Determining one or more initial conditions

Abstract

A mechanism for detecting initial conditions of a power source that provides an alternating input current to a four-chopper driving arrangement. Switches of the drive arrangement that receive the alternating input current are short-circuited, and the alternating input current monitored to determine the initial conditions of the power source.

Description

[0001] Determining one or more initial conditions

[0002] FIELD OF THE INVENTION

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

[0004] BACKGROUND OF THE INVENTION

[0005] There is an ongoing desire to improve lighting devices, which are used to provide artificial light in a wide variety of environments, such as in domestic, industrial and / or public settings. In particular, there has been a growing interest in LED lamps for replacing or retrofitting older lamps, and in particular high-intensity discharge (HID) lamps.

[0006] These retrofit LED lamps need to be appropriately designed so that they are able to draw power from a power source that was originally designed for powering an HID lamp. Whilst power is ultimately derived from a mains supply, i.e., a utility grid, a power source is any source to which an LED driving arrangement for an LED lamp may connect to draw power therefrom, e.g., and may comprise the mains supply and / or one or more ballasts, compensation capacitors, ignitors and so on. The LED lamp and any components, such as a ballast and / or compensation capacitors, connecting the LED lamp to the mains supply form an LED lighting system.

[0007] There is therefore a need for an LED driving arrangement that is able to convert or otherwise provide power to a lamp load from a wide range of possible power sources. One advanced technique, sometimes called a four-quadrant chopper, for forming an LED driving arrangement makes use of a switch arrangement connected between the power source and the LED load.

[0008] There is a desire to facilitate identification of one or more initial conditions of an LED driving arrangement and / or the power source for providing appropriate control of the LED driving arrangement.

[0009] SUMMARY OF THE INVENTION

[0010] The invention is defined by the claims. According to examples in accordance with an aspect of the invention, there is provided a driving arrangement for generating an output power for driving an LED load from a power source adapted to provide an alternating input current, wherein the power source comprises an electromagnetic ballast.

[0011] The driving arrangement comprises an input interface comprising a first terminal and a second terminal for receiving the alternating input current from the power source; an output interface comprising an output node for providing the output power for driving the LED load; a switch arrangement comprising: a first switch connected between the first terminal and the output node; a second switch connected between the second terminal and the output node; a third switch connected between the first terminal and a ground / reference voltage; and a fourth switch connected between the second terminal and a ground / reference voltage; a control arrangement configured to control the operation of the switch arrangement, wherein the control arrangement is configured to be operable in at least a sensing mode in which the control arrangement controls the switching arrangement so that the first and second terminals are effectively short-circuited together; and a sensing arrangement configured to, when the control arrangement operates in the sensing mode: monitor a current between the first and second terminals, to thereby monitor a current through the electromagnetic ballast; and process the monitored current to determine the phase and / or amplitude of the alternating input current.

[0012] The present disclosure provides a mechanism for determining initial conditions of a power source (comprising an electromagnetic ballast) that drives a four- quadrant chopper. The initial conditions include at least an amplitude and / or phase of a current supplied by the power source to the four-quadrant chopper. These initial conditions can be used, for instance, to control or define initial control parameters for controlling the switches of the switch arrangement of the four-quadrant chopper. This approach can significantly reduce the start-up time of the driving arrangement and reduce a risk of power surges that may damage the driving arrangement.

[0013] The relationship between the phase of the alternating input current and the phase of a voltage difference between the first and second terminals may define the (average) magnitude of the current at the output interface, and thereby the brightness of any LED load connected to the output interface. By determining the phase of the alternating input current, the control of the phase of the voltage difference between the first and second terminals can be immediately set or controlled to achieve a desired or expected current at the LED load, significantly reducing a settling time of the driving arrangement (e.g., without the need to wait for any feedback control).

[0014] In some examples, the sensing arrangement is configured to, when the control arrangement operates in the sensing mode: process the monitored current to determine the phase of the alternating input current; and process the monitored current to determine the amplitude of the alternating input current.

[0015] In some examples, the sensing arrangement is configured to determine the phase of a mains supply voltage to the electromagnetic ballast by processing the determined phase of the alternating input current.

[0016] The sensing arrangement is configured to determine the phase of the mains supply voltage by determining that the phase of the mains supply voltage leads the determined phase of the alternating input current by 0.5TI. It has been recognized that, when the switch arrangement is short-circuited, the phase of the mains supply voltage will lead the alternating input current by 0.5TT, i.e., 90°.

[0017] In some examples, the sensing arrangement is configured to determine an inductance of the electromagnetic ballast by dividing the determined phase of the mains current supply by the product of 2TI, a mains current frequency and the determined amplitude of the alternating input current.

