Ultra-high efficiency dimmable LED driver

Abstract

The present invention relates to a driver circuit for supplying power to a light source. The driver circuit includes a first driver adapted to supply power to the light source, having a first output power at a first optimal power conversion efficiency; a second driver adapted to supply power to the light source, having a second output power at a second optimal power conversion efficiency; and a controller for enabling and disabling the first driver in a first duty cycle and the second driver in a second duty cycle. The controller is adapted to receive a dimming signal and is configured to determine the first and second duty cycles based on the dimming signal, such that when active, the first driver operates at the first optimal power conversion efficiency and the second driver operates at the second optimal power conversion efficiency.

Description

Technical Field

[0003]

[0001] The present invention relates to a driver. The present invention further relates to a lighting device.

Background Art

[0002] For the lighting industry, the requirements for energy efficiency have become more stringent, especially with the new European Union energy labelling introduced on September 1, 2021. This new labelling follows the trend of improving the energy efficiency of lighting products. By that time, an increasing number of light sources had achieved an A+ or A++ label rating, making it impossible for customers to investigate the differences in luminous efficiency between products. With the new labelling, light sources will again become more dispersed across the labelling range. This also means that, for example, a lamp that was rated A++ under the old system is now labelled C. Therefore, it is desired to further improve the energy efficiency of light sources.

[0003] ​​​​​​​​​​​The objective of the present invention is to provide a solution that enables dimming while maintaining good overall efficiency. [Means for solving the problem]

[0005] To provide such a solution, a first embodiment of the present invention provides a driver circuit for driving a light source. The driver circuit is - A first driver adapted to supply power to the light source, the first driver having a first output power with a first optimal power conversion efficiency, - A second driver adapted to supply power to the light source, the second driver having a second output power with a second optimal power conversion efficiency, - It is a controller, - A first control signal for enabling and disabling the first driver, which generates a first control signal having a first duty cycle, - A second control signal for enabling and disabling the second driver, comprising a controller adapted to generate a second control signal having a second duty cycle, The controller is adapted to receive a dimming signal and is configured to determine the first and second duty cycles based on the dimming signal, such that when active, the first driver operates at the first optimal power conversion efficiency and the second driver operates at the second optimal power conversion efficiency, wherein the first and second control signals have a frequency of at least 100 Hz.

[0006] A first driver and a second driver are provided. Both drivers supply power to the same light source. Each driver has an output power that operates at its optimal conversion efficiency. This means that the drivers are designed to supply output power at the highest efficiency that can power the light source. The controller is used to control the first driver and the second driver. The controller generates a first control signal and a second control signal so that the controller can enable and disable the first driver and the second driver. The controller also receives a dimming signal. The dimming signal may be any type of dimming signal used in the lighting industry. Examples of dimming signals include a phase-cut dimming signal, a 0 to 10V dimming signal, a DALI dimming signal, a DMX dimming signal, or a wireless dimming signal. The controller uses the dimming signal to determine what duty cycle each of the drivers should operate on, i.e., what duty cycle each of the drivers should be enabled on. When a driver is enabled, it preferably supplies its corresponding power to the load at its optimal power conversion efficiency. This allows the driver's power to be combined with the load, while this is done in an energy-efficient manner when the driver is supplying power to the load. Controlling the duty cycle of the enabled driver allows for changing the power to the load while maintaining high overall efficiency of the driver circuit. In an example where two drivers are used and both are configured to supply similar amounts of power to the light source, the first driver may be used to supply variable power between a 0% dimming level and a 50% dimming level. In this case, the duty cycle of the first driver may vary accordingly between 0% and 100%. Preferably, after the 50% dimming level, in which the first driver operates on a 100% duty cycle, the second driver may be included in supplying power to the light source. Between the 50% dimming level and the 100% dimming level, the second driver may operate on a corresponding duty cycle between 0% and 100%.Providing the first and second control signals having a frequency of at least 100 Hz makes it possible to provide robust control of the driver without affecting the light quality.

[0007] In a further example, the driver circuit comprises a third driver adapted to supply power to the light source, the third driver having a third output power at a third optimal power conversion efficiency, and the controller is for enabling and disabling the third driver on a third duty cycle, and is adapted to determine the third duty cycle based on the dimming signal so that the third driver operates at the third optimal power conversion efficiency when active.

[0008] The third driver makes it possible to increase the total power to the light source, or to reduce the size of the drivers, as each driver may have a lower power rating.

[0009] In an example where three drivers are used and configured to supply similar amounts of power to the light source, the first driver may be used to supply variable power between a 0% dimming level and a 33.33% dimming level. In this case, the duty cycle of the first driver may vary accordingly between 0% and 100%. Preferably, after the 33.33% dimming level, in which the first driver operates on a 100% duty cycle, the second driver may be included in the power supply to the light source. Between the 33.33% dimming level and the 66.67% dimming level, the second driver may operate on a corresponding duty cycle between 0% and 100%. Preferably, after the 66.67% dimming level, in which the first and second drivers operate on a 100% duty cycle, the third driver may be included in the power supply to the light source. Between a dimming level of 66.67% and a dimming level of 100%, the third driver may operate with a corresponding duty cycle between 0% and 100%.

[0010] In a further example, the first driver and the second driver are configured to have the same rated power.

[0011] Preferably, all drivers have the same power rating for supplying power to the light source. Preferably, the first driver and the second driver supply substantially the same amount of power to the light source. This allows the drivers to be designed as the same module, which greatly simplifies the design of the driver circuit.

[0012] In a further example, the first driver and the second driver are configured to have different power ratings.

