LED driving arrangement

Abstract

An LED driving arrangement. A power converter connects an input interface to an output interface and controls the output power provided to the output interface. The power converter comprises a HF power switch and an integrated control circuit that controls an operation of the HF power switch. An intermediate control signal, generated and output by the integrated control circuit during control of the operation of the HF power switch, is both input by the integrated control circuit to control the switching of the high frequency power switch and output to a separate active component to control an operation of the separate active component.

Description

[0001] LED DRIVING ARRANGEMENT

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of LED circuitry, and in particular to LED driving arrangements for driving an LED load.

[0004] BACKGROUND OF THE INVENTION

[0005] There is an ongoing desire to improve artificial lighting arrangements, which are used to provide artificial light in a wide variety of environments, such as in domestic, industrial and / or public settings.

[0006] In particular, there is a demand for highly efficient LED driving arrangements that are able to control a dimming level of an LED load driven by the LED driving arrangement. However, there is a particular problem at low levels of dimming, as it is difficult to reliably reduce a magnitude of a current drawn by the LED load since the frontend LED driver’s output current has a minimum level and is unable to be reduced to lower than this minimum level.

[0007] One existing solution make use of a bleeder / dummy load (e.g., resistor arrangement) to bleed a certain amount of current away from the minimum output current linear of the LED driver, with the remainder passing to the LED load.

[0008] An example of such a configuration is illustrated by Figure 4. The working principle of this circuit arrangement is that there is provided an integrated circuit (IC) US1 that controls whether or not the dummy load draws current responsive to a voltage on a sensing resistor. More particularly, when the load current is high, the voltage on a sensing resistor R28 will also be high and exceed a threshold. The integrated circuit (IC) US1 will switch off, and cause the dummy load R30-R45 to be open (i.e., to not conduct current). When the load current goes low, e.g., due to phase cut dimming, the voltage on R28 will also drop, e.g., below the threshold. This causes the IC US1 to activate and cause the dummy load to draw some current. This will cause the load current for the LED load to drop, which can achieve deep dimming performance.

[0009] However, due to the quiescent working current of the (linear) IC. The IC is unable to be completely shut down, even when the voltage on sensing resistor R28 is above the threshold for causing the dummy load to draw current. Using a typical IC such as BP5131, the quiescent current can lead to a 40mW power consumption (designed for use as a boost topology and the LED load forward voltage is 400V). This causes a 1% efficiency loss on a 4W driver design. This can provide a significant power loss for driver design.

[0010] There is therefore a desire for an improved LED driving arrangement.

[0011] US20130038234A1 discloses a micro-controller outputs a PWM signal to control a switch in parallel with LEDs. US20140049241A1 discloses a driver can work in close loop when a amount of time of AC input voltage disconnection is less than or equal to a threshold and in open loop when the amount of time is greater than the threshold.

[0012] SUMMARY OF THE INVENTION

[0013] Most LED drivers are controlled by an integrated control circuit (IC controller), and this IC controller usually has a control terminal, such as a compensation terminal, on which the IC controller generates an intermediate control signal responsive to the dimming state of the LED driver. Conventionally, this control signal is designed to be sensed by the IC controller to control the control loop of LED driver. In other words, this control terminal provides an intermediate control signal, indicative of the dimming state, free of charge.

[0014] The underlying idea of the present invention is re-using the signal at this control terminal (i.e., the intermediate control signal) for a second function / purpose, besides the original function of being used in the control loop of the LED driver. More specifically, in order to solve various functions such as the above described bleeding function, the underlying idea of the present invention is the provision of a secondary active component in an LED driving arrangement that already comprises a high frequency power switch controlled by an integrated control circuit. In particular, the intermediate control signal produced by the integrated control circuit in controlling the high frequency power switch is used to activate or deactivate the secondary active component. This provides a mechanism that is able to activate or deactivate an active component dependent, for instance, on a dimming level of an LED load. This can be used to advantageously reduce a power consumption by the integrated control circuit at high or low dimming levels, since it saves the existence and power loss of a dedicated circuit to generate a signal indicative of the dimming level. The control terminal and intermediate control signal are originally designed for one purpose only: in the control loop of the integrated control circuit. The present application gives it a new purpose and this is not obvious. The proposed technique thereby balances the desire to provide highly efficient LED driving arrangements without (significantly) affecting performance of the overall LED lighting device at low dimming levels.

[0015] The invention is defined by the claims.

[0016] According to examples in accordance with an aspect of the invention, there is provided a LED driving arrangement.

