EP4611488A1

EP4611488A1 - Led lamp arrangement with controlled power

Info

Publication number: EP4611488A1
Application number: EP24160695.3A
Authority: EP
Inventors: Dolf Henricus Jozef Van Casteren
Original assignee: Seaborough Electronics Ip BV
Current assignee: Seaborough Electronics Ip BV
Priority date: 2024-02-29
Filing date: 2024-02-29
Publication date: 2025-09-03
Also published as: WO2025181236A1

Abstract

An LED lamp arrangement (100) for replacing a fluorescent lamp at least in a luminaire having an electronic ballast. The LED lamp arrangement (100) has a plurality of LEDs (31, 32); a plurality of capacitors (51, 52); a plurality of input terminals (11, 12); one or more rectifier circuits (21, 22, 23, 24); one or more inductive elements (41, 42) connected to receive at least part of the rectified current; a first control circuit (64) configured to estimate electrical current or electrical power received by or used by the LED lamp arrangement (100), and configured to generate an output on the basis of the estimate; and a switching circuit (60) including a first switch (61), for switching the LEDs (31, 32) and the capacitors (51, 52) between at least a first circuit configuration and a second circuit configuration at a switching frequency and according to a duty cycle.

Description

Technical Field

The invention relates generally to light emitting diode (LED) lamps and LED lighting, and more particularly to LED lamps suitable to replace a fluorescent lamp in a luminaire having a ballast for use with fluorescent lamps.

Background

Fluorescent lighting has been around for many years. This form of lighting started out as a highly efficient alternative for incandescent light bulbs, but has recently been surpassed by LED lighting in terms of efficiency and power consumption, and also in other aspects as set out below.
Fluorescent lamps generally comprise a tube filled with an inert gas and a small amount of mercury, capped at both ends with double pinned end caps. Both end caps contain a filament (glow wire). Before ignition the filaments are preheated to enable thermionic emission of electrons. After the user turns on a main switch (e.g. a wall switch or a cord switch on the ceiling), the fluorescent lamp is ignited and heat generated by the conducted current vaporize more mercury in order to increase the luminous output of the fluorescent lamp and keeps the fluorescent lamp in a stable operational condition. To facilitate starting of the lamp and to limit current through the lamp during operation, and thus limit the power consumed, a ballast is usually fitted in the fluorescent luminaire, connected between the mains power supply and the fluorescent lamp, and power is supplied to the lamp via the ballast.
When first introduced, the only available ballasts were simple inductive or reactive elements placed in series with the power supply to the fluorescent lamp, which limit consumed power by limiting the AC current as a result of the frequency dependent impedance of the inductor. These types of ballasts are usually referred to as magnetic ballasts.
More recently other types of ballasts have been introduced, such as electronic ballasts. These ballasts usually first convert AC mains power into DC power, and subsequently convert the DC power into high frequency AC power to drive the fluorescent lamp (e.g. 100-1 10Vac at a frequency typically in the range from 40kHz to 60kHz).
Electronic ballasts can further be categorized into two types: constant current ballasts and constant power ballasts. Most electronic ballasts are constant current ballasts, designed to deliver current at a substantially constant amplitude. These ballasts can be modelled as a constant AC current source. A constant power ballast delivers power close to the original fluorescent lamp power and the output current will vary depending on the load to try to maintain the design power output. If the load voltage is below the design level, constant power ballasts usually try to increase the output current to come closer to the designed power level.
LED lamps are more efficient than fluorescent lamps,and have many other advantages. For example, no mercury is required for LED lamps, the light output from LED lamps is more directional, power can be more easily control or regulated, and the lifetime of LEDs is generally much longer than fluorescent lamps. Thus, replacing fluorescent lamps with LED lamps is often desirable, and it is also desirable to be able to fit replacement LED lamps into existing luminaires designed for fluorescent lamps without needing to modify the luminaire. However, an LED lamp typically operates differently when used with different types of ballasts. A straightforward replacement of a florescent lamp by an LED lamp in a fluorescent luminaire entails a high risk of incompatibility which in some cases results in a failure of the entire luminaire.
WO 2013/024389 A1 describes a lighting driver including a rectifier having an output connected to supply a current to a plurality of light emitting diodes (LEDs), and a switching device disposed at the output of the rectifier and configured to receive a switching control signal and in response thereto to execute a switching operation to modulate an amount of power supplied to the plurality of LEDs so as to cause an average of the power supplied to the plurality of LEDs to be equal to a target power level.

