EP3376829B1

EP3376829B1 - Led lamp arrangement for replacing a fluorescent lamp

Info

Publication number: EP3376829B1
Application number: EP18152634.4A
Authority: EP
Inventors: Shounak ROY; Gaetano Navaro NAHAR
Original assignee: Silicon Hill BV
Current assignee: Silicon Hill BV
Priority date: 2017-03-13
Filing date: 2018-01-19
Publication date: 2020-10-21
Anticipated expiration: 2038-01-19
Also published as: HUE053043T2; DK3376829T3; PL3376829T3; WO2018167058A1; CN110547046A; SI3376829T1; CN110547046B; EP3376829A1

Description

Field of the invention

The invention relates to an LED lamp arrangement (e.g. a retrofit LED lamp) for replacing a fluorescent lamp suitable to be energized by a ballast, which can be either a magnet ballast or an electronic ballast.

Background of the invention

Fluorescent lighting has been around for many years now. 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. The end caps contain a glow wire to preheat the gasses inside the tube and to vaporize the mercury in order to assist with ignition of the fluorescent lamp. 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 keeps the fluorescent lamp in operational condition. To facilitate these starting conditions and to limit current through the fluorescent lamp during operation, and thus limit the power consumed, a ballast is 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. An undesirable result is a relatively low power factor and relatively high reactive power. 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.
LED lamps are more efficient than fluorescent lamps. Besides, they have many other advantages. For example, no mercury is required for LED lamps, LED lamps are more directional, LEDs require less effort to control or regulate power consumed, and the lifetime is increased over fluorescent lamps. Thus, replacing fluorescent lamps with LED lamps in an existing luminaire is often desirable.
US Patent No. 9,441,795 , discloses a retrofit LED-lamp using LED circuitry connected between the outputs of a rectifier circuit. The LED circuitry comprises strings of LEDs. When the ballast is a magnet ballast, the LED circuitry is switched in a configuration in which the strings of LEDs are connected in series. When the ballast is an electronic ballast, the LED circuitry is switched in a configuration in which the strings of LEDs are connected in parallel. The type of ballast is detected by sensing frequency of the AC current supplied by de ballast. A lower frequency indicates that the ballast is a magnet ballast, and a higher frequency indicates that the ballast is an electronic ballast.
On some commercial available electronic ballasts the retrofit lamp the output voltage of the ballast peaks in a type of burst mode during a few seconds after the lamp is switched off, resulting in the lamp generating visible light flashes. These light flashes are disturbing to the users.

