Primary-side switching converter for providing voltage supply to LED loads

Abstract

The present invention relates to a method (100) for operating an isolated primary side switching converter (300) for providing a voltage supply to an LED load (401), wherein the converter comprises a galvanic isolation stage (301), the method comprising the following steps: # detecting (101) a feedback signal at the primary side of the galvanic isolation stage (301), wherein the feedback signal corresponds to a secondary side voltage; # determining (103) an LED supply voltage based on the feedback signal; # calculating (105) a threshold value based on a constant reference voltage and an adjustment factor, wherein the adjustment factor is a dynamic factor whose absolute value increases as the LED current increases; and # interrupting (107) the voltage supply to the LED load (401) when the determined LED supply voltage exceeds the threshold value.

Description

Technical Field

[0001] The present invention relates to converters for light sources, in particular LEDs. In particular, the present invention relates to a method for operating a primary side switching converter for providing a voltage supply to an LED load, as well as an isolated primary side switching converter and a driver for a light source comprising such a converter. Background Art

[0002] The converter may be used as a DC / DC stage in an LED driver for supplying an LED load with a regulated output voltage. An example of such a converter is a primary side switching converter.

[0003] A primary side switching converter typically comprises a transformer arranged between a primary side and a secondary side of the converter, wherein the two sides are galvanically isolated from each other and wherein the primary side comprises at least one switch. A half-bridge LLC converter is an example of such a converter.

[0004] It is often important to ensure that the output voltage of such LED converters does not exceed a threshold of, for example, 60 volts. This threshold is specified by the corresponding standard for low-level operation of LEDs, since a user may accidentally touch a normally unprotected wire.

[0005] The output voltage of such a converter can be sensed via magnetic coupling with the secondary side winding of the converter. If the voltage is detected to reach a threshold, the LED converter shuts down.

[0006] However, the determination of the output voltage of such converters may be subject to certain fluctuations or tolerances. Such fluctuations may be coupled to magnetic behavior, in particular leakage flux, or current-dependent voltage drops of the output rectification and output filtering of the LED converter, and may be caused by a number of external and internal factors.

[0007] To ensure that the threshold is never exceeded, the driver is designed so that the voltage supply to the LED is already switched off when the output voltage reaches a switch-off level below the 60 volt threshold, for example at 50 volts. However, due to this limitation, the converter cannot provide a supply voltage around the 60 volt threshold.

[0008] Therefore, the object of the present invention is to provide an improved primary-side switching converter, an improved driver including such a converter and an improved method for operating a primary-side switching converter, which avoids the above-mentioned disadvantages. In particular, the object of the present invention is to provide an isolated primary-side switching converter which allows effective compensation of deviations of a determined output voltage. Summary of the invention

[0009] According to a first aspect, the invention relates to a method for operating an isolated primary side switching converter for providing a voltage supply to an LED load, wherein the converter comprises a galvanic isolation stage, the method comprising the following steps:

[0010] Detecting a feedback signal at the primary side of the galvanic isolation stage, wherein the feedback signal corresponds to the secondary side voltage,

[0011] Determine the LED supply voltage based on the feedback signal,

[0012] Calculating the threshold based on a constant reference voltage and an adjustment factor, where the adjustment factor is a dynamic factor whose absolute value increases as the LED current increases, and

[0013] When the determined LED supply voltage exceeds a threshold, interrupting the voltage supply to the LED load.

[0014] This achieves the advantage that current-dependent deviations of the calculated LED supply voltage can be effectively compensated. In particular, these deviations are taken into account when determining the threshold voltage for switching off the converter. Thus, a higher output voltage, for example 54 V, can be provided without the risk of the voltage exceeding the maximum value of 60 V.

[0015] The converter may be a resonant or hard-switching converter. In particular, the converter is one of the following types: LCC, flyback or synchronous flyback.

[0016] The converter may include a switch network on the primary side of the galvanic isolation stage. The switch network may include two or four switches.

[0017] The converter may be a DC / DC stage for supplying the LED load with a regulated output voltage. Specifically, the secondary side voltage corresponds to the output voltage.

[0018] The adjustment factor is a positive voltage value that increases as the LED current increases or a negative voltage value that decreases further as the LED current increases.

[0019] The threshold value represents a threshold voltage for supplying the LED. Specifically, the converter is configured to interrupt the voltage supply to the LED load once the LED supply voltage reaches the threshold value.