Known compatibility issues

Over the years, the applicant has developed several LED lamp arrangements geared towards solving one or more incompatibility issues that may arise when replacing a florescent lamp by an LED lamp in a fluorescent luminaire.
One known issue is that constant power ballasts are typically designed to operate at a power that is significantly higher than the designed operation power of the energy saving LED lamp (e.g. designed to save 50% energy). Consequently, when fitting such an LED lamp in the luminaire, the constant power ballast determines that the power is too low (e.g. by determining that the voltage across the lamp is too low), so the ballast increases the current supplied to the LED lamp to reach the designed power output of the ballast. As a result, the indicated energy savings of the LED lamp are not achieved. If the current becomes too high, this will result in shortening the life or failure of the lamp and/or the ballast.
This issue of constant power ballasts could be addressed by using adding an impedance in series with the LEDs to limit the current. However, doing so may cause incompatibility with constant current ballasts. Constant current ballasts typically comprise a self-protection/self-correcting mechanism to avoid potential problems of maintaining a constant current. If the LED lamp impedance deviates from the usual fluorescent tube impedance too much (e.g. having a large or different impedance), there is a risk that the LED lamp will be rejected by the ballast during the turn-on operation, i.e. the ballast will automatically shutdown or enter a safety mode.
An LED lamp arrangement addressing both issues at the same time is described in applicant's PCT application published as WO 2016/151125 A1 , herewith incorporated by reference in its entirety. This lamp arrangement comprises an inductive element and a switch which can be closed to short the inductive element, depending on whether the electronic ballast is a constant power ballast. If the ballast is a constant power ballast, the switch is open, so that the inductive element acts as an impedance to limit the current delivered by the constant power ballast. If the ballast is a constant current ballast, the switch is closed, so that the inductive element is bypassed to avoid the risk that the LED lamp is rejected by the ballast.
Another issue relates to a lack of good power regulation. The power output for different ballasts, in particular for constant current ballasts, varies widely when driving the same LED lamp, some ballasts outputting low power at around 20W or lower, while some ballasts drive the LED lamp at a power level up to 50W. This wide variation in ballast output power results in a corresponding variation in light output by the LED lamp when the LED lamp is installed into luminaries with different makes and models of ballasts. This situation is undesirable for lamp manufacturers who may advertise an LED lamp as having a certain light output, and for users who expect the same LED lamp to produce the same amount of light regardless of the design of luminaire into which the lamp is installed.
An LED lamp arrangement equipped with a power regulation mechanism is described in applicant's PCT application published as WO 2020/084087 A1 , herewith incorporated by reference in its entirety. This LED lamp arrangement comprises a plurality of LEDs arranged in two or more groups connected in series, and a switching circuit having a switch connected in parallel with one group of LEDs, which is bypassed when the switch is closed. The switching circuit operates according to a duty cycle in dependence on the electrical current or electrical power received by or used by the LED lamp. This enables a precise power control for constant current ballasts and power control for constant power ballasts to a certain degree. In this disclosure, the switch operates at a switching frequency from 300kHz to 1MHz (or even higher). The selection of a switching frequency much higher than the operating frequency of electronic ballasts (typically in a range 40kHz to 60kHz) aims to avoid disturbing the operation of an electronic ballast. This again relates to the above-mentioned issue that constant current ballasts usually include a sensing mechanism which may result in the ballast performing an unnecessary shutdown if the LED lamp does not behave like a fluorescent tube.
In addition to electrical issues discussed above, optical issues are also of concern. In particular the input power fluctuations (100/120Hz), related to the alternating mains current (50/60Hz), can cause some fluctuating light artefacts such as flicker. Flicker is a periodic, rapid and directly visible change in brightness of a light source, which can be due to fluctuations of the light source. Flicker can cause visual discomfort at work. It can also cause migraines and even epileptic seizures.
A related fluctuating light artefact concerns the so-called stroboscopic effect (sometimes called invisible flicker). This artefact relates to a disturbance in the perception of a moving object, such as how fast the object rotates. The fluctuation in the light intensity from a light source can result in a user having a wrong impression of how an object moves and/or rotates. This can be dangerous at e.g. a workplace having rotating machinery. At the end of 2021, a new EU Regulation EU 2019 / 2020 (Ecodesign) entered into force. This introduces inter alia a new requirement of limiting the stroboscopic effect, represented by a parameter "Stroboscopic Effect Visibility Measure (SVM)". This parameter can be objectively measured according to the IEC TR 63158:2018 standard. The new EU regulation has put into effect a phase out plan where it requires that the SVM level be 0.9 or lower starting from September 2021 onwards, and finally aiming to be lower than 0.4 starting from September 2024.
If the ballast is an electronic constant current ballast, flicker is normally not an issue, since those ballasts have (a) large internal buffer capacitor(s) to stabilize the output current. However, the same cannot be said for many constant power ballasts with respect to SVM. Both Flicker and SVM could be reduced to desired levels using a capacitor connected across the LEDs, having a sufficiently large capacitance, e.g. at or above 100 µF. However, when the capacitance reaches this level, the impedance of the LED lamp would become too low from the perspective of the ballast, thereby again entailing the risk that the LED lamp will be rejected by the ballast if it is a constant current ballast, resulting in turn-on failure.
An LED lamp arrangement that attains the desired SVM level while avoiding this turn-on compatibility issue is described in applicant's PCT application published as WO 2023/242327 , herewith incorporated by reference in its entirety. This LED lamp arrangement comprises a plurality of LEDs, a capacitor connected in series with a switch, and a measurement and control circuit adapted to measure the current drawn from the electronic ballast to detect whether the ballast is a constant current ballast or a constant power ballast. The capacitor and the switch are connected across the LEDs. If the ballast is a constant current ballast, the capacitor is disconnected to avoid the turn-on compatibility issue (while relying on intrinsic electronic circuits of constant current ballasts to attain the desired SVM level); if the ballast is a constant power ballast, the capacitor is connected to activate the SVM reduction circuit of the LED lamp arrangement.

