Logarithmic and deep dimming with variety of drivers for a single load

Abstract

The invention relates to a driver circuit for driving a load. The driving circuit comprises a plurality of drivers. The plurality of drivers comprise at least a first driver arranged to receive an input voltage and arranged to provide a fixed regulated current to the load, a second driver arranged to receive the input voltage and arranged to provide a variable regulated current to the load a controller arranged to control the plurality of drivers.

Description

[0001] 2024PF80317

[0002] 1

[0003] Logarithmic and deep dimming with variety of drivers for a single load

[0004] FIELD OF THE INVENTION

[0005] The invention relates to a driver circuit. The invention further relates to a system.

[0006] BACKGROUND OF THE INVENTION

[0007] For the lighting industry, the requirements for energy efficiency become more challenging, especially with the new European Union energy labelling introduced on 1 September 2021. This new labelling follows the trend of improvements in energy efficiency for lighting products. By then, more and more light sources achieved label ratings of A+ or A++, making it impossible for customers to see any light efficiency difference between products. With the new labelling, the light sources become more distributed over the labelling range again. This also means that lamps that were for example A++ rated in the old system are now labelled as C. It is therefore desired to further improve the energy efficiency of light sources.

[0008] Especially at dimmable light sources, there is a great desire to improve the efficiency. At dimming and especially deep dimming, the fixed losses in a driver e.g., losses caused in the control circuit, become a dominant part of the losses in a lighting apparatus. Drivers are generally designed for their rated power and the fixed losses are therefore also depending on the rated power of the driver. In general, a driver with a lower rated output power has also lower fixed power losses. This obviously impacts the total amount of power that can be provided to the load. A driver with a higher rated power can provide more power to its output, but this comes with more fixed losses. It is therefore desired to provide a lighting apparatus that can provide a good dimming function while operating at a very high efficiency.

[0009] SUMMARY OF THE INVENTION

[0010] It is an objective of the invention to provide a driver circuit that allows efficient operation in an operating window or dimming range, while maintaining a good operating performance. 2024PF80317

[0011] 2

[0012] To provide a solution, in a first aspect of the invention, a driver circuit is provided. The driver circuit comprises: a plurality of drivers, the plurality of drivers comprising at least: a first non-dimmable driver arranged to receive an input voltage and arranged to provide a fixed regulated current to the load; a second driver arranged to receive the input voltage and arranged to provide a regulated variable current to the load; a controller arranged to control the plurality of drivers.

[0013] A driver circuit has multiple drivers receiving a single input voltage and provide a regulated current to the load. The drivers therefore use a similar input voltage to provide a summed current to the load. One driver has a fixed regulated output current. The other driver has a variable regulated output current. This driver may provide a range of currents to the load. A controller is provided to control the drivers. Since the load requires a predefined amount of current, the controller may determine to enable or disable the first driver and determine the amount of current that is to be provided by the second driver. If the required load current is lower than the current that can be provided by the first driver, the first driver may not be activated at all. The controller may then only activate the second driver and set the current that is provided by the second driver. If the required load current is higher than the current that can be provided by the first driver, the first driver will be activated. In addition, the controller will activate the second driver and set the current that is provided by the second driver.

[0014] The first driver is a simple driver with a stable output current regulation. Since it is a fixed output i.e., non-dimmable, driver, the design can be very simple, efficient and cheap. For matching the total driver circuit current to the load, the second driver can be used to provide the remaining part of the current to the load. The second driver is a driver that has a variable output current. Such a driver requires more complexity resulting in additional losses and costs. Since the second driver does not have to provide the entire current to the load but only a fraction, the efficiency and cost impact can be kept relatively low.

[0015] In a further example, the fixed output current is larger than a maximum of the variable output current.

[0016] Preferably, a major part of current to the load is provided by the first driver. The first driver is the simplest driver and can easily be designed for higher currents. The second driver can then be used to provide the remaining current. The second driver is used for providing the remaining part of current, which is less than the current provided by the 2024PF80317

[0017] 3 first driver, to the load, which can be done with a relatively high accuracy with a reduced impact on the overall efficiency of the driver circuit.

