LED-based two-terminal retrofit lighting device for connection to a power supply

Abstract

A double-ended retrofit LED lighting device has two connection terminals (L1, L2) at a first end for connecting to a power supply, and two further connection terminals (R1, R2) at a second end for further connecting to the power supply, the LED lighting device comprising: at least one LED (D1) for emitting light; an LED driver arranged to receive an AC current from the power supply and to drive the at least one LED based on the received AC current; a filament circuit (RfilL) connected between the two connection terminals (L1, L2) for enabling a filament current to circulate back to the power supply to indicate to the power supply that the filament current is 100% of the rated current. The presence of an LED lighting device; and a pin safety circuit comprising two pin safety switches (SwLa, SwLb), wherein each pin safety switch is connected to a respective individual terminal of the two connection terminals (L1, L2) and comprises a switching contact, wherein the switching contact comprises: a center node (CC) arranged to be connected to the power supply; a normally closed node (NC) arranged to be connected to the filament circuit (RfilL); and a normally open node (NO) arranged to be connected to the LED driver, such that the filament circuit (RfilL) is functionally disconnected when the AC current flows into or out of the LED driver.

Description

Technical Field

[0001] The present disclosure relates to a light emitting diode (LED) based retrofit lighting device for connection to an electronic ballast, and more particularly, to a LED based retrofit lighting device with an improved pin safety circuit. Background Art

[0002] Lighting devices utilizing light-emitting diodes (LEDs) have been developed for various lighting applications. Due to their long lifespan and high energy efficiency, LED lamps are now also being designed to replace traditional fluorescent lamps, known as retrofit applications. For such applications, retrofit LED devices are typically designed to fit into the socket of a corresponding lamp fixture. Furthermore, since lamp maintenance is typically performed by the user, retrofit LED devices should ideally be easily operable with any suitable fixture type, without requiring rewiring of the fixture.

[0003] For example, US2016 / 0081147 discloses a retrofit LED device of this type. Here, the LED device is wired to receive current from any two electrode pins in a pair of pins at the ends of a tube, which houses a driver circuit. The input current is converted to DC by a rectifier circuit, filtered to remove unwanted frequencies and voltages by a filter circuit, and then controlled using a step-down constant current circuit to drive the LED array within the tube.

[0004] Achieving good compatibility of retrofit LED lighting fixtures with electronic ballasts (e.g., high-frequency HF fluorescent ballasts) has proven to be a challenge due to the wide variety of HF ballasts installed in the field. This is due to, among other things, the following: starting of the HF ballast must be ensured; no DC impedance or only very high-ohmic DC impedance is required between the two lamp ends; the pins must be safe; it is safe to touch the pins at one end of the lamp while the other end is inserted into the lamp holder; and the filament impedance (i.e., the impedance between the two pins at each end of the lamp) mimics the fluorescent lamp filament.

[0005] The latter is particularly a challenge. The filament impedance must not be too low, as this could cause overheating in the HF ballast, but conversely must not be too high, as this could cause overheating of the circuit elements (more specifically, resistors) used in implementing the filament impedance within the LED-based lighting device.

[0006] There are also HF ballasts, primarily for T5 lamps (i.e., having a tube diameter of 5 / 8"), that are designed to identify the type of lamp they are driving and adjust the lamp current or power they deliver to the lamp accordingly. Almost all HF ballasts with lamp recognition do so by determining the filament impedance or resistance at the end of the filament preheat phase, just prior to ignition of the fluorescent lamp.

[0007] For fluorescent lamps, this can be considered the most accurate time. The resistance of the filament in a fluorescent lamp is temperature-dependent. By the end of the preheat phase, the resistance has increased from its cold value, R0, to its hot value, RT, which is approximately four times greater than R0. At the high filament temperature at the end of the preheat phase, the emitter material deposited on the filament achieves thermionic emission, enabling smooth ignition of the fluorescent lamp at a limited starting voltage with minimal damage to the filament.

