A double ended retrofit light emitting diode (LED) based lighting device for connection to a power source, the LED based lighting device having an improved pin safety circuit

Abstract

The present invention provides a double-ended retrofit light-emitting diode (LED)-based lighting device for connection to a power source, the retrofit LED lighting device having two separate connection terminals L1, L2 at a first end of the LED lighting device for connecting the LED-based lighting device to the power source and two separate further connection terminals R1, R2 at a second end for further connecting the LED-based lighting device to the power source, the retrofit LED lighting device comprising: at least one LED for emitting light; an alternating current (AC) LED driver configured to receive AC current from the power source, the AC LED driver for driving the at least one LED based on the received AC current; a filament circuit disposed between the two separate connection terminals L1, L2 for supporting a filament current circulating and returning to the power source to indicate the presence of the lighting device to the power source; and a pin safety circuit including pin safety switches, each connected to a separate one of the two connection terminals L1, L2, such that the AC current does not flow through the filament circuit when the pin safety switches are closed.

Description

[Technical field]

[0001] The present disclosure relates to retrofit light emitting diode (LED) based lighting devices for connection to electronic ballasts, and more particularly to retrofit LED based lighting devices having improved pin safety circuits. [Background technology]

[0002] Lighting devices utilizing light emitting diodes (LEDs) have been developed for various lighting applications. Due to their long life and high energy efficiency, LED lamps are nowadays designed both to replace traditional fluorescent lamps, i.e., for retrofit applications. For such applications, the retrofit LED device is typically adapted to fit into the socket of a respective lamp fixture. Furthermore, since lamp maintenance is typically performed by the user, the retrofit LED device should ideally be easily operable in any type of suitable fixture without the need to rewire the fixture.

[0003] Such a retrofit LED device is disclosed, for example, in US 2016 / 0081147, where the LED device is wired to receive input current from any two of a pair of electrode pins at the end of a tube housing a driver circuit, the input current is converted to DC through a rectifier circuit, filtered to remove undesirable frequencies and voltages, and controlled with a step-down constant current circuit to drive an LED array within the tube.

[0004] Achieving a good compatibility of electronic ballasts, e.g. high frequency (HF) fluorescent ballasts with retrofit LED lighting devices has proven to be a challenge, due to the wide variety of HF ballasts installed in the field. This is due, among other things, to the combination of having to guarantee start-up of the HF ballast, needing only a very high ohmic DC impedance or no DC impedance between both lamp ends, a pin safety device that is safe to touch a pin at one end of the lamp while the pin at the other end of the lamp is inserted in the lampholder, and a filament impedance, i.e. an impedance that mimics a fluorescent filament, between the two pins at each end of the lamp.

[0005] The latter is particularly challenging: the filament impedance cannot be too low, as this could cause overheating in the HF ballast, but conversely, it cannot be too high, as this could cause overheating of the circuit elements, more specifically resistors, within the LED-based lighting device used to implement the filament impedance.

[0006] Some HF ballasts, primarily for T5 lamps, i.e. lamps with a 5 / 8 inch tube diameter, are designed to recognize the type of lamp they are driving and adjust the lamp current or power they provide to the lamp accordingly. Nearly all HF ballasts with lamp recognition perform lamp recognition by determining the filament impedance or resistance at the end of the filament preheat phase, just prior to ignition of the fluorescent lamp.

[0007] In the case of fluorescent lamps, this can be considered as the most accurate moment. The filament resistance of a fluorescent lamp is temperature dependent. At the end of the preheat phase, the resistance increases from a cold value R0 to a hot value RT, which is about four times R0. At the high filament temperature at the end of the preheat phase, the emitter material attached to the filament reaches thermionic emission, which allows smooth ignition of the fluorescent lamp with limited ignition voltage and little damage to the filament.

