Ultra-efficient dimmable LED driver

Abstract

The invention relates to a driver circuit for powering a light source. The driver circuit includes: a first driver adapted to provide power to a light source and having a first output power at a first optimal power conversion efficiency; a second driver adapted to provide power to the light source and having a second output power at a second optimal power conversion efficiency; and a controller for enabling and disabling the first driver having the first duty cycle and the second driver having the second duty cycle. The controller is adapted to receive the dimming signal and is arranged to determine a first duty cycle and a second duty cycle based on the dimming signal such that the first driver operates at a first optimal power conversion efficiency and the second driver operates at a second optimal power conversion efficiency.

Description

Technical Field

[0001] This invention relates to a driver. It also relates to a lighting device. Background Technology

[0002] For the lighting industry, energy efficiency requirements have become more challenging, especially with the introduction of the new European Union Energy Efficiency Labelling (EER) on September 1, 2021. This new labelling follows the trend of increasing energy efficiency in lighting products. Consequently, more and more light sources are achieving A+ or A++ labeling levels, making it impossible for consumers to perceive any difference in luminous efficiency between products. With the new labelling, light sources have again become more dispersed in their labeling range. This also means that, for example, a lamp rated A++ in the old system is now labeled C. Therefore, further improvements in the energy efficiency of light sources are expected.

[0003] Especially for dimmable light sources, high efficiency is highly desirable. During dimming, and particularly deep dimming, fixed losses in the driver (e.g., losses in the control circuitry) become a major component of the losses in the lighting fixture. Drivers are typically designed for their rated power, so fixed losses also depend on the driver's rated power. Generally, drivers with lower rated output power also have lower fixed power losses. This significantly affects the total power available to the load. Drivers with higher rated power can deliver more power to their output, but this introduces more fixed losses. Therefore, it is desirable to provide a lighting fixture that offers good dimming capabilities while operating with very high efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide a solution that allows dimming to be performed while maintaining good overall efficiency.

[0005] To provide such a solution, in a first aspect of the invention, a driver circuit for driving a light source is provided. The exciter circuit includes:

[0006] - A first driver adapted to provide power to a light source and having a first output power at a first optimal power conversion efficiency;

[0007] - A second driver adapted to supply power to a light source and having a second output power at a second optimal power conversion efficiency;

[0008] - A controller suitable for:

[0009] - Generate a first control signal for enabling and disabling the first driver, the first control signal having a first duty cycle, and

[0010] - Generate a second control signal for enabling and disabling the second driver, the second control signal having a second duty cycle.

[0011] The controller is adapted to receive a dimming signal and is arranged to determine a first duty cycle and a second duty cycle based on the dimming signal, such that the first driver operates with a first optimal power conversion efficiency when activated, and the second driver operates with a second optimal power conversion efficiency when activated, wherein the first control signal and the second control signal have a frequency of at least 100 Hz.

[0012] A first driver and a second driver are provided. Both drivers supply power to the same light source. Each driver has an output power operating at its optimal conversion efficiency. This means the drivers are designed to provide output power at the highest efficiency they can deliver to the light source. A controller is used to control the first and second drivers. The controller generates a first control signal and a second control signal, enabling and disabling the first and second drivers. The controller also receives a dimming signal. The dimming signal can be any kind of dimming signal used in the lighting industry. Examples of dimming signals are phase-cut dimming signals, 0-10V dimming signals, DALI dimming signals, DMX dimming signals, or wireless dimming signals. The controller uses the dimming signal to determine which duty cycle each driver operates at, i.e., which duty cycle each driver is enabled at. When the drivers are enabled, they preferably provide their corresponding power to the load at their optimal power conversion efficiency. This allows the power of the drivers to be combined to the load, and this is done in an energy-efficient manner when the drivers supply power to the load. Controlling the duty cycle of the driver to be enabled allows for changes in the power to the load while maintaining high overall efficiency of the driver circuitry. In an example using two drivers, both arranged to provide similar amounts of power to the light source, the first driver can be used to provide variable power between 0% and 50% dimming levels. Accordingly, the duty cycle of the first driver can vary between 0% and 100%. Preferably, after the first driver operates at a 50% dimming level with a 100% duty cycle, the second driver can be included in powering the light source. Between 50% and 100% dimming levels, the second driver can be operated with corresponding duty cycles between 0% and 100%. Providing a first control signal and a second control signal with a frequency of at least 100 Hz allows for robust control of the drivers without compromising light quality.

[0013] In another example, the driver circuit includes a third driver adapted to supply power to the light source and have a third output power at a third optimal power conversion efficiency, wherein the controller is configured to enable and disable the third driver at a third duty cycle and is adapted to determine the third duty cycle based on a dimming signal such that the third driver operates at the third optimal power conversion efficiency when activated.

[0014] The third driver allows for an increase in the total power to the light source or for making the driver smaller, as each driver can have a lower rated power.

[0015] In an example using three drivers arranged to provide similar amounts of power to the light source, the first driver can be used to provide variable power between 0% and 33.33% dimming levels. Accordingly, the duty cycle of the first driver can vary between 0% and 100%. Preferably, after the first driver operates at a dimming level of 33.33% with a 100% duty cycle, the second driver can be included in powering the light source. Between dimming levels of 33.33% and 66.67%, the second driver can operate with corresponding duty cycles between 0% and 100%. Preferably, after the first and second drivers operate at a dimming level of 66.67% with a 100% duty cycle, the third driver can be included in powering the light source. Between dimming levels of 66.67% and 100%, the third driver can operate with corresponding duty cycles between 0% and 100%.

[0016] In yet another example, the first and second drives are arranged to have the same rated power.

[0017] Preferably, all drivers have the same rated power for powering the light source. Preferably, the first and second drivers provide substantially similar amounts of power to the light source. This allows the drivers to be designed as identical modules. This greatly simplifies the design of the driver circuitry.

[0018] In another example, the first driver and the second driver are arranged to have different rated power from each other.

