Dimming control system for a light-emitting device

Abstract

The present invention provides a mechanism for controlling the dimming level of a lighting device. During initial dimming, the dimming level is controlled by controlling the maximum amplitude of the current that can be drawn by any light emitting module of the lighting device. During higher levels of dimming (for lower light intensities), the dimming level is controlled using a pulse width modulation strategy.

Description

[Technical field]

[0001] The present invention relates to the field of light emitting devices, and in particular to controlling the dimming of light emitting devices. [Background technology]

[0002] The use of lighting in commercial, home and healthcare environments is increasing. One growing trend is the adoption of dimmable lighting devices, which allow individuals to control or define the (average) intensity of light output by the lighting device. This advantageously allows individuals to control the light intensity to meet environmental needs and their own desires, for example depending on the ambient light conditions. Summary of the Invention [Problem to be solved by the invention]

[0003] There is a need for techniques to improve the dimming performance of light emitting devices. In particular, it would be advantageous to provide a dimming technique that can control the average intensity of the light output by a light emitting device without introducing flicker or ripple effects (e.g., perceptible to a user) into the output light. [Means for solving the problem]

[0004] The basic idea of ​​the present invention is to use different dimming strategies for different desired dimming levels. During initial dimming, an amplitude control strategy is implemented in which the maximum magnitude / amplitude of the available current for any light-emitting module is changed according to the desired dimming level. When the dimming level reaches a certain dimming level, a pulse-width modulation strategy is used to control the average available current for any light-emitting module. This provides a method in which the effective modulation depth during pulse-width modulation is minimized to reduce the apparent flicker effect.

[0005] According to an example according to an aspect of the present invention, there is provided a dimming control system for controlling a dimming level of a lighting device having one or more light emitting modules, the dimming level defining an average current that can be drawn by the one or more light emitting modules, ranging from a minimum dimming level to a maximum dimming level, the minimum dimming level providing an average current that can be drawn by the light emitting modules that is greater than the maximum dimming level, and for each light emitting module, an average intensity of light output by the light emitting module is responsive to the average current drawn by each light emitting module.

[0006] The dimming control system is configured to control the dimming level by controlling a maximum amplitude of current that can be drawn by the one or more light emitting modules for a first dimming range bounded on one side by the minimum dimming level and a first predetermined dimming level, and by performing pulse width modulation of the current that can be drawn by the one or more light emitting modules for a second dimming range bounded on one side by the first predetermined dimming level, wherein performing pulse width modulation includes performing repeated cycles, each cycle being a first time period, during which the dimming control system controls the maximum amplitude of current that can be drawn by the one or more light emitting modules. and a second period during which the dimming control system prevents or limits current from being drawn by the one or more light emitting modules, the second period during which the dimming control system controls a length of the second period to control the average current that can be drawn by each light emitting module, for each cycle, wherein light output by the light emitting device has a higher average intensity in the first dimming range compared to the second dimming range.

[0007] An embodiment provides a mechanism for dimming a light emitting device. A dimming control system is configured to control the dimming level of the light emitting device. For the first dimming range, the dimming control system controls the maximum amplitude of current that can be drawn by the dimming control system. This can be done by controlling the operation of a power supply or power converter for the light emitting device. For a second dimming range (wherein the light output by the light emitting device is less than during the first dimming range), the dimming control system controls the average current that can be drawn by the dimming control system using pulse width modulation.

[0008] An advantage of this approach is the reduction of flicker during initial dimming of the light emitting device. The proposed approach also avoids the introduction of any color shift when the one or more light emitting modules include multiple light emitting modules emitting light of different colors, since, for example, the proportion between different color channels is maintained during the dimming procedure.

[0009] Therefore, in the second dimming range, the frequency at which the pulse width modulation cycles are performed, i.e., the modulation frequency, varies depending on the dimming level.

[0010] In some examples, the dimming control system is configured to control the dimming level by maintaining a frequency of performing the pulse width modulation cycles at a predetermined frequency and controlling the length of the first period and the second period for each cycle of the pulse width modulation to thereby control the average current that can be drawn by each light emitting module, for a third dimming range, the second dimming range being bounded by the first predetermined dimming level and a second predetermined dimming level, and the third dimming range being bounded by the second predetermined dimming level and the maximum dimming level.

[0011] The predetermined frequency may be between 0.5 kHz and 5 kHz, for example the predetermined frequency may be 1 kHz.

