LED driver, system, and method for controlling LED driver

Abstract

The present disclosure generally relates to a LED driver, a system comprising the same, and a method for controlling the same. The LED driver comprises: an input port; a plurality of output ports, each output port being configured to be electrically connected to at least one LED; a switched power converter including a plurality of converter branches, each converter branch being electrically connected between the input port and a respective output port among the plurality of output ports and comprising a switch for power conversion; and a control unit configured to control the plurality of converter branches in an interleaved manner, the switch of each converter branch being switched on for a corresponding on-time interval within an interleaving period and switched off for a remainder of the interleaving period, wherein the control unit is configured to control the on-time intervals corresponding to the plurality of converter branches such that at least one converter branch has a corresponding on-time interval that is different from at least one other converter branch.

Description

[0001] LED DRIVER, SYSTEM, AND METHOD FOR CONTROLLING LED DRIVER

[0002] FIELD

[0003] The present disclosure generally relates to a driver for light-emitting diodes (LEDs). The present disclosure further relates to a system comprising such a driver, and a method for controlling the driver. The present disclosure may be especially useful for large-scale indoor and / or outdoor lighting applications, such as lighting for sports fields, stadiums, industrial areas, and crops (e.g., crop fields or greenhouses).

[0004] BACKGROUND

[0005] An LED driver, sometimes also referred to as an LED circuit, is an electrical circuit used to power one or more LEDs. Hereinafter, “LED driver” may also be simply referred to as “driver”.

[0006] Typically, the driver includes power conversion circuitry to adapt an input signal (e.g., a grid voltage) to a desirable output signal (e.g., a particular output voltage or output current) that is suitable for the LEDs. For example, the output voltage of the driver should be sufficient to forward-bias the LEDs, and an output current should be at a level that provides a desired operation of the LEDs, such as a particular light output or luminous flux.

[0007] A common approach is to series-connect a plurality of LEDs to form a LED string, and to power the LED string using the driver. Depending on the number of LEDs in the string, the input voltage may need to be converted up or down to ensure a suitable output voltage. To that end, the driver may include a switching power converter such as buck converter, boost converter, or buckboost converter circuitry. A boost converter may be preferred because of its good power factor characteristics and generally high efficiency.

[0008] As the number of LEDs in the LED string increases, however, there is an increasing strain on the switching elements (e.g., transistors) in such a circuit. For example, in applications such as sports field lighting, stadium lighting or open facility lighting, there may be a need for a large number of LEDs to be driven by a single driver, requiring transistors with high voltage ratings. Silicon Carbide (SiC) based transistors, for example, can be rated at voltages upwards of 1200 V and are thus suitable for high-voltage switching applications.

[0009] A known driver for handling the typical high voltages for the LEDs may employ a multilevel (boost) converter. However, such drivers may require a significant number of (relatively large) components, adding both to costs and complexity of the driver as a whole. Additionally, drivers that use multi-level converters may face a relatively high input current ripple, which demands larger and more expensive input filtering circuitry. Accordingly, there is a need for a driver which is able to drive a large number of LEDs at more favourable size, cost, and complexity.

[0010] SUMMARY

[0011] It is an object of the present disclosure to provide an LED driver for which the abovementioned problem(s) do not occur, or hardly so.

[0012] A summary of aspects of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects and / or a combination of aspects that may not be set forth in this section of the present disclosure.

[0013] According to an aspect of the present disclosure, an LED driver is provided, comprising: an input port; a plurality of output ports, each output port being configured to be electrically connected to at least one LED; a switched power converter including a plurality of converter branches, each converter branch being electrically connected between the input port and a corresponding output port among the plurality of output ports and comprising a switch for power conversion; and a control unit configured to control the plurality of converter branches in an interleaved manner, the switch of each converter branch being switched on for a corresponding on- time interval within an interleaving period and switched off for a remainder of the interleaving period, wherein the control unit is configured to control the on-time intervals corresponding to the plurality of converter branches such that at least one converter branch has a corresponding on-time interval that is different from at least one other converter branch (in duration).

[0014] The present disclosure provides a single-input multiple-output (SIMO) switched power converter, the converter branches of which are controlled in an interleaved manner. The SIMO converter enables the driving of multiple (high-voltage) LEDs or LED strings without the need for a multi-level converter. Additionally, the interleaved control by the control unit can reduce an input current ripple of the LED driver and, accordingly, enables a reduction in size of input filtering circuitry (e.g., an electromagnetic interference, EMI, filter) connected to or included in the LED driver.

[0015] The control unit of the LED driver according to the present disclosure is able to individually control the on-time of each converter branch, for example to account for tolerances or to implement user preferences, without or at least with minimal impact on the interleaved control. For example, different on-time intervals may be set for different converters to account for tolerances or user preferences regarding light output. To control the plurality of converter branches in an interleaved manner, the control unit may be configured to interleave respective time instances within the interleaving period at which the switches of the plurality of converter branches are switched on. In other words, the control unit may interleave the starting time of the on-time interval of each converter branch. In practice, the on-time intervals may or may not partially overlap. Accordingly, the control unit may be able to control, as parameters for the switched power converter, the moment of turning on a given converter branch, and its on-time interval (i.e., duration) following said moment of turning on. The control unit may interleave the moments of turning on given converter branches such that there is a phase difference between each of said moments, with respect to the interleaving period.

[0016] The control unit may be configured to: determine an output current of each of the plurality of output ports; and control the on-time interval corresponding to each converter branch based on the output current of the corresponding output port or based on an output power of the corresponding output port determined using said output current.

[0017] In an example, the LED driver may further comprise a plurality of current measuring units, such as shunt resistors, each being associated with a respective output port and converter branch and being configured to be coupled in series with the at least one LED. The control unit may then be configured to determine the output current of each output port using a corresponding current measuring unit.

[0018] The control unit may comprise a timing unit configured to generate a timer signal with an increasing function, wherein the control unit is configured to control the on-time of a given converter branch by starting the timing unit when switching on the switch of the given converter branch and switching off the switch of the given converter branch when the timer signal reaches a threshold value set by the controller. The control unit may preferably have a respective timing unit for each converter branch, or may re-use the same or at least some timing units for different converter branches by changing the threshold value based on which converter branch is switched on. After switching off the converter branch for which the on-time interval has expired, the timer signal of the corresponding timing unit may be reset for a next interleaving period.

[0019] In an example, the timing unit may include a digital counter or a ramp signal generator configured to generate the timer signal.