[0020] The LED supply voltage may be determined by passing the feedback signal through a voltage divider and / or converting the feedback signal into a digital voltage signal.

[0021] The LED current may be detected by a current sensing unit of the converter.The current sensing unit may comprise a further auxiliary winding on the primary side of the galvanic isolation stage, the further auxiliary winding being magnetically coupled to the at least one secondary side winding.

[0022] The LED load may include an LED module, an LED lamp and / or an LED track.

[0023] In one embodiment, the adjustment factor comprises a constant term and a dynamic term depending on the LED current. This achieves the advantage that current-dependent deviations of the determined output voltage can be effectively compensated.

[0024] In one embodiment, the adjustment factor comprises a linear function of the LED current.

[0025] For example, the threshold (V ref,comp ):

[0026] V ref,comp =V ref +(I LED *x1)+x2,

[0027] Where V ref is the reference voltage, and (I LED *x1)+x2 is the adjustment factor, where I LED is the LED current, and x1 and x2 are constant correction parameters.

[0028] In one embodiment, the linear function is determined by performing at least two calibration measurements at different LED currents. This provides the advantage that the adjustment factor can take device-specific deviations into account.

[0029] For example, the calibration measurements may include driving the converter at two different loads, ie at two different currents, and measuring the offset of the output voltage at each current.By fitting a linear regression to the two measurement points, the correction parameters x1 and x2 may be determined.

[0030] Alternatively, the adjustment factor may comprise a higher order function of the LED current.

[0031] In one embodiment, the adjustment factor comprises a temperature-dependent part. This achieves the advantage that temperature-dependent deviations of the determined output voltage can be effectively compensated.

[0032] The temperature may correspond to the ambient temperature, in particular a temperature close to or at the LED load.

[0033] In one embodiment, the temperature dependent part is a linear or higher order function of the temperature, or wherein the temperature dependent part is determined based on a look-up table.This achieves the advantage that temperature-dependent deviations of the determined output voltage can be effectively compensated.

[0034] The look-up table may be stored in a memory of the converter, in particular in a memory of an ASIC or a microcontroller of the converter.

[0035] For example, the threshold (V ref,comp ):

[0036] V ref,comp =V ref +(I LED *x1)+x2+x(T),

[0037] Where x(T) is the temperature dependent part. Specifically, T(X) is a linear equation such as x(T)=x*T, where T is the temperature and x is a constant factor.

[0038] In one embodiment, the adjustment factor depends on the dimming level of the LED load.

[0039] According to a second aspect, the present invention relates to an isolated primary side switching converter for providing a voltage supply to an LED load, the isolated primary side switching converter comprising: a galvanic isolation stage; an auxiliary winding located on the primary side of the galvanic isolation stage, the auxiliary winding being magnetically coupled to at least one secondary side winding, wherein the auxiliary winding is configured to receive a feedback signal corresponding to the secondary side voltage; a control unit configured to determine an LED supply voltage based on the feedback signal; a processing unit configured to calculate a threshold value based on a constant reference voltage and an adjustment factor, wherein the adjustment factor is a dynamic factor whose absolute value increases as the LED current increases, and wherein the converter is configured to interrupt the voltage supply to the LED load when the determined LED supply voltage exceeds the threshold value.

[0040] This achieves the advantage that current-dependent deviations of the calculated LED supply voltage can be effectively compensated. In particular, these deviations are taken into account when determining the threshold voltage for switching off the converter. Thus, a higher output voltage, for example 54 V, can be provided without the risk of the voltage exceeding the maximum value of 60 V.

[0041] The isolated primary side switching converter may be an LLC converter, in particular an LLC resonant half-bridge converter, a flyback converter or a synchronous flyback converter. The converter may include a switch network on the primary side of the galvanic isolation stage. The switch network may include two or four switches.

[0042] The converter may be a DC / DC stage for supplying the LED load with a regulated output voltage. Specifically, the secondary side voltage corresponds to the output voltage.

[0043] The adjustment factor is a positive voltage value that increases as the LED current increases or a negative voltage value that decreases further as the LED current increases.

[0044] The threshold value represents a threshold voltage for supplying the LED. Specifically, the converter is configured to interrupt the voltage supply to the LED load once the LED supply voltage reaches the threshold value.