[0018] The inductance of the electromagnetic ballast has a significant impact on the harmonics of the driving arrangement. In particular, the value of the inductance may affect the range of duty cycles for the voltage between the first and second terminals that achieve desired harmonic characteristics for the driving arrangement or overall LED lighting system. By identifying the inductance of the electromagnetic ballast, a suitable range of duty cycles can be identified and exploited during control of the switching arrangement.

[0019] In preferred examples, the control arrangement is configured to operate in the sensing mode upon startup of the driving arrangement. This facilitates identification of the properties of the power source during start of the driving arrangement, thereby allowing for initial control conditions to be set.

[0020] In preferred examples, control arrangement is further configured to be operable in an operational mode, in which the control arrangement is adapted to control the magnitude of voltage between the first and second terminals and the phase of the voltage between the first and second terminals relative to a phase of the alternating input current, so that energy transfer between the input arrangement and the output node is bi-directionally controllable to thereby control an average magnitude of the output power. In some examples, the control arrangement is configured to operate in the operational mode by being operable in at least two sub-modes, including at least: a first submode, in which the control arrangement allows current to flow through the first switch and the fourth switch, and prevents current from flowing through the second switch and the third switch, so that the voltage between the first and second terminals is equal in magnitude and polarity to the voltage across the capacitor; and a second sub-mode, in which the control arrangement allows current to flow through the second switch and the third switch, and prevents current from flowing through the second switch and the fourth switch, so that the voltage between the first and second terminals is equal in magnitude but opposite in polarity to the voltage across the capacitor.

[0021] The at least two sub-modes may comprise a third sub-mode, in which the control arrangement controls the switching arrangement so that the first and second terminals are effectively short-circuited together.

[0022] In some examples, when operating in the operational mode, the control arrangement is configured to iteratively perform a sequence of for a first period of time, operating in the first sub-mode; for a second, subsequent period of time, operating in the third sub-mode; for a third, subsequent period of time, operating in the second sub-mode; and for a fourth, subsequent period of time, operating in the third sub-mode.

[0023] The sensing arrangement may be configured to: when the control arrangement operates in the sensing mode process the monitored current to determine the phase of the alternating input current; and when the control arrangement operates in the operational mode, control the phase of the voltage between the first and second terminals responsive to the determined phase of the alternating input current.

[0024] There is also provided an LED lamp comprising the driving arrangement herein disclosed; and the LED load.

[0025] There is also provided an LED lighting system comprising the herein disclosed LED lamp and an electromagnetic ballast adapted to connect to a mains supply to provide the alternating input current to the input arrangement of the LED driving arrangement.

[0026] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment s) described hereinafter.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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:

[0029] Fig. 1 illustrates an existing LED system;

[0030] Fig. 2 illustrates a known LED lamp; and

[0031] Fig. 3 illustrates an LED lamp having a proposed LED driving arrangement.

[0032] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The invention will be described with reference to the Figures.

[0034] 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.

[0035] The invention provides a mechanism for detecting initial conditions of a power source that provides an alternating input current to a four-chopper driving arrangement. Switches of the drive arrangement that receive the alternating input current are short- circuited, and the alternating input current monitored to determine the initial conditions of the power source.

[0036] Figure 1 illustrates a LED system 1 comprising an LED lamp 10 and a power source 190, the configuration of which is known in the prior art.

[0037] The power source 190 comprises a main power supply 15A that generates a main supply voltage VM. The power source 190 was originally designed for powering an HID lamp and comprises a number of further elements designed for use with such HID lamps. These elements include at least an electromagnetic (EM) ballast 195, e.g., comprising a ballast inductor LB and (optionally) a compensation capacitor CB. The output of the electromagnetic ballast is an alternating input current IB that is provided to the LED lamp 10. The alternating input current IB passes through at least the inductor LB of the ballast, and can thereby be alternatively labelled a ballast current IB.

[0038] The power source 190 may further comprise an ignitor 15B. Different types of ignitors may be used, such as a parallel, semi-parallel and / or series ignitor. The LED lamp 10 and the elements of the power source 190 (excluding the mains supply 15A itself) together form an LED lighting system 19. When assessing power or harmonic characteristics in the content of the present invention, it is the power characteristics of the LED lighting system 19 with respect to the mains supply 15A that are considered.

[0039] The LED lamp 10 is adapted to draw power from the power source 190. The LED lamp 10 contains a driving arrangement adapted to appropriately drive an LED load.

[0040] The power source 190 provides an alternating input current IB for the LED lamp 10, via the electromagnetic ballast. The frequency of the alternating input current IB is identical to that provided by the mains power supply 15 A. Harmonic distortion in the alternating input current (e.g., caused by the LED lamp 10) results in undesirable harmonic distortion in the mains supply.

[0041] The present invention relates to a driving arrangement for an LED lamp.