[0018] In a further example, the controller is arranged to receive a dimming signal and to control the first driver and the second driver based on the received dimming signal, wherein a sum of the regulated current to the load and the variable regulated current to the load equals to a total required current to the load based on the received dimming signal.

[0019] Instead of a fixed current to the load, the load can also be dimmed. The controller receives a dimming signal, indicating how much dimming of the load is to be performed. This translates into a predetermined current to the load. The controller determines how many drivers are required to provide the predetermined current to the load. By controlling at least the first driver and the second driver based on the dimming signal, the total provided current corresponds to the total required current to the load.

[0020] In a further example, only the second driver has a variable regulated output current.

[0021] Preferably, of all drivers of the plurality of drivers, only the first driver had a variable regulated output current. All of the other drivers have a fixed regulated output current. This allows most of the drivers to be designed in an energy and cost effective way while keeping a good dimming current or desired current level regulation. The overall driver circuit can therefore be designed in an energy and cost effective design while maintaining a good current regulation at e.g. dimming.

[0022] In a further example, the controller is arranged to: enable and disable any of the plurality of drivers having a fixed regulated output current, and set a value for the variable regulated output current.

[0023] An example of controlling the drivers is provided. The drivers that have a fixed regulated output current are turned on or off to match the required current to the load. The total current provided by the drivers having the fixed regulated output current is lower than the desired current to the load. The remaining current is provided by the driver that provides the variable regulated output current. The controller sets the value for the variable regulated output current so the current provided by the driver circuit matches the desired load current.

[0024] In a further example, the fixed rated output current is twice as large as the maximum of the variable rated output current. 2024PF80317

[0025] 4

[0026] Having the drivers that provide the fixed rated output current arranged in a sequence with increasing rated output currents, every increase is twice as much as the preceding rated regulated current, effectively allows multiple drivers to be combined to provide a total fixed regulated current that is close to the desired load current. The doubling of the rated regulated current at each increase in the sequence allows any desired output current to be approached by the drivers. The remaining current is provided by the second driver, which provides a relatively small regulated current.

[0027] In a further example, the plurality of drivers comprises a third driver adapted to provide regulated fixed current equal to the maximum of the variable regulated current.

[0028] In the aforementioned example, it may occur that the desired load current cannot be exactly matched. To overcome this problem, an additional driver is introduced that has a fixed regulated output current that equals the maximum output current that can be provided by the second driver i.e., the driver providing the variable regulated output current. By providing the same current as the maximum current that can be provided by the second driver, the current provided by the driver circuit can be accurately matched to the required current for the load.

[0029] In a further example, the first driver comprises a resonant converter and the second driver comprises a flyback or a buck converter.

[0030] Since each driver may have different current ratings, different driver topologies may be required. The fixed regulated output drivers (e.g. the first driver) may be used for providing most of the current to the load and therefore need to provide a relatively large amount of power. An efficient topology for such driver is a resonant converter or LLC converter, a forward converter, or a full bridge converter, etc. The driver providing the variable regulated current (e.g. the first driver) provides a relatively low amount current to the load and therefore also a relatively low amount of power. An efficient topology for such a driver would be a buck converter or a flyback converter.

[0031] In a further example, the driver circuit comprises a rectifier arranged to receive a mains voltage and arranged to provide the input voltage.

[0032] Preferably, the driver circuit can be coupled to a mains power supply. A rectifier then rectifies the mains voltage into the input voltage.

[0033] In a further example, the controller is arranged to disable the first driver or the second driver based on the dimming signal.

[0034] A simple and effective way of controlling the driver circuit for providing the required current to the load is to disable the drivers that are not required for providing this 2024PF80317

[0035] 5 current. The disabled drivers do not consume any power and therefore do not negatively impact the efficiency of the driver circuit.

[0036] In another example, a system is provided. The system comprises the driver circuit and the load.

[0037] In a further example, the system is a lighting system and the load is a solid state lighting load.

[0038] BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Examples of the invention will now be described with reference to the accompanying drawings, in which:

[0040] Fig. 1 shows an example of a circuit diagram of a conventional driver circuit.

