WO2018137846A1

WO2018137846A1 - A light emitting diode, led, based lighting device for reducing arcing.

Info

Publication number: WO2018137846A1
Application number: PCT/EP2017/083067
Authority: WO
Inventors: Paul Joseph Maria BEERENS; Franciscus Hubertus Theodorus Lammers; John SCHATORIE; Geert Willem Van Der Veen
Original assignee: Philips Lighting Holding B.V.
Priority date: 2017-01-26
Filing date: 2017-12-15
Publication date: 2018-08-02

Abstract

A Light Emitting Diode, LED, based lighting device for detecting and reducing arcing occurring in said lighting device, said lighting device comprising an LED load arranged for emitting light, an LED driver arranged for receiving a supply voltage and for driving said LED load by providing an LED output current to said LED load, an arcing detector arranged for determining that arcing is occurring at said LED load by detecting spikes occurring in said LED output current provided by said driver to said LED load and a control device arranged for controlling said LED driver such that said LED driver reduces said LED output current based on detected arcing occurring at said LED load.

Description

A light emitting diode, LED, based lighting device for reducing arcing

FIELD OF THE INVENTION

The present invention relates to the field of lighting and more specifically to a Light Emitting Diode, LED, based lighting device. Even more specifically, the present invention relates to a LED based lighting device for the detecting and reducing, and to a corresponding method.

BACKGROUND OF THE INVENTION

Lighting devices have been developed that make use of Light Emitting Diodes, LEDs, for a variety of lighting applications. Owing to their long lifetime and high energy efficiency, LED lamps are nowadays also designed for replacing traditional fluorescent lamps, i.e. for retrofit applications. For such an application, a retrofit LED tube is typically adapted to fit into the socket of the respective lamp fixture to be retrofitted.

Moreover, since the maintenance of a lamp is typically conducted by a user, the retrofit LED tube should ideally be readily operational with any type of suitable fixture without the need for re- wiring the fixture.

Such a retrofit LED tube is, for example disclosed in US 2016/80081147. Here, an LED tube is wired to receive the current that is input from any two electrode pins from among the pairs of pins at the ends of the tube, which house the driver circuitry. The input current is converted to DC through a rectifier circuit, is filtered of unwanted

frequencies and voltage through a filter circuit, and is controlled with a step-down constant current circuit to drive an LED array within the tube.

One of the challenges for such retrofit LED lamps is to make them more robust, more resilient, to arcing. Arcing is a phenomenon that can occur in an LED device, more specifically at the LED's of the LED array of the LED device. Arcing can, for example, occur between the legs of an LED or between a leg of an LED and any other conducting material in the vicinity of it. Sustained occurrence of arcing could lead to reduced lifetime of the device and also to discoloration of surrounding components.

WO 2016/124480 discloses a driver circuit comprising a mains input and a switch mode power converter for delivering an output derived from the mains input by switching using a pulse width modulation signal. The switch mode power converter comprises a pulse width controller for controlling the pulse width of the pulse width modulation signal. A monitor is used for monitoring the pulse width of the pulse width modulation signal and for detecting a surge event from the pulse width, wherein the monitor is for detecting the surge event from changes in the pulse width and/or duty cycle over time, and comprises a monitor circuit for detecting a surge event based on the pulse width and/or duty cycle reducing to correspond to a first pulse from a second pulse, remaining at the first pulse for a time period falling within a first threshold range and then returning to the second pulse, wherein the width of the first pulse is narrower than the second pulse.

SUMMARY OF THE INVENTION

It would be advantageous to achieve a Light Emitting Diode, LED, based lighting device that is capable of detecting arcing occurring at the LED load and to reduce the occurrence of it. It would further be advantageous to achieve a corresponding method of operating an LED based lighting device.