[0008] To ensure correct lamp type detection by the HF ballast, the filament impedance / resistance of an LED-based retrofit lighting device may need to be the RT value of the fluorescent lamp type it is intended to replace. This is more restrictive than without lamp type identification. Summary of the Invention

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

[0010] Additional objects of the present disclosure include methods of operating such LED-based lighting devices and computer-readable media having instructions stored thereon that, when executed by an LED-based retrofit lighting device, cause the device to implement the methods according to the present disclosure.

[0011] In a first aspect, a double-ended retrofit lighting device based on a light emitting diode (LED) is provided, the retrofit lighting device being used to be connected to a power supply, the retrofit LED lighting device having two separate connection terminals (L1, L2) at a first end of the LED lighting device, the two separate connection terminals (L1, L2) being used to connect the LED-based lighting device to the power supply, and the retrofit LED lighting device having two separate further connection terminals (R1, R2) at a second end, the two separate further connection terminals (R1, R2) being used to further connect the LED-based lighting device to the power supply.

[0012] Double-ended LED-based retrofit lighting fixtures include:

[0013] - at least one LED for emitting light;

[0014] an alternating current (AC) LED driver arranged for receiving an AC current from said power source and for driving said at least one LED based on said received AC current,

[0015] a filament circuit, arranged between the two separate connection terminals (L1, L2), for enabling a filament current to be circulated back to the power supply for indicating the presence of the lighting device to the power supply, and

[0016] - a pin safety circuit comprising pin safety switches, wherein each switch is connected to a separate one of the two connection terminals (L1, L2) such that when the pin safety switches are closed, the AC current does not flow through the filament circuit.

[0017] The inventors have discovered that it can be beneficial if AC current does not flow through the filament circuit when the LED-based lighting device is turned on. This is achieved by introducing a pin-safe switch connected to both of two separate connection terminals (L1, L2). This can mean that each of the switches is connected to a corresponding connection terminal via a first side and to the electronics present in the LED-based lighting device, such as an AC LED driver, via a second side.

[0018] In the prior art, the current used to power the LED, or at least a portion of it, flows through the filament circuit, even when the LED-based lighting device is turned on. This causes heat to be generated in the filament circuit, which is undesirable for a number of reasons.

[0019] An advantage of the LED-based retrofit lighting device according to the present disclosure is that when the LED-based retrofit lighting device is turned on, the filament circuit can be bypassed as much as possible. That is, when the LED-based retrofit lighting device is turned on, the filament circuit can provide no or almost no filament current circulating back to the electronic ballast.

[0020] The LED-based retrofit lighting device can have L1 and L2 connection terminals for receiving AC current from an AC mains power source. The filament circuit can be placed between the L1 and L2 connection terminals. The L1 connection terminal can be connected to a first input of an AC LED driver (i.e., a rectifier), and the L2 connection terminal can be connected to a second input of the AC LED driver. Pin safety switches can be provided between these two connections (i.e., L1 to the AC LED driver and L2 to the AC LED driver).

[0021] The above results in a mode of operation in which when the LED-based lighting device is switched on, there is a direct connection between the AC mains supply and the AC LED driver so that at least the current intended for the LED does not flow through the filament circuit. This reduces the overall losses in the LED-based lighting device.

[0022] As described above, the pin safety circuit according to the present disclosure is intended to ensure safety during the installation of LED-based retrofit lighting devices. A hazardous situation may arise when a first end of an LED-based lighting device is installed in a fixture and the other end of the LED-based lighting device is left floating. In such a situation, it is possible that a dangerous voltage may be induced at the pin of the floating end of the LED-based lighting device.

[0023] The pin safety circuit according to the present disclosure is designed to address the aforementioned situation. The pin safety circuit ensures that there is no electrical connection, or at least a very high-ohmic electrical connection, between a first end and an opposite end of an LED-based retrofit lighting device. Only when both ends of the LED-based retrofit lighting device are properly installed does the pin safety circuit cancel the open circuit or high-ohmic connection. In other words, the electrical connection between the two ends of the LED-based retrofit lighting device is restored. According to the present disclosure, this is achieved by closing two pin safety switches in two separate connection terminals (L1, L2).

