Tubular LED lamp and circuit for such lamp

Abstract

A tubular LED lamp for use with an external electronic power control device, the external electronic power control device being adapted to supply an input voltage to the lamp, the tubular LED lamp comprising: an LED unit; a drive circuit for the LED unit; and a safety detection circuit adapted to detect whether the tubular LED lamp is correctly connected to an external luminaire; characterized in that it further comprises: a holding current supply circuit adapted to supply a holding current through the electronic control device to keep the electronic control device conducting; and a control circuit adapted to synchronize the safety detection circuit with the holding current supply circuit such that when the holding current supply circuit is adapted to supply the holding current and the electronic control device is conducting, the safety detection circuit is adapted to perform the detection; wherein the control circuit is adapted to deactivate the holding current supply circuit and the safety detection circuit after detection in one cycle of the input voltage, and reactivate and deactivate the holding current supply circuit and the safety detection circuit in a later cycle.

Description

Technical Field

[0001] The present invention relates to the field of LED lighting units, and more particularly to a rectifying arrangement for a tubular LED lamp. Background Art

[0002] DE102013108775A1 discloses an LED tube having the ability to detect a ground fault when contacting at least one pin contact, wherein the contact is made by a user / person. US 20180324925 of the present applicant also discloses a more specific topology for detecting whether there is a human body impedance between a power supply and a tubular LED lamp. WO2018097858A1 discloses a linear LED lamp having a current sensing device initially used to control the current flowing into an LED array, and the current sensing device is used in a manner that also detects a shock current. To meet safety requirements / regulations, such safety functions are becoming increasingly popular in tubular LED lamps.

[0003] There is another trend to make LED lamps, including tubular LED lamps, dimmable in order to save energy when needed. LED bulbs or luminaires compatible with TRIAC dimmers have been available for many years. However, for tubular LED lamps having a ground fault / human contact detection function, they are not directly compatible with TRIAC dimmers because TRIAC dimmers require a special operating current, which may interfere with the human contact detection of the tubular LED lamp. Summary of the Invention

[0004] The object of the present invention is to provide a tubular LED lamp having both a reliable human touch detection function and compatibility with an electronic switch such as a TRIAC dimmer.

[0005] As is well known in the art, an electronic switch such as a TRIAC dimmer requires a minimum operating current. For example, the TRIAC in a TRIAC dimmer needs to maintain a current to keep it on after it has been turned on (fired). The basic idea of an embodiment of the present invention is to provide a holding current synchronized with the safety detection function, so that the safety detection function can electrically access the input voltage to determine whether the lamp is correctly connected to the luminaire, preferably to determine whether there is a human body impedance therebetween. In addition, the basic idea of an embodiment of the present invention is to deactivate the holding current and the safety detection after detection in one cycle, and reactivate the holding current and the safety detection in a later cycle, so that the detection can be performed for several cycles to confirm a safe connection, while the detection is not continuous. The advantages are that the power loss of the detection is reduced, and the time-averaged current flowing through a potentially present person (including the holding current and the detection current) is reduced, so that the person is safer under this detection process.

[0006] According to a first aspect of the present invention, a tubular LED lamp for use with an external electronic power control device adapted to provide an input voltage to the lamp, comprises:

[0007] an LED unit;

[0008] a drive circuit for the LED unit;

[0009] a safety detection circuit for performing a safety detection to detect whether the tubular LED lamp is correctly connected to an external lamp;

[0010] characterized in that, for each cycle of the input voltage, it further comprises:

[0011] a holding current providing circuit for providing a holding current through the electronic control device to keep the electronic control device conducting;

[0012] a control circuit for synchronizing the safety detection circuit with the holding current providing circuit such that when the holding current providing circuit is adapted to provide the holding current and the electronic control device is conducting, the safety detection circuit is adapted to perform the safety detection;

[0013] wherein the control circuit deactivates the holding current providing circuit and the safety detection circuit after the safety detection in a cycle of the input voltage, and reactivates and deactivates them in a later cycle.

[0014] In short, the holding current providing circuit and the safety detection circuit do not operate continuously, but operate in a synchronous and pulsed manner in consecutive cycles of the input voltage. This reduces the duration during which the holding current and the safety detection current flow, reduces the power loss for safety detection and the average current through a potentially present human body, thus making people safer.

[0015] In another embodiment, the tubular LED lamp is used with a TRIAC dimmer circuit and further comprises a trigger circuit to trigger the electronic control device to become conducting according to the cycle of the input voltage, and the trigger circuit is adapted to draw an ignition current to charge an energy storage component in the TRIAC dimmer so as to reach the conduction voltage threshold of the TRIAC in the TRIAC dimmer, and the holding current providing circuit is adapted to provide a holding current which is adapted to keep the TRIAC in the TRIAC dimmer conducting.