Summary of the Invention

It is an object of the invention to provide an LED lamp which solves a plurality (preferably all) of the above-discussed incompatibility issues in an integrated manner, to reduce production complexity and cost and enables the production of LED lamps suitable for use in practice. In this context, it is desirable to reduce the components used to solve the various incompatibility issues, and to simplify the electrical connections between these components.
A first aspect of the invention concerns an LED lamp arrangement suitable for replacing a fluorescent lamp at least in a luminaire having an electronic ballast, as defined in claim 1.
The LED lamp arrangement may comprise one or more of: a plurality of LEDs; a plurality of capacitors; a plurality of (two or more) input terminals (which may be nodes within the lamp circuit, electrically connected to external pins that connect the lamp to the luminaire) for receiving an electrical current from the luminaire; one or more rectifier circuits for rectifying the electrical current received from the luminaire for supplying an rectified current to the LEDs; one or more inductive elements (e.g. inductor, transformer, or coupled inductor) connected to receive at least part of the rectified current (i.e. the so-called DC side connection); a first control circuit configured to estimate (e.g. measure) electrical current or electrical power (which may be performed by measuring or estimating both current and voltage) received by or used by the LED lamp arrangement, and configured to generate an output on the basis of the estimate (measurement); and a switching circuit including a first switch, for switching the LEDs and the capacitors between at least a first circuit configuration and a second circuit configuration at a switching frequency and according to a duty cycle.
In embodiments of the present invention, three measures are combined: (1) for each LED, at least one of the inductive elements is connected in series with said LED (including the situation in which a single inductor is connected in series with all the LEDs), irrespective of whether the ballast is a constant current ballast or a constant power ballast; (2) for each LED (connected in series with said at least one of the inductive elements), at least one of the capacitors is connected in parallel with the LED (the same capacitor may be connected in parallel with multiple LEDs) and in series with said at least one of the inductive elements, wherein said at least one of the capacitors has an (effective) capacitance in a range 100-1000 µF (such that the LED lamp arrangement has a desired stroboscopic effect visibility measure (SVM), e.g. at or below 0.4 during operation) ; and (3) the switching circuit is configured to adjust at least one of the duty cycle and the switching frequency, in dependence on the output of the first control circuit to adjust the electrical power used by the LED lamp arrangement.
The series connection of an inductive element avoids the excessive current delivered by constant power ballasts; the parallel connection of capacitors avoids the excessive flicker and SVM; and the switching of circuit configurations at an adaptive switching frequency and/or according to an adaptive duty cycle deals with power regulation. Each measure individually was known to be a cause of the turn-on failure problem, but it has been recognized by the inventor that, when these measures are combined, they work together to solve the turn-on failure problem. Specifically, connecting an inductive element in series with the capacitors while switching one the one hand allows the LED lamp to operate at a more reasonable effective impedance from the perspective of the ballast, and on the other hand, the series connection of the inductive element also enables an increased degree of freedom to select the switching frequency. The preferred range of switching frequency is a constant or variable in a range between 50-250 kHz, but a value outside this range may well be used. Synchronization of the switching frequency with the ballast operation frequency can be an option. For example, the switching circuit may be configured to adjust the switching frequency in accordance with an integer multiple of the ballast operation frequency (including 1 × the ballast operation frequency) or vice versa.
In this way, the components of the LED lamp arrangement according to the present invention work together to solve multiple incompatibility issues at the same time. This reduces the components required to make the LED lamp arrangement, reducing the production cost and complexity, providing a significant advantage for putting the LED lamp arrangement into practice such as in commercial products.
In addition, the countermeasures used in the known techniques for avoiding the turn-on failure can also be dispensed. For example, the one or more inductive elements may be connected without a switch operable to bypass the inductive element based on the type of the ballast; the plurality of capacitors may be connected without a switch operable to disconnect the capacitors in dependence on the type of the ballast; and/or the switching frequency may be lower than 300 kHz. Dispensing one or more of these countermeasures enables the production cost and complexity to be further reduced.
In preferred embodiments of the present invention, the one or more inductive elements, the first switch, and at least one of the capacitors form part of a switched-mode power supply, for supplying electrical power to at least a subset of the LEDs. Examples of these embodiments will be described in the below sections in more detail with reference to the various figures. When the luminaire has an electronic ballasts, the use of a switched-mode power supply enables the load current of LEDs (and brightness) to be stabilized. The switched-mode power supply also makes it possible to use the LED lamp arrangement in a luminaire having a magnetic or has no ballast. Such use of a switched-mode power supply has been described in applicant's PCT application published as WO 2020/021072 .
In a preferred embodiment, the switching frequency is in a range 50-250 kHz, each of the capacitors has a capacitance in a range 300-600 µF, and each of the inductive elements has an inductance in a range 100-300 µH. The moderately high frequency enables a precise power regulation while avoiding too much heat and dissipation. The capacitance range is suitable for achieving the desired SVM level for a variety of LED lamp configuration. The inductance in the given range is suitable for avoiding excessive current drawn from most constant power ballasts. Together, the combination of these ranges enables the avoidance of turn-on failure for a variety of constant current ballasts.
