Overvoltage protection current limiter for power supply of lighting control bus

Abstract

A current limiter for a power supply of a lighting control bus is disclosed. The current limiter comprises a first switch arranged in series in a current path of the lighting control bus. The first switch is configured to gate a current of the lighting control bus in dependence on a voltage applied to a control terminal of the first switch. The current limiter further comprises a voltage divider connected in parallel with the current path. The current limiter further comprises a second switch interposed between the control terminal of the first switch and an outer terminal of the voltage divider. The second switch is configured to shunt the voltage applied to the control terminal of the first switch in dependence on a current flowing into a control terminal of the second switch. The current limiter further comprises a zener diode interposed between the control terminal of the second switch and an inner terminal of the voltage divider.

Description

Technical Field

[0001] This disclosure relates in general to lighting technology, and more particularly to a current limiter for a power supply for a lighting control bus, a power supply including the current limiter, and a driver including the power supply for at least one LED. Background Technology

[0002] The lighting control bus, according to the Digital Addressable Lighting Interface (DALI) specification, uses a single pair of wires for communication and power supply. Signals are sent by briefly shorting the bus to a low voltage level, where the power supply of the lighting control bus needs to tolerate this situation, with the current limited to 250mA by means of a current limiter circuit.

[0003] To respond quickly to a short circuit in the bus, such current limiter circuits are typically positioned between the lighting control bus and the power supply for the lighting control bus, and include analog circuitry including a reference diode for cryogenic drift and a field-effect transistor (FET) for limiting current flow on the lighting control bus in the event of communication with any device attached to the lighting control bus (e.g., a driver, sensor, control).

[0004] Stacking, i.e. parallel connection, of power supplies for lighting control buses, as specified by the Digital Lighting Interface Alliance (DiiA) in conjunction with its D4i certification, introduces the possibility of multiple power supplies being connected to the lighting control bus with opposite polarities.

[0005] In such cases, the aforementioned FET of the current limiter may be subjected to excessive DC voltage, which could ultimately destroy the FET. Summary of the Invention

[0006] In view of the above-mentioned shortcomings and limitations, this disclosure aims to improve the current limiters of the prior art. One object is to provide an overvoltage protection current limiter.

[0007] A first aspect of this disclosure relates to a current limiter for a power supply of a lighting control bus. The current limiter includes a first switch arranged in series in the current path of the lighting control bus. The first switch is configured to gate the current of the lighting control bus based on the voltage applied to the control terminal of the first switch. The current limiter also includes a voltage divider connected in parallel with the current path. The current limiter further includes a second switch inserted between the control terminal of the first switch and the external terminal of the voltage divider. The second switch is configured to shunt the voltage applied to the control terminal of the first switch based on the current flowing into the control terminal of the second switch. The current limiter also includes a Zener diode inserted between the control terminal of the second switch and the internal terminal of the voltage divider. The Zener diode is configured to gate the current flowing into the control terminal of the second switch based on the voltage drop between the internal and external terminals of the voltage divider exceeding the reverse breakdown voltage of the Zener diode.

[0008] The control terminal of the first switch can be connected to the high side rail of the lighting control bus; and the first switch can be inserted into the low side rail of the lighting control bus.

[0009] The lighting control bus may include the DALI bus.

[0010] The first switch may include a field-effect transistor (FET).

[0011] The second switch may include an NPN bipolar junction transistor (BJT).

[0012] The Zener diode and the emitter diode of the second switch can be oriented in opposite directions.

[0013] Zener diodes can be designed for a reverse breakdown voltage of at least 9V.

[0014] A second aspect of this disclosure relates to a power supply for a lighting control bus. The power supply includes an interface DC / DC converter configured to supply power to the lighting control bus from an externally supplied logic power DC voltage; and a current limiter, as described in the first aspect or any specific embodiment thereof, interposed between the interface DC / DC converter and the lighting control bus.

[0015] The power supply may also include interface control circuitry configured to operate the interface DC / DC converter.

[0016] Interface DC / DC converters may include current isolation.

[0017] Interface DC / DC converters may include flyback converters or resonant converters.