To better address one or more of these concerns, in a first aspect of the present disclosure, there is presented a Light Emitting Diode, LED, based lighting device for detecting and reducing arcing occurring in said lighting device, said lighting device comprising:

- an LED load arranged for emitting light;

an LED driver arranged for receiving a supply voltage and for driving said LED load by providing an LED output current to said LED load;

an arcing detector arranged for determining that arcing is occurring at said LED load by detecting spikes occurring in said LED output current provided by said driver to said LED load;

a control device arranged for controlling said LED driver such that said LED driver reduces said LED output current based on detected arcing occurring at said LED load.

It was one of the insights of the inventors that the lifespan of the LED based lighting device is reduced to arcing occurring at the LED load of the LED based lighting device.

In order to combat that phenomena, the inventors have found that the fact that arcing is occurring at the LED load can be determined by detecting spikes occurring in the LED output current provided by the driver to the LED load. The control device will then control the LED driver such that the LED driver reduces the LED output current once it has been determined that arcing is occurring at the LED load. The probability that arcing occurs again is then reduced as the inventors have found that arcing is coupled to the amount of LED output current provided to the LED load. Reducing the LED output current therefore also reduced the probability that arcing occurs again.

It was one of the insights of the inventors that the repeated occurrence of arcing within the LED based lighting device, more specifically at the LED load, will lead to reduced operational life of the device and that it would be advantageous to detect arcing by monitoring the LED current for spikes and subsequently taking further actions so as to reduce the arcing within the lighting device.

There are typically two kinds of arcing that can occur within an electrical system:

Line fault arcing comprises arcing occurring between an active mains line and another mains line or between an active mains line and the ground or neutral;

Contact arcing may occur between any two conducting elements due to, for example, improper contact and/or due to presence of a non-conducting material in the path of current flow.

Normally, the voltage and current under conditions of line fault arcing are much higher than what the system is designed to operate at. Thus occurrence of such a fault will often trip the mains power supply and the circuit breaker will react to ensure that such arcing conditions are extinguished immediately.

Under conditions of contact arcing, the arcing voltage is often within the operating range of the LED driver and hence goes unnoticed by the circuit breaker and other protection mechanisms. Continued presence of such arcing conditions can, however, affect the operational life of the components in the lighting device as well as the fixture of the lighting device.

It was the insight of the inventors that arcing within a LED based lighting device can be detected by monitoring the output current that is being provided by the LED driver to the LED load. Under normal operating conditions, the value of the current falls within a predetermined range. Under conditions of arcing, however, there is, for example, a sharp increase in the value of current that results in the formation of spikes in the current waveform of the output current. Within the scope of this invention, it is intended to detect the occurrence of arcing by detecting the presence of such spikes in the current waveform of the LED output current.

Once an arc has been detected by an arcing detector, it may be advantageous to reduce the arc or the occurrence of the arcing condition. In order to do so, the inventors came up with the idea of reducing the LED output current of the driver by means of a control mechanism upon successful detection of an arc.

In other words, upon detection of an arc by the arcing detector, a control mechanism would act suitably such that the LED output current is reduced, thereby reducing the arcing that occurs at the LED load.

In accordance with the present disclosure, the LED based lighting device may be a retrofit LED tube, for example a retrofit LED tube for replacing a fluorescent tube. A LED tube is retrofitted in case it fits in conventional armatures for fluorescent tubes, for example fluorescent tubes suitable for T5, T12 or anything alike. In order to fit in these conventional armatures, the retrofit LED tube comprises conducting pens for connecting, and supporting, the retrofit LED tube in the conventional armatures.

In an embodiment, the arcing detector is arranged for detecting said spikes by: monitoring said LED output current;

detecting that arcing has occurred when said LED output current exceeds a predetermined value.

In this particular embodiment, the occurrence of arcing is detected by monitoring the LED current and confirming that an arcing has occurred when the value of a spike exceeds a predetermined value.

The predetermined value is, for example, between five to ten times the nominal value of the LED output current, more preferably around seven to eight times the nominal value of the LED output current.

In another embodiment, the arcing detector is arranged for determining that arcing is occurring at said LED load by detecting spikes occurring in said LED output current having a frequency of at least 400kHz.