[0012] In some examples, a minimum frequency for performing cycles of the pulse width modulation during the second dimming range is greater than or equal to the predetermined frequency.

[0013] For example, the predetermined length of time may be between 5 μs and 50 μs. Preferably, the predetermined length of time is between 10 μs and 50 μs, for example between 15 μs and 50 μs. The predetermined length of time may be 25 μs.

[0014] Optionally, the dimming control system is configured to prevent or limit current being drawn by the one or more light emitting modules by activating a bypass switch that, when activated, provides a conductive path for current to bypass the one or more light emitting modules.

[0015] In some examples, the dimming control system is configured to prevent or limit current being drawn by the one or more light emitting modules by activating an isolating switch that, when activated, isolates or disconnects the one or more light emitting modules from a power source configured to supply current to the one or more light emitting modules.

[0016] In at least one example, the lighting device includes a current control device configured to control a maximum amplitude of current available to the one or more lighting modules, and for the first dimming range, the dimming control system controls operation of the current control device, thereby controlling the maximum amplitude of current that can be drawn by the one or more lighting modules.

[0017] In at least one example, the lighting device includes a buck converter configured to supply current to the one or more lighting modules, and for the first dimming range, the dimming control system controls operation of the buck converter to thereby control a maximum amplitude of current that can be drawn by the one or more lighting modules.

[0018] In some examples, for the first dimming range, the dimming control system implements hysteretic control of the buck converter.

[0019] In at least one example, the dimming control system is configured to receive a user input indicating a desired dimming level of the lighting device and to control the dimming level in response to the desired dimming level.

[0020] A lighting device is also proposed comprising the dimming control system described herein and the light emitting device including the one or more light emitting modules.

[0021] Optionally, each light emitting module includes one or more light emitting diodes connected in series, a capacitor connected in parallel with the one or more light emitting diodes, and a diode connected in series with the one or more light emitting diodes and the capacitor, the diode being arranged to have an opposite polarity to the one or more light emitting diodes.

[0022] Preferably, each light emitting module comprises a module switch arranged to control the average current drawn by said light emitting module.

[0023] In some examples, the one or more lighting modules include a plurality of lighting modules, each configured to emit light of a different color and / or temperature.

[0024] The lighting device may comprise the current control device, the bypass switch and / or the cut-off switch as described above. The lighting device may be configured to connect to a power source, for example a converted mains power source, which supplies current to the light emitting module.

[0025] These and other aspects of the invention will be elucidated and elucidated with reference to the following embodiments. [Brief description of the drawings]

[0026] For a better understanding of the present invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which: [Figure 1] 1 illustrates a lighting device. [Diagram 2] 1 illustrates a technique for controlling dimming levels. [Diagram 3] 1 illustrates another approach for controlling dimming levels. [Figure 4] 1 illustrates the average current available for any light emitting module during a dimming procedure. [Diagram 5] 1 illustrates the average current available for any light emitting module during a dimming procedure. [Figure 6] 1 illustrates the current that can be drawn by a light emitting module during various control strategies. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The present invention will be described with reference to the drawings.

[0028] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the devices, systems and methods, are 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 devices, 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 denote the same or similar parts.

[0029] The present invention provides a mechanism for controlling the dimming level of a lighting device. During initial dimming, the dimming level is controlled by controlling the maximum amplitude of the current that can be drawn by any light emitting module of the lighting device. During higher levels of dimming (for lower light intensities), the dimming level is controlled using a pulse width modulation strategy.

[0030] 1 is a circuit diagram illustrating a lighting device 100 for use in embodiments. The lighting device comprises a light emitting device 110 and a dimming control system 120. Other components of the lighting device (e.g., driver circuitry, etc.) may be present but are not shown for simplicity.

[0031] The lighting device 100 is powered by a power supply (not shown) and is connected between a signal PWR provided by the power supply and a ground / reference voltage GND. The signal PWR may be a DC power signal, for example a DC voltage signal.

[0032] The illustrated light emitting device 110 includes a plurality of light emitting modules 115 for emitting light. In the illustrated example, the light emitting modules 115 are connected in parallel with each other.

[0033] However, in other examples, the lighting device includes only one lighting module.

[0034] The light emitting module may be connected between a first terminal 101 receiving a signal PWR from a power supply and a second terminal 102 connected to ground or a reference voltage GND.