In embodiments of the present invention, different circuit configurations differ in the manner in which the LEDs and capacitors are connected together into a circuit. The first and second circuit configurations may differ in the maximum number of LEDs and/or capacitors connected in series across the input terminals. In one embodiment, the first circuit configuration may comprise one or more of: a greater number of the LEDs connected in series than the second circuit configuration, and a greater number of the capacitors connected in series than the second circuit configuration. Switches may be any type of suitable switch, for example, an electromechanical switch such as a relay, or a semiconductor switch such as a transistor, MOSFET or the like.
In an embodiment, the plurality of LEDs include at least a first group of the LEDs connected in parallel with at least a first one of the capacitors and a second group of the LEDs connected in parallel with at least a second one of the capacitors, wherein the one or more inductive elements, the first switch, and one or more of the first and second ones of the capacitors form part of a switched-mode power supply, for supplying electrical power to at least the second group of the LEDs. This embodiment enables a simple implementation of the switched-mode power supply discussed above. For example, the plurality of LEDs may be divided into only the first group and second group, enabling simple switching between the groups of the LEDs. In this embodiment, the LED lamp arrangement may further comprise a diode forming part of the switched-mode power supply.
In an embodiment, the switched-mode power supply is operable to receive electrical power from the first group of the LEDs and to drive at least the second group of the LEDs. This embodiment enables a small switching circuit (switching cell) to be implemented between the two groups of the LEDs, reducing the size of the switching cell and electromagnetic interference (EMI).
In an embodiment, the switched-mode power supply is integrated with the first and second groups of the LEDs in a combined circuit, wherein the first and second groups of the LEDs are connected in a series string between at least one of the inductive elements and a diode forming part of the switched-mode power supply, and the first switch is connected across at least the second group of the LEDs. This embodiment enables a simpler physical arrangement of the relevant components on a circuit board, in exchange of a somewhat larger switching cell.
In an embodiment, the switching circuit further includes a second switch, wherein: in the first circuit configuration, the first and second switches are open, such that the first and second groups of the LEDs are connected in series; in the second circuit configuration, the first and second switches are closed, such that the first and second groups of the LEDs are connected in parallel. By switching the two groups of the LEDs between a series connection and a parallel connection, the difference between the current via one group of the LEDs versus the current via the other group of the LEDs can be eliminated. This allows a uniform brightness to be achieved across the LED lamp (LED tube), without having to rely on a more complex physical arrangement of LED cells as described in applicant's PCT application published as WO 2023/105091 A1 .
In an embodiment, the one or more inductive elements include a first inductive element connected in series with the first group of the LEDs, and a second inductive element connected in series with the second group of the LEDs, wherein in the first circuit configuration, the first and second inductive elements are connected in series, and in the second circuit configuration, the first and second inductive elements are connected in parallel. This ensures that in both the first and second circuit configurations, at least one of the inductive elements is connected in series with the plurality of LEDs, while allowing the two inductive elements to be physically arranged in a close proximity with respect to each other (a diode forming part of the switched-mode power supply may be arranged between the inductive elements), so that uniform brightness is achieved while low EMI is generated by a relatively small switching cell.
In an alternative embodiment, the one or more inductive elements include a first inductive element connected in series with the first and second groups of the LEDs respectively, irrespective whether the first and second groups of the LEDs are connected in series (first circuit configuration) or in parallel (second circuit configuration) with each other.
In an embodiment, the plurality of capacitors are connected into a voltage multiplier circuit operable in reaction to the switching circuit, wherein a first number of capacitors are connected across the input terminals in the first circuit configuration, and a second number of capacitors are connected across the input terminals in the second circuit configuration, the first number being greater than the second number. The second number may be one, corresponding to a single capacitor. In this embodiment, upon switching the circuit configuration, the ballast can effectively see a different forward voltage across the LED lamp arrangement due to the different number of (charged) capacitors across the input terminals. This embodiment enables a change of the circuit configurations of the LEDs and capacitors without changing the LED circuit itself, offering a significant advantage of using a simple LED string configuration while allowing equal brightness for all LEDs in the string.
In an embodiment, the first number is two times the second number and the voltage multiplier circuit is a voltage doubler circuit.
In an embodiment, the plurality of capacitors include a first capacitor and a second capacitor connected in a series string across at least the plurality of the LEDs, a first one of the rectifier circuits includes a first diode and a second diode, and the first switch is connected across a connection point between the first and second diodes and a connection point between the first and second capacitors, such that when first switch is closed during operation, substantially no electrical current flows through either the first diode or the second diode (e.g. leakage current equals less than 1% compared to the current flowing through the first switch). In this embodiment, in addition to change the effective forward voltage across the LED lamp arrangement for the purpose of power regulation, the capacitors also reduce the runtime of the diodes in the rectifier circuit (as both diodes are OFF when the first switch is closed). This measure reduces the conduction losses (dissipation) and improves the efficiency of the LED lamp (lm/W).

