CN108430129B

CN108430129B - LED lamp for placing in a fluorescent lamp fixture

Info

Publication number: CN108430129B
Application number: CN201710086821.5A
Authority: CN
Inventors: 丁实宇; 李志峰
Original assignee: Ledvance GmbH
Current assignee: Ledvance GmbH
Priority date: 2017-02-14
Filing date: 2017-02-14
Publication date: 2020-10-09
Anticipated expiration: 2037-02-14
Also published as: CN108430129A; DE102018102643A1; DE102018102643B4

Abstract

An LED lamp for placement in a fluorescent lamp fixture having a ballast (60) is provided, the LED lamp comprising: a plurality of light emitting diodes (11); a detection circuit (64) adapted to generate a control signal indicative of whether the ballast (60) is a conventional ballast or an electronic ballast; and a first control circuit (61,65) adapted to be coupled between the ballast (60) and the light emitting diode (11) during a start-up sequence of the ballast (60) in dependence on the control signal. During a start-up sequence, the first control circuit (61,65) stabilizes the voltage drop along the light emitting diode (11).

Description

LED lamp for placing in a fluorescent lamp fixture

Technical Field

The present invention relates to an LED lamp for placement in a fluorescent lamp fixture.

Background

Fluorescent lamps have been known and widespread as effective replacements for incandescent light bulbs for many years. However, with the advent of LED lamps, an even more efficient and longer life lighting device is available. Furthermore, the material of LED lamps is safer compared to fluorescent lamps, since for example mercury is not required. Therefore, there is a need to replace existing fluorescent lamps with LED lamps, preferably without changing the entire lighting device or luminaire.

Currently available fluorescent light fixtures include a conventional ballast (also known as a conventional control, CCG) or an electronic ballast (also known as an electronic control, ECG) for regulating and limiting the current provided to the fluorescent light.

Conventional ballasts (also known as magnetic ballasts) limit AC current by using an inductor with a frequency-dependent impedance. These ballasts operate the lamps at the operating frequency of the main voltage source, typically 50Hz or 60 Hz. About 10% to 20% of the lighting device power is lost in the form of heat due to ohmic losses in the inductor, making conventional ballasts less efficient.

In contrast to conventional ballasts, electronic ballasts operate the lamps at high frequencies of a few kHz (up to 50 kHz). The frequency of the electronic ballast is selected such that the resonant frequency of the lighting device, in particular the fluorescent gas, is reached, thereby enabling an effective control of the current through the fluorescent lamp. This improves the efficiency of the electronic ballast compared to conventional ballasts.

In order to provide an LED lamp compatible with the above-described luminaire, the LED lamp comprises an electronic driver for adapting the voltage and current provided by the ballast to meet the requirements of the light emitting diode. Otherwise, the electronic and/or optoelectronic components of the LED lamp may be damaged or destroyed by the ballast due to the high voltage generated, in particular, during the start-up sequence.

However, currently available LED lamps are only suitable for conventional ballasts or electronic ballasts. Furthermore, the electronic ballast may also require some changes in the lamp (e.g., changing electrical connections), and thus replacing the fluorescent lamp with an LED lamp is a complicated and uneconomical task.

Disclosure of Invention

In view of the above-mentioned disadvantages of currently available LED lamps, one object of the present invention is to: a universal LED lamp that can be placed in both fluorescent lamp fixtures with conventional ballasts and fluorescent lamp fixtures with electronic ballasts is provided without substantially changing the electrical connections of the conventional ballasts and the electronic ballasts.

This object is achieved by an LED lamp according to the independent claim. The dependent claims, the description and the drawings present preferred embodiments.

Accordingly, an LED lamp for placement in a fluorescent lamp fixture having a ballast is provided. The LED lamp comprises a plurality of light emitting diodes, a detection circuit and a first control circuit. The detection circuit is adapted to generate a control signal indicative of whether the ballast of the lamp is a conventional ballast or an electronic ballast. Furthermore, the first control circuit is adapted to be coupled between the ballast and the light emitting diode of the lamp during a start-up sequence of the ballast in dependence on the control signal, wherein during the start-up sequence the first control circuit stabilizes the voltage drop along the light emitting diode.