[0024] Note that the LED-based retrofit lighting device is suitable for connection to a power supply. Preferably, the power supply is a high frequency HF ballast. Other types of power supplies include mains power (e.g. 230Vac) or EM ballasts.

[0025] In one example, the safety switch is a normally open switch comprised of a single relay.

[0026] One advantage is that these variations are generally available at virtually no additional cost compared to single-pole relays. In this way, a pin-safe solution is created in which the on-state LED current does not flow through the filament impedance (or at least a portion of the filament impedance), thereby avoiding the associated on-state dissipation in the filament circuit.

[0027] In another example, the pin safety circuit includes two pin safety switches cascaded in series, the two pin safety switches cascaded in series being connected to each of the two separate connection terminals ( L1 , L2 ).

[0028] The above example adds a single-fault tolerance aspect to the present disclosure. From a pin safety perspective, the two switches described above are effectively connected in parallel. Each of the pin safety switches described above can have two switches connected in series. For single-fault tolerance, the second series switch may need to be a separate relay or other type of switch for safety purposes.

[0029] In another example, the retrofit LED lighting device further includes:

[0030] a capacitor, preferably a safety capacitor, connected in parallel to the pin safety switch for providing a reduced amount of power to the retrofit LED lighting device for controlling the pin safety switch when the pin safety switch is open.

[0031] The pin safety switch can be controlled by digital control logic. The digital control logic may also need to be powered by a power supply, either using a battery or anything similar. To ensure that sufficient power is available to control the pin safety switch, a capacitor (preferably a safety capacitor) or two or more safety capacitors can be provided. The safety capacitors can be selected so that sufficient power is provided to the digital control logic, but the amount of power received from the power supply cannot endanger anyone who touches any of the pins (when powered).

[0032] The benefit of a safety capacitor is that there is no dangerous situation in the event of a capacitor failure (for whatever reason).

[0033] According to the present disclosure, the retrofit LED lighting device is a double ended retrofit LED lighting device, wherein at each opposing end of the LED based retrofit lighting device, the device may include a filament circuit.

[0034] In the context of the present disclosure, the following are defined. A double-ended LED-based retrofit lighting device may include a single pin safety circuit that may include components at both ends of the LED-based retrofit lighting device. The double-ended LED-based retrofit lighting device may also include a filament circuit at a first end of the lighting device and an additional filament circuit at a second end of the lighting device opposite the first end.

[0035] In another example, an LED-based retrofit lighting device includes:

[0036] - a further filament circuit arranged between the two separate further connection terminals (R1, R2) for supporting a filament current circulating back to the power supply for indicating the presence of the lighting device to the power supply, and wherein the pin safety circuit comprises a further pin safety switch, wherein each further switch is connected to a separate further connection terminal of the two separate further connection terminals (R1, R2) such that when the further pin safety switch is closed, the AC current does not flow through the further filament circuit.

[0037] The above examples also add a single fault tolerance aspect to the present disclosure.

[0038] The retrofit LED lighting device may comprise a further capacitor connected in parallel across the further pin safety switch connected to both of the two separate further connection terminals (R1, R2) for providing a reduced amount of power to the retrofit LED lighting device for controlling the pin safety switch when the switch is open.

[0039] In yet another example, at least one of the pin safety switches includes a transfer contact, wherein the transfer contact includes:

[0040] - a central node arranged to be connected to said power supply;

[0041] - a normally closed node arranged to be connected to said corresponding filament circuit;

[0042] - a normally open node, arranged to be connected to the AC LED driver,

[0043] Such that when the AC current flows into or out of the AC LED driver, the filament circuit is functionally disconnected.

[0044] In addition to the above, at least one of the further pin safety switches may also include a switching contact, wherein the switching contact includes:

[0045] - a central node arranged to be connected to said power supply;

[0046] - a normally closed node arranged to be connected to said corresponding filament circuit;

[0047] - a normally open node, arranged to be connected to the AC LED driver,

[0048] Such that when the AC current flows into or out of the AC LED driver, the further filament circuit is functionally disconnected.