[0020] The control unit may be configured to control the on-time interval of each of the plurality of converter branches to account for a mismatch between converter branches during operations, such as a mismatch caused by tolerances of components in the LED driver, tolerances of the LEDs that are coupled to the output ports, differing inductor currents in the converter branches, differing output currents of the plurality of output ports. For example, the on-time interval of each of the plurality of converter branches may be controlled by the control unit such that at least one of the following applies: an output current of each output port is substantially equal; an output power of each output port is substantially equal; a light output from LEDs coupled to the plurality of output ports is substantially equal.

[0021] The control unit may be configured to receive a user input for setting the on-time interval for at least one converter branch among the plurality of converter branches, and to control the on- time interval for said at least one converter branch based on the user input. For example, the user input may represent a particular output current, output power, or LED light output, and the control unit may be configured to map said user input to an on-time interval for said at least one converter branch. Accordingly, a user of the LED driver can individually set on-time intervals for respective converter branches to individually control, for example, a light output of the LED(s) connected to its associated output port. In an example, the user input may correspond to a fraction, or percentage, of a maximum output current for each converter branch, such as 50% of 0.5 times the maximum current. The maximum output current may be programmed into the control unit depending on the application. Additionally, a user may provide separate inputs for respective converter branches, for example, 50% for a first converter branch and 70% for a second converter branch.

[0022] The plurality of converter branches may include N converter branches, and a phase difference between time instances of switching on the switch of consecutively controlled converter branches within the interleaving period may be substantially equal to 360 / N degrees, preferably ±10%. Such a phase difference may be sufficient to implement interleaved control in a manner that significantly reduces input current ripple compared to conventional, non-interleaved power converters. The present disclosure is however not limited thereto.

[0023] The control unit may be configured to control the plurality of converter branches in the interleaved manner based on an oscillation signal, for example synchronously to the oscillation signal such.

[0024] In a further example, the interleaving period may have a duration equal to that of N oscillation periods of the oscillation signal, with N being the number of converter branches included in the plurality of converter branches. In other words, each subsequent oscillation period of the oscillation signal may be associated with activating a subsequent converter branch of the plurality of converter branches.

[0025] The control unit may be configured to switch on the switch of a subsequent converter branch in the interleaving period after the oscillation signal crosses a predetermined threshold during its oscillation period.

[0026] In a further embodiment, each converter branch may comprise a corresponding zerocrossing detection unit configured to detect zero-crossings of a current flowing through said converter branch (e.g., through an inductor of the converter branch). After the oscillation signal has crossed the predetermined threshold, the control unit may be configured to switch on the switch of a subsequent converter branch when a zero-crossing is detected by the zero-crossing detection unit of said subsequent converter branch.

[0027] The LED driver may further comprise an oscillator configured to generate the oscillation signal. Of course, it is also envisaged that the oscillation signal is instead provided to the control unit by a source that is external to the LED driver.

[0028] The switched power converter may be a boost converter, a buck converter, or a buck-boost converter.

[0029] Each converter branch may further comprise an inductor. In the example including zerocrossing detection units, each (or at least one) zero-crossing detection unit may be realized using an auxiliary winding that is inductively coupled to the inductor of the corresponding converter branch. Alternatively, each (or at least one) zero-crossing detection unit is realized using a capacitive divider coupled to a node that connects the inductor, an output terminal of the switch, and a diode of the corresponding converter branch.

[0030] The switch of each converter branch may be realized using a transistor. For example, the transistor may be a metal-oxide-semiconductor field-effect transistor, ‘MOSFET’, an insulated gate bipolar transistor, ‘IGBT’, or a bipolar junction transistor, ‘BJT’. Additionally or alternatively, the transistor may be based on one of Silicon, ‘Si’, Silicon Carbide, ‘SiC’, or Gallium Nitride, ‘GaN’, technology.

[0031] The LED driver may further comprise a rectifying unit, such as a diode bridge, electrically connected between the input port and the switched power converter.

[0032] Alternatively to a conventional diode bridge implementation, the switched power converter may be realized in a totem-pole topology. Such a topology effectively eliminates the need for a separate rectifier (e.g., diode bridge) of conventional power converters by integrating the rectifying unit with the switched power converter. Other topologies of converters are of course also envisaged.

[0033] The LED driver may further comprise an electromagnetic interference, ‘EMI’, filter electrically connected between the input port and the switched power converter.

[0034] The switched power converter may be a single-stage converter.

[0035] The control unit may be configured to, when there is a mismatch or imbalance between any of the N converter branches during operation, operate at least one converter branch among the plurality of converter branches in boundary conduction mode, ‘BCM’, (also sometimes referred to as a critical conduction mode, CrCM) and to operate a remaining one or more converter branches among the plurality of converter branches in discontinuous conduction mode, ‘DCM’. Generally, operating in BCM or DCM may be preferred due to lower switching losses that can be achieved, improving the efficiency of the switched power converters. Each converter branch may further comprise an output capacitor coupled to the corresponding output port. The capacitance of said output capacitors can be suitably selected by the skilled person based on a root-mean-square (RMS) current ripple, low-frequency output current ripple (e.g., 2x the AC signal frequency from the input source), and / or desired maximum ripple in light intensity (e.g., luminance, luminous flux).

[0036] For the purpose of input filtering, the LED driver may further comprise an input capacitor coupled between an input of each of the converter branches and a reference terminal, such as ground.

[0037] In an embodiment, the input port may be configured to receive a three-phase input signal. That is, LED driver may be implemented in a three-phase topology and may be configured for converting a three-phase input signal into an output signal suitable for driving a plurality of LEDs.

[0038] According to another aspect of the present disclosure, a system is provided that comprises: the LED driver according to any of the embodiments of the present disclosure; and a plurality of LEDs. Each of the plurality of output ports of the LED driver is electrically connected to a respective at least one LED among the plurality of LEDs.

[0039] For example, the respective at least one LED includes a LED string of two or more LEDs. Additionally or alternatively, the plurality of LEDs of the system may together form an LED array.

[0040] The input port of the LED driver may be configured to be coupled to an (external) AC power source, such as a power grid. Alternatively, the LED system may further comprise an AC or DC power source, such as a generator or a battery, respectively, coupled to the input port.

[0041] The system according to the present disclosure may for example be a lighting system that is suitable for illuminating sports fields, stadiums, large industrial properties, or the like. The system may be particularly suitable for outdoor applications, though it is not limited thereto.

[0042] According to yet another aspect of the present disclosure, a method for controlling an LED driver is provided. The LED driver comprises: an input port; a plurality of output ports, each output port being configured to be electrically connected to at least one LED; and a switched power converter including a plurality of converter branches, each converter branch being electrically connected between the input port and a corresponding output port among the plurality of output ports and comprising a switch for power conversion. The method according to the present disclosure comprises controlling the plurality of converter branches in an interleaved manner, the switch of each converter branch being switched on for a corresponding on-time interval within an interleaving period and switched off for a remainder of the interleaving period, wherein the on- time intervals corresponding to the plurality of converter branches are controlled such that at least one converter branch has a corresponding on-time interval (i.e., duration) that is different from at least one other converter branch. It is noted that the method for controlling the LED driver as described above may further include steps that are based on the specific examples and functions of the control unit described above, as well as any further control-related aspects described in the detailed description below.