[0017] The LED driving arrangement comprises an input interface configured to receive an input power; an output interface configured to connect to an LED load and provide an output power for the LED load; a power converter, connected between the input interface and the output interface, and configured to convert the input power into the output power, wherein the power converter comprises a high frequency power switch for controlling the output power.

[0018] The power converter comprises an integrated control circuit configured to: receive a feed signal relating to the input power and / or the output power; generate and output a control signal, in relation to the feed signal, at a first terminal of the integrated control circuit; and input the control signal generated at the first terminal and control the switching of the high frequency power switch responsive to the input control signal.

[0019] Most notably, the LED driving arrangement also comprises an active component, separate to the integrated control circuit and the high frequency power switch, and connected to the first terminal to thereby be controlled responsive to the output control signal.

[0020] The present disclosure recognizes that it is typical to use an active component for various purposes when the output power provided to an LED load is very low, e.g., during deep dimming of the LED load when the current supplied to the LED load is intended to be extremely low. However, this active component is often driven by a dedicated driving circuit in a power lossy manner, such as the dedicated driving circuit disadvantageously still draws at least some power even when it is not to be used in non-dimming state (e.g., a trickle or parasitic charge will be lost).

[0021] The present disclosure proposes to use an existing control signal, originally produced whilst performing a feedback / feedforward control of a high frequency power switch, to activate and deactivate the active component. The feedback / feedforward control will depend upon the desired electrical characteristics of the input / output power. The active component may thereby be activated and deactivated as needed or desired (e.g., for certain electrical characteristics such as a load current drawn) by the control signal. In particular, the active component may activate an auxiliary circuit for certain electrical characteristics or deactivate the auxiliary circuit for certain electrical characteristics.

[0022] More particularly, the control signal used to control the active component is an already existing intermediate signal generated in the production of the signal that controls the switching of the high frequency power switch, and it mitigates a need of a dedicated driving circuit for the active component as well as the power loss thereof. This approach thereby activates and deactivates the active component separately to the high frequency power switch, thereby facilitating control over the power drawn by the LED driving arrangement, e.g., at least at low dimming levels for the LED load.

[0023] In a further embodiment, the active component is adapted to be controlled responsive to the control signal in low frequency, optionally PFC frequency, lower than that of the high frequency power switch.

[0024] In this embodiment, the high frequency integrated control circuit (originally designed for controlling the power switch in high frequency) is re-used for a second function of controlling a separate active component in low frequency. This double function is not obvious since the high and low frequency are usually considered in total different control domain and those skilled in the art would not consider using a single component in both high and low frequency control.

[0025] In some examples, the high frequency power switch is part of the integrated control circuit. This embodiment provides a more compact LED driving arrangement.

[0026] In other examples, the high frequency power switch is external to the integrated control circuit. This embodiment provides greater flexibility for designing or configuring the power converter to achieve a desired power conversion function.

[0027] The power converter may further comprise an output sensing component connected with the output interface and adapted to sense the output power, and the integrated control circuit may be connected to the output sensing component and the feed signal is a feedback signal of the output power. This causes the integrated control circuit to perform a feedback control function, thereby performing reliable control of the output power to have desired electrical characteristics.

[0028] Alternatively or additionally, the integrated control circuit is also able to perform a feedforward control function, and the feed signal would include a sense signal of the input power.

[0029] In some examples, the integrated control circuit is configured to switch between operating in: a closed-loop control mode in which the integrated control circuit is configured to make the sensed output power reach a reference output power by controlling the switching of the high frequency power switch; and an open-loop control mode, in which the integrated control circuit is configured to control the switching of the high frequency power switch to be a maximum switching pattern. This approach acts to provide a universal / multi-functional LED driver that outputs a constant lumen and is also dimmable and this universality / multi-function is preferred by the user.

[0030] In some examples, the integrated control circuit is configured to operate in the open loop control mode when the input power is less than a predetermined value. This provides dimmability of the LED driver. Even more, this avoids an input current going extremely high at dimming state (low input voltage) and improves a reliability of the control performed by the integrated control circuit. Otherwise, when the input voltage is low, if the LED driver is still controlled in the closed loop control mode, the input current would increase so as to achieve constant power, and this increased current may damage the LED driving arrangement.

[0031] In some examples, the integrated control circuit is configured to: operate in the open-loop control mode when the feed signal breaches a predetermined value in which case the control signal is above a certain value; and operate in the closed-loop control mode when the feed signal fails to breach the predetermined value in which case the control signal is below a certain value, wherein said control signal at the certain value is a threshold that activates the active component.

[0032] In this example, the active component is effectively driven by the control signal for free (i.e., no or negligible power loss), without needing a dedicated driver.

[0033] In some examples, the active component is configured to be activated during the open-loop control mode.