[0041] Fig. 2 shows an embodiment of a circuit diagram of a driver circuit.

[0042] Fig. 3 shows an example of a graphical relation between the dimming steps and an output power of the driver circuit.

[0043] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] The invention will be described with reference to the Figures.

[0045] 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 also 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.

[0046] Figure 1 shows an example of a conventional driver circuit. The driver circuit is arranged to provide a current to the load 4. A first driver 1 and a second driver 2 provide the regulated current to the load 4. The first driver 1 provides a fixed regulated current to the load 4 and the second driver 2 provides a variable regulated current to the load 4. The sum of the regulated current and the variable regulated current correspond to the total amount of current that is provided to the load 4. In conventional systems such as e.g., a computer power supply, the load 4 may vary its power consumption. A CPU may be part of such load 4 and may use more or less power depending on the processes to be performed. The driver circuit regulates the output voltage to a fixed value, regardless of the total power consumption of the 2024PF80317

[0047] 6 load 4. To improve the efficiency of such driver circuit, a controller is used to determine how many drivers have to be activated in order to provide the required power for the load 4. This may be done by sensing the power consumed by the load 4 and react accordingly to any variations in power consumption.

[0048] Figure 2 shows an example of a driver circuit. The driver circuit has a first driver 1 and a second driver 2. A controller 3 is provided to control the first driver 1 and the second driver 2. The first driver 1 and the second driver 2 provide output currents to load 4. A rectifier B 1 may be provided in case the driver circuit receives an AC voltage such as mains. The first driver l is a driver that generates a fixed regulated current to the load 4. The first driver 1 may be considered a constant current source that is capable of generating a single current amplitude. The second driver 2 is a driver that generates a variable regulated current to the load 4. The second driver 2 can be considered a constant current source that is capable of generating a range of current amplitudes. Together, the first driver 1 and the second driver 2 provide a total current to the load 4. The controller 3 is used to control the drivers. The controller 3 is provided with a value for the desired current for the load 4. This can be a preset value which can be preprogrammed when the driver circuit is connected to a load 4. Additionally or alternatively, the controller 3 may receive a dimming signal. Such a dimming signal may be provided via a commonly used dimming protocol. Such protocol may be a phase-cut dimmer, 0-10 V dimming, DALI, DMX or wireless dimming commands. The controller 3 determines the total amount of current that needs to be provided to the load 4. The following table shows an example of how the controller 3 determines which of the drivers are to be used to allow the driver circuit to provide the desired current to the load 4. In the example provided, four drivers are used. Driver 4 is the driver that provides the variable regulated current.

[0049] 2024PF80317

[0050] 7

[0051] Table 1. A granular step dimming example.

[0052] Table 1 shows an example of a driver circuit having four drivers. Driver 4 is the driver that provides a variable regulated current. This driver would correspond to the second driver 2 according to the rest of the description. The other drivers are drivers that provide a fixed regulated current. In the example provided, a dimming signal is provided to the controller 3, which is shown as the dim level.

[0053] The drivers have their own power ratings. Since the drivers provide a constant current, the voltage may be varied, depending on the load 4. This allows the constant current drivers to operate within an output voltage window. For the sake of clarity, instead of rated currents, rated powers of the drivers are presented. 2024PF80317

[0054] 8

[0055] Driver 1 has a rated power of 80 W, driver 2 has a rated power of 40 W, driver 3 has a rated power of 20 W and driver 4 has a rated power of 10 W and is the only dimmable driver.

[0056] If the controller receives a dimming level between 0.3 % and 6.7 %, driver 4 is the only active driver. Preferably, the other drivers are turned off so that they do not consume any energy at all. Within this dimming range, driver 1 changes its current to the load 4 and therefore also its output power. At a dimming level of 13.3 %, only driver 3 is active. Between dimming levels 13.3 % and 20 %, driver 4 is also used to provide the desired current. At dimming level 26.7 %, only driver 2 is active. Between dimming levels 26.7 % and 33.3 %, driver 4 is also used to provide the desired current. At dimming level 40 %, driver 2 and driver 3 are active. Between dimming level 40 % and 36.7 %, driver 4 is also used to provide the desired current. At dimming level 53.3 %, only driver 1 is active. Between dimming level 53.3 % and 60 %, driver 4 is also used to provide the desired current. At dimming level 66.7 %, drivers 1 and 3 are active. Between dimming level 66.7 % and 73.3 %, driver 4 is also used to provide the desired current. At dimming level 80 %, drivers 1 and 2 are active. Between dimming level 80 % and 86.7 %, driver 4 is also used to provide the desired current. At dimming level 93.3 %, drivers 1, 2 and 3 are active. Between dimming level 93.3 % and 100 %, driver 4 is also used to provide the desired current.