[0035] Each light emitting module 115 comprises one or more light emitting diodes (LEDs) LED1, LED2, LED3, LED4. The average magnitude of the current flowing through the light emitting diodes of a light emitting module defines the intensity of the light output by the light emitting module.

[0036] In particular, each light emitting module may be configured to selectively control the amount of current (of available current) drawn by the light emitting module by controlling the operation of module switches S1-S4, for example using pulse width modulation or similar techniques. Thus, each light emitting module may have module switches S1-S4 configured to control the average current drawn by the light emitting module. The operation of the module switches may be controlled by a switch control system (not shown). The average amplitude of the current drawn by the light emitting module defines the average intensity of the light output by the light emitting module.

[0037] Each light emitting module 115 may be configured to emit light of a different color and / or temperature. In these scenarios, the overall perceived / effective color and / or temperature of the light output by the lighting device 100 is defined by the average intensity of the light output by each light emitting module. In this manner, the overall perceived / effective color and / or temperature of the light output by the lighting device 100 is defined by the average amount of current drawn by each light emitting module 115.

[0038] More specifically, the proportions of current drawn by the different light emitting modules 115 define the overall perceived / effective color and / or temperature of the light.

[0039] For efficiency reasons, it may be preferable to prevent / limit each light emitting module 115 from drawing current at the same time as other light emitting modules 115 of the light emitting device 110. Thus, each light emitting module 115 may be controlled to operate under a pulse width modulation scheme where each light emitting module 115 draws the available current for only a portion or a percentage of the time within a recurring control cycle. The ratio between these percentages of time defines the overall perceived / effective color and / or temperature of the light output by the light emitting device 110. For efficiency reasons, the sum of the percentages of time (within each control cycle) for all light emitting modules 115 may be equal to 1.

[0040] However, those skilled in the art will understand that it is not necessary for each light emitting module 115 to individually control the current drawn by the light emitting module 115, and that the module switches S1-S4 may be omitted and / or replaced with direct circuit connections.

[0041] Likewise, it is not necessary for each light emitting module 115 to output light of a different color and / or temperature. In such embodiments, it may still be advantageous to prevent / limit each light emitting module 115 from drawing current simultaneously with other light emitting modules 115 of the lighting device 110.

[0042] The average current I that can be drawn by one or more light emitting modules 115 PWR By controlling the average available current ("average available current"), it is possible to control the average intensity of light output by the light emitting device 110. More specifically, controlling the average available current may include controlling the average current between the first terminal 101 and the second terminal 102 to which the light emitting modules 115 are connected. This process may be performed by the dimming control system 120, for example, depending on the desired dimming level. This can be performed independently of individual control (if performed / present) of the current drawn by each light emitting module 115.

[0043] Controlling the current that can be drawn by one or more light emitting modules 115 is functionally equivalent to controlling the dimming level of the light emitting device 110. In particular, for a minimum dimming level, the maximum possible (average) current may be allowed to be drawn, and for a maximum dimming level, the minimum possible (average) current may be allowed to be drawn. Intermediate dimming levels are defined by corresponding intermediate values ​​of the average current available to the light emitting modules 115.

[0044] Therefore, the dimming level is inversely proportional to the average available current of the lighting module.

[0045] Conceptually, the dimming level may be considered to be inversely proportional to the average light intensity output by the lighting device 100. However, this is not necessarily true in all light output scenarios, since the average current drawn by each light emitting module 115 may (in some embodiments) be individually controlled. Conversely, for scenarios in which each light emitting module 115 draws the same amount of current, it will be appreciated that the dimming level will be inversely proportional to the average light intensity output by the lighting device 100.

[0046] Roughly speaking, the average current I that can be drawn by one or more light emitting modules 115 PWR It is possible to define two approaches for controlling the dimmer level, thereby allowing control of the dimming level.

[0047] The first approach is to control the maximum or peak amplitude of the average current. This can be controlled by defining the maximum or peak amplitude of the available current to be drawn by each light emitting module using a current controller 121 connected in series with each light emitting module 115. The current controller 121 forms part of the dimming control system 120.

[0048] The current control device 121 may be formed from a buck converter or the like. In another example, the current control device 121 may be formed from a linear current regulator. Suitable current control devices will be apparent to those skilled in the art. The illustrated current control device 121 comprises two current control modules I1, I2, each connected in series with a respective diode D6, D7.

