Modes of operation for a synchronous converter

Abstract

A mechanism for defining a mode of operation for a control arrangement of a synchronous converter arrangement. The control arrangement is configured to control the activation and deactivation of switches in an inverter of the synchronous converter arrangement. The control arrangement operates in one of at least three different modes of operation responsive to a power to be output or provided by the synchronous converter arrangement.

Description

[0001] Modes of operation for a synchronous converter

[0002] FIELD OF THE INVENTION

[0003] The prevent invention relates to the field of synchronous converters, and in particular to modes of operation for synchronous converters.

[0004] BACKGROUND OF THE INVENTION

[0005] Synchronous converters, such as synchronous buck or boost converters, are becoming increasingly popular for use in driving loads with variable power demands, such as dimmable LED loads. Moreover, recent development of transistors, such as the production of GaN or SiC transistors, has made small and highly efficient synchronous buck or boost converters possible.

[0006] A synchronous converter will often be associated with a maximum load rating, being the maximum power rating of a load that can draw power from the synchronous converter. It is desirable for the synchronous converter to be able to efficiently provide power to loads having a power rating between zero (or negligible) and the maximum load rating. In other words, it is desirable for the synchronous converter to provide a full load range, with low losses.

[0007] There is therefore a desire to improve the performance of a synchronous converter.

[0008] SUMMARY OF THE INVENTION

[0009] The invention is defined by the claims.

[0010] According to examples in accordance with an aspect of the invention, there is provided a synchronous converter arrangement for driving a load comprising: a first switch connected between a first node and a switch node; a second switch connected between the switch node and a second node; a resonant circuit connected between the switch node and a third node, the third node being configured to connect to the load; and a control arrangement configured to controllably activate and deactivate the first switch and the second switch responsive to a control signal.

[0011] The control arrangement is operable in at least three modes of operation. The at least three modes of operation include a first mode of operation, in which the control arrangement controllably activates and deactivates the first switch and the second switch, responsive to the control signal, using a pulse-frequency control technique.

[0012] The at least three modes of operation also include a second mode of operation, in which: the control arrangement controls the length of time for which the first switch is activated, per activation of the first switch, responsive to the control signal; and the control arrangement fixes a constant length of time for which the second switch is activated per activation of the second switch.

[0013] The at least three modes of operation also include a third mode of operation in which the control arrangement controls a frequency of activation and deactivation of the first switch and the second switch, using a switching frequency control technique, responsive to the control signal.

[0014] The control arrangement is configured to control in which mode of operation the control arrangement operates responsive to a desired power to be provided by the synchronous converter arrangement.

[0015] The control arrangement of the proposed synchronous converter arrangement is able to control or modify the power supplied by the synchronous converter arrangement responsive to a control signal. The mode of operation of the control arrangement is dependent upon the desired power to be delivered. This means that the control arrangement is able to switch a mode of operation, e.g., to a more efficient, less lossy or less noisy mode of operation, dependent upon the desired power. The present disclosure recognizes that different levels of power delivery benefit would benefit from different control techniques for supplying the power using a first and second switch.

[0016] The present disclosure proposes three distinct modes of operation for controlling the switches of the synchronous converter arrangement dependent upon the power to be delivered. Each mode of operation controls the power delivered by the synchronous converter arrangement responsive to a control signal.

[0017] The desired power to be provided by the synchronous converter arrangement may be indicated by the control signal. This provides a reliable mechanism for performing control of the power provided by the synchronous converter arrangement whilst operating in a most appropriate control mode for the power to be provided by synchronous converter arrangement. In this way, the control arrangement may be configured to (in each mode of operation) effectively control the power delivered by the synchronous converter arrangement responsive to the desired power to be delivered.

[0018] The indication provided by the control signal may, for instance, be an absolute indication (e.g., directly identifying a desired power level) or a relative / feedback indication (e.g., indicating an error between a current power level and the desired power level). Appropriate approaches for controlling the activation and deactivation of the switches responsive to such parameters will be apparent to the skilled person.

[0019] In some examples, the synchronous converter arrangement comprises a feedback arrangement configured to generate a feedback signal responsive to a power at the third node, wherein the control signal is responsive to the feedback signal. In this way, the control of the activation and deactivation of the switches is responsive to a power output by the synchronous converter arrangement, thereby providing more accurate and reliable control over the power output by the synchronous converter arrangement.