[0018] A third aspect of this disclosure relates to a driver for at least one LED. The driver includes a power factor correction (PFC) AC / DC converter configured to supply power from AC mains power to a DC bus; a first DC / DC converter configured to supply power from the DC bus to at least one LED; a second DC / DC converter configured to provide a logic power supply DC voltage from the DC bus; and a power supply according to the second aspect or any specific embodiment thereof, configured to supply power from the logic power supply DC voltage provided by the second DC / DC converter to a lighting control bus capable of being connected to the driver.

[0019] The driver may also include a communication interface entity configured to communicate via a lighting control bus; and a driver control entity configured to operate the first DC / DC converter according to lighting control commands that can be received by the communication interface entity.

[0020] A fourth aspect of this disclosure relates to a lighting control system. The lighting control system includes a driver for at least one LED as described in the third aspect or any specific embodiment thereof. The driver is connected to a lighting control bus and configured to drive at least one LED according to lighting control commands that can be received via the lighting control bus. The lighting control system also includes at least one bus participant connected to the lighting control bus and configured to issue lighting control commands for the driver via the lighting control bus.

[0021] Beneficial effects

[0022] This disclosure provides an overvoltage protection current limiter for a power supply of a lighting control bus, specifically a DALI bus, wherein a first FET-type switch for overvoltage protection is overvoltage protected by a second BJT-type switch. When an excessive DC voltage on the lighting control bus triggers reverse breakdown of a reverse-biased Zener diode connected to the control terminal of the second switch, the second switch becomes on (closed, open, ON). This shunts (short-circuit, hot-wires) the voltage applied to the control terminal of the first switch (which is drawn from the high-side rail to the low-side rail of the lighting control bus), causing the first switch to become off (open, off). Therefore, the first FET-type switch is turned off / protected by the second BJT-type transistor.

[0023] Protection is usually for preventing overheating / overload, not just for preventing incorrect polarity of the power supply.

[0024] Overvoltage protection current limiters may generate fewer customer complaints (when the power supply is installed incorrectly).

[0025] Despite using low-cost BJT transistors, this protection also includes temperature stability.

[0026] The aforementioned technical effects and advantages related to current limiters also apply to power supplies that include current limiters, as well as drivers that include power supplies. Attached Figure Description

[0027] The above aspects and specific implementations will now be explained with reference to the accompanying drawings, in which the same or similar reference numerals refer to the same or similar elements.

[0028] Unless otherwise specified, these aspects and features of specific implementations may be combined with each other.

[0029] The accompanying drawings should be considered schematic diagrams, and the elements shown in the drawings are not necessarily drawn to scale. Rather, the various elements are represented such that their function and general purpose will be obvious to those skilled in the art.

[0030] Figure 1 A driver including a power supply, which includes a current limiter, is shown, all according to this disclosure; and

[0031] Figure 2 Showing more details Figure 1 The current limiter.

[0032] Figure 3 Even more detailed Figure 2 The current limiter. Detailed Implementation

[0033] Figure 1 A driver 3 is shown, comprising a power supply 2, which includes a current limiter 1, all according to this disclosure.

[0034] The driver 3 for at least one LED 5 includes a PFC AC / DC converter 31 configured to supply power from an AC mains power supply 4 to a schematically shown dual-rail DC bus 32; a first DC / DC converter 33 configured to supply a load power supply DC voltage, such as 400V, from the DC bus 32 to at least one LED 5; a second DC / DC converter 34 configured to provide a logic power supply DC voltage, such as 12V, from the DC bus 32; and a power supply 2 according to the second aspect or any specific embodiment thereof. The power supply 2 is configured to supply power from the logic power supply DC voltage provided by the second DC / DC converter 34 to a lighting control bus 6, such as a DALI bus, capable of being connected to the driver 3.

[0035] The driver 3 may also include a communication interface entity 35, such as a DALI communication interface, configured for bidirectional communication via the lighting control bus 6; and a driver control entity 36, such as a microcontroller, configured to operate the first DC / DC converter 33 according to lighting control commands that can be received by the communication interface entity 35. For example, the driver control entity 36 may be configured to dim at least one LED 5 according to such lighting control commands received from one or more sensors 7 or one or more controls 8, such as serial dimmer communication (S-DIM) controls or DALI controls.