[0008] To ensure proper detection of lamp type by the HF ballast, the filament impedance / resistance of a retrofit LED-based lighting device may need to be the RT value of the fluorescent lamp type it is replacing, which is more restrictive than having no lamp type recognition. Summary of the Invention [Problem to be solved by the invention]

[0009] It is an object of the present disclosure to provide a retrofit light emitting diode (LED) based lighting device having an improved pin safety circuit.

[0010] Further objects of the present disclosure include methods of operating such LED-based lighting devices, and a computer-readable medium having instructions stored thereon that, when executed by a retrofit LED-based lighting device, cause the device to perform a method according to the present disclosure. [Means for solving the problem]

[0011] In a first aspect, there is provided a double ended retrofit light emitting diode (LED) based lighting device for connection to a power source, the retrofit LED lighting device having two separate connection terminals (L1, L2) at a first end of the LED lighting device for connecting the LED based lighting device to the power source and two separate further connection terminals (R1, R2) at a second end for further connecting the LED based lighting device to the power source.

[0012] 2. The double ended retrofit LED based lighting device, - at least one LED for emitting light; - an alternating current (AC) LED driver configured to receive an AC current from the power source, the AC LED driver for driving the at least one LED based on the received AC current; - a filament circuit disposed between said two separate connection terminals (L1, L2) for supporting a filament current circulating and returning to said power supply to indicate the presence of said lighting device to said power supply; - a pin safety circuit including pin safety switches, each connected to a separate one of the two connecting terminals (L1, L2) such that when the pin safety switches are closed, the AC current does not flow through the filament circuit.

[0013] The inventors have found that it may be beneficial if the AC current does not flow through the filament circuit when the LED-based lighting device is switched on. This is achieved by the introduction of the pin safety switches that are connected to both of the two separate connection terminals (L1, L2). This may mean that each of the switches is connected via a first side to a respective connection terminal and via a second side to the electronics present in the LED-based lighting device, e.g. the AC LED driver.

[0014] In the state of the art, even when the LED-based lighting device is switched on, the current for powering the LED, or at least a part of it, flows through the filament circuit, which generates heat in the filament circuit, which is undesirable for many reasons.

[0015] An advantage of a retrofit LED-based lighting device according to the present disclosure is that when the retrofit LED-based lighting device is turned on, the filament circuit may be bypassed to the greatest extent possible, i.e. the filament circuit may provide little or no filament current circulating back to the electronic ballast when the retrofit LED-based lighting device is turned on.

[0016] The retrofit LED-based lighting device may have L1 and L2 connection terminals for receiving AC current from an AC mains power supply. The filament circuit may be arranged between the L1 and L2 connection terminals. The L1 connection terminal may be connected to a first input of the AC LED driver, i.e., a rectifier, and the L2 connection terminal may be connected to a second input of the AC LED driver. Pin safety switches may be provided at both of these connections, i.e., at both the L1 to AC LED driver connection and the L2 to AC LED driver connection.

[0017] The above results in an operating scheme where there is a direct connection between the AC mains and the AC LED driver, so that when the LED-based lighting device is turned on, at least the current intended for the LED does not flow through the filament circuit, which reduces the total losses in the LED-based lighting device.

[0018] As described above, the pin safety circuit of the present disclosure is for ensuring safety during installation of the retrofit LED-based lighting device. A dangerous situation can occur when a first end of the LED-based lighting device is attached to a fixture and the other end of the LED-based lighting device is floating. In such a case, a dangerous voltage can be induced on the pins of the floating end of the LED-based lighting device.

[0019] A pin safety circuit according to the present disclosure is configured to address the above situation. The pin safety circuit may ensure that there is no electrical connection, or at least a very high ohmic electrical connection, between the first end of the retrofit LED-based lighting device and the other opposite end. Only when both ends of the retrofit LED-based lighting device are properly attached, the pin safety circuit cancels the open circuit or high ohmic connection, i.e. the electrical connection between both ends of the retrofit LED-based lighting device is restored. This is achieved according to the present disclosure by closing both pin safety switches at the two separate connection terminals (L1, L2).