[0045] The LED supply voltage may be determined by passing the feedback signal through a voltage divider and / or converting the feedback signal into a digital voltage signal via a control unit.

[0046] The LED load may include an LED module, an LED lamp and / or an LED track.

[0047] In one embodiment, the converter includes a current sensing unit configured to detect the LED current.

[0048] In one embodiment, the current sensing unit comprises an additional auxiliary winding on the primary side of the galvanic isolation stage, which additional auxiliary winding is magnetically coupled to at least one additional secondary side winding. This achieves the advantage that the LED current can be effectively detected for calculating the threshold value.

[0049] In one embodiment, the converter comprises a temperature sensing unit for sensing the ambient temperature, wherein the adjustment factor comprises a temperature-dependent part. This achieves the advantage that temperature-dependent deviations of the output voltage can be effectively compensated.

[0050] Specifically, the calculated temperature is configured to sense a temperature near or at the LED load.

[0051] In one embodiment, the temperature sensing unit is arranged at the LED load and connected to the processing unit via a communication interface, in particular a DALI or Bluetooth interface. This achieves the advantage that the temperature can be effectively detected for calculating the threshold value.

[0052] In one embodiment, the control unit is configured to control at least one primary side switch of the converter.

[0053] In one embodiment, the control unit is configured to interrupt the voltage supply to the LED load when the calculated output voltage exceeds a threshold value. This achieves the advantage that the voltage supply to the LED load can be interrupted immediately once the voltage exceeds the threshold value.

[0054] Specifically, the control unit interrupts the voltage supply to the LED load by shutting down the converter, for example, by controlling a primary side switch of the converter to interrupt the voltage supply to the LED load.

[0055] In one embodiment, the control unit comprises an ASIC and / or the processing unit comprises a microcontroller.

[0056] Alternatively, the control unit and the processing unit may be integrated in the same unit, such as a single microcontroller or ASIC.

[0057] The converter may be adapted to perform the method according to the first aspect of the invention.

[0058] According to a third aspect, the invention relates to a driver for a light source, in particular an LED, comprising an isolated primary side switching converter according to the second aspect of the invention.

[0059] The driver may be an LED converter for converting the AC mains voltage to a voltage suitable for driving the LED load.

[0060] The converter may be a DC / DC stage of the driver.The driver may also comprise an AC / DC stage for supplying the converter with a DC input voltage.

[0061] The driver can be a SELV (Safety Extra Low Voltage) device. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] The present invention will be described below with reference to the accompanying drawings.

[0063] Figure 1 A schematic diagram showing a method for operating an isolated primary side switching converter according to one embodiment;

[0064] Figure 2 A schematic diagram showing LED supply voltage determined at different LED currents according to one embodiment;

[0065] Figure 3 shows a schematic diagram of an isolated primary side switching converter for providing a voltage supply to an LED load according to one embodiment;

[0066] Figure 4a to Figure 4b shows schematic diagrams of voltage sensing units according to two different embodiments;

[0067] Figure 5 shows a schematic diagram of a control unit and a processing unit of a converter according to one embodiment;

[0068] Figure 6a shows a schematic diagram of a driver for an LED load according to one embodiment;

[0069] Figure 6b shows a schematic diagram of a driver for an LED load according to one embodiment; and

[0070] Figure 6c A schematic diagram of a driver for an LED load according to one embodiment is shown. DETAILED DESCRIPTION

[0071] The present invention is described more fully below with reference to the accompanying drawings, in which various aspects of the invention are shown. However, the present invention can be embodied in many different forms and should not be construed as limited to the various aspects of the invention presented by the present disclosure. On the contrary, these aspects are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The various aspects of the invention shown in the accompanying drawings may not be drawn to scale. On the contrary, the sizes of various feature structures may be enlarged or reduced for clarity. In addition, some drawings may be simplified for clarity. Therefore, the drawings may not show all the components of a given device.

[0072] Various aspects of a converter will be presented. However, as will be readily appreciated by those skilled in the art, these aspects may be extended to various aspects of a driver for a light source without departing from the invention.

[0073] The term "LED lamp" shall refer to a lamp having a light source including one or more LEDs. LEDs are well known in the art and, therefore, will only be discussed briefly to provide a complete description of the present invention.