[0020] The synchronous converter arrangement may further comprise a comparative arrangement configured to compare the feedback signal to a reference signal to generate the control signal. The reference signal may effectively represent a desired power level to be provided by the synchronous converter arrangement. In this way, the control signal may indicate an error between a current power level and the desired power level.

[0021] In some examples, the feedback arrangement comprises a single resistor connected in series with the load driven by the synchronous converter arrangement; and the feedback signal may change responsive to a current through the single resistor. In this way, the synchronous converter arrangement may perform electrical current feedback control of the power provided to the load of the synchronous converter arrangement.

[0022] In some examples, the resonant circuit comprises a transformer connected between the switch node and the third node.

[0023] The resonant circuit may comprise a capacitor arrangement connected between the switch node and the second node.

[0024] The synchronous converter arrangement may comprise a rectifying arrangement connected between the resonant circuit and the third node. The rectifying arrangement may comprise or be formed from a single diode connected between the resonant circuit and the third node.

[0025] The control arrangement may be configured to operate in the first mode of operation responsive to the desired power falling below a first threshold. This approach recognizes that a pulse-frequency control technique is particularly advantageous, e.g., more efficient than other techniques, when used to supply or provide a relatively low level of power.

[0026] The first mode of operation has an advantage in avoiding the (further) reduction of transferred energy per switching cycle of the switching arrangement when targeting very low power levels. It is recognized that the attempted transfer of very small levels of energy per switching cycle is difficult to achieve in an accurate way. By reducing the frequency of energy pulses (using the first mode of operation), accurate control over the power delivered by the synchronous converter arrangement can be achieved even at low power levels.

[0027] In some examples, the first threshold is no greater than 5% of a maximum power that the synchronous converter arrangement is able to deliver.

[0028] The control arrangement may be configured to operate in the second mode of operation responsive to the desired power falling between the first threshold and a second, higher threshold.

[0029] If pulse-frequency control is maintained for increasing levels of power, then the switching frequency of the first and second switches would similarly increase. As power levels continue to increase, this would disadvantageously create electromagnetic emissions at undesirable frequencies (e.g., at frequencies greater than 150 kHz). The second mode of approach effectively decreases the switching frequency as the power level to be delivered increases.

[0030] In some examples, the second threshold is no less than 60% of a maximum power that the synchronous converter arrangement is able to deliver.

[0031] The control arrangement may be configured to operate in the third mode of operation responsive to the desired power rising above the second threshold.

[0032] The third mode of operation recognizes that, if the length of time that the second switch is activated is fixed whilst the length of time that the first switch is activated increases (i.e., as performed during the second mode of operation), then a point will be reached at which the two periods are equal. Further increasing the length of time that the first switch is activated would reduce the converter power. An alternative mode of operation can therefore be employed to facilitate further increases to the power output by the synchronous converter arrangement.

[0033] In some examples, the resonant circuit is an LLC resonant circuit or an LLCC resonant circuit. In some examples, the synchronous converter arrangement comprises a halfbridge inverter or a full-bridge inverter. The first and second switches form part of the halfbridge inverter or full-bridge inverter.

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

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] 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:

[0037] Fig. 1 illustrates a proposed synchronous converter arrangement;

[0038] Fig. 2 illustrates waveforms for a proposed control technique; and

[0039] Fig. 3 illustrates a relationship between modes of operation and desired power.

[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 defining a mode of operation for a control arrangement of a synchronous converter arrangement. The control arrangement is configured to control the activation and deactivation of switches in an inverter of the synchronous converter arrangement. The control arrangement operates in one of at least three different modes of operation responsive to a power to be output or provided by the synchronous converter arrangement.

[0044] Embodiments are at least partially based on the realization that different possible modes of operation of the control arrangement are advantageous for efficient or effective use of the inverter for providing different levels of power using the synchronous converter arrangement.

[0045] Figure 1 illustrates a proposed synchronous converter arrangement 100 for driving a load LED.

[0046] The synchronous converter arrangement 100 comprises a first switch SI, a second switch S2, a resonant circuit 110 and a control arrangement 150.

[0047] The first switch SI is connected between a first node N1 and a switch node NX. The second switch S2 is connected between the switch node NX and a second node N2, which may be connected to a ground or reference voltage. The resonant circuit 110 is connected between the switch node NX and a third node N3. The third node is configured to connect to the load LED.