[0020] It is noted that the retrofit LED-based lighting device is suitable for connection to a power source. Preferably, the power source is a high frequency (HF) ballast. Other types of power sources include mains power, e.g. 230Vac, or EM ballasts.

[0021] In an example, the safety switch is a normally-open switch constituted by a single relay.

[0022] One of the advantages of this is that these variants are usually available at almost no additional cost compared to single pole relays.In this way, a pin-safe solution is created where the on-state LED current does not flow through the filament impedance, or at least a part of the filament impedance, preventing the occurrence of associated on-state dissipation in the filament circuit.

[0023] In a further example, the pin safety circuit comprises two in series cascaded pin safety switches connected to each of the two separate connection terminals (L1, L2).

[0024] The above example adds a single fault tolerance aspect to the present disclosure. The two switches as above are effectively in parallel from a pin safety perspective. Each of the pin safety switches above may have two switches in series. For single fault tolerance, the second series switch may need to be another relay, or other type of switch, for safety purposes.

[0025] In a further example, the retrofit LED lighting device further comprises a capacitor, preferably a safety capacitor, connected in parallel across the pin safety switch for supplying a reduced amount of power to the retrofit LED lighting device for controlling the pin safety switch when the pin safety switch is open.

[0026] The pin safety switch may be controlled by a digital control logic, which may in turn need to be powered from the power supply or using a battery or the like. A capacitor, preferably a safety capacitor, or two or more safety capacitors, may be provided to ensure that sufficient power is available to control the pin safety switch. The safety capacitor may be selected such that sufficient power is provided to the digital control logic, but the amount of power received from the power supply cannot cause harm to anyone touching any of the live pins.

[0027] The advantage of a safety capacitor is that there is no dangerous situation if the capacitor fails for any reason.

[0028] According to the present disclosure, the retrofit LED lighting device may be a double-ended retrofit LED lighting device, the device having a filament circuit at each opposing end of the retrofit LED based lighting device.

[0029] In the context of this disclosure, the following are defined: the double ended retrofit LED based lighting device may have a single pin safety circuit, the pin safety circuit may have components at both ends of the retrofit LED based lighting device, the double ended retrofit LED based lighting device may further have a filament circuit at a first end of the lighting device and a further filament circuit at a second end of the lighting device opposite the first end.

[0030] In another example, the retrofit LED-based lighting device has a further filament circuit disposed between the two separate further connection terminals to support a filament current circulating back to the power source to indicate the presence of the lighting device to the power source, the pin safety circuit having further pin safety switches, each further switch connected to a separate further connection terminal of the two separate further connection terminals such that when the further pin safety switches are closed, the AC current does not flow through the further filament circuit.

[0031] The above example also adds a single fault tolerance aspect to the present disclosure.

[0032] The retrofit LED lighting device may have a further capacitor connected in parallel across the further pin safety switch connected to both of the two separate further connection terminals (R1, R2) to supply a reduced amount of power to the retrofit LED lighting device for controlling the pin safety switch when the switch is open.

[0033] In yet another example, at least one of the pin safety switches has a changeover contact, the changeover contact configured to: - a central node arranged to be connected to said power supply; a normally-closed node arranged to be connected to a corresponding said filament circuit; a normally open node arranged to be connected to said AC LED driver;

[0034] Further to the above, at least one of the further pin safety switches may also have a switching contact, the switching contact being configured to: - a central node arranged to be connected to said power supply; - a normally closed node arranged to be connected to a corresponding said filament circuit; a normally open node arranged to be connected to said AC LED driver;

[0035] One of the advantages of the above example is that the filament circuit can be effectively electrically disconnected from the rest of the electronics when the AC current starts to flow. Thus, one of the switches may be formed as a three-node switch, through which the connection between the filament circuit and the power supply is provided, or between the rest of the LED-based lighting device, i.e. the rectifier and the LEDs, and the power supply is provided.

[0036] Such a switch allows the filament circuit to become functionally disconnected once the AC current begins to flow through the LED-based lighting device.

