A load driving arrangement

Abstract

A mechanism for controlling a power provided to a main load. A load driving arrangement is configured for powering a main load and an auxiliary load. The load driving arrangement has a switched mode power supply and a tuning circuit. The tuning circuit switches a value of an intrinsic circuit parameter of the switched mode power supply when switching between two different operation modes. This effectively modifies a gain of the switched mode power supply, therefore modifying a power provided to the main load between the two operation modes. More specifically, the switched-mode power converter comprises a resonant converter with a resonant component which comprises a resonant capacitive arrangement and the tuning circuit is adapted to tune a capacitance of the resonant capacitive arrangement as the intrinsic circuit parameter of the switched-mode power converter.

Description

[0001] A LOAD DRIVING ARRANGEMENT

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of load driving arrangements, and in particular to load driving arrangements comprising a switched-mode power supply.

[0004] BACKGROUND OF THE INVENTION

[0005] In modern electrical circuits, there is usually a need to provide accurate and reliable driving of a main load. Thus, there is a need for an accurate and reliable load driving arrangement. One use case scenario for a load driving arrangement is in artificial lighting, e.g., to drive an LED load that functions as the main load.

[0006] There is an increasing interest in also facilitating the powering or driving of an auxiliary load, alongside the main load (e.g., an LED load). Examples of auxiliary loads include control circuitry, communication circuitry, sensor circuitry and so on. There are a number of circumstances where it may be desirable to activate or drive the auxiliary load, without powering the main load. This may, for instance, be useful for fully starting up the auxiliary load and making it operatable to properly activate the main load, or be useful or placing the electrical circuit in a standby mode wherein the auxiliary load is powered while the main load is deactivated. For example, for a DALI-based LED driver, according to DALI's test standards, the driver will have a delay time of 500ms during the startup process, and the output LED should have no current output.

[0007] There is therefore a demand for a load driving circuit that is capable of driving both a main load and an auxiliary load, whilst also facilitating the driving of only the auxiliary load.

[0008] Figure 1 illustrates an existing load driving arrangement, comprising a main output interface and an auxiliary output interface. The main and auxiliary output interfaces are galvanically isolated from an input interface that receives an input power (e.g., a rectified mains power).

[0009] US2023113700A1 discloses a power converter that can pulls a DIM signal to zero when power is first applied and removes the DIM pull-down later. US20170176916A1 discloses a resonant converter in which the primary winding can be switched depending on the load is in stand-by mode or normal mode.

[0010] SUMMARY OF THE INVENTION

[0011] The inventor has found that, in some topologies wherein the auxiliary load and the main load are tightly coupled, it is very difficult to power the auxiliary load alone without activating the main load. Here tightly coupled means that the output power to the auxiliary load and the main load are provided by the driver mostly together via a single switched power path. For example, the main and auxiliary loads may be considered tightly coupled when a main winding for powering the main load and an auxiliary winding for powering the auxiliary load are magnetically and / or electrically coupled in the switched power path, so that the driver converts power into the main winding and the auxiliary winding at the same time when switching power into the switched power path and provides output power simultaneously to the main load and the auxiliary load.

[0012] The present disclosure recognizes the need to switch a power provided to a main output interface (for driving a main load) between two different values depending on the condition of the auxiliary output interface (for driving an auxiliary load). The proposed technique is to employ a tuning circuit for tuning at least one intrinsic circuit parameter of the load driving arrangement depending on the condition of the auxiliary output interface. This effectively changes the power level provided to the main load between two different levels depending on the condition of the auxiliary output interface. The inventors have advantageously identified that using a tuning circuit to control this circuit parameter thereby facilitates a built-in capability to suppress or enhance a power provided to a main load depending on the condition of the auxiliary output interface. The proposed approach can be exploited, for instance, to suppress a power provided to a main load during a start-up of the loads especially the auxiliary load driven by a load driving arrangement, without deactivating the main load during this time. This can, for instance, be useful for reducing a power drawn by the main load, providing a more efficient system, and / or preventing the main load from undesirably activating (e.g., emitting light if formed from an LED arrangement).

[0013] In prior art US20170176916A1, it is the winding / coil to be adjusted. The inventor finds some drawbacks. Firstly, a relatively large amount of inductance would be varied so as to influence the output of the resonant converter, which means the inductor arrangement should be designed in a bulky size and high cost to accommodate the relatively large variable inductance. Also, the tolerance of inductor is relatively large and makes the accuracy of output regulation difficult. Moreover, the bulky size of the inductor arrangement limits the design freedom of other circuit components. Even more, the bulky inductor arrangement potentially has more EMI leakage.

[0014] The invention is defined by the claims.

[0015] According to examples in accordance with an aspect of the invention, there is provided a load driving arrangement comprising: an input interface configured to receive an input power; a main output interface configured to connect to a main load; an auxiliary output interface configured to connect to an auxiliary load; a switched-mode power converter connected to the input interface and comprising a switched path magnetically and / or electrically coupled to both the main output interface and the auxiliary output interface, wherein the switched-mode power converter is adapted to, via switching the input power via the switched path, simultaneously convert the input power into first converted power at the main output interface and second converted power at the auxiliary output interface, wherein the switched-mode power converter comprises a resonant converter with a resonant component which comprises a resonant capacitive arrangement; and a tuning circuit configured to controllably tune an (effective) intrinsic circuit parameter of the switched-mode power converter, wherein the tuning circuit is adapted to tune a capacitance of the resonant capacitive arrangement as the intrinsic circuit parameter of the switched-mode power converter.