[0042] Figure 2 illustrates an LED lamp 10 according to a known example. More particularly, the LED lamp 10 is disclosed by European Patent No. EP 4049516 BL The LED lamp 10 can be used as in the LED system described with reference to Figure 1.

[0043] The LED lamp 10 is adapted for use with the power source 190 comprising the electromagnetic ballast 195, which capability is commonly referred to as “Type A”. The LED lamp 10, together with some components of the power source, may together form the overall LED lighting system.

[0044] The LED lamp 10 comprises an LED driving arrangement 200 and an LED load 290, e.g., comprising a string of one or more LEDs.

[0045] The LED driving arrangement 200 comprises an input interface 210, an output interface 220, a switching arrangement 230 and a control arrangement 240. A (buffer) capacitor C2 connects the output interface 220 to a ground / reference voltage. The LED load 290, of the LED lamp 10, is powered by the output interface 220.

[0046] The input arrangement 210 comprises a first terminal AC1 and a second terminal AC2, and receives the alternating input current IB from the power source 190, which comprises an electromagnetic ballast 195.

[0047] The value of the alternating input current IB is here defined at the first terminal AC1, where positive current flow moves towards the remainder of the LED driving arrangement and negative current flow moves away from the remainder of the LED driving arrangement. There is, of course, a corresponding current present at the second terminal AC2, which is opposite in polarity to the measurement of the alternating input current IB. For the sake of convenience, the LED driving arrangement 200 can be conceptually divisible into an “AC-side” and a “DC-side”. The AC-side is the portion of the LED driving arrangement 200 between the power source 190 (when connected to the power source) and the switching arrangement 230. The DC-side is the portion of the LED driving arrangement 200 between the switching arrangement 230 and the LED load 290 (when the driving arrangement 200 is connected to the LED load).

[0048] The illustrated switching arrangement 230 comprises a first switch Ml directly connecting the first terminal to the output node; a second switch M2 directly connecting the second terminal to the output node; a third switch M3 directly connecting the first terminal to the ground / reference voltage; and a fourth switch M4 directly connecting the second terminal to the ground / reference voltage.

[0049] The switching arrangement 230 may further comprise a coupling capacitor Cl to reduce (e.g., electromagnetic interference) noise between the first AC1 and second AC2 terminals. It also serves to limit the time-derivative of the voltage between the first and second terminals, which, if too high, may cause audible noise in the (windings of the) EM ballast.

[0050] The first, second, third and fourth switches may each comprise a transistor, such as a BJT, JFET or MOSFET. In the context of the present invention, the term “switch” refers to any component that can be controlled to selectively permit or prevent charge from flowing between two nodes. The skilled person would be readily capable of adapting any such transistors for such purposes, for example, by including an anti-parallel diode for a BJT.

[0051] The control arrangement 240 is adapted to control the operation of the switches M1-M4 of the switching arrangement, e.g., by controlling a gate / base voltage of a transistor, which is commonly referred to as the control electrode of the switch. Other methods of controlling a switch will be apparent to the skilled person.

[0052] The illustrated switching arrangement 240 provides or facilitates, with appropriate control of the switches Ml - M4, 4-quadrant operation of the power at the input arrangement. 4-quadrant operation means that the phase of the voltage between the first AC1 and second terminals AC2 (measured from AC1 to AC2) can be controlled relative to the alternating input current IB. In this way, the driving arrangement can operate as a four- quadrant chopper.

[0053] Effectively, 4-quadrant operation means that when the voltage between the first AC1 and second AC2 terminals is positive, the input current may be negative or positive (not simultaneously), and conversely, when the voltage between the first and second terminals is negative, the input current may be positive and negative.

[0054] In other words, the switching arrangement is able to operate in four different states of current flow.

[0055] A first state exists when the alternating input current IB is positive and the voltage between the first AC1 and second AC2 terminals is positive (i.e., V(AC1) > V(AC2). This is achieved by (when the alternating input current is positive) making the first and fourth switches Ml and M4 conductive (and preventing the second and third switches from being conductive) so that charge flows (i.e., power is transferred) from the AC-side of the LED driving arrangement to the DC-side of the driver. Thus, current flows from the first terminal AC1 to the output node. This can also be called a “power deliver” phase whilst the AC1, AC2 voltage is positive, and the current is positive. This may be called “first quadrant” operation.

[0056] A second state exists when the alternating input current IB is positive and the voltage between the first AC1 and second AC2 terminals is negative. This is achieved by making the second and third switches M2 and M3 conductive (and preventing the first and fourth switches from being conductive) so that the voltage between the first and second terminals is forced to be negative. In particular, we return power from the buffer capacitor C2 to the AC-side of the switching arrangement 230 to keep the voltage between AC1 and AC2 negative. Thus, current flows from the output node to the second terminal AC2. This can also be called a “power return” phase whilst the AC1, AC2 voltage is negative, and the current is positive. This may be called “second quadrant” operation.

