Tubular device for mounting to a tubular lamp fitting

Abstract

The lamp comprises an input for connection to a high frequency ballast for a gas discharge lamp. A power supply unit derives power from an LED on voltage of the LED of the lamp, and the power supply unit powers a disconnector at the input. During a preheat phase of the ballast, the power supply unit does not close the disconnector, but when the high frequency ballast is in a later state, i.e. a strike phase, the disconnector is closed.

Description

TECHNICAL FIELD

[0001] The present invention relates to tubular lamp fittings, and in particular to tubular lighting devices housed in such fittings. BACKGROUND

[0002] Solid state lighting (SSL) is rapidly becoming the standard in many lighting applications. This is because SSL elements such as light emitting diodes (LEDs) can exhibit superior lifetime and energy consumption, as well as enabling controllable light output color, intensity, beam spread and / or illumination direction.

[0003] Tubular lighting devices are widely used in commercial lighting applications, such as for office lighting, for retail environments, for hallways, for hotels, etc. Conventional tubular lamp fittings have a socket connector at each end for mechanical and electrical connection with connection pins of each end of a tubular lamp. Conventional tubular lamps are in the form of fluorescent lamp tubes. There is a huge installed base of luminaires equipped with electronic ballasts for fluorescent lamp tubes. The ballast circuit is external to the lamp tube and includes a ballast (inductor) and starter circuit in the case of a magnetic ballast. The ballast, starter circuit and two pairs of connection pins form a closed circuit. In a conventional fluorescent lamp tube, the heated filaments between each pair of connection pins complete the circuit. Electronic ballasts do not require a separate starter.

[0004] There are now tubular LED ("TLED") solid state lamps, which can be used as a direct replacement for traditional fluorescent lamp tubes. In this way, the advantages of solid state lighting can be obtained without the expense of replacing existing luminaires.

[0005] Figure 1 An example of a generally known tubular solid state lamp 10 is shown, which includes a tubular housing 12 (only one shown) with end caps 14 at each end. Figure 1 A non-circular tube is shown, just to illustrate that tubular LEDs are not limited to the circular profile of conventional fluorescent tubes, although of course, circular tubular LEDs are equally well known. The end caps 14 carry external connectors 16 in the form of two pins offset to each side from a central axis of the end cap 14, which is parallel to the elongate axis 15 of the tubular housing 12. The end caps 14 are electrically connected to an internal driver board and circuit board, which mounts solid state lighting elements (e.g. LEDs) within the tubular housing 12.

[0006] Figure 2 A basic circuit of a standard fluorescent tube luminaire is shown. It includes a glow starter 17, a ballast 18 and a mains AC supply 19. Together with the filaments, the pairs of contact pins at each end of the tube 10 form a closed circuit. Such as Figure 2The basic electromagnetic (EM) ballast shown can operate at mains frequency, while electronic ballasts have electronic components that operate at high frequency, such as 20 kHz.

[0007] Figure 2 It is shown how to safely access the unconnected end of the tube for a fluorescent lamp tube. A conventional fluorescent lamp tube can be inserted into such a live mains equipment without any danger, because the connecting pins on either side of the lamp are electrically insulated from each other by the glass tube of the lamp and the gas inside it. An electrical contact between the two ends of the lamp is only established when the gas inside the lamp is ignited, and this is only possible after both ends of the lamp have been inserted into the luminaire.

[0008] Removing the lamp from the luminaire will immediately stop both the current flowing through it and the gas discharge in it, and thus immediately re-establish the electrical insulation between the two ends of the lamp.

[0009] However, inserting a TLED lamp into a luminaire is potentially dangerous, because it is possible to access the connecting pin on one end of the lamp while the other end of the lamp is already inserted and in contact with a dangerous voltage.

[0010] The reason is that a typical TLED retrofit lamp contains a LED PCB and a LED driver PCB that provide little electrical insulation between the connecting pins at both ends of the TLED. Therefore, inserting such a TLED into live mains equipment can be dangerous, because there is a conductive path between the two ends of the tube.

[0011] Various pin safety measures have been proposed to overcome this safety problem. These pin safety measures typically interrupt the relatively low electrical connection / impedance between the two ends of the TLED by at least one switch that only closes when both ends of the TLED are inserted into a luminaire.

[0012] Both electrical and mechanical pin safety mechanisms are known. The present invention relates to electrical pin safety solutions.

[0013] In one known electrical pin safety solution, power is only taken from the first side of the tube, while the other side is isolated from the first side and arranged as a short circuit between the two pin connections on the other side. The glow starter 17 Figure 2 ) has to be replaced by a dummy starter with a bridging wire or fuse inside, closing the current loop. This method has its limitations, because it only works with luminaire equipment that contains a starter Figure 2 ). For example, for electronic ballast devices, there is no starter in the circuit, so the dummy starter method does not work. For electronic ballast devices, and for some other types of ballast, other pin safety solutions are needed.