[0049] One advantage of the above example is that once AC current begins to flow, the filament circuit can be effectively electrically disconnected from the rest of the electronic device. Thus, one of the switches can be formed as a switch with three nodes, wherein a connection is provided between the filament circuit and the power supply, or a connection is provided between the rest of the LED-based lighting device (i.e., the rectifier and LEDs) and the power supply.

[0050] Such a switch allows the filament circuit to become functionally disconnected once AC current begins flowing through the LED-based lighting device.

[0051] In another example, the LED-based lighting device further includes:

[0052] - an impedance matching circuit for matching the input impedance of the AC LED driver with the output impedance of the power supply.

[0053] Impedance matching can be beneficial in improving power transfer between a power supply and an LED-based lighting device, or in reducing signal reflections from an LED-based lighting device back to the power supply.

[0054] Here, the impedance matching circuit may include at least one of the following:

[0055] - an inductor placed after the output of the AC LED driver;

[0056] - An inductor with two magnetically coupled windings, where each winding is connected to a separate terminal of any of the following:

[0057] - the two separate connection terminals, or

[0058] - the further connection terminal;

[0059] - at least two inductors, wherein each of the two inductors is connected to a separate one of the connection terminals or to a separate one of the further connection terminals.

[0060] For example, the inductor may be placed in series with at least one LED, or may be placed in series with a combination of at least one LED and any other electronic components connected in parallel. Figure 5 , where a buffer capacitor is connected in parallel to at least one LED. This places the inductor on the DC side of the rectifier. This has the advantage of allowing the use of only one signal inductor as an impedance matching circuit.

[0061] The inductor can also be implemented as an inductor with two magnetically coupled windings connected to either of two separate connection terminals or additional connection terminals. In this case, the inductor is placed on the AC side of the LED-based lighting device.

[0062] According to the present disclosure, two non-magnetically coupled inductor sections may also be used.

[0063] In another example, the impedance matching circuit includes two impedance matching capacitors, wherein each of the two impedance matching capacitors is connected to a separate terminal of the two separate connection terminals (L1, L2) and to a separate terminal of the two separate additional connection terminals (R1, R2).

[0064] Note that the LED-based retrofit lighting device according to the present disclosure can be formed as a tube for replacing a conventional fluorescent tube lamp. In this case, the two connection terminals (L1, L2) are oriented at a first end of the tube, and the further connection terminals (R1, R2) are oriented at a second end of the tube opposite the first end. This requires electrical connections to be made across most of the length of the tube to achieve: as described above, 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).

[0065] In its example,

[0066] - a first impedance matching capacitor of the two impedance matching capacitors comprises two capacitors placed in series between one of the two separate connection terminals (L1, L2) and one of the two separate other connection terminals (R1, R2); and

[0067] - a second impedance matching capacitor of the two impedance matching capacitors comprises two capacitors placed in series between the other of the two separate connection terminals (L1, L2) and the other of the two separate further connection terminals (R1, R2),

[0068] wherein the center taps of the two capacitors connected in series between one of the two separate connection terminals (L1, L2) and one of the two separate other connection terminals (R1, R2) are connected to the center taps of the two capacitors placed in series between the other of the two separate connection terminals (L1, L2) and the other of the two separate other connection terminals (R1, R2).

[0069] The advantage of the above is that only a single electrical connection (i.e., a wire or track or anything similar) needs to span the length of the LED-based retrofit lighting device. Two electrical connections are not required. This single electrical connection can consist of a single wire, track or anything similar that connects the center taps of two capacitors placed in series between the two separate connection terminals (L1, L2) to the center taps of two capacitors placed in series between the two separate additional connection terminals (R1, R2). This therefore reduces the complexity and cost of implementing the LED-based retrofit lighting device.

[0070] In a second aspect, there is provided a method for operating a light emitting diode (LED) based retrofit lighting device according to the first aspect, wherein the method comprises the following steps:

[0071] - receiving an AC current from the power source by the AC LED driver;

[0072] - driving, by the AC LED driver, the at least one LED based on the received AC current;

[0073] - enabling the filament current to be circulated back to the power supply by the filament circuit for indicating the presence of the lighting device to the power supply, and

[0074] - The pin safety switch connected to both of the two separate connection terminals (L1, L2) is controlled by the pin safety circuit so that when the pin safety switch is closed, the AC current does not flow through the filament circuit.