[0034] Notably, dimming mode often causes a lot of problems / incompatibility between the LED driving arrangement and an external phase cut dimmer. In this embodiment, the active component is activated in dimming mode to provide one or more of various functions to solve the problems associated with the dimming mode. Therefore the LED driving arrangement can be improved with low power loss and low cost.

[0035] In some examples, the output sensing component is a current sensor adapted to sense the electrical current of the output power, and the control signal represents a difference from a desired electrical current to the electrical current of the output power.

[0036] In some examples, the integrated control circuit is configured to, during the closed-loop control mode, increase the duty cycle of a switching of the high frequency power switch responsive to the control signal increasing and the sensed electrical current decreasing. This provides a negative feedback close-loop control to regulate the electrical current of the output power to reach the desired electrical current.

[0037] In some examples, the active component is connected to the output interface for further control of the output power provided at the output interface.

[0038] In this example, the active component is at the output for fine tuning the output power to the LED load, this can mitigate the influence from the dimming mode and provide more adaptive light output. Alternatively, the active component can also be connected elsewhere such as at the input interface or at an internal location of the power converter, for various purposes. Therefore the location of the active component should not be considered to be limited to only a location at the output interface.

[0039] In some examples, the LED driving arrangement comprises a first auxiliary circuit connected in parallel with the output interface, optionally for diverting power away from the output interface, and the active component comprises a first transistor configured to, when activated (i.e., made conductive), activate a first auxiliary circuit.

[0040] This example provides the above-mentioned bleeding at low dimming level. In particular, the first transistor may only be activated when the control signal meets one or more predetermined conditions (e.g., has a voltage breaching a certain threshold or the like). The predetermined condition may be a condition that indicates a desire by the control signal to control the output power to have a predefined electrical characteristics, e.g., a current below a predefined level.

[0041] In some examples, the first transistor is configured to, when activated, activate a first auxiliary circuit. Thus, the first auxiliary circuit may be activated one when the control signal meets one or more predetermined conditions - indicating that there is a desire for the output to have one or more predetermined conditions.

[0042] The first auxiliary circuit may be a transistor arrangement comprises one or more transistors that draw power when activated, e.g., when current is allowed to flow therethrough. The transistor arrangement provides the bleeding function previously described.

[0043] The LED driving arrangement may further comprise a second auxiliary circuit, such as a linear regulator, connected in series with the output interface, optionally for regulating a current through the output interface to be constant. The active component may comprise a second transistor configured to, when activated (i.e., made conductive), bypass or deactivate the second auxiliary circuit. The second transistor may be activated when the active component is activated. This example provides another function of constant current regulation at deep dimming. In particular, the second transistor may only be activated when the control signal meets one or more predetermined conditions (e.g., has a voltage breaching a certain threshold or the like). The predetermined condition may be a condition that indicates a desire by the control signal to control the output power to have a predefined electrical characteristics, e.g., a current regulated more constant.

[0044] If the LED driving arrangement comprises both the first auxiliary circuit and the second auxiliary circuit, then preferably the two transistors are configured such that the first auxiliary circuit is activated when the second auxiliary circuit is deactivated, and vice versa.

[0045] Please note that other functions are also applicable to be implemented in the LED driving arrangement and be controlled by the active component / control signal.

[0046] In a preferred example, the first terminal may be a compensation terminal / pin of the integrated control circuit and the active component comprises a MOSFET.

[0047] In this example, the widely-existing compensation terminal is re-used as the first terminal to drive the MOSFET. The compensation terminal would produce a voltage dependent on the input power, and the MOSFET is a voltage driven component, thus the compensation terminal can drive the MOSFET well. MOSFET can also be replaced by other voltage-driven components such as a GaN component. Alternatively, if the first terminal is able to provide a proper current, the active component could be implemented by a BJT.

[0048] Please note that the compensation terminal is just an example, and another terminal, capable of producing a signal responsive and being used in the control loop of the integrated control circuit, can also be used for connecting and driving the active component.

[0049] There is also proposed an LED lighting device comprising any herein disclosed LED driving arrangement and the LED load. The LED load may comprise two or more LEDs, e.g., connected in series or parallel.

[0050] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment s) described hereinafter.

[0051] BRIEF DESCRIPTION OF THE DRAWINGS

[0052] 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:

[0053] Figure 1 illustrates a proposed LED driving arrangement;

[0054] Figure 2 illustrates another proposed LED driving arrangement; Figure 3 illustrates an integrated control system for use in proposed embodiments; and

[0055] Figure 4 illustrates a circuit schematic of a known LED driving arrangement.

[0056] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0057] The invention will be described with reference to the Figures.

