Safe operation of an LED lamp

A lamp and an operating method for a lamp with an LED element 22 are described. An electrical circuit with the LED element 22 is covered by a cover member 12. A separation device 28 is provided to mechanically severe the electrical conductor 16a, 16b arrange to supply electrical power to the LED element 22 if the detector element 24 detects a defect of the cover member 12.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C. §371 of International Application No. PCT/EP2015/052221, filed on Feb. 3, 2015, which claims the benefit of European Patent Application No. 14154333.0, filed on Feb. 7, 2014. These applications are hereby incorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to a lamp and to a method of operating a lamp. In particular, the invention relates to a lamp including an LED element.

BACKGROUND OF THE INVENTION

Due to their known advantages such as high energy efficiency, small size and long lifetime, LEDs are increasingly used today in lighting and signaling applications. Retrofit LED lamps are replacing other technologies such as incandescent lamps or fluorescent lamps.

Such LED lamps are designed safe for the user, i.e. any life electrical parts, such as the electrical circuit comprising the LED element, are covered, so that a direct contact with the operating voltage, which could result in an electric shock, is prevented in normal operation and handling of the LED lamp. However, problems may arise if the LED lamp is damaged.

WO 2011/027278 A1 describes an LED lamp with at least one LED in a housing. An isolation monitoring device determines a defect of the housing and in this case disconnects the LED from power. The isolation monitoring device may comprise a detection circuit integrated with the housing, or a pressure sensor to detect a defect. Switches may be provided for all-pole disconnection of the LED, or to short-circuit a fuse for permanently disconnecting the LED from power.

SUMMARY OF THE INVENTION

It may be considered an object to provide an LED lamp with increased safety even in case of damage.

This object is achieved by an LED lamp according to claim1and by an operating method according to claim14. Dependent claims refer to preferred embodiments of the invention.

An LED lamp according to the invention comprises an electrical circuit which includes at least one LED element. This comprises single elements as well as arrays of any type of solid state lighting elements, including light emitting diodes and organic light emitting diodes (OLED).

The lamp further comprises a cover member. The cover member is provided to cover at least a part of the electrical circuit in order to provide protection for a user to handle the lamp without a danger of electrical shock from touching life parts, i.e. parts of the circuit energized with operating voltage. The cover member may preferably be a housing provided to fully isolate the electrical circuit (except for supply terminals).

The electrical circuit of the lamp comprises at least one electrical conductor, which is arranged to supply electrical power to the LED element. According to the invention, the lamp comprises a separation device provided to mechanically server the conductor if a detector element detects a defect of the cover member.

The detector element allows to distinguish between a normal state of the lamp which allows safe operation, and a defect state, where at least a part of the cover member may be broken, opened, missing or otherwise comprise a defect which may present a danger that it does no longer fulfill the function of securely isolating any life parts of the electrical circuit. In particular, the detector element may detect mechanical damage to the cover member.

In case of a defect detected by the detector element, the electrical conductor arranged in the supply line of electrical power to the LED element is mechanically severed, i.e. electrically conducting material of the electrical conductor, such as preferably metal material, is e. g. cut, ripped apart or otherwise mechanically acted upon so that the material is permanently separated and no further electrical conduction is possible. Thus, supply of further electrical power is permanently disrupted and any further operation of the LED element is permanently inhibited.

By mechanically severing the electrical conductor, and thus permanently disconnecting the LED element, unsafe operation is avoided. Permanent disconnection ensures that in cases of a defect of a cover member, e. g. a broken housing, the LED lamp is permanently disabled and must be exchanged.

According to a preferred embodiment of the invention, the separation device may comprise an impulse element suited to be triggered to provide a motion force for severing the electrical conductor. The impulse element may be any element suited to provide the required force if triggered. A mechanical member may be propelled by the motion force for severing the electrical conductor. As will become apparent in connection with preferred embodiments, the propelled mechanical member may be a part of a carrier (e. g. circuit board) on which the electrical conductor is provided, or may be a separate element arranged to mechanically act on the electrical conductor.