The use of the detection circuit in combination with the first control circuit ensures that the LED lamp can be installed in a luminaire with a conventional ballast as well as in a luminaire with an electronic ballast. In order to allow use with an electronic ballast, high voltages that may occur during a start-up sequence of the electronic ballast are balanced and stabilized by the first control circuit. Preferably, the voltage drop along the light emitting diode is reduced during the start-up sequence.

Here and in the following, the "start-up sequence" of the electronic ballast is a short duration just after switching on the lamp installed in the luminaire. In the case of a fluorescent lamp installed in a lamp, the start-up sequence of the ballast includes preheating and ignition. During preheating, the fluorescent lamp connected to the ballast acts as a high value resistor, resulting in an increase in the voltage at the lamp. In the ignition mode, the electronic ballast generates a high voltage (in excess of 600V, up to about 1.1kV) to ignite the fluorescent lamp. During ignition, current flows through the fluorescent gas, switching the fluorescent gas to a low impedance mode that can cause the output voltage of the electronic ballast to drop. After the start-up sequence, the electronic ballast of the lamp switches into a so-called normal operating mode. Preferably, the LED lamp is operated in the normal operation mode during the entire operation period except for the duration of the start-up sequence.

The startup sequence of the electronic ballast can cause damage to the electronic components in the LED lamp. In particular, LED lamps comprise an electronic driver with a main control circuit for transforming the voltage and/or current provided by the lamp into the operating conditions of the light emitting diodes. For example, the driver ensures that a constant output current is provided to the light emitting diodes of the LED lamp. The main control circuit of the drive may then comprise, for example, a switched mode power supply with an AC/DC controller. If the driver starts slowly, especially if the driver has a constant current output, the electronic ballast can skip the preheat mode and the ballast can go directly to the ignition mode. This behavior is triggered by the internal controller of the ballast of the lamp. By skipping the preheat mode, a high voltage is generated by the electronic ballast connected to the driver (which ultimately damages the driver or other electronic components of the LED lamp). On the other hand, if the ballast is unable to provide enough voltage to start the driver, the light emitting diode will flash during the preheating of the ballast.

The above-mentioned problems can be overcome by adding the first control circuit to a driver of, for example, an LED lamp, and the LED lamp can be installed in a conventional luminaire with an electronic ballast. In conjunction with the detection circuit, a universal LED lamp is provided that can be used with an electronic ballast or a conventional ballast. Here, in case the ballast is an electronic ballast, the first control circuit may be coupled between the input of the driver and the main control circuit of the driver.

According to at least one embodiment of the LED lamp, during a start-up sequence, an impedance between a ballast and a light emitting diode of the luminaire is increased by the first control circuit. In particular, in case the ballast is an electronic ballast, the first control circuit may provide a known impedance which is added to the impedance of the driver. This results in a voltage change along the driver, thereby protecting the driver.

According to a preferred embodiment of the LED lamp, the first control circuit is coupled between the ballast and the light emitting diode of the luminaire only in case the ballast is an electronic ballast. That is, in the case where the ballast is a conventional ballast, the first control circuit is not coupled between the ballast and the light emitting diode. For example, the conventional ballast may be directly coupled with the main control circuit of the driver of the LED lamp, thereby ensuring that losses that may occur due to additional electronic components of the first control circuit are reduced (preferably avoided).

According to at least one embodiment, the LED lamp includes a main control circuit. The main control circuit is adapted to be coupled between the light emitting diode and the ballast of the lamp after a start-up sequence and/or in case the ballast is a conventional ballast. The main control circuit preferably corresponds to the above-described main control circuit as part of the driver of the LED lamp. The LED lamp may comprise a switch (e.g. a transistor or MOSFET) allowing switching between the first control circuit and the main control circuit. The main control circuit may supplement or replace the first control circuit in the case of a conventional ballast and/or after a start-up sequence of the electronic ballast. Preferably, the first control circuit is replaced by a main control circuit. In other words, after the start-up sequence and/or in case of a conventional ballast, the first control circuit may be decoupled from the ballast and the light emitting diode. Then, the LED lamp enters a normal operation mode. For example, the first control circuit and/or the main control circuit may comprise electronic components adapted to determine the end of the start-up sequence, thereby allowing the main control circuit to replace the first control circuit after the start-up sequence. Preferably, the main control circuit comprises or is a switched mode power supply.

