Lighting circuit

Abstract

The lighting circuit comprises a series connection of multiple lighting channels of different output colors driven by a current source, some or all of the lighting channels comprising an LED device, a shunt switch in parallel with the LED device, and a current leakage path in parallel with the LED device, the current leakage path being used to calibrate the current through the LED device, thereby taking into account the characteristics of the LED.

Description

[Technical Field]

[0001] The present invention relates to a lighting circuit, and more particularly to a lighting circuit having multiple lighting channels. [Background technology]

[0002] Multi-channel lighting circuits are well known. By providing light sources with different colors (i.e., color points) for different channels, a desired overall color point can be achieved for the overall light output of the lighting circuit.

[0003] For example, it is well known to use shunt switching in a multi-channel light source using pulse-width modulation (PWM) switching signals. A drive current is applied to the illumination load. Different channels are operated on different duty cycles to produce the desired mixture of light outputs from multiple channels. This technique has the advantage that the spread of the drive current does not affect the overall color consistency of the light output, as all channels experience the same fluctuations. As a result, the mixed color remains essentially the same, with only the luminous flux fluctuating.

[0004] However, variations in the luminous flux (and color) of LEDs across different channels need to be compensated for by the controller software. For this purpose, information from the LED bins (which define the characteristics of the specific LEDs used in each channel) needs to be sent to the controller, or calibration measurements need to be performed. These bin characteristics include, among other things, the luminous flux, color point, and forward voltage of different channels.

[0005] To implement this communication with the controller, the characteristics of the LEDs need to be recorded and managed. The need to transfer data between the LED device (on the so-called L2 board) and the controller means that the controller and the L2 board must be paired. This means they cannot be swapped independently. The need to transfer data from the L2 board to the controller also means that a considerable amount of additional data storage, handling, and processing is required. Calibration measurements are an alternative, but they are costly.

[0006] In this shunt drive system, color consistency is adjusted in software by applying a PWM signal. This means that, because color correction is at the level of each individual channel and L2 board switch, it is not possible to connect several L2 boards in parallel using the same shunt switch.

[0007] Another known way to control a multi-channel light source is to connect all channels (even for multiple L2 boards) in parallel to a voltage bus. A single switch can be used to activate all channels of the same color. The current flowing to each channel in accordance with the common voltage can be adjusted by adding a series resistor to the LED string of each channel. Choosing the appropriate adjusting resistor means that the luminous flux of the channel's light output is constant, regardless of the luminous flux bins of the LEDs within the channel. The influence of the channel's luminous flux on the color point of the resulting overall light output is greater than the variation in the color point of individual channels, and therefore an acceptable overall variation in color point is achieved.

[0008] This method isolates the L2 board from the controller, but the circuit is less efficient than the current-driven method and more susceptible to bus voltage fluctuations. To prevent excessive losses, all channels must have nearly the same string voltage, which imposes further design constraints. [Overview of the project] [Problems that the invention aims to solve]

[0009] An improved multi-channel lighting circuit is needed that is energy-efficient and eliminates the need for extensive calibration processes and associated computing power. [Means for solving the problem]

[0010] The present invention is defined by the claims.

[0011] According to an example of a certain aspect of the present invention, A light source device including a series or parallel connection of multiple lighting channels with different output colors, A lighting circuit having a current source for supplying a drive current to the light source device, Each lighting channel, LED device, and A lighting circuit is provided having a current leakage path in parallel with the LED device, wherein each current leakage path (Radd FW, Radd Lime, Radd CW) is configured to bypass the current from the corresponding LED device (12, 14, 16) such that the light output of each LED device (12, 14, 16) is approximately equal when each LED device (12, 14, 16) is driven by substantially the same current.