[0037] In a further example, the LED-based lighting device further comprises an impedance matching circuit for matching an input impedance of the AC LED driver to an output impedance of the power supply.

[0038] Impedance matching may be beneficial to improve power transfer between the power source and the LED-based lighting device, or may be beneficial to reduce signal reflections from the LED-based lighting device back to the power source.

[0039] Here, the impedance matching circuit is - an inductor disposed after the output of said AC LED driver; an inductor comprising two magnetically coupled windings, each winding having: - the two separate connection terminals, or - an inductor connected to a separate terminal of any of said further connection terminals; - at least two inductors, each of said at least two inductors being connected to a separate terminal of said connection terminal or said further connection terminal.

[0040] The inductor may be, for example, arranged in series with the at least one LED, or in series with a combination of the at least one LED cascaded in parallel with any other electronic components. This is shown, for example, in FIG. 5, where a buffer capacitor is connected in parallel across the at least one LED. The inductor is therefore arranged on the DC side of the rectifier. The advantage of this is that only one signal inductor needs to be used as the impedance matching circuit.

[0041] The inductor may also be implemented as an inductor with two magnetically coupled windings connected either to the two separate connection terminals or to the further connection terminal, in which case the inductor is located on the AC-side of the LED-based lighting device.

[0042] According to the present disclosure, two non-magnetically coupled inductor sections may also be used.

[0043] In a further example, the impedance matching circuit comprises two impedance matching capacitors, each of which is connected to a different one of the two separate connection terminals (L1, L2) and to a different one of the two further separate connection terminals (R1, R2).

[0044] It is noted that the retrofit LED-based lighting device according to the present disclosure may be shaped as a tube to replace a conventional fluorescent tube lamp. In such a case, the two connection terminals (L1, L2) are directed towards a first end of the tube and the further connection terminals (R1, R2) are directed towards a second end of the tube opposite to the first end. This entails that, as described above, electrical connections are made over most of the length of the tube to achieve that each of the two capacitors is connected to one of the two separate connection terminals (L1, L2) and to one of the two separate further connection terminals (R1, R2).

[0045] In this example, - a first one of the two impedance matching capacitors comprises two capacitors arranged in series between one of the two separate connection terminals (L1, L2) and one of the two further separate connection terminals (R1, R2), - a second one of the two impedance matching capacitors comprises two capacitors arranged in series between another one of the two separate connection terminals (L1, L2) and another one of the two further separate connection terminals (R1, R2), The center taps of the two capacitors arranged in series between one of the two separate connection terminals (L1, L2) and one of the two further separate connection terminals (R1, R2) are connected to the center taps of the two capacitors arranged in series between another one of the two separate connection terminals (L1, L2) and another one of the two further separate connection terminals (R1, R2).

[0046] The advantage of the above is that only a single electrical connection, i.e. a wire or track or similar, needs to run the length of the retrofit LED-based lighting device. Two electrical connections are not needed. The single electrical connection can consist of a single wire, track or similar connecting the center taps of the two capacitors arranged in series between the two separate connection terminals (L1, L2) with the center taps of the two capacitors arranged in series between the two further separate connection terminals (R1, R2). This therefore reduces the complexity and costs of realizing a retrofit LED-based lighting device.

[0047] In a second aspect, there is provided a method for operating a retrofit Light Emitting Diode (LED) based lighting device according to any one of claims 1 to 11, comprising the steps of: - receiving, by said AC LED driver, an AC current from said power source; - driving, by the AC LED driver, the at least one LED based on the received AC current; - supporting, by said filament circuit, a filament current that circulates back to said power source to indicate the presence of said lighting device to said power source; - controlling the pin safety switch, which is connected to both of the two separate connection terminals (L1, L2), by the pin safety circuit such that when the pin safety switch is closed, the AC current does not flow through the filament circuit.

[0048] 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, which is a method of operating a retrofit Light Emitting Diode (LED) based lighting device.

