LED power supplies and lights

Abstract

Power supply (1) for an LED load (2), comprising: - an isolation transformer (13) configured to inductively transfer the power of a rectified mains supply (17) from a primary side (11) of the power supply (1) to a secondary side (12) of the power supply (1); and - a first capacitor (18) that capacitively couples the primary and secondary sides (11, 12); wherein the secondary side (12) comprises: - Output terminals (16) that can be connected to the LED load (2); - an LED driver (15) configured to drive the LED load (2) with the power transferred to the secondary side (12); - a second capacitor (19) connected in series with the first capacitor (18), wherein the first and second capacitors (18, 19) are configured to capacitively couple a primary side reference potential (11) and a secondary side reference potential (12); - a processing unit (22) configured to evaluate a voltage across the second capacitor (19) and, based on the voltage across the second capacitor (19), to determine the presence and / or a value (e.g. a frequency) of a mains supply voltage (17).

Description

Technical field:

[0001] The present disclosure relates to the conversion of electrical energy and specifically to a power supply unit. State of the art:

[0002] D4i is an extension of the DALI-2 certification program for compliance with Digital Addressable Lighting Interface (DALI) standards. D4i-certified LED drivers have a mandatory set of features regarding smart data capabilities and power supply requirements. The latter includes the standardized acquisition and storage of diagnostic data according to the mandatory DALI standard Part 253, which specifies procedures that allow for the real-time reading of driver operating information (such as power data) and enable predictive maintenance. Among other things, the power data can include the driver's external supply frequency (i.e., the frequency of the external supply voltage). Therefore, D4i-certified power supplies must specifically measure the frequency of their AC mains input.

[0003] Conventional frequency measurement methods involve the use of a step-down transformer or an additional winding in a forward transformer (flux transformer) in conjunction with a frequency counter circuit. Since the measurement is generally performed by a microcontroller located on the safety extra-low voltage (SELV) side of the power supply, reinforced insulation and sufficient creepage and clearance distances must be considered. This results in increased costs and space requirements. Summary of the invention:

[0004] Therefore, one objective of the present disclosure is to provide a power supply capable of measuring the frequency of the AC mains input using a low-voltage and cost-effective solution, thereby avoiding expensive and bulky components with reinforced insulation.

[0005] The invention is defined by the attached independent claims. Preferred embodiments are specified in the dependent claims, as well as in the following description and in the drawings.

[0006] A first aspect of the present disclosure relates to a power supply for an LED load. The power supply comprises: an isolation transformer (configured to inductively transfer the power of a rectified mains supply from a primary side to a secondary side of the power supply) and a first capacitor (for capacitive coupling of the primary and secondary sides). The secondary side comprises: output terminals for connecting the LED load; an LED driver that drives the LED load with the power transferred to the secondary side; and a second capacitor connected in series with the first capacitor. The first and second capacitors are configured to capacitively couple a reference potential of the primary side and a reference potential of the secondary side. The secondary side further comprises a processing unit (e.g., a processor, a computer, or a computer).a microcontroller) that evaluates a voltage across the second capacitor and, based on this, determines the presence and / or a value (e.g., a frequency) of a mains supply voltage.

[0007] The secondary side can further include an operational amplifier that amplifies the voltage across the second capacitor. The operational amplifier can be designed such that its open-loop gain decreases with increasing frequency. The amplified voltage can be in the form of a square wave. The processing unit can also be configured to determine the value of the mains supply voltage based on the voltage across the second capacitor within a reference period encompassing a multitude of square wave cycles.

[0008] The capacitance of the second capacitor can be many times greater than the capacitance of the first capacitor (for example, two or more orders of magnitude larger). For instance, the capacitance of the second capacitor could be approximately 1 µF, which is about 500 times the exemplary capacitance of the first capacitor (2.2 nF). The first capacitor could be a Y-capacitor (class Y).

[0009] The secondary side may also include a bandpass filter whose passband is essentially centered on the fundamental frequency of the mains supply. This is designed to smooth the voltage across the second capacitor and reference it to zero.

[0010] The processing unit can further be configured to record the specified value of the mains voltage in a memory. In addition, the processing unit can transmit the recorded value to a communication interface, preferably via a transmission circuit across an isolation barrier between the primary and secondary sides. The communication interface can be configured to allow communication according to a wireless or wired standard, in particular a DALI standard.

[0011] A second aspect of the present disclosure relates to a luminaire comprising a power supply of the first aspect (or one of its embodiments) and an LED load connected to the output terminals of the power supply. Advantages of the invention:

[0012] The proposed solution utilizes an existing component with reinforced insulation (class Y capacitor) in the circuit, but it is used on the low-voltage side without affecting the safety-relevant insulation properties provided by the class Y capacitor and without degrading the EMC or transient characteristics.