According to a preferred embodiment, the impulse element may be provided to be electrically triggered. The electrical signal provided as a trigger may serve to deliver the energy for providing the motion force. Alternatively, the electrical trigger signal may serve to release pre-stored energy e. g. in electrical, chemical or mechanical form.

In a particularly preferred embodiment, an electrical triggering signal may be provided through a triggering conductor, which is electrically isolated from the electrical conductor to the LED element. Thus, preferably, the electrical triggering signal is not conducted through the electrical conductor itself, but separately through a triggering conductor.

In embodiments of the invention, different elements may serve to provide a motion force for severing the electrical conductor. For example, a chemical charge may be provided, which, if triggered, propels a mechanical member. Alternatively, a spring element may be provided with pre-stored mechanical energy, which is released if triggered, e. g. by removing a lock element. Further, it is possible to provide a driving coil to electromagnetically propel a ferromagnetic element. Alternative embodiments and combinations of the above described embodiments are also possible.

Preferably, the electrical conductor may be a bond wire. Wire bonding is a flexible and cost-effective interconnect technology widely used on an industrial scale in semiconductor packaging. A bond wire may in particular consist of aluminum, copper or gold with diameters of 15 μm to several hundred μm. In particular preferred are diameters of 30 μm-100 μm. A bond wire is well suited to permanently interrupt the power supply if severed. Due to its small dimensions, it may be easily cut, ripped apart or otherwise severed.

According to a preferred embodiment of the invention, the electrical conductor may be provided on a first carrier part and on a second carrier part. The carrier parts may be any element suited to mechanically hold the electrical conductor. In particular, the carrier parts may be parts of one or more circuit board. The electrical conductor may then be severed by separating the first and second carrier parts. The electrical conductor between the carrier parts then breaks, such that the desired mechanical separation is effected.

In one embodiment of the invention, a plurality of breakage zones are arranged along the length of the electrical conductor, i.e. electrically in series. The separation device may server the electrical conductor not only in a single location, but may act such that the conductor is severed at least in two of the breakage zones. Due to the sequential arrangement of the breakage zones and the resulting electrical series connection, this ensures electrical isolation even in case that separation in one of the breakage zones may be incomplete.

The lamp may comprise electrical terminals, where it is connected to a supply of electrical operating power, e.g. from a lighting fixture, ballast, mains connection etc. A rectifier circuit and a driver circuit may be arranged electrically between the LED element and the electrical terminals, such that AC electrical power is rectified. Preferably, AC electrical power delivered at the electrical conductors may be rectified to DC electrical power delivered to the driver circuit. The driver circuit may serve to supply electrical power to the LED element as suited for lighting operation thereof, e. g. regulate voltage, current or power.

The electrical conductor that in case of a defect is severed by the separation device may be connected between the electrical terminals and the rectifier circuit. Alternatively, the electrical conductor may be provided between the rectifier circuit and the LED element. In both cases, separation of the electrical conductor inhibits further operation of the LED element. Providing the breakage zone of the electrical conductor between an electrical terminal and the rectifier circuit serves to disable this circuit as well.

Any type of detector element may be used which is suited to signal a defect of the cover member. In one preferred embodiment, the detector element may include at least one conductive track provided on a breakable substrate, such as a plastic member or glass member. The breakable substrate may either be part of the cover member, or it may be provided in close mechanical contact with the cover member. Thus, if forces or deformations act on the cover member which may lead to a defect, the breakable substrate may break and thus interrupt the conductive track, such that the cover member defect is electrically sensed. In preferred embodiments, the breakable substrate may be provided in elongated form, e. g. as a bar of round or rectangular cross-section, as an elongated flat cover over the LED element, or as a tube within which the LED element is provided.

These and other aspects of the invention will become apparent from and elucidated with reference to the embodiments described hereinafter.

DESCRIPTION OF EMBODIMENTS

FIG. 1shows a circuit diagram of a first embodiment of an LED lamp10including a housing12from which electrical terminals14project. If the LED lamp10is installed in a lighting fixture, electrical operating power is supplied at the terminals14, such as by a mains connection.

The terminals14are electrically connected by conductors16a,16bto a rectifier18, which rectifies AC electrical power and provides DC electrical power to a driver circuit20.