[0075] Note that the advantages and limitations 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 lighting device based on light emitting diodes LEDs.

[0076] In a third aspect, there is provided a computer program product comprising program code means stored on a computer readable medium, said program code means being arranged to, when executed by an LED-based retrofit lighting device, perform the method according to the second aspect as provided above.

[0077] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 Shows a commonly used prior art TLED lighting retrofit solution;

[0079] Figure 2 An LED-based retrofit lighting device according to the present disclosure is shown;

[0080] Figure 3 An LED-based retrofit lighting device according to the present disclosure is shown;

[0081] Figure 4 An LED-based retrofit lighting device according to the present disclosure is shown;

[0082] Figure 5 An LED-based retrofit lighting device according to the present disclosure is shown;

[0083] Figure 6 An LED-based retrofit lighting device according to the present disclosure is shown;

[0084] Figure 7An LED-based retrofit lighting device according to the present disclosure is shown. DETAILED DESCRIPTION

[0085] Fluorescent TL tubes are inherently safe because the gas inside the tube must first ignite before a conductive path exists between the two ends of the tube. The tube is connected to an AC mains voltage power supply, such as that commonly found in residential buildings. The tube, or the fixture to which it is mounted, may include additional components such as a ballast and a jumper or starter element.

[0086] This safety is necessary when the tube is being installed into a fixture with the lamp socket energized (i.e., live voltage present). With one end of the tube inserted into the socket and energized, and the other end not inserted into the socket and not energized, the pins at the free end should not become live.

[0087] This is not a problem for gas-filled fluorescent tubes, but when using LED lighting, there is a conductive path between the two ends of the tube, as indicated by L1 / L2 and R1 / R2. When the pins are touched by a person, that is, when a human body is present in the power loop, the internal LED driver tends to conduct current, which often exceeds safety limits and poses a shock hazard.

[0088] One known solution to this problem is to apply the mains input to only one side of the tube. The other side is thus isolated from the mains current. In this case, there is no conductive path between the two sides of the tube, but the glow starter must be replaced with a short-circuiter for the lamp to operate.

[0089] More specifically, in some applications, it is unacceptable for a retrofit LED lighting device to exhibit significant asymmetry under single-fault conditions. Specifically, a diode in a rectifier becoming open circuit can create such a condition. In some retrofit LED lighting devices, each diode in the rectifier can then be connected in parallel with a second diode.

[0090] The present disclosure relates to a double ended LED based retrofit lighting device, where a power source is to be connected to both ends of the LED based retrofit lighting device, ie to L1 / L2 and R1 / R2 .

[0091] Figure 1 A known double-ended LED-based retrofit lighting device 1 is shown in FIG.

[0092] Here, part of the AC current flowing through either pin (e.g., entering through L1 and / or L2 and exiting through R1 and / or R2) can flow directly to its output via the rectifier. No part of the AC current needs to flow through the filament circuit or part of the filament circuit. Thus, losses in the filament circuit due to this AC current are substantially avoided. However, as shown Figure 1 The prior art circuit cannot be easily combined with a pin-safe switch Sw and / or matching impedance. Furthermore, when used with a dimmable HF fluorescent ballast, the filament heating current during dimming can still significantly overheat the Rfil filament resistor.

[0093] Figure 2 An LED-based retrofit lighting device 11 according to the present disclosure is shown.

[0094] An object of the present disclosure is to provide a circuit for LED-based retrofit lighting devices that provides solutions to the above-mentioned problems and challenges, maximizes compatibility with mounting bases of HF fluorescent ballasts, and can also allow dimming of LED-based retrofit lighting devices (such as TLED lamps).

[0095] By placing pin safety switches in both the L1 and L2 pin connections to the rectifier, pin safety is achieved while still preventing at least a portion of the AC current from flowing through the filament impedance Rfill. The inventors discovered that pin safety can be achieved by including 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 can be controlled using the same control signal, resulting in identical behavior. This ensures that, using these switches, the first end of the lighting device can be electrically disconnected from the other, opposite side of the lighting device.