[0014] For example, in some other electrical pin safety solutions, a solenoid relay is closed when both ends of the TLED are inserted into the lamp holder in the luminaire. When only one end is inserted, the relay remains open. The TLED insertion into the luminaire is detected and the solenoid relay is closed using the current and voltage originating from the electronic ballast. The advantage of the relay pin safety solution is that it is foolproof and maintains the normal lamp look and feel.

[0015] The control of the relay, in particular the closing of the relay, requires a continuous supply of electrical power. Currently, the use of solenoid relays requires a complex circuit of discrete components, which is difficult to place in the limited PCB space of a TLED, especially for T5 tubes. A low dropout LDO circuit can be used as a power supply for the relay, but the circuit is inefficient and can create an open circuit if the input voltage is too high, thus giving rise to compatibility performance issues. Some other solutions directly use the power at the input to drive the relay, but the power at the input is usually a high frequency AC signal and is very unstable.

[0016] Therefore, there is a need for an improved electrical pin safety solution that is compact and low cost and is compatible with different types of electronic (high frequency) ballasts.

[0017] US20180279430A1 and US20160227622A1 disclose tubular LED lamps with a safety relay, wherein the power supply of the relay is more or less directly from the high frequency output of the ballast. SUMMARY

[0018] The invention is defined by the claims.

[0019] The concept of the invention is to provide an isolation switch at the input of the lamp, such as a tubular LED lamp, and to keep the isolation switch open during the preheat phase of a high frequency ballast for gas discharge lamps. This provides pin safety, because the isolation switch is only closed after the preheat state and the lamp then has to be connected correctly. Another concept of the invention is to use the driving voltage established over the light emitting unit, more specifically the LED on voltage established over the LEDs when the LEDs are on, which is more stable, to power the relay. This also does not require a high frequency compatible power converter to directly convert the high frequency output of the ballast, thus saving cost and complexity.

[0020] According to an example in accordance with an aspect of the invention, there is provided a lamp, comprising:

[0021] an input adapted to be connected to a high frequency ballast for a gas discharge lamp;

[0022] a light emitting unit comprising a LED for receiving power from the input and establishing a LED turn-on voltage over the LED;

[0023] at least one isolating switch coupled between the input and the light emitting unit; and

[0024] a power supply unit adapted to obtain power from the established LED turn-on voltage and use this power for powering the isolating switch to close the switch and thereby electrically connect the input to the light emitting unit,

[0025] wherein the lamp is configured to:

[0026] a voltage amplitude sufficient for the power supply unit to close the isolating switch cannot be established when the high frequency ballast is in a pre-heat state; and a voltage amplitude sufficient for the power supply unit to close the isolating switch is established when the high frequency ballast is in a later state after the pre-heat state.

[0027] The lamp keeps the isolating switch open during the initial pre-heat state of the high frequency ballast and this fulfils some high frequency ballast correct connection detection requirements. Thereafter, the power supply unit closes the isolating switch only when a later stage such as the full ignition phase is reached. Thus, the lamp is by default isolated from human contact. The closing of the isolating switch can only occur when the lamp is correctly connected to a fluorescent ballast.

[0028] The turn-on voltage of the light emitting unit can for example be used (directly or after down-conversion) to power the power supply unit. When this voltage is not sufficient for the power supply unit to close the isolating switch, the light emitting unit remains isolated from the input. The lamp is designed such that the required voltage is not reached during the pre-heat phase. The turn-on voltage established over the light emitting unit is typically more stable and thus provides a good voltage supply for the relay.

[0029] The voltage used to power the power supply unit can be a tap voltage from an intermediate position along the LED string, as long as the forward voltage is sufficient to power the power supply unit.

[0030] The isolating switch can be adapted to be open in the pre-heat state such that the lamp is adapted to be seen as a high impedance by the high frequency ballast to allow the high frequency ballast to start.

[0031] The lamp can further comprise an output capacitor in parallel with the light emitting unit.

[0032] The output capacitor forms an energy storage component for buffering purposes to reduce LED current ripples and also to stabilize the voltage over the LED. Thus, it also stabilizes the voltage of the power supply unit.

[0033] In one embodiment, the lamp comprises a detection circuit adapted to detect that the lamp is connected to a high frequency ballast; and a control circuit for enabling the power supply unit when the detection circuit detects that the lamp is connected to the high frequency ballast.