According to at least one embodiment of the LED lamp, the first control circuit accelerates the start of the main control circuit of the LED lamp. For example, in case the main control current is a switched mode power supply, the output of the first control circuit is coupled to a start-up circuit of the main control circuit to support the accumulation of current with the main control circuit. This embodiment is particularly advantageous when the electronic ballast skips the preheat mode and directly enters the ignition mode with the LED lamp coupled to the electronic ballast. Skipping the preheat mode when the LED lamp is connected to the ballast of the fixture may be a characteristic of some electronic ballasts, particularly constant current electronic ballasts. The start-up of a switched-mode power supply is usually relatively slow compared to the start-up of an electronic ballast. Thus, during start-up, a high voltage is generated in the switched-mode power supply of the main control circuit (said voltage is added to the high ignition voltage). This high voltage can damage the electronic components of the LED lamp. Accelerating the start-up of the main control circuit enables the constant current source to interact correctly with the main control circuit, thereby protecting the electronic components of the main control circuit from high voltages.

In accordance with at least one embodiment of the LED lamp, the first control circuit includes a first transistor that is activated during a startup sequence and a second transistor that is deactivated during the startup sequence. Additionally or alternatively, the first transistor may be deactivated during a normal mode of operation and the second transistor may be activated during the normal mode of operation. In this context, "activated" means that the transistor is turned on (i.e., conducting and/or through-connected). Vice versa, "deactivate" means that the transistor is switched off (i.e., blocked). For example, the first transistor is coupled to an output of the detection circuit that provides the control signal. The second transistor may be coupled to an output of the first control circuit that may provide a signal at the end of the start-up sequence. In addition or as an alternative, the second transistor may be coupled to a feedback circuit of the light emitting diode, which allows to control the voltage provided at the light emitting diode.

In accordance with at least one embodiment of the LED lamp, the first control circuit is coupled to a flyback controller coupled to an output of the first transistor. The flyback controller may include, for example, a schottky diode or a zener diode. Preferably, the flyback controller is coupled to the second transistor. During the start-up sequence, the flyback controller may block current flow to the second transistor. After the start-up sequence, the voltage provided by the ballast may be reduced, deactivating the first transistor and causing the flyback controller to switch to a conduction mode and activating the second transistor.

According to at least one embodiment of the LED lamp, after the start-up sequence, the first control circuit is decoupled (in particular, fully decoupled) from the light emitting diode and the ballast of the luminaire. Decoupling may be achieved, for example, by using a transistor (particularly the second transistor described above) in conjunction with the flyback controller and/or the start-up circuit. The start-up circuit may correspond to a common start-up circuit for a switched-mode power supply.

According to at least one embodiment of the LED lamp, the first control circuit is a constant current circuit. Preferably, the constant current circuit provides a constant current to the light emitting diode during the start-up sequence. Preferably, the constant current circuit has a fast turn-on behavior, such that the high voltage provided by the ballast of the lamp during the start-up sequence is balanced and preferably reduced.

According to at least one embodiment of the LED lamp, the first control circuit is a suppression circuit, in particular, having a low impedance. Due to the low impedance, the current provided by the ballast of the lamp can flow directly to the light emitting diode and the start-up of the main control circuit of the LED lamp can be accelerated. In addition, the first control circuit can provide a low impedance loop for the electronic ballast during the startup sequence, thereby preventing the electronic ballast from generating a high voltage.

According to a preferred embodiment of the LED lamp, the detection circuit determines an operating frequency of a ballast of the luminaire in order to provide the control signal. In the case of an electronic ballast, the operating frequency may be relatively high. Conventional ballasts typically operate at the lower frequency provided by the main power supply. Thus, the type of ballast can be determined by determining the operating frequency. Preferably, the measurement of the operating frequency is performed before the rectifier circuit of the LED lamp.

Drawings

Hereinafter, preferred embodiments of the present invention will be described in consideration of the accompanying drawings.