[0049] The second approach is to control the amount of time per unit time or time cycle that current is allowed to be drawn, for example using pulse width modulation techniques. The second approach can be implemented by selectively bypassing the light emitting module 115 using a bypass switch S5 or the like to limit or prevent current from being drawn by the light emitting module 115. The bypass switch S5 may also form part of the dimming control system 120.

[0050] The proposed embodiments provide a new control scheme for a lighting device 110 having one or more lighting modules, such as the lighting device 110 illustrated in Figure 1. Some proposed embodiments also provide improvements to the lighting device 110.

[0051] The proposed embodiments propose, among other things, a new approach for controlling the operation of the light emitting device 110 according to a desired dimming level.

[0052] For purposes of understanding, the dimming levels are considered to range from a minimum dimming level (MIN) to a maximum dimming level (MAX) using a predetermined numerical scale, such as from 0 to 1. Other suitable scales for dimming levels may be used (e.g., 0 to 10, 0 to 63, 0 to 100, 1 to 10, 1 to 64, 1 to 100). [Table 1] Table 1 illustrates a first control scheme for controlling the dimming of the light emitting device 110. The first control scheme is implemented by the dimming control system 120.

[0053] In the first control scheme, an amplitude control strategy (AMP) is implemented if the desired dimming level is within a first dimming range (MIN to TH1), the first dimming range being bounded by a minimum dimming level MIN and a first predetermined dimming level TH1.

[0054] The amplitude control strategy AMP involves controlling the maximum amplitude of the current that can be drawn by one or more light emitting modules, for example the maximum amplitude of the current between the first terminal 101 and the second terminal 102. With reference to the light emitting device 110 of FIG. 1, this can be implemented by controlling the operation of the current control device 121.

[0055] Notably, to increase the dimming level, the dimming control system 120 may decrease the maximum amplitude of the current that can be drawn by one or more of the light emitting modules 115 (or vice versa).

[0056] In the case where the current control device 121 includes a buck converter configured to supply current to one or more light emitting modules 110, the dimming control system 120 may be configured to control the operation of the buck converter, thereby controlling the maximum amplitude of the current that can be drawn by the one or more light emitting modules 115 (i.e., during an amplitude control strategy).

[0057] In a particularly preferred embodiment, during the amplitude control strategy, the dimming control system 120 may be configured to implement hysteretic control of the buck converter. This type of control allows the buck converter to have a very fast response.

[0058] During the amplitude control strategy, no pulse width modulation is performed.

[0059] In the first control scheme, a pulse width modulation strategy (PWM) is implemented when the desired dimming level is within a second dimming range (TH1 to MAX), the second dimming range being bounded by a first predetermined dimming level TH1 and a maximum dimming level MAX.

[0060] The pulse width modulation strategy involves repeatedly performing a cycle that includes a first period followed by a second period.

[0061] During a first period (of each cycle), the dimming control system allows current to be drawn by one or more light emitting modules, the length of the first period being fixed to the same predetermined amount of time for each cycle (i.e., for all dimming levels within the second dimming range).

[0062] The predetermined length of time may be between 5 μs and 50 μs. Preferably, the predetermined length of time is between 10 μs and 50 μs, for example between 15 μs and 50 μs. For example, the predetermined length of time may be 25 μs. It has been recognized that these periods provide a good compromise between the available dimming range and the resolution of the different color / temperature channels (if any). For example, experimental analysis has revealed that a 12-bit resolution can be achieved when the predetermined length of time has a length of 25 μs.

[0063] Furthermore, there is a transition time when switching from low or no current to high current (i.e., the switching is not instantaneous). Typically, the length of this transition time is negligible compared to the length of time during which current can flow in each cycle. However, as the predetermined length of time becomes shorter, the transition time becomes more and more prevalent, affecting the accuracy of dimming at low dimming levels. By limiting the predetermined length of time to have a length of 5 μs or more, e.g., 10 μs or more, this effect can be reduced.

[0064] During a second period (of each cycle), dimming control system 120 prevents or limits current from being drawn by one or more of the light emitting modules 115. Dimming control system 120 is configured to control the length of the second period to control the average current that can be drawn by each light emitting module 115. In other words, the length of the second period varies for different dimming levels within the second dimming range.

[0065] In particular, to increase the dimming level within the second dimming range, dimming control system 120 may increase the length of the second time period. To decrease the dimming level within the second dimming range, dimming control system 120 may decrease the length of the second time period.