[0036] In addition to the aforementioned driver 3, similar drivers 3 can be connected to the same lighting control bus 6.

[0037] The driver 3 connected to the lighting control bus 6 can form part of the lighting control system; however, at least one bus participant (e.g., sensor 7 and / or control 8) is connected to the lighting control bus 6 and configured to issue lighting control commands to the driver 3 via the lighting control bus 6.

[0038] The power supply 2 includes an interface DC / DC converter 22 configured to supply power to the lighting control bus 6 from an externally supplied logic power DC voltage (such as the logic power DC voltage provided by the second DC / DC converter 34 of the driver 3); and a current limiter 1 disposed between the interface DC / DC converter 22 and the lighting control bus 6, as described in the first aspect or any specific embodiment thereof.

[0039] The power supply 2 may also include an interface control circuit 21 configured to operate the interface DC / DC converter 22, such as an integrated circuit (IC).

[0040] The driver control entity 36 and the interface control circuit 21 can be combined into a single control entity that performs both functions, for example, by combining them into a single integrated circuit.

[0041] The interface DC / DC converter 22 may include current isolation and specifically includes a flyback converter or a resonant converter.

[0042] Figure 2 Showing more details Figure 1 Current limiter 1.

[0043] The current limiter 1 includes a first switch 12 disposed in the current path of the lighting control bus 6. The first switch 12 may include a FET. The control terminal of the first switch 12 may be connected to the high side rail of the lighting control bus 6; and the first switch 12 may be inserted into the low side rail of the lighting control bus 6.

[0044] The first switch 12 is configured to gate the current I of the lighting control bus 6 according to the voltage V applied to the control terminal of the first switch 12. This may also refer to a portion of the voltage V, such as that derived from the voltage V by means of the voltage drop across one or more resistors (not shown) located at the control terminal of the switch 12.

[0045] As used in this article, "gate" can refer to the passage or flow of current / voltage controlled by a gate according to some other parameter.

[0046] As used herein, a high side rail may refer to a specific electrical connection in a pair of electrical connections between a power source (such as power source 2) and a load (such as sensor 7 or control 8 connected to lighting control bus 6) that has a higher potential in that pair, and a low side rail may refer to the other electrical connection in that pair that has a lower potential in that pair.

[0047] The current limiter 1 may also include a resistor 11 arranged in series with the first switch 12. The resistor 11 may be configured to sense the current I gated by the first switch 12 as the voltage drop across the resistor 11.

[0048] The current limiter 1 may also include a reference diode 13, such as a TL431 adjustable shunt regulator circuit. In simple terms, the reference diode 13 is configured to act as a temperature-compensated variable / adjustable Zener diode. The control terminal of the reference diode 13 can be connected to the common terminal of the resistor 11 and the first switch 12; and the reference diode 13 can be interposed between the other terminal of the resistor 11 and the control terminal of the switch 12. The current limiter 1 is configured to shunt the voltage V applied to the control terminal of the switch 12 based on the voltage drop across the resistor 11.

[0049] Therefore, if any device connected to the lighting control bus 6 (i.e., sensor 7, control 8, or driver 3) communicates by briefly shorting the high and low side rails of the lighting control bus 6 to a low voltage level, the current I is limited by the current limiter 1.

[0050] The current limiter 1 may also include a capacitor 14 connected in parallel with the reference diode 13 to mitigate the switching behavior of the first switch 12.

[0051] Especially if multiple drivers 3, including the corresponding power supply 2, are connected to the lighting control bus 6, there is a possibility of them having opposite polarities. In such a case, the first switch 12 of the current limiter 1 may be subjected to excessive DC voltage as follows: The power supply 2 of one driver 3 can regulate the bus power supply voltage to, for example, 15 V. If the power supply 2 of another driver 3 is connected to the lighting control bus 6 with the reverse polarity of 15 V, then a total drop of almost 30 V must occur across the first switch 12 (and the series resistor 1). Therefore, the second switch 12 may eventually be damaged.

[0052] Overvoltage protection (including protection against incorrect polarity) of current limiter 1 can be implemented as follows.

[0053] The current limiter 1 also includes voltage dividers 15 and 16 connected in parallel with the current path.