The LED output current of the driver that drives the LED load can have ripples within it. This is the result of, for example, improper rectification and/or improper filtering. The frequency of such ripples is often in the range of 50-150 kilo Hertz. However, under conditions of arcing, when spikes are present in the current waveform, the frequency can be higher than 400 kilo Hertz, or somewhere between 400 kilo Hertz and 1 mega Hertz. This also provides an opportunity to confirm the occurrence of arcing condition. Therefore, in this particular embodiment, arcing can be detected by monitoring the frequency of the output current and confirming the occurrence of an arc when the frequency exceeds 400kHz.

The advantage of the above is that the spikes in the LED output current can be distinguished from any ripples occurring in the LED output current based on improper filtering or improper rectification.

In a further embodiment, the arcing detector is further arranged for determining that said arcing is occurring at said LED load by detecting a plurality of subsequent spikes occurring in said LED output current such that said arcing detector is more resilient to fluctuations in the LED output current due to high frequency, HF, noise or other factors in the driver surroundings.

The advantage of this particular embodiment is its ability to be resilient to random fluctuations within the circuit such as due to High Frequency, HF, noise. Often, the presence of other electromagnetic components in the vicinity of the driver circuit will cause the presence of additional ripples and/or spikes in the output LED output current. This could lead to triggering the arcing detector when in reality arcing occurs. It was the insight of the inventors, therefore, to detect a plurality of subsequent spikes before taking action. This has the advantage that the LED based lighting device is not interrupted incorrectly and that the system is more resilient to, for example, High Frequency noise from the surroundings of the device.

In a further embodiment, the arcing detector is arranged to accumulate said detected plurality of subsequent spikes for a predetermined time duration, and for determining that said arcing is occurring by determining that said accumulated spikes exceed a predetermined spike threshold. In this particular embodiment, a plurality of subsequent spikes within a predetermined time are detected before determining that arcing has occurred.

So, in case a number of subsequent spikes have been detected within a predetermined time threshold, it is decided, by the arcing detector, that arcing has occurred, and the control device will act accordingly, i.e. it will reduce the LED output current.

In a further embodiment, the arcing detector is arranged to accumulate said detected plurality of subsequent spikes by at least one of:

- counting a number of detected spikes occurring within said predetermined time duration;

accumulating a total amount of power in said detected spikes occurring within said predetermined time duration. The inventors have found that a repeated behavior of spiked occurring in the LED output current can at least be sensed, i.e. determined, by either counting the number of detected spiked or accumulating a total amount of power in the detected spikes.

So, in this scenario, presence of an arcing is detected by either detecting that a number of spikes have occurred within a predetermined time duration and that this number is greater than a predetermined spike threshold, or detecting that the total power contained in the spikes occurring within a specified time duration is greater than a predefined threshold.

There are of course several ways in which said function can be realized. In an embodiment according to the first option, the number of spikes can be counted using an analog/digital counter and the counter may be reset after the predetermined time duration has elapsed. An occurrence of an arcing condition can be detected if the count exceeds a predetermined spike threshold within a predetermined time duration. Another option is to use a moving average in which the number of spikes within a predefined spike threshold is tracked in a more continuous manner.

In the context of the present disclosure, the control device may be a micro process, a microcontroller or a Field Programmable Gate Array, FPGA, or anything alike.

In the embodiment according to the second option, the power of the spikes is accumulated in an electrical device such as capacitor. Once the power exceeds a

predetermined spike threshold within a predetermined time duration, arcing is said to have occurred. If, however, the accumulated value does not exceed the predetermined spike threshold, the value of the capacitor may be reset by allowing the charge to be drained off by means of a bleeding resistor.

In a further embodiment, the control device comprises a digital control device such as a microcontroller, wherein said digital control device is arranged for any of maintaining a log of detected spikes, shutting down the system and initiating a restart of the LED based lighting device.