[0066] As previously described, limiting or preventing current from being drawn by one or more light-emitting modules 115 can be accomplished, for example, by using a bypass switch S5 to allow current to bypass the light-emitting module 115.

[0067] In another example, the dimming control system may be configured to prevent or limit current being drawn by one or more light emitting modules 115 by activating an isolating switch that, when activated, isolates or disconnects the one or more light emitting modules 115 from a power source configured to provide current to the one or more light emitting modules 115. The isolating switch may be connected in series between the first terminal 101 and the light emitting module 115 or between the light emitting module and the second terminal 102.

[0068] Controlling the second period effectively controls the pulse width frequency of the pulse width modulation. The total on-time of the light emitting module 115 is fixed for each cycle. The total on-time may be, for example, the total time that current can be drawn by the light emitting module 115 for each cycle. This reduces or avoids potential ripple and / or color shift of the light emitting device 110.

[0069] During the pulse width modulation strategy, the maximum amplitude of the current that can be drawn by the one or more light emitting modules 115 may be fixed. In particular, the maximum amplitude of the current that can be drawn by the one or more light emitting modules 115 may be fixed to the smallest maximum amplitude of the current during the amplitude control strategy. This may be, for example, the maximum amplitude of the available current at the first predetermined dimming level TH1.

[0070] The first control scheme is particularly advantageous for the lighting device 110 illustrated in FIG. 1, and it includes several optional, but advantageous, features.

[0071] In a particular example, each light-emitting module 115 of the light-emitting device 110 further includes one or more capacitors C1, C2, C3, C4, e.g., a single capacitor, connected in parallel with one or more light-emitting diodes LED1, LED2, LED3, LED4. Each capacitor C1, C2, C3, C4 may be an electrolytic capacitor. Each light-emitting module 115 also includes a diode D1, D2, D3, D4 connected in series with the parallel arrangement of one or more light-emitting diodes and corresponding one or more capacitors. For each light-emitting module 115, the diode D1, D2, D3, D4 is arranged to have the same polarity as the one or more light-emitting diodes LED1, LED2, LED3, LED4.

[0072] The use of the capacitors C1, C2, C3, C4 serves to filter or smooth the effect of pulse width modulation, e.g., caused by the dimming control system 120 and / or the module control system (not shown), on the current through the light emitting diodes of the light emitting module 115. An unsmoothed current would result in a flickering effect in the light emitted by the light emitting diodes, e.g., due to the square wave-like nature of the current caused by PWM. The proposed use of the capacitors serves to make the current through the LEDs of the light emitting module 115 continuous with reduced ripple. Thus, the use of the capacitors in the light emitting diodes reduces the apparent flickering.

[0073] In other words, the use of a capacitor in each light emitting module 115 reduces the current made available to the light emitting module 115 and / or the 100% modulation depth of the light emitting module 115 provided by the PWM control of the light emitting module 115 .

[0074] Diodes D1, D2, D3, and D4 prevent current from flowing from capacitors C1, C2, C3, and C4 to other parts of the light emitting module 115 without passing through the LEDs. This prevents leakage currents, undesirable powering of other LEDs, and improves efficiency.

[0075] As mentioned above, the first control scheme is particularly advantageous for use in such a light emitting device, in particular because it allows the use of capacitors C1 to C4 with relatively small capacitance in each light emitting module.

[0076] The exact value of the capacitance of the capacitors C1-C4 may depend on various factors, including the required (minimum) amplitude of the LED current, the dynamic resistance of the LEDs, the type of capacitor, and the required / desired maximum allowable ripple of the current through the LEDs of the light emitting module 115. As an example, a 100 μF capacitor may be used as a good compromise to meet such requirements for a standard or conventional set up.

[0077] By way of explanation, by controlling dimming using an amplitude control strategy initially (i.e., for a lower dimming level), the amount of charge that needs to be stored by the capacitor to provide a relatively smooth current during dimming controlled by a pulse-width modulation strategy is relatively smaller because the average current (and therefore the amount of charge) that needs to be stored by the capacitor to smooth / filter the effect of the pulse-width modulation strategy is higher (due to the larger maximum amplitude of the current).

[0078] In contrast, when a pulse-width modulation strategy is used at low dimming levels, the amount of charge that needs to be stored by the capacitor to ensure a relatively constant and smooth current through the LED is relatively large, which requires a much larger capacitor compared to when the proposed control scheme is used.