[0013] For example, in deep dimming, the dimming steps may be much more perceptible to the observer. It may be preferable to have a first driver with a lower power rating than a second driver. For example, the first driver may have a power rating of 1W and the second driver may have a power rating of 9W, resulting in a total power of 10W. This 10W may be linearly divided across the dimming range, for example, so that the power to the light source can vary between 0W and 10W across dimming levels between 0% and 100%. In the dimming range between 0% and 10%, the first driver may be used, and in the dimming range, the first driver may operate with a corresponding duty cycle between 0% and 100%. The first driver may not be able to be enabled with a duty cycle with infinite steps. Instead, the duty cycle itself has resolution. In an extremely exaggerated example, only 10 duty cycle steps may be provided. In that case, these steps are mapped across the power range that the driver can supply. In this example, a 0% duty cycle corresponds to 0W supplied to the light source, and in this case, a 100% duty cycle may correspond to 1W supplied to the light source. Each duty cycle step increases the power to the load by 100mW. In this case, the minimum power that can be supplied to the light source is 100mW. If the second driver were to be used in this dimming range, assuming a similar amount of duty cycle steps, only a minimum power of 900mW would be possible. Therefore, it is desirable to use the driver with the lowest rated power at the deepest dimming level so that the lowest minimum power can be supplied to the light source by the driver circuit.

[0014] In further examples, the first driver and / or the second driver are not dimmable.

[0015] If the driver is not dimmable, it is configured to supply a fixed amount of power. Therefore, the driver can only supply one power level that is possible within its rated power. The driver has optimal power efficiency because it is optimized in its design to supply this single amount of power with the highest possible efficiency. Therefore, the average power supplied by the driver circuit depends on the duty cycle in which each driver is enabled / active.

[0016] In a further example, the driver circuit further comprises a capacitor and a switching element, the capacitor and the switching element forming a series configuration between the first input of the first driver and the second input of the first driver.

[0017] Providing a switchable capacitor at the input of the driver makes it possible to compensate for disturbances caused by the activation and deactivation of the driver. For example, if at a particular time none of the drivers are drawing current from, for example, the AC input, the capacitor can be connected to the AC input voltage to enable the drawing of a desired current.

[0018] In a further example, the driver circuit is configured to receive an AC voltage, and the switching element is configured to close when the voltage across the capacitor exceeds the amplitude of the AC voltage.

[0019] When the capacitor is charged, if the voltage across the capacitor exceeds the AC input voltage, current from the capacitor can be supplied to the driver.

[0020] In a further example, the driver circuit includes an auxiliary driver adapted to supply power to the controller and to be electrically isolated from the light source.

[0021] The controller typically requires its own power supply. The controller has its own power requirements. Therefore, it is desirable to provide an auxiliary driver with optimized power efficiency for the power consumed by the controller. This can be done when the auxiliary driver is used only for powering the controller. Preferably, the auxiliary driver is electrically isolated from the light source so that the auxiliary driver cannot power the light source.

[0022] In a further example, the driver circuit has a further auxiliary driver, and the further auxiliary driver is adapted to power the controller when the driver circuit is in standby mode.

[0023] During standby, the controller may consume less power than during normal operation. It is preferable to provide good power efficiency also during the standby mode of the driver circuit. The further auxiliary driver can have optimized power efficiency for the power consumed by the controller during standby. During standby, the controller can still be active, for example, to receive a wireless control signal.

[0024] In a further example, at the dimming level where the first driver and the second driver supply power to the light source, the first driver and the second driver operate in an interleaved mode of operation.

[0025] At the dimming level where both drivers supply power with their optimized power efficiency, it is desirable for the drivers to operate in an interleaved mode of operation. The controller can control the two drivers so that the two drivers operate with a relative phase delay. The phase delay is preferably 180 degrees when two drivers are used, or 360° / n for any number n of drivers. This results in a ripple in the output current that has a doubled frequency but a reduced amplitude between the peaks.

[0026] In a further example, the controller is configured to control the first driver to operate at a 100% duty cycle from a dimming level representing the power required for the light source that exceeds the rated power of the first driver, and to control the second driver to operate at a duty cycle between 0% and 100%.

[0027] When the dimming level is related to the desired power to the light source that exceeds the rated power of the first driver, the controller may adjust the first driver to supply its maximum rated power so that the desired power level is supplied to the light source, and further may adjust the second driver to supply additional power.

[0028] In a further example, the controller is configured to enable the first driver and the second driver by supplying control signals to the first driver and the second driver, and the controller is configured to disable the first driver and the second driver by not supplying the control signals to the first driver and the second driver.

[0029] The controller C may supply an enabling or disabling signal to each of the drivers, for example, to control the enabling and disabling of the drivers.

[0030] In another example, a lighting device is provided. The lighting device includes - a driver circuit according to any of the previous examples, and - the light source.

[0031] In another example, the controller is configured to control the first driver and the second driver based on the dimming level such that the efficiency of the lighting device increases when the dimming level decreases.

[0032] Preferably, the efficiency of the lighting device increases when dimming. This can be done by turning off one driver when the dimming level is such that, for example, only one driver is required to power the light source. In this case, the light source is configured to receive current only from the first driver, while no current is supplied by the second driver. This means that less current is supplied to the light source, resulting in a decrease in the current density in the light source. The light source has improved efficiency at the reduced current density, and therefore the efficiency of the lighting device is increased.

[0033] In another example, the light source is a semiconductor light source, preferably an LED load, and more preferably in the form of a filament.