[0043] According to yet another aspect of the present disclosure, a non-transitory machine- readable medium is provided, comprising instructions which, when executed by a processor, cause said processor to perform the method(s) according to the present disclosure.

[0044] Further aspects and / or embodiments not mentioned in the above may become apparent from the detailed description below.

[0045] BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Next, the present disclosure will be described in more detail with reference to the appended drawings, wherein:

[0047] FIG. 1 is a schematic diagram of an LED system in accordance with an embodiment of the present disclosure;

[0048] FIG. 2A is a schematic diagram of an LED driver in accordance with an embodiment of the present disclosure;

[0049] FIG. 2B is a signal diagram representing an operation of the LED driver of FIG. 2 A;

[0050] FIG. 2C is a schematic diagram of a control unit of the LED driver of FIG. 2 A;

[0051] FIG. 3 is a schematic diagram of an LED driver in accordance with another embodiment of the present disclosure; and

[0052] FIG. 4 is a schematic diagram of a LED driver in a three-phase topology in accordance with an embodiment of the present disclosure.

[0053] DETAILED DESCRIPTION

[0054] The present disclosure is described below in conjunction with the appended figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

[0055] In the appended figures, similar components and / or features in different figures may be assigned the same reference label. Further, various components of the same type may be distinguished by following the reference label by a letter, or a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label. Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." As used herein, the terms "connected," "coupled," or any variant thereof means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, electromagnetic, or a combination thereof. Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the detailed description using the singular or plural number may also include the plural or singular number respectively. The word "or," in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

[0056] The teachings of the technology provided herein can be applied to other systems, not necessarily the system described below. The elements and acts of the various examples described below can be combined to provide further implementations of the technology. Some alternative implementations of the technology may include not only additional elements to those implementations noted below, but also may include fewer elements.

[0057] These and other changes can be made to the technology in light of the following detailed description. While the description describes certain examples of the technology, and describes the best mode contemplated, no matter how detailed the description appears, the technology can be practiced in many ways. Details of the system may vary considerably in its specific implementation, while still being encompassed by the technology disclosed herein. As noted above, particular terminology used when describing certain features or aspects of the technology should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the technology with which that terminology is associated. In general, the terms used in the following description should not be construed to limit the technology to the specific examples. Accordingly, the actual scope of the technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the scope of the appended claims.

[0058] FIG. 1 shows a schematic diagram of a LED system 100 according to an embodiment of the present disclosure. In this embodiment, LED system 100 comprises a LED driver 1 including an input filter 10, a rectifying unit 20, a switched power converter 30, and a control unit 40. As shown in FIG. 1, LED driver 1 comprises an input port 2 and a plurality of output ports 3a-3N. Accordingly, LED driver 1 is a Single-Input Multiple-Output (SIMO) driver, and switched power converter 30 includes a plurality of converter branches (not shown in FIG. 1). For convenience, only output ports 3a and 3N are explicitly illustrated and indicated in FIG. 1. LED driver 1 will be further described below with reference to FIG. 2 A, 2B, and 3.

[0059] LED system 100 further comprises a plurality of LEDs 120, for example in the form of an LED array. The LED array may comprise a plurality of LED strings, such as rows or columns, each LED string comprising at least one LED and being coupled to one of the plurality of output ports 3a-3N, where N is the number of output ports. Switched power converter 30 may accordingly be configured to drive the plurality of LED strings of the plurality of LEDs 120 through corresponding output ports 3a-3N.

[0060] LED system 100 further comprises an power source 110 configured to provide an input signal to LED driver 1. LED driver 1 is configured to convert the input signal received at input port 2 into a plurality of output signals at output ports 3a-3N that are suitable for driving the plurality of LEDs 120. For example, LED driver 1 may need to up-convert a voltage of the input signal provided by power source 110, such that the plurality of output signals have a voltage that is sufficiently high to drive the plurality of LED strings of the plurality of LEDs 120. In that case, switched power converter 30 may be a boost converter that is able to achieve this up-conversion.

[0061] Although input filter 10 and rectifying unit 20 are shown as being included in LED driver 1, those skilled in the art will appreciate that one or both of these elements may also instead be external to LED driver 1 or may even be omitted entirely in alternative implementations. For example, the input signal may be an AC signal, in which case a rectifying unit may be used to rectify the AC input signal. Such a rectifying unit can be included in LED driver 1 (e.g., rectifying unit 20) but may also be coupled between power source 110 and LED driver 1. In another example, the input signal from input source 110 is a DC signal, in which case rectifying unit 20 is not needed and can be omitted.

[0062] Control unit 40 of LED driver 1 is configured to control operation of LED driver 1. In particular, control unit 40 is configured to control switched power converter 30 to perform the power conversion of the input signal into the plurality of output signals, and may receive one or more signals from switched power converter 30 based on which the control is performed. Control unit 40 may furthermore receive one or more signals from input filter 10 and / or rectifying unit 20, such as the input signal (e.g., AC input voltage) or for the purpose of output signal inrush limiter control.

[0063] In accordance with the present disclosure, control unit 40 is configured to apply interleaved control to switched power converter 30, such that its converter branches are controlled (i.e., switched on) in an interleaved manner. Control unit 40 can individually control the on-time interval of each converter branch within each interleaving period. In examples of the present disclosure, each converter branch is switched on once during each interleaving period, and the time instance at which each converter branch is switched on is interleaved by control unit 40 to reduce an input current ripple.

[0064] FIG. 2A shows switched power converter 30 of LED driver 1 in more detail, in accordance with an embodiment of the present disclosure. A first converter branch is formed by a first inductor LI, a first diode DI, a first transistor QI, and a first output capacitor Cl, and is coupled between input port 2 and a first output port 3a of LED driver 1. A second converter branch is formed by a second inductor L2, a second diode D2, a second transistor Q2, and a second output capacitor C2, and is coupled between input port 2 and a second output port 3b. Additionally, FIG. 2A shows a first LED string 120a coupled to first output port 3a, in series with a first shunt resistor R1 (i.e., an embodiment of a first current measuring unit), and a second LED string 120b coupled to second output port 3b, in series with a second shunt resistor R2 (i.e., an embodiment of a second current measuring unit). Switched power converter 30 can optionally further comprise an input capacitor Cin that is coupled to input port 2 for input filtering purposes.

