

2. The lighting device as defined in claim 1, wherein the light source is in electrical connection to the driver via a solder connection.

3. The lighting device as defined in claim 1 or 2, wherein the light source is a LED-based light source or a gas discharge light source.

4. The lighting device as defined in any one of the preceding claims, wherein the constant current driver is configured to regulate the output voltage such that the light source is driven at a constant current for a given light intensity of the light source.

5. The lighting device as defined in any one of the preceding claims, wherein the monitoring circuit comprises a comparator (7) configured to compare the monitored output voltage with a reference voltage for detecting if the output voltage exceeds the threshold.

6. The lighting device as defined in claim 5, wherein the reference voltage is equal to or higher than an output voltage of the constant current driver required for driving the light source at an originally designed electrical resistance between the light source and the constant current driver and/or in the light source.

7. The lighting device as defined in claim 5 or 6, wherein the lighting device is configured to be set in a calibration mode, in which the monitoring circuit is configured to measure the output voltage and set the reference voltage based on the measured output voltage.

8. The lighting device as defined in claim 5, wherein the reference voltage is predetermined.

9. The lighting device as defined in any one of claims 5-8, further comprising a memory (6) for storing the reference voltage.

10. The lighting device as defined in any one of the preceding claims, wherein the monitoring circuit is configured to measure the output voltage continuously or at predetermined time intervals.

11. The lighting device as defined in any one of the preceding claims, wherein the lighting device is configured to be set in a test mode, in which the monitoring circuit is configured to perform said monitoring of the output voltage.

12. The lighting device as defined in any one of the preceding claims, wherein the failure indicator is provided by one or more of: an indicator LED, a failure indication signal to a communication network, an adjustment of the light output of the light source and an audible signal.

13. The lighting device as defined in any one of the preceding claims, wherein the light source comprises at least one light emitting diode (9).

14. A method of indicating an incipient failure in a lighting device comprising a light source, the method comprising the steps of:

monitoring (201) an output voltage used for driving the light source, detecting (202) when the output voltage exceeds a threshold, and actuating (203) a failure indicator based on said detection.