Brief Description of the Drawings

The advantages of the invention will be apparent upon consideration of the following detailed disclosure of exemplary non-limiting embodiments of the invention, especially when taken in conjunction with the accompanying drawings wherein:

Fig. 1 is a diagram of an LED lamp configured to operate in a luminaire designed for a fluorescent tube;
Fig. 2 shows a simplified schematic diagram of an embodiment of an LED lamp arrangement 100.
Fig. 3 shows a simplified schematic diagram of another embodiment of an LED lamp arrangement 100.
Figs. 4A and 4B show another embodiment of an LED lamp arrangement 100, using a two-switch configuration.
Fig. 5 shows another embodiment of an LED lamp arrangement 100, using a two-switch configuration similar to Fig. 4.
Fig. 6 shows a simplified schematic of another embodiment of an LED lamp arrangement 100, using a voltage doubler circuit.
Figs. 7A-7D shows operation states of the embodiment of an LED lamp arrangement 100 in Fig. 6.

Description of Illustrative Embodiments

The following is a more detailed explanation of exemplary embodiments of the invention. Components having the same reference number are the same in the various drawings except as described herein. Note that the term "connected" is used herein to indicate an electrical connection between circuit elements, which may be a direct connection or may be a connection made via one or more other circuit elements.
Fig. 1 is a diagram of an LED lamp arrangement 100 which is configured so that it can operate in a luminaire 2 designed for a fluorescent tube. The LED lamp arrangement 100 preferably has a same or similar length and shape as a standard fluorescent tube to enable the LED lamp arrangement 100 to fit into the luminaire 2 without modification. Two electrical connectors 11' (usually in the form of an end-cap with two conductive pins) are provided at one end of the LED lamp arrangement 100 and another two electrical connectors 12' are provided at the other end of the LED lamp arrangement 100, for releasably connecting to corresponding connectors 4 of the luminaire 2. The luminaire 2 may include a ballast 5, which may be for example a magnetic ballast, an electronic ballast which operates as a constant current ballast, or an electronic ballast which operates as a constant power ballast.
The luminaire 2 provides electrical power to the LED lamp arrangement 100 via the connectors 11', 12'. The electrical power provided by the luminaire 2 which is input to the LED lamp arrangement 100 will vary depending on the design of the luminaire, i.e. whether the luminaire has a ballast and if so, what type of ballast. Note that in the context of the present application, the term "AC voltage" or "AC current" generally refers to a signal that changes its polarity (alternating between positive and negative) over time and is not limited to a sine wave or a fixed periodicity; outputs from magnetic ballasts and electronic ballasts are also to be understood as AC signals.
Fig. 2 shows a simplified schematic diagram of an embodiment of an LED lamp arrangement 100 having a plurality of (groups of) LEDs 31, 32, an inductive element 41 (e.g. an inductor, transformer or a coupled inductor), a plurality of capacitors 51, 52 (preferably using polarized capacitors), and a first switch 61 and a first control circuit 64 for switching between different circuit configurations of the LEDs and capacitors.
The LED lamp arrangement 100 receives an electrical current from the luminaire via the input terminals (nodes) 11, 12. In the embodiment shown, the LED lamp arrangement 100 comprises one node 11, 12 at each end. Filament circuits (not part of the schematic in Fig. 2) interconnects the two conductive pins of the end-cap with the single AC node on each side of the tube. An example is described in applicant's PCT application published as WO 2015/044311 A1 . The LED lamp arrangement 100 comprises one or more rectifier circuits for rectifying the electrical current received from the luminaire for supplying an rectified current to the LEDs 31, 32. The rectifier circuit may be implemented using one or more diodes. In the embodiment shown, two diodes 21, 22 are used at one and another two diodes 23, 24 are used at the other end. Different implementations of rectifier circuits with a different number of diodes and/or using different electrical components (such as transistors) may also be used.
The LED lamp arrangement 100 includes a plurality of LEDs electrically coupled to an output of the rectifier circuit to receive electrical current output by the rectifier circuit. In this embodiment, the LEDs are arranged in two groups, i.e. a first group of LEDs 31 and second group of LEDs 32, connected in a series string. Each group of LEDs is connected in parallel with at least one capacitor 51, 52. The inductive element 41 is connected in series with the LEDs and in series with the capacitors.
The first switch 61 is connected in parallel with the second group of LEDs 32. The first switch 61 operates to switch the LEDs between two different circuit configurations in which the two groups of LEDs 31, 32 and capacitors 51, 52 are connected differently into the circuit of the LED lamp arrangement 100. In addition, in the embodiment of Fig. 2, the inductive element 41, capacitor 52 and the first switch 61 additionally form part of a switched-mode power supply for supplying power to the second group of the LEDs 32.
When the first switch 61 is open, the LEDs are connected in a first circuit configuration with the second group of LEDs 32 not bypassed. In that case, part of the rectified current flows through both groups of LEDs 31, 32 in series, and part of the rectified current charges the capacitors 51, 52. The capacitors 51, 52 function to absorb voltage ripples and thereby reducing flicker and SVM. Thanks to the inductor 41 connected in series with the capacitors, the load impedance seen from the ballast does not become too low compared to fluorescent lamps. This combination of inductor and capacitor therefore avoids the turn-on compatibility issue described above while reducing flicker and SVM. In a suitable combination, each capacitor 51, 52 may have a capacitance in a range 300-600 µF (e.g. 470 µF), the inductive element 41 may have an inductance in a range 100-300 µH (e.g. 150 µH), and the switching frequency may be fixed at a frequency in a range 50-250 kHz or may vary within this range depending on the output of the first control circuit 64.
When the first switch 61 is closed, the LEDs are connected in a second circuit configuration with the second group of LEDs 32 being bypassed (i.e. substantially short-circuited) by the first switch 61 so that the electrical current output by the rectifier 21-24 flows through the first switch 61 and first group of LEDs 31, bypassing the second group of LEDs 32. In this state, the second capacitor 52 is discharged to provide some current through the second group of LEDs 32. In the embodiment shown, a diode 25 is connected in series with both groups of the LEDs 31, 32 to prevent reverse current from flowing through the first capacitor 51.
In the first circuit configuration when the first switch 61 is closed, the total forward voltage across the LED lamp arrangement 100 decreases (due to bypassing the second group of the LEDs 32), so that the LED lamp consumes a relatively lower power. In the second circuit configuration when the first switch 61 is open, the total forward voltage across the LED lamp arrangement 100 increases (due to two groups of LEDs 31, 32 conducting current in a series connection), so that the LED lamp consumes a relatively higher power. Switching the circuit configuration of the groups of LEDs provides control of lamp power most effectively when operating with constant-current electronic ballasts, but nevertheless also enables control of lamp power for constant-power electronic ballasts. The first switch 61 preferably switches at a moderately high frequency (e.g. in a range 50-250 kHz) and according to a duty cycle, to provide power regulation in a similar way as described in WO 2020/084087 A1 , while allowing the switching of circuit configurations at a lower frequencies (thereby lower heat and dissipation) and a more stable current flow and brightness.