[0016] During a first operation mode, the tuning circuit is to tune the intrinsic circuit parameter to have a first value; and during a second operation mode, the tuning circuit is to tune the intrinsic circuit parameter to have a second value, different to the first value. The first operation mode and the second operation mode are differentiated in relation to the auxiliary output interface and / or the second converted power.

[0017] In some examples, during the second operation mode, the tuning circuit is adapted to tune the intrinsic circuit parameter of the switched-mode power converter to suppress the first converted power with respect to the first converted power in the first operation mode.

[0018] This provides a technique for reducing the power provided or available to the main load. This can be exploited, for instance, to loosen the tight coupling / relation between the first output power to the main output interface and the second output power to the auxiliary output interface and to more freely control the power to the main load without being limited by the power to the auxiliary load. Compared with adjusting the windings in the prior art US20170176916A1, adjusting the capacitance of the resonant capacitive arrangement brings many advantages. The capacitor has smaller tolerance thus it can accurately regulate the power to the main load. A small capacitance change is sufficient to regulate the power to the main load thus the size and cost for the resonant capacitive arrangement can be small and it gives more freedom to other circuit components. The capacitor also has less EMI leakage than inductor.

[0019] In some examples, during the second operation mode, the tuning circuit is adapted to tune the intrinsic circuit parameter of the switched-mode power converter to suppress the first converted power below a threshold of activating the main load thereby deactivating the main load, and in the first operation mode, the tuning circuit is adapted to tune the intrinsic circuit parameter of the switched-mode power converter to provide the first converted power no less than said threshold thereby activating the main load. Optionally in both of the first and the second operation mode, the tuning circuit is adapted to tune the intrinsic circuit parameter of the switched-mode power converter to provide the second converted power with an amplitude sufficiently for the auxiliary output interface and / or the auxiliary load.

[0020] This provides a technique for effectively deactivating the main load when the load driving arrangement operates in the second operation mode without deactivating the auxiliary load. This can be exploited for ease of placing the main load into standby / deactivation without deactivating the auxiliary load.

[0021] In some examples, the load driving arrangement operates in the second operation mode between a time at which the load driving arrangement was powered up and a time at which the auxiliary output interface has been provided with the second converted power from the switched-mode power converter for no longer than a predetermined length of time since the load driving arrangement was powered up. This allows the auxiliary load to undergo a startup or setup procedure without the main load (undesirably or unintentionally) activating. This can advantageous be exploited to power or drive control circuitry (acting as the auxiliary load) for the main load.

[0022] In some examples, said predetermined length of time is a time duration for said auxiliary output interface and / or said second converted power to fully operate the auxiliary load and / or a time duration required by said auxiliary load connected to the auxiliary output interface and powered by said second converted power. This provides a technique for allowing the auxiliary load to be fully powered before the load driving arrangement is permitted to exit the second operation mode. This can increase a reliability of the system.

[0023] In some examples, the load driving arrangement operates in the first operation mode after the predetermined length of time for providing the auxiliary output interface with the second converted power has elapsed after the load driving arrangement was powered up. This provides a technique for automatically activating or driving the main load after the auxiliary load has been able to power up.

[0024] In some examples, the load driving arrangement is configured to operate in the second operation mode responsive to: an instruction to provide the auxiliary output interface with the second converted power so as to power the auxiliary load but deactivate the main load connected to the main output interface. This approach provides a technique for placing the main load in standby, whilst still powering the auxiliary load. This advantageously reduces a power drawn by the main load during standby meanwhile still provides sufficient power to the auxiliary load.

[0025] In some examples, the load driving arrangement is configured to operate in the second operation mode responsive to, prior to said instruction, the load driving arrangement has been operating in the first operation mode, or the load driving arrangement has been just powered up. This approach means that main load can be switched off or deactivated to reduce a power drawn thereby.

[0026] In some examples, the tuning circuit is adapted to tune the capacitance of the resonant capacitive arrangement as the intrinsic circuit parameter of the switched-mode power converter thereby tuning a gain of the switched-mode power converter for the first converted power. This provides a technique for tuning or controlling the power provided to the main load without compromising the power provided to the auxiliary loads.

[0027] In other examples, the switched-mode power converter comprises a resonant converter with a resonant component, and the tuning circuit is adapted to tune an effective resonance-related electrical parameter of the resonant component as the intrinsic circuit parameter of the switched-mode power converter thereby tuning a gain of the switched-mode power converter for the first converted power; or the switched-mode power converter comprising a feedback control loop for regulating the first converted power, and the tuning circuit is adapted to tune an intrinsic circuit parameter in the feedback so as to adjust the gain of the feedback control loop thereby tuning the first converted power according to the first mode and the second mode.

[0028] For instance, the resonant component may comprise a resonant capacitive arrangement; and the tuning circuit may be adapted to tune a capacitance of the resonant capacitive arrangement as the intrinsic circuit parameter of the switched-mode power converter. This approach provides a reliable mechanism for adjusting the gain of the switched- mode power converter, and therefore the power provided to at least the main load. The tuning circuit may be adapted to increase the capacitance of the resonant capacitive arrangement in the second operation mode, compared to the first operation mode, to thereby suppress the first converted power with respect to the first converted power in the first operation mode. This provides a technique for lowering the power provided to the main load to facilitate suppression of the main load during the second operation mode.