[0013] According to the present disclosure, a capacitive divider is used to “sniff out” an AC voltage signal that has the same (or a related) frequency as the AC mains frequency, but without affecting the normal functioning of the circuit.

[0014] The simplest version requires only two components to convert the signal containing the mains frequency information into a square wave with a frequency related to the mains frequency (e.g., twice the mains frequency). A more complex version of this circuit can use additional circuitry to convert the square wave into a DC voltage proportional to the frequency of the square wave.

[0015] The proposed solution is characterized by low complexity and low cost. Since only SELV-rated components are used, the costs are lower than for frequency measurement methods that operate on the high-voltage side (the latter requiring more expensive components with reinforced insulation).

[0016] Another advantage is that the technique is practically non-invasive to the normal operating characteristics of the circuit (negligible or no impact on EMC, transients, etc.). The result is a quasi-real-time measurement of the mains frequency with a very short delay (~µs).

[0017] The solution also works for other mains frequencies (e.g., 60 Hz systems in the USA, western Japan, etc.). Furthermore, it is also suitable for DC systems, provided that proper grounding is ensured to prevent the formation of ground loops. In this case, the measured frequency reading would be zero.

[0018] The technical effects and advantages described above with regard to the power supply apply equally to the process with corresponding features as well as to the luminaire with the power supply. Brief description of the drawings:

[0019] The aspects and embodiments described above will now be explained with reference to the accompanying drawings, in which identical or similar reference numerals denote identical or similar elements. The features of these aspects and embodiments may be combined arbitrarily unless expressly stated otherwise. The drawings are schematic representations; the elements depicted are not necessarily to scale, but are shown in such a way as to make their function and general purpose apparent to those skilled in the art. Fig. Figure 1 shows a light fixture (3) according to the present disclosure, which includes a power supply unit (1) according to the present disclosure. Fig. Figure 2 shows a bandpass filter (20) of the power supply according to the present disclosure. Fig. Figure 3 shows a power supply (1) according to the present disclosure with a wired communication interface (27). Fig. Figure 4 shows a power supply (1) according to the present disclosure with a wireless communication interface (28). Fig. Figure 5 shows a method (4) according to the present disclosure for operating a power supply for an LED load. Detailed description of the drawings:

[0020] Fig. 1: Fig. Figure 1 shows a light fixture 3 according to the present disclosure, which includes a power supply unit 1 according to the present disclosure. Fig. 1. An LED load 2 can be connected to output terminals 16 of the power supply 1, and an AC mains supply 17 can be connected to input terminals of the power supply 1.

[0021] In the Fig. In the embodiment shown, the power supply 1 comprises a rectifier circuit 14, for example a full-bridge rectifier, which effectively doubles the frequency of the AC mains supply 17. Furthermore, the power supply 1 comprises an isolation transformer 13, which is configured to inductively transfer the power of the rectified mains supply 17 from a primary side 11 of the power supply 1 to a secondary side 12.

[0022] The power supply 1 also includes a first capacitor 18, which capacitively couples the primary and secondary sides 11, 12. The first capacitor 18 is typically required for electromagnetic compatibility (EMC) reasons and must have reinforced insulation, as it connects the high-voltage primary side (AC, rated at ~220-240 V) to the secondary side. Specifically, the first capacitor 18 can be a Y-capacitor. Y-capacitors (EMI / RFI suppression capacitors, also called "line-to-ground capacitors") are safety-certified and are used in many electronic devices for mains filtering. For example, the capacitance of the first capacitor 18 can be approximately 2.2 nF.

[0023] The secondary side 12 of the power supply 1 comprises output terminals 16, which can be connected to the LED load 2; an LED driver 15, which drives the LED load 2 with the power transferred to the secondary side 12; and a second capacitor 19, which is connected in series with the first capacitor 18. The first and second capacitors 18, 19 are configured to capacitively couple a reference potential of the primary side 11 and a reference potential of the secondary side 12. In other words, the series connection of the first capacitor 18 and the second capacitor 19 forms a capacitive voltage divider.

[0024] The capacitance of the second capacitor 19 is a multiple of the capacitance of the first capacitor 18 (generally two or more orders of magnitude). For example, the capacitance of the second capacitor 19 can be 1 µF, which is approximately 500 times the exemplary capacitance of the first capacitor 18 (2.2 nF). In this embodiment, the second capacitor 19 has no or a negligible effect at the frequencies relevant to EMC because it exhibits a very low impedance at very high frequencies.