[0034] This embodiment ensures that the input is a high frequency input, and avoids false activation of the power supply unit and the disconnection switch when there is also an LED on voltage present without specification.

[0035] In another embodiment, the lamp optionally has a further input for connection to a low frequency power supply comprising at least one of an AC mains and an output of an electromagnetic ballast, the detection circuit optionally comprises a frequency detector for detecting a frequency of the input to determine whether the lamp is connected to a high frequency ballast, and the control circuit optionally comprises a switch for coupling the LED on voltage to the power supply unit when the detection circuit detects that the lamp is connected to the high frequency ballast, and otherwise decoupling the LED on voltage from the power supply unit.

[0036] In this embodiment, since the further input is adapted to receive low frequency power and drive the LEDs, when the lamp detects that it is indeed connected to a high frequency ballast, only the disconnection switch needs to be turned on to close the power path designed for the high frequency ballast. This avoids power dissipation on the power supply unit when the lamp is connected to a low frequency power supply. In a more specific implementation, the detection is via frequency detection.

[0037] The current from the high frequency ballast to the light emitting unit in the pre-heat state can be in the range of 10% to 20% of the rated current in the normal drive state, which is in the range of 100 mA to 1 A. Thus, the current during the pre-heat state is typically tens of mA, and this current is typically too small to allow the light emitting unit to turn on and build up sufficient voltage.

[0038] The later state for example comprises a strike state of the high frequency ballast, wherein in the strike state a strike current to the light emitting unit is in the range of 100% to 200% of the rated current in the normal drive state, which is between 200 mA to 1 A, and the light emitting unit is capable of being turned on and is adapted to build up a voltage amplitude within a time period of 1 ms to 20 ms.

[0039] The disconnection switch is closed during the strike state to allow powering the light emitting unit through a low impedance path.

[0040] The disconnection switch is for example provided with a parallel bypass capacitor to allow the high frequency strike current to flow before the disconnection switch is closed. Thus, the voltage on the lighting element can start to rise, but is not sufficient during the pre-heat state to activate the power supply unit.

[0041] The power supply unit for example comprises a switched mode power supply, and the disconnection switch comprises a relay (or a set of relays). The switched mode power supply for example comprises a buck converter.

[0042] The switched mode power supply for example comprises an IC controller to operate the switched mode power supply, which IC controller is activated by a supply voltage above a threshold voltage, which threshold voltage corresponds to a voltage amplitude, wherein the lamp further comprises a voltage divider to generate the supply voltage from the LED on voltage. Thus, the supply for the IC is a scaled version of the LED on voltage built on the LED.

[0043] Alternatively, the power supply unit comprises a voltage dividing power supply or a direct power supply. Here voltage dividing power supply means that there is an impedance element to take some of the LED on voltage and provide the rest of the LED on voltage to drive the isolating switch. And direct power supply means that there is a direct electrical connection with substantially no voltage drop, so that substantially all of the LED on voltage is used to drive the isolating switch. This provides a simpler implementation of the power supply unit than the switched mode power supply implementation.

[0044] In one embodiment, the voltage dividing power supply comprises a resistor voltage dividing circuit. Here the resistor can take the excess voltage and provide enough of the rest of the voltage to drive the isolating switch.

[0045] In another embodiment, the voltage dividing power supply comprises a capacitor-resistor voltage dividing circuit. Here the capacitor-resistor voltage dividing circuit is a parallel connection of a capacitor and a resistor. When the LED on voltage is established and the switch SW1 is closed (by detecting that the lamp is connected to a high frequency ballast), the capacitor Cl wants to suppress the voltage built up on itself and this provides a large part of the LED on voltage to the coil to drive the isolating switch. This provides an enhanced actuation to close and hold closed an isolating switch such as a relay. Over time, the voltage on the capacitor increases, but the rest of the (albeit) reduced LED on voltage is still enough to maintain the isolating switch in a closed state. This initial boost to the drive voltage is highly preferred for a relay and this embodiment achieves this by using a combination of the LED on voltage and a capacitor-resistor voltage dividing circuit.

[0046] The lamp can comprise a tubular LED lamp, wherein the light emitting unit comprises an LED arrangement, and the lamp fixture comprises:

[0047] a first pair of input terminals at one end and a second pair of input terminals at an opposite end; and

[0048] a first isolating switch at the first pair of input terminals and a second isolating switch at the second pair of input terminals.

[0049] Thus, there is isolation at both ends of the lamp.

[0050] The isolating switches at each pair of input terminals can be provided with a respective parallel bypass capacitor as mentioned above to allow a strike current to flow before the isolating switch is closed.