[0016] This embodiment is particularly directed to compatibility with a TRIAC dimmer. The tubular LED lamp draws an ignition current and a holding current for the TRIAC in the TRIAC dimmer, so that the TRIAC dimmer can conduct and remain normally conducting.

[0017] In another embodiment, the control circuit is adapted to detect a voltage front edge to determine that the electronic control device has become conducting, and to activate the holding current providing circuit and the safety detection circuit.

[0018] This embodiment is designed for a front edge dimmer. When the dimmer becomes conducting, the voltage to the tubular lamp will rise rapidly, so this can be used to indicate that the dimmer has become conducting.

[0019] In one embodiment, the control circuit is adapted to activate the safety detection circuit with a delay after activating the holding current providing circuit.

[0020] This delay can prevent some oscillations or unstable currents from affecting the safety detection.

[0021] In another embodiment, the trigger circuit is adapted to accumulate a specific amount of energy when triggering the electronic device, and the holding current providing circuit is also adapted to discharge the trigger circuit within a delay to prevent the specific energy from flowing to the safety detection circuit and to allow the trigger circuit to trigger the electronic device in a later cycle of the input voltage.

[0022] The trigger circuit is typically implemented by an RC circuit to draw the firing current. On the one hand, the RC circuit needs to be at least partially discharged so that it can trigger the TRIAC again in the next cycle; and on the other hand, the energy in the RC circuit should not interfere with the safety detection. Therefore, the holding current providing circuit, which acts as a voltage divider, also discharges the RC circuit to prevent the energy in the RC circuit from affecting the safety detection circuit, such as flowing through the safety detection circuit and causing inaccurate detection.

[0023] In another embodiment, the holding current providing circuit and the safety detection circuit respectively include a first switch and a second switch.

[0024] The advantage of having two corresponding switches is that they are controlled separately, and this makes it easier to implement the control.

[0025] In another embodiment, the holding current providing circuit is adapted to provide the holding current via the LED unit. In this embodiment, at the circuit level, the holding current providing circuit can share the current path through the LED unit, thus saving a dedicated current path / component and some costs.

[0026] In another embodiment, the safety detection circuit is adapted to close the second switch with a specific impedance and to detect a detection current exceeding a specific threshold passing through the second switch to determine that the tubular LED lamp is correctly connected to the external lamp fixture. Preferably, if the human body impedance is in series with the lamp with respect to the input voltage, the specific threshold is at a level that the detection current cannot reach.

[0027] This provides a reliable way to detect whether the human body impedance is in series with the tubular lamp. Since the human body impedance (if present) increases the total impedance, the detection current is small and cannot reach a high level; otherwise, the total impedance is small and the detection current may be high.

[0028] In one embodiment, the first switch and the second switch are in parallel, so that the holding current and the detection current are superimposed and detected by the safety detection circuit, which is adapted to exclude the holding current when detecting whether the tubular LED lamp is correctly connected to the external lamp.

[0029] For simplicity of the circuit, the safety detection circuit detects the superimposed current but needs to exclude the holding current. This can be achieved by increasing the amplitude of the holding current to the above specific threshold.

[0030] In one embodiment, the control circuit is adapted to activate the safety detection circuit for several cycles and operate the drive circuit when the safety detection circuit detects that the tubular lamp is correctly connected to the external lamp several times.

[0031] This embodiment repeats the continuous number of times in several cycles respectively, increasing the reliability of the detection.

[0032] In one embodiment, the tubular LED lamp further includes a safety switch between the drive circuit and the input voltage, and the control circuit is adapted to close the safety switch to operate the drive circuit.

[0033] This embodiment provides a safety mechanism to activate the drive circuit to avoid the drive circuit drawing an operation current that is dangerously high for humans when it is not safe.

[0034] In a second aspect of the present invention, a circuit for a tubular LED lamp and an external electronic power control device is proposed, and the circuit includes basic dimming compatibility and safety detection functions. The circuit includes:

[0035] A safety detection circuit for detecting whether the tubular LED lamp is correctly connected to the external lamp;

[0036] Characterized in that for each cycle of the input voltage, it further includes:

[0037] A holding current providing circuit for providing a holding current through the electronic control device to keep the electronic control device conducting;

[0038] A control circuit for synchronizing the safety detection circuit with the holding current providing circuit, so that when the holding current providing circuit is adapted to provide the holding current and the electronic control device is conducting, the safety detection circuit is adapted to perform the detection;

[0039] The control circuit deactivates the hold current supply circuit and the safety detection circuit after detection in one cycle of the input voltage, and re - activates and de - activates the hold current supply circuit and the safety detection circuit in a later cycle of the input voltage.