[0048] The first switch SI and the second switch S2 may both be embodied as a respective field-effect transistor, such as a MOSFET or an HEMT (e.g., a GaN HEMT). However, any suitable form of electrically controllably switch could be employed, e.g., any form of transistor having a body diode or diode conduction mode.

[0049] A switch is activated when it is controlled to allow bidirectional current flow therethrough, and is deactivated when it is controlled to prevent or restrict bidirectional current flow. Of course, each switch may comprise or define a body diode that permits or allows unidirectional current when deactivated. The control arrangement 150 may be configured, for instance, to control a gate-source voltage at a switch in order to controllably activate and deactivate the switch.

[0050] Thus, the control arrangement may be configured to: control a voltage at a gate of the first switch (e.g., first FET) to controllably activate and deactivate the first switch; and control a voltage at a gate of the second switch (e.g., second FET) to controllably activate and deactivate the second switch.

[0051] In particular, the control arrangement 150 may define or output a first gate control signal SGI that controls the voltage at the gate of the first switch and a second gate control signal SG2 that controls the voltage at the gate of the second switch.

[0052] An alternative label for the first switch SI is a high-side switch. An alternative label for the second switch S2 is a low-side switch. Where the switches are embodied as FETs, the first switch SI may be labelled a first FET or a high-side FET and the second switch S2 may be labelled a second FET or low-side FET.

[0053] To function as an isolated load-resonant DC-DC converter, a power supply VIN is provided to the first node Nl. The voltage at the third node N3 acts as the output to the converter. Thus, when the converter 100 operates as DC-DC converter, a load will be connected to draw power from the third node N3. Different approaches for controlling the activation of the first and second switches to perform a flyback DC-DC conversion process are well-established in the art. For instance, one example approach is disclosed by Medina- Garcia, Alfredo, et al. "Resonant hybrid flyback, a new topology for high density power adaptors." Electronics 7.12 (2018): 363.

[0054] The power supply VIN may, for instance, be generated by a rectifying bridge (not illustrated in Figure 1) connected between an AC mains power supply and the synchronous converter arrangement. As another example, the power supply VIN may be provided by a battery or cell arrangement. It will be apparent that the power supply VIN is a (generally) DC power supply, although a ripple voltage (e.g., no more than ±10% or ±5%) is considered acceptable.

[0055] It will be appreciated that the control arrangement 150 is configured to controllably activate and deactivate the first switch SI and the second switch S2. In the proposed approach, this is performed responsive to a control signal Sc.

[0056] In particular, the control signal may identify, indicate or be otherwise response to changes to a desired power to be delivered by the synchronous converter arrangement to the load, known simply as a “desired power”. As a first example, the control signal may indicate a desired power to be delivered by the synchronous converter arrangement. As a second example, the control signal may whether to increase, decrease or maintain a power delivered by the synchronous converter arrangement, e.g., produced using a feedback loop as later described. In this way, the desired power to be provided by the synchronous converter arrangement may be effectively indicated by the control signal.

[0057] Thus, the control signal may directly indicate the desired power to be delivered by the synchronous converter arrangement. Alternatively, the control signal may indicate a change in the desired power (e.g., which may be used to modify or change a buffered or stored value representing the desired power).

[0058] The control arrangement 150 may process the control signal Sc to determine in what manner to control the first switch and the second switch. In particular, the control arrangement 150 may generate the gate control signals SGI, SG2 for controlling the activation and deactivation of the first and second switches, as previously described.

[0059] In particular, the control arrangement 150, first switch SI and second switch S2 may be considered to form an inverter for the synchronous converter arrangement, more specifically a half-bridge inverter, in that they function to convert a DC voltage into an AC voltage. The control arrangement 150 controls an activation and deactivation of the first and second switches to effectively control the characteristics of the AC voltage received at the resonant tank.

[0060] The resonant circuit 110 may comprise or be formed from a resonant tank.

[0061] In the illustrated example, the resonant circuit 110 comprises a first inductor Ls, a second inductor Lp and a first capacitor arrangement Cs connected in series with a first side of a transformer wl, w2. The first inductor Ls and the first capacitor arrangement Cs are both connected, in series, between the switch node NX and the second node N2. The windings wl, w2 of the transformer further act as an inductive element for the resonant circuit. The resonant circuit 110 may further comprise, as illustrated, a second capacitor arrangement Cp connected in parallel to the transformer wl, w2.