Summary of the invention

It is an object of the invention to avoid the light flashes after an LED lamp arrangement is switched off.
The invention relates to an LED lamp arrangement according to claim 1.
The LED lamp arrangement is suitable for replacing a fluorescent lamp suitable to be energized by a ballast, e.g. the LED lamp arrangement is suitable for replacing a fluorescent lamp in a luminaire having such a ballast.
The ballast can be a magnet ballast operating at a first frequency or an electronic ballast operating at a second frequency, higher than the first frequency. A typical operating frequency of a magnet ballast (first frequency) may be for example 50 Hz, and a typical operating frequency of an electronic ballast (second frequency) may be for example 40 kHz.
The LED lamp arrangement according to the invention may also be suitable for replacing a fluorescent lamp when the electronic ballast has an operation mode in which the electronic ballast generates a series of bursts and outputs the series of bursts to the LED lamp arrangement. This operation mode may relate to an operation after the lamp is switched off. The luminaire may be controlled by a main switch (e.g. a switch on the wall). The operation mode of the electronic ballast may be a turn-off operation within less than 10 seconds after the main switch is turned off (e.g. by a user).
In this way, the user can feel free to install the LED lamp arrangement to a luminaire to replace a fluorescent lamp, without having to worry whether the ballast is a magnet ballast or an electronic ballast, and furthermore in the latter case whether the electronic ballast has the (turn-off) operation mode which generates the series of bursts.
The LED lamp arrangement comprises a rectifier circuit for rectifying a current drawn from the ballast to generate a rectified current, and an LED circuit connected to receive the rectified current.
The LED circuit comprises a plurality of groups of LEDs switchable between at least a first circuit configuration and a second circuit configuration. The first circuit configuration comprises a greater number of groups of LEDs connected in series than the second circuit configuration. Different circuit configurations may have different circuit arrangement of the groups of LEDs in which at least a portion of the groups of LEDs are connected into the circuit differently. For example, the plurality of circuit configurations may differ in the number of groups of LEDs connected in series versus the number of groups of LEDs connected in parallel. This allows the LED circuit to change its circuit configuration suitable for a corresponding ballast. For example, the LED lamp arrangement may be arranged to switch to the first circuit configuration when the ballast is a magnetic ballast, and switch to the second circuit configuration when the ballast is an electronic ballast.
The LED lamp arrangement comprises an auxiliary circuit, which defines a conductive path connected in parallel with the plurality of groups of LEDs in the second circuit configuration. This can be achieved by connecting a wiring (e.g. a wire, a metal layer, etc.) across at least one group of the LEDs and other components (such as a capacitor) along the wiring. In this way, when this group of LEDs is connected into a parallel connection with other groups of LEDs in the second circuit configuration, the conductive path will also be connected into a parallel connection with the other groups of the LEDs.
The auxiliary circuit comprises a capacitor in the conductive path, wherein the LED lamp arrangement is arranged to bypass the groups of LEDs and charges the capacitor when the LED lamp arrangement receives the series of bursts from the electronic ballast, and to discharge the capacitor during a time interval between the series of bursts.
As the LEDs are bypassed and the capacitor is charged when a burst arrive, during that period the current is primarily conducted via the parallel conductive path rather than the LEDs. As a result, the LEDs do not produce light or barely produces any light so that the user can barely see; as the capacitor is sufficiently discharged (doesn't need to be 100% discharged) during the interval between the bursts, the conductive path will be able to perform the above-mentioned function again when the next burst arrive. In this way, the problem of the light flashes can be avoided.
The capacitance of the capacitor should be high enough to avoid quickly approaching a maximum charged state when the burst is received, and should be low enough to be sufficiently discharged during the time intervals. In a preferred embodiment, the capacitor has a capacitance in a range of 10 µF - 50 µF.
The series of bursts may represent a voltage source. The voltage during the time interval between the series of bursts may be less than 1 V_RMS.
The time interval between the series of bursts may be in a range from 1 millisecond to 300 milliseconds.
The time interval between the series of bursts may be substantially a constant.
In order to bypass the LEDs, the conduction path (which is connected in parallel with the groups of LEDs) should have a lower impedance than the LEDs. At the operation frequency of electronic ballasts (e.g. 40k Hz), an inductor has a high impedance because its impedance is proportional to the signal frequency. For this reason, the conduction path via the capacitor (which has a low impedance at the operation frequency of electronic ballasts) should have a low inductance and preferably has no inductance. In a preferred embodiment, the conductive path does not comprise an inductive element (e.g. an inductor) connected in series with the capacitor.
In an embodiment, the auxiliary circuit further comprises a control circuit for controlling an operation of the LED lamp arrangement. A first end of the capacitor may be electrically connected to a voltage supply terminal (e.g. a Vcc terminal) of the control circuit and a second end of the capacitor is connected to a common (e.g. a return connection line connected to the rectifier circuit). In this way, the capacitor not only can function to deal with the bursts, but also can function to stabilize the voltage supplied to the control circuit of the LED lamp arrangement.

Brief description of the drawings

These and other aspects of the invention will be apparent from and elucidated further with reference to the embodiments described by way of example in the following description and with reference to the accompanying drawings.

Fig. 1 shows an embodiment of the LED lamp arrangement according to the invention.
Fig. 2 shows a switch-off behavior of the output voltage of some commercial available electronic ballasts.