[0049] In a third aspect there is provided a computer program product comprising program code means stored on a computer readable medium, the program code means being configured to, when executed by a retrofit LED based lighting device, perform the method according to the second aspect as provided above.

[0050] These and other aspects of the invention will be elucidated and elucidated with reference to the following embodiments. [Brief description of the drawings]

[0051] [Figure 1] 1 shows a retrofit solution for a commonly used prior art TLED lighting device. [Diagram 2] 1 illustrates a retrofit LED-based lighting device according to the present disclosure. [Diagram 3] 1 illustrates a retrofit LED-based lighting device according to the present disclosure. [Figure 4] 1 illustrates a retrofit LED-based lighting device according to the present disclosure. [Diagram 5] 1 illustrates a retrofit LED-based lighting device according to the present disclosure. [Figure 6] 1 illustrates a retrofit LED-based lighting device according to the present disclosure. [Figure 7] 1 illustrates a retrofit LED-based lighting device according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] Fluorescent TL tubes are inherently safe because the gas within the tube must first be ignited before a conductive path exists between the two ends of the tube. The tube is connected to an alternating current (AC) mains voltage supply such as those commonly found in domestic buildings. The tube, or the fixture to which it is attached, may have additional elements such as ballasts and jumper or starter elements.

[0053] This safety is necessary when the tube is installed in the fixture while the lamp socket is energized, i.e. while live voltage is present: in the situation where one end of the tube is inserted in the socket and energized and the other end is not inserted, the pin at the free end must not become live.

[0054] This is not a problem with gas-filled fluorescent tubes, but it is a problem when using LED lighting devices where there is a conductive path between the two ends of the tube as shown by L1 / L2 and R1 / R2.When the pins are touched by a human, i.e., when the human body is in the power loop, the built-in LED driver tends to conduct current, which usually exceeds safety limits and creates a shock hazard.

[0055] A known solution to this problem is to apply the mains input to only one side of the tube, so that the other side is galvanically isolated from the mains. In this case there is no conductive path between the two sides of the tube, but the glow starter needs to be replaced by a short circuit to operate the lamp.

[0056] More specifically, in some applications, it is not acceptable for a retrofit LED lighting device to exhibit substantial asymmetry under a single fault condition. In particular, an open diode in the rectifier can result in such a condition. In some retrofit LED lighting devices, each diode in the rectifier can then be paralleled by a second diode.

[0057] The present disclosure is directed to a double-ended retrofit LED-based lighting device where a power source is to be connected to both ends of the retrofit LED-based lighting device, i.e., L1 / L2 and R1 / R2.

[0058] A known double ended retrofit LED based lighting device 1 is shown in FIG.

[0059] Here, the portion of the AC current flowing through any pin, for example entering through L1 and / or L2 and leaving through R1 and / or R2, can flow directly through the rectifier to its output. There is no need for a portion of the AC current to flow through the filament circuit or a part of said filament circuit. Thus, losses in the filament circuit due to this AC current are substantially avoided. However, the prior art circuit of FIG. 1 as shown cannot be easily combined with a pin safety switch Sw and / or a matching impedance. Furthermore, when used with a dimmable HF fluorescent ballast, the filament heating current during dimming can still substantially overheat the Rfil filament resistor.

[0060] FIG. 2 shows a retrofit LED-based lighting device 11 according to the present disclosure.

[0061] It is an object of the present disclosure to provide a solution to the above problems and challenges, and to provide a circuit for retrofit LED-based lighting devices that maximizes compatibility with the installed base of HF fluorescent ballasts and may also allow dimming of the retrofit LED-based lighting devices, such as TLED lamps.

[0062] By including pin safety switches in both the L1 and L2 pin connections to the rectifier, pin safety is achieved and still prevents at least a portion of the AC current from flowing through the filament impedance Rfill. The inventors have found that pin safety can be achieved by incorporating at least two switches, a switch in the L1 pin connection to the rectifier and a switch in the L2 pin connection to the rectifier. These switches may be controlled with the same control signal so that they provide the same behavior. This ensures that by using these switches, a first end of the lighting device can be electrically disconnected from the other opposite side of the lighting device.