[0034] 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. [Brief explanation of the drawing]

[0035] Here, an example of the present invention will be described with reference to the attached drawings. [Figure 1] An example of a circuit diagram is shown. [Figure 2] Here is another example of a circuit diagram. [Figure 3] Here is another example of a circuit diagram. [Figure 4] Here is another example of a circuit diagram. [Figure 5] Here is another example of a circuit diagram. [Figure 6] Here is another example of a circuit diagram. [Figure 7] Here is another example of a circuit diagram. [Modes for carrying out the invention]

[0036] The present invention will be described with reference to the figures.

[0037] 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 understood as being intended 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. It should also be understood that the figures are for illustrative purposes only and are not drawn to scale. It should also be understood that throughout the figures, the same reference numerals are used to indicate the same or similar parts.

[0038] Figure 1 shows an example circuit diagram of a lighting device having a driver circuit that supplies output power to a light source LED. The driver circuit may be coupled to the mains power supply via a rectifier circuit having four diodes D10, D11, D12, and D13. The rectifier circuit supplies a rectified mains power voltage. In the example shown, a first driver D1 and a second driver D2 receive the rectified mains power voltage. A controller C is used to control the first driver D1 and the second driver D2. Controller C may receive a dimming signal Dim. The dimming signal Dim may be supplied by a dimmer or an external device that supplies dimming commands. Examples of devices that can supply dimming signals include phase-cut dimmers, 0-10V dimmers, DALI dimmers, DMX dimmers, or wireless remote devices for supplying dimming signals. The first driver D1 and the second driver D2 are configured to supply power to the same load, which is the light source LED in this example.

[0039] The light source LED has a first input to which the output of a first driver D1 and the output of a second driver D2 are coupled. Preferably, the light source LED is an LED light source. The LED light source may be a string of LEDs coupled in series, preferably a string of LEDs forming a filament. Other devices or combinations of devices, such as laser diodes or VCSELs, may also be coupled in series. For clarity, the example shows LEDs as the light source. Preferably, the size of the LED string cannot be changed. This means that the LED string has only one input for receiving current and one return for returning current. Therefore, the forward voltage cannot be changed, for example, by a shunt switch that shunts a portion of the LED string. In this way, the power consumed by the light source LED is not due to a change in the size of the light source LED, but is regulated by the driver supplying power to the light source LED. The light source LED may preferably have two LED strings in parallel with approximately the same forward voltage. Further details regarding this topology are shown in further examples.

[0040] Controller C receives a dimming signal and uses this dimming signal to supply a first control signal for the first driver D1 and a second control signal for the second driver D2. Preferably, Controller C associates the dimming level with the corresponding power level of the light source LED. The first driver D1 and the second driver D2 can be controlled by Controller C by supplying a first control signal to the first driver D1 and a 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 supply a 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 to the light source LED can be adjusted. Preferably, the drivers are controlled using pulse width modulation (PWM) technique. This means that the drivers are enabled and disabled at frequencies that have a dedicated on-time, also called a duty cycle. Preferably, the frequency at which the PWM is generated is high enough that it does not affect the quality of light, i.e., does not cause light flicker. The PWM frequency may be on the order of at least 100 Hz, preferably higher than 1 kHz, and more preferably higher than 2 kHz. Preferably, when the driver is supplying power to the light source, i.e., when the driver is enabled, the driver supplies power to the light source at the driver's optimal current level. This means that the current amplitude supplied to the light source does not change. In this case, the reduction in the average current to the light source is achieved by reducing the duty cycle, i.e., the driver's on time. Operating at the optimal current amplitude allows the driver to operate at its maximum efficiency. The driver has an optimal operating point, where the driver design is specifically tailored to that optimal operating point. This dedicated design results in a current amplitude at which the driver supplies power to the light source LED at the driver's highest efficiency. Operation at this optimal current amplitude can also be considered as operation at the driver's optimal power conversion efficiency.

[0041] For example, the total power supplied to the light source LED by the driver circuit is 10W. In this example, two drivers are used to supply power to the light source LED. For example, both drivers are configured to supply the same maximum power to the light source. This means that the first driver D1 is configured to supply a maximum power of 5W to the light source LED, and the second driver D2 is configured to supply a maximum power of 5W to the light source LED. Controller C receives a dimming signal. For example, controller C may decide that in the dimming range between 0% and 50%, only the first driver D1 is configured to supply power to the light source LED. The second driver D2 may be disabled so that it does not supply power to the light source LED.

[0042] At a dimming level of 0%, the first driver D1 is preferably configured not to supply power to the light source LED.

[0043] At dimming levels between 1% and 50%, controller C may supply a first control signal to the first driver D1. For example, the first control signal supplies the first driver D1 with a duty cycle corresponding to the dimming level. For instance, at a dimming level of 25%, the first driver D1 may receive a 50% duty cycle. This means that the first driver D1 will power the light source LED for 50% of the time, resulting in 2.5W being supplied to the light source LED. At a dimming level of 50%, the first driver D1 may receive a 100% duty cycle. This means that the first driver D1 will power the light source LED for 100% of the time, resulting in 5W being supplied to the light source LED.

[0044] At dimming levels between 51% and 100%, the second driver D2 may be controlled to contribute power to the light source LEDs second only to the first driver D1. In this dimming range, the first driver D1 may be controlled to supply power at a 100% duty cycle. For example, at a dimming level of 75%, the first driver D1 may be configured to supply power at a 100% duty cycle and therefore supply 5W, in which case the second driver D2 is configured to supply power at a 50% duty cycle and therefore supply 2.5W. The total power supplied to the light source LEDs is 7.5W. At a dimming level of 100%, the first driver D1 may be configured to supply power at a 100% duty cycle and therefore supply 5W, in which case the second driver D2 is configured to supply power at a 100% duty cycle and therefore supply 5W. The total power supplied to the LED light source is 10W.