[0029] The switched-mode power converter may comprise: a main inductive arrangement connected in parallel to the resonant capacitance arrangement, said main inductive arrangement is adapted to couple with the main output interface; and an auxiliary inductive arrangement connected in series with the resonant capacitance, said auxiliary inductive arrangement is adapted to couple with the auxiliary output interface. This approach can be used to galvanically isolate the output interfaces from the input interface, for improved reliability, as well as providing a technique for ready modification to the circuit parameter of the switched- mode power converter.

[0030] In some examples, the tuning circuit is configured to selectively connect or disconnect a tuning capacitance arrangement to the resonant capacitance arrangement to thereby tune the effective capacitance of the resonant capacitance arrangement.

[0031] The switched-mode power converter may comprise an LLC converter. This provides a reliable switched-mode power converter.

[0032] The applicant also submits that the present application is not limited to only resonant converters and other converters is also applicable. For example, embodiments may also be employed using flyback converter. In such examples, an intrinsic circuit parameter, in the feedback control loop for regulating the first converted power, is according tunable according to the first mode and the second mode. By tuning the intrinsic circuit parameter in the feedback loop, the gain of feedback in the control loop is adjusted, such that the first converted power is tuned.

[0033] There is also proposed an LED circuit comprising: any herein disclosed load driving arrangement; an LED load, connected to the main output interface, configured to function as the main load; and an auxiliary load connected to the auxiliary output interface, said auxiliary load optionally being a micro-controller unit.

[0034] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0036] Figure 1 illustrates a known load driving arrangement;

[0037] Figure 2 illustrates a proposed load driving arrangement;

[0038] Figure 3 illustrates a switching arrangement for use in the proposed load driving arrangement; and

[0039] Figure 4 illustrates another proposed load driving arrangement.

[0040] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The invention will be described with reference to the Figures.

[0042] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

[0043] The invention provides a mechanism for controlling a power provided to a main load according to a condition of a power provided to an auxiliary load. A load driving arrangement is configured for powering a main load and an auxiliary load. The load driving arrangement has a switched mode power supply and a tuning circuit. The tuning circuit switches a value of an intrinsic circuit parameter of the switched mode power supply when switching between two different operation modes respectively for different conditions of the power provided to the auxiliary load. This effectively modifies a gain of the switched mode power supply, therefore modifying a power provided to the main load between the two operation modes according to the condition of the power provided to the auxiliary load.

[0044] Figure 1 illustrates a known example of a load driving arrangement 100, for improved contextual understanding.

[0045] The load driving arrangement 100 comprises an input interface 110, a main output interface 120, an auxiliary output interface 130 and a switched-mode power converter 140. The input interface 110 is configured to receive an input power VIN. The input power may, for instance, be a DC input power such as a power output by a rectifying arrangement (not illustrated in Figure 1) configured to rectify an AC mains power (not illustrated in Figure 1) or an input power provided by a battery or cell arrangement.

[0046] The main output interface 120 is configured to connect to a main load (not illustrated in Figure 1) and the auxiliary output interface 130 is configured to connect to an auxiliary load (not illustrated in Figure 1). As a working example, the main load may comprise an LED load (e.g., comprising one or more LEDs for outputting light). As a working example, the auxiliary load may be a processing and / or control arrangement, such as a micro-controller unit (MCU). One example of a load driving arrangement may be a DALLbased load driving arrangement, and the auxiliary load may form a control arrangement for the DALLbased load driving arrangement.

[0047] The switched-mode power converter 140 is connected to the input interface and comprises a switched path QI, Q2, LI, L2, Cl magnetically and / or electrically coupled to both the main output interface and the auxiliary output interface. In particular, the switched-mode power converter is adapted to, via switching of the input power via the switched path, simultaneously convert the input power VIN into first converted power VM at the main output interface and second converted power VA at the auxiliary output interface.

[0048] In the illustrated example, the switched-mode power converter 140 comprises an LLC converter. More particularly, the switched-mode power converter comprises a switch array QI, Q2, formed of a high-side switch QI connected between a high-side / voltage node NH and a switch node Nx and a low-side switch connected between the switch node Nx and a low-side / voltage node NL. The high-side and low-side switches may, for instance, be embodied as a respective transistor, such as a MOSFET, BJT or (GaN) HEMT, although other examples will be readily apparent to the skilled person. An auxiliary inductive arrangement LI and a main inductive arrangement L2 are connected, in series, between the switch node Nx and the low-side node NL. A capacitance arrangement Cl (e.g., a capacitor) is connected in parallel with the main inductive arrangement L2. Control signals SI, S2 control the conductivity of each switch QI, Q2 to control the flow of current through the inductive arrangements LI, L2. Approaches for controlling the switching operation of the switch array are well known and established in the field of LLC converters.

[0049] To provide power to the main output interface 120, the switched-mode power converter comprises a main set of one or more windings LMI, LM2 magnetically coupled to the main inductive arrangement L2. Current flow in the main inductive arrangement L2 causes current to flow in the main set of one or more windings LMI, LM2. This current flow is rectified (using a main rectifying arrangement DMI, DM?) and provided to a main capacitive arrangement CM, which stores the charge from the rectified current flow to function as first converted power VM at the main output interface 120.

[0050] To provide power to the auxiliary output interface 130, the switched-mode power converter comprises an auxiliary set of one or more windings LA magnetically coupled to the auxiliary inductive arrangement LI. In the illustrated example, the auxiliary inductive arrangement LI is different to the main inductive arrangement. Current flow in the auxiliary inductive arrangement LI causes current to flow in the auxiliary set of one or more windings LA. This current flow is rectified (using an auxiliary rectifying arrangement DA) and provided to an auxiliary capacitive arrangement CA, which stores the charge from the rectified current flow to function as second converted power VA at the auxiliary output interface 130.