[0058] 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.

[0059] The invention provides an LED driving arrangement. A power converter connects an input interface to an output interface and controls the output power provided to the output interface. The power converter comprises a high frequency (HF) switched power switch and an integrated control circuit that controls an operation of the HF power switch. An intermediate control signal, generated by the integrated control circuit during control of the operation of the HF power switch, is used to control an operation of a separate active component. The active component is preferably controlled in low frequency operation, and it can provide various functions as below.

[0060] Figure 1 illustrates an LED driving arrangement 100 according to a proposed approach. The LED driving arrangement comprises an input interface 110, an output interface 120, a power converter 130 and an active component 140.

[0061] The input interface 110 is configured to receive an input power with a voltage VIN. The input power may be a rectified AC voltage (e.g., output by a diode bride or other rectifying arrangement) or a PFC bus voltage output by a frontend PFC converter.

[0062] The output interface 120 is configured to connect to an LED load 190 and provide an output power with a voltage VOUT for the LED load 190. The LED load comprises one or more LEDs, e.g., a plurality of LEDs connected in series or in parallel. Please note that the output power may be regulated in terms of the voltage VOUT and / or the current. The LED driving arrangement may further comprise an output capacitor Co connected between the output interface and a ground / reference voltage, e.g., between two terminals of the output interface. This performs a smoothing function on the output power.

[0063] The power converter 130 is connected between the input interface 110 and the output interface 120. The power converter 130 is configured to convert the input power VIN into the output power VOUT. The power converter 130 comprises a high frequency power switch QI (for controlling or defining one or more characteristics of the output power) and an integrated control circuit 135.

[0064] The high frequency power switch QI may, for instance, be field-effect transistor, such as a MOSFET. However, other examples of switches are readily apparent to the skilled person, such as a GaN component, BJTs or the like.

[0065] In the illustrated example, the high frequency power switch QI is external to the integrated control circuit. However, in other examples, the high frequency power switch is integrally formed with the integrated control circuit. A suitable example of this approach is provided later in this disclosure.

[0066] The integrated control circuit 135 is configured to receive at least one feed signal SFI, SF2 relating to the input power and / or the output power. Thus, the integrating control circuit may receive a feedforward signal SFI relating to the input power and / or a feedback signal SF2 relating to the output power. As shown, the SF2 is preferably provided from the source of the power switch QI, but it could also at the output interface.

[0067] The integrated control circuit is configured to generate a control signal, in relation to the feed signal(s) - i.e., responsive to the feed signal(s). The control signal is provided at a first terminal Ti of the integrated control circuit. The integrated circuit is also configured to control the switching of the high frequency power switch responsive to the control signal. Thus, the control signal functions as an intermediate signal in the control of the high frequency power switch, e.g., in the generation of a switch signal that directly controls the high frequency power switch.

[0068] There is also preferably a buffer component connected at the first terminal to smooth it, and it may be implemented by a capacitor CCOMP as shown.

[0069] In particularly preferable examples, the feed signal and control signals are configured such that the control signal is responsive to a (average) difference between a desired current and the real feed current, either the input current, the current through the high-frequency power switch and / or a current provided to the LED load. This effectively means that the control signal is responsive to a dimming level of the LED load, as the dimming level is directly related to said difference which will be described in more detail later.

[0070] When the input voltage is low for high dimming level / low output lumen, the above-mentioned difference is large thus the first terminal’s voltage is high.

[0071] The active component 140 is separate to both the integrated control circuit 135 and the high frequency power switch QI. Nonetheless, the active component 140 is connected to the first terminal Ti to thereby (also) be controlled responsive to the control signal.

[0072] In the illustrated example, the active component 140 is configured to controllably bypass the LED load, i.e., short circuit the output interface.

[0073] More particularly, the active component 140 comprises a (first) transistor is configured to, when activated, divert at least some power away from the output interface. In this scenario, the (first) transistor may, for instance, only be activated when the control signal rises above a predetermined level (e.g., if a current drawn by the LED load drops below a predetermined current level), and be deactivated otherwise.

[0074] This approach advantageously facilitates even more dimming down or even complete turning off of the LED load responsive to a feed signal, thereby mitigating the minimum output current limit of the LED driving arrangement 100. This effectively provides an auxiliary control system for the current of the output power.

[0075] Additionally, as shown in Figure 1, the (first) transistor may be connected in series with a one or more bleed resistors Ri. This facilitates the leaving of only part of the current from the output interface to the LED load to achieve deep dimming. This can also move the voltage / thermal stress of bleeding from the active component 140 to the resistor.