In this specific embodiment, the means for controlling the driver circuit upon detection of an arcing condition may be implemented using a digital element such as a microcontroller. When an element such as a microcontroller is employed in the circuit, there are more options available to make the device more intelligent. The usage of a

microcontroller allows the possibility of maintaining a log of the detected spikes and of detected arcing situations. This could be useful to end users and/or to personnel who intend to make changes in the device after installation and use. Another option available to the user upon incorporation of a digital control means such as a microcontroller is the option to shut down the system upon detection of continued arcing and to force the system to remain shut down for a certain duration of time. After the certain duration of time has elapsed, a restart of the system can be initiated. This allows for the operation of the system with reduced human intervention.

In a second aspect of the present disclosure, there is provided a method for detecting and reducing arcing occurring in a lighting device according to any of the previous claims, wherein said method comprises the steps of:

driving, by said LED driver, said LED load by providing an LED output current to said LED load;

determining, by said arcing detector, that arcing is occurring at said LED load by detecting spikes occurring in said LED output current provided by said driver to said LED load;

controlling, by said control device, said LED driver such that said LED driver reduces said LED output current based on detected arcing occurring at said LED load.

It is noted that the advantages and definitions as disclosed with respect to the embodiments of the first aspect of the invention also correspond to the embodiments of the second aspect of the invention, being the method of detecting and reducing arcing occurring in an LED load.

In an embodiment, the step of determining comprises:

monitoring said LED output current;

In a further embodiment, the step of determining comprises:

determining that arcing is occurring at said LED load by detecting spikes occurring in said LED output current having a frequency of at least 400kHz.

In another embodiment, the step of determining comprises:

detecting a plurality of subsequent spikes occurring in said LED output current such that said arcing detector is more resilient to fluctuations in the LED output current due to high frequency, HF, noise or other factors in the driver surroundings.

In a further embodiment, the step of detecting comprises:

accumulating said detected plurality of subsequent spikes for a predetermined time duration, and determining that said arcing is occurring by determining that said accumulated spikes exceed a predetermined spike threshold.

In another embodiment, the step of accumulating comprises:

counting a number of detected spikes occurring within said predetermined time duration;

accumulating a total amount of power in said detected spikes occurring within said predetermined time duration.

In a further embodiment, the step of controlling comprises a digital control device such as a microcontroller, wherein said digital control device is arranged for any of: - maintaining a log of detected spikes;

shutting down the system;

initiate a restart of the device.

A third aspect of the present disclosure deals with a computer program product, comprising a readable storage medium, comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out the method according to any of the examples as provided above.

It is noted that the advantages and definitions as disclosed with respect to the embodiments of the first and second aspect of the invention, being the LED based lighting device and the corresponding method of arc detection and reduction, respectively, also correspond to the third aspect of the invention, being the computer program product which is capable of storing the method of detection and reducing arcing as discussed in the second aspect.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 shows the variation occurring in the LED current as a function of time, wherein spiked during arcing are depicted.

Fig. 2 shows a schematic diagram of an example of the Light Emitting Diode, LED, based lighting device for detecting and reducing arcing.

Fig. 3 shows a specific embodiment of a part of the LED based lighting device in accordance with an example of the present disclosure.

DESCRIPTION

Figure 1 shows the variation occurring in the LED output current as a function of time. Reference number 100 shows the variation of LED current 101 over time. As can be seen in the figure, the value of the LED output current is typically not entirely constant over time. Usually, there are always small fluctuations in the LED output current with respect to time. These fluctuations are called ripples and are present in the LED output current due to a number of reasons such as noise from surroundings and improper

rectification AC input signal.

In spite of presence of such ripples, the magnitude of the current may remain between a minimum and a maximum level, which levels are indicated with reference numeral 102. So, under normal operating conditions, the LED output current should remain within the levels as indicated with reference numeral 102.

Under conditions of arcing, however, there may occur a sharp rise/fall in the value of current beyond the minimum and maximum level. Such a sharp rise or fall in the value of current are referred to as spikes, which are indicated in figure 1 with reference numeral 103. It was the insight of the inventors that the arcing condition could be

successfully detected by monitoring the LED current for such spikes.