[0057] A third state exists when the alternating input current IB is negative and the voltage between the first AC1 and second AC2 terminals is negative (i.e., V(AC1) < V(AC2). This is achieved by (when the alternating input current is negative) making the second and third switches M2 and M3 conductive (and preventing the first and fourth switches from being conductive) so that charge flows from the AC-side of the LED driving arrangement to the DC-side of the driver. Thus, current flows from the second terminal AC2 to the output node. This can also be called a “power deliver” phase whilst the AC1, AC2 voltage is negative while the current is negative. This may be called “third quadrant” operation.

[0058] A fourth state exists when the alternating input current IB is negative and the voltage between the first AC1 and second AC2 terminals is positive. This is achieved by making the first and fourth switches Ml and M4 conductive (and preventing the second and third switches from being conductive) so that the voltage between the first and second terminals is forced to be positive. In particular, we return power from the buffer capacitor C2 to the AC-side of the switching arrangement 230 to keep the voltage between AC1 and AC2 positive. Thus, current flows from the output node to the first terminal AC1. This can also be called a “power return” phase whilst the AC1, AC2 voltage is positive while the current is negative. This may be called “fourth quadrant” operation.

[0059] In the first and fourth states (for the circuit illustrated in Fig 3), the voltage between the first AC1 and second AC2 terminals is held to be substantially equal in magnitude and polarity to the voltage across the (buffer) capacitor C2. This voltage is configured to be substantially constant, e.g., equal to the forward voltage of a connected LED load, barring some minor discharging of the capacitor.

[0060] In the second and third states (for the circuit illustrated in Fig 3), the voltage between the first AC1 and second AC2 terminals is held to be equal in magnitude, but opposite in polarity, to the voltage across the (buffer) capacitor C2. This is configured to be substantially constant, e.g., equal to the forward voltage of a directly connected LED load, barring some minor discharging of the capacitor.

[0061] It has been described how, in the first through fourth states, the magnitude of voltage between the first and second terminals may be effectively / substantially identical to the voltage across the (buffer) capacitor. In this context “substantially identical” means effectively identical given practical circumstances and implementation requirements (i.e., non-ideal nature of components). Thus, the magnitude of the voltages may be identical, excepting for any voltage drop across circuit elements positioned between the terminals and the capacitor (such as a voltage drop across the switches M1-M4), any introduction of noise (e.g., EMI noise) or the like. In some circumstances, this magnitude of the voltage between the first and second terminals may be the same as the voltage across the capacitor, ±1% or ±3%.

[0062] Thus, 4-quadrant operation is enabled, and the net amount of power transfer (energy per mains half-cycle) can be controlled by adjusting the balance between the (DC-to- AC side) retuned power and the (AC-to-DC side) delivered power, by adjusting the switching moments of the switches M1-M4.

[0063] In this way, 4-quadrant operation enables the control arrangement to control a magnitude and phase of the voltage between the first AC1 and second AC2 terminals (by selectively allowing charge stored by the (buffer) capacitor C2 to flow back to these terminals). This enables control over the power supplied to the LED load 290 without needing to shunt power to a ground / reference voltage, improving the power factor of the LED lamp and reducing an amount of current made to flow through the power source (which may overheat a ballast of the power source).

[0064] As previously explained, the control arrangement 240 is configured to control the operation of the switches M1-M4, using known techniques. The control arrangement is thereby able to control the power provided to the DC-side by the AC-side.

[0065] Accordingly, the control arrangement 240 may be configured to be operable in at least an operational mode. In the operational mode, the control arrangement is adapted to control the magnitude of voltage between the first and second terminals and the phase of the voltage between the first and second terminals to control the power provided to the DC-side by the AC-side.

[0066] One option for appropriately controlling the switching arrangement to control the power provided to the DC-side by the AC-side could be to adapt the control arrangement to (when operating in the operational mode) switch between two sub-modes, including a first- sub-mode and a second sub-mode.

[0067] In the first sub-mode, the control arrangement allows current to flow through the first switch and the fourth switch, and prevents current from flowing through the second switch and the third switch, so that the voltage between the first and second terminals is equal in magnitude and polarity to the voltage across the capacitor.

[0068] In the second sub-mode, the control arrangement allows current to flow through the second switch and the third switch, and prevents current from flowing through the first switch and the fourth switch, so that the voltage between the first and second terminals is equal in magnitude but opposite in polarity to the voltage across the capacitor.

[0069] When the control arrangement operates in the first sub-mode, the switching arrangement operates in the fourth and / or first states. Thus, the voltage between the first and second terminals is held to be substantially equal in magnitude and polarity to the (substantially constant) voltage across the capacitor.