[0019] In situations like deep dimming, the dimming steps can be better perceived by the observer. Providing a first driver with a lower rated power than the second driver may be preferred. For example, the first driver could have a rated power of 1W, and the second driver could have a rated power of 9W, resulting in a total power of 10W. This 10W can be divided, for example, linearly across the dimming range, such that the power of the light source can vary between 0W and 10W at dimming levels between 0% and 100%. The first driver can be used within a dimming range between 0% and 10%, where the first driver can operate with corresponding duty cycles between 0% and 100%. The first driver may not be enabled with a duty cycle of infinite steps. Instead, the duty cycle itself has resolution. As an extremely exaggerated example, only 10 duty cycle steps can be provided. These steps are then mapped to the power range that can be provided by the driver. In this example, a 0% duty cycle corresponds to 0W supplied to the light source, while a 100% duty cycle could involve 1W supplied to the light source. Each duty cycle step increases the load power by 100mW. Therefore, the minimum power that can be supplied to the light source is 100mW. If a second driver is used within this dimming range, assuming a similar duty cycle step, only a minimum power of 900mW is possible. Therefore, it is desirable to use the driver with the lowest rated power at the deepest dimming level, so that the lowest possible minimum power can be supplied to the light source by the driver circuitry.

[0020] In another example, the first driver and / or the second driver are not dimmable.

[0021] If the driver is non-dimmable, it is arranged to provide a fixed amount of power. Therefore, the driver can only provide one power level, which can be the driver's rated power. The driver has optimal power efficiency because it is designed to provide that single amount of power with the highest possible efficiency. Therefore, the average power provided by the driver circuitry depends on the duty cycle during which each driver is enabled / activated.

[0022] In another example, the driver circuit also includes capacitors and switching elements, wherein the capacitors and switching elements are configured in series between a first input terminal and a second input terminal of the first driver.

[0023] Providing a switchable capacitor at the driver's input allows for compensation against interference caused by enabling and disabling the driver. For example, when no driver is drawing current from, for instance, the AC input at a given moment, the capacitor can be connected to the AC input voltage to allow the desired current to be drawn.

[0024] In another example, the driver circuit is arranged to receive an AC voltage, and the switching element is arranged to close when the voltage across the capacitor exceeds the amplitude of the AC voltage.

[0025] If the capacitor is charged, current from the capacitor can be supplied to the driver when the capacitor voltage exceeds the AC input voltage.

[0026] In another example, the driver circuit includes an auxiliary driver adapted to power the controller and adapted to be electrically isolated from the light source.

[0027] Controllers typically require their own power supply. Controllers have their own power requirements. Therefore, it is desirable to provide an auxiliary driver whose power efficiency is optimized for the power consumed by the controller. This can be done when the auxiliary driver is used only to power the controller. Preferably, the auxiliary driver is electrically decoupled from the light source, so that the auxiliary driver cannot power the light source.

[0028] In another example, the driver circuitry includes another auxiliary driver, wherein the other auxiliary driver is adapted to supply power to the controller when the driver circuitry is in standby mode.

[0029] In standby mode, the controller can consume less power than during normal operation. Preferably, good power efficiency is also provided during the standby mode of the driver circuitry. Another auxiliary driver can optimize its power efficiency for the power consumed by the controller during standby. During standby, the controller can, for example, remain active to receive wireless control signals.

[0030] In another example, at the dimming level where the first and second drivers power the light source, the first and second drivers operate in an interleaved operation mode.

[0031] The desired dimming level is achieved when both drivers provide power at their optimized power efficiency, with the drivers operating in an interleaved mode. The controller can manage the two drivers such that they operate with a relative phase delay. When using two drivers, the phase delay is preferably 180 degrees, or when using any number of n drivers, the phase delay is preferably 360° / n. This results in ripple in the output current with double the frequency but with reduced peak-to-peak amplitude.

[0032] In another example, the controller is arranged to control the first driver to operate at a 100% duty cycle and to control the second driver to operate at a duty cycle between 0% and 100% based on a dimming level indicating that the required power of the light source exceeds the rated power of the first driver.

[0033] When the dimming level involves a desired power of the light source that exceeds the rated power of the first driver, the controller can adjust the first driver to provide its maximum rated power and additionally adjust the second driver to provide additional power, so that the desired power level is provided to the light source.

[0034] In another example, the controller is arranged to enable the first driver and the second driver by providing control signals to the first driver and the second driver, and wherein the controller is arranged to disable the first driver and the second driver by not providing control signals to the first driver and the second driver.

[0035] Controller C can, for example, provide enable or disable signals to each driver to control the enabling and disabling of the drivers.

[0036] In another example, a lighting device is provided. The lighting device includes:

[0037] - The driver circuit according to any of the foregoing examples; and

[0038] - Light source.

[0039] In another example, the controller is arranged to control the first and second drivers based on the dimming level, such that the effectiveness of the lighting device increases when the dimming level is reduced.

[0040] Preferably, the efficiency of the lighting device increases as dimming occurs. This can be achieved by turning off one driver when the dimming level is, for example, at a level where only one driver is needed to power the light source. The light source is configured to receive current only from the first driver, while the second driver does not provide current. This means that the current supplied to the light source is smaller, resulting in a reduced current density in the light source. The light source has improved efficiency at the reduced current density, thus improving the efficiency of the lighting device.

[0041] In another example, the light source is a semiconductor light source, preferably an LED load, and more preferably in the form of a filament.

[0042] Preferably, the light source is a semiconductor light source. Examples of semiconductor loads are LEDs, laser diodes, and vertical-cavity surface-emitting lasers (VCSELs). Preferably, the LED is formed as a filament. Attached Figure Description

[0043] Examples of the invention will now be described with reference to the accompanying drawings, in which:

[0044] Figure 1 An example of a circuit diagram is shown.

[0045] Figure 2 Another example of a circuit diagram is shown.

[0046] Figure 3 Another example of a circuit diagram is shown.

[0047] Figure 4 Another example of a circuit diagram is shown.

[0048] Figure 5 Another example of a circuit diagram is shown.

[0049] Figure 6 Another example of a circuit diagram is shown.

[0050] Figure 7 Another example of a circuit diagram is shown. Detailed Implementation

[0051] The invention will be described with reference to the accompanying drawings.