Further, in figure 1 it is shown that the spikes normally occur several times after each other. The spikes may occur, for example, in a periodic manner. The period is, for example, related to the period that is inputted to the LED based lighting device.

In such a case, the control device may even be arranged to take pre-emptive measures to make sure that a spike that is likely to occur does not occur at all. As such, the control device may be arranged to reduce the LED output current at the end of the above mentioned period.

The period, as mentioned above, may be a static period originating from the period of the Alternating Current power source provided to the LED based lighting device, but may also be any other period. The control device may be arranged to detect the period itself by keeping track of time periods between detected spikes in the LED output current.

Figure 2 shows a schematic diagram of an example of the Light Emitting Diode, LED, based lighting device for detecting and reducing arcing.

Reference number 200 designates a LED based lighting device comprising a Light emitting Diode, LED load 203, which LED based lighting device is capable of a detecting and reducing arcing occurring within the device. It is noted that the LED load 203 can be a single LED or an array of LED connected in series or in parallel arranged or emitting light. Further, those skilled in the art will appreciate that in practical embodiments the LEDs are evenly distributed and spaced apparat across the length of the LED based lighting device, to provide for an evenly as possible lighting by the LED based lighting device over its entire length. The present disclosure is not limited to any specific type of LED, nor to any color LEDs. Typically, white colored LEDs are used.

It is noted that the present disclosure is especially suitable for LED loads which are based on power LEDs. High power LEDs or high output LEDs may be driven at LED output currents ranging from hundreds of mA to more than a single ampere, compared with, for example, the tens of mA for other LEDs. Some of these high power LEDs can emit over a thousand lumens. Typically, the high power LEDs may be mounted on a heat sink to allow for heat dissipation. As these high power LEDs are typically driven with a nominally higher LED output current, the risk or arcing occurring at these high power LEDs is also increased. This is especially the case as for high power LEDs heat sinks may be used, which heat sinks could also form a basis for receiving any arc.

The LED based lighting device 200 comprises two groups of components.

Components grouped within 201 can perform the function of arc detection and reduction as described in this disclosure in an analogue manner. If however, a digital control of the LED based lighting device, as described in the present disclosure, is required, components within group 202 may also have to be included in the system.

Under normal operation of the system, the LED driver, indicated as the Driver output stage with reference numeral 212 receives a supply voltage from the mains power supply or any other device capable of supplying electrical power. The driver 212 converts the received supply voltage, for example an AC supply voltage or an DC supply voltage, into a form that can drive the LED based lighting load and supplies an LED output current 101 to the LED load 203.

If, for example, the driver 212 is connected to a mains power supply, the input voltage could be 230Vac, or 1 lOVac. Subsequently, the role of the driver 212 is to convert the supplied voltage into an DC voltage and also ensure that the LED load 203 is supplied with a proper level of current that would enable its operation.

If, for example, the driver 212 is connected to an alternate source of power such as a battery, the role of the driver is to ensure that it is able to provide at its output a voltage and current level that would enable the operation of the LED load 203.

As described before, it was the insight of the inventors that arcing conditions could be detected by monitoring the LED output current 101 for the presence of spikes. The spikes are detected using a detector 204. A possible physical embodiment of the detector block is by employing an inductance. The potential difference across an inductance is directly proportional to the rate of change of current flowing through the inductance. Hence, under conditions of constant current, there is no potential difference between the two ends of the coil. If, however there is a spike in the LED output current 204, there is a large rate of change of current and consequently a large potential difference developed across the terminals of the coil.

The advantage of using an inductor as a spike detector is that most LED based driver circuits already contain an inductance for filtering the effect of external Electro- Magnetic Interference, EMI, in the circuit. Therefore, by making use of the same inductance, there is a considerable savings in space on the Printed Circuit Board, PCB, and hence a consequent savings in associated cost. A skilled person is aware of the different

implementations to detect a sharp rise/fall in the LED output current 203.