[0079] The use of a capacitor in each light emitting module 115 allows the dimming level of the light emitting device to be increased using a pulse width modulation strategy beyond the point where flicker would otherwise be noticeable / perceptible by humans. Specifically, without the capacitor, flicker may be noticeable at low pulse width modulation frequencies, e.g., frequencies below 1 kHz. With the capacitor, this flicker becomes less perceptible at low frequencies (<1 kHz).

[0080] For completeness, FIG. 2 is a flow chart illustrating a method 200 that may be employed by a dimming control system to implement the first control scheme.

[0081] The method 200 includes obtaining 210 a desired dimming level, which may be obtained at an input interface of the dimming control system, for example, which receives input from a user interface and / or a communication module.

[0082] The method 200 then determines, in step 220, whether the desired dimming level is within a first dimming range, i.e., whether it falls between a minimum dimming level MIN and a first predetermined dimming level TH1 (inclusive).

[0083] In response to the desired dimming level being within the first dimming range, the method performs step 230 of controlling the light-emitting device according to an amplitude control strategy, otherwise, the method performs step 240 of controlling the light-emitting device according to a pulse width modulation strategy.

[0084] Referring again to FIG.

[0085] Table 2 illustrates a second control scheme for controlling the dimming of the light emitting device 110. The second control scheme is implemented by the dimming control system 120. [Table 2] In the second control scheme, an amplitude control strategy (AMP) is implemented if the desired dimming level is within a first dimming range (MIN to TH1). The first dimming range is bounded by a minimum dimming level MIN and a first predetermined dimming level TH1. The operation of the amplitude control strategy is described above with reference to the first control scheme.

[0086] In the second control scheme, if the desired dimming level is within the second dimming range, a pulse width modulation strategy (PWM) is implemented. For the second control scheme, the second dimming range is bounded by a first predetermined dimming level TH1 and a second predetermined dimming level TH2. The first predetermined dimming level TH1 is less than the second predetermined dimming level TH2. The operation of the pulse width modulation strategy is described above with reference to the first control scheme.

[0087] In the second control scheme, a frequency control strategy (CREQ) is implemented if the desired dimming level is within a third dimming range, the third dimming range being bounded by a second predetermined dimming level TH2 and a maximum dimming level MAX.

[0088] The frequency control strategy FREQ is similar to the pulse width modulation strategy in that it involves performing pulse width modulation of the current that can be drawn by one or more light emitting modules, where performing the pulse width modulation involves performing a repeated cycle.

[0089] However, the frequency control strategy FREQ involves maintaining the frequency at which cycles of pulse width modulation are performed at a predetermined frequency, as opposed to the varying frequency in the pulse width modulation strategy.

[0090] The predetermined frequency may be 0.5 kHz or more, for example 1 kHz or more. When a space vector modulation (SVM) technique is used to control the operation of the light emitting module, the requirement of precise space vector modulation is met or is not a significant issue when the predetermined frequency is greater than these values.

[0091] In some examples, the predetermined frequency may be 5 kHz or less, which provides a suitable range for varying the frequency to maximize dimming during a pulse width modulation strategy without significantly affecting the control scheme of the individual light emitting modules.

[0092] As a suitable example, the predetermined frequency may be equal to 1 kHz.

[0093] The frequency control strategy also includes controlling the lengths of the first and second periods for each cycle of the pulse width modulation, thereby controlling the average current that can be drawn by each light emitting module. In particular, to increase the dimming level, the length of the first period is shortened and the length of the second period is correspondingly lengthened. Similarly, to decrease the dimming level, the length of the first period is lengthened and the length of the second period is correspondingly shortened.

[0094] Similar to the pulse width modulation strategy, during the frequency control strategy, the maximum amplitude of the current that can be drawn by the one or more light emitting modules may be fixed. In particular, the maximum amplitude of the current that can be drawn by the one or more light emitting modules may be fixed to the smallest maximum amplitude of the current during the amplitude control strategy (i.e., the maximum amplitude of the available current at the first predetermined dimming level TH1).

[0095] Operating according to a frequency control strategy reduces the resolution (e.g. color and / or temperature accuracy) of the lighting device, however, it is recognized that this is advantageously less important at high dimming levels due to the reduced perception of the human eye to changes at high dimming levels.

[0096] For completeness, FIG. 3 is a flow chart illustrating a method 300 that may be employed by a dimming control system to implement the second control scheme.