[0051] Appropriate approaches for defining and controlling the power provided to the main and auxiliary output interfaces, by appropriate switching of the switch array QI, Q2, are well established in the art - e.g., by controlling the duty cycle of switching each of the switches QI, Q2 in the switch array.

[0052] The load driving arrangement 100 may comprise additional circuitry and / or components, such as resistive elements, which are not depicted for the sake of illustrative clarity.

[0053] The skilled person will readily appreciate that the switched-mode power converter 140 illustrated in Figure 1 is merely a suitable representative example, and that variations on such switched-mode power converters are well known to the skilled person. Other examples include, for instance, single-switch (buck) power converters, boost converters, buckboost converters, flyback converters and so on.

[0054] A number of example topologies and control methods for switched-mode power supplies are described and illustrated in Kamil, Mohammad. "Switch Mode Power Supply (SMPS) Topologies (Part I)." AN1114, Microchip Technology Inc (2007), any of which could be readily adapted for providing an auxiliary output interface by positioning an auxiliary winding to be magnetically coupled to an inductive arrangement directly connected to a switch node.

[0055] In the illustrated example, the main output interface 120 and the auxiliary output interface 130 are galvanically isolated from the input interface 110. However, this approach is not essential, and each output interface 120, 130 may instead be electrically connected to the input interface, e.g., using any well-known switched-mode power converter configuration. It can be seen that by operating the two switches QI and Q2, the input power is simultaneously switched into the inductor LI and the inductor L2 and is converted into the coupled windings LA and LMI / LM2. The magnitudes of the power on the main output interface and the auxiliary output interface are tightly co-related with each other. For example, the circuit should be designed such that during normal operation, an appropriate or proper power is provided to activate the main load and an appropriate proper power is provided to activate the auxiliary load. Correspondingly, the parameters of the components in the circuit should be designed to meet these requirements. But it has been recognized that there may be some circumstances where there is a desire to provide power to only one of the main and auxiliary loads, or to change a ratio of power provided to the two loads. This may, for instance, be useful upon startup of the load driving arrangement to initially provide power to the auxiliary load before powering the main load. As another example, this may be useful to place a main load in standby operation whilst still powering the auxiliary load. The existing circuit, however, is unable to provide such flexibility. The moment the circuit generates the second output power sufficient to activate the auxiliary load, the circuit also generates the first output power sufficient to activate the main load.

[0056] The present disclosure provides a technique that facilitates the switching of the load driving arrangement in controlling the first output power to the main load between two operation modes according to the condition of the second output power. More particularly, the present disclosure introduces a tuning circuit configured to controllably tune an intrinsic circuit parameter of the switched-mode power converter according to the condition of the second output power.

[0057] More specifically, during a first operation mode, the tuning circuit is configured to tune the intrinsic circuit parameter to have a first value; and during a second operation mode, the tuning circuit is configured to tune the intrinsic circuit parameter to have a second value, different to the first value. The first operation mode value and the second operation mode value are differentiated (from one another) in relation to the auxiliary output interface and / or the second converted power.

[0058] As a working example, during the second operation mode, the tuning circuit may be adapted to (in the second operation mode) tune the intrinsic circuit parameter of the switched-mode power converter to suppress the first converted power with respect to (i.e., compared to) the first converted power (provided) in the first operation mode. In other words, in the second operation mode, the gain of the converting arrangement with respect to the first converted power is less than the gain during the first operation mode. More particularly, in some examples, during the second operation mode, the tuning circuit is adapted to tune the intrinsic circuit parameter of the switched-mode power converter to suppress the first converted power below a threshold of activating the main load thereby deactivating the main load. Correspondingly, in the first operation mode, the tuning circuit may be adapted to tune the intrinsic circuit parameter of the switched-mode power converter to provide the first converted power at no less than said threshold thereby activating the main load.

[0059] It is further recognized that tuning the intrinsic circuit parameter may affect the second converted power as well. In particular, tuning the intrinsic circuit parameter will influence both the gain with respect to the first converted power (i.e., VM / VIN) and the gain with respect to the second converted power (i.e., VA / VIN). The tuning circuit is preferably adapted such that, during both the first and the second operation mode, the second converted power is no less than a second threshold for activating or powering the second load. The value of the second threshold may depend upon the precise nature of the second load. In other words, in the second operation mode, the gain of the converting arrangement with respect to the second converted power is sufficient for powering the auxiliary load.

[0060] The first and second operation modes are the essence of invention for tuning the circuit parameter to adjust the first converted power at the first output interface. The two operations modes are different with respect to different conditions in the second converted power and / or the second output interface. This makes the first converted power no longer follow a fixed relation with respect to the second converted power, but rather provides more flexible operation of the load driving arrangement.

[0061] The first and second operation modes can depend on various conditions so as to solve various problems and achieve various advantages.

[0062] In some preferred examples, in order to solve the above-mentioned technical problem of too-early or simultaneous activation of the main load when activating the auxiliary load, the condition in the second converter power and / or the second output interface relates to time of providing the second converted power during the start up (of the load driving arrangement). More specifically, the load driving arrangement is configured to operate in the second operation mode between a time at which the load driving arrangement was powered up and a time at which the auxiliary output interface has been provided with the second converted power from the switched-mode power converter for no longer than a predetermined length of time since the load driving arrangement was powered up. In some examples said predetermined length of time is a time duration for said auxiliary output interface and / or said second converted power to fully operate the auxiliary load. In some examples, said predetermined length of time is a time duration required by said auxiliary load connected to the auxiliary output interface and powered by said second converted power.