[0051] The lamp can further comprise a rectifier arrangement between the input terminals and the light emitting unit, the rectifier arrangement comprising a first bridge rectifier connected to a first pair of terminals by a first disconnecting switch and a second bridge rectifier connected to a second pair of input terminals by a second disconnecting switch.

[0052] The power supply unit can have a single output for controlling the first and second disconnecting switches. This provides a simple structure with one relay control signal.

[0053] The lamp can comprise a first filament emulation circuit and a second filament emulation circuit, wherein when the first disconnecting switch and the second disconnecting switch are open:

[0054] The first filament emulation circuit is connected between the first pair of input terminals at one end of the lamp; and

[0055] The second filament emulation circuit is connected between the second pair of input terminals at the other end of the lamp.

[0056] A preheat current flows through the filament emulation circuits. A small current can also flow from the input terminals at one end to the input terminals at the opposite end. The ignition current instead flows between the ends of the lamp.

[0057] When the first disconnecting switch and the second disconnecting switch are closed, the first filament emulation circuit and the second filament emulation circuit are preferably electrically floating. They then do not play a role in the functioning of the lamp.

[0058] The invention also provides a lighting arrangement comprising:

[0059] An electronic fluorescent lighting ballast for a gas discharge lamp; and a lamp as defined above mounted to the fluorescent lighting ballast.

[0060] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0061] For a better understanding of the present invention, and to show how it can be put into effect, reference will now be made, purely by way of example, to the accompanying drawings in which:

[0062] Figure 1 A substantially known tubular LED lamp is shown;

[0063] Figure 2 An example of an electromagnetic ballast is shown;

[0064] Figure 3 A related control circuit based on a switched mode power supply is shown;

[0065] Figure 4A lighting circuit is shown;

[0066] Figure 5A and Figure 5B Another lighting circuit is shown; and

[0067] Figures 6A to 6C Other embodiments for a power supply unit are shown. DETAILED DESCRIPTION

[0068] The present application will be described with reference to the accompanying drawings.

[0069] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of apparatuses, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the present application. These and other features, aspects, and advantages of the apparatuses, systems and methods of the present application will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the drawings are only schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings for like or similar items.

[0070] The present application provides a lamp comprising an input for connection to a high frequency ballast for a gas discharge lamp. A power supply unit derives power from the LED on voltage of a light emitting unit of the lamp and the power supply unit powers a disconnector at the input. During a preheat state of the ballast the power supply unit does not close the disconnector, but when the high frequency ballast is in a later state, i.e. the ignition phase, the disconnector is closed. The selection is made automatically by whether or not a sufficient voltage is built up over the light emitting unit in the different preheat state and later state.

[0071] The present application relates in particular to a lamp in which an electrical pin safety solution is employed that makes use of a disconnector, such as a relay, to enable tubular LEDs to be used with a high frequency fluorescent tube ballast.

[0072] Conventionally, such a relay is driven by a circuit of discrete components, resulting in a complex circuit that is difficult to fit in the limited space of a TLED's PCB, especially for T5 tubes.

[0073] A low dropout LDO circuit can alternatively be used as a power supply for the relay, but the circuit is inefficient, which poses a risk of generating too much heat, and there are compatibility issues with some ballasts, such as dimming ballasts. The LDO circuit uses a MOSFET that operates in linear mode, and therefore has high power loss under high bus voltage (Vbus) conditions.

[0074] The invention is based on using a switching power supply circuit as relay control circuit, which switching power supply circuit comprises a switching power supply IC. This provides a solution for the limited PCB space of a TLED lamp. It also enables high efficiency and thus better lumen output without the risk of overheating.

[0075] Figure 3 A relay control circuit is shown based on a switching mode power supply based pulse switch modulated IC controller 30. The IC controller 30 is for example a buck converter comprising a main converter switch and a feedback control circuit.

[0076] The IC controller has a sense terminal VSEN for receiving a feedback control voltage, and the circuit controls switching of the main converter switch (which is integrated in the controller IC 30) to regulate the feedback voltage.

[0077] The buck converter circuit comprises an inductor L0, a diode D0 and a load in the form of a resistor R0 and a capacitor C0.

[0078] The relay control voltage V_RELAY is the output voltage of the converter.

[0079] The feedback voltage for the sense terminal is obtained by a resistive divider R1, R2, R3 between the output V_RELAY of the IC controller and the ground terminal.

[0080] The IC controller has a ground terminal GND, a supply terminal VIN, a voltage sense input VSEN, a current set input ISET and a terminal LX connected to the drain of the main switch (high voltage MOSFET).