Fig. 1A shows a start-up sequence for an electronic ballast of a lamp according to an embodiment of an LED lamp of the present invention.

FIG. 1B shows an exemplary embodiment of an alternative lamp.

Fig. 2, 3, 4 and 5 show embodiments of LED lamps according to the invention.

Fig. 6A and 6B illustrate an exemplary embodiment of an alternative LED lamp.

Fig. 7A, 7B, 7C, 7D, 8A, 8B and 8C show measurement results for an embodiment of an LED lamp according to the present invention.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Here, in the drawings, elements that are the same, similar, or have the same or similar effects are provided with the same reference numerals. The drawings and the dimensional relationships between elements shown in the drawings should not be considered to be proportional. Rather, individual elements may be shown with exaggerated dimensions to enable better illustration and/or better understanding.

With reference to fig. 1A, an exemplary embodiment of a start-up sequence of an electronic ballast of a luminaire of LED lamps according to the present invention will be described in detail. Here, the first exemplary voltage drop 14 in the case where a load is connected to the ballast and the second exemplary voltage drop 15 in the case of the ballast without a load are described in units of volts. The no-load condition 15 may correspond to a condition after ignition (ignition) of the fluorescent gas of the fluorescent lamp.

After turning on the lamp, the electronic ballast enters a preheat mode 100 in which the operating frequency v is reduced and the first exemplary voltage drop 14 is increased accordingly. The ignition mode 101 is entered at a specific frequency, which may correspond to the resonance frequency of the fluorescent gas. At this time, the fluorescent gas is lit (i.e., ignited). Fluorescent lamps are now substantially unloaded due to ignition. Thus, the voltage drops to the second exemplary voltage drop 15 of the post-ignition mode 102, where the operating frequency v remains unchanged. The operating frequency v is then further reduced until the operating point of the operating mode 103 is reached.

Referring to fig. 1B, an exemplary embodiment of an alternative lamp without a detection circuit and/or a first control circuit according to the present invention is detailed. The replacement lamp may comprise a conventional fluorescent lighting fixture 10. The lighting device 10 is connected to the ballast 60 via several electronic components which may be part of the driver of the lamp. Thus, the replacement lamp may be a conventional fluorescent lamp with ballast 60. Two transistors 20 and two diodes 50 may be coupled between ballast 60 and lighting device 10 to provide a rectifier circuit. For example, the rectifier circuit may convert an AC current provided by the ballast 60 into a DC current. As another example, the rectifier circuit protects the lighting device 10 if the lamp is installed in the fixture in the wrong orientation, resulting in the wrong polarity of the electrical connection.

The transistor 20 may be a FET transistor or a MOSFET transistor. Although the respective transistors 20 and the respective diodes 50 are described with the same reference numerals, the respective transistors 20 and the respective diodes 50 may be differently implemented. That is, the two transistors 20 and/or the two diodes 50 may have different characteristics depending on the particular application of the driver.

The lighting device 10 is also connected in parallel with the first capacitor 31 and in series with the second capacitor 32 and the first inductor 41. The first capacitor 31 serves as a smoothing capacitor for the light emitting diode 11 of the lighting device 10. For example, the first capacitor 31 may be an electrolytic capacitor. These electronic components ensure the compatibility of the light emitting diodes of the lighting device 10 with the ballast 60.

The ballast 60 of fig. 1B in place of the lamp may be, for example, an electronic ballast. Here, the rectifier circuit, the first inductor 41 and the first capacitor 31 may be considered as part of the electronic ballast.

If the lighting device 10 in a replacement lamp is changed to a light emitting diode in order to provide an LED lamp, the ballast 60 may destroy some components of the lighting device 10. This is because the electronic ballast 60 may skip the preheat mode and go directly to the ignition mode when connected to the LED lighting device 10. By providing the LED lamp according to the present invention, the conventional fluorescent lamp 10 replacing the lamp can be replaced by the LED lighting device 10, so that an LED lamp as a retrofit of the fluorescent lamp can be provided without damaging the components of the LED lamp.

Referring to fig. 2 and 3, an embodiment of the LED lamp according to the present invention is described in detail. In the described embodiment, the LED lamp comprises a first control circuit implemented as a constant current circuit 61 (also referred to as a constant sink current circuit).