[0052] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatuses, systems, and methods, are for illustrative purposes only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatuses, systems, and methods of the present invention will become more readily apparent from the following description, the appended claims, and the accompanying drawings. It should also be understood that the drawings are merely schematic and not drawn to scale. Furthermore, it should be understood that the same reference numerals are used throughout the drawings to denote the same or similar parts.

[0053] Figure 1 An example circuit diagram of a lighting device with a driver circuit that provides output power to a light source LED is shown. The driver circuit can be coupled to mains power via a rectifier circuit with four diodes D10, D11, D12, and D13. The rectifier circuit provides rectified mains voltage. In the provided example, a first driver D1 and a second driver D2 receive the rectified mains voltage. A controller C is used to control the first driver D1 and the second driver D2. The controller C can receive a dimming signal Dim. The dimming signal Dim can be provided by a dimmer or an external device that provides a dimming command. Examples of devices that can provide a dimming signal are phase-cut dimmers, 0-10V dimmers, DALI dimmers, DMX dimmers, or wireless remote devices for providing dimming signals. The first driver D1 and the second driver D2 are arranged to power the same load, which in this example is a light source LED.

[0054] The light source LED has a first input terminal, to which the output terminals of a first driver D1 and a second driver D2 are coupled. Preferably, the light source LED is an LED light source. The LED light source can be a series-coupled LED string, preferably forming a filament. Other devices or combinations of devices can also be series-coupled, such as laser diodes or VCSELs. For clarity, these examples illustrate LEDs as light sources. Preferably, the size of the LED string cannot be changed. This means that the LED string has only one input terminal for receiving current and one return terminal for returning current. Therefore, the forward voltage is not changed by, for example, a shunt switch that shunts a portion of the LED string. Thus, the power consumed by the light source LED is regulated by the driver powering the light source LED, rather than by changing the size of the light source LED. The light source LED can have two parallel LED strings, preferably with approximately the same forward voltage. More details about this topology will be provided in further examples.

[0055] Controller C receives a dimming signal and uses it to provide a first control signal for a first driver D1 and a second control signal for a second driver D2. Preferably, controller C associates the dimming level with the corresponding power level of the light source LED. Controller C can control the first driver D1 and the second driver D2 by providing the first control signal to the first driver D1 and the second control signal to the second driver D2. The first control signal can be used to enable and disable the first driver D1. Controller C can also provide the second control signal to the second driver D2. The second control signal can be used to enable and disable the second driver D2. By enabling and disabling the first driver D1 and the second driver D2 in a controllable manner, the power of the light source LED can be adjusted. Preferably, pulse width modulation (PWM) technology is used to control the drivers. This means that the drivers are enabled and disabled at a frequency with a dedicated on-time (also known as duty cycle). Preferably, the frequency at which the PWM is generated is high enough that it does not affect the quality of the light, i.e., cause light flicker. The PWM frequency can be on the order of at least 100 Hz, preferably greater than 1 kHz, and more preferably greater than 2 kHz. Preferably, when the drivers power the light source, i.e., when the drivers are enabled, they power the light source at their optimal current level. This means that the current amplitude supplied to the light source remains unchanged. The average current to the light source is then reduced by decreasing the duty cycle (i.e., the on-time of the driver). Operating at the optimal current amplitude allows the drivers to operate at their maximum efficiency. The drivers have an optimal operating point specifically designed for them. This dedicated design results in the driver supplying power to the LED light source at the current amplitude with its highest efficiency. Operating at this optimal current amplitude can also be referred to as operating at the driver's optimal power conversion efficiency.

[0056] For example, the driver circuit provides a total power of 10W to the LED light source. In this example, two drivers are used to power the LED light source. For example, both drivers are arranged to provide the same maximum power to the light source. This means that the first driver D1 is arranged to provide a maximum power of 5W to the LED light source, and the second driver D2 is arranged to provide a maximum power of 5W to the LED light source. Controller C receives a dimming signal. As an example, controller C can determine that within the dimming range between 0% and 50%, only the first driver D1 is arranged to provide power to the LED light source. The second driver D2 can be disabled, so that the second driver D2 does not provide power to the LED light source.

[0057] At a dimming level of 0%, preferably, the first driver D1 is arranged not to supply power to the light source LED.

[0058] At dimming levels between 1% and 50%, controller C can provide a first control signal to first driver D1. For example, the first control signal provides first driver D1 with a duty cycle corresponding to the dimming level. For instance, at a dimming level of 25%, first driver D1 can receive a 50% duty cycle. This means that first driver D1 supplies power to the LED light source for 50% of the time, resulting in a power supply of 2.5W to the LED. At a dimming level of 50%, first driver D1 can receive a 100% duty cycle. This means that first driver D1 supplies power to the LED light source for 100% of the time, resulting in a power supply of 5W to the LED.

[0059] At dimming levels between 51% and 100%, the second driver D2 can be controlled to contribute power to the LED light source adjacent to the first driver D1. Within this dimming range, the first driver D1 can be controlled to provide power with a 100% duty cycle. For example, at a 75% dimming level, the first driver D1 can be arranged to provide power with a 100% duty cycle, thus providing 5W, while the second driver D2 is arranged to provide power with a 50% duty cycle, thus providing 2.5W. The total power supplied to the LED light source is 7.5W. At a 100% dimming level, the first driver D1 can be arranged to provide power with a 100% duty cycle, thus providing 5W, while the second driver D2 is arranged to provide power with a 100% duty cycle, thus providing 5W. The total power supplied to the LED light source is 10W.

[0060] Alternatively, the first driver D1 and the second driver D2 can be configured to simultaneously provide power within the dimming range at an adjusted duty cycle. For example, at a 25% dimming level, both the first driver D1 and the second driver D2 can be controlled to operate with a 25% duty cycle. This allows both the first driver D1 and the second driver D2 to supply 1.25W to the LED, resulting in a total power supply of 2.5W to the LED. At a 50% dimming level, both the first driver D1 and the second driver D2 can be controlled to operate with a 50% duty cycle. This allows both the first driver D1 and the second driver D2 to supply 2.5W to the LED, resulting in a total power supply of 5W to the LED. At a 100% dimming level, both the first driver D1 and the second driver D2 can be controlled to operate with a 100% duty cycle. This allows both the first driver D1 and the second driver D2 to supply 5W to the LED, resulting in a total power supply of 10W to the LED. For simplicity, the duty cycle for operating the first driver D1 and the second driver D2 is chosen to be the same. Other combinations are also possible to achieve the desired power to the light source at a dedicated dimming level.