The driver circuit20supplies regulated operating power to an LED element22shown only symbolically.

The LED lamp10includes a safety device comprised of a detector element24, a safety circuit26and a separation device28. The detector element24is connected to the safety circuit26and serves to electrically detect a defect of a housing12. The safety circuit26is electrically connected through triggering conductors30a,30bto the separation device28to trigger the separation device if a defect of the housing12is detected. The separation device28is provided to mechanically server the electrical conductors16a,16bif triggered.

Different embodiments of the detector element24and its arrangement relative to the LED element22are possible. Examples are shown inFIGS. 7-9. In each of these embodiments, an electrical conductor track36is provided on a breakable substrate, preferably glass. If forces and deformations act on the lamp housing12, the glass substrate breaks and the conductor track36is interrupted, which is electrically detected by the safety circuit26.

In the embodiments ofFIGS. 7-9, the LED element22is in each case provided as a plurality of light emitting diodes arranged on a circuit board32. The breakable substrate in the embodiment ofFIG. 7is a glass bar34aarranged next to the LED element24, so that it will break if the circuit board32is broken or deformed.

In the embodiment ofFIG. 8, the breakable substrate is a flat glass cover plate34bprovided above the LED element24, such that it will also break if the lamp is deformed. In the embodiment ofFIG. 9, the breakable substrate is a glass tube34cprovided around the LED element24.

In each of the above embodiments, conductive tracks36provided on the breakable substrate will be interrupted if the substrate34a,34b,34cbreaks. As a still further embodiment, the LED element24may be mounted on a breakable circuit board, e.g. made of glass, also comprising a conductive track36, which is interrupted if the circuit board breaks.

Back inFIG. 1, the safety circuit26monitors conductivity of the conductive track36of the detector element24. In case the conductive track36is interrupted, this signals a potential defect of the housing12. In this situation, the safety circuit26acts to permanently disable further operation of the lamp10.

This is effected by sending an electrical triggering signal through the triggering conductors30a,30bto the separation devices28. As will be explained below, the separation device28mechanically severs the electrical conductors16a,16b, and thus permanently disables the lamp10.

FIG. 2shows a circuit diagram of a second embodiment of an LED lamp110. The circuit of the lamp110according to the second embodiment is in many ways similar to the first embodiment. Like parts are designated by like reference numerals. In the following, only the differences between the first and second embodiment will be explained.

While in the first embodiment of the lamp10the separation device28is arranged at the electrical conductors16a,16barranged between the supply terminals14and the rectifier18, the separation device28is arranged in a different position of the same circuit. Electrical conductors40a,40bare provided to connect the rectifier18to the driver circuit20. The separation device28is arranged at these electrical conductors40a,40bto disconnect them if triggered.

In both the first and second embodiment, all (two) poles of the electrical power supply are interrupted by the separation device28.

Also, in both embodiments the safety circuit26is supplied with electrical operating power from the rectified input voltage. The triggering signal from the safety circuit26to the separation device28is supplied via triggering conductors30a,30belectrically isolated from the electrical conductors16a,16b;40a,40bin the supply line from the terminals14to the LED element22.

In the following, different embodiments of the separation device28will be described with reference to the drawingsFIG. 3-FIG. 6c.

FIG. 3shows in a schematical side view a first embodiment of a separation device28. The electrical conductor, which may be the electrical conductor16aaccording to the first embodiment or the electrical conductor40aaccording to the second embodiment, is provided as a conductive track on a printed circuit board42. The conductive track is interrupted at a breakage zone44which is provided at a position where the electrical conductor16a,40ashould be interrupted in case of a housing defect. Within the breakage zone44, the electrical conductor is provided as a bond wire46.

Proximate to the bond wire46, a coil48is provided with a piston50. The piston50is comprised of ferromagnetic material, and preferably includes a permanent magnet. At least the tip is electrically insulated to avoid conduction by the piston50. The triggering signal provided by the safety circuit26is applied to the coil48, which generates a magnetic field that propels the ferromagnetic piston50, such that the sharpened tip thereof cuts through the bond wire46and thus mechanically severs it. As a consequence, the electrical conductor16a,40ais permanently interrupted.