[0076] The first auxiliary circuit (e.g., either the active component 140 alone or the combination of the active component 140 and the bleed resistor(s) Ri) thereby act(s) as an auxiliary circuit that is only activated, by the active component 140, when the control signal meets one or more predetermined conditions, e.g., the magnitude of the control signal is below a predetermined threshold. In particular, the auxiliary circuit may only be activated responsive to the magnitude of the electrical current of the output power being below a certain threshold (as indicated by the control signal).

[0077] Alternative forms of circuits for use as a first auxiliary circuit will be readily apparent to the suitable skilled person. For instance, the first auxiliary circuit may instead or further comprise an inductor or other form of impedance. As another example, the active component 140 alone may act as an auxiliary circuit, e.g., by diverting power away from the output interface. Figure 2 illustrates an alternative LED driving arrangement 200 according to a proposed approach. The LED driving arrangement again comprises an input interface 110, an output interface 120, a power converter 130 and an active component 240.

[0078] In this example, the LED driver comprises a second auxiliary circuit 250, e.g., a linear regulator, connected in series with the output interface 120 (e.g., in series with the LED load). This linear regulator is adapted to closely regulate the current of the output power to be constant so as to reduce flicker / ripple in the light emitted by the LED load. However, such a ripple / flicker smoothing function is more essential when the LED load is dimmed down at low output lumen; whereas in high output lumen such flicker / ripple is not apparent since the ratio of the flicker to the total output lumen is relatively low and may not be needed to be reduced so as to prevent loss of the linear regulator.

[0079] For controlling this second auxiliary circuit 250, the active component 240 here comprises a (second) transistor configured to, when activated, bypass the second auxiliary circuit. In this scenario, the (second) transistor may, for instance, only be activated when the control signal drops below a predetermined level (e.g., if a current drawn by the LED load drops below a predetermined current level), and be deactivated otherwise.

[0080] This approach can be used to advantageously deactivate the second auxiliary circuit (e.g., a linear regulator or a ripple remover) for the LED load for particular electrical characteristics of the output power - as indicated by the control signal. For instance, the second auxiliary circuit may be deactivated at low dimming levels / high lumen level. This improves the power efficiency at low dimming levels / high lumen level without affecting flicker in light provided by the LED load, as such flicker only apparent at high dimming levels / low lumen level.

[0081] In a similar manner to the embodiment described with reference to Figure 1, when the input voltage is low for high dimming level / low output lumen, the above-mentioned difference is large thus the first terminal’s voltage is high. A NOT logic transfers this high voltage into a low logic such that the active component 240 is turned off and the second auxiliary circuit is not bypassed thereby. Thus, the second auxiliary circuit (e.g., linear regulator) is only activated when the output power has certain electrical characteristics, e.g., a current below a certain threshold or voltage below a certain threshold. Other forms of auxiliary circuit will be readily apparent to the skilled person, e.g., noise filtering arrangements and so on.

[0082] Of course, a combination of the two examples of active components (and optionally auxiliary circuits) may be used in some embodiments. Thus, there may be an LED driving arrangement comprising a first active component configured to activate a first auxiliary circuit to bypass the LED load, i.e., short circuit the output interface, when activated, and a (second) active component configured to, when activated, bypass a second auxiliary circuit (e.g., a linear regulator) connected in series with the output interface. Preferably, the first active component is activated when the second active component is deactivated and vice versa.

[0083] The power converter 130 may comprise one or more further power conversion elements, such as one or more inductors L and / or one or more capacitors, for performing the power conversion function.

[0084] In particular, the power converter may be configured or designed as any form of switched-mode power supply, such as a buck converter, a boost converter or a buck-boost converter. The high frequency power switch may function as a switch for such a switched- mode power supply, such that the control of the switching performed by the high frequency power switch effectively controls the output power.

[0085] Figure 3 illustrates an integrated control circuit 300 for use in embodiments. The first terminal and the voltage thereon will be introduced in further detail.

[0086] For the sake of conciseness, only those elements of the integrated control circuit that are relevant to the underlying proposed concept are hereafter disclosed in detail. The skilled person would readily understand the full operation of the integrated control circuit 300 from an inspection of Figure 3 and applying their common general knowledge.

[0087] The integrating control circuit 300 comprises an output interface terminal To connected to the output interface (e.g., via one or more additional elements, not illustrated) and an input interface terminal TIN connected to the input interface (e.g., via one or more additional elements, not illustrated).

[0088] The high frequency power switch QI may, as illustrated, take the form of a transistor (e.g., MOSFET) which (when activated) is the power switch QI in figures 1 and 2.