[0045] In other examples, the first driver D1 and the second driver D2 may be configured to supply power simultaneously with a controlled duty cycle across the dimming range. For example, at a dimming level of 25%, both the first driver D1 and the second driver D2 may be controlled to operate on a 25% duty cycle. This allows both the first driver D1 and the second driver D2 to supply 1.25W to the light source LED, resulting in a total power of 2.5W to be supplied to the light source LED. At a dimming level of 50%, both the first driver D1 and the second driver D2 may be controlled to operate on a 50% duty cycle. This allows both the first driver D1 and the second driver D2 to supply 2.5W to the light source LED, resulting in a total power of 5W to be supplied to the light source LED. At a dimming level of 100%, both the first driver D1 and the second driver D2 may be controlled to operate on a 100% duty cycle. This allows both the first driver D1 and the second driver D2 to supply 5W to the light source LED, resulting in a total power of 10W to be supplied to the light source LED. For ease of understanding, the duty cycles for operating 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 specific dimming levels.

[0046] Another example is where a first driver D1 and a second driver D2 supply different amounts of maximum power to the light source LED. For example, the total power supplied to the light source LED by the driver circuit is 10W. The first driver D1 may be designed to supply a maximum power of 4W, and the second driver D2 may be designed to supply a maximum power of 6W. For example, the controller C may decide that in the dimming range between 0% and 40%, only the first driver D1 supplies power to the light source LED. The second driver D2 may be disabled so that it does not supply power. At a dimming level of 0%, preferably, the first driver D1 is configured not to supply power to the light source LED. At dimming levels between 1% and 40%, the controller C may supply a first control signal to the first driver D1. For example, the first control signal supplies 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 may receive a 50% duty cycle. This means that the first driver D1 supplies power to the light source LED for 50% of the time, resulting in 2W being supplied to the light source LED. At a dimming level of 40%, the first driver D1 may receive a 100% duty cycle. This means that the first driver D1 supplies power to the light source LED for 100% of the time, resulting in 4W being supplied to the light source LED. At dimming levels between 41% and 100%, the second driver D2 may be controlled to contribute power to the light source LED after the first driver D1. In this dimming range, the first driver D1 may be controlled to supply power with a 100% duty cycle. For example, at a dimming level of 70%, the first driver D1 may be configured to supply power at a 100% duty cycle and therefore supply 4W, while the second driver D2 may be configured to supply power at a 50% duty cycle and therefore supply 3W. The total power supplied to the light source LED is 7W. At a dimming level of 100%, both the first driver D1 and the second driver D2 may be controlled to operate at a 100% duty cycle.This allows the first driver D1 to supply 4W to the light source LED, and the second driver D2 to supply 6W to the light source LED, resulting in a total power of 10W to be supplied to the light source LED.

[0047] In other examples, the first driver D1 and the second driver D2 may be configured to supply power simultaneously with a controlled duty cycle across the dimming range. For example, at a dimming level of 25%, both the first driver D1 and the second driver D2 may be controlled to operate on a 25% duty cycle. This allows the first driver D1 to supply 1W to the light source LED and the second driver D2 to supply 1.5W to the light source LED, resulting in a total power of 2.5W to be supplied to the light source LED. At a dimming level of 50%, both the first driver D1 and the second driver D2 may be controlled to operate on a 50% duty cycle. This allows the first driver D1 to supply 2W to the light source LED and the second driver D2 to supply 3W to the light source LED, resulting in a total power of 5W to be supplied to the light source LED. At a dimming level of 100%, both the first driver D1 and the second driver D2 may be controlled to operate on a 100% duty cycle. This allows the first driver D1 to supply 4W to the light source LED and the second driver D2 to supply 6W to the light source LED, resulting in a total power of 10W to be supplied to the light source LED. For ease of understanding, the duty cycles for operating 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 specific dimming levels.

[0048] As described in this example, when both drivers supply power simultaneously, power loss is divided between both drivers, allowing for better heat distribution across the driver circuitry.

[0049] Figure 2 shows an example of a detailed circuit diagram of the circuit shown in Figure 1. In the example shown, rectifier circuits D10, D11, D12, and D13 are provided. The rectifier circuits supply the rectified voltage that is supplied to the first driver D1 and the second driver D2. The first driver D1 and the second driver D2 are designed as boost converters. The first driver D1 and the second driver D2 are coupled in parallel at their inputs to supply 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. These diodes form freewheeling diodes for the boost converter topology and allow the outputs of the first diode D5 and the second diode D6 to be coupled to each other. In topologies other than boost converters, such as buck converters, additional diodes may be required for each driver to enable coupling of drivers at the driver output. Controller C supplies control signals to the first driver D1 and the second driver D2. In this example, the control signals may be supplied directly to the gates of the first switching element M1 and the second switching element M2, respectively. Thus, Controller C determines the power that can be supplied to the light source LED. Preferably, Controller C controls the drivers such that the power supplied to the light source LED corresponds to the power required for the light source LED according to the dimming level. Controller C may control the first switching element M1 and the second switching element M2 using a PWM signal at a relatively high frequency, for example, 200 kHz or higher. This high-frequency PWM signal is used to ensure that the boost converter operates properly and supplies a regulated current amplitude to the light source LED. In addition to this high-frequency PWM signal, a low-frequency signal may be superimposed at the gates of each switching element. This low-frequency PWM signal may be supplied based on the activation or deactivation of each switching element.When the driver is to be disabled, the corresponding switching element is kept off. Therefore, at the moment the switching element is turned off during the low-frequency off-time, no power is supplied. The low-frequency PWM signal may preferably have a frequency around 2 kHz. This prevents any visible effects on the optical output from being perceived. In this example, the activation and deactivation of the driver are performed by the direct interaction between the controller C and the first switching element M1 and the second switching element M2.