[0070] When the control arrangement operates in the second sub-mode, the switching arrangement operates in the second and / or third states. Thus, the voltage between the first and second terminals is held to be substantially equal in magnitude, but opposite in polarity, to the (substantially constant) voltage across the capacitor.

[0071] Thus, switching the control arrangement between the first and second submodes effectively results in the generation of a square wave voltage between the first and second terminals, having an amplitude essentially equal to the voltage across the (buffer) capacitor C2 and hence, in the illustrated example, the LED load 290 forward voltage. This square wave should have a frequency equal to the frequency of the mains input current, and a phase that is adjusted to balance the amount of returned and delivered energy per mains half cycle to match the desired amount of energy per mains half-cycle that is to be delivered to the LED load.

[0072] Thus, control of the phase of the voltage between the first and second terminals allows control over the power provided to the LED load, and thereby the brightness of light output by the LED load.

[0073] For example, if the phase of the voltage between the first and second terminals is equal to the phase of the alternating input current, then current continually flows from the AC-side of the LED driving arrangement to the DC-side of the LED driving arrangement, (and the average current through the LED load is at a maximum. This results in the LED load outputting light of a maximum brightness.

[0074] If there is a phase difference between the alternating input current and the voltage between the first and second terminals, then the average amount of power delivered to the DC side is reduced (as the DC-side will periodically deliver power back to the AC- side). Thus, the amount of power available for powering the LED load is reduced (compared to the in-phase example), reducing the brightness of light output by the LED load.

[0075] Forming the voltage between the first and second terminals (i.e. the AC1, AC2 voltage) as a square wave and adjusting the phase of the square wave with respect to the EM ballast current IB allows us to achieve a substantially improved power factor at a suitably selected string voltage and allows us to control (average) LED current, provided that the conduction of each switch pair Ml, M4 and M2, M3 starts by returning power (i.e. current flow from the DC-side to the AC-side) and ends with receiving power (i.e. current flows from the AC-side to the DC-side).

[0076] This effectively results in the voltage between the first and second terminals leading the alternating input current IB from the power source. Having this voltage lead the alternating input current IB results in the LED lamp appearing to have a partial inductive impedance. This is effectively added to the EM ballast inductance, thus reducing the EM ballast current and lamp current and reducing EM ballast losses.

[0077] If the voltage between the first and second terminals lags the alternating input current, then the LED lamp has a partially capacitive behavior. As the LED lamp is in series with the inductance of the EM ballast, this capacitive behavior of the LED lamp would effectively subtract from the inductive impedance of the EM ballast, rendering a higher current in the EM ballast and hence more losses. Thus, to improve the power factor of the overall LED lighting system, the control arrangement should control the phase of the voltage between the first and second terminals so that it leads the alternating input current. This can be performed through appropriate timings of switching between the first / second modes.

[0078] Referring to the possible states of switching arrangement (previously described), the switching arrangement may therefore move from the fourth state, to the first state, to the second state to the third state. This process should be iteratively repeated.

[0079] However, simulations have shown that forming the voltage between the first and second terminals as a square wave can still result in the overall LED lamp having undesirable levels of THD (total harmonic distortion) and individual harmonics on the mains supply (which eventually powers the LED lamp). It has been recognized that this THD must be caused by the harmonic content of the square-wave voltage between the first and second terminals, as it is effectively the only source of harmonic distortion in the system.

[0080] A full square wave voltage contains substantial harmonics; e.g., the 3rd harmonic is then 230% (1 / 3) of the first harmonic, the 5th harmonic 20% (1 / 5), the 7th harmonic 14% (1 / 7), et cetera.

[0081] It has been recognized that the harmonic content of a square-wave signal depends on the duty-cycle of that square-wave. A duty-cycle represents the proportion of time that the voltage between the first and second terminals is non-zero. By providing a mechanism for defining a duty cycle and adjusting the duty-cycle of the voltage (between the first and second terminals), it is therefore possible able to adjust or steer the harmonic content of the square-wave voltage and thus the EM ballast and mains current.

[0082] The switching arrangement 230 offers the option to shunt or short the first AC1 and second AC2 terminals. This can be achieved by simultaneously causing either both Ml and M2 to be conductive or both M3 and M4 to be conductive. Preferably, for reasons of easy gate-drive, a shunting-phase is achieved by simultaneously causing the third and fourth switch to be conductive.

[0083] The voltage between the first AC1 and second AC2 terminals is effectively / substantially zero when the first and second terminals are shorted together.

[0084] Thus, by proper gate drive operation, the switching arrangement is capable of 4-quadrant operation and a shunting-phase, and thus is able to synthesize a duty-cycle limited voltage between the first and second terminals. More particularly, the duty-cycle represents the proportion of time that the switching arrangement is in one of the four states previously described (and not in a shunting phase or shunting state). The control arrangement may therefore be operable, during the operational mode, in a third sub-mode, in which the control arrangement controls the switching arrangement so that the first and second terminals are effectively short-circuited together.