[0089] In the illustrated example, the high frequency power switch QI is formed as part of the integrated control circuit 300, and is connected between the output terminal To and a feed terminal TF or sensing terminal for sensing a current through the power switch QI when the power switch QI is on and provides a peak current detection. However, in alternative examples, the high frequency power switch is positioned externally to the integrated control circuit 300. Components forming part of the integrated control circuit 300 may be housed in a same package or chip, illustrated by dashed lines in Figure 3. Components that are not part of the integrated control circuit may be positioned externally to the housing.

[0090] In either approach, the feed terminal TF may be coupled to a ground or reference voltage GND via a (external) resistor or impedance (not visible in Fig. 3). In this way, the voltage of the feed signal SF is responsive to a magnitude of the current flowing through the high frequency power switch QI, and thereby being indicative of the (magnitude of the) current of the output power. More specifically, the greater the current flowing through the high frequency power switch QI, the less the current of the output power.

[0091] Put more generally, the overall power converter comprises an output sensing component (here; the external resistor or impedance) that is connected with the output interface and adapted to sense the output power. In preferred examples, the output sensing component may be a current sensor adapted to sense the electrical current of the output power.

[0092] The integrated control circuit is connected to the output sensing component and the feed signal is a feedback signal of the output power.

[0093] The high frequency power switch QI is controlled by control circuitry 390 of the integrated control circuit, responsive to at least a control signal Sc that is generated using a feed signal SF (e.g., a feedback signal) present at the feed terminal TF of the integrated control circuit.

[0094] In the illustrated example, the control signal Sc is produced by comparing the feed signal to a reference value VREF. This comparison may be performed using a first comparator Gi. The reference value VREF represents a desired value for an electrical characteristic of the output signal, e.g., representative of a desired current level for the output power and therefore a desired dimming level.

[0095] In this way, the control signal Sc represents a difference between a desired electrical current (represented by the reference value VREF) and a magnitude of the electrical current of the output power (as defined by the magnitude of the feed signal). The magnitude of the reference value VREF controls or defines the (desired) dimming level of the LED load, i.e., the amount of current in the output power to be drawn by the dimming load. The greater the magnitude of the reference value VREF, the greater the dimming level.

[0096] The feed signal may undergo a sample and hold process before being compared to the reference value VREF. This advantageously reduces a risk of any sudden changes or shifts in the value of the feed signal (as it is sampled and held), and therefore of the operation of the integrated control circuit. It is noted that the control signal Sc is provided to a first terminal Ti of the integrated control circuit 300, e.g., for use in controlling the active component as previously explained. The first terminal may, for instance, be a compensation terminal of an integrated control circuit, examples of which are well known in the art.

[0097] The control signal Sc is further used to control the operation of the high frequency power switch QI.

[0098] The integrated control circuit may, in particular, be configured to increase the amount of current drawn by the high frequency power switch QI responsive to a decrease in the magnitude of the feed signal. Similarly, the integrated control circuit may be configured to decrease the amount of current drawn by the high frequency power switch QI responsive to an increase in the magnitude of the feed signal.

[0099] In the illustrated example, the voltage of the control signal Sc is configured to control the duty cycle of the high frequency power switch QI, e.g., the conduction time per cycle of the input power or per a predetermined time period. Increasing a duty cycle means that, averaged over time, the high frequency power switch will conduct a greater proportion of current at the output node. Thus, the greater the duty cycle of the high frequency power switch QI, the less the current available at the output interface for the LED load (e.g., due at least to Kirchhoff s current law). As later exemplified, the greater the voltage of the control signal, the greater the duty cycle of the high frequency power switch QI (i.e., the more current diverted away from the output power). This facilitates control over the current of the output power for the LED load.

[0100] In this way, the illustrated integrated control circuit is configured to function as a phase-cut dimming control circuit.

[0101] In more detail, when the feed signal decreases, the difference between reference VRef and the feed signal SF increases, thus the control signal Sc increases. The voltage of the control signal Sc is compared to a saw-tooth waveform, e.g., using a second comparator G2. The frequency of the saw-tooth waveform is high frequency, e.g., a higher frequency than the frequency of a mains AC supply that powers the LED arrangement. The saw-tooth waveform may be generated by a waveform generator (not illustrated in Figure 3). The duty cycle of the resultant signal from this comparison will be higher for reducing magnitudes of the control signal Sc and lower for increasing magnitudes of the control signal.