[0097] The method 300 includes obtaining 310 a desired dimming level, which may be obtained at an input interface of the dimming control system, which receives input from, for example, a user interface and / or a communication module.

[0098] The method 300 then determines, in step 320, whether the desired dimming level is within a first dimming range, i.e., whether it falls between a minimum dimming level MIN and a first predetermined dimming level TH1 (inclusive).

[0099] In response to the desired dimming level being within the first dimming range, the method performs step 330 of controlling the lighting device according to an amplitude control strategy.

[0100] Otherwise, the method performs step 340 of determining whether the desired dimming level is within the second dimming range, i.e., whether it falls between the first predetermined dimming level TH1 and the second predetermined dimming level TH2 (including the boundaries).

[0101] In response to the desired dimming level being within the second dimming range, the method performs step 350 of controlling the light-emitting device according to a pulse width modulation control strategy. Otherwise, the method proceeds to step 360 of controlling the light-emitting device according to a frequency control strategy.

[0102] To further improve understanding, Figures 4 and 5 illustrate the dimming procedure of a light-emitting device according to the concept proposed herein. Both figures show the average current that can be drawn by the light-emitting module over time t (x-axis).

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[0103] FIG. 4 shows the average available current as the dimming level increases from the minimum dimming level (and therefore the maximum average current) at time t1 to the maximum dimming level at time t3 during the first control scheme.

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[0104] During the time period between time t1 and time t2, the average available current is equal to or greater than a maximum value I MAX and a first predetermined value I TH1 When the average available current is between time t2 and time t3, the dimming control system operates according to the amplitude control strategy. TH1 and the minimum value I MIN (eg, between 0 and 1), the dimming control system operates according to a pulse width modulation strategy.

[0105] FIG. 5 shows that during the second control scheme, the dimming level increases from a minimum dimming level at time t4 to a maximum dimming level at time t7, and therefore the average available current increases from the maximum available current I MAX Minimum available current I MIN When the current decreases to

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[0106] During the time period between time t4 and time t5, the average available current is equal to or exceeds a maximum value I MAX and a first predetermined value I TH1 When the average available current is between time t5 and time t6, the dimming control system operates according to the amplitude control strategy. TH1 and a second predetermined value I TH2 When the average available current is between time t6 and time t7, the dimming control system operates according to a pulse width modulation strategy. TH2 and the minimum value I MIN (eg, 0), the dimming control system operates according to the frequency control strategy.

[0107] To further improve understanding, FIG. 6 shows a current I that can be drawn by a light emitting module during a pulse width modulation strategy or a frequency control strategy. PWR ("available current"). Available current is to be distinguished from average available current.

[0108] Available current I PWR is controlled to alternate between a non-zero current value I1 and a near-zero or zero current value I0, ie, to be pulse-width modulated, during a pulse-width modulation or frequency control strategy.

[0109] In particular, both strategies are implemented for a total length (in time) of T T Each cycle is formed of a first period T1 and a second period T2.

[0110] During a first period T1, the dimming control system allows current to be drawn by one or more light emitting modules, i.e., an available current I PWR is non-zero, for example, a non-zero current value I1.

[0111] During a second period T2, the dimming control system allows current to be drawn by one or more light emitting modules, i.e., an available current I PWR is zero or close to zero, for example, a current value I0 that is close to zero or zero.

[0112] In the case of a pulse width modulation strategy, the first period T1 is T In this strategy, the length of the second period T2 is controlled to control or vary the average current that can be drawn by each light emitting module. Thus, the total length of the cycle T T may vary.

[0113] For the frequency control strategy, the total length of the cycle, T T is fixed. In this strategy, the length of the first period T1 is controlled to control or vary the average current that can be drawn by each light emitting module, and therefore the length of the second period T2 is controlled to control or vary the average current that can be drawn by each light emitting module.

[0114] Returning to FIG. 1, a further optional feature of lighting device 100 is illustrated.

[0115] In particular, the lighting device 100 may comprise a smoothing capacitor C5 connected in parallel to one or more light emitting modules, the smoothing capacitor serving to smooth a signal supplied to the lighting device, for example from a power supply.

[0116] The lighting device 100 may have an input impedance R1.

[0117] Those skilled in the art can understand and effect variations to the disclosed embodiments in the practice of the claimed invention, from a study of the drawings, the specification and the appended claims. In the claims, the word "comprises" does not exclude other elements or steps, and the singular form "a" does not exclude a plurality.