[0063] Preferably, SwLa and SwLb are the two normally open contacts of a single relay. The location of the Cy capacitor may not be important. As shown, the Cy capacitor may be placed across SwLb from L1 to the DL3, DL4 node or from L2 to the DL1, DL2 node.

[0064] In Figure 2, two pin safety switches are used, each connecting a pin at one end of an LED lighting device to the input of a rectifier. With the pin safety switches closed, as in Figure 2, AC current can flow to / from the rectifier directly through any pin without having to flow partially or fully through the filament impedance.

[0065] Thus, a pin-safe solution is created in which the on-state AC current does not flow through any portion of the filament impedance, preventing the associated on-state dissipation in the filament circuit.

[0066] As mentioned above, the "said" pin safety switch is often implemented as a series connection of two switches for single fault tolerance reasons. Since the two switches SwLa and SwLb are essentially in parallel from the point of view of pin safety, each of the two switches may then have two switches in series. For single fault tolerance, the second series switch may be another relay, or another type of switch.

[0067] Alternatively, two additional switches may be connected to opposite ends of the LED lighting device, as shown in LED lighting device 21 of FIG.

[0068] A second set of pin safety switches may provide single fault tolerance. Placing that second set at the other end of the lamp may provide symmetry between both LED lighting device ends and allow the relay to be physically located at a different end of the lamp. A second CY capacitor CYR may need to be added to create a current path to detect proper lamp insertion while the pin safety switch is open. Here, the CY capacitor may not need to be a safety type capacitor since CYL and CYR are effectively in series, i.e., if one is shorted, there is still the other CY capacitor operating correctly. Thus, the retrofit LED-based lighting device is still single fault tolerant.

[0069] The two relays may be operated by a shared detect and drive signal, a shared detect signal and separate drive signals, or separate detect and drive signals.

[0070] Thus, single-fault tolerance is added to the previous pin-safe solution in that the on-state AC current does not flow through (any part of) the filament impedance, preventing associated on-state dissipation in the filament circuit.

[0071] A further insight is that multiple relay output contacts are often available as changeover contacts having three nodes: a central node CC, a normally closed node NC which is connected to the central node CC when the relay is not actuated and disconnected from the central node when the relay is actuated, and a normally open node NO which is disconnected from the central node when the relay is not actuated and connected to the central node when the relay is actuated. Relay variations with changeover contacts are available at almost no additional cost compared to variations with only normally open or normally closed contacts.

[0072] This allows at least one of the two switches Sw at each end of the LED lighting device to be changed into a change-over contact, effectively electrically disconnecting the filament circuit from the rest of the circuit when the relay is actuated.

[0073] This is illustrated in FIG. 4, which shows a retrofit LED-based lighting device 31 according to the present disclosure.

[0074] The filament circuit is electrically removed from the circuit, i.e., functionally isolated or functionally disconnected, when the relay is actuated by replacing at least one of the switches on either end of the LED lighting device with a changeover contact whose central node CC connects to the power source, whose normally closed node NC connects to the filament circuit, and whose normally open node NO connects to the rectifier input. This allows for further elimination of dissipation in the filament resistor during ON-state operation of the lamp and also enables / simplifies dimming.

[0075] Electrically removing the filament circuit from the circuit during ON lamp operation is desirable for compatibility with some fixed output HF fluorescent ballasts, and is a big enabler of dimming operation since there is no dissipation in the filament circuit resistor when the relay / switch is actuated.

[0076] Figure 4 also makes clear why it is attractive to physically place the relays, each at their own end of the lamp: all of the circuits and signals to be switched are located at that end of the lamp.

[0077] In the case of HF ballasts with lamp type recognition, the filament resistor may need to be chosen to have a resistance essentially equal to the RT value of the fluorescent lamp it is replacing, which is four times the cold filament impedance R0 of that lamp. The R0 value of fluorescent lamps is standardized by lamp type and may be specified in the fluorescent lamp specifications.