[0061] Another example could be that the first driver D1 and the second driver D2 provide different amounts of maximum power to the LED light source. For example, the total power supplied to the LED light source by the driver circuit is 10W. The first driver D1 can be designed to provide a maximum power of 4W, while the second driver D2 is designed to provide a maximum power of 6W. As an example, the controller C can determine that within a dimming range between 0% and 40%, only the first driver D1 is arranged to provide power to the LED light source. The second driver D2 can be disabled, so that the second driver D2 does not provide power. At a dimming level of 0%, preferably, the first driver D1 is arranged not to provide power to the LED light source. At dimming levels between 1% and 40%, the controller C can provide a first control signal to the first driver D1. For example, the first control signal provides the first driver D1 with a duty cycle corresponding to the dimming level. For example, at a dimming level of 20%, the first driver D1 can receive a 50% duty cycle. This means that the first driver D1 provides power to the LED light source for 50% of the time, resulting in a power supply of 2W to the LED light source. At a 40% dimming level, the first driver D1 can receive a 100% duty cycle. This means that the first driver D1 supplies power to the LED light source for 100% of the time, resulting in a 4W supply to the LED light source. At dimming levels between 41% and 100%, the second driver D2 can be controlled to contribute power to the LED light source adjacent to the first driver D1. Within this dimming range, the first driver D1 can be controlled to provide power with a 100% duty cycle. For example, at a 70% dimming level, the first driver D1 can be arranged to provide power with a 100% duty cycle, thus providing 4W, while the second driver D2 is arranged to provide power with a 50% duty cycle, thus providing 3W. The total power supplied to the LED light source is 7W. At a 100% dimming level, both the first driver D1 and the second driver D2 can be controlled to operate with a 100% duty cycle. This allows the first driver D1 to supply 4W to the light source LED and allows the second driver D2 to supply 6W to the light source LED, resulting in a total power supply of 10W to the light source LED.

[0062] Alternatively, the first driver D1 and the second driver D2 can be configured to simultaneously provide power within the dimming range at an adjusted duty cycle. For example, at a 25% dimming level, both the first driver D1 and the second driver D2 can be controlled to operate with a 25% duty cycle. This allows the first driver D1 to supply 1W to the LED and the second driver D2 to supply 1.5W, resulting in a total power supply of 2.5W to the LED. At a 50% dimming level, both the first driver D1 and the second driver D2 can be controlled to operate with a 50% duty cycle. This allows the first driver D1 to supply 2W to the LED and the second driver D2 to supply 3W, resulting in a total power supply of 5W to the LED. At a 100% dimming level, both the first driver D1 and the second driver D2 can be controlled to operate with a 100% duty cycle. This allows the first driver D1 to supply 4W to the LED and the second driver D2 to supply 6W, resulting in a total power supply of 10W to the LED. For simplicity, the duty cycles of the first driver D1 and the second driver D2 are chosen to be the same. Other combinations are also possible to achieve the desired power to the light source at a dedicated dimming level.

[0063] When two drivers provide power simultaneously, as described in this example, power losses are distributed between the two drivers, allowing for better heat distribution on the driver circuitry.

[0064] Figure 2 It shows Figure 1An example of a detailed circuit diagram of the circuit shown. In the provided example, rectifier circuits D10, D11, D12, and D13 are provided. The rectifier circuits provide a rectified voltage, which is supplied to the first driver D1 and the second driver D2. The first driver D1 and the second driver D2 are designed as a boost converter. The first driver D1 and the second driver D2 are coupled in parallel at their inputs and provide parallel power to the light source LED. The first driver D1 has a first inductor L1, a first switching element M1, and a first diode D5. The second driver D2 has a second inductor L2, a second switching element M2, and a second diode D6. The first diode D5 and the second diode D6 provide two functions. The diodes form freewheeling diodes for the boost converter topology, and they allow the outputs of the first driver D1 and the second driver D2 to be coupled together. In the case of another topology besides a boost converter (e.g., a buck converter), each driver may require an additional diode to allow the driver to be coupled at its output. Controller C provides control signals to the first driver D1 and the second driver D2. In this example, control signals can be directly provided at the gates of the first switching element M1 and the second switching element M2, respectively. Therefore, the controller C determines the power that can be delivered to the light source LED. Preferably, the controller C controls the driver such that the power supplied to the light source LED according to the dimming level corresponds to the power required by the light source LED. The controller C can control the first switching element M1 and the second switching element M2 with a relatively high-frequency PWM signal, for example, 200 kHz or higher. This high-frequency PWM signal is used for the boost converter to operate appropriately and to provide a regulated current amplitude to the light source LED. In addition to this high-frequency PWM signal, a low-frequency signal can be superimposed on the gates of the respective switching elements. This low-frequency PWM signal can be provided based on the enabling or disabling of the respective switching elements. When the driver is to be disabled, the corresponding switching element remains off. Therefore, during the low-frequency off-time, no power will be provided during the off-time of the switching elements. The low-frequency PWM signal can have a frequency preferably around 2 kHz. This prevents any perceived visible effects in the light output. In this example, the enabling and disabling of the driver is achieved through direct interaction between the controller C and the first switching element M1 and the second switching element M2.

[0065] Figure 3An example circuit diagram of a lighting device with a driver circuit that provides output power to a light source LED is shown. The driver circuit can be coupled to mains power via a rectifier circuit with four diodes D10, D11, D12, and D13. The rectifier circuit provides rectified mains voltage. In the provided example, the first driver D1, the second driver D2, and the third driver D3 receive the rectified mains voltage. A controller C is used to control the first driver D1 and the second driver D2. The controller C can receive a dimming signal Dim. The dimming signal Dim can be provided by a dimmer or an external device that provides a dimming command. Examples of devices that can provide a dimming signal are phase-cut dimmers, 0-10V dimmers, DALI dimmers, DMX dimmers, or wireless remote devices for providing dimming signals. The first driver D1 and the second driver D2 are arranged to power the same load, which in this example is a light source LED.