[0054] The current limiter 1 also includes a second switch 17 disposed between the control terminal of the first switch 12 and the external terminals of the voltage dividers 15 and 16. The second switch 17 may include an NPN BJT. The second switch 17 is configured to respond to a current I flowing into the control terminal of the second switch 17. B The current limiter 1 also includes a Zener diode 18 inserted between the control terminal of the second switch 17 and the internal terminals of the voltage dividers 15 and 16. The Zener diode 18 is configured to shunt the current I flowing into the control terminal of the second switch 17 if the voltage drop between the internal and external terminals of the voltage dividers 15 and 16 exceeds the reverse breakdown voltage of the Zener diode 18. B Implement gating.

[0055] In other words, the voltage drop across resistor 15 of voltage dividers 15 and 16 exceeds the reverse breakdown voltage of the reverse-biased Zener diode 18 connected to the control terminal of the second switch 17, triggering the reverse breakdown of Zener diode 18. Zener diode 18 can be designed for a reverse breakdown voltage of at least 9V.

[0056] In response to the reverse breakdown of Zener diode 18, the current I flowing into the control terminal of the second switch 17 B The rapid increase causes the second switch 17 to become conductive (closed, on, connected) and shunts (short-circuit, hot-wires) the voltage applied to the control terminal of the first switch from the high side rail of the lighting control bus to the low side rail of the lighting control bus, causing the first switch to become non-conductive (off, off). Therefore, the first FET type switch 12 is protected by the second BJT type transistor 17.

[0057] The Zener diode 18 and the emitter diode of the second switch 17 can be oriented in opposite directions. In this case, the temperature coefficient (TC) of the Zener diode 18 compensates for the TC of the BJT base-emitter junction. Therefore, overvoltage protection is also a temperature-stable function despite the deployment of the low-cost BJT 17.

[0058] Figure 3Even more detailed Figure 2 The current limiter.

[0059] In this specific implementation, the interface DC / DC converter 22 may include an isolation converter, such as a flyback converter or a resonant converter. Figure 3 A specific example is presented as the secondary / load side of a flyback converter, which includes the secondary winding / inductor 221 of an isolation transformer, a rectifier diode 222, and a smoothing capacitor 223. Figure 3 The aforementioned interface control circuit 21 is also shown.

[0060] Furthermore, the current limiter 1 includes a power diode 19 in the current path of the lighting control bus 6 (more specifically, in the low-side current path of the lighting control bus 6) and is configured to allow the current I of the lighting control bus 6 to be drawn.

[0061] According to the aforementioned D4i certification, up to four power supplies 2 can be connected to the lighting control bus 6, thereby introducing the possibility of mutually reversed polarities of the power supplies 2.

[0062] Without reverse polarity, multiple power supplies 2, more specifically corresponding interface DC / DC converters 22, independently regulate their (same) power supply voltages according to, for example, a common power supply voltage of 15 V.

[0063] When a single power supply 2 out of multiple power supplies 2 is reversed (i.e., has reverse polarity), the effect depends on the total number of power supplies 2. For a total of four power supplies 2, the multiple power supplies 2 with correct polarity (i.e., a clear majority) each detect the correct power supply voltage, for example, 15V. However, for a total of three power supplies 2, a clear majority is no longer established. In any case, the inductor 221 of the interface DC / DC converter 22 of the reversed power supply 2 will be reflected to the primary side of the interface DC / DC converter 22, and the interface control circuit 21 of the interface DC / DC converter 22 will attempt to maintain, for example, a power supply voltage of 15V, i.e., the voltage V across the smoothing capacitor 223. ps This will result in a relatively high voltage of approximately 28 V across the current path of switch 12 of reverse power supply 2, subsequent temporary shutdown of reverse power supply 2, such as for a period of time lasting, for example, 14 seconds, and possible subsequent permanent shutdown of reverse power supply 2 unless the relatively high voltage across switch 12 disappears during that period.

