Improvements in high-frequency PFC converters

Abstract

The invention relates to a driver for driving a load. The driver includes a first node adapted to be coupled to a fluctuating voltage, a second node adapted to be coupled to a stabilized voltage, a switched mode power converter configured to convert the fluctuating voltage to the stabilized voltage or to convert the stabilized voltage to the fluctuating voltage, a first ceramic capacitor coupled to the first node, and a second ceramic capacitor coupled to the second node. And a second ceramic capacitor coupled between the first node and the second node.

Description

Technical Field

[0001] The present invention relates to a driver and also to a lamp comprising the driver. Background Art

[0002] Drivers with switch-mode power converters are used in many applications that require electronic devices to be powered. Laptops, mobile phones, and lighting applications all require power supplies that can provide regulated power while preventing or minimizing electrical noise, electromagnetic interference (EMI), emitted to the power grid. Capacitors are often used to filter EMI at high frequencies. To achieve this function, capacitors are usually ceramic or film capacitors because these types of capacitors are well suited to filtering high-frequency components from voltages. Ceramic capacitors come in many variations, from low-quality X5R types to X7R types (i.e., Class 2 ceramic capacitors) and even to NP0 types (i.e., Class 1 ceramic capacitors). NP0 capacitors are considered to be the most technically interesting capacitors because these capacitors offer low-tolerance capacitance values ​​and the capacitance values ​​are the least sensitive to the voltage applied to the capacitor. However, NP0 capacitors are very expensive and are also limited in terms of capacitance. When the voltage across the capacitor is large, a small capacitance drop occurs. If a larger capacitance value is required, multiple NP0 capacitors are required, which significantly increases the cost and size of the power supply. The capacitance value of X5R capacitors has a very high tolerance and is very sensitive to the voltage applied to the capacitor. When the voltage across the capacitor is large, a large capacitance drop occurs. Therefore, in order to provide a large total capacitance at the rated voltage of the multilayer ceramic capacitor MLCC, many capacitors need to be used.

[0003] Figure 1 An example of the relationship between the capacitance value of a capacitor and the voltage across the capacitor is shown. On the X-axis, the voltage across the capacitor is defined as 0V to the maximum voltage vCmax that will be applied to the capacitor. On the Y-axis, the relative capacitance of the capacitor is defined. C defines the actual capacitance, and C0 defines the absolute capacitance of the capacitor. The maximum relative capacitance is 1, where C is equal to C0. The minimum capacitance is the capacitance value Cmin. Therefore, the relative minimum capacitance is defined as Cmin / C0. Cmin / C0 is defined as the maximum voltage vCmax. Preferably, the voltage across the capacitor does not exceed this voltage. The capacitance of the capacitor is highest at the lowest voltage. The voltage across the capacitor increases significantly, almost exponentially, reducing the capacitance. At higher voltages, the filter function is severely reduced due to the lower capacitance value. Therefore, in order to provide a good filtering function at higher voltages, the size of the capacitor is specified so that the capacitance is still high enough at the highest voltage. This causes the capacitor to be oversized, resulting in a higher volume and / or cost of the capacitor. It is desirable to provide a driver in which the total capacitance of the capacitor can be better used without having to provide a more expensive or larger capacitor. Summary of the invention

[0004] The object of the present invention is to provide a driver with improved capacitance utilization. This means that it is desirable to use the same number of capacitors as in conventional solutions, e.g. placing two capacitors in parallel to double the effective capacitance, but achieve a higher effective capacitance, especially when the voltage across the capacitors is increased.

[0005] In a first aspect of the present invention, a driver for driving a load is provided, the driver comprising:

[0006] - a first node adapted to be coupled to a fluctuating voltage;

[0007] - a second node adapted to be coupled to a stable voltage;

[0008] - a switch mode power converter configured to convert a fluctuating voltage into a regulated voltage or to convert a regulated voltage into a fluctuating voltage;

[0009] - a first ceramic capacitor coupled to the first node;

[0010] - a second ceramic capacitor coupled between the first node and the second node, wherein the second ceramic capacitor is arranged to provide a primary capacitance between the first node and the second node, and the first ceramic capacitor is arranged to provide a primary capacitance to the first node.