Once a sharp rise/fall in the LED output current 203 has been detected, it is advantageous to ensure that the said rise/fall is not due to external high frequency (HF) noise or due to improper rectification in the driver. The inventors have found that spikes in the LED output current 101 due to arcing behave different that for examples ripples present in the LED output current 101. Such a differentiation can then be made by the control device of the present disclosure.

This is implemented using a DC Blocking/High pass filter 206. The function of such a component is to ensure that low frequency ripples are not transmitted through to the comparator 209 stage. Such low frequency ripples may be present in the signal as a result of improper rectification. At the same time the block should also function effectively in transmitting High frequency signals to be transmitted efficiently. The spikes typically have a high fundamental frequency, in the range of 400 kHz or higher. Hence the physical implementation of this block can be realized by using a capacitor of suitable value that blocks the low frequency and DC components and at the same time allows high frequency components and spikes to be transmitted to the next block.

Once the low frequency components have been eliminated, a peak rectifier 207 is included in the system. The function of this block is to ensure that the peak value of the spike is detected. This is beneficial as only the peak value is compared with the threshold value in order to detect the occurrence of arcing. In addition, it would also be advantageous to ensure that the system is more resilient to High Frequency noise from its surroundings. If the system reacts with a high level of sensitivity to noise from its surroundings, there is a possibility that this will lead to light flicker and erratic behavior by the LED based lighting device. Hence the peak detector 207 may also include an accumulating component.

The function of such an accumulating component within the peak detector 207 is to accumulate the values of the spike as detected by the peak detector 207. The

accumulated values are stored for a predetermined duration of time. In this case, an arc is detected if the total accumulated value within the predetermined duration of time exceeds a certain threshold. This ensures that the system is more resilient to high frequency, HF, noises from its surroundings.

In an alternate embodiment, the accumulator may also be replaced by a counter that counts a number of spikes occurring within a predetermined duration of time. As described before, a successful arc detection will occur if the number of spikes occurring within a predetermined duration of time is greater than a predetermined threshold number of spikes.

The next part of the system is the comparator 209, wherein the presence of the spike, and therefore the occurrence of arcing, is detected. The function of the comparator 209 is to compare the peak value of the spike with a detection set point 208. If the value of the spike is found to be higher than the detection set point 208, then an arcing condition is said to have occurred. Physically, this can be realized by a transistor or an Operational Amplifier, OP-AMP. The person skilled in the art may be able to implement a comparator in a variety of manners.

Once the comparator 209 has detected the occurrence of an arcing condition, this is to be conveyed to the control circuitry 211 by means of a feedback and/or coupling mechanism 210. The function of the coupler is to ensure that the nature of the signal is capable of being processed by the control clock. This block of the device needs to be dependent on the topology of the circuit and especially that of the driver. Hence the physical implementation of this block will differ between applications and the person skilled in the art is aware of the different implementations that are possible.

The feedback and control circuitry 211 is then responsible for controlling the driver 212 in such a manner that the LED output current 101 is reduced in order to reduce the arcing that has been detected.

In an optional embodiment of the present disclosure, it was the insight of the inventors that it would be advantageous to include an element of digital control in the device. This would enable to perform actions in a smart manner with decreased human interference. Therefore, components within the group 202 are included in the device. These include the pulse shaper 213 and digital control means such as a microcontroller 214. The objective of the pulse shaper 213 is to ensure that the signal that will be relayed to the digital control means 214 is capable of being understood by the said digital control means. In other words, the signal conforms with the voltage and current requirements of the digital control means so that the signal can be readily transmitted to one of the input terminals of the said control means.

The digital control means such as a microcontroller 214 serve the purpose of receiving said signal from the comparator 209, after being suitably adapted, and taking consequent actions in a manner so as to either:

- give signal to the analog control circuitry to act in a manner that would enable the reduction of the LED current, or

directly control the parameters of the driver 212 so as to reduce the LED output current 101.

In addition to performing the control process digitally, the inclusion of a digital control means such as a microcontroller adds extra value to the device in terms of its capability to perform additional functions. Some examples of such additional examples could include maintaining a log arcing events, shutting down system after arcing condition continues to exist, and initiating a restart of the system after such a shutdown period.