[0062] The transformer wl, w2 comprises a pair of windings wl, w2, formed from a first winding wl and a second winding w2. The pair of windings wl, w2 are magnetically coupled to one another, but electrically isolated from one another. Elements electrically connected to a first winding wl (of the pair of windings) may be considered to lie on a first or input side of the transformer. Elements electrically connected to a second winding w2 (of the pair of windings) may be considered to lie on a second or output side of the transformer.

[0063] The transformer wl, w2 may, in practice, form or define the second inductor Lp for the resonant circuit. Thus, the second inductor Lp may be omitted in a practical implementation of the resonant circuit. More particularly, the mutual inductance of the transformer wl, w2 may perform the function of the second inductor.

[0064] The first winding wl is connected, in series with the first inductor Ls and in parallel to the second inductor Lp (if present) as well as the first capacitor arrangement, between the switch node NX and the second node N2. The second winding w2 is electrically connected to the third node N3, here: in parallel with the second capacitor arrangement Cp.

[0065] In this way, the illustrated resonant circuit is formed as an LLCC resonant circuit. One alternative resonant circuit is an LLC resonant circuit (which can be achieved by omitting the second capacitor Cp arrangement).

[0066] In other embodiments, the transformer wl, w2 may be omitted, e.g., and replaced by the second inductor Lp (connected in series with the first inductor Ls and first capacitance arrangement Cs). If present, the second capacitor arrangement Cp may be connected in parallel to the second inductor Lp. This approach, of course, provides a nonisolating synchronous converter arrangement 100. The synchronous converter arrangement 100 may further comprise, as illustrated, a rectifying arrangement 120 connected between the resonant circuit 110 and the third node N3. More specifically, for the illustrated example, the rectifying arrangement 120 is connected between the second winding w2 (of the transformer wl, w2) and the third node N3. If the transformer wl, w2 is omitted, the rectifying arrangement 120 may be connected from an intermediate node (located between the first inductor Ls and second inductor Lp) and the third node N3.

[0067] In the illustrated example, the rectifying arrangement is a single diode connected between the resonant circuit and the third node.

[0068] The synchronous converter arrangement 100 may further comprise a buffer capacitor CB connected between the third node N3 and a ground or reference voltage GND, which may be defined as a voltage at a fourth node N4. Preferably, the fourth node N4 is electrically isolated from the first side of the transformer, and more particularly from the second node N2.

[0069] A voltage between the third node N3 and the ground or reference voltage GND may define the voltage supplied or provided to the load LED.

[0070] In the illustrated example, the load LED is embodied as an LED arrangement (e.g., comprising one or more LEDs). In this way, there is also provided a lighting arrangement comprising the synchronous converter arrangement 100 and an LED arrangement LED powered by the synchronous converter arrangement 100.

[0071] However, the load LED may be replaced by any other suitable load for being driven by a synchronous converter arrangement 100, such as a speaker, sensing arrangement, antenna arrangement and so on.

[0072] The present disclosure proposes to configure the control arrangement 150 to be operable in at least three modes of operation (or simply, “operation modes”). The control arrangement 150 selects the mode of operation (in which to operate) responsive to a desired power to be provided by the synchronous converter arrangement, i.e., a (desired) power to be drawn by the load. As previously mentioned, this may be indicated by the control signal Sc.

[0073] The different operation modes are designed for operating at different load levels, i.e., different levels of power to be drawn by a load. This improves an efficiency of the synchronous converter arrangement.

[0074] The desired power to be drawn by the load may change as a result of, for example, a change in the impedance of the load (e.g., if an LED of an LED arrangement forming the load fails); and / or a change in the desired current through the load (e.g., for dimmable control of an LED load).

[0075] In general, the modes of operation share a common characteristic in that the control arrangement controls the first switch and the second switch such that only one of the two switches is activated at a time. This is a characteristic of a synchronous converter arrangement. Generally, the first and second switches are controlled to be alternately activated and deactivated.

[0076] In some examples, a deadtime is introduced between the deactivation of one switch and the activation of the other switch. During the deadtime, neither the first switch nor the second switch is activated. The deadtime can allow for the voltage at the switch node to swing to a voltage at the first node or the second node, e.g., to target zero voltage switching. The deadtime following deactivation of the first switch may be labelled a first deadtime and the deadtime following deactivation of the second switch may be labelled a second deadtime.