The first control circuit 64 is configured to estimate the electrical current, voltage or power received by or used by the LED lamp arrangement 100, and is configured to generate an output on the basis of the estimate for controlling the first switch 61, as described in WO 2020/084087 A1 . The estimate may be derived, for example, by measuring an electrical current or voltage and the measurement used as an input to the first control circuit 64. The measurement may be made at various locations in the circuit of the LED lamp arrangement 100, for example at an input to the rectifier, at an output of the rectifier, in series with the LEDs, etc. In the embodiment shown in FIG. 2, an optional sensor element 71 is connected in series with the LEDs for measuring the electrical current flowing through the LEDs. The sensor element 71 may be, for example, a (shunt) resistor across which a voltage is measured to derive an input for first control circuit 64.
The first control circuit 64 may comprise logic to calculate how the duty cycle should be adjusted based e.g. on the output of sensor element 71. The first control circuit 64 may be implemented using hardwired logic or hardware in combination with software, for example using an ASIC, FPGA, microprocessor, microcontroller or other suitable means. In one embodiment, first control circuit 64 implements an algorithm or formula to control the switching of switching circuit 20 to produce a certain predetermined power consumption of LED lamp arrangement 100, to achieve regulation of the lamp power. In another embodiment, the first control circuit 64 implements a look-up table, which comprises measured values with corresponding duty cycle. The lookup table may comprise a series of values stored in memory, or may be contained in the software code (e.g. as a state machine or as a series of if-then statements in the code). The first control circuit 64 and first switch 61 may be separate components or may be integrated in a single component.
If the ballast is a constant power ballast, the first switch 61 may be kept open (0% duty cycle) or operate at a low duty cycle. In this case, the (DC side) inductive element 41 primarily functions to limit the current drawn from the ballast.
If the ballast is a magnetic ballast (or if the luminaire has no ballast), the switched-mode power supply may operate at a different switching frequency and/or a different duty cycle than in the case of electronic ballasts. For example, the switched-mode power supply may operate as described in WO 2020/021072 (e.g. at a switching frequency at 25 kHz). The first control circuit 64 may be configured to react to an input from a frequency sensing circuit to distinguish an electronic ballast from a magnetic ballast or direct mains. For a magnetic ballast or direct mains the frequency of the AC voltage and current supplied to LED lamp arrangement 100 is substantially the mains frequency, e.g. 50 or 60 Hz. This is much lower than the typical output frequency of an electronic ballast, which is typically in the range of 20 to 200 kHz. Thus, switching circuit 60 may be configured to act upon this detection to operate depending on the type of ballast in use. For the magnetic ballasts and no ballast applications, the LED lamp arrangement 100 having a two-pin configuration as shown in Fig. 1 may be used.
In the embodiment shown in Fig. 2, the inductive element 41, first switch 61 and diode 25 form a switching cell 60 of a boost converter, operable to receive power from the first group of the LEDs 31 and to drive the second group of the LEDs 32. This embodiment provides an additional advantage that the physical size of the switching cell 60 can be made very small. Since electromagnetic interference (EMI) is correlated with the physical size of the switching cell, the embodiment of Fig. 2 can operate at a relatively low EMI and does not require any additional EMI filter.
Although the present embodiment includes two groups of LEDs connected in series, the LED lamp 1 may include three or more groups of LEDs and/or the interconnection of the groups of LEDs may be different, and the number of LEDs in each group may be the same or may differ among the groups. Each group of LEDs may comprise a plurality of LEDs, the LEDs in a group being connected in series or parallel or a combination of both, and it is also possible to have one or more groups comprising a single LED. Furthermore, although the present embodiment includes a first switch 61 connected in parallel with one of the groups of LEDs, the LED lamp arrangement 100 may include more than one switch for altering the configuration of the groups of LEDs (see e.g. Figs. 4A, 4B and 5 described below). Additionally or alternatively, the first switch 61 (or switches) may be connected in different ways to define different circuit configurations of the groups of LEDs. For example, the LED lamp arrangement 100 may comprise two or more groups of LEDs connected in parallel, with the first switch 61 connected in series with one of the groups of LEDs having a different number of LEDs than one or more of the other groups of LEDs.
Fig. 3 shows a simplified schematic diagram of another embodiment of an LED lamp arrangement 100. Similar to Fig. 2, the LED lamp arrangement 100 of Fig. 3 comprises two groups of the LEDs 31, 32, each group connected in parallel with at least one capacitor 51, 52, a first switch 61 operable to bypass the second group of the LEDs 32 depending on an input of the first control circuit 64, an inductive element 41 and an optional sensor element 71. These components may perform the same functions as described above in connection to Figs. 1 and 2.
In the embodiment of Fig. 3, the two groups of the LEDs 31, 32 are directly connected to each other (a back-to-back connection), preferably disposed between the inductive element 41 and the diode 25 as shown in Fig. 3. The advantage of this configuration is that the connections between the LED groups (e.g. strings) can be simplified, reducing the construction cost of the LED circuit board. As a trade-off, the switching cell 60 of this embodiment is larger than in the embodiment of Fig. 2.
Figs. 4A and 4B show another embodiment of an LED lamp arrangement 100, using a two-switch configuration. The LED lamp arrangement 100 of this embodiment may comprise the same components as in Figs. 1-3 and additionally comprises a second switch 62 and a second inductor 42.
In this embodiment, the switching circuit 60 includes the first and second inductive elements 41, 42, a diode connected in series between the first and second inductive elements 41, 42, and the first and second switches 61, 62. The first switch 61 is connected across the diode 25, the second inductive element 42 and the second group of the LEDs 32 (and second capacitor 52). The second switch is connected across the first group of the LEDs 31 (and first capacitor 51), the first inductive element 41 and the diode 25. The circuit configuration of the LEDs and capacitors can be changed by operating the first switch 61 and the second switch 62.
The first and second groups of LEDs groups 31 and 32 are connected in series (through diode 25) when switches 61 and 62 are both open (i.e. not-conductive), as shown in Fig. 4A. In this case, both inductive elements 41 and 42 are connected in series with all the LEDs to limit the current drawn from the (constant power) ballast, while the series connection between the inductors and capacitors while switching allows the capacitors 51, 52 to limit the SVM while avoiding the turn-on failure.