[0081] The controller IC 30 is powered by a voltage at the terminal VIN based on a resistive divider R4, R5 between the voltage V_LED and ground GND. Note that the voltage supplied to the controller IC can also be a tap voltage at an intermediate position along the LED string, as long as the forward voltage is sufficient to power the supply. The divider R4, R5 in the shown example determines when V_LED is sufficient to turn on the IC. A capacitor C5 buffers the result of the divider to eliminate jitter or spikes.

[0082] The input of the buck converter is V_LED. The current flows in via terminal LX and out via ISET and to the inductor L0. The feedback control implemented by the controller IC is for providing voltage regulation of the output voltage V_RELAY. The current set input ISET is for setting the current limit.

[0083] During the preheat state, the TLED (as Figure 4The lamp current through the ballast between the two ends (V_LED) is very small. Typically, it will last less than 2 seconds. The current is about 10-20% of the normal operating current. The normal operating current is for example a few hundred mA. The current during the preheat state is not enough to establish a sufficient voltage across the LEDs (across the storage capacitor C7, C8 as shown) to turn on the LEDs. Therefore, the LED voltage V_LED is very small. Figure 4

[0084] Some smart ballasts will detect the circuit impedance during the preheat state and if the lamp impedance is too low, the ballast is not able to start properly. If the isolation relay is open, the circuit will have a high impedance and this helps the ballast to detect and operate.

[0085] The controller IC typically also implements an under voltage protection voltage (Vuvp). This can be set based on the following equation:

[0086] Vuvp = (R4 + R5) / R5 * VIN_on

[0087] VIN_on is the voltage at which the IC turns on.

[0088] For example, Vuvp can be set to about 80% of the normal LED string voltage. When the voltage across the capacitor C5 is less than Vuvp, the IC 30 stops working and the relay will be turned off (i.e. the relay will open).

[0089] The circuit is for example designed such that the LED string voltage during the preheat state is less than 50% of the normal LED string voltage. As a result, the IC stops. When the capacitor C5 is charged to VIN_on, the lamp will start operating and this happens during the ballast ignition phase.

[0090] Therefore, during the preheat state, the voltage V_LED only reaches for example 50% of the normal LED string voltage and therefore not Vuvp, and the voltage VIN does not reach VIN_on.

[0091] Due to the charging of the capacitor C7, C8 (in Figure 4 ), the voltage reached by V_LED depends on the delivered current. Therefore, the circuit is designed based on the known current flow during the preheat state and the known duration of the preheat state (or range of durations for different types of ballasts) such that the divided voltage VIN_on is not reached during the preheat state.

[0092] As an example only, VIN_on = 15V, R5 = 50kQ, R4 = 250kQ. In this case, Vuvp = 90V, V_LED (nominal) = 120V (so Vuvp is about 80% of V_LED).

[0093] ​During the preheat state, V LED reaches 50% of the nominal LED string voltage (i.e. 60V), so Vuvp is not reached by V LED and VIN on does not reach VIN (VIN is about 10V).

[0094] During ignition, V LED rises quickly. When it passes 90V, IC 30 turns on and the isolation switch closes.

[0095] Setting Vuvp to about 80% of the nominal value of V LED (instead of a lower value as is conventional), makes IC 30 not misfire during the preheat state, and the IC will only be triggered by the undervoltage protection during normal operating conditions.

[0096] Figure 4 A lighting circuit according to the application is shown.

[0097] The lighting circuit is integrated in Figure 1 a tubular lamp of the type shown. The tubular lamp has a first (left) end with external connectors PinL1 and PinL2 and a second (right) end with external connectors PinR1 and PinR2. Each external connector defines an input adapted to be connected to a high frequency ballast for a gas discharge lamp.

[0098] Each pin is connected in series with a respective electrical isolation switch in the form of a relay. Relay Relaya_L at pin PinL1, relay Relayb_L at pin PinL2, relay Relaya_R at pin PinR1 and relay Relayb_L at pin PinR2.

[0099] Relay Relaya_L at one pin at one end has a Y-capacitor CyL in parallel, while relay Relaya_R at the corresponding pin at the other end also has a Y-capacitor CyR in parallel.

[0100] These capacitors provide a high frequency conduction path when the isolation switches are open.

[0101] Each end of the TLED lamp has a filament emulation circuit. The first end has a filament emulation circuit F1 in the form of a resistor, which is connected between the pins at the first end when the isolation switches are open. Similarly, the second end has a filament emulation circuit F2 in the form of a resistor, which is connected between the pins at the second end when the isolation switches are open. The filament emulation circuits F1 and F2 are only used for lamp detection in the preheat state. The actual load seen by the ballast is the LED load when in normal operation (after ignition).

[0102] The pair of pins at each end are connected to a full-bridge diode rectifier with a buffer capacitor at the output end. The first rectifier D1-D4 and buffer capacitor C7 at the first (left) end and the second rectifier D5-D8 and buffer capacitor C8 at the second (right) end.