[0074] It should also be understood that aspects of the present invention may include integrated circuits that are readily fabricated using conventional semiconductor technology (such as complementary metal oxide semiconductor technology, referred to as "CMOS" for short). In addition, aspects of the present invention may be implemented using other manufacturing processes used to manufacture optical devices as well as electrical devices. Reference will now be made in detail to specific implementations of exemplary aspects as illustrated in the accompanying drawings. The same reference numerals will be used throughout the drawings and the following detailed description to refer to the same or similar components.

[0075] Figure 1 A schematic diagram is shown of a method 100 for operating an isolated primary side switching converter for providing a voltage supply to an LED load, according to one embodiment.

[0076] The method 100 comprises the following steps: detecting a feedback signal 101 at the primary side of a galvanic isolation stage, wherein the feedback signal corresponds to a secondary side voltage; determining an LED supply voltage 103 based on the feedback signal; calculating a threshold 105 based on a constant reference voltage and an adjustment factor, wherein the adjustment factor is a dynamic factor whose absolute value increases as the LED current increases; and interrupting the voltage supply 107 to the LED load when the feedback signal exceeds the threshold.

[0077] The LED supply voltage 103 may be determined by passing the feedback signal through a voltage divider and / or converting the feedback signal into a digital voltage signal.

[0078] The adjustment factor may include a constant term and a dynamic term depending on the LED current. Specifically, the adjustment factor includes a linear function of the LED current.

[0079] For example, the threshold (V ref,comp ):

[0080] V ref,comp =V ref +(I LED *x1)+x2,

[0081] Where V ref is the reference voltage, and (I LED *x1)+x2 is the adjustment factor, where I LED is the LED current, and x1 and x2 are constant correction parameters.

[0082] Preferably, by taking into account the current-dependent factor of the threshold, the accuracy deviation of the voltage sensing of about 6V can be reduced to an accuracy deviation of about 1V.

[0083] Figure 2 A schematic diagram 200 showing LED supply voltage 201 determined at different LED currents according to one embodiment is shown.

[0084] The graph 200 illustrates the deviation from linearity of the LED supply voltage as the LED current increases.

[0085] The linear function may be determined by performing at least two calibration measurements at different LED currents.

[0086] During the calibration measurement, the converter can be driven at two different load points, such as a first load point defined by the maximum voltage and the maximum current at the voltage and a second load point defined by the maximum voltage and the minimum current at the voltage. The sensed voltages at the two load points can be read out. By fitting a linear regression to the two measurement points, the correction parameters x1 and x2 can be determined.

[0087] Preferably, these calibration measurements are performed during the production of each converter. Thus, individual adjustment factors incorporating component tolerances of the converter can be determined and later used to adjust the threshold values. Specifically, the correction parameters x1 and x2 represent the individual converter tolerances.

[0088] The LED current can also be adjusted in production with two or three load points, which means that no additional adjustment points are required in production.

[0089] Additionally, the adjustment factor may include a temperature dependent portion.

[0090] The temperature dependent portion may be a linear or higher order function of temperature.

[0091] For example, the threshold value (Vref,comp) is calculated according to the following equation:

[0092] Vref,comp =V ref +(I LED *x1)+x2+ X (T),

[0093] Wherein T(X) is the temperature dependent part. Specifically, T(X) is a linear equation such as x(T)=x*T, where T is the temperature and x is a constant factor.

[0094] Alternatively, T(x) may be a higher order equation.

[0095] Furthermore, the temperature dependent portion may be determined based on a look-up table in which different parameters are stored for each temperature.

[0096] By taking into account the LED converter tolerances, LED current and ambient temperature, it is possible to set the shutdown level to 57V (allowing 3V for SELV limits and 3V for the maximum LED voltage) and achieve a robust 54V output voltage device. By reducing the temperature dependency, it is possible to set the shutdown level and output voltage even higher.

[0097] For example, at the shutdown thresholds, device tolerances (represented by x1 and x2) may cause a deviation of up to 3V in the determined LED supply voltage, the LED current may cause a deviation of up to 6V in the determined LED supply voltage, and the ambient temperature may cause a deviation of up to 2V in the determined LED supply voltage.

[0098] Figure 3 A schematic diagram of an isolated primary side switching converter 300 for providing a voltage supply to an LED load is shown according to one embodiment.