[0040] With reference to the (s) embodiment(s) described below, these and other aspects of the invention will become apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] For a better understanding of the present invention, and to more clearly show how the present invention may be implemented, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0042] Figure 1 is a block diagram showing the components of an embodiment;

[0043] Figure 2 provides waveforms showing synchronization and pulsed hold current and safety detection in a cycle of the input voltage;

[0044] Figure 3 is a circuit diagram showing an embodiment of the hold current supply circuit and the safety detection circuit; and

[0045] Figure 4 shows current waveforms in both the determined safe and unsafe situations Figure 3 therein. DETAILED DESCRIPTION

[0046] The present invention will be described with reference to the accompanying drawings.

[0047] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are for illustrative purposes only and are not intended to limit the scope of the invention. These and other features, aspects and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, the appended claims and the drawings. It should be understood that the drawings are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings to denote the same or similar parts.

[0048] As Figure 1 shown, a basic embodiment of a tubular LED lamp is used with an external electronic power control device (which is a TRIAC dimmer in Figure 1 ) that is adapted to provide an input voltage Vin to the lamp, the input voltage being AC, and the tubular LED lamp comprising:

[0049] an LED unit, as shown by the LEDs in Figure 1 ;

[0050] A drive circuit for an LED unit, which can be a switching mode power converter, a linear converter, or just a direct electrical connection between the LED and the input voltage; and

[0051] A safety detection circuit for detecting whether the tubular LED lamp is correctly connected to an external lamp, and in Figure 1 it is shown as a leakage current detection circuit;

[0052] It is characterized in that, as also Figure 2 shown, for each cycle of the input voltage, it further includes:

[0053] A holding current supply circuit for providing a holding current through an electronic control device to keep the electronic control device conducting; and

[0054] A control circuit for synchronizing the safety detection circuit with the holding current supply circuit such that when the holding current supply circuit is adapted to provide the holding current and the electronic control device is conducting, the safety detection circuit is adapted to perform the detection.

[0055] As Figure 2 shown, the control circuit deactivates the holding current supply circuit and the safety detection circuit after detection in one cycle of the input voltage, and reactivates and deactivates them in subsequent cycles.

[0056] More specifically, making the LED lamp compatible with a TRIAC dimmer more involves correctly fabricating and keeping the TRIAC dimmer on. To turn on, the tubular LED lamp can have a trigger circuit. The trigger circuit can be implemented as an RC circuit to provide a firing current path for the TRIAC. A resistor and a capacitor are connected in series at the output of an optional bridge rectifier BD of the tubular LED lamp. The TRIAC dimmer is initially in a high impedance state where the TRIAC is off. After the zero crossing of the AC supply voltage, as Figure 2 shown by the top curve in, the AC supply voltage charges the internal energy storage component of the TRIAC dimmer via the trigger circuit of the present invention, and the charging current via the trigger circuit can also be referred to as the firing current If. When the voltage of the energy storage component reaches the threshold for turning on the TRIAC, the TRIAC is turned on, and the TRIAC dimmer becomes low impedance to conduct the input voltage Vin to the tubular LED lamp. This is represented by a cycle on the AC supply curve. As shown, the TRIAC dimmer conducts for approximately 90 degrees of phase, which may mean that the dimming position of the TRIAC dimmer is set at a 50% brightness setting level. It can be understood that the start-up / turn-on of the TRIAC dimmer can vary according to the dimming position of the dimmer and the ability of the trigger circuit to draw a start-up current. In any case, the TRIAC dimmer is turned on.

[0057] Voltage detection (not shown) in the tubular LED lamp can sense a sharp input of the input voltage or the voltage front edge to the tubular lamp and realize that the TRIAC dimmer is turned on. Before the tubular LED lamp starts to work, safety detection must be performed.

[0058] Therefore, in order to perform safety detection, an embodiment of the present invention proposes that after the TRIAC dimmer is turned on, the hold current supply circuit is adapted to provide a hold current Ih, and the hold current Ih is adapted to keep the TRIAC in the TRIAC dimmer conducting. This is shown in Figure 2 the third waveform of. Moreover, during the time period when there is a hold current, it means that the TRIAC dimmer is turned on, and the safety detection circuit performs detection. This is shown in Figure 2 the second waveform of.