[0103] At the first end, the output of the rectifier D1-D4 defines the LED voltage V LED. This is the LED on voltage across the light emitting unit in the form of LEDs LED1-LEDn. There can be a series circuit of LEDs or a combination of series and parallel LEDs. This LED on voltage provides the supply voltage to the buck converter 40. The buck converter is one example of a possible power supply unit that derives power from the established LED on voltage and uses this power to control the isolation switch. Closing the isolation switch electrically connects the respective input end to the light emitting unit.

[0104] At the second end, the external terminals are connected to the rectifier D5-D8 through coils EE8a and EE8b. These are matching inductors for regulating the LED current when connected to different ballasts.

[0105] The output of the rectifier D5-D8 also defines the LED voltage V LED.

[0106] The buck converter 40 comprises Figure 3 All of the components shown. Thus, the supply voltage is converted by a resistive voltage divider before being provided to the controller IC 30 of the buck converter 40.

[0107] The output voltage V RELAY drives both relay coils Relaycoil L and Relaycoil L. One coil drives the pair of relays synchronously at one end, while the other coil drives the pair of relays synchronously at the other end.

[0108] The isolation switch (relay) is closed (i.e. the switch is closed) during the preheat state of the ballast and is opened during the ignition state. During the preheat state, the current from the high frequency ballast to the light emitting unit in the preheat state is in the range of 10% to 20% of the rated current in the normal driving state, for example. The rated current is in the range of 100 mA to 1 A, for example, so the current to the light emitting unit during the preheat state is thus in the tens of mA. This small current will flow between PinL1 and PinR1. During the preheat state, a current of typically a few hundred mA will flow through the filament emulation circuits F1 and F2.

[0109] The capacitors CyL and CyR are in series with the LED string. Thus, the circuit has a high impedance, which facilitates the correct operation of the ballast.

[0110] A small current of tens of mA cannot build up a voltage amplitude sufficient for the power supply unit 40 to switch on and thereby close the disconnector on the buffer capacitors C7, C8 and the LEDs.

[0111] After the preheat state, the ballast delivers a strike current. During the preheat state, most of the current flows from one pin to the other pin at the same terminal (e.g. Pin L1 to Pin L2 and Pin R1 to Pin R2). The strike current instead flows between the two terminals (for ionizing the gas in the gas lamp). This current flows over part of the diode bridge at one end, over the LED arrangement and part of the diode bridge at the other end.

[0112] This strike current is sufficient to reach a voltage amplitude sufficient to power the power supply unit 40. Then the disconnector is closed. Then the first and second filament simulation circuits are electrically floating. They then do not play a role in the normal functioning of the lamp.

[0113] Thus, only when the strike phase is reached, the power supply closes the disconnector. Thus, the lamp is safe to touch before the preheat state is completed.

[0114] More realistically, during the strike state of a high frequency ballast, the strike current delivered to the light emitting unit is in the range of 100% to 200% of the rated current in the normal driving state. The strike current is for example between 200 mA and 1 A.

[0115] Then, the light emitting unit is able to build up a voltage amplitude to switch on the power supply unit 40 in a time period of 1 ms to 20 ms.

[0116] Capacitors C2, C4, C5 and C6 are matching capacitors to adjust the LED current when connected to different ballasts.

[0117] Figure 5A and Figure 5B A circuit diagram of another LED tube lamp using the inventive concept is shown. Figure 5A An additional capability of the LED tube in Fig. 1 is that it can support an AC mains input or a magnetic ballast input between Pin 1 and Pin 2 at the left end. For the AC mains input or the magnetic ballast input, the energy enters the rectifier formed by diodes D6, D7, D8 and D9 and reaches the DCDC converter to power the LEDs. In addition, it can support a high frequency ballast input between the left end to the right end similar to the above. Similar to the above, for the high frequency ballast input, Pin 1 and Pin 2 are the same voltage, Pin 3 and Pin 4 are the same voltage, the energy enters via Ycap and the diodes first and switches on the LEDs, then the LED on voltage between V+ and V- powers the relay driver to switch on the relay and to bypass Ycap.

[0118] The inventors realized that in case of AC mains input or electromagnetic ballast input, the relay driver is not needed. However, since the relay driver gets the LED on voltage to drive the relay, the relay driver will still be powered when the LED is turned on by the AC mains input or electromagnetic ballast input. This results in wasted power. Furthermore, in a high voltage test, an AC frequency high voltage is applied between the left and right end, which can pass through the Ycap and also turn on the LED. In this case, the LED on voltage will power the relay driver and close the relay, the closed relay is a low impedance path that causes the high voltage test voltage and the high voltage test will fail. The inventors also want to avoid this problem.