The LED lamp has a lighting device 10, wherein the lighting device 10 has a light emitting diode 11 connected to a ballast 60 via several electronic components of a driver of the LED lamp. The ballast 60 may be a conventional ballast or an electronic ballast.

The ballast 60 is connected to the electronic circuit of the driver via several resistors 70 in parallel. After the driver, the rectifier circuit with four diodes (i.e. the first diode 51, the second diode 52, the third diode 53 and the fourth diode 54), the bulk capacitor 33 and the connection to ground GND ensure the correct polarity and frequency of the current and/or voltage provided by the ballast 60.

The output of the rectifier circuit is provided to the constant current circuit 61 via a general connection 610. The ballast 60 is also directly coupled to the detection circuit 64. The detection circuit 64 provides a control signal depending on whether the ballast 60 is a conventional ballast or an electronic ballast. The output of the detection circuit 64 is transmitted to the constant current circuit 61 via the first connection 611 and the second connection 612. The third connection 613 leads to a delay circuit 63 and a flyback controller 62 as further components of the driver. The output of the AC/DC controller 62 is then provided to the lighting device 10 via a first transistor 21 (e.g., a FET or MOSFET) in series with a first resistor 71. In parallel with the above components, the output of ballast 60 may also be coupled to lighting device 10 via a direct path.

The lighting device 10 is connected to an LC circuit with a first capacitor 31 and a second inductor 42, wherein the second inductor 42 in combination with a further second inductor 42 constitutes a transformer. The transformer may transform the voltage provided by the switched mode power supply into the operating voltage of the light emitting diodes 11.

Fig. 3 shows the constant current circuit 61 and the AC/DC controller 62 in detail. Here, the bus voltage U_BIs provided to the electronic components at the rectifier circuit. The constant current circuit 61 and the flyback controller 62 include resistors, specifically, a second resistor 72, a third resistor 73, a fourth resistor 74, and a fifth resistor 75. In addition, the constant current circuit 61 and the flyback controller 62 include a fifth diode 55 (which may be a schottky diode or a zener diode) and the second transistor 22. In particular, the flyback controller 62 may correspond to the fifth diode 55. Both the first transistor 21 and the second transistor 22 may be implemented as FETs or MOSFETs.

When the LED lamp is turned on, the detection circuit 64 determines which type of ballast 60 is connected to the LED lamp, for example, by measuring the operating frequency v. Then, the control signal of the detection circuit 64 is supplied to the constant current circuit 61 and the flyback controller 62 via the first connection 611 and the second connection 612. In particular, the first transistor 21 is controlled by the detection circuit 64. The first transistor 21 is only activated when the ballast 60 is an electronic ballast. In this case, the first transistor 21 operates in a constant current mode, and the constant current circuit 61 is coupled between the ballast 60 and the light emitting diode 11.

The first transistor 21 is activated when the voltage at the input of the first transistor 21 reaches the threshold of the transistor. Then, a current will flow through the first resistor 71. The gate voltage of the first transistor 21 is regulated via the fifth diode 55 so that the first transistor 21 operates in the constant current mode. Furthermore, this may allow the functionality of an AC/DC controller to be provided.

After the start-up sequence, the fifth diode 55 and/or the flyback controller 62 switches from the blocking mode to the conducting mode due to a voltage drop in the circuit. This causes the second transistor 22 to be activated (i.e., turned on). The first transistor 21 and the second transistor 22 are connected such that the second transistor 22 can turn off the first transistor 21 when the second transistor 22 is activated. Thus, after the start-up sequence, the first transistor 21 is turned off, and the first control circuit (i.e., the constant current circuit 61) is decoupled from the ballast 60 and the lighting device 10 having the light emitting diode 11.

In case the ballast 60 is a conventional ballast, the first transistor 21 is not activated, which results in the constant current circuit 61 not being coupled to the ballast 60 and/or the light emitting diode 11.

The above-described embodiments of the LED lamp according to the present invention not only achieve a reduction in the ignition voltage of the electronic ballast to avoid damage to the driver, but also achieve easy control of the operating voltage, improved system efficiency due to the constant current circuit 61 not generating additional losses in the normal operation mode after the start-up sequence, and a reduction in response time when the electronic ballast 60 is switched on or off quickly.