It would be advantageous to maintain a log of the arcing events because it would enable the user or the maintenance and repair time to understand the frequency and severity of the arcing conditions that have occurred as it could have a direct correlation with the operational life of the device and the associated components. Additionally, in case the arcing condition continues to exist it would be advantageous to automatically shut down the Led based lighting device as a whole for a certain duration of time.

Once the system is shut down, and it remains shut down for a certain duration of time, a restart of the system can be initiated. This too can be done by the digital control means such as a microcontroller. After restart, if the LED based lighting device continues to exhibit arcing conditions, the LED based lighting device can be shut down again. If arcing does not happen anymore, normal operation can be restored. This can be advantageous for the user because in such a scenario, the LED based lighting device is, on its own, capable of deciding and executing steps without the intervention of the user or maintenance personnel.

Figure 3 shows a specific embodiment of the arc detection and reduction system. Reference number 300 indicates a specific embodiment of the system which is realized without digital control means. It is important to note that this figure shows one of the many possible embodiments of the invention contained within this disclosure. The features and components listed below should not be construed as being limiting to the scope of the invention as discussed in this disclosure. The person skilled in the art is aware of suitable alternatives that can achieve the same results.

The driver output stage 212, comprised by the driver, supplies the LED output current to the LED load 203. The output filter 311 serves the purpose of the detector 204 in order to detect the presence of a sharp rise/fall in the value of the LED output current. The presence of the such sharp rise/fall in the current is transmitted by means of a DC blocking/ High pass filter.

In this specific embodiment, such a filter is implemented by means of a capacitor 301 and resistor 302. By selection of the values of the resistor 302 and the capacitor 301, it can be ensured that electrical signals with frequencies less than a certain threshold frequency are blocked and higher frequency signals are transmitted without significant loss.

The next elements are the physical realization of the peak rectifier block 207 according to Figure 2. These elements include the diode 303, resistor 304, the capacitor 305 and the bleeding resistor 306. This arrangement helps in identifying the peak value of the signal, which will be later compared with the predetermined value. In addition, the configuration as shown is also capable of accumulating said peak values for a predetermined time duration.

The predetermined time duration can be chosen by the choice of the values of the resistor 304 and the capacitor 305. The peak values of spikes occurring within the predetermined time duration will be stored in the capacitor. If it exceeds the threshold value, an arcing condition is considered as detected by the Led based lighting device. If, however, within the predetermined time duration, the accumulated value of spikes in the capacitor does not exceed the threshold value, the capacitor will be reset. This is achieved by draining the capacitor of the stored value via the bleeding resistor 306. The amount of time taken to reset the capacitor is determined by the values of capacitor 305 and the bleeding resistor 306. Once the capacitor 305 is reset, it is capable of accumulating the peak values of spikes again for a next predetermined time duration.

Reference number 307 represents a Metal Oxide Semiconductor Field Effect

Transistor, MOSFET. In this specific embodiment the function of the comparator block 209 is realized with the help of this component. The person skilled in the art is aware of other methods in which the function of the comparator may be realized. The MOSFET has three terminals, i.e. Source, Drain and Gate. In this particular embodiment, the voltage at the "Gate" terminal (V_gate) is used to determine the threshold value. So, for example, if the voltage across the capacitor 305 exceeds V_gate, an arcing condition will be detected by the system. This is achieved by the fact that the MOSFET 307 is turned ON when voltage across capacitor 305 is greater than V_gate.

As seen in the Figure 3, when the MOSFET 307 is turned ON, it provides a path for current to flow through the opto-coupler 308. This gives a signal at the output pins of the opto-coupler 308. This signal is then transmitted to the feedback circuit.