[0012] When multiple LED devices are arranged in series or parallel, the light output may differ between each LED device when driven by the same current due to LED tolerances. These tolerances can be caused, for example, by the manufacturing process of the LEDs. These tolerances can be within a range of approximately ±10%. By placing a current leakage path in parallel with the LED devices, the light output between the LED devices (when the same current is supplied to each LED device) can be brought closer. Therefore, the light output deviation can be significantly reduced rather than having a ±10% light output deviation. The current leakage path needs to be configured so that it can bypass current from the corresponding LED device so that the light output of each LED device is approximately equal when each LED device is driven by substantially similar currents.

[0013] In a further example, the lighting system has a controller, the light source device has the series connection, each lighting channel has a shunt switch in parallel with the LED device, and the controller is configured to control the shunt switch.

[0014] In this example, the lighting circuit uses a shunt switch to perform luminous flux control, which has the advantage of maintaining the same color point in a simple manner at various brightness levels. However, in order to eliminate the need to provide bin data (i.e., the performance of the LEDs used in the channel) to the controller and to eliminate the need for a calibration phase, each current leakage path is used to adapt the response of at least some of the LED devices to the supplied drive current. Thus, these current leakage paths result in a hardware implementation of a compensation scheme to compensate for different LED characteristics, such as different LEDs being from different bins. The design of the current leakage paths is adapted to the characteristics of the relevant LED devices without the need to relay any information to the controller or to perform calibration measurements. In this way, the advantages of a known voltage-driven system (which does not require calibration) are combined with the advantages of shunt switching (which is more efficient and less dependent on drive current or voltage).

[0015] Each of the LED devices in the lighting channel may have a current leakage path. However, there may be some LED devices that do not require the leakage path (i.e., the current leakage path is effectively infinite resistance, i.e., an open circuit). This is because some LED devices may be the default (minimum luminous flux bin), representing the default to which compensation for all other LED devices is made.

[0016] It should be noted that "different colors" is only intended to mean different color points. For example, warm white, cool white, and flame white may be considered different colors.

[0017] Each current leakage path comprises, for example, a resistance circuit. This provides a simple way of implementing a current leakage path. The resistance is selected such that the remaining current reaching said LED device provides a predetermined (i.e., calibrated) light output luminous flux.

[0018] Alternatively, said current leakage path may comprise a current regulating circuit. This is an alternative way of diverting current away from said LED device such that said remaining current produces the desired light output. Said current regulating circuit makes the bypass current more independent and more constant, and functions as a constant current bypass circuit.

[0019] The controller may be adapted to apply different shunt switch PWM duty cycles for different luminous flux settings of the light source device. This is more efficient than a constant voltage driving scheme.

[0020] The controller may further be adapted to apply different driving currents for different luminous flux settings of the light source device. Therefore, in order to set the luminous flux, for example for deep dimming, there may be not only PWM control but also amplitude control.

[0021] For each LED device, said current leakage path is adapted, for example, such that the luminous flux of the light output is calibrated to a desired value with respect to a default driving current.

[0022] Therefore, said light output luminous flux is at a known level (for a given driving current) without requiring feedback to the controller.

[0023] Said default driving current is based on, for example, the expected color point and luminous flux for each channel, by which the desired color point of said light source device is achieved in a state where the actual luminous flux matches the expected luminous flux. Said default driving current is the driving current for the minimum required luminous flux for each of the channels for the lowest luminous flux bin of said light source device, that is, said driving current at which the lowest luminous flux bin of each of said LED channels can still satisfy the minimum lighting requirement.

[0024] In the case of an LED device from the lowest luminous flux bin, the bypass can be completely blocked with a very high resistance such that the entire current of said driver flows through these LEDs. Therefore, in the case of an LED device provided with the lowest luminous flux bin, no current leakage path is required since the entire current will pass through said LED device.

[0025] Therefore, said current leakage path ensures that, for the lowest luminous flux bin and the minimum light requirement (i.e., the minimum brightness level), various channels provide the required light output luminous flux so as to produce the desired overall color point and luminous flux. This ensures that the desired color point and luminous flux are generated up to the minimum light output (brightness) level.