Referring to fig. 4 and 5, an embodiment of the LED lamp according to the present invention is described in detail. In the depicted embodiment, the LED lamp includes a first control circuit implemented as a suppression circuit 65.

As mentioned before, the driver of the LED lamp comprises a rectifier circuit with four

diodes

51, 52, 53, 54. The output of the rectifier is coupled to a start-up circuit 621 and then to the AC/DC controller 67.

Furthermore, the detection circuit 64 is coupled to the ballast 60 and the suppression circuit 65, wherein the first connection 651 and the second connection 652 lead to the suppression circuit 65. The third connection 653 constitutes the output to the lighting device 10 with the light emitting diode 11, the first capacitor 31 and the suppression circuit 65 of the second inductor 42 (which again constitutes a transformer with the further second inductor 42). The circuitry of the lighting device 10 may also include a resistor 70 and a diode 50 for further regulating the current and/or voltage provided to the light emitting diode 11.

The overall connection 650 connects the suppression circuit 65 to the AC/DC controller 67 via the further second inductor 42, the transistor 20 and the resistor 70. Transistor 20 may function as a flyback circuit, particularly when combined with a transformer formed by inductor 42. Further, the feedback circuit 66 is connected to the AC/DC controller 67 and the circuit of the lighting device 10, which enables optimization of the operating voltage of the light emitting diode 11.

Fig. 5 shows the suppression circuit 65 according to fig. 4 in detail. Here, all electronic components in fig. 4 are not described in detail.

The suppression circuit 65 includes a first resistor 71, a second resistor 72, a third resistor 73, a fourth resistor 74, and a fifth resistor 75. Further, the suppression circuit 65 includes the first and

second transistors

25 and 26, the second capacitor 32, and the sixth diode 56. The sixth diode 56 may be, for example, a zener diode or a schottky diode. The third resistor 73 is connected in parallel with the second capacitor 32 and in turn connected in parallel with the sixth diode 56. The output of the parallel circuit is then coupled to a seventh diode 57 providing an output at a third connection 653. Then, the output of the seventh diode 57 is coupled to the start-up circuit 621 via the eighth diode 58 and the fifth resistor 75. A coupling to ground GND is provided via a fourth resistor 74 and the second transistor 26.

If the LED lamp is connected to the electronic ballast, the second transistor 26 is switched off (i.e., deactivated) by the control signal provided by the detection circuit 64. Therefore, there is no connection to ground GND. The rising voltage provided by the electronic ballast during the start-up sequence activates the first transistor 25. Thus, the output current of the electronic ballast will flow to the light emitting diode 11, the first capacitor 31 and, if applicable, the diode 50 connected in parallel to the light emitting diode 11 (see fig. 4). Then, the high voltage is suppressed by the load of the electronic component.

The accumulated current (built-up current) at the third connection 653 flows through the eighth diode 58 into the start-up circuit 621. This allows to prevent or at least reduce the flickering of the light emitting diode 11 during the start-up sequence due to low voltages in the main circuit during the warm-up process.

After the main circuit is started up, the whole circuit switches to a low impedance mode, which results in the input voltage being lower than the operating voltage of the light emitting diode 11, resulting in deactivation of the first transistor 25. The suppression circuit 65 is thus deactivated and decoupled from the ballast 60 and the light emitting diode 11.

If ballast 60 is a conventional ballast, second transistor 26 is activated and suppression circuit 65 is coupled to ground GND. Therefore, the suppression circuit 65 is not coupled between the ballast 60 and the light emitting diode 11. The output of the ballast 60 is then transmitted directly to the light emitting diode 11 via other components, in particular the transformer consisting of two second inductors 42 as shown in fig. 4.

The embodiments of the LED lamp shown in fig. 4 and 5 provide improved compatibility of the LED lamp with an electronic ballast. In particular, the ignition voltage is reduced and the high voltage generated by the electronic ballast is suppressed. Furthermore, the reliability of the driver circuit is improved due to the use of durable and reliable electronic components. In the normal operating mode after the start-up sequence or in the case where ballast 60 is a conventional ballast, the suppression circuit 65 will not consume any power.