[0066] The light source LED has a first input terminal, to which the output terminals of a first driver D1, a second driver D2, and a third driver D3 are coupled. Preferably, the light source LED is an LED light source. The LED light source can be a series-coupled LED string, preferably forming a filament. Other devices or combinations of devices can also be series-coupled, such as laser diodes or VCSELs. For clarity, these examples show an LED as a light source. Preferably, the size of the LED string cannot be changed. This means that the LED string has only one input terminal for receiving current and one return terminal for returning current. Therefore, the forward voltage is not changed by, for example, a shunt switch that shunts a portion of the LED string. Thus, the power consumed by the light source LED is regulated by the driver that powers the light source LED, rather than by changing the size of the light source LED. The light source LED can have two LED strings connected in parallel, preferably with approximately the same forward voltage. More details about this topology will be provided in further examples.

[0067] Controller C receives a dimming signal and uses it to provide control signals to the first driver D1, the second driver D2, and the third driver D3. Preferably, controller C associates the dimming level with the corresponding power level of the light source LED. Controller C can control the first driver D1, the second driver D2, and the third driver D3 by providing a first control signal to the first driver D1, a second control signal to the second driver D2, and a third control signal to the third driver D3. The first control signal can be used to enable and disable the first driver D1. Controller C can also provide a second control signal to the second driver D2. The second control signal can be used to enable and disable the second driver D2. The third control signal can be used to enable and disable the third driver D3. By enabling and disabling the first driver D1, the second driver D2, and the third driver D3 in a controllable manner, the power of the light source LED can be adjusted. Preferably, pulse width modulation (PWM) technology is used to control the drivers. This means that the drivers are enabled and disabled at a frequency with a dedicated on-time (also known as a duty cycle). Preferably, the frequency at which the PWM is generated is high enough that it does not affect the quality of the light, i.e., cause light flicker. The PWM frequency can be on the order of at least 100Hz, preferably greater than 1kHz, and more preferably greater than 2kHz. Preferably, when the drivers power the light source, i.e., when the drivers are enabled, they power the light source at their optimal current level. This means that the current amplitude supplied to the light source does not change. The average current to the light source is then reduced by decreasing the duty cycle (i.e., the on-time of the driver). Operating at the optimal current amplitude allows the drivers to operate at their maximum efficiency. The drivers have an optimal operating point specific to the driver design. The specific design results in the driver supplying power to the LED light source at the current amplitude with its highest efficiency. Operating at this optimal current amplitude can also be referred to as operating at the driver's optimal power conversion efficiency.

[0068] For example, the total power supplied to the LED light source by the driver circuit is 12W. In this example, three drivers are used to power the LED light source. For example, all three drivers are arranged to provide the same maximum power to the light source. This means that the first driver D1 is arranged to provide a maximum power of 4W to the LED light source, the second driver D2 is arranged to provide a maximum power of 4W to the LED light source, and the third driver D3 is arranged to provide a maximum power of 4W to the LED light source. Controller C receives a dimming signal. For example, controller C can determine that within the dimming range between 0% and 33.33%, only the first driver D1 is arranged to provide power to the LED light source. The second driver D2 and the third driver D3 can be disabled, so that the second driver D2 and the third driver D3 do not provide power to the LED light source.

[0069] At a dimming level of 0%, preferably, the first driver D1 is arranged not to supply power to the light source LED.

[0070] At dimming levels between 1% and 33.33%, controller C can provide a first control signal to first driver D1. For example, the first control signal provides first driver D1 with a duty cycle corresponding to the dimming level. For instance, at a dimming level of 11.11%, first driver D1 can receive a 33.33% duty cycle. This means that first driver D1 supplies power to the LED light source for 33.33% of the time, resulting in 1.33W being supplied to the LED light source.

[0071] At a dimming level of 33.33%, the first driver D1 can receive 100% duty cycle. This means that the first driver D1 supplies power to the LED light source for 100% of the time, resulting in a power supply of 4W to the LED light source. Between dimming levels of 33.34% and 66.66%, the second driver D2 can be controlled to contribute power to the LED light source adjacent to the first driver D1. Within this dimming range, the first driver D1 can be controlled to provide power with a 100% duty cycle. For example, at a dimming level of 44.44%, the first driver D1 can be arranged to provide power with a 100% duty cycle, thus providing 4W, while the second driver D2 is arranged to provide power with a 33.33% duty cycle, thus providing 1.33W. The total power supplied to the LED light source is 5.33W. At a dimming level of 66.66%, both the first driver D1 and the second driver D2 can receive 100% duty cycle. This means that the first driver D1 and the second driver D2 supply power to the LED light source 100% of the time, resulting in an 8W supply to the LED light source.

[0072] At dimming levels between 66.67% and 100%, the third driver D3 can be controlled to contribute power to the LEDs adjacent to the first and second drivers D1 and D2. Within this dimming range, the first and second drivers D1 and D2 can be controlled to provide power with a 100% duty cycle. For example, at a dimming level of 77.77%, the first and second drivers D1 and D2 can be arranged to provide power with a 100% duty cycle, thus providing 8W, while the third driver D3 is arranged to provide power with a 33.33% duty cycle, thus providing 1.33W. The total power supplied to the LEDs is 9.33W. At a 100% dimming level, the first, second, and third drivers D3 can receive a 100% duty cycle. This means that the first, second, and third drivers D1 and D2 supply power to the LEDs for 100% of the time, resulting in 12W being supplied to the LEDs.

[0073] Another example could be that the first driver D1, the second driver D2, and the third driver D3 provide different amounts of maximum power to the light source. For instance, the total power supplied to the LED light source by the driver circuit is 18W. The first driver D1 could be designed to provide a maximum power of 3W, the second driver D2 could be designed to provide a maximum power of 6W, and the third driver D3 could be designed to provide a maximum power of 9W. For example, the controller C could determine that within a dimming range between 0% and 16.67%, only the first driver D1 is arranged to provide power to the LED light source. The second driver D2 and the third driver D3 can be disabled, so that they do not provide power.