[0085] To reduce total harmonic distortion, it is preferable that, when operating in the operational mode, the control arrangement is configured to iteratively perform a sequence of: for a first period of time, operating in the first sub-mode; for a second, subsequent period of time, operating in the third sub-mode; for a third, subsequent period of time, operating in the second sub-mode; and for a fourth, subsequent period of time, operating in the third submode.

[0086] Further specific details on appropriate and advantageous control mechanisms for the switch arrangement, e.g., for improved power characteristics, are set out in European Patent No. EP 4049516 Bl.

[0087] In general, using techniques set out above and in in European Patent No. EP 4049516 Bl, control of the switch arrangement facilitates control over at least two variables for controlling electrical characteristics (such as the output voltage, power factor, total harmonic distortion and ballast loss) of the LED lighting system. These two variables are: the phase of the voltage between the first and second terminals (“phase shift”) and the duty cycle of the voltage between the first and second terminals (“duty cycle”).

[0088] The phase of the voltage between the first and second terminals will define the current available or output at the output interface, e.g., to be drawn by the LED load. Thus, the phase of the voltage between the first and second terminals can control or define the brightness of light emitted by the LED load.

[0089] In the context of the present disclosure, the duty cycle of the voltage between the first and second terminals represents a portion of time that the control arrangement does short circuit the first and second terminals (i.e., does not operate in the third sub-mode) during the operational mode for each cycle of the mains supply voltage VM or alternating input current IB. The value of the duty cycle will affect at least the total harmonic distortion of the driving arrangement and / or overall LED lighting system. Of course, there is a natural consequence that the value of the duty cycle will also affect the power available at the output interface, and therefore the brightness of light emitted by the LED load.

[0090] The present disclosure proposes a technique to determine, identify or predict the phase and / or amplitude of the alternating input current IB output by the electromagnetic ballast 195. This can be advantageously used, for example, to determine the phase of the mains supply voltage VM provided to the electromagnetic ballast. More particularly, this approach can be used to determine an initial value for the phase and / or amplitude of the alternating input current IB (and other electrical characteristics of the power source) to initialize or define the control of the switching arrangement 230.

[0091] Figure 3 illustrates a modified version of the LED lamp 10 comprising the LED driving arrangement 200.

[0092] The driving arrangement 200 further comprises a sensing arrangement 250, 255. The sensing arrangement 250, 255 is configured to operate when the control arrangement 240 operates in a sensing mode. In the sensing mode, the control arrangement 240 is configured to control the switching arrangement 230 so that the first AC1 and second AC2 terminals are effectively short-circuited together.

[0093] As previously mentioned, shunting or shorting the first AC1 and second AC2 terminals can be achieved by simultaneously causing either both Ml and M2 to be conductive or both M3 and M4 to be conductive. Preferably, for reasons of easy gate-drive, this is achieved by simultaneously causing the third and fourth switch to be conductive.

[0094] When operational (i.e., when the control arrangement 240 operates in the sensing mode), the sensing arrangement is configured to monitor a current between the first AC1 and second AC2 terminals. This effectively monitors a current through the inductor LB of the electromagnetic ballast 195. The monitored current is then processed to determine or detect the phase and / or amplitude of the alternating input current.

[0095] In this way, the sensing arrangement 250, 255 is able to determine or define the initial conditions of the alternating input current provided to the remainder of the circuit. These initial conditions may, for instance, be used by the control arrangement to set or define the phase and / or duty cycle of the voltage between the first and second terminal, e.g., during a later operational mode of the control arrangement.

[0096] In the illustrated example, the sensing arrangement 250, 255 comprise a sensing resistor Rs connected between the first terminal AC1 and the first / third switch and a sensing processor 255 configured to monitor the voltage across the sensing resistor Rs, to thereby monitor the current of the electromagnetic ballast 195. The sensing processor 255 may process the monitored voltage to determine or detect the phase and / or amplitude of the alternating input current.

[0097] In an alternative configuration, the sensing resistor is connected between the second terminal AC2 and the second / fourth switch.

[0098] In a preferred alternative configuration, the sensing resistor is connected between the third switch M3 and ground or the fourth switch M4 and ground. This significantly reduces a power loss across the sensing resistor Rs, and thereby an efficiency of the overall LED lighting system.

[0099] In some examples, the sensing arrangement is configured to determine the phase of a mains supply current VM to the electromagnetic ballast by processing the determined phase of the alternating input current. This can be performed by, for instance determining that the phase of the mains supply voltage leads the determined phase of the alternating input current by 0.5TT or 90°.