FIGS. 4a, 4bshow a second embodiment of a separation device28. The electrical conductors16a,16b(or:40a,40b) are provided on a circuit board42and are each interrupted in two consecutive breakage zones44a,44b, where bond wires46are provided. The circuit board42comprises a cutout element52only loosely connected to the rest of the circuit board42. A chemical charge54is provided with an ignition contact connected to the triggering conductors30a,30b.

The chemical charge54may be any combustible material, which, if ignited, is able to rapidly expand and thus produce a propelling force. For example, the chemical charge54may a fluid or solid, which upon ignition is rapidly turned into a gas. In particular, the material may be enclosed in a cavity, piston or otherwise confined to achieve a directed force. An example of a combustible solid, which is safe (i.e. protected against spontaneous ignition) may be for example paraffin as used in household matches.

Different electrical components may be used as ignition for the chemical charge54, such as e. g. a glow-wire or filament, for example made of tungsten, gold, silver, aluminum, carbon etc. In a particularly preferred embodiment, a simple resistor, such as an SMT resistor may be used as ignition source for a pyrotechnic chemical charge54, such as paraffin. When producing the lamp with a chemical charge54, it may be advisable to apply the material of the chemical charge54after a soldering step to avoid ignition during the manufacturing process.

In normal operation, electrical operating power is conducted through the conductors16a,16b;40a,40b.

In case of a detected housing defect, the safety circuit26sends a triggering signal through triggering conductors30a,30b, such that the ignition element of the explosive charge54is activated. This sets off the charge54arranged between the cutout element52and the rest of the circuit board42. The mechanical force generated by the explosion separates the cutout52from the rest of the circuit board42as shown inFIG. 4b. As the cutout52is separated from the rest of the circuit board42, the bond wires46are ripped apart in each of the breakage zones44a,44b. Thus, each of the conductors16a,40a;16b,40bis mechanically severed at two consecutive positions, leading to safe interruption of any further conduction.

FIGS. 5a, 5bshow a third embodiment of a separation device28. The third embodiment closely resembles the above described second embodiment according toFIGS. 4a, 4b. Like reference numerals refer to like parts. In the following, only differences will be explained. As in the second embodiment according toFIGS. 4a, 4b, the electrical conductor16a,40a;16b,40bare provided on a circuit board42with a cutout52, and two breakage zones44a,44bare arranged at the borders of the cutout52. Triggering conductors30a,30bare connected to a chemical charge54.

Differently from the second embodiment, the cutout52in the third embodiment according toFIGS. 5a, 5bis pivotably mounted to the rest of the circuit board42, and a compressed spring56is arranged below it. A seal58holds the cutout52in place against the spring force.

If a triggering signal is send through triggering conductors30a,30band the chemical charge54is set off, this removes the seal58, setting the cutout52free. Under the force of the compressed spring56, the cutout52pivots as shown inFIG. 5b, thereby severing the bond wires46arranged in the breakage zones44a,44b.

FIGS. 6a-6cshow a fourth embodiment of a separation device28. The fourth embodiment closely resembles the above described third embodiment according toFIGS. 5a, 5b. Like reference numerals refer to like parts. In the following, only differences will be explained.

According to the fourth embodiment, a first pivotable cutout52aand a second pivotable cutout52bare provided, loaded by a compressed spring56underneath. The cutouts52a,52bare held together by a seal58to which a chemical charge54with an ignition is fixed. Three consecutive breakage zones44a,44b,44care formed in each of the electrical conductors16a,40a;16b,40bby bond wires.

As the charge54is ignited, the seal58is removed and the cutouts52a,52bpivot like opening doors (FIG. 6b), thereby severing the bond wires in each of the breakage zones44a,44b,44c.

For example, any of the disclosed circuit arrangements, embodiments of separation devices and embodiments of detection devices may be arbitrarily combined. While the disclosed all-pole disconnection is preferred, it is alternatively also possible to disconnect only one pole, which would suffice to prohibit further operation of the LED element22.