[0059] Safety detection, more specifically ground fault detection or pin safety detection, is to determine that there is no human impedance between Vin and the lamp, which can be that the user touches one side pin of the lamp. Pin safety detection is described in DE102013108775A1 and US 20180324925. The basic principle is to detect the magnitude of the current in the loop using a detection impedance before the driver operates: if the current Id is large enough, it means that the impedance in the loop is small (or only the detection impedance), and it is very likely that there is no large human impedance; if the current Id is small, it means that the impedance in the loop is large, and there may be an additional human impedance. If it is determined that there is no person, the tubular LED lamp can work and the driver is enabled with a low impedance; otherwise, the lamp does not work and the driver remains disabled and stays in a high impedance state to limit the current and prevent electric shock to people.

[0060] After a short period of detection, the detection can stop in this period. Along with the stop of the detection, the hold current supply circuit can also stop drawing the hold current Ih. The TRIAC dimmer then turns off, as shown by the triangle in the first curve, reducing the current to the potential human body and power loss. The control circuit will reactivate and deactivate the hold current supply circuit and the safety detection circuit in one or more subsequent cycles, as Figure 2 shown. Of course, the trigger circuit also turns on the TRIAC dimmer in one or more subsequent cycles before the hold current supply circuit is reactivated.

[0061] In one embodiment, the trigger circuit is adapted to accumulate specific energy when triggering the electronic device, such as charging a capacitor in an RC circuit. The hold current supply circuit is also adapted to discharge the trigger circuit within a delay to avoid the flow of specific energy to the safety detection circuit and allow the trigger circuit to trigger the electronic device in subsequent cycles of the input voltage. After activating the hold current supply circuit, the control circuit activates the safety detection circuit through a delay. This can be in Figure 2as seen in. Alternatively, the energy in the trigger circuit is used by the control circuit, the hold current supply circuit, and the safety detection circuit, and thus in subsequent cycles, it can draw sufficient ignition current via the TRIAC dimmer again.

[0062] For a more reliable determination, the control circuit is adapted to activate the safety detection circuit and perform the detection for several cycles, as Figure 2 shown, and operate the drive circuit when the safety detection circuit detects that the tubular lamp is correctly connected to the external lamp fixture several times. As shown by the bottom curve, after four detections with no one touching, the safety signal is pulled high.

[0063] As Figure 1 shown, the tubular LED lamp further includes a safety switch between the drive circuit and the input voltage, and the control circuit is adapted to close the safety switch to close the power loop of the drive circuit. The safety signal can be used to enable / disable the safety switch. After the tubular LED lamp operates, the safety detection circuit can be disabled. The hold current supply circuit can also be disabled. Alternatively, if the current of the drive circuit is very small for dimming purposes and cannot reach the hold current, the hold current supply circuit can supplement the lack of hold current. And if the drive circuit can trigger the TRIAC of the dimmer, the trigger circuit can also be disabled; otherwise, it can be used to supplement the ignition current to turn on the TRIAC correctly.

[0064] Figure 3 The circuit diagram showing the hold current supply circuit and the detection circuit, which includes corresponding first and second switches, is shown. First, the hold current supply circuit turns on the first switch (shown as a MOSFET) in series with the current source Ih to draw the hold current Ih. After the above delay, the second switch (also shown as a MOSFET) is turned on to conduct the Id current to be detected, and the magnitude of the Id current determines whether there is a ground leakage (via a person). If the current is small, the driver circuit blanking circuit will consider that someone is touching and blank the drive / operation of the tubular LED lamp without outputting a safety signal; otherwise, it outputs a safety signal. In the figure, the hold current supply circuit is shown as being different from the LED unit. However, this is just an example. In another embodiment, the hold current supply circuit is adapted to provide the hold current via the LED unit, in other words, the safety switch and the drive circuit can be activated to draw a small current from the input in the sense of providing the hold current. Of course, in the sense of normal illumination / driving of the LED unit, the safety switch and the drive circuit are not operated at full power.

[0065] To simplify the circuit, the first switch and the second switch are connected in parallel, and the holding current Ih and the detection current Id are superimposed to form the current Itotal sensed by the sense resistor Rsense. When detecting whether the tubular LED lamp is correctly connected to the external lighting fixture, the safety detection circuit is adapted to exclude the holding current. More specifically, the reference of the Op-amp used to compare Itotal should be the holding current Ih plus the safety threshold.