[0077] Figure 2 graphically illustrates waveforms of the first gate control signal SGI and the second gate control signal SG2, which illustrates a general control procedure or technique performed by the control arrangement (e.g., regardless of the mode of operation). The waveforms are illustrated in terms of voltage over time.

[0078] The waveform for the first gate control signal SGI is illustrated using a solid line. The waveform for the second gate control signal SG2 is illustrated using a dashed line.

[0079] The first gate control signal SGI is configured to alternately activate (e.g., when at a high voltage VH) and deactivate (e.g., when at a low voltage VL) the first switch. Similarly, the second gate control signal SG2 is configured to alternately activate (e.g., when at a high voltage VH) and deactivate (e.g., when at a low voltage VL) the second switch. The first and second gate control signals are synchronously controlled such that the first and second switches are not activated at a same time.

[0080] A length of time that the first switch is activated (per activation of the first switch) may be labelled a first switch activation time toNi. A length of time that the second switch is activated (per activation of the second switch) may be labelled a second switch activation time toN2. A length of time between deactivation of the first switch and activation of the second switch (per deactivation of the first switch) may be labelled a first deadtime tai. A length of time between deactivation of the second switch and activation of the first switch (per deactivation of the second switch) may be labelled a second deadtime td2. The first and second deadtimes may, for simplicity of control, be the same. Alternatively, the first and second deadtimes may differ from one another, e.g., depending upon the resonance of the resonant circuit, to target zero voltage switching.

[0081] In other embodiments, the first and second deadtimes are omitted (i.e., the deadtimes are equal to 0).

[0082] From the foregoing, and as illustrated in Figure 2, it will be clear that the control arrangement may be configured to (in each mode of operation) iteratively or cyclically perform a predetermined sequence of steps. The predetermined sequence may include (performed in the listed order): activating the first switch, waiting a first switch activation time, deactivating the first switch, waiting a first deadtime, activating the second switch, waiting a second switch activation time, deactivating the second switch and waiting a second deadtime.

[0083] Figure 3 shows schematically three modes of operation for the control arrangement 150. In each mode of operation, the control arrangement is configured to control a value of the first switch activation time toNi (illustrated with a solid line) and a value of the second switch activation time toN2 (illustrated with a dashed line), responsive to the control signal.

[0084] For the purpose of the illustrated example, in each mode of operation, the control arrangement is configured to control the first and / or second switch activation time responsive to a desired power P to be delivered by the synchronous converter arrangement to the load, i.e., a “desired power”, which is indicated by the control signal.

[0085] In a first mode of operation 310, the control arrangement controllably activates and deactivates the first switch and the second switch, responsive to the control signal, using a pulse-frequency control technique.

[0086] In a pulse-frequency control technique, the frequency at which the first switch is activated is controlled responsive to the control signal. As previously explained, the control signal may identify or indicate changes to a power to be delivered by the synchronous converter arrangement.

[0087] More particularly, the majority of the control over the power delivered by the synchronous converter arrangement is achieved by controlling the length of the time for which the second switch is activated per activation of the second switch (i.e., the second switch activation time). In particular, the second switch activation time may reduce for an increasing power to be delivered by the synchronous converter arrangement (i.e., so that the first switch is activated more frequently). Thus, during the first mode of operation, the control arrangement may be configured to reduce the second activation time responsive to the desired power (to be drawn from the synchronous converter arrangement) increasing. The control arrangement may also be configured to prevent the reduction of the first activation time responsive to the desired power (to be drawn from the synchronous converter arrangement) increasing, e.g., either maintaining or increasing the first activation time.

[0088] Preferably, during the first mode of operation, the magnitude of the rate at which the second switch activation time changes (responsive to changes in the control signal) is greater than the magnitude of the rate at which the first switch activation time changes. In particular, during the first mode of operation, the magnitude of the rate at which the second switch activation time changes (responsive to changes in the control signal) may be no less than 5 times greater than the magnitude of the rate at which the first switch activation time changes.

[0089] As a working example, the first switch activation time may be fixed during the first mode of operation. This ensures that control over the power delivered by the synchronous converter arrangement is achieved by controlling the length of the time for which the second switch is activated per activation of the second switch. Thus, in some examples, when performing a pulse-frequency control technique, the length of time for which the first switch is activated (i.e., the first switch activation time), per activation of the first switch, is fixed.

[0090] The second switch activation time may, during the first mode of operation, reduce from a first maximum toN2MAx (associated with a minimum switching frequency fs.min of the switches) to a first minimum toN2MiN (associated with a maximum switching frequency fs.max of the switches).