[0026] Said light source device may comprise a plurality of lighting substrates each having a respective series connection of a plurality of lighting channels of different output colors, and each shunt switch is shared among said LED devices of corresponding channels of said plurality of lighting substrates.

[0027] Therefore, a lighting substrate (a so-called L2 substrate) may be added to said lighting circuit. Said shunt switch is shared among all of said lighting substrates because the same duty cycle can be applied to different substrates. This is because compensation for differences in said L2 substrate is implemented on the substrate itself by said current leakage path.

[0028] Each lighting board has, for example, its own current leakage path in parallel with each LED device.

[0029] Each lighting board has its own current leakage path, while the shunt switching is shared between boards.

[0030] The present invention also provides a lighting fixture having a lighting circuit as defined above. The lighting fixture is, for example, a spotlight.

[0031] These and other aspects of the present invention will be described and clarified with reference to the embodiments described below.

[0032] In another example, the lighting system is It has a first lighting circuit and a second lighting circuit, and each lighting circuit is A light source device including a series connection of multiple lighting channels with different output colors, A current source for supplying drive current to the aforementioned light source device, It has a controller, Each lighting channel is: LED device, and The LED device has a shunt switch in parallel with it, Each lighting channel further has a current leakage path in parallel with the LED device, The controller is configured to control the shunt switch, Each current leakage path is configured to bypass current from the corresponding LED device such that the light output of the first lighting circuit and the light output of the second lighting circuit are approximately equal when each lighting circuit is driven by substantially similar currents.

[0033] In this example, a first lighting circuit and a second lighting circuit may be provided. They may be the same lighting circuit, for example, similar lamps, which also need to supply similar light output at a single given setpoint. By providing a shunt switch, the light output of each lighting circuit can be controlled to a desired light. To eliminate the need to calibrate the shunt switch in the corresponding LED device, a current leakage path is provided across each LED device. The current leakage path is configured such that the light output of the first lighting circuit and the light output of the second lighting circuit are approximately equal when each lighting circuit is driven by substantially similar currents. This makes it possible to bring the light outputs of each lighting circuit closer to each other without requiring a calibration step. By omitting calibration, the controller can be simplified. [Brief explanation of the drawing]

[0034] For a better understanding of the present invention and to more clearly illustrate how it can be carried out, the accompanying drawings are referenced here, as merely one example. [Figure 1] A known current-driven lighting circuit using a shunt switch is shown. [Figure 2] This shows a voltage drive device equipped with a voltage source that supplies bus voltage. [Figure 3] An example of a lighting circuit according to the present invention is shown. [Figure 4] Current and voltage are shown to illustrate the operation of the current leakage path. [Modes for carrying out the invention]

[0035] The present invention will be described with reference to the figures.

[0036] The detailed descriptions and specific examples illustrate exemplary embodiments of the apparatus, systems, and methods, but are for illustrative purposes only and should not be used to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems, and methods of the invention will be better understood from the following description, the appended claims, and the appended drawings. The figures are for illustrative purposes only and are not drawn to scale. The same reference numerals are used throughout the figures to indicate the same or similar parts.

[0037] The present invention provides a lighting circuit having a series connection of multiple lighting channels of different output colors, driven by a current source. Each lighting channel has an LED device and a shunt switch in parallel with the LED device. Some or all of the lighting channels have a current leakage path in parallel with the LED device. The current leakage path is used to calibrate the current flowing through the LED device, thereby taking into account the characteristics of the LEDs.

[0038] Figure 1 shows a known current-driven lighting circuit using a shunt switch. The circuit has a current source 10 that supplies current to a series connection of multiple (three in this example) lighting channels of different output colors.

[0039] Each lighting channel has its own LED device 12, 14, 16 and shunt switches 22, 24, 26 in parallel with the LED device.

[0040] The different colors in this example are cool white (CW, 6500K), flame white (FW, 2200K), and lime (with a dominant wavelength in the range of 550nm to 590nm). There is a forward voltage drop Vf through each LED device, and therefore, V f,FW , V f,CW and V f,Lime There is.