[0102] More specifically, an S-R latch (also known as a flip-flop) connects the output of the second comparator G2 to the high frequency power switch QI. More particularly, the output of the second comparator G2 is connected to a reset (R) node of the S-R latch. A non- reset value and a reset value (e.g., “1” or “0”) of the output (Q) of the S-R latch defines whether the high frequency power switch QI is activated or deactivated respectively. The output Q will be reset (e.g., to 0) when the output of the second comparator is high and will be set (e.g., to 1) when the output of the second comparator is low. This approach assumes that the value at a set (S) node of the S-R latch is appropriately controlled, e.g., to achieve zero current switching of the high frequency power switch QI. This functionality can be achieved using an appropriately controlled zero current switching component 392 that monitors a current through the high frequency power switch and controls the signal provided to the set (S) node of the S-R latch appropriately.

[0103] The S-R latch thereby effectively acts as a controlled inverter of the output of the second comparator, e.g., an inverter that is appropriately designed to achieve zero current switching of the high frequency power switch QI. In some examples, the S-R latch could be replaced by a simple inverter.

[0104] In this way, as the voltage of the feed signal SF decreases with respect to the reference voltage VREF (e.g., a dimming level increases - such that VREF increases) then the duty cycle of the high frequency power switch QI will increase (i.e., the high frequency power switch QI will conduct more power when averaged over time). This reduces the average current available to the LED load. In this negative feedback close loop mode, the output power will be regulated to reach the desired value corresponding to the reference VRef.

[0105] From the foregoing, it will be apparent that if the input voltage decreases, then the feed signal will decrease and the voltage magnitude of the control signal Sc will increase so as to implement negative feedback close loop control. But the integrated control circuit has an upper limit for the max on time of the power switch QI, provided by the signal SONM.

[0106] As mentioned above, when the control signal Sc is high, the duty cycle of the signal from the comparator G2 is small, but the signal SONM gives a minimum high voltage duration for it. Thus the input to the R-S latch has a minimum high voltage duration, so does the output of the R-S latch has a maximum high voltage duration / on time. Therefore, the control loop switches to open loop and the output power would be dependent on the input voltage: when the input voltage is decreased by the phase cut dimmer, the output power decreases and the light become darker.

[0107] In this duration, the difference from the reference signal to the feed signal becomes larger and larger, and the control signal Sc will also increase and finally will reach a cap defined by the max output of the comparator Gl. This control signal Sc is adapted to activate the active component as mentioned above. The present disclosure proposes to exploit the increase of the control signal Sc to control the operation of a separate active component. In particular, the active component may be activated or deactivated responsive to the magnitude of the control signal.

[0108] Referring back to Figure 1, consider a scenario in which the LED driving arrangement comprises a first auxiliary circuit and the active component comprises a first transistor is configured to, when activated, activate the first auxiliary circuit to divert power away from the output interface. In this scenario, the first transistor may be activated responsive to the magnitude of the control signal falling below a (first) predetermined value, and deactivated otherwise.

[0109] Referring back to Figure 2, consider a scenario in which the LED driving arrangement comprises a second auxiliary circuit connected in series with the output interface and the active component comprises a second transistor configured to, when activated, bypass the second auxiliary circuit. In this scenario, the second transistor may be activated responsive to the magnitude of the control signal rising above a (second) predetermined value, and deactivated otherwise.

[0110] From the foregoing, it will be apparent that the frequency at which the high frequency power switch is controlled is higher than the frequency at which the active component is controlled.

[0111] Turning again to Figure 3, in some examples, the integrated control circuit 300 will define, e.g., using a signal generator 391, a minimum time value SONM that limits the maximum duty cycle / on time of the high frequency power switch QI.

[0112] In the illustrated example, the minimum time value SONM may be connected to the reset node of the S-R latch via an OR gate (which also receives at least the output of the second comparator G2 as input). This means the input to the S-R latch has a minimum high voltage duration, and the on time / duty cycle of the high frequency power switch is therefore inverted to have a maximum duration.

[0113] The integrated control circuit is thereby able to switch between operating in a closed-loop control mode and an open-loop control mode.

[0114] In the closed-loop control mode, the control of the high frequency power switch is responsive to the control signal Sc, i.e., to the sensed output power. Thus, the integrated control circuit is configured to make the sensed output power reach a reference output power by controlling the switching of the high frequency power switch. In the open-loop control mode, the integrated control circuit is configured to control the switching of the high frequency power switch to be a maximum switching pattern (defined by the maximum duty cycle signal / on time).

[0115] The illustrated integrated control circuit will operate in the open loop control mode when the input power is less than a predetermined value. In particular, when the input power drops below a certain value, then the current magnitude of the current through the high frequency power switch will naturally decrease. This will cause an increase in the magnitude of the control signal Sc until the duty cycle of the output of the second comparator G2 is less than and clamped by the minimum time signal SONM.