[0063] In other words, the predetermined length of time may be defined or demanded by the auxiliary load powered by the second converted power. In particular, the predetermined length of time may represent at least a time required or defined for the auxiliary load to power up and become active. As a working example, if the auxiliary load is a control arrangement for a DALI-based system, then the predetermined length of time may be no less than 500 ms.

[0064] In preferred examples, the load driving arrangement operates in the first operation mode after the predetermined length of time for providing the auxiliary output interface with the second converted power has elapsed after the load driving arrangement was powered up.

[0065] Other reasons and triggers for switching or changing the operation mode will be readily apparent to the person skilled in the art, and may depend upon the use-case scenario for the load driving arrangement. As an example, the load driving arrangement may operate in the second operation mode responsive to an indication to deactivate the main load (e.g., enter a stand-by mode), whilst keeping the auxiliary load powered. As another example, the load driving arrangement may enter the first operation mode responsive to an indication to activate both the main load and the auxiliary load.

[0066] Further and more specific examples will be provided later in this disclosure.

[0067] Figure 2 conceptually illustrates a proposed load driving arrangement 200. The load driving arrangement differs from the previously described load driving arrangement by further comprising a tuning circuit 210.

[0068] The tuning circuit is configured to controllably tune an intrinsic circuit parameter of the switched-mode power converter. Here, the intrinsic circuit parameter of the switched-mode power converter is embodied as an effective capacitance of a resonant capacitive arrangement C 1. Tuning the capacitance of the resonant capacitive arrangement C 1 will effectively tune a gain of the switched-mode power converter for the first converted power.

[0069] In the illustrated example, the tuning circuit is configured to controllably connect or disconnect a tuning capacitance arrangement C2 to the resonant capacitance arrangement Cl to thereby tune the effective capacitance of the resonant capacitance arrangement. In particular, the tuning capacitance arrangement C2 may, when connected to the resonant capacitance arrangement Cl, be connected in parallel to the resonant capacitance arrangement. Thus, connecting the tuning capacitance arrangement C2 will increase the effective capacitance of the resonant capacitive arrangement Cl and disconnecting the tuning capacitance arrangement C2 will decrease the effective capacitance of the resonant capacitive arrangement Cl.

[0070] Changing the effective capacitance of the resonant capacitive arrangement changes resonance frequency and changes the characteristics of the transfer of power from the inductor arrangement LI, L2 to at least the main output interface. In particular, the properties of at least the first converted power will change. The component values of the resonant capacitive arrangement Cl and the tuning capacitive arrangement C2 may be appropriately selected to suppress the power provided by the main output interface, i.e., the first converted power. In particular, the component values may be selected such that one or more properties of the first converted power fall below corresponding one or more threshold values for activating or powering a known main load (which values may be determined in advance). As an example, the component values may be selected such that a voltage of the first converted power VM is below a threshold voltage for powering a main load, e.g., a forward voltage of an LED arrangement forming the main load.

[0071] More specifically, changing the effective capacitance of the resonant capacitance arrangement effectively modifies a gain of the converting arrangement, both with respect to the first converted power and the second converted power. The gain, with respect to the first converted power (i.e., VM / VIN), can be controlled such that, when operating in the first operation mode, the main load is provided with sufficient power to be activated and, when operating in the second operation mode, the main load is not provided with sufficient power to be activated. In both operation modes, the gain with respect to the second converted power (i.e., VA / VIN) should be sufficient to drive or activate the auxiliary load (e.g., drive or activate a control arrangement operating as the auxiliary load).

[0072] The tuning circuit may comprise a switching arrangement SW to control the selective connection and disconnection of the tuning capacitance arrangement.

[0073] In a simple example, the switching arrangement is embodied as a single switch (e.g., a single transistor such as a MOSFET, BJT or (GaN) FEMT). The operation of the switching arrangement SW may be controlled by a third control signal S3. A more complex example circuit for functioning as the switching arrangement will be later described.

[0074] In some preferred examples, the tuning circuit may be adapted to increase the capacitance of the resonant capacitive arrangement in the second operation mode, compared to the first operation mode. This approach will thereby suppress the first converted power (in the second operation mode) with respect to the first converted power in the first operation mode.

[0075] The above-described embodiment provides an example in which, more generally, the switched-mode power converter comprises a resonant converter with a resonant component, in the form of a resonant capacitor whose effective capacitance is tuned using the tuning circuit 210.

[0076] However, the proposed approach can also be embodied by tuning an effective resonance-related electrical parameter of one or more other resonant components of the switched mode power supply converter.

[0077] For instance, the tuning circuit may be configured to modify an effective inductance of an inductive arrangement of the switched mode power supply. This could, for instance, be achieved by a tuning circuit configured to selectively connect and bypass a tuning inductive arrangement in series with the main and / or auxiliary inductive arrangements LI, L2.

[0078] Of course, a combination of these techniques could also be employed. For instance, the tuning circuit may be configured to modify / tune an effective inductance of an inductive arrangement of the switched mode power supply and modify / tune an effective capacitance of a capacitive arrangement of the switched mode power supply.

[0079] Other suitable examples will be apparent to the skilled person.

[0080] Figure 3 is a circuit diagram of an example switching arrangement SW to control the selective connection and disconnection of the tuning capacitance arrangement C2. The switching arrangement SW is illustrated with its connection to the tuning capacitance arrangement C2 and the high node NH illustrated for the sake of understanding.