[0099] The converter 300 includes: a current isolation stage 301; an auxiliary winding L51c located on the primary side of the current isolation stage 301, the auxiliary winding being magnetically coupled to at least one secondary side winding L51a, L51b, wherein the auxiliary winding L51c is configured to receive a feedback signal corresponding to the secondary side voltage; a control unit 303, the control unit being configured to determine the LED supply voltage based on the feedback signal; a processing unit 305, the processing unit being configured to calculate a threshold value based on a constant reference voltage and an adjustment factor, wherein the adjustment factor is a dynamic factor whose absolute value increases as the LED current increases, and wherein the converter 300 is configured to interrupt the voltage supply to the LED load when the determined LED supply voltage exceeds the threshold value.

[0100] Preferably, the converter 300 comprises a transformer unit. The transformer unit may comprise a primary side winding L51d, which is magnetically coupled to at least one secondary side winding L51a, L51b. Specifically, the converter is an LLC converter, a flyback converter or a synchronous flyback converter.

[0101] Preferably, the converter 300 further comprises a switching network on the primary side of the galvanic isolation stage 301. Figure 3 In FIG. 4 , the switch network includes two switches M40 and M41.

[0102] The converter 300 may further include a rectification circuit on the secondary side of the isolation stage 301 , the rectification circuit including two diodes D52a , D52b and a capacitor C52 .

[0103] Preferably, the control unit 303 is configured to control the primary-side switches M40 , M41 , in particular based on a comparison result between the determined LED supply voltage and a threshold value.

[0104] Specifically, the control unit 303 is configured to control the primary side switches M40 , M41 to interrupt the voltage supply to the LED load when the calculated output voltage exceeds a threshold value.

[0105] exist Figure 3 In an exemplary embodiment of , the control unit 303 is an ASIC, and the processing unit 305 is a microcontroller connected to the ASIC via a serial communication interface such as I2C (Inter-Integrated Circuit) or SPI (Serial Peripheral Interface).

[0106] Alternatively, the control unit 303 and the processing unit 305 may be integrated into a single unit, such as an ASIC or a microcontroller.

[0107] The control unit 303 may include a comparator configured to compare the LED supply voltage with a threshold value and detect whether the LED supply voltage reaches or exceeds the threshold value.

[0108] Figure 3 The converter 300 in FIG. 3 further includes a voltage sensing unit 307, wherein the voltage sensing unit includes an auxiliary winding L51c and a voltage divider having two resistors R51 and R52. The voltage sensing unit 307 also includes a diode D50 and a capacitor C55.

[0109] The voltage sensing unit 307 may be configured to allow the received feedback signal to reach the control unit 303 through a voltage divider, so as to convert the signal into a digital LED supply voltage signal.

[0110] Preferably, the converter further comprises a current sensing unit 309 configured to detect the LED current.

[0111] The current sensing unit 309 may include an additional auxiliary winding L52a on the primary side of the galvanic isolation stage, which is magnetically coupled to at least one additional secondary side winding L52c, L52b. The current sensing unit 309 may include additional components, such as switches, resistors 3, 120 and conductors 220n. Specifically, the current sensing unit 309 is configured to forward the detected current to the control unit 303.

[0112] The control unit 303 may include an analog-to-digital converter (ADC), in particular a 12-bit ADC, to convert the LED supply voltage detected from the voltage sensing unit 307 into a digital signal, and to convert the LED current detected from the current sensing unit 309 into a digital signal.

[0113] The control unit may further comprise a temperature sensing unit 311 for sensing the ambient temperature. The sensed temperature may be used to determine the temperature dependent part of the adjustment.

[0114] Figure 4a and Figure 4b Schematic diagrams of the voltage sensing unit 307 according to two different embodiments are shown.

[0115] Figure 4a The voltage sensing unit 307 in φ50 uses the discrete peak and holds the discrete peak, and includes a capacitor C55 and a diode D50 and a voltage divider having two resistors R51 and R52.

[0116] on the contrary, Figure 4b The voltage sensing unit 307 in includes resistors R51 and R52, but does not include capacitor C55 and diode D50. Therefore, Figure 4b The voltage sensing unit 307 in FIG. 1 has a simpler structure.

[0117] Figure 5 A schematic diagram of a control unit 303 and a processing unit 305 of a converter according to one embodiment is shown.