[0118] 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. It should be noted that, where the term "adapted to" is used in the claims or the description, the term "adapted to" is intended as equivalent to the term "configured to". It should be noted that, where the term "configuration" is used in the claims or the description, the term "configuration" is intended as equivalent to the term "system", and vice versa. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. 1. A dimming control system for controlling a dimming level of a lighting device having one or more light emitting modules, comprising: a dimming level defining an average current that can be drawn by the one or more light emitting modules, ranging from a minimum dimming level to a maximum dimming level, the minimum dimming level providing an average current that can be drawn by the light emitting modules that is greater than the maximum dimming level; for each light emitting module, an average intensity of light output by said light emitting module is responsive to an average current drawn by each light emitting module; The dimming control system comprises: for a first dimming range bounded by the minimum dimming level and a first predetermined dimming level, controlling a maximum amplitude of current that can be drawn by the one or more light emitting modules; For a second dimming range bounded on one side by the first predetermined dimming level, the dimming level is controlled by performing pulse width modulation of current capable of being drawn by the one or more light emitting modules, wherein performing pulse width modulation includes performing repeated cycles, each cycle comprising: a first time period, during which the dimming control system allows current to be drawn by the one or more light emitting modules, the first time period being fixed at the same predetermined length of time for each cycle; a second period during which the dimming control system prevents or limits current drawn by the one or more light emitting modules, and for each cycle, the dimming control system controls the length of the second period to control the average current allowed to be drawn by each light emitting module; A dimming control system wherein the light output by the light emitting device has a higher average intensity in the first dimming range compared to the second dimming range.

2. The dimming control system, for a third dimming range, maintaining a frequency at which the pulse width modulation cycles are performed at a predetermined frequency; configured to control the dimming level by controlling, for each cycle of the pulse width modulation, lengths of the first period and the second period, thereby controlling the average current that can be drawn by each light emitting module; 2. The dimming control system of claim 1, wherein the second dimming range is bounded by the first predetermined dimming level and a second predetermined dimming level, and the third dimming range is bounded by the second predetermined dimming level and the maximum dimming level.

3. 3. The dimming control system of claim 2, wherein the predetermined frequency is between 0.5 kHz and 5 kHz.

4. 4. The dimming control system according to claim 2, wherein a minimum frequency at which the pulse width modulation cycles are performed during the second dimming range is equal to or greater than the predetermined frequency.

5. 4. The dimming control system of claim 1, wherein the predetermined amount of time is between 5 [mu]s and 50 [mu]s.

6. 6. The dimming control system of claim 5, wherein the predetermined amount of time is 25 [mu]s.

7. 2. The dimming control system of claim 1, wherein the dimming control system is configured to prevent or limit current drawn by the one or more light emitting modules by activating a bypass switch that, when activated, provides a conductive path for current to bypass the one or more light emitting modules.

8. 2. The dimming control system of claim 1, wherein the dimming control system is configured to prevent or limit current being drawn by the one or more light emitting modules by activating an isolation switch that, when activated, isolates or disconnects the one or more light emitting modules from a power source configured to provide current to the one or more light emitting modules.

9. the light emitting device comprising a buck converter configured to supply current to the one or more light emitting modules; 2. The dimming control system of claim 1, wherein for the first dimming range, the dimming control system controls operation of the buck converter to thereby control a maximum amplitude of current that can be drawn by the one or more light emitting modules.

10. 10. The dimming control system of claim 9, wherein for the first dimming range, the dimming control system implements hysteretic control of the buck converter.

11. The dimming control system comprises: receiving a user input indicating a desired dimming level of the light emitting device; The dimming control system of claim 1 , configured to control the dimming level in response to the desired dimming level.

12. The dimming control system of claim 1; and the light emitting device including the one or more light emitting modules.

13. Each light-emitting module is one or more light emitting diodes connected in series; a capacitor connected in parallel with the one or more light emitting diodes; and 13. The lighting device of claim 12, further comprising a diode connected in series with the one or more light emitting diodes and the capacitor, the diode being arranged to have an opposite polarity to the one or more light emitting diodes.

14. 14. A lighting device according to claim 12 or 13, wherein each light emitting module comprises a module switch configured to control the average current drawn by the light emitting module.

15. 13. The lighting device of claim 12, wherein the one or more light emitting modules comprise a plurality of light emitting modules, each light emitting module configured to emit light of a different color and / or temperature.

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