[0065] In the embodiment shown in FIG. 2A, switched power converter 30 comprises two converter branches. However, the present disclosure is not limited thereto, and switched power converter 30 may comprise any feasible number of converter branches implementing any feasible number of output ports. Each converter branch may be substantially identical in components and their arrangements.

[0066] The operation of each converter branch will be readily understood to the skilled person. As an example, referring to the first converter branch when transistor QI is activated (switched on) and in conducting mode, an input current flows through inductor LI, causing a buildup in current through inductor LI during the on-time interval for the corresponding converter branch due to energy being stored in the magnetic field of inductor LI. When transistor Q2 is subsequently deactivated, the polarity of the voltage across inductor LI is reversed and the input voltage and inductor voltage will add together and be redirected through diode DI towards first LED string 120a. First output capacitor Cl is provided to reduce a ripple of the output current at output port 3a.

[0067] To switch on or switch off the active switch of the first converter branch, control unit 40 may provide a drive signal DRV1 (e.g., a logical ‘high’ or logical ‘low’, respectively) to first transistor QI. Similarly, to switch on or switch off the active switch of the second converter branch, control unit 40 may provide a drive signal DRV2 (e.g., a logical ‘high’ or logical ‘low’, respectively) to second transistor Q2.

[0068] Control unit 40 is configured to control the converter branches of switched power converter 30 in an interleaved manner. That is, first transistor QI and second transistor Q2 are alternatingly switched on for a given time period, hereinafter referred to as the on-time interval. More in particular, control unit 40 interleaves a time instance of starting the on-time interval of each converter branch, but the on-time intervals of different converter branches may partially overlap. For example, the on-time interval of the second converter branch may start while the on- time interval of the first converter branch is still ongoing, and / or vice versa. Within an interleaving period, the switch of every converter branch may be activated once for the corresponding on-time interval.

[0069] To achieve the interleaving, an oscillator-based control may be implemented that controls a phase difference between switching on the converter branches. For example, control unit 40 receives or generates an oscillation signal that is used to synchronize the time instances at which each converter branch is switched on.

[0070] The interleaved control by control unit 40 is asymmetrical, meaning that the on-time interval of at least one converter branch (e.g., the first converter branch) is different from the on- time interval of at least one other converter branch (e.g., the second converter branch), while nevertheless maintaining the benefits of interleaving by controlling a phase difference between respective converter branches in the interleaving period. In this manner, control unit 40 can for example account for a mismatch in the inductance value of inductors LI, L2, a mismatch in the forward- voltage of diodes DI, D2, or a mismatch in the forward- voltages of the diodes in LED strings 120a, 120b, by adjusting the on-time interval for the corresponding converter branch accordingly while maintaining the desired interleaved operation.

[0071] Control unit 40 can also, in addition or alternatively to the above, deliberately set the on- time interval of one converter branch to be different from another, for example based on a user input. The user input may be representative of a desired output current or output power of a particular converter branch, or a desired light output of LED strings 120a, 120b, and control unit 40 may adjust the on-time interval of the corresponding converter branch accordingly. In this manner, a user of LED driver 1 can individually set an operation point of LED strings 120a, 120b without compromising the interleaved control. In a practical implementation, user input UI may represent a percentage of light output, ranging from 0 to 100%, and control unit 40 may map user input UI to appropriate control signals for LED driver 1.

[0072] A first output voltage Vol across first resistor R1 and a second output voltage Vo2 across second resistor can be obtained by control unit 40. Control unit 40 is able to determine the output current of each converter branch (i.e., a current flowing through output ports 3a, 3b), compare said output current to a required or desired output current, and set the on-time intervals of the converter branches based on the corresponding comparison. For example, the on-time interval for the first converter branch may be controlled based on a first output current of first output port 3a, determined using first output voltage Vol and a known value of first resistor Rl, and the on-time interval for the second converter branch may be controlled based on a second output current of second output port 3b, determined using second output voltage Vo2 and a known value of second resistor R2. Of course, alternative current measuring unit implementations are equally envisaged, through which output currents can be determined for control unit 40 to control the on-time intervals.

[0073] As shown in FIG. 2A, the first converter branch may further comprise an first auxiliary winding LI aux that is inductively coupled to first inductor LI and that provides a zero current detection signal ZCD1 that can be used to detect zero-crossings in the current through the first converter branch (e.g., by a zero-crossing detection unit). Similarly, the second converter branch may further comprise a second auxiliary winding L2aux that is inductively coupled to second inductor L2 and providing a zero current detection signal ZCD2. An alternative, which is not shown in FIG. 2A, is that each (or at least one) zero-crossing detection unit is realized using a capacitive divider coupled to a node that connects the inductor, an output terminal of the switch, and a diode of the corresponding converter branch.

[0074] A control of switched power converter 30 of FIG. 2A is now described in more detail with reference to FIG. 2B, which is a signal diagram showing a first current II through first inductor LI, a second current 12 through second inductor L2, a first drive signal DRV1 associated with first transistor QI, a second drive signal DRV2 associated with second transistor Q2, a first timer signal TS1, a second timer signal TS2, a first zero-crossing signal ZC1, a second zero-crossing signal ZC2, an oscillation signal OSC, a first clock signal CLK1, and a second clock signal CLK2. Also indicated in FIG. 2B are an interleaving period TO, a first on-time interval Toni associated with first transistor QI, a second on-time interval Ton2 associated with second transistor Q2, a first threshold value thl first timer signal TS1, a second threshold value th2 for second timing timer TS2, a third threshold value th3 for oscillation signal OSC, and time instances 11 -t6.

[0075] In this example, oscillation signal OSC is a triangular oscillation signal. This may be provided to control unit 40 from an external source or may be generated by control unit 40 using an oscillator. A triangular (i.e., linearly increasing / decreasing) oscillation signal may be beneficial in view of its linear correspondence with time, though other types of oscillation signals may of course be equally applicable. For example, the oscillation signal may instead be a periodic ramp signal, a sinusoidal signal, or the like.

[0076] The interleaving control for the plurality of converter branches can be controlled in this embodiment by setting third threshold value th3 to an appropriate value for oscillation signal OSC. In particular, a subsequent converter branch in the interleaving control may be activated after oscillation signal OSC crosses third threshold value th3, along with optional further conditions. For example, third threshold value th3 may be a minimum of oscillation signal OSC or may be a value in between a minimum and maximum of oscillation signal OSC. In this manner, the time instances tl, t4, t5 at which the switch of a particular converter branch is switched on by control unit 40 can be performed synchronously to oscillation signal OSC to ensure an appropriate phase difference between converter branches within interleaving period TO, while still being able to independently control on-time intervals Toni and Ton2.