[0081] The switching arrangement comprises a switch Q3 (e.g., a BJT or other transistor) which selectively connects or disconnects the tuning capacitance arrangement C2 in parallel to the resonant capacitance arrangement (not illustrated). When activated, the switch Q3 connects the tuning capacitance arrangement C2 to the resonant capacitance arrangement. When deactivated, the switch Q3 disconnects the tuning capacitance arrangement C2 from the resonant capacitance arrangement.

[0082] The switching arrangement further comprises additional circuitry for controlling the activation and deactivation of the switch Q3. In particular a first MOSFET Ml, a second MOSFET M2 and a third MOSFET M3 are controlled or configured for controlling the activation and deactivation of the switch. Appropriate pull-up, pull-down and biasing resistors Rl, R2, R3, R4, R5 are provided where appropriate. A Zener diode DZ restricts the maximum voltage at the gate of the first MOSFET to improve turn off speed of the first MOSFET.

[0083] The illustrated switching arrangement SW is configured to connect the tuning capacitance arrangement C2 to the resonant capacitive arrangement when the load driving arrangement is first powered.

[0084] In particular, when the load driving arrangement is first powered (i.e., the voltage at the high node NH reaches an operational voltage), then the second MOSFET M3 and the switch Q3 are switched on. The activation or switching on of the second MOSFET M2 pulls the gate voltage of the first MOSFET to ground, thereby keeping the first MOSFET Ml deactivated or off. As the first MOSFET Ml is deactivated, the gate / base voltage of the switch Q3 is pulled to the voltage at the high node NH, thereby keeping the switch Q3 activated or on. The third MOSFET M3 is initially off (i.e., a third control signal S3 for the third MOSFET initially keeps the third MOSFET off).

[0085] When the third control signal S3 goes high, then the third MOSFET is activated or switched on. This causes the gate of the second MOSFET M2 to connect to ground, switching off the second MOSFET M2. This, in turn causes the gate voltage of the first MOSFET to be pulled towards the voltage at the high node NH, although limited by the breakdown voltage of the Zener diode DZ, activating the first MOSFET Ml. The activation of the first MOSFET pulls the gate / base voltage of the switch Q3 to ground, thereby deactivating the switch Q3 and disconnecting the tuning capacitance arrangement C2 from the resonant capacitance arrangement.

[0086] The third control signal S3 may, for instance, be generated by a processing system that is powered by the second converted power at the auxiliary output interface. In this way, the control signal may only be a high voltage when the second converted power is available (i.e., at a point in time after the load driving arrangement is first powered.

[0087] After this period, the control signal can be controlled (e.g., by the processing system) to selectively connect and disconnect the tuning capacitance arrangement C2 with respect to the resonant capacitance arrangement.

[0088] Previously described embodiments provide techniques for changing an intrinsic circuit parameter of a switched-mode power converter between two modes of operation. The switching arrangement of Figure 3 is particularly suited for an approach when the auxiliary load is the control arrangement that provides at least the third control signal (which effectively controls in which mode of operation the load driving arrangement operates). Figure 4 illustrates another example of a proposed load driving arrangement 400, here embodied as a flyback converter.

[0089] The load driving arrangement 400 again comprises an input interface 410, a main output interface 420, an auxiliary output interface 430, a switched-mode power converter 440 and a tuning circuit 450.

[0090] The input interface 410 is configured to receive an input power VIN, examples of which have been previously described. The main output interface 420 is configured to connect to a main load (not illustrated in Figure 4) and the auxiliary output interface 430 is configured to connect to an auxiliary load (not illustrated in Figure 4). Examples of suitable main and auxiliary loads have been previously described.

[0091] The switched-mode power converter 440 is connected to the input interface and comprises a switched path R11, Cl 1, LI 1, DI 1, QI 1 magnetically and / or electrically coupled to both the main output interface and the auxiliary output interface. In particular, the switched- mode power converter is adapted to, via switching of the input power via the switched path, simultaneously convert the input power VIN into first converted power VM at the main output interface and second converted power VA at the auxiliary output interface.

[0092] In the illustrated example, the switched-mode power converter 140 comprises a flyback converter. The operation of a flyback converter is well established in the art, and is not described in detail for the sake of conciseness. In general, the flyback converter is configured to convert the input power VIN at the input interface into the first converted power VM at the main output interface using a pair of magnetically coupled inductor arrangements Li l, L12. Of interest, the proposed flyback converter further comprises an auxiliary inductive arrangement LI 3 magnetically coupled to the pair of magnetically coupled inductor arrangements for producing the second converted power VA.

[0093] A control signal SI 1 controls the switching of a switch QI 1 in the switched path to thereby control at least the first converted power VM. Appropriate techniques for controlling the switching operation of the switch QI 1 are well known and established in the field of flyback converters.

[0094] In flyback converters, the operation of the switch Ql l may be responsive to a voltage feedback VFB, which indicates the voltage of the first converted power VM. One approach to obtaining the voltage feedback VFB is for the switched-mode power converter 140 to comprise feedback circuitry L14, R18, R19. The feedback circuitry comprises a feedback inductor arrangement L14 (magnetically coupled to at least the pair of magnetically coupled inductor arrangements) and a voltage sensing arrangement R18, R19 connected in series. In the illustrated example, the voltage sensing arrangement is formed from a voltage divider comprises a first dividing resistor R18 and a second dividing resistor R19, in which a voltage across the second dividing resistor operates as the voltage feedback VFB. In other examples, the voltage sensing arrangement may comprise a single resistor, the voltage across which defines the voltage feedback VFB.