[0096] Preferably, SwLa and SwLb are two normally open contacts of a single relay. The location of the Cy capacitor is not important. It can be placed across SwLb as depicted, from L1 to the DL3, DL4 nodes or from L2 to the DL1, DL2 nodes.

[0097] exist Figure 2 In , two pin safety switches are used, each pin safety switch connects a pin at one end of the LED lighting device to the input of the rectifier. Figure 2 In the case of a pin safety switch closed, AC current can flow directly into / out of the rectifier through any pin without having to flow partially or completely through the filament impedance.

[0098] Thus, a pin-safe solution is created in which the on-state AC current does not flow through (a portion of) the filament impedance, thereby avoiding the associated on-state dissipation in the filament circuit.

[0099] As mentioned previously, for single-fault tolerance reasons, "the" pin safety switch is typically implemented as a series connection of two switches. Since the two switches, SwLa and SwLb, are effectively in parallel from a pin safety perspective, each of the two switches can then have two switches in series. For single-fault tolerance, the second series switch can be a separate relay or other type of switch.

[0100] Alternatively, two additional switches may be connected at opposite ends of the LED lighting device, such as Figure 3 The LED lighting device 21 is shown.

[0101] A second set of pin safety switches can provide single fault tolerance. Placing the second set at the other end of the lamp creates symmetry between the two LED lighting device ends and can allow the relay to be physically placed at different ends of the lamp.

[0102] A second CY capacitor, CYR, may need to be added to create a current path for detecting proper lamp insertion when the pin safety switch is disconnected. Since CYL and CYR are now effectively connected in series, the CY capacitor need not be a safety type; if one capacitor becomes short-circuited, the other CY capacitor will still operate correctly. Thus, the LED-based retrofit lighting device remains single-fault tolerant.

[0103] The two relays can be activated by a shared detection and drive signal, a shared detection signal and independent drive signals, or by independent detection and drive signals.

[0104] Thus, single fault tolerance is added to the previous pin-safe solution, where the on-state AC current does not flow through (any part of) the filament impedance, thereby avoiding the associated on-state dissipation in the filament circuit.

[0105] Another insight is that a plurality of relay output contacts are typically available as changeover contacts having three nodes: a center node CC; a normally closed node NC, connected to the center node CC when the relay is not activated and disconnected from the center node when the relay is activated; and a normally open node NO, disconnected from the center node when the relay is not activated and connected to the center node when the relay is activated. Relay variants with changeover contacts are available at little additional cost compared to variants having only normally open or normally closed contacts.

[0106] This now allows changing at least one of the two switches Sw at each end of the LED lighting device to a changeover contact and permits effectively electrically removing the filament circuit from the rest of the circuit when the relay is activated.

[0107] This is Figure 4 is shown in Figure 4 An LED-based retrofit lighting device 31 according to the present disclosure is shown.

[0108] By replacing at least one of the switches at either end of the LED lighting device with a changeover contact, the filament circuit is electrically removed from the circuit, i.e., functionally isolated or functionally disconnected, once the relay is activated; the center node CC of the changeover contact is connected to the power supply, the normally closed node NC of the changeover contact is connected to the filament circuit, and the normally open node NO of the changeover contact is connected to the input of the rectifier. This allows for even greater elimination of dissipation in the filament resistor during lamp-on operation and enables / simplifies dimming.

[0109] To achieve compatibility with some fixed output HF fluorescent ballasts and a significant enabler of dimming operation, it is desirable to electrically remove the filament circuit device from the circuit during on-state lamp operation because no dissipation occurs in the filament circuit resistor once the relay / switch is activated.

[0110] Figure 4 It also clearly illustrates why it is attractive to physically place the relays each at their own end of the lamp. All signals and circuits to be switched are located at this end of the lamp.

[0111] In the case of an HF ballast with lamp type identification, the filament resistor may need to be selected to have a resistance substantially equal to the RT value of the fluorescent lamp it is intended to replace, i.e., four times the cold filament impedance R0 of that fluorescent lamp. The R0 value for fluorescent lamps may be standardized according to lamp type and is defined in fluorescent lamp specification tables.