[0074] At a dimming level of 0%, preferably, the first driver D1 is arranged not to supply power to the light source LED.

[0075] At dimming levels between 1% and 16.67%, controller C can provide a first control signal to first driver D1. For example, the first control signal provides first driver D1 with a duty cycle corresponding to the dimming level. For instance, at a dimming level of 8.33%, first driver D1 can receive a 50% duty cycle. This means that first driver D1 supplies power to the LED light source for 50% of the time, resulting in a power supply of 1.5W to the LED. At a dimming level of 16.67%, first driver D1 can receive a 100% duty cycle. This means that first driver D1 supplies power to the LED light source for 100% of the time, resulting in a power supply of 3W to the LED.

[0076] At dimming levels between 16.68% and 50%, the second driver D2 can be controlled to contribute power to the LED light source adjacent to the first driver D1. Within this dimming range, the first driver D1 can be controlled to provide power with a 100% duty cycle. For example, at a dimming level of 33.33%, the first driver D1 can be arranged to provide power with a 100% duty cycle, thus providing 3W, while the second driver D2 is arranged to provide power with a 50% duty cycle, also providing 3W. The total power supplied to the LED light source is 6W. At a dimming level of 50%, both the first driver D1 and the second driver D2 can be controlled to operate with a 100% duty cycle. This allows the first driver D1 to provide 3W to the LED light source and allows the second driver D2 to provide 6W, resulting in a total power supply of 9W to the LED light source.

[0077] At dimming levels between 50.1% and 100%, the third driver D3 can be controlled to supply power to the LEDs adjacent to the first and second drivers D1 and D2. Within this dimming range, the first and second drivers D1 and D2 can be controlled to supply power at a 100% duty cycle. As an example, at a dimming level of 75%, the first and second drivers D1 and D2 can be arranged to supply power at a 100% duty cycle, thus supplying a total of 9W to the LEDs, and the third driver D3 is then arranged to supply power at a 50% duty cycle, thus supplying 4.5W. The total power supplied to the LEDs is 13.5W.

[0078] At 100% dimming level, the first driver D1, the second driver D2, and the third driver D3 can be controlled to operate with a 100% duty cycle. This allows the first driver D1 to supply 3W to the LED, the second driver D2 to supply 6W, and the third driver to supply 9W, resulting in a total power supply of 18W to the LED.

[0079] Alternatively, the first driver D1, the second driver D2, and the third driver D3 can be configured to simultaneously provide power within the dimming range at an adjusted duty cycle. For example, at a 25% dimming level, the first driver D1, the second driver D2, and the third driver D3 can be controlled to operate with a 25% duty cycle. This allows the first driver D1, the second driver D2, and the third driver D3 to supply 1W to the LED, resulting in a total power supply of 3W to the LED. At a 50% dimming level, the first driver D1, the second driver D2, and the third driver D3 can be controlled to operate with a 50% duty cycle. This allows the first driver D1, the second driver D2, and the third driver D3 to supply 2W to the LED, resulting in a total power supply of 6W to the LED. At a 100% dimming level, the first driver D1, the second driver D2, and the third driver D3 can be controlled to operate with a 100% duty cycle. This allows the first driver D1 and the second driver D2 to supply 5W to the LED, resulting in a total power supply of 10W to the LED. For simplicity, the duty cycles of the first driver D1 and the second driver D2 are chosen to be the same. Other combinations are also possible to achieve the desired power to the light source at a dedicated dimming level.

[0080] When two drivers provide power simultaneously, as described in this example, power losses are distributed between the drivers, allowing for better heat distribution across the driver circuitry.

[0081] Figure 4An example circuit diagram of a lighting fixture with a driver circuit that provides output power to an LED light source is shown. The lighting fixture can be designed based on any of the designs provided in any of the foregoing examples. Two or more drivers may be provided. Using a PWM signal to enable and disable the drivers can cause interference with the current drawn from the input (e.g., AC mains power). Especially with variations in the number of active drivers, the input current may vary, causing the current waveform to potentially not meet power factor requirements.

[0082] A series configuration of buffer capacitor C1 and switch J1 can be provided at the outputs of rectifier circuits D10, D11, D12, and D13. The switch is shown as a simple controllable switching element, but additional circuitry can be provided to perform the desired function, namely, controlling the current flow through buffer capacitor C1. This means that a switching device with one or more switching elements and a control circuit system can be used instead of the switch. Switch J1 can be controlled by controller C. Switch J1 is used to regulate the current through buffer capacitor C1. This allows buffer capacitor C1 to charge and discharge in a controlled manner. Buffer capacitor C1 can be used to draw current from the mains when any driver is not drawing current or is not drawing enough current. This allows the current from the mains to be smoothed. Preferably, controller C controls switch J1 and the driver such that the driver circuitry provides power factor correction. This means that the current drawn from the mains follows the voltage waveform. The mains voltage can be, for example, a sine wave with a frequency of 50Hz or 60Hz. The current waveform then follows the voltage waveform in phase. This can also be achieved by placing a common-input PFC (Power Factor Correction) stage between the rectifier and drivers D1 and D2. The common-input PFC stage draws a sinusoidal current from the mains, and the buffer capacitor placed at the output of the PFC stage acts as a buffer for the pulsating current drawn by drivers D1 and D2.