[0078] As previously mentioned, the recognition of the lamp type by filament impedance can be performed at or towards the end of the preheat phase.

[0079] As previously indicated, the retrofit-based LED lighting device may include an impedance matching circuit having a capacitor Cpar and / or an inductor L1, not shown in FIG. 4 but described with respect to FIGS.

[0080] FIG. 5 shows a further retrofit LED-based lighting device 41 according to the present disclosure.

[0081] Since it is not specified how the rectifier input current is split between DR1, DR2 (as shown) and DR3, DR4, it may not be possible to use a single matching inductor L1 unless the inductor is brought to the DC side of the rectifier. Although it is possible, this would change the impact on the impedance match, which may not be desirable.

[0082] In FIG. 5 the above is shown, with inductor L1 in the DC side of the retrofit LED-based lighting device.

[0083] FIG. 6 shows a retrofit LED-based lighting device 51 according to the present disclosure.

[0084] Since it is not specified where exactly the current flows, i.e. through L1, L2 and R1, R2, it may be necessary to add at least two impedance matching capacitances, shown here as Cpar1 and Cpar2. The right hand connections of Cpar1 and Cpar2 may be swapped between L1b, SwRb and L1a, SwRa.

[0085] Following from the above, since it is not clear in advance whether the current will flow through L1 or L2 (and through R1 or R2), the rectifier shown in Fig. 6 essentially has multiple inputs. Thus, for example, DL1 is provided for the current flowing through L1, and DL3 is provided for the current flowing through L2. The same or similar explanations are valid for the DR1 / DR3 pair, the DR4 / DR2 pair, and the DL2 / DL4 pair.

[0086] It should be noted that Figures 6 and 7 also show that the impedance circuit comprises an inductor with two magnetically coupled windings L1a / L1b connected to one of the further connection terminals. More specifically, the inductor with two magnetically coupled windings L1a / L1b connects at its first end to the AC LED driver and at its second end to a switch supplied by a pin safety circuit.

[0087] It should be noted that, to achieve single fault tolerance for the retrofit LED-based lighting device, each of Cpar1 and Cpar2 may be implemented essentially as two capacitors in series.

[0088] FIG. 7 shows a retrofit LED-based lighting device 61 according to the present disclosure.

[0089] The inventors have found that implementing each of the capacitors Cpar1 and Cpar2 as essentially two capacitors connected in series has further advantages. In such a case, a single junction node may be realized that is utilized to make an electrical connection between a first end of the retrofit LED-based lighting device and a second end opposite the first end. This is described in more detail with respect to FIG. 7.

[0090] Here, it is shown that capacitor Cpar1 is substantially implemented as CparL1 connected in series with CparR1. Capacitor Cpar2 is substantially implemented as CparL2 connected in series with CparR2. The inventors have found that the center taps may be connected together. That is, the center taps of CparL1 and CparR1 may be connected to the center taps of CparL2 and CparR2. This achieves a junction node as shown in FIG. 7. The junction node may be implemented as an electrical connection, PCB track, or the like, between two ends of the retrofit LED-based lighting device, as explained above. In such a case, there is no need to provide two separate electrical connections between the two ends of the retrofit LED-based lighting device.

[0091] Those skilled in the art can understand and achieve other variations to the disclosed embodiments in the practice of the claimed invention, from a study of the drawings, the specification and the appended claims. In the claims, the word "comprise" does not exclude other elements or steps, and the singular does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain means are recited in mutually different dependent claims does not indicate that a combination of these means cannot be used to advantage. The computer program may be stored / distributed on an appropriate medium, such as an optical storage medium or a solid medium, provided together with or as part of other hardware, but also 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 interpreted as limiting the scope of the claims.