In other words, if peak value is detected by inductor (311), the following steps occur:

- the spike is transmitted via capacitor 301 blocking any low frequency components;

the peak value of the spike is detected and stored with help of diode 303, Resistor 304 and capacitor 305;

the peak values are accumulated for a certain duration time in the capacitor 305, the certain duration of time being determined by the resistor and capacitor pairing 304 and 305 respectively;

the accumulated value is compared against a threshold value, the threshold value being determined by the voltage at the gate terminal, V_gat_e;

if the accumulated value is greater than the threshold value, the MOSFET 307 is turned ON providing a path for current;

this in turn activates the opto-coupler 308 which gives a signal to the feedback circuit 309 that an arc has been detected.

Once a signal of successful arc detection reaches the Feedback circuit 309, it modifies parameters of the power converter controller 310 such that the LED output current is reduced.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims, In the claims, the word "Comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems, any reference signs in the claims should not be construed as limiting the scope thereof.

Claims

CLAIMS:

1. A Light Emitting Diode, LED, based lighting device (200) for detecting and reducing arcing occurring in said lighting device (200), said lighting device (200)

comprising:

an LED load (203) arranged for emitting light;

an LED driver (212) arranged for receiving a supply voltage and for driving said LED load (203) by providing an LED output current to said LED load (203), the LED output current having a magnitude between a minimum and a maximum level;

an arcing detector (204) arranged for determining that arcing is occurring at said LED load (203) by detecting spikes occurring in said LED output current provided by said driver (212) to said LED load (203), wherein a spike has a magnitude beyond the minimum level or beyond the maximum level;

a control device (211) arranged for controlling said LED driver (212) such that said LED driver (212) reduces said LED output current based on detected arcing occurring at said LED load (203).

2. A device according to claim 1 wherein said arcing detector is arranged for detecting said spikes by:

monitoring said LED output current;

3. A device according to any of the previous claims, wherein said arcing detector is arranged for determining that arcing is occurring at said LED load by detecting spikes occurring in said LED output current having a frequency of at least 400kHz.

4. A device according to any of the preceding claims, wherein said arcing detector is further arranged for determining that said arcing is occurring at said LED load by detecting a plurality of subsequent spikes occurring in said LED output current such that said arcing detector is more resilient to fluctuations in the LED output current due to high frequency, HF, noise or other factors in the driver surroundings.

5. A device according to claim 4, wherein said arcing detector is arranged to accumulate said detected plurality of subsequent spikes for a predetermined time duration, and for determining that said arcing is occurring by determining that said accumulated spikes exceed a predetermined spike threshold.

6. A device according to claim 5, wherein said arcing detector is arranged to accumulate said detected plurality of subsequent spikes by at least one of:

7. A device according to any of the preceding claims, wherein said control device comprises a digital control device such as a microcontroller, wherein said digital control device is arranged for any of:

maintaining a log of detected spikes;

- shutting down the system;

initiate a restart of the device.

8. A method for detecting and reducing arcing occurring in a lighting device according to any of the previous claims, wherein said method comprises the steps of:

- driving, by said LED driver, said LED load by providing an LED output current to said LED load;

- controlling, by said control device, said LED driver such that said LED driver reduces said LED output current based on detected arcing occurring at said LED load.

9. The method for detecting and reducing arcing according to claim 8, wherein said step of determining comprises: monitoring said LED output current;

10. The method for detecting and reducing arcing according to any of the claims 8 - 9, wherein said step of determining comprises:

11. The method for detecting and reducing arcing according to any of the claims 8 - 10, wherein said step of determining comprises:

12. The method for detecting and reducing arcing according to claim 11, wherein said step of detecting comprises:

accumulating said detected plurality of subsequent spikes for a predetermined time duration, and

determining that said arcing is occurring by determining that said accumulated spikes exceed a predetermined spike threshold.

13. The method for detecting and reducing arcing according to claim 12, wherein said step of accumulating comprises:

14. The method for detecting and reducing arcing according to any of the claims 8 - 13, wherein said control device comprises a digital control device such as a

microcontroller, wherein said digital control device is arranged for any of:

maintaining a log of detected spikes; shutting down the system;

initiate a restart of the device.

15. Computer program product, comprising a readable storage medium, comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out the method according to any of the claims 8 - 14.