[0095] Thus, there may be a control circuit (not illustrated) configured to receive the voltage feedback VFB from the feedback circuitry and control the switching of the switch QI 1 responsive thereto.

[0096] The tuning circuit 450 is configured to controllably tune an intrinsic circuit parameter of the switched-mode power converter. In the illustrated approach, this intrinsic circuit parameter is a resistance of the feedback circuitry.

[0097] In particular, the tuning circuit 450 comprises a switching arrangement SW connected in series with a tuning resistor R17. The switching arrangement is configured to selectively connected the tuning resistor R17 to the voltage sensing arrangement R18, R19, e.g., selectively in parallel with the first dividing resistor, to effectively modify the value of the voltage feedback VFB. This provides a mechanism for controlling the first converted power. An appropriate value for the tuning resistor R17 may be selected so as to appropriately control the first converted power to achieve a desired goal, e.g., a reduction of the first converted power below a threshold voltage for activating a main load connected to the main output interface 420. In the second operation mode, the switch SW is in on state so the resistor R17 is parallel connected with the resistor R18, and the voltage division ratio becomes large so the control circuit would suppress the first converted power with respect to the first converted power in the first operation mode wherein the switch SW is in off state.

[0098] In this way, the switched-mode power converter may comprise a feedback control loop (e.g., comprising the feedback circuitry and a control arrangement) for regulating the first converted power. The tuning circuit 450 is adapted to effectively tune an intrinsic circuit parameter in the feedback so as to adjust the gain of feedback the control loop thereby tuning the first converted power according to the first mode and the second mode.

[0099] As previously mentioned, tuning the intrinsic circuit parameter may affect the second converted power as well. In this embodiment, tuning the intrinsic circuit parameter will influence the gain of the feedback control loop, thereby influencing both the gain with respect to the first converted power (i.e., VM / VIN) and the gain with respect to the second converted power (i.e., VA / VIN). The tuning circuit, e.g., the component values thereof, is preferably adapted such that, during both the first and the second operation mode, the second converted power is no less than a second threshold for activating or powering the second load. The value of the second threshold may depend upon the precise nature of the second load. In other words, in the second operation mode, the gain of the converting arrangement with respect to the second converted power is sufficient for powering the auxiliary load.

[0100] Figure 3 provides a suitable example of a switching arrangement SW that may also be employed for use in the tuning circuit 450 of the load driving arrangement 400 illustrated in Figure 4. However, in other examples, the switching arrangement SW may comprise a single transistor.

[0101] With reference to both Figures 3 and 4, the use of the switching arrangement SW is advantageous because, when the load driving arrangement is first on, this power will be automatically detected and used to make switch Q3 conductive. This causes tuning resistor R17 and the first dividing resistor R18 to be connected in parallel, affecting the voltage feedback and thereby reducing the voltage of the first converted power. After a period of time, e.g., when a microcontroller powered via the auxiliary output interface is ready to operate, then the switch Q3 is deactivated to ensure that it does not affect the normal working state and parameters.

[0102] The load driving arrangement 400 may comprise additional circuitry and / or components, such as resistive elements, which are not depicted for the sake of illustrative clarity.

[0103] In the above-described embodiments, the transistors are assumed to be N- channel or N-type transistors. The skilled person would be readily capable of replacing any transistor with a p-channel or p-type transistor and reconfiguring the circuitry accordingly.

[0104] There is proposed an LED circuit comprising any herein disclosed load driving arrangement; an LED load, connected to the main output interface, configured to function as the main load; and an auxiliary load connected to the auxiliary output interface.

[0105] The proposed approach can be used to control the power provided to the LED load (as the main load) to be below a threshold power when the load driving arrangement operates in the second operation mode. This can prevent activation of the LED mode during the second operation mode, e.g., reducing or avoiding a likelihood that the LED load will emit light or glow when operating in the second operation mode. This can solve a problem of glow upon start up of the LED circuit, especially if the load driving arrangement is configured to enter the second operation mode responsive to the LED circuit being powered up. The auxiliary load may be a control arrangement, such as a micro-controller unit (MCU). In some examples, the control arrangement is configured to control the operation of the tuning circuit, e.g., the switching arrangement of the tuning circuit, so as to control the mode of operation of the load driving arrangement.

[0106] In the above embodiments, the load driving arrangement should be designed with a reasonable margin with respect to the second converted power such that the second converted power is still within an acceptable / operable range for the auxiliary output interface and / or an auxiliary load, regardless of the intrinsic circuit parameter being tuned in the first and second operation mode. In other words, the gain on the second converted power does not vary to such an extent, when switching between the first and second operation modes, that would deactivate the auxiliary load.

[0107] For example, consider a scenario in which the main load is an LED load (having a known forward voltage), and the auxiliary load is a control arrangement, such as an MCU. As an example, a known MCU may be able to function or support a voltage of 2.4V to 3.6V. In the second operation mode, the intrinsic circuit parameter is tuned such that the first converted output is less than the forward voltage of the LED load while the second converted power can be 2.6V to keep the MCU operating; and when switching to the first operation mode, the intrinsic circuit parameter is tuned such that the first converted output is sufficiently to provide the forward voltage of the LED load while the second converted power can rise up to 3.6V for powering the MCU.

[0108] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0109] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0110] If the term "adapted to" is used in the claims or description, it is noted the term "adapted to" is intended to be equivalent to the term "configured to". If the term "arrangement" is used in the claims or description, it is noted the term "arrangement" is intended to be equivalent to the term "system", and vice versa.