[0083] Figure 5A circuit diagram of a lighting device with an improved LED light source, shown as another simple example, is illustrated. This LED light source can operate with the driver circuit provided in the example. The LED light source receives power from the driver circuit. The LED light source has a first LED load LED1 and a second LED load LED2. The first LED load LED1 and the second LED load LED2 are coupled in parallel. Preferably, the forward voltage of the first LED load LED1 is higher than the forward voltage of the second LED load LED2. A resistor R1 is placed in series with the second LED load LED2. The driver circuit provided in the example provides a current that can vary based on the amount of power supplied to the light source. At relatively low currents, all current will flow through the second LED load LED2 and the resistor R1. The sum of the forward voltage of the second LED load LED2 and the voltage drop across the resistor R1 is lower than the forward voltage of the first LED load LED1. If the current increases, the forward voltage of the second LED load LED2 will increase only slightly, but the voltage across the resistor R1 will drop more significantly. Further increasing the current to the light source LED will cause the sum of the forward voltage of the second LED load LED2 and the voltage drop across resistor R1 to increase until this sum reaches or exceeds the forward voltage of the first LED load LED1. Under this increased current, the first LED load LED1 will also begin to conduct. Therefore, increasing or decreasing the current to the light source allows for a simple distribution of the current through the first LED load LED1 and the second LED load LED2. Preferably, the first LED load LED1 is a cool white LED load, and the second LED load LED2 is a warm white LED load. At low currents, primarily the warm white LEDs are active, while with increased currents, the cool white LEDs also become active. This allows for a very simple mimicking of a dimmable incandescent filament or halogen lamp.

[0084] Figure 6A circuit diagram of a lighting device with a simpler example of an improved light source LED is shown, which can work with the driver circuit provided in the example. The light source LED receives power from the driver circuit. The light source LED has a first LED load LED1 and a second LED load LED2. The first LED load LED1 and the second LED load LED2 are coupled in parallel. Preferably, the forward voltage of the first LED load LED1 is lower than the forward voltage of the second LED load LED2. Preferably, the first LED load LED1 and the second LED load LED2 are configured as filaments. The first LED load LED1 and the second LED load LED2 are shown as single LEDs, but more LEDs can be coupled in series to form an LED string or filament. A first series switch M10 is arranged in series with the first LED load LED1. A control circuit 1 is arranged to control the first series switch M10. The control circuit is arranged to sense parameters of the voltage or current supplied by the driver circuit. Examples of parameters may be the frequency, duty cycle, or amplitude of the voltage or current. The control circuit 1 uses these parameters to determine how to control the first series switch M10. For example, frequency modulation of the voltage or current supplied by the driver circuit can provide information for the control circuit 1 to control the first series switch M10. For example, frequency modulation can provide control circuit 1 with an indication to close the first series switch M10, while no modulation can provide control circuit 1 with an indication to open the first series switch M10. When the first series switch M10 is open, the current supplied by the driver circuit can only flow through the second LED load LED2. When the first series switch M10 is open, the current supplied by the driver circuit can flow through the first LED load LED1. When the forward voltage of the first LED load LED1 is approximately equal to the forward voltage of the second LED load LED2, closing the first series switch M10 will allow current to flow through both the first LED load LED1 and the second LED load LED2. If the forward voltage of the first LED load LED1 is lower than the forward voltage of the second LED load LED2, the current will only flow through the first LED load LED1. As another example, similar control can be provided by changing the amplitude of the voltage or current supplied by the driver circuit. Changes in voltage can alter the control of the first series switch M10. The advantage of controlling the LED configuration according to the example above is that power and data can be sent from the driver circuit to the light source using only two wires. This is particularly beneficial when the LED is designed as a filament in a light bulb, such as a reconfigurable bulb with a screw or bayonet base. In this case, the number of wires that can be provided by the rod may be limited. The dimming technique provided in the example allows for easy dimming of the filament, while the control circuit 1 allows for the distribution of the supplied power between the filaments. Preferably, the first LED load LED1 and the second LED load LED2 have different colors or color temperatures from each other.Preferably, the first LED load LED1 has a warm color temperature, and the second LED load LED2 has a cool color temperature. Therefore, this parameter can be used to allow the control circuit 1 to adjust the color or color temperature emitted by the light source LEDs. The opening and closing of the first series switch M10 can be a time-continuous process, wherein the first series switch M10 opens or closes with a duty cycle controlled, for example, by PWM. Preferably, this switching process is performed at a frequency higher than 100Hz, more preferably higher than 2kHz. Alternatively, to provide simple control of the control circuit 1, the opening and closing of the first series switch M10 can be a single event, such as when the lighting device is started. During operation, the open or closed state of the first series switch M10 can be changed by different commands, such as commands for changing the color or color temperature.

[0085] Figure 7An example circuit diagram is shown, in which an improved light source LED is provided, which can work with the driver circuit provided in the example. The light source LED receives power from the driver circuit. The light source LED has a first LED load LED1 and a second LED load LED2. The first LED load LED1 and the second LED load LED2 are coupled in parallel. Preferably, the first LED load LED1 and the second LED load LED2 have approximately the same forward voltage. Preferably, the first LED load LED1 and the second LED load LED2 are configured as filaments. The first LED load LED1 and the second LED load LED2 are shown as single LEDs, but more LEDs can be coupled in series to form an LED string or filament. A first series switch M10 is configured in series with the first LED load LED1. A second series switch M11 is configured in series with the second LED load LED2. A control circuit 1 is arranged to control the first series switch M10 and the second series switch M11. The control circuit is arranged to sense parameters of the voltage or current supplied by the driver circuit. Examples of parameters may be the frequency, duty cycle, or amplitude of the voltage or current. The control circuit 1 uses these parameters to determine how to control the first series switch M10 and the second series switch M11. For example, frequency modulation of the voltage or current supplied by the driver circuit can provide information to control circuit 1 to determine which series switch to control. For instance, 1 kHz frequency modulation can instruct control circuit 1 to close the first series switch M10 and open the second series switch M11, 2 kHz modulation can open the first series switch M10 and close the second series switch M11, and 3 kHz modulation can close both the first and second series switches. As another example, similar control can be provided by changing the amplitude of the voltage or current supplied by the driver circuit. Changes in voltage or current can alter the control of the first and second series switches M10 and M11. An advantage of controlling the LED configuration according to the above example is that power and data can be transmitted from the driver circuit to the light source using only two wires. This is particularly beneficial when the LED is designed as a filament in a bulb, such as a modifiable bulb with, for example, a screw or bayonet base. In this case, the number of wires that can be supplied via a rod may be limited.