[0112] As previously mentioned, lamp type identification via filament impedance can be performed near the end of the preheating phase or at the end of the preheating phase.

[0113] As previously indicated, the LED-based retrofit lighting device may include an impedance matching circuit comprising a capacitor Cpar and / or an inductor L1. Figure 4 is shown, but will be about Figure 5-Figure 7 To clarify.

[0114] Figure 5 A further LED-based retrofit lighting device 41 according to the present disclosure is shown.

[0115] Since it is undefined how the rectifier input current will be divided between DR1, DR2 and DR3, DR4 (as depicted), 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 possible, the impact on impedance matching then changes and may not be preferred.

[0116] Above Figure 5 , where the inductor L1 is within the DC side of the LED based retrofit lighting device.

[0117] Figure 6 An LED-based retrofit lighting device 51 according to the present disclosure is shown.

[0118] Since it is not defined where exactly the current will flow (i.e. L1, L2 and R1, R2), it may be necessary to add at least two impedance matching capacitors Cpar, depicted here as Cpar1 and Cpar2. The right-hand side connections of Cpar1 and Cpar2 can be swapped between L1b, SwRb and L1a, SwRa.

[0119] Continuing from the above, Figure 6 The rectifier shown in FIG has multiple inputs because it is not clear in advance whether the current will flow through L1 or L2 (and R1 or R2). Thus, for example, DL1 is provided for current flowing through L1, and DL3 is provided for 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.

[0120] Notice, Figure 6 and Figure 7 The impedance circuit is also shown to include an inductor having two magnetically coupled windings L1a / L1b connected to any of the other connection terminals. More specifically, the inductor having two magnetically coupled windings L1a / L1b is connected at a first end to the AC LED driver and at a second end to a switch provided by the pin safety circuit.

[0121] Note that each of Cpar1 and Cpar2 can actually be implemented as two capacitors in series for achieving single fault tolerance of LED-based retrofit lighting devices.

[0122] Figure 7 An LED-based retrofit lighting device 61 according to the present disclosure is shown.

[0123] The inventors have discovered that there is an additional benefit to actually implementing each of the capacitors Cpar1 and Cpar2 as two capacitors connected in series. In this case, a single junction node can be implemented, wherein the single junction node is used to create an electrical connection between a first end and a second end opposite the first end of the LED-based retrofit lighting device. This is in relation to Figure 7 is explained in more detail.

[0124] Here, it is shown that capacitor Cpar1 is actually implemented as a series connection of CparL1 and CparR1. Capacitor Cpar2 is actually implemented as a series connection of CparL2 and CparR2. The inventors have found that the center taps can be connected to each other. That is, the center parts of CparL1 and CparR1 can be connected to the center parts of CparL2 and CparR2. This achieves the following Figure 7 As explained above, the joining node can be implemented as an electrical connection between the two ends of the LED-based retrofit lighting device, a PCB track, or anything similar. In this case, there is no need to provide two separate electrical connections between the two ends of the LED-based retrofit lighting device.

[0125] By studying the drawings, the disclosure and the appended claims, those skilled in the art can understand and implement other variations to the disclosed embodiments when practicing the claimed invention. 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 can perform the functions of several items recited in the claims. The fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used advantageously. The computer program may be stored / distributed on a suitable medium, such as an optical storage medium or solid-state medium supplied with or as part of other hardware, but the computer program may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems. Any reference signs in the claims should not be construed as limiting their scope.