[0057] It can be seen that there are interruptions in the dimming level where no data (e.g. between 20 % to 26.7 %) is provided. At these dimming levels, no change in total power may occur since there is no driver available that can provide power to match the required power at these dimming ranges. A solution may be to introduce a further driver that has the same rated power or current as the single dimmable driver. This allows the driver circuit to cover the entire dimming range without any interruptions.

[0058] Figure 3 shows a graphic relationship between the dimming steps and the output power of the driver circuit. Compared to the previous control of drivers as explained in relation to the table 1, it may be possible to control the drivers such that there are no interruptions over the dimming range. When an interruption would occur because no driver can provide power to match the required power, a step can be made to a higher power level of a driver so that at least a single driver can provide the power. As an example, at dimming level 11 %, driver 4 is at its maximum power of 10 W. This means that the next dimming step cannot be followed by any driver. Therefore, a step in output has been made at the next step by activating driver 3 and provide an output power of 20 W. Instead of an interruption of 2024PF80317

[0059] 9 total power change from this dimming level, a step of total power is provided. This allows for a full utilization of the dimming range.

[0060] Other 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. 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. Any reference signs in the claims should not be construed as limiting the scope.

Claims

2024PF8031710CLAIMS:

1. A driver circuit for driving a load (4), the driving circuit comprising: a plurality of drivers, the plurality of drivers comprising at least: a first non-dimmable driver (1) arranged to receive an input voltage and arranged to provide a fixed regulated current to the load (4); a second driver (2) arranged to receive the input voltage and arranged to provide a variable regulated current to the load (4); a controller (3) arranged to control the plurality of drivers.

2. The driver circuit according to claim 1, wherein the fixed output current is larger than a maximum of the variable output current.

3. The driver circuit according to any of the preceding claims, wherein the controller (3) is arranged to receive a dimming signal and to control the first driver (1) and the second driver (2) based on the received dimming signal, wherein a sum of the fixed regulated current to the load (4) and the variable regulated current to the load (4) equals to a total required current to the load (4) based on the received dimming signal.

4. The driver circuit according to claim 1, wherein only the second driver (2) has a variable regulated output current.

5. The driver circuit according to any of the preceding claims, wherein the controller (3) is arranged to: enable and disable any of the plurality of drivers having a fixed regulated output current, and set a value for the variable regulated output current.

6. The driver circuit according to claim 1, wherein each driver of the plurality of drivers has a rated output current, wherein the plurality of drivers are arranged to provide a sequence of rated output currents, each subsequent rated output current of the sequence of2024PF8031711 rated output currents being twice as large as a preceding rated output current of the sequence of rated output currents.

7. The driver circuit according to any of the preceding claims, wherein the plurality of drivers comprises a third driver adapted to provide a regulated fixed current equal to the maximum of the variable regulated output current.

8. The driver circuit according to any of the preceding claims, wherein the first driver (1) comprises a resonant converter and the second driver (2) comprises a flyback or a buck converter.

9. The driver circuit according to any of the preceding claims, further comprising a rectifier (Bl) arranged to receive a mains voltage and arranged to provide the input voltage.

10. The driver circuit according to any of the claims 3 or 4 to 9, when depending on claim 3, wherein the controller (3) is arranged to disable the first driver (1) or the second driver (2) based on the dimming signal.

11. A system comprising a driver circuit according to any of the preceding claims and the load (4).

12. The system according to claim 11, wherein the system is a lighting system and the load (4) is a solid state lighting load.

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