[0111] Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A load driving arrangement comprising: an input interface configured to receive an input power (VIN); a main output interface (120) configured to connect to a main load; an auxiliary output interface (130) configured to connect to an auxiliary load; a switched-mode power converter (140) connected to the input interface and comprising a switched path magnetically and / or electrically coupled to both the main output interface (120) and the auxiliary output interface (130), wherein the switched-mode power converter is adapted to, via switching the input power via the switched path, simultaneously convert the input power into first converted power (VM) at the main output interface (120) and second converted power (VA) at the auxiliary output interface (130), wherein the switched- mode power converter comprises a resonant converter with a resonant component which comprises a resonant capacitive arrangement (Cl, C2); and a tuning circuit (250) configured to controllably tune an intrinsic circuit parameter of the switched-mode power converter, wherein the tuning circuit is adapted to tune a capacitance of the resonant capacitive arrangement (Cl, C2) as the intrinsic circuit parameter of the switched-mode power converter, wherein: during a first operation mode, the tuning circuit (250) is to tune the intrinsic circuit parameter to have a first value; during a second operation mode, the tuning circuit (250) is to tune the intrinsic circuit parameter to have a second value, different to the first value; and the first operation mode and the second operation mode are differentiated in relation to the auxiliary output interface (130) and / or the second converted power (VA).

2. The load driving arrangement of claim 1, wherein, during the second operation mode, the tuning circuit (250) is adapted to tune the intrinsic circuit parameter of the switched- mode power converter (1 0) to suppress the first converted power (VM) with respect to the first converted power (VM) in the first operation mode.

3. The load driving arrangement of claim 2, wherein, during the second operation mode, the tuning circuit (250) is adapted to tune the intrinsic circuit parameter of the switched- mode power converter (140) to suppress the first converted power (VM) below a threshold of activating the main load thereby deactivating the main load, and in the first operation mode, the tuning circuit (250) is adapted to tune the intrinsic circuit parameter of the switched-mode power converter (140) to provide the first converted power (VM) no less than said threshold thereby activating the main load, optionally in both of the first and the second operation mode, the tuning circuit (250) is adapted to tune the intrinsic circuit parameter of the switched-mode power converter (140) to provide the second converted power (VA) with an amplitude sufficiently for the auxiliary output interface (130) and / or the auxiliary load.

4. The load driving arrangement of any one of claims 1 to 3, wherein the load driving arrangement operates in the second operation mode between a time at which the load driving arrangement was powered up and a time at which the auxiliary output interface (130) has been provided with the second converted power (VA) from the switched-mode power converter (140) for no longer than a predetermined length of time since the load driving arrangement was powered up.

5. The load driving arrangement of claim 4, wherein said predetermined length of time is a time duration for said auxiliary output interface (130) and / or said second converted power (VA) to fully operate the auxiliary load and / or a time duration required by said auxiliary load connected to the auxiliary output interface (130) and powered by said second converted power (VA).

6. The load driving arrangement of any one of claims 4 or 5, wherein the load driving arrangement operates in the first operation mode after the predetermined length of time for providing the auxiliary output interface (130) with the second converted power (VA) has elapsed after the load driving arrangement was powered up.

7. The load driving arrangement of any one of claims 1 to 6, wherein the load driving arrangement is configured to operate in the second operation mode responsive to:an instruction to provide the auxiliary output interface (130) with the second converted power (VA) SO as to power the auxiliary load but deactivate the main load connected to the main output interface (120).

8. The load driving arrangement of claim 7, wherein the load driving arrangement is configured to operate in the second operation mode responsive to, prior to said instruction, the load driving arrangement has been operating in the first operation mode, or the load driving arrangement has been just powered up.

9. The load driving arrangement of any one of claims 1 to 8, wherein the tuning circuit (250) is adapted to tune the capacitance of the resonant capacitive arrangement (Cl, C2) as the intrinsic circuit parameter of the switched-mode power converter (140) thereby tuning a gain of the switched-mode power converter (140) for the first converted power (VM).

10. The load driving arrangement of claim 1, wherein the tuning circuit (250) is adapted to increase the capacitance of the resonant capacitive arrangement (Cl, C2) in the second operation mode, compared to the first operation mode, to thereby suppress the first converted power (VM) with respect to the first converted power (VM) in the first operation mode.

11. The load driving arrangement of any one of claims 1 or 10, wherein the switched-mode power converter (140) comprises a main inductive arrangement (L2) connected in parallel to the resonant capacitance arrangement (Cl, C2), said main inductive arrangement (L2) is adapted to couple with the main output interface (120); and an auxiliary inductive arrangement (LI) connected in series with the resonant capacitance (Cl, C2), said auxiliary inductive arrangement (LI) is adapted to couple with the auxiliary output interface (130).

12. The load driving arrangement of any one of claims 10 to 11, wherein the tuning circuit (250) is configured to selectively connect or disconnect a tuning capacitance arrangement (C2) to the resonant capacitance arrangement (Cl, C2) to thereby tune the effective capacitance of the resonant capacitance arrangement (Cl, C2).

13. The load driving arrangement of any one of claims 1 to 12, wherein the switched-mode power converter (140) comprises an LLC converter.

14. A LED circuit comprising: the load driving arrangement of any one of claims 1 to 13; an LED load, connected to the main output interface, configured to function as the main load; and an auxiliary load connected to the auxiliary output interface, said auxiliary load optionally being a micro-controller unit, MCU.

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