[0119] To solve at least these two problems, the inventors propose that the relay driver is powered by the LED on voltage only when the input of the LED tube lamp is a high frequency ballast (excluding the case of a low frequency AC mains or electromagnetic ballast input or a low frequency high voltage test voltage). There is a detection circuit to detect the presence of a high frequency ballast, more specifically, the detection circuit can be a frequency detector to detect the frequency of the input high frequency signal. Implementations of frequency detectors to identify high frequencies and filter out low frequencies are well known to the person skilled in the art, such as high pass filters. As Figure 5B shown, when the detection circuit detects that the lamp is connected to a high frequency ballast, there is a switch SW1 closed to couple the LED on voltage to the power supply unit / relay driver 40, otherwise the switch SW1 is open and decouples the LED on voltage from the power supply unit / relay driver 40. The switch SW1 can be implemented by a MOSFET, a bipolar transistor or even a relay. The output of the detection circuit can be appropriately converted to drive the switch SW1, the driving of the switch is also a very common implementation for the person skilled in the art. This description will not give further details.

[0120] Instead of implementing the power supply unit by a switched mode power supply, we can implement it by a voltage divider or even a direct current power supply.

[0121] Direct current power supply means a direct electrical connection with substantially no voltage drop, so that the LED on voltage is used substantially all for driving the isolation switch. This provides a simpler implementation for the power supply unit than the switched mode power supply implementation. Figure 6A This implementation is shown.

[0122] Voltage divider power supply means having impedance elements to take some voltage and provide the remaining LED on voltage to drive the isolation switch.

[0123] As Figure 6BAs shown, we are able to select one or more LEDs whose sum of turn-on voltage is higher than the driving voltage. A resistor R1 is used to take part of the LED turn-on voltage, and the remaining part of the LED turn-on voltage is reserved to drive the isolation switch. The voltage dividing power supply has better efficiency.

[0124] In a further improved solution, a capacitor-resistor voltage dividing circuit is used, as shown in Figure 6C The capacitor-resistor voltage dividing circuit refers to the parallel connection of a capacitor and a resistor. Since the capacitor is intended to suppress the voltage built thereon, the capacitor gives a larger part of the LED turn-on voltage to drive the isolation switch. This provides enhanced actuation to close the isolation switch such as a relay. As time elapses, the voltage on the capacitor increases, and the remaining part of the LED turn-on voltage taken by the isolation switch is sufficient to maintain the closed state of the isolation switch. Therefore, the efficiency is also high.

[0125] Variations to the disclosed embodiments can become apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings, and it is intended that the scope of the application disclosed by the appended claims should include all such variations. 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.

[0126] The mere fact that measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0127] If the term "adapted to" is used in the claims or specification it should be noted that the term "adapted to" is intended to be equivalent to the term "configured to".

[0128] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A lamp comprising: input terminals (PinLl, PinL2, PinRl, PinR2) adapted to be connected to a high frequency ballast for a gas discharge lamp; a light emitting unit (LEDl...LEDn) comprising LEDs for receiving power from the input terminals and for establishing an LED turn-on voltage (V_LED) across the LEDs when the LEDs are conductive; at least one relay (Relaya_L, Relayb_L, Relaya_R, Relayb_R) coupled between the input terminals and the light emitting unit; and a power supply unit (40) adapted to obtain power from the established LED turn-on voltage and to use the power for powering the at least one relay to close the relay and thereby electrically connect the input terminals to the light emitting unit, wherein the lamp is configured to: not be able to establish the LED turn-on voltage sufficient for the power supply unit to close the at least one relay when the high frequency ballast is in a preheat state; and establish the LED turn-on voltage sufficient for the power supply unit to close the at least one relay when the high frequency ballast is in a later state after the preheat state.

2. The lamp according to claim 1, wherein the at least one relay (Relaya_L, Relayb_L, Relaya_R, Relayb_R) is adapted to be open in the preheat state, such that the lamp is adapted to be seen as a high impedance by the high frequency ballast to allow the high frequency ballast to start up, and the lamp further comprises an output capacitor (C7, C8) in parallel with the light emitting unit.

3. The lamp according to claim 1 or 2, further comprising: a detection circuit adapted to detect that the lamp is connected to the high frequency ballast; and a control circuit to enable the power supply unit (40) when the detection circuit detects that the lamp is connected to the high frequency ballast.

4. The lamp according to claim 3, wherein the lamp has another input terminals for connection to a low frequency power supply comprising at least one of an AC mains and an electromagnetic ballast output.