[0066] Figure 4 Two different current waveforms in the presence and absence of a human body are shown. Ih is the holding current and Id is the detection current (appearing after the holding current with a delay, as described above). In the upper curve (a), Itotal is less than the leakage current detection ref., indicating that the current is small and there may be a human body impedance in series with the lamp; in the lower curve (b), Itotal is greater than the leakage current detection ref., which means that the current is small and there may be no human body impedance, so it is safe to turn on the drive circuit.

[0067] The above embodiments describe the present invention by taking the TRIAC dimmer as an example of an external electronic power control device. Those skilled in the art can understand that there are other types of electronic power control devices, such as smart wall panels or switches, which also require a minimum operating / holding current. The embodiments of the present invention are also applicable to those devices.

[0068] By studying the drawings, the disclosure, and the appended claims, those skilled in the art can understand and implement variations of the disclosed embodiments when practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The fact that certain measures are recited in mutually different dependent claims does not mean that a combination of these measures cannot be used advantageously. If the term "adapted to" is used in the claims or the specification, it should be noted that the term "adapted to" is intended to be equivalent to the term "configured to". Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A tubular LED lamp, which is used together with an external electronic power control device, the external electronic power control device being adapted to supply an input voltage to the lamp, the tubular LED lamp comprising: an LED unit; a drive circuit for the LED unit; and a safety detection circuit, the safety detection circuit being adapted to perform a safety detection to detect whether the tubular LED lamp is correctly connected to an external lamp; characterized in that the tubular LED lamp further comprises: a holding current supply circuit, the holding current supply circuit being adapted to supply a holding current through the electronic control device so as to maintain the electronic control device in a conducting state; and a control circuit, the control circuit being adapted to synchronize the safety detection circuit with the holding current supply circuit such that when the holding current supply circuit is adapted to supply the holding current and the electronic control device is conducting, the safety detection circuit is adapted to perform the safety detection; wherein the control circuit is adapted to deactivate the holding current supply circuit and the safety detection circuit after the safety detection in one cycle of the input voltage, and reactivate and deactivate the holding current supply circuit and the safety detection circuit in a later cycle.

2. The tubular LED lamp according to claim 1, the tubular LED lamp being used together with a TRIAC dimmer circuit, and the tubular LED lamp further comprising a trigger circuit, the trigger circuit being adapted to trigger the electronic control device to become conducting according to the cycle of the input voltage, wherein the trigger circuit is adapted to draw an ignition current to charge an energy storage component in the TRIAC dimmer so as to reach the conduction voltage threshold of the TRIAC in the TRIAC dimmer, and the holding current supply circuit is adapted to supply the holding current, the holding current being adapted to hold the TRIAC in the TRIAC dimmer to maintain conduction.

3. The tubular LED lamp according to claim 1, wherein the control circuit is adapted to detect a voltage front edge to determine that the electronic control device has become conducting, and activate the holding current supply circuit and the safety detection circuit.

4. The tubular LED lamp according to claim 2, wherein the control circuit is adapted to activate the safety detection circuit with a delay after activating the holding current supply circuit.

5. The tubular LED lamp according to claim 4, wherein the trigger circuit is adapted to accumulate a specific energy when triggering the electronic device, and the holding current supply circuit is further adapted to discharge the trigger circuit within the delay to prevent the specific energy from flowing to the safety detection circuit and allow the trigger circuit to trigger the electronic device in a later cycle of the input voltage.

6. The tubular LED lamp according to claim 5, wherein the holding current supply circuit and the safety detection circuit respectively comprise a first switch and a second switch, and / or the holding current supply circuit is adapted to supply the holding current via the LED unit.

7. The tubular LED lamp according to claim 6, wherein the safety detection circuit is adapted to close the second switch with a specific impedance and detect a detection current exceeding a specific threshold passing through the second switch to determine that the tubular LED lamp is correctly connected to an external lamp.

8. The tubular LED lamp according to claim 6 or 7, wherein the first switch and the second switch are in parallel such that the holding current and the detection current are superimposed and detected by the safety detection circuit, and the safety detection circuit is adapted to exclude the holding current when detecting whether the tubular LED lamp is correctly connected to an external lamp.

9. The tubular LED lamp according to claim 7, wherein if the human body impedance is in series with the lamp with respect to the input voltage, the specific threshold is at a level that the detection current cannot reach.

10. The tubular LED lamp according to claim 1, wherein the control circuit is adapted to activate the safety detection circuit for several cycles and operate the drive circuit when the safety detection circuit detects that the tubular lamp is correctly connected to the external lamp several times, wherein the tubular LED lamp further includes a safety switch between the drive circuit and the input voltage, and the control circuit is adapted to close the safety switch to operate the drive circuit.

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