[0086] The dimming technique provided in the example allows for easy dimming of the filaments, while control circuit 1 allows for the distribution of the supplied power among the filaments. Preferably, the first LED load LED1 and the second LED load LED2 have different colors or color temperatures from each other. Preferably, the first LED load LED1 has a warm color temperature, and the second LED load LED2 has a cool color temperature. Therefore, this parameter can be used to allow control circuit 1 to adjust the color or color temperature emitted by the light source LEDs. The opening and closing of the first series switch M10 and the second series switch M11 can be a time-continuous process, wherein either the first series switch M10 is closed or the second series switch M11 is closed, and each switch has its own duty cycle, such as PWM control. Preferably, the switching process is performed at a frequency higher than 100 Hz, more preferably higher than 2 kHz. Alternatively, to provide simple control of control circuit 1, the opening and closing of the first series switch M10 and the second series switch M11 can be a single event, such as when the lighting device is started. During operation, the open or closed state of the first series switch M10 and the second series switch M11 can be changed by different commands, such as commands for changing the color or color temperature.

[0087] In the provided example, the controller C and additional peripheral electrical components can also be powered using a dedicated power supply. An auxiliary power supply can be provided to power the controller C. Preferably, the auxiliary power supply is electrically isolated from the LED light source. Therefore, the auxiliary power supply is a dedicated power supply for the controller C. Since the auxiliary power supply cannot provide power to the LED light source, it can be optimized for powering the controller C.

[0088] During the standby mode of the lighting fixture, no power is supplied to the LED light source, thus the driver can be turned off. However, the controller C can be required to operate in standby mode to, for example, receive control commands to activate the lighting fixture. The controller C thus requires less power than during the operating mode of the lighting fixture. An additional auxiliary power supply can be provided to power the controller C and peripheral electrical components during standby. Another auxiliary device is optimized for powering the controller C in standby mode.

[0089] In the provided example, the drive can be a separate device with separate components. To improve space and component utilization, some components can be reused among the drives.

[0090] In the example provided, the dimming level is linearly related to the power required by the LED light source. Other relationships, such as logarithmic or nonlinear relationships, are also conceivable and lead to the desired effect.

[0091] In the example provided, when cycling through the dimming level, it is expected that only the duty cycle of one driver will change.

[0092] By studying the accompanying drawings, the disclosure, and the appended claims, those skilled in the art can understand and implement other variations of the disclosed embodiments in practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. The fact that certain measures are recited in mutually different dependent claims does not imply that combinations of these measures cannot be advantageously used. Any reference numerals in the claims should not be construed as limiting the scope.

Claims

1. A driver circuit for powering a light source (LED), the driver circuit comprising: - A first driver (D1) adapted to supply power to the light source (LED) and having a first output power at a first optimal power conversion efficiency; - A second driver (D2) adapted to supply power to the light source (LED) and having a second output power at a second optimal power conversion efficiency; - Controller (C), the controller being adapted to: - Generate a first control signal for enabling and disabling the first driver (D1), the first control signal having a first duty cycle, and - Generate a second control signal for enabling and disabling the second driver (D2), the second control signal having a second duty cycle. The controller (C) is adapted to receive a dimming signal and is arranged to determine a first duty cycle and a second duty cycle based on the dimming signal, such that the first driver (D1) operates at the first optimal power conversion efficiency when activated, and the second driver (D2) operates at the second optimal power conversion efficiency when activated. The first control signal and the second control signal have a frequency of at least 100 Hz.

2. The driver circuit of claim 1 further includes a third driver (D3) adapted to provide power to the light source (LED) and have a third output power at a third optimal power conversion efficiency, wherein the controller (C) is configured to enable and disable the third driver (D3) with a third duty cycle and is adapted to determine the third duty cycle based on the dimming signal such that the third driver (D3) operates at the third optimal power conversion efficiency when activated.

3. The driver circuit according to any one of the preceding claims, wherein the first driver (D1) and the second driver (D2) are arranged to have the same rated power.

4. The driver circuit according to claim 1 or 2, wherein the first driver (D1) and the second driver (D2) are arranged to have different rated power from each other.

5. The driver circuit according to any one of the preceding claims, wherein the first driver (D1) and / or the second driver (D2) are non-dimmable.

6. The driver circuit according to any one of the preceding claims further includes a capacitor (C1) and a switching element (J1), wherein the capacitor (C1) and the switching element (J1) are configured in series between a first input terminal of the first driver (D1) and a second input terminal of the first driver (D1).

7. The driver circuit of claim 6, wherein the driver circuit is arranged to receive an AC voltage, and wherein the switching element (J1) is arranged to close when the voltage across the capacitor (C1) exceeds the amplitude of the instantaneous AC voltage.

8. The driver circuit according to any one of the preceding claims further includes an auxiliary driver, the auxiliary driver being adapted to power the controller (C) and to be electrically disconnected from the light source (LED).

9. The driver circuit according to any one of the preceding claims further includes an additional auxiliary driver, wherein the additional auxiliary driver is adapted to supply power to the controller (C) when the driver circuit is in standby mode.

10. The driver circuit according to any one of the preceding claims, wherein at the dimming level where the first driver (D1) and the second driver (D2) supply power to the light source (LED), the first driver (D1) and the second driver (D2) operate in an interleaved operating mode.

11. The driver circuit according to any one of the preceding claims, wherein the controller (C) is arranged to control the first driver (D1) to operate at a 100% duty cycle according to a dimming level indicating that the required power of the light source (LED) exceeds the rated power of the first driver (D1), and to control the second driver (D2) to operate at a duty cycle between 0% and 100%.

12. The driver circuit according to any one of the preceding claims, wherein the controller (C) is arranged to enable the first driver (D1) and the second driver (D2) by providing control signals to the first driver (D1) and the second driver (D2), and wherein the controller (C) is arranged to disable the first driver (D1) and the second driver (D2) by not providing the control signals to the first driver (D1) and the second driver (D2).

13. A lighting device, comprising: - The driver circuit according to any one of the preceding claims; as well as - The light source (LED).

14. The lighting device according to claim 13, wherein the controller (C) is arranged to control the first driver (D1) and the second driver (D2) based on the dimming level, such that the efficiency of the lighting device increases when the dimming level is reduced.

15. The lighting device according to any one of claims 13 or 14, wherein the light source (LED) is a semiconductor light source.

Images