[0025] For the same reason, the second capacitor 19 experiences a voltage approximately 500 times lower during a transient test. For example, the impulse voltage across the second capacitor 19 is only about 4 V during a 2 kV transient pulse. Therefore, the second capacitor 19 does not need to be rated for high voltage; it can be a SELV-rated capacitor, meaning its physical size can be kept small. The capacitance of the second capacitor 19 can be adapted to the application, but the principle is to use a significantly larger capacitance in series with the first capacitor 18 (Y-capacitor) without affecting the normal operation of the circuit.

[0026] The secondary side 12 of the power supply 1 can further include an operational amplifier 21, which amplifies the voltage across the second capacitor 19. For example, the operational amplifier 21 can be a TLV9001 circuit. It is evident to those skilled in the art that an operational amplifier is a high-gain electronic amplifier with differential inputs, which typically has a one-sided output and produces an output voltage relative to ground that is typically 100,000 times higher than the potential difference between its inputs. That is, the operational amplifier 21 is configured to operate as a zero-crossing detector, or zero-threshold comparator. Thus, with an alternating voltage applied to the differential inputs, the amplified voltage (i.e., the output voltage of the operational amplifier 21) has a square waveform.For example, a fraction of the mains supply 17 can produce a square wave with a frequency of approximately 50 Hz. A fraction of the rectified mains voltage can, for example, generate a square wave with a frequency of approximately 100 Hz. Ideally, no current is drawn from the differential input of the operational amplifier 21, which is located after the second capacitor 19.

[0027] The operational amplifier 21 can also be configured to amplify the voltage across the second capacitor 19 in an open-loop configuration. In other words, the operational amplifier 21 operates without negative feedback and compares the voltage across the second capacitor 19 with the ground potential of the secondary side 12. This implies that the operational amplifier 21 has a gain that decreases with increasing frequency starting at a few dozen Hz (the dominant pole of the operational amplifier, depending on the specific component). Thus, the operational amplifier 21 already acts as a low-pass filter against higher harmonics and / or RF noise.

[0028] The secondary side 12 of the power supply 1 further includes a processing unit 22 (e.g., a microcontroller µC) configured to evaluate the voltage across the second capacitor 19 and, based on this voltage, determine the presence and / or a value (e.g., the frequency) of a voltage from the power supply 17. The microcontroller can employ various techniques to detect the frequency of the square wave, such as counting transitions from LOW to HIGH within a reference period (e.g., one second) and / or calculating a moving average over a large number of such measurements.

[0029] In particular, the microcontroller can perform averaging over many samples to increase measurement accuracy. Accordingly, the processing unit 22 can be configured to determine the value of the mains frequency based on the voltage across the second capacitor 19 within a reference period encompassing several cycles of the square wave. The processing unit 22 can store the determined value of the mains frequency in a memory (not shown).

[0030] Fig. 2: Fig. Figure 2 shows a bandpass filter 20 according to the present disclosure for the power supply 1. Although the square wave mentioned above is related to the frequency of the AC power supply 17, it may contain additional low- and high-frequency signal components (e.g., an unwanted DC component, harmonics, and RF noise). Therefore, filtering may be necessary between the second capacitor 19 and the operational amplifier 21.

[0031] Accordingly, the secondary side 12 of the power supply 1 can further comprise a bandpass filter 20 having a passband bandwidth essentially centered on the fundamental frequency of the power supply 17, and configured to smooth and DC-free the voltage across the second capacitor 19. In the example of the Fig. The bandpass filter 20 comprises an RC low-pass filter 23, 24 and a CR high-pass filter 25, 26. For example, the RC low-pass filter 23, 24 can be implemented with a 100 kΩ resistor and a 10 nF capacitor, and the CR high-pass filter 25, 26 can be implemented with a 10 nF capacitor and a 1 MΩ capacitor. This results in a passband of approximately 15 Hz to 250 Hz, essentially centered on the mains frequency 17 (here: 50 Hz). RF interference peaks are thereby reduced or eliminated, and any DC component is also eliminated.

[0032] As mentioned above, the mandatory DALI standard Part 253 specifies procedures that allow operating data from drivers to be reported back to a central controller in real time. For this purpose, the processing unit 22 can be configured to transmit the recorded value to a communication interface 27, 28. The interface 27, 28 can be designed to enable wireless or wired communication, in particular according to a DALI standard.

[0033] Fig. 3: Fig. Figure 3 shows a power supply unit 1 according to the present disclosure with a wired communication interface 27. In the Fig. In the embodiment shown in Figure 3, the processing unit 22 is configured to transmit the recorded value via a transmission circuit 29 (e.g., an optocoupler) across an isolation barrier 30 between the primary side 11 and the secondary side 12 to the wired communication interface 27 (e.g., a DALI interface). A separate transmission circuit 29 is provided for each transmission direction. The exemplary optocouplers 29 in Fig. Three diagrams are shown without external circuitry to keep the drawing clear and to allow for flexibility regarding inverting or non-inverting implementations. The DALI interface is configured to enable DALI-based connection to the aforementioned central controller via a DALI bus.