Referring to fig. 6A and 6B, an exemplary embodiment of an alternative LED lamp is described in detail. The alternative LED lamp does not comprise the

first control circuit

61,65 according to the invention. In contrast, the first resistor 71 is connected in parallel with the ignition capacitor of the ballast 60. Since the first resistor 71 shifts the resonant frequency of the LC circuit of the lighting device 10 to a lower frequency, the first resistor 71 may reduce the ignition voltage during the start-up sequence.

This can be seen in fig. 6B, which shows the simulated voltage drop (arbitrary units, a.u.) as a function of the operating frequency v (arbitrary units, a.u.). Here, the first curve 81, the second curve 82, the third curve 83, the fourth curve 84, the fifth curve 85, and the sixth curve 86 are shown when the value of the first resistor 71 is 200 Ω, 400 Ω, 600 Ω, 800 Ω, 1000 Ω, and 800k Ω, respectively.

An increase in the value of the first resistor 71 results in a higher shift in the resonance frequency, so that the ignition voltage decreases. However, the first resistor 71 causes high loss of the system and reduces the efficiency of the system.

Referring to fig. 7A, 7B, 7C, 7D, 8A, 8B and 8C, an embodiment of the LED lamp according to the present invention is explained in detail. Here, the measurement results of the ECG output voltage 91, the LED driver output current 92, the current 93 flowing through the constant current circuit 61, and the LED driver input current 94 are shown. The ECG output voltage 91 may correspond to the LED input voltage after the rectifier bridge circuit. Fig. 7A, 7C and 8A show measurement results for LED lamps without the

first control circuit

61,65 according to the invention, fig. 7B and 7D show measurement results for LED lamps with the first control circuit 61 according to the embodiment of fig. 2 and 3, and fig. 8B and 8C show measurement results for LED lamps with the first control circuit 65 according to the embodiment of fig. 4 and 5.

For the measurements of fig. 7A, 7C and 8A, an electronic ballast (ECG) is connected to the LED lamp without the

first control circuit

61,65 as explained in connection with fig. 2 to 5. Here, different types of electronic ballasts were selected for the measurement results of fig. 7A, 7C, and 8A (Osram QT-FIT 5/81X 18-39 in fig. 7A, Osram QT-FIT81X18 in fig. 7C, and Osram QT FIT 5/81X 54-58 in fig. 8A). The electronic ballast is then switched on and off very quickly so that the electronic ballast skips the preheat phase and measures the ECG output voltage 91. The electronic ballast provides high output voltages up to 588V (fig. 7A), up to 606V (fig. 7C), or up to 605V (fig. 8A).

For the measurement results of fig. 7B and 7D, a first control circuit implemented as the constant (sink) current circuit 61 explained with reference to fig. 2 and 3 is connected to the electronic ballast of fig. 7A and 7C, respectively. The lower part of fig. 7B and 7D show the start-up sequence t, respectively_ZThe amplified measurement during time. Again, the electronic ballast is switched on and off quickly and the preheat phase is skipped. Thus, the current 93 flowing through the first transistor 21 and thus the constant current circuit 61, the LED driver output current 92 and the ECG output voltage 91 are measured. The constant current circuit 61 reduces the ECG output voltage 91 to a maximum of 210V (fig. 7B) or 284V (fig. 7D). In a start sequence t_ZMeanwhile, the constant current circuit 61 is in the start-up sequence t_ZDuring which it is coupled between the electronic ballast and the light emitting diode 11 of the LED lamp, so that the current through the constant current circuit 61 increases. LED driver output current 92 during start-up sequence t_ZThe period is relatively constant. In a start sequence t_ZThereafter, when the driver enters a normal operating mode, the LED driver outputsCurrent 92 increases and reaches a steady state value.