[0116] Other possible components and functional elements of the integrated control circuit 300 are illustrated, but not described in detail for the sake of conciseness and because they do not directly relate to the concept underlying this disclosure. Such components and / or functional elements may be configured for performing over-voltage protection (OVP), overcurrent protection (OCP), voltage management and clamping, fault management, over temperature protection (OTP) and so on.

[0117] The skilled person will readily appreciate how there is also provided an LED lighting device comprising any herein disclosed LED driving arrangement and the LED load.

[0118] Ordinal numbers (e.g. “first”, “second” and so on) have been used purely to distinguish different elements from one another for the sake of clarity, and reference to a non- “firsf ’ (e.g. “second” or “third”) element does not necessitate that a “first” element be present. The skilled person would be capable of relabeling any such elements as appropriate (e.g. relabeling a “second” element as a “first” element if only the second element is present).

[0119] 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.

[0120] 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.

[0121] 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.

[0122] Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A LED driving arrangement (100, 200) comprising: an input interface (110) configured to receive an input power (VIN); an output interface (120) configured to connect to an LED load (190) and provide an output power (VOUT) for the LED load; a power converter (130), connected between the input interface and the output interface, and configured to convert the input power into the output power, wherein the power converter comprises a high frequency power switch (QI) for controlling the output power, wherein said power converter comprises an integrated control circuit (135, 300) configured to: receive a feed signal (SF, SFI, SF?) relating to the input power and / or the output power; generate and output a control signal (Sc), in relation to the feed signal, at a first terminal (T i) of the integrated control circuit; and input the control signal (Sc) generated at the first terminal (T i) and control the switching of the high frequency power switch responsive to the input control signal; and an active component (140, 240), separate to the integrated control circuit and the high frequency power switch, and connected to the first terminal to thereby be controlled responsive to the output control signal.

2. The LED driving arrangement of claim 1, wherein the active component is adapted to be controlled responsive to the control signal in low frequency, optionally PFC frequency, lower than that of the high frequency power switch (QI).

3. The LED driving arrangement of claim 1, wherein the high frequency power switch is either part of the integrated control circuit or external to the integrated control circuit.

4. The LED driving arrangement of any of claims 1 to 3, wherein the power converter further comprises an output sensing component connected with the output interface and adapted to sense the output power, and the integrated control circuit is connected to the output sensing component and the feed signal is a feedback signal of the output power.

5. The LED driving arrangement of claim 4, wherein the integrated control circuit is configured to switch between operating in: a closed-loop control mode in which the integrated control circuit is configured to make the sensed output power reach a reference output power by controlling the switching of the high frequency power switch; and an open-loop control mode, in which the integrated control circuit is configured to control the switching of the high frequency power switch to be a maximum switching pattern.

6. The LED driving arrangement of claim 5, wherein the integrated control circuit is configured to operate in the open loop control mode when the input power is less than a predetermined value.

7. The LED driving arrangement of claim 5 or 6, wherein the integrated control circuit is configured to: operate in the open-loop control mode when the feed signal breaches a predetermined value in which case the control signal is above a certain value; and operate in the closed-loop control mode when the feed signal fails to breach the predetermined value in which case the control signal is below a certain value, wherein said control signal at the certain value is a threshold that activates the active component.

8. The LED driving arrangement of any one of claims 5 to 7, wherein the active component is configured to be activated during the open-loop control mode.

9. The LED driving arrangement of any one of claims 5 to 8, wherein the output sensing component is a current sensor adapted to sense the electrical current of the outputpower, and the control signal represents a difference from a desired electrical current to the electrical current of the output power.

10. The LED driving arrangement of claim 9, wherein the integrated control circuit is configured to, during the closed-loop control mode, increase the duty cycle of a switching of the high frequency power switch responsive to the control signal increasing and the sensed electrical current decreasing.

11. The LED driving arrangement of any one of claims 1 to 10, wherein the active component is connected to the output interface for further control of the output power provided at the output interface.

12. The LED driving arrangement of claim 11, further comprising a first auxiliary circuit connected in parallel with the output interface, optionally for diverting power away from the output interface, wherein the active component comprises a first transistor configured to, when activated, activate the first auxiliary circuit.

13. The LED driving arrangement of claim 11, further comprising a second auxiliary circuit connected in series with the output interface, optionally for regulating a current through the output interface to be constant, wherein the active component comprises a second transistor configured to, when activated, bypass or deactivate the second auxiliary circuit.

14. The LED driving arrangement of any of claims 1 to 13, wherein the first terminal is a compensation terminal of the integrated control circuit and the active component comprises a MOSFET.

15. An LED lighting device comprising the LED driving arrangement of any of claims 1 to 14 and the LED load.

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