[0050] Figure 3 shows an example of a circuit diagram for a lighting device having a driver circuit that supplies output power to a light source LED. The driver circuit may be coupled to the mains power supply via a rectifier circuit having four diodes D10, D11, D12, and D13. The rectifier circuit supplies a rectified mains power voltage. In the example shown, a first driver D1, a second driver D2, and a third driver D3 receive the rectified mains power voltage. A controller C is used to control the first driver D1 and the second driver D2. Controller C may receive a dimming signal Dim. The dimming signal Dim may be supplied by a dimmer or an external device that supplies dimming commands. Examples of devices that can supply dimming signals include phase-cut dimmers, 0-10V dimmers, DALI dimmers, DMX dimmers, or wireless remote devices for supplying dimming signals. The first driver D1 and the second driver D2 are configured to supply power to the same load, which is the light source LED in this example.

[0051] The light source LED has a first input to which the outputs of the first driver D1, the second driver D2, and the third driver D3 are coupled. Preferably, the light source LED is an LED light source. The LED light source may be a string of LEDs coupled in series, preferably a string of LEDs forming a filament. Other devices or combinations of devices, such as laser diodes or VCSELs, may also be coupled in series. For clarity, the example shows LEDs as the light source. Preferably, the size of the LED string cannot be changed. This means that the LED string has only one input for receiving current and one return for returning current. Therefore, the forward voltage cannot be changed, for example, by a shunt switch that shunts a portion of the LED string. In this way, the power consumed by the light source LED is not due to a change in the size of the light source LED, but is regulated by the driver supplying power to the light source LED. The light source LED may preferably have two LED strings in parallel with approximately the same forward voltage. Further details regarding this topology are shown in further examples.

[0052] Controller C receives a dimming signal and uses this signal to supply control signals for 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. The first driver D1, the second driver D2, and the third driver D3 can be controlled by Controller C by supplying 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 may be used to enable and disable the first driver D1. Controller C may also supply a second control signal to the second driver D2. The second control signal may be used to enable and disable the second driver D2. The third control signal may 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 to the light source LED can be adjusted. Preferably, the driver is controlled using pulse width modulation (PWM) technology. This means that the driver is enabled and disabled at a frequency that has a dedicated on-time, also called a duty cycle. Preferably, the frequency at which the PWM is generated is high enough that it does not affect the quality of light, i.e., does not cause light flickering. The PWM frequency may be on the order of at least 100 Hz, preferably higher than 1 kHz, and more preferably above 2 kHz. Preferably, when the driver is powering the light source, i.e., when the driver is enabled, the driver powers the light source at the driver's optimal current level. This means that the current amplitude supplied to the light source does not change. In this case, the reduction of the average current to the light source is achieved by reducing the duty cycle, i.e., the driver's on-time. Operating at the optimal current amplitude allows the driver to operate at its maximum efficiency. The driver has an optimal operating point, where the driver design is dedicated to that optimal operating point. This dedicated design results in a current amplitude at which the driver powers the light source LED at the driver's highest efficiency.This operation at the optimal current amplitude can also be considered as operation at the driver's optimal power conversion efficiency.

[0053] For example, the total power supplied to the light source LED by the driver circuit is 12W. In this example, three drivers are used to supply power to the light source LED. For example, all three drivers are configured to supply the same maximum power to the light source. This means that the first driver D1 is configured to supply a maximum power of 4W to the light source LED, the second driver D2 is configured to supply a maximum power of 4W to the light source LED, and the third driver D3 is configured to supply a maximum power of 4W to the light source LED. Controller C receives a dimming signal. For example, controller C may decide that in the dimming range between 0% and 33.33%, only the first driver D1 is configured to supply power to the light source LED. The second driver D2 and the third driver D3 may be disabled so that they do not supply power to the light source LED.

[0054] At a dimming level of 0%, the first driver D1 is preferably configured not to supply power to the light source LED.

[0055] At dimming levels between 1% and 33.33%, controller C may supply a first control signal to the first driver D1. For example, the first control signal supplies the first driver D1 with a duty cycle corresponding to the dimming level. For instance, at a dimming level of 11.11%, the first driver D1 may receive a duty cycle of 33.33%. This means that the first driver D1 will power the light source LED for 33.33% of the time, resulting in 1.33W being supplied to the light source LED.

[0056] At a dimming level of 33.33%, the first driver D1 can receive a 100% duty cycle. This means that the first driver D1 supplies power to the light source LED for 100% of the time, resulting in 4W being supplied to the light source LED. At dimming levels between 33.34% and 66.66%, the second driver D2 can be controlled to contribute power to the light source LED after the first driver D1. In this dimming range, the first driver D1 can be controlled to supply power with a 100% duty cycle. For example, at a dimming level of 44.44%, the first driver D1 may be configured to supply power with a 100% duty cycle and therefore supply 4W, while the second driver D2 may be configured to supply power with a 33.33% duty cycle and therefore supply 1.33W. The total power supplied to the light source LED is 5.33W. At a dimming level of 66.66%, the first driver D1 and the second driver D2 can receive a 100% duty cycle. This means that the first driver D1 and the second driver D2 will supply power to the light source LED for 100% of the time, resulting in 8W being supplied to the light source LED.