[0041] There can be any number of individually addressable channels and any set of colors.

[0042] A PWM switching method is used to control the shunt switch. Different channels operate on different duty cycles to produce a desired mixture of light outputs from multiple channels to create the desired color and luminous flux output. Variations in the luminous flux (and color) of LEDs from different channels are compensated for by software in a system controller (not shown). For this purpose, information on the luminous flux and color point from the LED bins is sent to the system controller, for example. The need for data transfer from the lighting board to the controller necessitates requirements for data storage, handling, and processing.

[0043] Figure 2 shows a voltage drive device equipped with a voltage source 30 that supplies bus voltage. The bus voltage can be supplied to multiple lighting boards L2_1 and L2_2.

[0044] In this example, each lighting board has a parallel lighting channel. Each lighting channel has LED devices 120, 140, and 160 in series with calibration resistors Radd FW, Radd Lime, and Radd CW.

[0045] Each channel is also in series with series switches 220, 240, and 260. Therefore, each series switch either allows current to flow through a channel or prevents current from flowing through it. The series switches are shared among channels on multiple lighting boards. This is possible because compensation for the characteristics of different LED devices is provided by additional resistors. Thus, even with the same drive voltage and shared series switches, different currents can flow through different channels.

[0046] This method isolates the L2 board from the controller, but the circuit is less efficient than the current-driven method and more susceptible to bus voltage fluctuations. To prevent excessive losses, all channels must have nearly the same string voltage, which imposes further design constraints.

[0047] Figure 3 shows an example of a lighting circuit according to the present invention. This can be considered a modification of the current-driven circuit in Figure 1. The same reference numerals as in the circuit in Figure 1 are used.

[0048] In this case, as before, the lighting circuit has a series connection of multiple lighting channels with different output colors.

[0049] Each lighting channel has LED devices 12, 14, and 16, and shunt switches 22, 24, and 26 in parallel with one of the LED devices. Each LED device may be a single LED or an LED string, and for clarity, in this example it is represented as a single LED symbol.

[0050] The current source 10 supplies drive current to the light source device. This can be any suitable current source, such as a switch-mode current regulator (e.g., a hysteresis buck converter) that maintains the LED drive current at a quasi-constant level through measurement and adjustment, regardless of the actual voltage level of the LED device.

[0051] The desired color output is achieved by the desired relationship between the PWM settings of the shunt switch. To control brightness, the controller may adjust only the PWM settings (synchronously with each other). However, in other examples, this PWM control may be combined with amplitude modulation. This can address the PWM resolution problem at very deep dimming brightness settings (<2% brightness).

[0052] The shunt switches can be controlled by any desired timing arrangement. For example, the shunt switches may all be open simultaneously so that the drive current flows through all three channels at the same time. The switches may then be closed at different times within the duty cycle control period to create bypass paths and thereby turn off the channels. For example, all switches may be closed at the start of the duty cycle period and then opened when a desired duty cycle is reached for each channel.

[0053] Instead, to reduce the period without light output, some channels may be designed to emit light at the beginning of the duty cycle, while others may be designed to emit light at the end of the duty cycle.

[0054] The simplest embodiment involves starting all channels simultaneously. However, it is preferable to stagger the on-times, not only for the sake of light continuity, but also to limit voltage changes resulting from different LED forward voltages connected in the circuit, as large voltage jumps make it more difficult to maintain a stable current.

[0055] Figure 3 also shows a controller 40 for controlling the shunt switches 22, 24, and 26. By adjusting the duty cycles proportionally to each other, the color point is maintained, but the luminous flux is controlled, i.e., controlled to perform dimming. The controller 40 can also control the drive current level, for example, during deep dimming, as described above.