Detailed description of the embodiments

Fig. 1 shows an embodiment of the LED lamp arrangement 1 according to the invention. The LED lamp arrangement 1 is arranged to replace a fluorescent lamp, such as a fluorescent tube.
The LED lamp arrangement 1 comprises an LED circuit 8 which comprises a plurality of groups of LEDs 9, 10, 11, 12, 13 which emit light when a current flows through the LEDs. In the embodiment shown, the LED circuit 8 comprises five groups of LEDs 9, 10, 11, 12, 13 via connection diodes. The number of groups may be other than five, e.g. the LED lamp arrangement 1 may comprise two, three, or other number of groups of LEDs, as described in WO 2016/151125 A1 . Each group of LEDs may comprise a plurality of LEDs 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. In an embodiment the LED string comprises plural (e.g.10 - 20) LEDs connected in series.
The LED lamp arrangement 1 comprises a rectifier circuit 4, 5. The rectifier circuit may comprise multiple parts. In the embodiment shown, the rectifier circuit comprises two bridge rectifiers. Other types of rectifiers may also be used. The rectifier circuit 4, 5 may be electrically connected to a first connection line 6 and a second connection line 7 which is connected to a common. The current drawn from the ballast received via pin pairs 2-2' and 3-3' of the LED lamp arrangement 1 is rectified by the rectifier circuit 4, 5, and a rectified current is supplied the LED circuit 8 via the first connection line 6 and the second connection line 7.
The connection between the groups of LEDs 9, 10, 11, 12, 13 may be switched in a plurality of circuit configurations, including a first circuit configuration and a second configuration, by controlling switches 26 and 27, as described in US 9,441,795 . In the embodiment shown, the first circuit configuration corresponds to a state in which both switches 26 and 27 are open. In this circuit configuration, the groups of LEDs 9, 10, 11, 12, 13 may be connected in series between the first and second connection lines 6, 7. In the second circuit configuration, both switches 26 and 27 may be closed. In this circuit configuration, the groups of LEDs 9, 10, 11, 12, 13 may be connected in parallel between the first and second connection lines 6 and 7.
In the embodiment shown, when the groups of LEDs 9, 10, 11, 12, 13 are connected in series (e.g. in the first circuit configuration), the voltage across the LED circuit 8 is represented by the sum of the forward voltages of a greater number of groups of LEDs. When the groups of LEDs are connected in parallel (e.g. in the second circuit configuration), the voltage across the LED circuit 8 is represented by the forward voltage across a smaller number of groups of LEDs, e.g. roughly 1/5 of the voltage in the first circuit configuration. The lower voltage is suitable when the LED lamp arrangement 1 is energized by an electronic ballast, whilst the higher voltage is suitable when the LED lamp arrangement is energized by a magnetic ballast.
The switches 26 and 27 may be controlled by a signal which indicates whether the ballast is a magnet ballast or an electronic ballast, such that the LED circuit 8 is switch to an appropriate circuit configuration (e.g. the first or second circuit configuration as described above). The signal which controls the switches 26 and 27 are described in US 9,441,795 .
The LED lamp arrangement 1 further comprises an auxiliary circuit 31. The auxiliary circuit may comprise a conduction path connected in parallel with at least one group of LEDs 13. In the embodiment shown, the conduction path comprises a capacitor 39.
Fig. 2 shows a typical switch-off behavior with bursts occurring in electronic ballasts. In the time interval t₀-t₁, the LED lamp arrangement 1 is in its normal operation, and receives a current from the electronic ballast at a frequency of substantially 40 kHz. During a few seconds after the lamp is switched off at t₁, the ballast generates a series of burst voltages and supplies those burst voltages to the LED lamp arrangement. The burst voltage may have the frequency as the operation frequency of the ballast (e.g. substantially 40k), and the interval between burst voltages may be a few milliseconds to a few hundreds of milliseconds.
In the embodiment shown in Fig. 1, the auxiliary circuit 31 is arranged to discharge the capacitor 39 during the time interval between t₁ and the first burst voltage, and during the time intervals between the burst voltages. When a burst voltage occurs, in particular during peaks 41 of each burst, the sufficiently discharged capacitor 39 conducts the current and bypasses the LEDs. In this way, as the LEDs do not conduct a current or barely conducts any current, those LEDs do not emit light or merely emit little amount of light that the user can barely see, the flashes caused by the bursts can therefore be avoided.
In the embodiment shown, the capacitance of the capacitor 39 is high enough to absorb the burst current, and is low enough to be sufficiently discharged during the relevant time intervals, so that it can absorb the current from the next burst. Preferably, the capacitor 39 has a capacitance in a range of 10 µF - 50 µF.
Referring back to Fig. 1. Optionally, the auxiliary circuit 31 may further comprise a control circuit 36 for controlling at least a part of the operation of the LED lamp arrangement 1. In the embodiment shown, the auxiliary circuitry 31 comprises a control circuit 36, which may be an integrated circuit, for controlling one or both of the switches 26, 27. In the embodiment shown, the voltage supply terminal of the control circuit 36 is connected to the capacitor 39. In this way, as the capacitor 39 is connected in parallel with at least one group of LEDs 13, the forward voltage of LEDs can be used as a voltage source. In this embodiment, the capacitor 39 also function to stabilize the voltage supplied to the control circuit 36.
Optionally, the LED lamp arrangement 1 may comprise an elongated cylindrical housing to form a tube. The pairs of connector pins 2- 2 and 3-3' may be arranged at both ends of the elongated cylindrical housing to connect the LED lamp arrangement 1 to the ballast.
Optionally, the LED lamp arrangement 1 may further comprise an inductive element 28 and a switch 29 connected across the inductive element 28, for controlling the current when a special type of electronic ballasts is detected. This type of electronic ballast is known as constant power ballasts. The operation of the inductive element 28 and switch 29, as well as the detection of a constant power ballast, are described in detail in WO 2016/151125 . For example, the LED lamp arrangement 1 may be arranged to detect whether the current drawn from the ballast exceeds a reference vale, and if so, to open the switch 29. This results in that the current flows through the LED circuit 8 and the inductive element 28 which has a high impedance at the operating frequency of the electronic ballast, thereby limiting the current. The current drawn from the ballast may be estimated using a sensor circuit. The sensor circuit may comprises a resistor 30 as shown in Fig. 1. As the voltage across a resistor is substantially proportional to the current, the current drawn from the ballast can be estimated by measuring the voltage across the resistor 30.
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 (1) for replacing a fluorescent lamp suitable to be energized by a ballast, the ballast being a magnet ballast operating at a first frequency or an electronic ballast operating at a second frequency, higher than the first frequency, the LED lamp arrangement comprising:
- a rectifier circuit (4, 5), configured to rectify a current drawn from the ballast to generate a rectified current, and