[0057] At dimming levels between 66.67% and 100%, the third driver D3 may be controlled to contribute power to the light source LEDs after the first driver D1 and the second driver D2. Within this dimming range, the first driver D1 and the second driver D2 may be controlled to supply power with a 100% duty cycle. For example, at a dimming level of 77.77%, the first driver D1 and the second driver D2 may be configured to supply power with a 100% duty cycle, and therefore supply 8W, in which case the third driver D3 may be configured to supply power with a 33.33% duty cycle, and therefore supply 1.33W. The total power supplied to the light source LEDs is 9.33W. At a dimming level of 100%, the first driver D1, the second driver D2, and the third driver D3 may all receive a 100% duty cycle. This means that the first driver D1, the second driver D2, and the third driver D3 supply power to the light source LED 100% of the time, resulting in a total power output of 12W to the light source LED.

[0058] Another example is where the first driver D1, the second driver D2, and the third driver D3 supply different amounts of maximum power to the light source. For example, the total power supplied to the light source LED by the driver circuit is 18W. The first driver D1 may be designed to supply a maximum power of 3W, the second driver D2 may be designed to supply a maximum power of 6W, and the third driver D3 may be designed to supply a maximum power of 9W. For example, the controller C may be configured to supply power to the light source LED only by the first driver D1 in the dimming range between 0% and 16.67%. The second driver D2 and the third driver D3 may be disabled so that power is not supplied by the second driver D2 and the third driver D3.

[0059] At a dimming level of 0%, the first driver D1 is preferably configured not to supply power to the light source LED.

[0060] At dimming levels between 1% and 16.67%, controller C may supply a first control signal to the first driver D1. For example, the first control signal supplies the first driver D1 with a duty cycle corresponding to the dimming level. For instance, at a dimming level of 8.33%, the first driver D1 may receive a 50% duty cycle. This means that the first driver D1 supplies power to the light source LED for 50% of the time, resulting in 1.5W being supplied to the light source LED. At a dimming level of 16.67%, the first driver D1 may receive a 100% duty cycle. This means that the first driver D1 supplies power to the light source LED for 100% of the time, resulting in 3W being supplied to the light source LED.

[0061] At dimming levels between 16.68% and 50%, the second driver D2 may be controlled to contribute power to the light source LEDs second only to the first driver D1. In this dimming range, the first driver D1 may be controlled to supply power on a 100% duty cycle. For example, at a dimming level of 33.33%, the first driver D1 may be configured to supply power on a 100% duty cycle and therefore supply 3W, while the second driver D2 may be configured to supply power on a 50% duty cycle and therefore supply 3W. The total power supplied to the light source LEDs is 6W. At a dimming level of 50%, both the first driver D1 and the second driver D2 may be controlled to operate on a 100% duty cycle. This allows the first driver D1 to supply 3W to the light source LEDs and the second driver D2 to supply 6W, resulting in a total power of 9W to be supplied to the light source LEDs.

[0062] At dimming levels between 50.1% and 100%, the third driver D3 may be controlled to contribute power to the light source LEDs after the first driver D1 and the second driver D2. Within this dimming range, the first driver D1 and the second driver D2 may be controlled to supply power with a 100% duty cycle. For example, at a dimming level of 75%, the first driver D1 and the second driver D2 may be configured to supply power with a 100% duty cycle, thus supplying a total of 9W to the light source LEDs, while the third driver D3 may be configured to supply power with a 50% duty cycle, thus supplying 4.5W. The total power supplied to the light source LEDs is 13.5W.

[0063] At a 100% dimming level, the first driver D1, the second driver D2, and the third driver D3 can be controlled to operate at a 100% duty cycle. This allows the first driver D1 to supply 3W to the light source LED, the second driver D2 to supply 6W to the light source LED, and the third driver D3 to supply 9W to the light source LED, resulting in a total power of 18W to be supplied to the light source LED.

[0064] In other examples, the first driver D1, the second driver D2, and the third driver D3 may be configured to supply power simultaneously with a controlled duty cycle across the dimming range. For example, at a dimming level of 25%, the first driver D1, the second driver D2, and the third driver D3 may 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 light source LED, resulting in a total power of 3W to be supplied to the light source LED. At a dimming level of 50%, the first driver D1, the second driver D2, and the third driver D3 may 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 light source LED, resulting in a total power of 6W to be supplied to the light source LED. At a 100% dimming level, the first driver D1, second driver D2, and third driver D3 can be controlled to operate on a 100% duty cycle. This allows both the first driver D1 and the second driver D2 to supply 5W to the light source LED, resulting in a total power of 10W to be supplied to the light source LED. For ease of understanding, the duty cycles operating 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 specific dimming levels.

[0065] When both drivers supply power simultaneously, as described in this example, power loss is divided between the drivers, allowing for better thermal distribution across the driver circuits.

[0066] Figure 4 shows an example circuit diagram of a lighting device having a driver circuit that supplies output power to a light source LED. The lighting device may be designed according to any of the designs shown in any of the previous examples. Two or more drivers may be provided. Using PWM signals to enable and disable the drivers may result in disturbances in the input, for example, the current drawn from the mains power supply. In particular, if the number of active drivers changes, the input current may change, resulting in a current waveform that may not meet power factor requirements.