For the measurement results of fig. 8B and 8C, at the start-up sequence t_ZMeanwhile, a first control circuit implemented as the suppression circuit 65 as explained in connection with fig. 4 and 5 is connected with the electronic ballast. In fig. 8B, only the start-up sequence is measured. In fig. 8C, the electronic ballast is switched on and off quickly. The lower part of FIG. 8C shows the start sequence t_ZThe amplified measurement during time. Here, the ECG output voltage 91 (which corresponds to the LED driver input voltage after the rectifier bridge voltage) and the LED driver input current 94 (which flows through the light emitting diode 11) are measured. The suppression circuit 65 reduces the maximum voltage to 114.7V (fig. 8B) or 135.9V (fig. 8C).

The present invention is not limited to the description based on the embodiment. Rather, the invention encompasses any novel feature and any combination of features, in particular any combination of features in the patent claims, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.

List of reference numerals

10: lighting device

100: preheating mode

101: ignition mode

102: post-ignition mode

103: mode of operation

11: light emitting diode

14: first exemplary Voltage drop

15: second exemplary Voltage drop

20: transistor with a metal gate electrode

21. 25: a first transistor

22. 26: second transistor

31: first capacitor

32: second capacitor

33: large-capacity capacitor

41: first inductor

42: second inductor

50: diode with a high-voltage source

51. 52, 53, 54, 55, 56, 57, 58: a first diode, a second diode, a third diode, a fourth diode, a fifth diode, a sixth diode, a seventh diode, and an eighth diode

60: ballast with a current limiting circuit

61: constant current circuit

610. 650: general connection

611. 651: first connection

612. 652: second connection

613. 653: third connection

62: flyback controller

621: starting circuit

63: delay circuit

64: detection circuit

65: suppression circuit

66: feedback circuit

67: AC/DC controller

71. 72, 73, 74, 75: first, second, third, fourth and fifth resistors

81. 82, 83, 84, 85, 86: a first curve, a second curve, a third curve, a fourth curve, a fifth curve and a sixth curve

91: ECG output voltage

92: LED driver output current

93: current flowing through constant current circuit

94: LED driver input current

V: frequency of operation

U_B: bus voltage

GND: ground

t_Z: start-up sequence

Claims

1. An LED lamp for placement in a fluorescent lamp fixture having a ballast (60), the LED lamp comprising:

a plurality of light-emitting diodes (11),

a detection circuit (64) adapted to generate a control signal indicative of whether the ballast (60) is a conventional ballast or an electronic ballast,

a first control circuit (61,65) adapted to be coupled between a ballast (60) of the lamp and the light emitting diode (11) during a start-up sequence of the ballast (60) in dependence of the control signal, and

a main control circuit adapted to be coupled between the light emitting diode (11) and a ballast (60) of the luminaire after a start-up sequence and/or in case the ballast (60) is a conventional ballast

Wherein during the start-up sequence the first control circuit (61,65) stabilizes a voltage drop along the light emitting diode (11) and

wherein the first control circuit (61,65) accelerates the start-up of the main control circuit.

2. The LED lamp of claim 1, wherein during a start-up sequence the first control circuit (61,65) increases the impedance between the ballast (60) of the luminaire and the light emitting diode (11).

3. LED lamp according to claim 1 or 2, wherein the first control circuit (61,65) is coupled between the ballast (60) of the luminaire and the light emitting diode (11) only if the ballast (60) is an electronic ballast.

4. LED lamp according to claim 1 or 2, wherein the first control circuit (61,65) comprises a first transistor (21,25) which is activated during a start-up sequence and a second transistor (22,26) which is deactivated during a start-up sequence.

5. The LED lamp of claim 4, wherein the first control circuit (61,65) is coupled with a flyback controller (62) coupled to an output of the first transistor (21, 25).

6. LED lamp according to claim 1 or 2, wherein the first control circuit (61,65) is decoupled from the light emitting diode (11) and a ballast (60) of the luminaire after a start-up sequence.

7. LED lamp according to claim 1 or 2, wherein the first control circuit (61,65) is fully decoupled from the light emitting diode (11) and the ballast (60) of the luminaire.

8. The LED lamp of claim 1 or 2, wherein the first control circuit (61,65) is a constant current circuit (61).

9. The LED lamp of claim 1 or 2, wherein the first control circuit (61,65) is a suppression circuit (65).

10. LED lamp according to claim 1 or 2, wherein the detection circuit (64) determines an operating frequency of a ballast (60) of the luminaire to provide the control signal.