[0034] Fig. 4: Fig. Figure 4 shows a power supply unit 1 according to the present disclosure with a wireless communication interface 28. In the alternative embodiment of Fig. 4. The processing unit 22 is configured to transmit the recorded value to the wireless communication interface 28 (for example, a Bluetooth Low Energy (BLE) interface). The BLE interface is configured to provide a Bluetooth-based connection to the central controller.

[0035] Fig. 5: Fig. Figure 5 shows a method 4 according to the present disclosure for operating a power supply 1 for an LED load 2. The method 4 can be carried out with a power supply 1 according to the first aspect (or one of its embodiments). The power supply 1 has a primary side 11 and a secondary side 12.

Claims

[1] Power supply (1) for an LED load (2), comprising: - an isolation transformer (13) configured to inductively transfer the power of a rectified mains supply (17) from a primary side (11) of the power supply (1) to a secondary side (12) of the power supply (1); and - a first capacitor (18) that capacitively couples the primary and secondary sides (11, 12); wherein the secondary side (12) comprises: - Output terminals (16) that can be connected to the LED load (2); - an LED driver (15) configured to drive the LED load (2) with the power transferred to the secondary side (12); - a second capacitor (19) connected in series with the first capacitor (18), wherein the first and second capacitors (18, 19) are configured to capacitively couple a primary side reference potential (11) and a secondary side reference potential (12); - a processing unit (22) configured to evaluate a voltage across the second capacitor (19) and, based on the voltage across the second capacitor (19), to determine the presence and / or a value (e.g. a frequency) of a mains supply voltage (17). [2] Power supply (1) according to claim 1, characterized by , that the secondary side (12) further comprises an operational amplifier (21) configured to amplify the voltage across the second capacitor (19). [3] Power supply (1) according to claim 2, characterized by , that the operational amplifier (21) is further configured to amplify the voltage across the second capacitor (19) with an open-loop gain that decreases with increasing frequency. [4] Power supply (1) according to claim 2 or 3, characterized by that the amplified voltage has a rectangular waveform. [5] Power supply (1) according to claim 4, characterized by, that the processing unit (22) is configured to determine the value of the mains supply voltage (17) based on the voltage across the second capacitor (19) within a reference period comprising a multitude of cycles of the square waveform. [6] Power supply (1) according to any one of the preceding claims, characterized by , that the capacitance of the second capacitor (19) is a multiple of the capacitance of the first capacitor (18). [7] Power supply (1) according to claim 6, characterized by that this multiple encompasses two or more orders of magnitude. [8] Power supply (1) according to any one of the preceding claims, characterized by , that the first capacitor (18) is a class-Y capacitor. [9] Power supply (1) according to any one of the preceding claims, characterized by, that the secondary side (12) further comprises a bandpass filter (20) having a passband bandwidth centered essentially on the fundamental frequency of the mains supply (17) and configured to smooth and reference to zero the voltage across the second capacitor (19). [10] Power supply (1) according to any one of the preceding claims, characterized by , that the processing unit (22) is configured to record the specified value of the mains supply voltage (17) in a memory. [11] Power supply (1) according to claim 10, characterized by , that the processing unit (22) is configured to transmit the recorded value to a communication interface (27, 28), preferably via a transmission circuit (29) over an isolation barrier (30) between the primary side (11) and the secondary side (12). [12] Power supply (1) according to claim 11, characterized by, that the communication interface (27, 28) is configured to perform communication according to a wireless or wired communication standard, in particular based on a DALI standard. [13] Luminaire (3), comprising a power supply (1) according to any one of the preceding claims, and an LED load (2) connected to the output terminals (16) of the power supply (1). [14] Power supply (1) designed to perform the following method (4) for operating a power supply (1) for an LED load (2), wherein the power supply (1) comprises a primary side (11) and a secondary side (12); comprising the steps: - Connecting (41) the LED load (2) to the output terminals (16) of the power supply (1) arranged on the secondary side (12); - inductive transfer (42) of the power of a rectified mains supply (17) from the primary side (11) to the secondary side (12); - Driving (43) the LED load (2) with the power transferred to the secondary side (12); - capacitive coupling (44) of a reference potential of the primary side (11) and a reference potential of the secondary side (12) by means of a first capacitor (18) which capacitively couples the primary and secondary sides (11, 12) and a second capacitor (19) which is arranged on the secondary side (12) and connected in series with the first capacitor (18); - Evaluating (45) a voltage across the second capacitor (19); and - Determining (46) the presence and / or value (e.g. a frequency) of a mains supply voltage (17) based on the voltage across the second capacitor (19).

Images