[0056] According to the present invention, some or all of the channels also have a current leakage path in parallel with the LED device. In the example shown, each channel has a current leakage path, and each current leakage path is a bypass resistor Radd FW, Radd Lime, and Radd CW. The current leakage path eliminates the need to provide bin data (i.e., the performance of the LEDs used in the channel) to the controller and eliminates the need for a calibration phase.

[0057] There are common types of LEDs used in lighting boards for use within lighting circuits. The controller software is set to the expected color point for each channel based on the common LED type, and to the luminous flux corresponding to the default drive current for the LED in the lowest expected luminous flux bin. Thus, it is assumed that the LED has a certain range of possible characteristics defined by the luminous flux bin of the LED, with the lowest luminous flux bin being used as the default.

[0058] In the case of the lowest luminous flux bin (since the lowest luminous flux bin corresponds to the lowest luminous flux for a given current), all current must pass through the LED device to reach the default luminous flux, which can correspond to an infinite parallel resistance (open circuit).

[0059] The light output from the LED device in the lowest luminous flux bin is Φ at the drive current I. min It can be assumed that this is defined as follows. More generally, this is the default drive current, Φ min This is the default light output luminous flux, which is the default light output luminous flux from which the bins of other luminous fluxes are calibrated to the said default light output luminous flux.

[0060] At the same current I, the luminous flux Φ bin (I) brings about V f,bin Under the operating conditions of (I), the parallel resistor required to adjust the LED string with a bin value that yields a forward voltage (for the entire string for that channel) can be determined.

[0061] Using the characteristic relationship between the luminous flux of an LED and the current, the required current is [Math.]] that satisfies the above formula.

[0062] Accordingly, the current I flowing through an LED device from this specific bin bin produces an output luminous flux corresponding to the luminous flux produced by an LED from the minimum luminous flux bin.

[0063] This gives the required bin current. By definition, I bin is less than or equal to I (for the lowest bin, I=I bin ). The simplest relationship is a linear relationship for I bin , but a more accurate estimation may be used. Using a linear approximation, I bin is [Math.]] defined as follows.

[0064] The required resistance is [Math.]] can be calculated as follows.

[0065] In this case, the default current I, which corresponds to the lowest luminous flux setting, is set by PWM control and / or amplitude modulation of a preset driving current. The required resistance value is determined as part of the manufacturing of the lighting circuit and is independent of the controller.

[0066] In FIG. 4, current and voltage are shown.

[0067] The efficiency of the system is defined by the efficiency of the lowest luminous flux bin. The overall system efficiency loss caused by the bypass path depends on the PWM ratio of the channel and the overall bin width.

[0068] For example, the range of luminous flux bins depends on the LED device provided by the supplier. For instance, for a typical bin value, an LED device could fall between the lowest luminous flux bin (10% lower than the typical luminous flux value) and the highest luminous flux bin (10% higher than the typical luminous flux value).

[0069] This 20% range means that, for the bin with maximum luminous flux, approximately 20% of the current needs to be bypassed. In that case, the resistor rating will be 20% of the power consumption of that color.

[0070] The present invention involves leaking current from the main path. The use of a resistive circuit (e.g., a simple resistor) is the easiest and cheapest way to generate leakage current. However, other ways of achieving leakage current are also possible, for example, by adding a linear current regulator to the leakage path.

[0071] Figure 3 shows a single L2 lighting board. However, the light source device may have multiple lighting boards, each having a series connection of multiple lighting channels with different output colors. However, the shunt switch may be shared among the LED devices of the corresponding channels of the multiple lighting boards. Thus, multiple lighting boards may be controlled by the same controlled, shared set of shunt switches. Current leakage paths are implemented at the level of individual lighting boards.

[0072] The number of connected LED boards determines the preset current. This preset current setting is generally not changed dynamically. Therefore, the current level may be configured as part of the installation procedure and set by changing the setting value in software, or it may be set in hardware, for example, by setting the drive current with a setting resistor.