Claims

1. a double-ended retrofit LED based lighting device for connection to a power source, the retrofit LED lighting device having two connection terminals at a first end of the LED lighting device for connecting the LED based lighting device to the power source and two separate further connection terminals at a second end for further connecting the LED based lighting device to the power source; at least one LED for emitting light; an AC LED driver configured to receive an AC current from the power source, the AC LED driver for driving the at least one LED based on the received AC current; a filament circuit disposed between the two separate connection terminals for supporting a filament current that circulates and returns to the power source to indicate the presence of the lighting device to the power source; a pin safety circuit including pin safety switches, each pin safety switch connected to a respective one of the two connection terminals such that when the pin safety switch is closed, the AC current does not flow through the filament circuit, the pin safety switch being closed only when both the first end and the second end are attached to a lamp fixture, one of the pin safety switches having a switching contact such that the filament circuit is functionally disconnected when the AC current flows to or from the AC LED driver through the one of the pin safety switches; a central node arranged to be connected to said power source; a normally closed node disposed to be connected to a corresponding one of the filament circuits; a normally open node disposed to be connected to said AC LED driver.

2. 2. The retrofit LED based lighting device of claim 1, further comprising a capacitor connected in parallel across the pin safety switch for supplying a reduced amount of power to the retrofit LED lighting device for controlling the pin safety switch when the pin safety switch is open.

3. 3. A retrofit LED-based lighting device as claimed in any one of claims 1 to 2, further comprising a further filament circuit disposed between the two separate further connection terminals to support a filament current circulating back to the power supply to indicate the presence of the lighting device to the power supply, the pin safety circuit comprising further pin safety switches, each further switch being connected to a separate further connection terminal of the two separate further connection terminals such that when the further pin safety switches are closed no AC current flows through the further filament circuit.

4. At least one of the further pin safety switches has a switching contact configured to functionally disconnect the further filament circuit when the AC current flows to or from the AC LED driver. a central node arranged to be connected to said power source; a normally closed node arranged to be connected to a corresponding further filament circuit; 4. The retrofit LED-based lighting device of claim 3, further comprising a normally open node disposed to be connected to said AC LED driver.

5. 5. The retrofit LED-based lighting device of claim 1, further comprising an impedance matching circuit for matching an input impedance of the AC LED driver to an output impedance of the power supply.

6. The impedance matching circuit is an inductor disposed after the output of the AC LED driver; 1. An inductor comprising two magnetically coupled windings, each winding having: the two separate connection terminals; or an inductor connected to a separate terminal of any of said further connection terminals; 6. The retrofit LED-based lighting device of claim 5, comprising one of at least two inductors, each of the at least two inductors being connected to a separate terminal of the connection terminal or the further connection terminal.

7. 7. A retrofit LED-based lighting device according to any one of claims 5 to 6, wherein the impedance matching circuit comprises two impedance matching capacitors, each of the two impedance matching capacitors being connected to a different terminal of the two different connection terminals and to a different terminal of the two different further connection terminals.

8. a first one of the two impedance matching capacitors comprises two capacitors arranged in series between one of the two separate connection terminals and one of the two further separate connection terminals, a second impedance matching capacitor of the two impedance matching capacitors comprising two capacitors arranged in series between another one of the two separate connection terminals and another one of the two further separate connection terminals; 8. The retrofit LED-based lighting device of claim 7, wherein a centre tap of the two capacitors arranged in series between one of the two separate connection terminals and one of the two separate further connection terminals is connected to a centre tap of the two capacitors arranged in series between another one of the two separate connection terminals and another one of the two separate further connection terminals.

9. A method of controlling a retrofit LED-based lighting device according to any one of claims 1 to 8, comprising the steps of: receiving an AC current from the power source by the AC LED driver; driving, by the AC LED driver, the at least one LED based on the received AC current; supporting, by the filament circuit, a filament current that circulates back to the power supply to indicate the presence of the lighting device to the power supply; and controlling the pin safety switch, connected to both of the two separate connection terminals, by the pin safety circuit such that when the pin safety switch is closed, the AC current does not flow through the filament circuit.

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