[0077] In this example, with two converter branches (i.e., N = 2), the phase difference is about 180 degrees, relative to interleaving period TO. In practice, with N converter branches, the phase difference between switching on subsequent converter branches may be about 360 / N degrees, though slight deviations are still possible without significantly compromising the input current ripple of switched power converter 30.

[0078] At time instance tl, first transistor QI is switched on by control unit 40 by setting first drive signal DRV1 to ‘high’. Control unit 40 keeps first transistor QI switched on for a duration of first on-time interval Toni. To determine when the on-time interval Toni has expired, control unit 40 can for example use a first timing unit configured to provide first timer signal TS1 in the form of a counter, a ramp signal, or the like, which is initiated at the same time as setting first drive signal DRV1 to ‘high’. When first timer signal TS1 reaches first threshold value thl set by control unit 40, first transistor QI is switched off by setting first drive signal DRV1 to ‘low’ (e.g., zero Volts), and first timer signal TS1 is reset for a subsequent interleaving period TO.

[0079] At time instance t2, second current 12 reaches zero. At this stage, a zero-crossing detection unit of control unit 40 for the second converter branch detects zero-crossings in second current 12 and outputs, for example, second zero-crossing signal ZC2 in the form of one or more pulses (only one shown in FIG. 2B) representing moments in time that zero-crossings are occurring. For example, a rising edge in zero-crossing signal ZC2 reflects a zero-crossing in the second converter branch. In practice, when second current 12 approaches zero, oscillation may occur due to a resonance between inductor L2 and the effective capacitance coupled to inductor L2, for example formed at least partially by a parasitic capacitance of second transistor Q2. The frequency of pulses in zero-crossing signal ZC2 may correspond to the resonance frequency. This oscillation is not explicitly indicated in second current 12 of FIG. 2B.

[0080] At time instance t3, oscillation signal OSC crosses third threshold value th3. This may indicate to control unit 40 that the phase for the second converter branch should be initiated by switching on second transistor Q2. This may occur immediately, i.e., without taking into account the instantaneous value of second current 12. However, to minimize switching losses, second transistor Q2 may be switched on when second current 12 is at or near zero, referred to as ‘valley switching’. Accordingly, control unit 40 may first set second clock signal CLK2 to ‘high’, indicating that second transistor Q2 should be switched on at or near the next zero-crossing.

[0081] At time instance t4, when control unit 40 detects that second clock signal CLK2 is ‘high’ and a zero-crossing is detected by the zero-crossing detector of the second converter branch (represented by a pulse or rising edge in zero-crossing signal ZC2), second drive signal DRV2 is set to ‘high’ and second clock signal CLK2 is reset for a subsequent interleaving period. Similarly to the first timing unit, control unit 40 may control a second timing unit to initiate second timer signal TS2 to start increasing at time instance t4, simultaneously with setting second drive signal DRV2 to ‘high’. First timing unit and second timing unit may be substantially identical.

[0082] At time instance t5, control unit 40 detects that second timer signal TS2 has reached second threshold value th2 and may switch off the second converter branch by setting second drive signal DRV2 to low. Second timer signal TS2 may then be reset for a subsequent interleaving period. If applicable, zero-crossing signal ZC2 may be reset as well, as shown in FIG. 2B, for example automatically by switching off the second converter branch, which is then reflected accordingly in zero-crossing detection signal ZCD2 and zero-crossing signal ZC2.

[0083] At time instance t6, control unit 40 detects that oscillation signal OSC has crossed third threshold value th3 and sets first clock signal CLK1 to ‘high’, such as to indicate that the subsequent control phase for the first converter branch should be initiated.

[0084] At time instance t7, the zero-crossing detection unit detects a zero-crossing in first current Il (e.g., using zero-crossing detection signal ZCD1 received from first auxiliary winding Llaux in FIG. 2A), represented by a pulse or ‘high’ signal for zero-crossing signal ZC1. Since first clock signal CLK1 is already set to ‘high’, control unit 40 can activate first transistor QI again by setting first drive signal DRV1 to high and can reset first clock signal CLK1 for a subsequent interleaving period. Again, first timer signal TS 1 may be initiated at time instance t7 for control unit 40 to determine whether first on-time interval Toni has expired.

[0085] The above cycle may be repeated for a plurality of interleaving periods TO. In the example shown in FIG. 2B, first on-time interval Toni is longer in duration than second on-time interval Ton2 (i.e., Toni > Ton2), and a peak of first current II is greater than a peak of second current (i.e., Il > 12).

[0086] The input current of switched power converter corresponds to the sum of currents of each converter branch (in this case, Il + 12). Due to the fact that different converter branches are operated at different times (i.e., different phases), the input current ripple of switched power converter 30 can be reduced.

[0087] An oscillation frequency of oscillation signal OSC may be appropriately set such that each converter branch is controlled in boundary current mode (BCM) or discontinuous current mode (DCM). In this example, the first converter branch is operated in BCM, and the second converter branch is operated in DCM. In this example, interleaving period TO is roughly N times an oscillation period of oscillation signal OSC, each period corresponding to a respective control phase of the interleaved control, and each phase corresponding to a respective converter branch being switched on. Generally, an interleaving frequency, being the inverse of interleaving period TO, may be orders of magnitude greater than a frequency of the (rectified) input signal, preferably at least 100 times greater, more preferably at least 1000 times greater. In an example, the rectified input signal is 100 Hz (e.g., double the grid frequency in Europe), and the interleaving frequency is in the order of magnitude of 100 kHz. On the other hand, for the purpose of power factor correction, a rate at which the on-time interval is adjusted by control unit 40 (for example, in response to a user input) is preferably slow compared to the frequency of the (rectified) input signal.

[0088] Zero-crossing signals ZC1, ZC2 may correspond directly to zero-crossing detection signals ZCD1, ZCD2 of FIG. 2 A, respectively, or may be processed versions thereof (e.g., processed by a module of control unit 40). For example, limiters may be used to convert zero-crossing detection signals ZCD1, ZCD2 into a (digital) signal usable by control unit 40 for the purpose of detecting when exactly a zero-crossing occurs. In that sense, zero-crossing signals ZC1, ZC2 may simply represent a ‘flag’ which indicates a moment in time that the zero-crossing occurs, and the exact implementation of the signal shape may be variously provided as will be appreciated by the skilled person.

[0089] In an embodiment, zero-crossing signals ZC1, ZC2 may be processed by control unit 40 by specifically determining whether a rising-edge occurs in the pulse. That is, a rising-edge in signals ZC1, ZC2 may be used to determine whether (and when) a zero-crossing has occurred, which may trigger the start of the next phase (i.e., switching on the next converter branch in the interleaving period).