LED groups 31 and 32 are connected in parallel when switches 61 and 62 are both closed (i.e. conducting current), as shown in Fig. 4B. In this case, the first inductive element 41 is connected in series with the first group of the LEDs 31 and the first capacitor 51, and the second inductive element 42 is connected in series with the second group of the LEDs 32 and the second capacitor 52. Also in this case, protection against excessive current drawn from ballasts is provided, while SVM is reduced by the capacitors 51, 52 that are connected in series with a respective inductive element 41, 42 while switching.
In both circuit configurations, the two groups of the LEDs conduct an equal amount of current with respect to each other, allowing equal brightness across the entire LED lamp arrangement 100 (e.g. an LED tube) while using a relatively small switching circuit 60.
Fig. 5 shows another embodiment of an LED lamp arrangement 100, using a two-switch configuration similar to Fig. 4. The LED lamp arrangement 100 of this embodiment may comprise the same components as described with reference to the previous figures.
In this embodiment, a single inductive element 41 is connected in series with the first and second groups of the LEDs 31, 32 respectively, irrespective whether the first and second groups of the LEDs are connected in series or in parallel with each other. In the first circuit configuration, where the first and second switches 61, 62 are open, the inductive element 41 is connected to both groups of the LEDs (and their corresponding capacitors 51, 52) in a single series connection. In the second circuit configuration, where the first and second switches 61, 62 are closed, the inductive element 41 forms a series connection with the first group of the LEDs (and first capacitor 51), and forms a separate series connection with the second group of the LEDs (and second capacitor 52). Similarly to the embodiments described above, the inductive element 41 and the capacitors 51, 52 form part of a switched-mode power supply, with the same advantage of uniform brightness across the lamp similar to Figs. 4A and 4B.
Fig. 6 shows a simplified schematic of another embodiment of an LED lamp arrangement 100, which shows an example of using the plurality of capacitors to form voltage multiplier circuit. In the embodiment shown, the capacitors 51, 52 form part of a voltage doubler circuit, and a first and second inductive elements (both may have the same inductance as in the inductive elements described in the previous embodiments) form part of a switched-mode power supply together with the capacitors 51, 52.
The first and second capacitors 51, 52 are connected in a series string across the LEDs 31, 32. Although the figure shows two groups of LEDs, a single group of LEDs may also be used; alternatively, more than two groups of LEDs may be connected in a similar manner. The first switch 61 is connected across a connection point between diodes 23, 24 and a connection point between the capacitors 51, 52.
During operation, the capacitors 51, 52 are charged to reach a certain equilibrium state, at which each capacitor carries some voltage. When the first switch 61 is open, the capacitors 51, 52 receive ripple current while being charged, so that the voltage across the two capacitors together can for example be roughly at the same level as the total forward voltage across the LEDs 31, 32. When the first switch 61 is closed, the ballast sees only one capacitor (either capacitor 51 or capacitor 52 depending on whether current flows from input terminal 11 to input terminal 12 or vice versa). In that case, the number of capacitors across the input nodes (11, 12) is halved (e.g. only roughly half the total forward voltage of the LEDs). In this way, upon switching the circuit configuration, the ballast can effectively see a different forward voltage across the LED lamp arrangement due to the different number of (charged) capacitors across the input nodes (11, 12). This embodiment enables a change of the circuit configurations without changing the LED circuit itself, offering a significant advantage of using a simple LED string configuration while allowing equal brightness for all LEDs in the string. As shown in Fig. 6, the plurality of LEDs can be connected in a simple string, offering a significant advantage of simplify the LED circuit board design.
Similarly to the embodiments of Figs. 1-5, in the embodiment of Fig. 6 the inducive elements 41, 41 and capacitors 51, 52 form part of a switched-mode supply. This switched-mode supply operates in at least four states, as described below in connection to Figs. 7A-7D.
Fig. 7A shows a first state, in which the ballast is in a first half cycle (current flow from connector 11 to connector 12) and the first switch 61 is open. In the figure, the major current flow is designated as the grey dots, and small arrows indicate the direction of the current. In this state, the capacitors 51, 52 are being charged, and their parallel connection to the LEDs allows these capacitors to act as a normal flicker-and-SVM reduction circuit. The diodes 23, 24 also work as part of a normal rectifier circuit.
Fig. 7B shows a second state, in which the ballast is in a first half cycle (current flow from connector 11 to connector 12) and the first switch 61 is closed. In this state, the voltage across the input nodes (11, 12) are halved while the inductive element 41, being part of the switched-mode power supply, resists a sudden change of the current. This provides a significant advantage where power can be effectively halved during this state without sacrificing much of the current drawn by the LEDs or their brightness, which is a desired outcome for providing a low-power LED lamp arrangement.
Another significant advantage offered by this embodiment is the low power dissipation of the diodes 23, 24 increasing the efficiency of the LED lamp (lm/W). During operation of rectifiers, power is dissipated in diodes as some power is converted to heat within the diode due to the forward voltage drop and the current passing through it (conduction loss). When a diode is conducting current, it experiences a voltage drop across its terminals, and this results in power being dissipated as heat.
As shown in Fig. 7B, in the second state both diodes 23, 24 are turned off as diode 24 is short-circuited by the first switch 61. Instead of flowing through the rectifier, current flows directly from the capacitors 51, 52 to the connector 12 (as capacitor 51 is being charged while capacitor 52 is being discharged). In other words, virtually no current flows through the diodes 23, 24 (e.g. leakage current equals less than 1% compared to the current flowing through the first switch), resulting in low dissipation and also allowing the diodes to cool down during this state.
Fig. 7C shows a third state, in which the ballast is in a second half cycle (current flow from connector 12 to connector 11) and the first switch 61 is open. When switch is open, effective voltage across the LEDs 31, 32 is increased, capacitors 51, 52 are being charged, the second inductive element 42 acts to resist a sudden drop in the current, and the diodes 23, 24 work as a normal rectifier.
Fig. 7D shows a fourth state, in which the ballast is in a second half cycle (current flow from connector 12 to connector 11) and the first switch 61 is closed. In this state, the LEDs 31, 32 draw current discharged by the capacitor 51 and controlled by the second inductive element 42. Apart from this, the operation of the forth state is similar to the second state shown in Fig. 7B and provides similar advantages as described above.
It will be appreciated by the skilled person that the embodiments described herein all relate to an LED lamp arrangement having means to regulate the lamp power. While the principles of the invention have been set out above in connection with specific embodiments, it is to be understood that this description is merely made by way of example and not as a limitation of the scope of protection, which is determined by the appended claims.