[0067] A series configuration of a buffer capacitor C1 and a switch J1 may be provided at the outputs of the rectifier circuits D10, D11, D12, and D13. Although the switch is shown as a simple controllable switching element, additional circuitry may be provided to perform the required function, i.e., to control the flow of current through the buffer capacitor C1. This means that a switching device having one or more switching elements and control circuits may be used instead of the switch. Switch J1 may be controlled by a controller C. Switch J1 is used to regulate the current through the buffer capacitor C1. This allows the buffer capacitor C1 to be charged and discharged in a controlled manner. Buffer capacitor C1 may be used to draw current from the mains power supply when no current is drawn, or insufficient current is drawn, by any of the drivers. This allows for smoothing of the current from the mains power supply. Preferably, the controller C controls switch J1 and the drivers so that the driver circuits provide power factor correction. This means that the current drawn from the mains power supply follows the voltage waveform. The main power supply voltage may be a sine wave with a frequency of, for example, 50 Hz or 60 Hz. The current waveform, in this case, will follow this voltage waveform in phase. This can also be achieved by having a common input PFC (power factor correction) stage placed between the rectifier and drivers D1 and D2. The common PFC stage draws a sine wave current from the main power supply, and a buffer capacitor placed at the output of the PFC stage acts as a buffer for the pulsating current drawn by drivers D1 and D2.

[0068] Figure 5 shows a circuit diagram of a lighting device with a simpler example of an improved light source LED that can operate with a driver circuit as shown 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 has a forward voltage 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, as shown in the example, supplies a current that can vary depending on the number of drivers supplying power to the light source. At relatively low currents, all the current flows 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. As the current increases, the forward voltage of the second LED load LED2 increases only slightly, but a larger voltage drop occurs across the resistor R1. Further increases in current to the light source LED increase the sum of the forward voltage of the second LED load LED2 and the voltage drop across resistor R1 until this sum reaches or exceeds the forward voltage of the first LED load LED1. At this increased current, the first LED load LED1 also begins to conduct. Thus, increasing or decreasing the current to the light source makes it possible to achieve a simple distribution of current through the first LED load LED1 and the second LED load LED2. Preferably, the first LED load LED1 is a cold white LED load, and the second LED load LED2 is a warm white LED load. At low currents, mainly the warm white LED is active, while at increased currents, the cold white LED also becomes active. This allows for a very simple imitation of a dimmable incandescent filament lamp or halogen lamp.

[0069] Figure 6 shows a circuit diagram of a lighting device with a simpler example of an improved light source LED that can operate with a driver circuit as shown 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 has a forward voltage lower than the forward voltage of the second LED load LED2. Preferably, the first LED load LED1 and the second LED load LED2 are provided as filaments. Although the first LED load LED1 and the second LED load LED2 are shown as single LEDs, more LEDs may be coupled in series to form a string or filament of LEDs. A first series switch M10 is provided in series with the first LED load LED1. A control circuit 1 is configured to control the first series switch M10. The control circuit is configured to sense parameters of the voltage or current supplied by the driver circuit. Examples of parameters may be frequency, duty cycle, or voltage or current amplitude. The parameters are used by the control circuit 1 to determine how the first series switch M10 is controlled. For example, frequency modulation in the voltage or current supplied by the driver circuit can provide the control circuit 1 with information to control the first series switch M10. For example, frequency modulation can instruct the control circuit 1 to close the first series switch M10, while the absence of modulation can instruct the control circuit 1 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. If the forward voltage of the first LED load LED1 is approximately the same as the forward voltage of the second LED load LED2, closing the first series switch M10 allows 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, current flows only 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. The voltage change can change the control of the first series switch M10. The advantage of controlling the light source LED configuration according to the above example is that power and data can be sent from the driver circuit to the light source with only two wires, which is particularly beneficial when the light source LED is designed as a filament in a light bulb, such as a retrofit bulb with a screw base or bayonet base. In such a situation, the number of wires that can be provided through the stem may be limited. Using the dimming technique shown in the example allows for easy dimming of the filaments, while the control circuit 1 allows the supplied power to be divided 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 cold color temperature. Therefore, parameters can be used to enable 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 may be a continuous process over a duty cycle, for example, by PWM control. Preferably, this switching process is carried out at a frequency above 100 Hz, more preferably above 2 kHz. In other examples, to provide simple control of the control circuit 1, the opening and closing of the first series switch M10 may be a single event, for example, when the lighting device is started. During operation, the open / closed state of the first series switch M10 can be changed by different commands, for example, commands to change the color or color temperature.

[0070] Figure 7 shows an example of a circuit diagram that includes an improved light source LED that can operate with a driver circuit as shown 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 provided as filaments. Although the first LED load LED1 and the second LED load LED2 are shown as single LEDs, more LEDs may be coupled in series to form a string or filament of LEDs. A first series switch M10 is provided in series with the first LED load LED1. A second series switch M11 is provided in series with the second LED load LED2. A control circuit 1 is configured to control the first series switch M10 and the second series switch M11. The control circuit is configured to sense the voltage or current parameters supplied by the driver circuit. Examples of parameters may be the frequency, duty cycle, or amplitude of the voltage or current. The parameters are used by the control circuit 1 to determine how the first series switch M10 and the second series switch M11 are controlled. For example, frequency modulation of the voltage or current supplied by the driver circuit may provide the control circuit 1 with information to determine which of the series switches should be controlled. For example, frequency modulation at 1 kHz may instruct the control circuit 1 to close the first series switch M10 and open the second series switch M11, modulation at 2 kHz may cause the first series switch M10 to open and the second series switch M11 to close, and modulation at 3 kHz may cause the first series switch M10 to close and the second series switch M11 to close. As another example, similar control can be provided by changing the amplitude of the voltage or current supplied by the driver circuit. A change in voltage or current may change the control of the first series switch M10 and the second series switch M11.The advantage of controlling the LED light source configuration as described above is that power and data can be transmitted from the driver circuit to the light source with just two wires, which is particularly beneficial when the LED light source is designed as a filament in a light bulb, such as a retrofit bulb with a screw-in or plug-in base. In such situations, the number of wires that can be provided through the stem may be limited.