[0064] exist Figure 3In a specific implementation, the interface control circuit 21 of the interface DC / DC converter 22 can indirectly detect the activity of the current limiter 1 (i.e., no current supply / consumption) and the need to deactivate the power supply 2 by observing the extreme values ​​of the power control parameters, where the power control parameters depend on the operating mode of the interface DC / DC converter 22. In continuous conduction mode (CCM) operation, the interface DC / DC converter 22 is frequency-controlled, and the activity of the current limiter 1 can be detected by switching the extreme values ​​of the frequency. However, in discontinuous conduction mode (DCM) operation, the interface DC / DC converter 22 is duty cycle-controlled (constant frequency), and the activity of the current limiter 1 can be detected by the extreme values ​​of the duty cycle.

Claims

1. A current limiter (1) for a power supply (2) of a lighting control bus (6), the current limiter (1) comprising: A first switch (12) is arranged in the current path of the lighting control bus (6); the first switch (12) is configured to gate the current (I) of the lighting control bus (6) according to the voltage (V) applied to the control terminal of the first switch (12); Voltage dividers (15, 16), which are connected in parallel with the current path; A second switch (17) is inserted between the control terminal of the first switch (12) and the external terminals of the voltage divider (15, 16). The second switch (17) is configured to respond to the current (I) flowing into the control terminal of the second switch (17). B ) to shunt the voltage applied to the control terminal of the first switch (12); and A Zener diode (18) is inserted between the control terminal of the second switch (17) and the internal terminals of the voltage divider (15; 16). The Zener diode (18) is configured to control the current (I0) flowing into the control terminal of the second switch (17) based on the voltage drop between the internal and external terminals of the voltage divider (15, 16) exceeding the reverse breakdown voltage of the Zener diode (18). B Gating is performed.

2. The current limiter (1) according to claim 1. The control terminal of the first switch (12) is connected to the high side rail of the lighting control bus (6); and The first switch (12) is inserted in the lower side rail of the lighting control bus (6).

3. The current limiter (1) according to claim 1 or 2. The lighting control bus (6) includes the DALI bus.

4. The current limiter (1) according to claim 1 or 2. The first switch (12) includes a FET.

5. The current limiter (1) according to claim 1 or 2. The second switch (17) includes an NPN BJT.

6. The current limiter (1) according to claim 5. The Zener diode (18) is oriented opposite to the emitter diode of the second switch (17).

7. The current limiter (1) according to claim 1 or 2. The Zener diode (18) is designed for a reverse breakdown voltage of at least 9V.

8. A power supply (2) for a lighting control bus (6), the power supply (2) comprising An interface DC / DC converter (22) configured to supply power to the lighting control bus (6) from an externally supplied logic power supply DC voltage; and The current limiter (1) according to any one of the preceding claims is inserted between the interface DC / DC converter (22) and the lighting control bus (6).

9. The power supply (2) according to claim 8, wherein the power supply further comprises... An interface control circuit (21) is configured to operate the interface DC / DC converter (22).

10. The power supply (2) according to claim 8 or claim 9. The interface DC / DC converter (22) includes current isolation.

11. The power supply (2) according to claim 10. The interface DC / DC converter (22) includes a flyback converter or a resonant converter.

12. A driver (3) for at least one LED (5), the driver (3) comprising A power factor correction (PFC) AC / DC converter (31) is configured to supply power from an AC mains power supply (4) to a DC bus (32); A first DC / DC converter (33) is configured to supply power from the DC bus (32) to the at least one LED (5); A second DC / DC converter (34) is configured to provide a logic power DC voltage from the DC bus (32); and The power supply (2) according to any one of claims 8 to 11 is configured to supply power from the logic power supply DC voltage provided by the second DC / DC converter (34) to a lighting control bus (6) that can be connected to the driver (3).

13. The driver (3) according to claim 12, the driver further comprising: A communication interface entity (35), configured to communicate via the lighting control bus (6); and A driver control entity (36) is configured to operate the first DC / DC converter (33) according to instructions that can be received by the communication interface entity (35).

14. A lighting control system, comprising A driver (3) for at least one LED (5) according to claim 12 or 13, the driver being connected to a lighting control bus (6) and configured to drive the at least one LED (5) according to lighting control commands that can be received via the lighting control bus (6); and At least one bus participant (7, 8) is connected to the lighting control bus (6) and is configured to issue the lighting control command for the driver (3) via the lighting control bus (6).

Images