[0091] In a second mode of operation 320, the control arrangement controls or modifies the length of time for which the first switch is activated (i.e., the first switch activation time), per activation of the first switch, responsive to the control signal. In particular, the control arrangement may increase the first switch activation time for an increasing desired power to be delivered by the synchronous converter arrangement.

[0092] In the second mode of operation, the control arrangement fixes a / the length of time for which the second switch is activated per activation of the second switch (i.e., the second switch activation time). In other words, during the second mode of operation, the second switch activation time may be fixed or constant, e.g., within a reasonable or measurable margin of error (e.g., ±5% or, more preferably ±1%). In this context, the second switch activation time is fixed or constant (e.g., ±5% or, more preferably ±1%) for different values of the first switch activation time and across different activation / deactivation cycles of the second switch. Preferably, the length of time for which the second switch is activated per activation of the second switch is larger than zero.

[0093] In a third mode of operation 330, the control arrangement controls a frequency of activation and deactivation of the first switch and the second switch, using a switching frequency control technique, responsive to the control signal. In this approach, the greater the power to be drawn, the lower the frequency of activating and deactivating the first and second switches.

[0094] During the third mode of operation, the ratio between the first switch activation time and the second switch activation time may be the same. As an example, the first switch activation time and the second switch activation time may be the same.

[0095] Approaches for performing a switching frequency control technique are well known in the art.

[0096] Figure 3 also illustrates one approach by which the control arrangement to determine in which mode of operation to operate.

[0097] In particular, the control arrangement is configured to select a mode of operation dependent upon into which of a plurality of ranges the desired power P falls. More particularly, each mode of operation is associated with a different range of values for the desired power.

[0098] In particular, the control arrangement may be configured to operate in the first mode of operation responsive to the desired power falling below a first threshold Pl. Thus, the control arrangement may be configured to operate in the first mode of operation responsive to the desired power falling with a first range (e.g., ranging from 0 to the first threshold).

[0099] Similarly, the control arrangement may be configured to operate in the second mode of operation responsive to the desired power falling between a / the first threshold Pl and a second threshold P2. Thus, the control arrangement may be configured to operate in the second mode of operation responsive to the desired power falling with a second range (e.g., ranging from the first threshold to the second threshold).

[0100] Similarly, the control arrangement may be configured to operate in the third mode of operation responsive to the desired power rising or being above a / the second threshold P2. Thus, the control arrangement may be configured to operate in the third mode of operation responsive to the desired power falling with a third range (e.g., ranging from the second threshold P2 to a maximum power PMAX deliverable by the synchronous converter arrangement).

[0101] The threshold(s) may be defined by a percentage of the maximum power PMAX deliverable by the synchronous converter arrangement.

[0102] In particular, the first threshold Pl may be no greater than 5% of a maximum power that the synchronous converter arrangement is able to deliver, e.g., no greater than 2% of the maximum power, e.g., no greater than 1% of the maximum power (e.g., 1% of the maximum power).

[0103] The second threshold P2 may be defined as being no greater than (e.g., equal to) a desired power at which, if the control arrangement were to operate in the first mode of operation, the switching frequency of the first and second switches would be no greater than a predetermined maximum frequency fs.MAX. The predetermined maximum frequency may be defined as a frequency at which any stray electromagnetic emissions meet one or more predetermined frequency criteria. For instance, the predetermined maximum frequency fs.MAX may be no greater than 150kHz, e.g. no greater than 130kHz. The precise power level may, for instance, depend upon the characteristics and / or component values of the synchronous converter arrangement.

[0104] The second threshold P2 may be no less than 60% of a maximum power that the synchronous converter arrangement is able to deliver, e.g., no less than 70% of the maximum power, e.g., no less than 75% of the maximum power (e.g., 75% of the maximum power).

[0105] The second threshold P2 may be defined as being no greater than (e.g., equal to) a desired power at which, if the control arrangement is operating in the second mode of operation, the first switch activation time would be equal to the second switch activation time. This advantageously avoids the first switch activation time exceeding the second switch activation time.

[0106] Turning back to Figure 1, an approach for generating the control signal (for the control arrangement) and using the control signal (at the control arrangement) is hereafter described.

[0107] In particular, the synchronous converter arrangement may further comprise a feedback arrangement 160 configured to generate a feedback signal VFB responsive to a power at the third node N3, wherein the control signal is responsive to the feedback signal.