- an LED circuit (8) connected to receive the rectified current, the LED circuit (8) comprising a plurality of groups of LEDs (9, 10, 11, 12, 13) switchable between at least a first circuit configuration and a second circuit configuration, wherein the first circuit configuration comprises a greater number of groups of LEDs connected in series than the second circuit configuration,
wherein the LED lamp arrangement is arranged to switch to the first circuit configuration when the ballast is a magnetic ballast, and switch to the second circuit configuration when the ballast is an electronic ballast, characterized in that
the LED lamp arrangement (1) further comprises an auxiliary circuit (31), configured to define a conductive path connected in parallel with the plurality of groups of LEDs in the second circuit configuration,
wherein the auxiliary circuit (31) comprises a capacitor (39) in the conductive path, wherein the auxiliary circuit (31) is arranged to bypass the plurality of groups of LEDs and to charge the capacitor (39) when the LED lamp arrangement (1) receives a series of bursts from the electronic ballast, and to discharge the capacitor (39) during a time interval between the series of bursts, wherein the time interval between the series of bursts is in a range from 1 millisecond to 300 milliseconds, and wherein the time interval between the series of bursts is substantially a constant.
The LED lamp arrangement (1) according to claim 1, wherein the capacitor (39) has a capacitance in a range of 10 µF - 50 µF.
The LED lamp arrangement (1) according to claims 1 or 2, wherein the conductive path does not comprise an inductor connected in series with the capacitor.
The LED lamp arrangement (1) according to any of the preceding claims, wherein the auxiliary circuit (31) further comprises a control circuit (36), configured to control an operation of the LED lamp arrangement (1).
The LED lamp arrangement (1) according to claim 4, wherein a first end of the capacitor (39) is electrically connected to a voltage supply terminal of the control circuit (36), and a second end of the capacitor (39) is connected to a common.