[0073] In the example above, the PWM setting is used to change the brightness while keeping the same color point. In more advanced control techniques, the PWM setting can also be used to set different color points, or to set different color points at different light output levels so that the color point is dynamically controlled as a function of the dimming level.

[0074] In the example shown, the LED devices are arranged in series. Instead of a series configuration, the LED devices 12, 14, and 16 can be arranged in parallel.

[0075] In the example shown, a shunt switch is provided in parallel with each lighting channel, along with the LED devices 12, 14, and 16. However, it should be understood that the shunt switch is not essential for the present invention to provide the desired effect of matching the light output of each LED device when each LED device is driven by substantially the same current.

[0076] The current leakage path shown in the example may also be useful when multiple lighting circuits are desired to supply similar light outputs when given a single setpoint. The current leakage path can provide matching of the light outputs produced by each lighting circuit by ensuring that the light outputs of the first lighting circuit and the second lighting circuit are approximately equal when each lighting circuit is driven by substantially similar currents, for example, when given a single setpoint.

[0077] A lighting system is a part of a lighting fixture, such as a spotlight.

[0078] A person skilled in the art will be able to understand and achieve, in carrying out the claimed invention, variations to the disclosed embodiments by studying the drawings, specification and appended claims. In the claims, the word “has” does not exclude other elements or steps, and singular nouns do not exclude plural nouns.

[0079] A single processor or other unit may perform the functions of multiple items listed in the claims.

[0080] The mere fact that certain means are mentioned in different dependent claims does not mean that combinations of these means cannot be used to one's advantage.

[0081] Note that when the term "adapted to..." is used in the claims or specification, it is intended to be equivalent to the term "configured to...".

[0082] No reference numeral in the claims should be construed as limiting the scope.

Claims

1. A light source device including a series connection of multiple lighting channels, A current source for supplying drive current to the aforementioned light source device, A lighting circuit having a controller, Each lighting channel has an LED device, a current leakage path in parallel with the LED device, and a shunt switch in parallel with the LED device, and each current leakage path has a resistor circuit or a linear current adjustment circuit. Each current leakage path is configured to bypass current from the corresponding LED device so that the luminous flux of the light output of each LED device is approximately equal when each lighting channel is driven by substantially similar currents. A lighting circuit configured such that the controller controls the shunt switch.

2. The lighting circuit according to claim 1, wherein the controller is adapted to apply different shunt switch PWM duty cycles to different luminous flux settings of the light source device.

3. The lighting circuit according to claim 2, wherein the controller is adapted to apply different current source drive currents for different luminous flux settings of the light source device.

4. The lighting circuit according to claim 1, wherein for each LED device, the current leakage path is adapted such that the luminous flux of the light output is calibrated to a desired value with respect to the default drive current.

5. The lighting circuit according to claim 4, wherein the default drive current is the drive current for the minimum required luminous flux for each channel for the lowest luminous flux bin of the light source device.

6. The lighting circuit according to claim 1, wherein the light source device includes a plurality of lighting boards, each having a series connection of a plurality of lighting channels, each with a different output color, and each shunt switch is shared among the LED devices of the corresponding channels of the plurality of lighting boards.

7. The lighting circuit according to claim 6, wherein each lighting substrate has its own current leakage path in parallel with each LED device.

8. A lighting fixture having the lighting circuit described in claim 1.

9. A lighting fixture according to claim 8, having a spotlight.

10. A lighting system having a first lighting circuit and a second lighting circuit, wherein each lighting circuit is A light source device including a series connection of multiple lighting channels with different output colors, A current source for supplying drive current to the aforementioned light source device, It has a controller, Each lighting channel, LED device, and The LED device has a shunt switch in parallel with it, Each lighting channel further has a current leakage path in parallel with the LED device, The controller is configured to control the shunt switch, A lighting system in which each current leakage path is configured to bypass current from the corresponding LED device such that the light output of the first lighting circuit and the light output of the second lighting circuit are approximately equal when each lighting circuit is driven by substantially the same current.

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