[0090] FIG. 2C illustrates control unit 40 according to an embodiment of the present disclosure, for example for controlling switched power converter 30 of FIG. 2A and for generating the signals of FIG. 2B. Control unit 40 comprises a main controller 41, a phase management unit 42, an on- time controller 43, a first driving unit 44 (e.g., an SR-latch), and a second driving unit 45 (e.g., an SR-latch).

[0091] Main controller 41 may be configured to receive user input UI (e.g., for controlling a light output at respective output ports of switched power converter 30), first output voltage Vol, and second output voltage Vo2. Main controller 41 may determine, from first and second output voltage Vol, Vo2, an output current of each converter branch. Of course, it is also envisaged that main controller 41 directly receives signal representing the output current.

[0092] Based on user input UI and the output currents of each converter branch, main controller 41 provides one or more signals to on-time controller 43 for controlling the on-time interval of each converter branch. For example, main controller 41 may determine that user input UI represents a light output of 90% by each converter branch, whereas the output current is currently at 80% in each converter branch. In that case, main controller 41 may control on-time controller 43 to (slowly) increase the on-time intervals of the converter branches until the set-point desired by the user is reached.

[0093] User input UI may represent a light output from 0 to 100 %, wherein 100 % represents the maximum light output possible or allowed by LED driver 1. This set-point may be for all converter branches or may be set for individual converter branches by the user. Even in the case that the light output is set to a same value for each converter branch, on-time intervals between converter branches may differ due to various conditions, such as component tolerances. Control unit 40 according to the present disclosure is able to perform interleaved control synchronously (i.e., with uniform or at least substantially uniform phase difference between respective converter branches) while asymmetrically regulating the on-time intervals of the converter branches.

[0094] Phase management unit 42 receives zero-crossing detection signals ZCD1, ZCD2. Additionally, an oscillation capacitor Cose can be coupled to phase management unit 42, with which an oscillation frequency of an internal oscillator is set for the purpose of generating oscillation signal OSC. In an example, oscillation capacitor Cose may be a variable capacitor such that the oscillation frequency of oscillation signal OSC can be tuned, optionally by main controller 41 (e.g., via a user input).

[0095] Phase management unit 42 may generate zero-crossing signals ZC1, ZC2, and may generate first and second clock signals CLK1, CLK2 based on oscillation signal OSC and third threshold value th3. Additionally, phase management unit 42 may control a set-terminal of driving units 44, 45 based on clock signals CLK1, CLK2 and zero-crossing signals ZC1, ZC2, as discussed above with reference to FIG. 2B. Accordingly, phase management unit 44 may control when first drive signal DRV1 and second drive signal DRV2 are set to ‘high’ and may thereby ensure interleaved control synchronously with oscillation signal OSC.

[0096] On-time controller 43 may include the timing unit(s) described above and may for example control a reset-terminal of driving units 44, 45. Accordingly, on-time controller 43 may control when drive signals DRV1, DRV2 are returned to a ‘low’ (e.g., zero) value, indicating that the on- time interval for the corresponding converter branch has expired. In particular, on-time controller 43 may receive, from main controller 41, one or more information signals necessary to derive the required on-time for each converter branch of switched power converter 30. Although only one (unidirectional) arrow is drawn between main controller 41 and on-time controller 43, a plurality of signals may be exchanged in both directions. For example, main controller 41 may provide a respective signal corresponding to each converter branch such that on-time controller 43 can appropriately control the on-time intervals of each converter branch. Said respective signals may in turn be based on processing of output voltages Vol, Vo2 (or output currents, or output powers) of respective converter branches, as well as user input UI. Furthermore, although not shown in FIG. 2C, main controller 41 can optionally provide a maximum current signal to on-time controller 43 which is used to limit the output current of each converter branch to a corresponding maximum current. That is, main controller 41 may limit the amount of current to be output by each converter branch, for example for safety purposes.

[0097] Of course, as will be appreciated by the skilled person, when switched power converter 30 comprises three or more converter branches, a corresponding three or more driving units may be provided, along with three or more zero-crossing signals, clock signals, drive signals, and so forth.

[0098] Furthermore, those skilled in the art will appreciate that control unit 40 as described with reference to FIG. 2C is but one exemplary implementation and should not be construed as limiting. Various portions of control unit 40 may be implemented using analogue techniques and / or digital techniques. For example, at least some of the various signals may be analogue signals in which a signal value is represented by a magnitude of the signal. In other examples, at least some of the various signals may be digital signals, such as binary signals, in which two discrete signal levels can be distinguished. In yet other examples, at least some of the signals are pulse-width modulated signals, wherein a pulse width ranges from 0 to 100% and represents the signal level as a time interval.

[0099] Additionally or alternatively, main controller 41 may be configured to control on-time controller 43 such that only some of the plurality of converter branches are used in an interleaving manner. For example, in an embodiment in which switched power converter 30 comprises more than two converter branches, giving four purely as an example, main controller 41 may control on- time controller 43 such that only two of said four converter branches are operated in an interleaved manner, and the remaining converter branches remain switched off. This may for example be useful in the event of defects in a particular converter branch or to optimize power consumption depending on the particular demands of the application at a given time. A phase difference between consecutively controlled converter branches should of course be adjusted accordingly, preferably to substantially satisfy 360 / N degrees, wherein N is the number of converter branches that are to be controlled by control unit 40 (i.e., not including those that remain switched off).

[0100] FIG. 3 illustrates a switched power converter 30’ according to another embodiment of the present disclosure. This embodiment differs from the embodiment of FIG. 2A mainly in that switched power converter 30’ is realized in a totem-pole topology. The first converter branch comprises first inductor LI, transistors Qla and Qlb, diodes Dla and Dlb, and first output capacitor Cl, whereas the second converter branch comprises second inductor L2, transistors Q2a and Q2b, diodes D2a and D2b, and second output capacitor C2. Of course, more than two branches may be implemented in switched power converter 30’.

[0101] The control of switched power converter 30’ by control unit 40 may be similar to that of LED driver 1 of FIG. 2 A. In particular, transistor Qla may be driven by a drive signal DRV la that is identical or similar to DRV1 of FIG. 2A-2C, and transistor Qlb may be driven by a drive signal DRVlb that is the logical (digital) inverse of DRVla, i.e., when DRVla is high, DRVlb should be low and vice versa, preferably also providing a sufficient dead-time between deactivating one of DRVla and DRVlb and activating the other of DRVla and DRVlb. Similarly, drive signal DRV2a may be similar to DRV2 of FIG. 2A-2C and DRV2b may be the logical inverse of DRV2a. A detailed description of the control of LED driver 1 ’ is therefore omitted and can be readily derived with reference to FIG. 2A-2C.