[0118] exist Figure 5 In the embodiment, the control unit 303 is an ASIC and is configured to supply the detected LED current I to the processing unit 305. LED and temperature T. The processing unit is a microcontroller and is configured to calculate a threshold value (V ref,comp ).

[0119] Preferably, the process of setting the threshold comprises the following steps:

[0120] 1. Read out the actual temperature (T) and the actual LED current (I LED ).

[0121] 2. By considering the defined threshold (constant reference value V ref,des ), correction parameters (x1 and x2) and the temperature dependent part (x(T)), a new threshold level is calculated within the microcontroller 305.

[0122] 3. Set the register of ASIC 303 to the new threshold level (eg, via I2C).

[0123] The process may be performed sequentially or may be triggered by certain events, for example by setting another dimming level or by a certain temperature increase / decrease.

[0124] In this way, the control unit 303 can act as a comparator that compares the determined LED supply voltage with the new threshold. If the control unit 303 detects that the determined LED supply voltage exceeds the threshold, the module generating the half-bridge signal can be disabled and the output of the LED converter 300 is turned off.

[0125] Figure 6a A schematic diagram of a driver 400 for an LED load 401 is shown according to one embodiment.

[0126] Figure 6a The LED load 401 in FIG. 4 is an LED module including an LED track.

[0127] The driver 400 comprises a rectifier unit 403 which forwards the 230V AC voltage to an AC / DC converter 405. The AC / DC converter 405 supplies a DC / DC converter 407 with a 400V DC voltage which is converted into a lower LED supply voltage by a DC / DC converter 404 and forwarded to the LED module 401.

[0128] The DC / DC converter further detects the LED current of the LED module and forwards this current to a control unit 303 in the form of an ASIC, which is connected to a processing unit 305 in the form of a microcontroller.

[0129] Figure 6a The LED module in the embodiment includes an external temperature sensing unit 409 which is arranged at the LED module and configured to detect an ambient temperature.

[0130] The temperature sensor may be connected to the drive 400 via a wireless or wired communication connection (eg DALI or Bluetooth) for forwarding temperature measurements to the processing unit 305 for calculating the threshold value.

[0131] The DC / DC converter 407, the control unit 303 and the processing unit 305 may correspond to Figure 3 Converter 300.

[0132] Figure 6b A schematic diagram of a driver 400 for an LED load 401 is shown according to one embodiment.

[0133] exist Figure 6b In , the external unit 411 is configured to calculate the correction parameters x1 and x2 and to provide the driver 400 with these parameters, measured values ​​or new calculated threshold values. This has the benefit that no specific equations for calculating the threshold values ​​need to be programmed in the processing unit 305 .

[0134] Figure 6c A schematic diagram of a driver 400 for an LED load 401 is shown according to one embodiment.

[0135] Figure 6c It is shown in Figure 6b In this embodiment, the information for calculating the new threshold value of the LED voltage may be provided by the driver 400 and / or from an external logic component 413 external to the driver 400 (e.g., a temperature sensor on the load). Via an interface (e.g., DALI) of the driver 400, it is possible to set the new threshold value (V ref,comp ) or update / change the correction parameters (x1, x2) and calculate the thresholds in the internal microcontroller 305.

[0136] Figure 6a-6c The driver 400 in the embodiment may be an LED converter for converting an AC mains voltage into a voltage suitable for driving an LED load.

[0137] All features of all embodiments described, illustrated and / or claimed herein may be combined with each other.

[0138] Although various embodiments of the present invention have been described above, it should be understood that these embodiments are given by way of example only and not by way of limitation. Without departing from the spirit of the scope of the present invention, various changes may be made to the embodiments disclosed in the present invention according to the disclosure herein. Therefore, the breadth and scope of the present invention should not be limited by any of the above-described embodiments. On the contrary, the scope of the present invention should be defined according to the following claims and their equivalents.

[0139] Although the present invention has been shown and described with respect to one or more specific embodiments, equivalent alternatives and modifications will occur to those skilled in the art after reading this specification and understanding of the accompanying drawings. In addition, although specific features of the present invention may be disclosed only with respect to several specific implementations, such features may be combined with one or more other features of other specific implementations according to the expectations and advantages of any given or specific application.