Claims

1. A double-ended retrofit light emitting diode (LED)-based lighting device for connection to a power supply, the lighting device having two separate connection terminals (L1, L2) at a first end of the lighting device, the two separate connection terminals (L1, L2) being used to connect the LED-based lighting device to the power supply, and the lighting device having two separate further connection terminals (R1, R2) at a second end, the two separate further connection terminals (R1, R2) being used to further connect the LED-based lighting device to the power supply, the lighting device comprising: - at least one LED for emitting light; an alternating current (AC) LED driver arranged for receiving an AC current from said power source and for driving said at least one LED based on said received AC current, a filament circuit, arranged between the two separate connection terminals (L1, L2), for enabling a filament current to be circulated back to the power supply for indicating the presence of the lighting device to the power supply, and - a pin safety circuit comprising pin safety switches, wherein each switch is connected to one of the two separate connection terminals (L1, L2) such that when the pin safety switches are closed, the AC current does not flow through the filament circuit, wherein one of the pin safety switches comprises a changeover contact, wherein the changeover contact comprises: - 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 the AC LED driver, Such that when the AC current flows into or out of the AC LED driver, the filament circuit is functionally disconnected.

2. The retrofit LED-based lighting device of claim 1 , wherein the lighting device further comprises: - a capacitor connected in parallel to the pin safety switch for providing a reduced amount of power to the lighting device for controlling the pin safety switch when the pin safety switch is open.

3. The retrofit LED-based lighting device according to claim 1 or 2, further comprising: - a further filament circuit arranged between the two separate further connection terminals (R1, R2) for supporting a filament current circulating back to the power supply for indicating the presence of the lighting device to the power supply, and wherein the pin safety circuit comprises a further pin safety switch, wherein each further switch is connected to a separate further connection terminal of the two separate further connection terminals (R1, R2) such that when the further pin safety switch is closed, the AC current does not flow through the further filament circuit.

4. The retrofit LED-based lighting device of claim 3, wherein at least one of the additional pin safety switches comprises a transfer contact, wherein the transfer contact comprises: - a central node arranged to be connected to said power supply; - a normally closed node arranged to be connected to a corresponding said further filament circuit; - a normally open node, arranged to be connected to the AC LED driver, Such that when the AC current flows into or out of the AC LED driver, the further filament circuit is functionally disconnected.

5. The retrofit LED-based lighting device of any one of claims 1, 2, and 4, wherein the LED-based lighting device further comprises: - an impedance matching circuit for matching the input impedance of the AC LED driver with the output impedance of the power supply.

6. The retrofit LED-based lighting device of claim 5, wherein the impedance matching circuit comprises at least one of the following: - an inductor placed after the output of the AC LED driver; - An inductor with two magnetically coupled windings, where each winding is connected to a separate terminal of any of the following: - the two separate connection terminals, or - the further connection terminal; - at least two inductors, wherein each of the two inductors is connected to a separate one of the connection terminals or to a separate one of the further connection terminals.

7. The retrofit LED-based lighting device of claim 5 , wherein the impedance matching circuit comprises two impedance matching capacitors, wherein each of the two impedance matching capacitors is connected to a separate terminal of the two separate connection terminals ( L1 , L2 ) and to a separate terminal of the two separate further connection terminals ( R1 , R2 ).

8. The retrofit LED-based lighting device of claim 7, wherein: - a first impedance matching capacitor of the two impedance matching capacitors comprises two capacitors placed in series between one of the two separate connection terminals (L1, L2) and one of the two separate other connection terminals (R1, R2); and - a second impedance matching capacitor of the two impedance matching capacitors comprises two capacitors placed in series between the other of the two separate connection terminals (L1, L2) and the other of the two separate further connection terminals (R1, R2), wherein the center taps of the two capacitors connected in series between one of the two separate connection terminals (L1, L2) and one of the two separate other connection terminals (R1, R2) are connected to the center taps of the two capacitors placed in series between the other of the two separate connection terminals (L1, L2) and the other of the two separate other connection terminals (R1, R2).

9. The retrofit LED-based lighting device of claim 2, wherein the capacitor is a safety capacitor.

10. A method for controlling a retrofitted light emitting diode (LED)-based lighting device according to any one of claims 1 to 9, wherein the method comprises the following steps: - receiving an AC current from the power source by the AC LED driver; - driving the at least one LED by the AC LED driver based on the received AC current; - enabling the filament current to be circulated back to the power supply by the filament circuit for indicating the presence of the lighting device to the power supply, and - The pin safety switch connected to both of the two separate connection terminals (L1, L2) is controlled by the pin safety circuit so that when the pin safety switch is closed, the AC current does not flow through the filament circuit.

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