[0102] This embodiment integrates the rectifying unit and the switching circuitry of the converter branches in a manner that also eliminates the need for a separate rectifier bridge, and losses due to power dissipation can be reduced.

[0103] Alternatively to diodes Dla, Dlb, D2a, and D2b, active components (e.g., transistors) can also be used. For example, control unit 40 may switch on such transistors (i.e., in a conducting mode) similarly to when diodes Dla, Dlb, D2a, D2b would be forward-biased, and switch off such transistors (i.e., in an open mode) when diodes Dla, Dlb, D2a, D2b would be reverse-biased.

[0104] FIG. 4 illustrates a switched power converter 30” according to yet another embodiment of the present disclosure, in which a three-phase topology is adopted rather than a single-phase topology. More in particular, the embodiment shown in FIG. 4 is a three-phase topology with two single-switch three-phase boost converter branches in SIMO configuration, and each output port is coupled to a respective at least one led 120a, 120b similarly to the previous embodiments. For the three-phase implementation, respective phases of the three-phase input supply, which are presented to the input port of switched power converter 30”, are schematically represented by a first AC voltage source va, a second AC voltage source Vb, and a third AC voltage source vc.

[0105] In this embodiment, input filter 10 may optionally comprise a respective inductor (e.g., a first input filter inductor Lfa, a second input filter inductor Lfb, and a third input filter inductor Lfc) and a respective capacitor (e.g., a first input filter capacitor Cfa, a second input filter capacitor Cfb, and a third input filter capacitor C&) associated with each phase of the three-phase input.

[0106] A diode bridge rectifier 20a, 20b is optionally implemented in each converter branch and for each respective phase of the three-phase input. Although resulting in a favourable embodiment, the present disclosure is not limited thereto and alternative implementations in which the rectifying unit is provided between input filter 10 and are equally envisaged.

[0107] In the embodiment shown in FIG. 4, the plurality of converter branches (e.g., two in the embodiment shown in FIG. 4) are configured to receive a three-phase input signal at its input. Each converter branch may comprise respective inductors corresponding to respective phases of the three-phase input. For example, a first converter branch (e.g., the top converter branch shown in FIG. 4) of switched power converter 30” comprises inductors Lai, LM, and Lcithat are respectively coupled between respective phases of the three-phase input and the first output port (e.g., the top output port shown in FIG. 4), and a second converter branch (e.g., the bottom converter branch shown in FIG. 4) of switched power converter 30” comprises inductors La2, Lb2, and LC2 that are respectively coupled between respective phases of the three-phase input and the second output port (e.g., the bottom output port shown in FIG. 4).

[0108] Diodes Dbl and Db2 of FIG. 4 may serve an identical or similar purpose to diodes Db3 and Db4 of FIG. 2 A. Optionally, diodes Db3, Db4 may be included in the return path of each converter branch to prevent or at least mitigate cross-talk between converter branches during operation.

[0109] In this example, two three-phase single switch power factor correction (PFC) circuits can be provided and configured to work as close as possible to the critical state between DCM and CCM. The drive signals of the two switches are 180° phase shifted. In this way, the sum of the currents of the two modules is continuous. This can significantly reduce the harmonics in the input current. The advantage of interleaving is that it not only reduces the total harmonic distortion of the mains input current, but also doubles the equivalent switching frequency of the system. Therefore, the cut-off frequency of the EMI filter can be increased. These two aspects can further reduce the volume and quality of EMI input filter. This advantageous effect also applies to the previous embodiments described with reference to FIG. 1-3.

[0110] Other than being a three-phase implementation with respect to the single-phase implementation of the previous embodiments, power converter 30” as shown in FIG. 4 may use a same or similar control scheme for transistors QI, Q2 as described above, for example as shown in FIG. 2B, in an identical or similar manner. That is, respective drive signals DRV1, DRV2 may be applied to the control terminal (e.g., gate terminal) of transistors QI and Q2, similarly to the embodiment shown in FIG. 2A. Furthermore, one or more aspects of the previous embodiments described with reference to FIG. 1-3 (e.g., the zero-crossing detection unit(s), the current measuring unit(s), the control unit and its functionality, and the like) may be similarly applied to the embodiment of FIG. 4. A detailed description thereof is therefore omitted for the embodiment of FIG. 4.

[0111] Transistors QI and Q2 in the schematic diagram of FIG. 4 are illustrated with symbols representing IGBTs. However, other implementations are likewise envisaged. For example, transistors QI and Q2 may be MOSFETs, or other suitable types of transistors.

[0112] Although a single switch topology is illustrated in FIG. 4, it will be appreciated by those skilled in the art that other (e.g., multi-switch) topologies can be similarly implemented without departing from the scope of the present disclosure.

[0113] At least part of the control steps performed by control unit 40 for LED driver 1 (e.g., for switched power converter 30) may be embodied in software. For example, a non-transitory computer readable medium (e.g., a memory, such as a read-only memory, ROM) may comprise instructions which, when executed by a processor, cause the processor (e.g., a control unit such as control unit 40) to perform control of LED driver 1 as described above. Hence, modules of control unit 40 may be modules of a conventional processor that are realized using software. In other words, control unit 40 and its functionality may be partially or entirely realized using software executed by a processor. Alternatively, control unit 40 may be implemented in an applicationspecific integrated circuit (ASIC) and / or may be at least partially realized using discrete components.

[0114] In the above, the present disclosure is explained using detailed embodiments thereof.

[0115] However, the present disclosure is not limited to these embodiments in particular. Various modifications are possible without deviating from the scope of the present disclosure as defined by the appended claims.

Claims

CLAIMS1. A light-emitting diode, ‘LED’, driver, comprising: an input port; a plurality of output ports, each output port being configured to be electrically connected to at least one LED; a switched power converter including a plurality of converter branches, each converter branch being electrically connected between the input port and a corresponding output port among the plurality of output ports and comprising a switch for power conversion; and a control unit configured to control the plurality of converter branches in an interleaved manner, the switch of each converter branch being switched on for a corresponding on-time interval within an interleaving period and switched off for a remainder of the interleaving period, wherein the control unit is configured to control the on-time intervals corresponding to the plurality of converter branches such that at least one converter branch has a corresponding on-time interval that is different from at least one other converter branch.

2. The LED driver according to claim 1, wherein, to control the plurality of converter branches in an interleaved manner, the control unit is configured to interleave respective time instances within the interleaving period at which the switches of the plurality of converter branches are switched on.

3. The LED driver according to claim 1 or 2, wherein the control unit is configured to: determine an output current of each of the plurality of output ports; and control the on-time interval corresponding to each converter branch based on the output current of the corresponding output port or based on an output power of the corresponding output port determined using said output current.