[0108] The feedback arrangement may, for instance, comprise a single resistor Rs configured to connect in series with the load LED driven by the synchronous converter arrangement. The feedback signal VFB may change responsive to a current through the single resistor. In particular, a voltage across the single resistor Rs may function as the feedback signal VFB.

[0109] The feedback arrangement 160 may comprise a comparative arrangement 161 configured to compare the feedback signal VFB to a reference signal VREF to generate the control signal Sc.

[0110] The reference signal VREF indicates an expected or desired power to be provided by the synchronous converter arrangement, e.g., a desired current to flow through the load. This desired current may, for instance, change in order to change or modify a dimming level of the load, when the load is formed from a lamp such as an LED arrangement. In other examples, the expected or desired power is constant.

[0111] In particular, the comparative arrangement 161 may comprise an error amplifier 162 to generate an error signal Sethat indicates a difference between the feedback signal VFB and the reference signal VREF. This difference effectively represents an error in the power supplied to the load LED.

[0112] In the above approach, the error signal Seeffectively indicates an error between a current flowing through the load and a reference current. However, the skilled person would readily appreciate how other forms of power monitoring or feedback may be used to advantage. For instance, the feedback arrangement 160 may be configured such that the error signal indicates a difference between a voltage supplied to the load (e.g., a voltage at the third node N3) and a reference voltage.

[0113] The comparative arrangement 161 may further comprise an amplifier 163 configured to amplify the error signal Seand produce the control signal.

[0114] In particular examples, the amplifier 163 is a proportional -integral amplifier configured to amplify the error signal and the integral of the error signal (e.g., using different gains), before summing both amplifications to produce the control signal. In this way, the control signal effectively acts to represent an average error over time.

[0115] More particularly, in approaches in which a comparative arrangement 161 is used, then the control signal Cs produced from the comparative arrangement represents a change in the desired power to be output by the synchronous converter arrangement.

[0116] The control processor 150 may use this indicated to change to modify or adjust an internally stored or buffered value representing the desired power (e.g., to increase the desired power or reduce the desired power). The mode of operation of the control arrangement may be dependent upon this internally stored or buffered value representing the desired power, and is therefore dependent upon the control signal. It will similarly be appreciated that, in any mode of operation, the control performed by the control arrangement will also be dependent upon the control signal.

[0117] One alternative to using a feedback arrangement 160 is to use an open control loop system, in which the desired power is defined without reference to the actual power output by the synchronous converter arrangement. For instance, the reference signal VREF may simply be used as the control signal.

[0118] In some examples, in which the feedback arrangement 160 is used, an electrically isolating element 170, such as an optocoupler, is configured to provide electrical isolation between (i.e., electrically decouple) the feedback arrangement and the first and second switches. For instance, the electrically isolating element is positioned between the feedback arrangement 160 and the control arrangement 150, to thereby electrically decouple the control arrangement from the feedback arrangement.

[0119] In some examples, the synchronous converter arrangement further comprises a memory or storage device 180. The memory or storage device may store one or more predefined parameters, values or characteristics for use by the control arrangement. For instance, the memory or storage device may store a minimum switching frequency, a maximum switching frequency, a minimum first switch activation time, a minimum second switch activation time, a first switch activation time for use during the first mode of operation (i.e., during PFC), a first deadtime and / or a second deadtime.

[0120] The control arrangement 150 may be appropriately configured to make use of any one or more of the stored value(s). The skilled person would readily appreciate how the function of the control arrangement (e.g., in any mode of operation) can be bounded by these values.

[0121] In the illustrated examples, the synchronous converter arrangement comprises only two switches that function as a half-bridge inverter for powering the resonant circuit. In other examples, the synchronous converter arrangement comprises four switches that function as a full-bridge inverter for powering the resonant circuit. In such approaches, the four switches may be divided into two sets of switches, wherein switches in a same set of switches are controlled in the same manner as one another (i.e., activated and deactivated as a same time). In this approach, a first set of switches comprises the first switch and a second set of switches comprises the second switch.

[0122] Embodiments make of a control arrangement. The control arrangement can be implemented in numerous ways, with software and / or hardware, to perform the various functions required. A processor is one example of a control arrangement which employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform the required functions. A control arrangement may however be implemented with or without employing a processor, and also may be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions.