5. The lamp according to claim 3, wherein the detection circuit comprises a frequency detector to detect a frequency of an input to determine whether the lamp is connected to the high frequency ballast.

6. The lamp according to claim 3, wherein the control circuit comprises a switch (SWl) to couple the LED turn-on voltage to the power supply unit (40) when the detection circuit detects that the lamp is connected to the high frequency ballast, and otherwise to decouple the LED turn-on voltage from the power supply unit (40).

7. The lamp according to any one of claims 1 to 2, wherein a current from the high frequency ballast to the light emitting unit (LEDl...LEDn) in the preheat state is in a range of 10% to 20% of a rated current in a normal driving state, the rated current being in a range of 100 mA to 1 A. ​ ​ 8. The lamp according to any one of claims 1 to 2, wherein the later state comprises a strike state of the high frequency ballast, wherein in the strike state a strike current to the light emitting unit is in the range of 100% to 200% of the rated current in a normal driving state, the strike current is between 200 mA and 1 A, and the light emitting unit (LED1...LEDn) is adapted to establish the sufficient LED turn-on voltage within a time period of 1 ms to 20 ms.

9. The lamp according to claim 8, wherein the at least one isolating switch (Relaya_L, Relaya_R) is provided with a parallel bypass capacitor (CyL, CyR) to allow a high frequency strike current to flow before the at least one isolating switch (Relaya_L, Relaya_R) is closed.

10. The lamp according to any one of claims 1 to 2, wherein the power supply unit (40) comprises a switch mode power supply, or alternatively a voltage dividing power supply or a direct current power supply, wherein the voltage dividing power supply comprises a resistor voltage dividing circuit or a capacitor-resistor voltage dividing circuit, and the at least one isolating switch (Relaya_L, Relayb_L, Relaya_R, Relayb_R) comprises at least one relay.

11. The lamp according to claim 10, wherein when the power supply unit (40) comprises the switch mode power supply, the switch mode power supply comprises an IC controller (30) to operate the switch mode power supply, the IC controller (30) is activated by a voltage supply higher than a threshold voltage, the threshold voltage corresponds to the sufficient LED turn-on voltage, wherein the lamp further comprises a voltage divider to generate the voltage supply from the LED turn-on voltage.

12. The lamp according to claim 8, comprising a tubular LED lamp, and the lamp comprises: a first pair of input terminals (PinL1, PinL2) at one end of the input and a second pair of input terminals (PinR1, PinR2) at an opposite end of the input; and a first isolating switch (Relaya_L, Relayb_L) of the at least one isolating switch at the first pair of input terminals (PinL1, PinL2) and a second isolating switch (Relaya_R, Relayb_R) of the at least one isolating switch at the second pair of input terminals (PinR1, PinR2).

13. The lamp according to claim 12, wherein one isolating switch (Relaya_L, Relayb_L) of the at least one isolating switch at each pair of input terminals is provided with a respective parallel bypass capacitor (CyL, CyR) to allow the strike current of high frequency to flow before the one isolating switch is closed. ​ ​ ​ ​ 14. The lamp according to claim 12 or 13, further comprising a rectifier arrangement between the input terminals and the light emitting unit, the rectifier arrangement comprising a first bridge rectifier (D1-D4) and a second bridge rectifier (D5-D8), the first bridge rectifier (D1-D4) being connected to the first pair of terminals (PinL1, PinL2) through the first isolating switch (Relaya_L), the second bridge rectifier (D5-D8) being connected to the second pair of input terminals (PinR1, PinR2) through the second isolating switch (Relaya_R).

15. The lamp according to claim 12 or 13, wherein the power supply unit has a single output for controlling the first isolating switch (Relaya_L, Relayb_L) and the second isolating switch (Relaya_R, Relayb_R).

16. The lamp according to any one of claims 12 to 13, comprising a first filament simulation circuit (Fl) and a second filament simulation circuit (F2), wherein, When the first isolating switch (Relaya_L, Relayb_L) and the second isolating switch (Relaya_R, Relayb_R) are open: the first filament simulation circuit (F1) is connected between the first pair of input terminals (PinL1, PinL2) at one end of the lamp; and the second filament simulation circuit (F2) is connected between the second pair of input terminals (PinR1, PinR2) at the other end of the lamp.

17. The lamp according to claim 16, wherein when the first isolating switch (Relaya_L, Relayb_L) and the second isolating switch (Relaya_R, Relayb_R) are closed, the first filament simulation circuit (F1) and the second filament simulation circuit (F2) are electrically floating.

18. A lighting fixture comprising: an electronic fluorescent lighting ballast for a gas discharge lamp; and a lamp according to any one of claims 1 to 17, the lamp being mounted to the fluorescent lighting ballast.

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