Claims

1. A method (100) for operating an isolated primary side switching converter (300) for providing a voltage supply to an LED load (401), wherein: The isolated primary side switching converter (300) comprises: A galvanic isolation stage (301); A transformer unit, the transformer unit comprising a primary side winding (L51d), the primary side winding (L51d) being magnetically coupled to at least one secondary side winding (L51a, L51b); an auxiliary winding (L51c), the auxiliary winding (L51c) being located on the primary side of the galvanic isolation stage (301), the auxiliary winding (L51c) being magnetically coupled to the at least one secondary side winding (L51a, L51b), wherein the auxiliary winding (L51c) is configured to receive a feedback signal corresponding to a secondary side voltage; and a current sensing unit (309) configured to detect the LED current, wherein the current sensing unit (309) comprises a further auxiliary winding (L52a) on the primary side of the galvanic isolation stage (301), the further auxiliary winding being magnetically coupled to at least one further secondary side winding (L52c, L52b), The method comprises the following steps: detecting a feedback signal at the primary side of the galvanic isolation stage (301), wherein the feedback signal corresponds to the secondary side voltage, Determining the LED supply voltage based on the feedback signal, Calculating a threshold based on a constant reference voltage and an adjustment factor, wherein the adjustment factor is a dynamic factor whose absolute value increases linearly as the LED current increases, and When the determined LED supply voltage exceeds the threshold value, interrupting the voltage supply to the LED load (401).

2. The method (100) according to claim 1, wherein: The adjustment factor includes a constant term and a dynamic term that depends on the LED current.

3. The method (100) according to claim 1 or 2, wherein: The adjustment factor comprises a linear function of the LED current.

4. The method (100) according to claim 3, wherein: The linear function is determined by performing at least two calibration measurements at different LED currents.

5. The method (100) of claim 1, wherein: The adjustment factor includes a temperature dependent portion.

6. The method (100) according to claim 5, wherein: The temperature dependent portion is a linear or higher order function of temperature, or wherein the temperature dependent portion is determined based on a look-up table.

7. An isolated primary side switching converter (300) for providing a voltage supply to an LED load (401), the isolated primary side switching converter (300) comprising: Galvanic isolation level (301), A transformer unit, the transformer unit comprising a primary side winding (L51d), the primary side winding (L51d) being magnetically coupled to at least one secondary side winding (L51a, L51b), an auxiliary winding (L51c), the auxiliary winding (L51c) being located on the primary side of the galvanic isolation stage (301), the auxiliary winding (L51c) being magnetically coupled to at least one secondary side winding (L51a, L51b), wherein the auxiliary winding (L51c) is configured to receive a feedback signal corresponding to a secondary side voltage, a current sensing unit (309) configured to detect the LED current, wherein the current sensing unit (309) comprises a further auxiliary winding (L52a) on the primary side of the galvanic isolation stage (301), the further auxiliary winding being magnetically coupled to at least one further secondary side winding (L52c, L52b), a control unit (303), the control unit (303) being configured to determine an LED supply voltage based on the feedback signal, a processing unit (305) configured to calculate a threshold value based on a constant reference voltage and an adjustment factor, wherein the adjustment factor is a dynamic factor whose absolute value increases linearly with the increase of the LED current, and The isolated primary side switching converter (300) is configured to interrupt the voltage supply to the LED load when the determined LED supply voltage exceeds the threshold.

8. The isolated primary side switching converter (300) according to claim 7, wherein: The isolated primary side switching converter (300) comprises a temperature sensing unit (311, 409) for sensing ambient temperature, wherein the adjustment factor comprises a temperature dependent portion.

9. The isolated primary side switching converter (300) according to claim 8, wherein: The temperature sensing unit (311, 409) is arranged at the LED load (401) and is connected to the processing unit (305) via a communication interface, in particular a DALI or Bluetooth interface.

10. The isolated primary side switching converter (300) according to claim 7, wherein: The control unit (303) is configured to control at least one primary side switch (M40, M41) of the isolated primary side switching converter.

11. The isolated primary side switching converter (300) according to claim 7, wherein: The control unit (303) is configured to interrupt the voltage supply to the LED load (401) when the calculated output voltage exceeds the threshold value.

12. The isolated primary side switching converter (300) according to claim 10 or 11, wherein: The control unit (303) comprises an ASIC and / or wherein the processing unit (305) comprises a microcontroller.

13. A driver (400) for a light source, the driver (400) comprising the isolated primary side switching converter (300) according to any one of claims 7 to 12.

Images