[0123] Examples of control arrangement components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

[0124] In various implementations, a processor or control arrangement may be associated with one or more storage media such as volatile and non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM. The storage media may be encoded with one or more programs that, when executed on one or more processors and / or control arrangements, perform the required functions. Various storage media may be fixed within a processor or control arrangement or may be transportable, such that the one or more programs stored thereon can be loaded into a processor or control arrangement.

[0125] 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.

[0126] Functions implemented by the control arrangement may be implemented by a single processor or by multiple separate processing units which may together be considered to constitute a "processor". Such processing units may in some cases be remote from each other and communicate with each other in a wired or wireless manner.

[0127] 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.

[0128] There is also proposed a non-transitory storage medium that stores or carries a computer program or computer code that, when executed a control arrangement, causes the control arrangement to perform its herein proposed functions. If a computer program is discussed above, it may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. 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. 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.

[0129] Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A synchronous converter arrangement (100) for driving a load (LED) comprising: a first switch (SI) connected between a first node (Nl) and a switch node (NX); a second switch (S2) connected between the switch node and a second node (N2); a resonant circuit (110) connected between the switch node and a third node (N3), the third node being configured to connect to the load; and a control arrangement (150) configured to controllably activate and deactivate the first switch and the second switch responsive to a control signal (Sc), wherein the control arrangement is operable in at least three modes of operation including:- a first mode of operation (310), in which the control arrangement controllably activates and deactivates the first switch and the second switch, responsive to the control signal, using a pulse-frequency control technique;- a second mode of operation (320), in which:- the control arrangement controls the length of time (toNi) for which the first switch is activated, per activation of the first switch, responsive to the control signal; and- the control arrangement fixes a constant length of time (toN2) for which the second switch is activated per activation of the second switch; and- a third mode of operation (330) in which the control arrangement controls a frequency of activation and deactivation of the first switch and the second switch, using a switching frequency control technique, responsive to the control signal, wherein the control arrangement is configured to control in which mode of operation the control arrangement operates responsive to a desired power to be provided by the synchronous converter arrangement.

2. The synchronous converter arrangement of claim 1, wherein the desired power to be provided by the synchronous converter arrangement is indicated by the control signal.

3. The synchronous converter arrangement of any one of claims 1 or 2, further comprising a feedback arrangement (160) configured to generate a feedback signal (VFB) responsive to a power at the third node, wherein the control signal is responsive to the feedback signal.

4. The synchronous converter arrangement of claim 3, further comprising a comparative arrangement (161) configured to compare the feedback signal to a reference signal to generate the control signal.

5. The synchronous converter arrangement of any one of claims 3 or 4, wherein: the feedback arrangement comprises a single resistor (Rs) connected in series with the load driven by the synchronous converter arrangement; and the feedback signal changes responsive to a current through the single resistor.

6. The synchronous converter arrangement of any one of claims 1 to 5, wherein the resonant circuit comprises a transformer (wl, w2) connected between the switch node and the third node.

7. The synchronous converter arrangement of any one of claims 1 to 6, wherein the resonant circuit comprises a capacitor arrangement (Cs) connected between the switch node and the second node.

8. The synchronous converter arrangement of any one of claims 1 to 7, further comprising a rectifying arrangement (DI) connected between the resonant circuit and the third node.

9. The synchronous converter arrangement of claim 8, wherein the rectifying arrangement is a single diode connected between the resonant circuit and the third node.

10. The synchronous converter arrangement of any one of claims 1 to 9, wherein the control arrangement is configured to operate in the first mode of operation responsive to the desired power falling below a first threshold (Pl).

11. The synchronous converter arrangement of claim 10, wherein the first threshold is no greater than 5% of a maximum power (PMAX) that the synchronous converter arrangement is able to deliver.

12. The synchronous converter arrangement of any one of claims 10 or 11, wherein the control arrangement is configured to operate in the second mode of operation responsive to the desired power falling between the first threshold and a second, higher threshold (P2).

13. The synchronous converter arrangement of claim 12, wherein the second threshold is no less than 60% of a maximum power (PMAX) that the synchronous converter arrangement is able to deliver.

14. The synchronous converter arrangement of any one of claims 12 or 13, wherein the control arrangement is configured to operate in the third mode of operation responsive to the desired power rising above the second threshold.

15. The synchronous converter arrangement of any one of claims 1 to 14, wherein the resonant circuit is an LLC resonant circuit or an LLCC resonant circuit.

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