[0100] The sensing arrangement may be further configured to determine an inductance of the electromagnetic ballast (i.e., the inductance of the inductor LB) by dividing the determined phase of the mains current supply by the product of 2TI, a mains current frequency (which will be predetermined or set based on the relevant jurisdiction) and the determined amplitude of the alternating input current. Mathematically, this can be defined as:

[0101] Where L is the inductance of the inductor LB, V(L, N) is the determined phase of the mains supply current VM, f is the frequency of the mains supply voltage VM and IB is the ballast current or alternating input current. The value of IB may be defined as the root mean squared value of the alternating input current.

[0102] It may also be possible to determine or predict a capacitance of the compensation capacitor CB using the determined inductance of the inductor LB. For instance, a table or other mapping element may map or otherwise identify an expected capacitance of a compensation capacitor CB for different values of the inductance of the inductor LB. Such a table may be used to identify the capacitance of the compensation capacitor CB.

[0103] In preferred examples, the control arrangement is configured to operate in the sensing mode upon startup of the driving arrangement. Thus, the sensing mode may be the default or initial mode of the control arrangement.

[0104] The control arrangement may then switch to the operational mode, an example of which is previously described. As previously mentioned, the control arrangement is effectively configured to control the phase and / or the duty cycle of the voltage between the first and second terminals. More particularly, the control arrangement may control the phase and / or duty cycle of the voltage responsive to determined characteristics of the power supply (e.g., characteristics of the mains supply and / or electromagnetic ballast) that are determined by the sensing arrangement during the sensing mode of the control arrangement.

[0105] For instance, an improved power factor has been identified as an outcome of the control arrangement controlling the phase of the voltage between the first and second terminals so that it leads the alternating input current. This can be achieved, for instance, by initially matching the phase of the voltage between the first and second terminals to the determined phase of the mains supply current VM (which leads the ballast current IB). Of course, the phase may be adjusted to achieve a desired current level (and therefore brightness level) for the LED lamp, but may be defined with respect to a baseline of the phase of the mains supply voltage VM.

[0106] It is possible to determine or produce a table that correlates or maps characteristics of the power supply (e.g., phase of the mains power supply, inductance of the ballast and so on) and desired output(s) of the driving arrangement to control parameters (i.e., duty cycle and / or phase of the voltage between the first and second terminals), e.g., using one or more simulations that aim to minimize or reduce disadvantageous attributes such as THD and improve power factors. Such tables can be used by a control arrangement to define the control of the switch arrangement when entering the operational mode.

[0107] In particular examples, multiple different tables may be defined, each table representing a different combination of possible values for the inductance of the inductor (and capacitance of the compensation capacitor). Each table may map a desired output voltage and / or current to one or more duty cycles that meet desired noise characteristics. The relevant table may be identified by the control arrangement, and the relevant duty cycle identified. The phase may be defined to achieve a desired current to be output at the output interface.

[0108] Table 1 illustrates an example of a table produced for a power source having the following component values: LB: 250mH and CB: with a target output power of the LED load of 95W.

[0109] From this table an appropriate duty-cycle and buffer capacitor voltage VC for the LED lamp can be selected to meet desired performance criteria.

[0110] By way of example, consider a scenario in which the desired performance criteria is to maintain a power factor greater than 0.9, a total harmonic distortion less than 20% and harmonic values meeting the IEC 61000-3-2 criteria (H3 < 27%, H5 < 10%, H7 < 7%, H9 < 5% and Hl 1 <3%). As can be seen from Table 1, there is only one combination of buffer capacitor voltage VC and duty-cycle (140V and 0.38 respectively) that meet these desired performance criteria for the LED lamp connected to the power source.

[0111] Vc Duty-cycle PF THD (%) H3(%) H5(%) H7(%) H9(%) Hl l(%)

[0112] 130 0.333 0.76 10.2 0.2 8.8 4.4 0.04 1.8

[0113] 130 0.35 0.79 10.6 4.6 7.5 5.3 1.5 1.0

[0114] 130 0.38 0.84 15.2 13.3 3.5 5.1 3.4 1.2

[0115] 140 0.333 0.84 12.3 0.2 10.6 5.4 0.05 2.2

[0116] 140 0.35 0.88 12.8 5.5 9.0 6.4 1.8 1.2

[0117] 140 0.38 0.92 18.2 16.0 4.2 6.1 4.0 1.5

[0118] 150 0.333 0.92 14.5 0.2 12.6 6.4 0.05 2.6

[0119] 150 0.35 0.95 15.0 6.4 10.6 7.6 2.1 1.4

[0120] 150 0.38 0.97 20.9 18.3 4.8 7.0 5.04.6 1.7

[0121] 160 0.333 0.97 16.6 0.2 14.3 7.3 0.05 3.0

[0122] 160 0.35 0.98 16.8 7.2 11.3 8.5 2.3 1.6

[0123] 160 0.38 0.97 22.5 19.8 5.2 7.5 5.0 1.9

[0124] TABLE 1

[0125] Further details on appropriate control methods and relationships between parameters are set out in European Patent No. EP 4049516 B 1. The present disclosure provides a mechanism for determining or detecting characteristics of the power source for the driving arrangement, which define or delimit the desirable control methods and parameters for the switching arrangement.