Claims

An LED lamp arrangement (100) for replacing a fluorescent lamp at least in a luminaire having an electronic ballast, the LED lamp arrangement (100) comprising:
- a plurality of LEDs (31, 32);

- a plurality of capacitors (51, 52);

- a plurality of input terminals (11, 12) for receiving an electrical current from the luminaire;

- one or more rectifier circuits (21, 22, 23, 24) for rectifying the electrical current received from the luminaire for supplying a rectified current to the LEDs (31, 32);

- one or more inductive elements (41, 42) connected to receive at least part of the rectified current;

- a first control circuit (64) configured to estimate electrical current or electrical power received by or used by the LED lamp arrangement (100), and configured to generate an output on the basis of the estimate; and

- a switching circuit (60) including a first switch (61), for switching the LEDs (31, 32) and the capacitors (51, 52) between at least a first circuit configuration and a second circuit configuration at a switching frequency and according to a duty cycle,

wherein, for each LED (31, 32), at least one of the inductive elements (41, 42) is connected in series with said LED (31, 32), irrespective of whether the ballast is a constant current ballast or a constant power ballast, and at least one of the capacitors (51, 52) is connected in parallel with said LED (31, 32) and in series with said at least one of the inductive elements (41, 42), wherein said at least one of the capacitors (51, 52) has a capacitance in a range 100-1000 µF, and

wherein the switching circuit (60) is configured to adjust at least one of the duty cycle and the switching frequency, in dependence on the output of the first control circuit (64) to adjust the electrical power used by the LED lamp arrangement (100).
The LED lamp arrangement according to claim 1, wherein the one or more inductive elements (41, 42), the first switch (61), and at least one of the capacitors (51, 52) form part of a switched-mode power supply, for supplying electrical power to at least a subset of the LEDs (32).
The LED lamp arrangement (100) according to claim 1 or 2, wherein the switching frequency is in a range 50-250 kHz, each of the capacitors (51, 52) has a capacitance in a range 300-600 µF, and each of the inductive elements (41, 42) has an inductance in a range 100-300 µH.
The LED lamp arrangement (100) according to any of the preceding claims, wherein the first circuit configuration comprises a greater number of LEDs (31, 32) connected in series than the second circuit configuration.
The LED lamp arrangement (100) according to any of the preceding claims, wherein the first circuit configuration comprises a greater number of capacitors (51, 52) connected in series than the second circuit configuration.
The LED lamp arrangement (100) according to any of the preceding claims, wherein the plurality of LEDs (31, 32) include at least a first group of the LEDs (31) connected in parallel with at least a first one of the capacitors (51) and a second group of the LEDs (32) connected in parallel with at least a second one of the capacitors (52), wherein the one or more inductive elements (41, 42), the first switch (41), and one or more of the first and second ones of the capacitors (51, 52) form part of a switched-mode power supply, for supplying electrical power to at least the second group of the LEDs (31, 32).
The LED lamp arrangement (100) according to claim 6, wherein the switched-mode power supply is operable to receive electrical power from the first group of the LEDs (31) and to drive at least the second group of the LEDs (32).
The LED lamp arrangement (100) according to claim 6, wherein the switched-mode power supply is integrated with the first and second groups of the LEDs (31, 32) in a combined circuit, wherein the first and second groups of the LEDs (31, 32) are connected in a series string between at least one of the inductive elements (41) and a diode (25) forming part of the switched-mode power supply, and the first switch (61) is connected across at least the second group of the LEDs (32).
The LED lamp arrangement (100) according to claim 6, wherein the switching circuit (60) further includes a second switch (62), wherein:
- in the first circuit configuration, the first and second switches (61, 62) are open, such that the first and second groups of the LEDs (31, 32) are connected in series;

- in the second circuit configuration, the first and second switches (61, 62) are closed, such that the first and second groups of the LEDs (31, 32) are connected in parallel.
The LED lamp arrangement (100) according to claim 9, the one or more inductive elements include a first inductive element (41) connected in series with the first group of the LEDs (31), and a second inductive element (42) connected in series with the second group of the LEDs (32), wherein in the first circuit configuration, the first and second inductive elements (41, 42) are connected in series, and in the second circuit configuration, the first and second inductive elements (41, 42) are connected in parallel.
The LED lamp arrangement (100) according to claim 9, wherein the one or more inductive elements include a first inductive element (41) connected in series with the first and second groups of the LEDs respectively, irrespective whether the first and second groups of the LEDs are connected in series or in parallel with each other.
The LED lamp arrangement (100) according to any of the preceding claims, wherein the plurality of capacitors (51, 52) are connected in parallel with the plurality of LEDs (31, 32) into a voltage multiplier circuit operable in reaction to the switching circuit (60), wherein a first number of capacitors are connected across the input terminals (11, 12) in the first circuit configuration, and a second number of capacitors are connected across the input terminals (11, 12) in the second circuit configuration, the first number being greater than the second number.
The LED lamp arrangement (100) according to claim 12, wherein the first number is two times the second number and the voltage multiplier circuit is a voltage doubler circuit.
The LED lamp arrangement (100) according to claim 12 or 13, wherein the plurality of capacitors include a first capacitor (51) and a second capacitor (52) connected in a series string across at least the plurality of the LEDs (31, 32), a first one of the rectifier circuits includes a first diode (23) and a second diode (24), and the first switch (61) is connected across a connection point between the first and second diodes (23, 24) and a connection point between the first and second capacitors (51, 52), such that when first switch (61) is closed during operation, substantially no electrical current flows through either the first diode (23) or the second diode (24).