4. The LED driver according to claim 3, further comprising a plurality of current measuring units, such as shunt resistors, each being associated with a respective output port and converter branch and being configured to be coupled in series with the at least one LED, wherein the control unit is configured to determine the output current of each output port using a corresponding current measuring unit.

5. The LED driver according to claim 3 or 4, wherein the control unit comprises a timing unit configured to generate a timer signal with an increasing function, wherein the controlunit is configured to control the on-time of a given converter branch by starting the timing unit when switching on the switch of the given converter branch and switching off the switch of the given converter branch when the timer signal reaches a threshold value set by the controller.

6. The LED driver according to claim 5, wherein the timing unit includes a digital counter or a ramp signal generator configured to generate the timer signal.

7. The LED driver according to any of the claims 3-6, wherein the control unit is configured to control the on-time interval of each of the plurality of converter branches to account for a mismatch between converter branches during operations, such as a mismatch caused by tolerances of components in the LED driver, tolerances of the LEDs that are coupled to the plurality of output ports, differing inductor currents in the converter branches, differing output currents of the plurality of output ports, wherein, preferably, the on-time interval of each of the plurality of converter branches is controlled such that at least one of the following applies: an output current of each output port is substantially equal; an output power of each output port is substantially equal; a light output from LEDs coupled to the plurality of output ports is substantially equal.

8. The LED driver according to claim 3-6, wherein the control unit is configured to receive a user input for setting the on-time interval for at least one converter branch among the plurality of converter branches, and to control the on-time interval for said at least one converter branch based on the user input.

9. The LED driver according to claim 8, wherein the user input represents a particular output current, output power, or LED light output, and the control unit is configured to map said user input to an on-time interval for said at least one converter branch.

10. The LED driver according to any of the previous claims, wherein the plurality of converter branches includes N converter branches, and wherein a phase difference between time instances of switching on the switch of consecutively controlled converter branches within the interleaving period is substantially equal to N / 360 degrees, preferably within ±10%.

11. The LED driver according to any of the previous claims, wherein the control unit is configured to control the plurality of converter branches in the interleaved manner based on an oscillation signal.

12. The LED driver according to claim 11, wherein the interleaving period has a duration equal to that of N oscillation periods of the oscillation signal, wherein N is the number of converter branches in the plurality of converter branches.

13. The LED driver according to claim 12, wherein the control unit is configured to switch on the switch of a subsequent converter branch in the interleaving period after the oscillation signal crosses a predetermined threshold during its oscillation period.

14. The LED driver according to claim 13, wherein each converter branch comprises a corresponding zero-crossing detection unit configured to detect zero-crossings of a current flowing through said converter branch, wherein, after the oscillation signal has crossed the predetermined threshold, the control unit is configured to switch on the switch of a subsequent converter branch when a zero-crossing is detected by the zero-crossing detection unit of said subsequent converter branch.

15. The LED driver according to any of the claims 11-14, further comprising an oscillator configured to generate the oscillation signal.

16. The LED driver according to any of the previous claims, wherein the switched power converter is a boost converter, a buck converter, or a buck-boost converter.

17. The LED driver according to any of the previous claims, wherein each converter branch further comprises an inductor.

18. The LED driver according to claims 14 and 17, wherein each zero-crossing detection unit is realized using an auxiliary winding inductively coupled to the inductor of the corresponding converter branch, or wherein each zero-crossing detection unit is realized using a capacitive divider coupled to a node that connects the inductor, an output terminal of the switch, and a diode of the corresponding converter branch.

19. The LED driver according to any of the previous claims, wherein the switch of each converter branch is realized using a transistor.

20. The LED driver according to claim 19, wherein the transistor is a metal-oxide- semiconductor field-effect transistor, ‘MOSFET’, an insulated gate bipolar transistor, ‘IGBT’, or a bipolar junction transistor, ‘BJT’.

21. The LED driver according to claim 19 or 20, wherein the transistor is based on one of Silicon, ‘Si’, Silicon Carbide, ‘SiC’, or Gallium Nitride, ‘GaN’, technology.

22. The LED driver according to any of the previous claims, wherein the LED driver further comprises a rectifying unit, such as a diode bridge, electrically connected between the input port and the switched power converter.

23. The LED driver according to any of the claims 1-21, wherein the switched power converter is realized in a totem-pole topology.

24. The LED driver according to any of the previous claims, further comprising an electromagnetic interference, ‘EMI’, filter electrically connected between the input port and the switched power converter.

25. The LED driver according to any of the previous claims, wherein the switched power converter is a single-stage converter.

26. The LED driver according to any of the previous claims, wherein the control unit is configured to, operate at least one converter branch among the plurality of converter branches in boundary conduction mode, ‘BCM’, and to operate a remaining one or more converter branches among the plurality of converter branches in discontinuous conduction mode, ‘DCM’.

27. The LED driver according to any of the previous claims, wherein each converter branch further comprises an output capacitor coupled to the corresponding output port.

28. The LED driver according to any of the previous claims, further comprising an input capacitor coupled between an input of each of the converter branches and a reference terminal, such as ground.

29. The LED driver according to any of the previous claims, wherein the control unit is further configured to apply power factor correction by modulating the on-time interval of each converter branch over time based on a frequency of a signal presented at the input port, such that an input current at the input port is substantially proportional to a rectified input voltage at the input port.

30. The LED driver according to any of the previous claims, wherein the input port is configured to receive a three-phase input signal.

31. A system, comprising: the LED driver according to any of the previous claims; and a plurality of LEDs, wherein each of the plurality of output ports of the LED driver is electrically connected to a respective at least one LED among the plurality of LEDs.

32. The system according to claim 31, wherein the respective at least one LED includes a LED string of two or more LEDs, and / or wherein the plurality of LEDs together forms an LED array.

33. The system according to claim 31 or 32, wherein the input port of the LED driver is configured to be coupled to an AC power source, such as a power grid, or wherein the LED system further comprises a three-phase power source or an AC or DC power source, such as a generator or a battery, respectively, coupled to the input port.

34. A method for controlling an LED driver, the LED driver comprising: an input port; a plurality of output ports, each output port being configured to be electrically connected to a respective at least one LED; and a switched power converter including a plurality of converter branches, each converter branch being electrically connected between the input port and a corresponding output port among the plurality of output ports and comprising a switch for power conversion, wherein the method comprises controlling the plurality of converter branches in an interleaved manner, the switch of each converter branch being switched on for a corresponding on- time interval within an interleaving period and switched off for a remainder of the interleaving period, andwherein the on-time intervals corresponding to the plurality of converter branches are controlled such that at least one converter branch has a corresponding on-time interval that is different from at least one other converter branch.

35. A non-transitory machine -readable medium comprising instructions which, when executed by a processor, cause said processor to perform the method according to claim 34.

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