[0126] 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.

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

Claims

CLAIMS:

1. An LED driving arrangement (200) for generating an output power (Io) for driving an LED load (290) from a power source (190) adapted to provide an alternating input current (IB), wherein the power source (190) comprises an electromagnetic ballast (195), the driving arrangement comprising: an input interface (210) comprising a first terminal (AC1) and a second terminal (AC2) for receiving the alternating input current from the power source; an output interface (220) comprising an output node (01) for providing the output power for driving the LED load (290); a switch arrangement comprising: a first switch (Ml) connected between the first terminal and the output node; a second switch (M2) connected between the second terminal and the output node; a third switch (M3) connected between the first terminal and a ground / reference voltage; and a fourth switch (M4) connected between the second terminal and a ground / reference voltage; a control arrangement (140) configured to control the operation of the switch arrangement, wherein the control arrangement is configured to be operable in at least a sensing mode in which the control arrangement controls the switching arrangement so that the first and second terminals are effectively short-circuited together; and a sensing arrangement (250, 255) configured to, when the control arrangement operates in the sensing mode: monitor a current between the first and second terminals, to thereby monitor a current through the electromagnetic ballast; and process the monitored current to determine the phase and / or amplitude of the alternating input current.

2. The LED driving arrangement of claim 1, wherein the sensing arrangement is configured to, when the control arrangement operates in the sensing mode: process the monitored current to determine the phase of the alternating input current; andprocess the monitored current to determine the amplitude of the alternating input current.

3. The LED driving arrangement of claim 2, wherein the sensing arrangement is configured to determine the phase of a mains supply voltage to the electromagnetic ballast by processing the determined phase of the alternating input current.

4. The LED driving arrangement of claim 3, wherein the sensing arrangement is configured to determine the phase of the mains supply voltage by determining that the phase of the mains supply voltage leads the determined phase of the alternating input current by O.57t.

5. The LED driving arrangement of claim 4, wherein the sensing arrangement is configured to determine an inductance of the electromagnetic ballast by dividing the determined phase of the mains current supply by the product of 2TT, a mains current frequency and the determined amplitude of the alternating input current.

6. The LED driving arrangement of any of claims 1 to 5, wherein the control arrangement is configured to operate in the sensing mode upon startup of the driving arrangement.

7. The LED driving arrangement of any of claims 1 to 6, wherein the control arrangement is further configured to be operable in an operational mode, in which the control arrangement is adapted to control the magnitude of voltage between the first and second terminals and the phase of the voltage between the first and second terminals relative to a phase of the alternating input current, so that energy transfer between the input arrangement and the output node is bi-directionally controllable to thereby control an average magnitude of the output power.

8. The LED driving arrangement of claim 7, wherein the control arrangement is configured to operate in the operational mode by being operable in at least two sub-modes, including at least: a first sub-mode, in which the control arrangement allows current to flow through the first switch and the fourth switch, and prevents current from flowing through thesecond switch and the third switch, so that the voltage between the first and second terminals is equal in magnitude and polarity to the voltage across the capacitor; and a second sub-mode, in which the control arrangement allows current to flow through the second switch and the third switch, and prevents current from flowing through the second switch and the fourth switch, so that the voltage between the first and second terminals is equal in magnitude but opposite in polarity to the voltage across the capacitor.

9. The LED driving arrangement of claim 8, wherein the at least two sub-modes comprise a third sub-mode, in which the control arrangement controls the switching arrangement so that the first and second terminals are effectively short-circuited together.

10. The LED driving arrangement of claim 9, wherein, when operating in the operational mode, the control arrangement is configured to iteratively perform a sequence of for a first period of time, operating in the first sub-mode; for a second, subsequent period of time, operating in the third sub-mode; for a third, subsequent period of time, operating in the second sub-mode; and for a fourth, subsequent period of time, operating in the third sub-mode.

11. The LED driving arrangement of any of claims 7 to 10, wherein the sensing arrangement is configured to: when the control arrangement operates in the sensing mode process the monitored current to determine the phase of the alternating input current; and when the control arrangement operates in the operational mode, control the phase of the voltage between the first and second terminals responsive to the determined phase of the alternating input current.

12. An LED lamp (10) comprising: the LED driving arrangement of any of claims 1 to 11; and the LED load (290).

13. An LED lighting system comprising the LED lamp of claim 12 and an electromagnetic ballast adapted to connect to a mains supply to provide the alternating input current to the input arrangement of the LED driving arrangement.

Images