[0071] The dimming technique shown in the example allows for easy dimming of the filaments, while the control circuit 1 allows the supplied power to be divided between the filaments. Preferably, the first LED load LED1 and the second LED load LED2 have different colors or color temperatures. Preferably, the first LED load LED1 has a warm color temperature, and the second LED load LED2 has a cool color temperature. Therefore, parameters 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 and the second series switch M11 may be a continuous process of time, each with its own duty cycle, for example, in PWM control, where the first series switch M10 is closed or the second series switch M11 is closed. Preferably, this switching process is carried out at a frequency above 100 Hz, more preferably above 2 kHz. In other examples, to provide simple control of the control circuit 1, the opening and closing of the first series switch M10 and the second series switch M11 may be a single event, for example, when the lighting device is started up. During operation, the open / closed states of the first series switch M10 and the second series switch M11 can be changed by different commands, such as commands to change the color or color temperature.

[0072] In the example shown, the controller C and additional peripheral electrical components may also be powered using a dedicated power supply. An auxiliary power supply may be provided for powering the controller C. Preferably, the auxiliary power supply is electrically isolated from the light source LEDs. Therefore, the auxiliary power supply is a dedicated power supply for the controller C. The auxiliary power supply cannot supply power to the light source LEDs and can therefore be optimized for powering the controller C.

[0073] During the standby mode of the lighting device, the light source LEDs are not powered, and therefore the driver can be turned off. However, the controller C may need to operate in standby mode, for example, to receive control commands to activate the lighting device. In that case, the controller C requires less power than when the lighting device is operating. An additional auxiliary power supply may be provided to power the controller C and surrounding electrical components during standby. The additional auxiliary power supply is optimized to power the controller C in standby mode.

[0074] In the example shown, the drivers may be separate devices comprising distinct components. To improve the use of space and components, some components may be reused among the drivers.

[0075] In the example shown, the dimming level is linearly related to the power required for the LED light source. Other relationships, such as logarithmic or nonlinear, are possible and may produce the desired effect.

[0076] In the example shown, when the dimming level is cycled through, it is desirable to change the duty cycle of only one driver.

[0077] A person skilled in the art will be able to understand and achieve, in carrying out the claimed invention, other variations of 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 notation does not exclude plurality. The mere fact that certain means are listed in different dependent claims does not mean that combinations of these means cannot be used favorably. No reference numeral in the claims should be construed as limiting the scope.

Claims

1. This is a driver circuit for supplying power to the light source. A first driver adapted to supply power to the light source, the first driver having a first output power with a first optimal power conversion efficiency, A second driver adapted to supply power to the aforementioned light source, the second driver having a second output power with a second optimal power conversion efficiency, It is a controller, A first control signal for enabling and disabling the first driver, which generates a first control signal having a first duty cycle, A driver circuit comprising a second control signal for enabling and disabling the second driver, and a controller adapted to generate the second control signal having a second duty cycle, The controller is adapted to receive a dimming signal and is configured to determine the first and second duty cycles based on the dimming signal, such that when active, the first driver operates at the first optimal power conversion efficiency and the second driver operates at the second optimal power conversion efficiency. A driver circuit in which the first control signal and the second control signal have a frequency of at least 100 Hz.

2. A third driver adapted to supply power to the light source, further comprising a third driver having a third output power at a third optimal power conversion efficiency, wherein the controller is for enabling and disabling the third driver at a third duty cycle, and is adapted to determine the third duty cycle based on the dimming signal so that the third driver operates at the third optimal power conversion efficiency when active, according to claim 1.

3. The driver circuit according to claim 1 or 2, wherein the first driver and the second driver are configured to have the same rated power.

4. The driver circuit according to claim 1 or 2, wherein the first driver and the second driver are configured to have different power ratings.

5. The driver circuit according to any one of claims 1 to 4, wherein the first driver and / or the second driver cannot be dimmed.

6. The driver circuit according to any one of claims 1 to 5, further comprising a capacitor and a switching element, wherein the capacitor and the switching element form a series configuration between the first input of the first driver and the second input of the first driver.

7. The driver circuit according to claim 6, wherein the driver circuit is configured to receive an AC voltage, and the switching element is configured to close when the voltage across the capacitor exceeds the amplitude of the AC instantaneous voltage.

8. The driver circuit according to any one of claims 1 to 7, further comprising an auxiliary driver adapted to supply power to the controller and adapted to be electrically isolated from the light source.

9. The driver circuit according to any one of claims 1 to 8, further comprising a further auxiliary driver, wherein the further auxiliary driver is adapted to supply power to the controller when the driver circuit is in standby mode.

10. The driver circuit according to any one of claims 1 to 9, wherein, at the dimming level in which the first driver and the second driver supply power to the light source, the first driver and the second driver operate in an interleaved operation mode.

11. The driver circuit according to any one of claims 1 to 10, wherein the controller is configured to control the first driver to operate on a duty cycle of 100% from a dimming level representing the power required for the light source that exceeds the rated power of the first driver, and to control the second driver to operate on a duty cycle between 0% and 100%.

12. The driver circuit according to any one of claims 1 to 11, wherein the controller is configured to enable the first driver and the second driver by supplying control signals to the first driver and the second driver, and the controller is configured to disable the first driver and the second driver by not supplying the control signals to the first driver and the second driver.

13. A driver circuit according to any one of claims 1 to 12, A lighting device having the aforementioned light source.

14. The lighting device according to claim 13, wherein the controller is configured to control the first driver and the second driver based on the dimming level such that the efficiency of the lighting device increases when the dimming level decreases.

15. The lighting device according to claim 13 or 14, wherein the light source is a semiconductor light source.

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