[0011] The driver has a switch mode power converter, which is arranged to convert a fluctuating voltage into a stable voltage. This stable voltage can be provided to a load. The load can be any type of load that requires a stable voltage. The load can also be another switch mode power converter, which uses a stable voltage to convert to another voltage for another load. The operation of the switch mode power converter causes EMI or noise, which needs to be filtered out. In order to reduce the noise from the switch mode power converter to the input terminal (such as the mains voltage connection), a capacitor is used. As is well known, capacitors are used to filter out high frequency noise. A first ceramic capacitor is coupled to a first node. At this first node, an input voltage is received. The input voltage is a fluctuating voltage. This can be a rectified mains voltage. The rectified mains voltage is still fluctuating. Therefore, a first ceramic capacitor is used to provide a filtering function at a first node. A second ceramic capacitor is coupled between the first node and the second node. Therefore, the second ceramic capacitor provides a filtering function at the first node and the second node. The voltage at the second node is a stable voltage generated by the switch mode power converter. As a stable voltage, voltage can be understood as having a stable DC voltage value, which has a superimposed ripple due to the operation of the switch mode power converter. Therefore, the second ceramic capacitor is placed between the stable voltage at one end and the fluctuating voltage at the other end. The second ceramic capacitor is arranged to provide a main capacitance between the first node and the second node. The first ceramic capacitor is arranged to provide a main capacitance to the first node. This means that any other capacitor (such as, electrolytic capacitor) does not provide any significant capacitance at these nodes. The capacitance of these other capacitors at these nodes, such as the capacitance in parallel with the first capacitor or the second capacitor, is negligible for the capacitance behavior of the driver. Positioning the two capacitors in this way allows the capacitor to provide an improved capacitance value at the input end of the switch mode power converter within the entire range of the fluctuating voltage. The relationship between the total capacitance value and the voltage across the two capacitors has been changed in a defined manner to increase the total capacitance, i.e., improved. If the fluctuating voltage is low, the capacitance of the first ceramic capacitor is high. The voltage across the second ceramic capacitor is relatively large, so the capacitance is low. This will also be described in further detail in the detailed description of the embodiment. However, the total capacitance is relatively large, ie the total capacitance is still larger than when the second ceramic capacitor is placed in parallel with the first capacitor, especially at higher voltage levels of the fluctuating voltage.

[0012] In another example, a ratio between the capacitance of the first ceramic capacitor and the capacitance of the second ceramic capacitor is based on a ratio between a peak voltage of the fluctuating voltage and a magnitude of the regulated voltage.

[0013] The ratio between the capacitance of the first ceramic capacitor and the second ceramic capacitor can be determined based on the ratio between the peak voltage of the fluctuating voltage and the amplitude of the regulated voltage. This allows the use of an optimized capacitance value based on the type of the switch mode power converter.

[0014] In further examples, the switch-mode power converter is a boost converter, wherein the first node is coupled to an input of the switch-mode power converter, and wherein the second node is coupled to an output of the switch-mode power converter and to a load.

[0015] In one example, the switch mode power converter is a boost converter. Then, the first node is used as the input of the switch mode power converter, and is arranged to receive a fluctuating voltage, which can be a mains or a rectified mains. Then, the second node is used as the output of the switch mode power converter. The second ceramic capacitor is then coupled between the input and output of the switch mode power converter.

[0016] In another example, the switch mode power converter is a buck converter, wherein the second node is coupled to the input of the switch mode power converter, and wherein the first node is coupled to the output of the switch mode power converter and the load. The boost converter can be arranged to provide a stable voltage at the second node.

[0017] Instead of a boost converter, the switch mode power converter may also be a buck converter. The buck converter may receive a stable voltage. The second node is the input of the switch mode power converter. The first node is the output of the switch mode power converter. The voltage at the output of the switch mode power converter (i.e., buck converter) may fluctuate. Fluctuations are provided to allow the power provided to the load to be changed. Increasing the voltage may cause an increase in the power of the load, and vice versa. The increase or decrease in voltage is defined within the output voltage range of the driver. This is also referred to as the operating window of the driver. Such drivers may be referred to as window drivers. Fluctuations may not be as large as mains voltage fluctuations. Therefore, the effect achieved with the first ceramic capacitor and the second ceramic capacitor may be smaller, but an improvement to the conventional placement of capacitors (i.e., placing two capacitors in parallel) will still be provided.

[0018] In another example, the driver includes a third node adapted to be coupled to an additional fluctuating voltage, wherein the switch-mode power converter is a two-stage converter, wherein the first stage is a boost converter and the second stage is a buck converter, wherein the output of the boost converter is coupled to the input of the buck converter, wherein the first node is coupled to the input of the boost converter, the second node is coupled to the output of the boost converter and the input of the buck converter, and the third node is coupled to the output of the buck converter and a load, wherein the boost converter is adapted to provide a regulated voltage to the second node and the buck converter is adapted to provide an additional fluctuating voltage to the third node.

[0019] In further examples, the driver includes a third capacitor coupled between the second node and the third node.

[0020] The driver can be a two-stage driver. The first stage of the driver is a boost converter that converts a fluctuating voltage into a stable voltage. The second stage is a buck converter that converts a stable voltage into another fluctuating voltage. The definition of the fluctuating voltage can be the same as that already defined for the buck converter. Since there are two stages, some adjustments to the capacitor configuration are also required. The first ceramic capacitor is coupled to the first node. The second ceramic capacitor is coupled between the first node and the second node. The second node is the output of the boost converter and the input of the buck converter. The third capacitor can be placed between the second node and the third node. The third node is the output of the buck converter. The two-stage driver receives a fluctuating voltage, such as a mains or rectified mains, at a first node. The boost converter converts the fluctuating voltage into a stable voltage at a second node. The stable voltage is provided to the buck converter. The buck converter converts the stable voltage into another fluctuating voltage and provides the voltage at a third node. The fluctuating voltage is provided to the load. The fluctuating voltage is then used to provide variable power to the load, such as dimming when the load is a lighting load. The two-stage driver allows both power factor correction and good power regulation to the load.

[0021] In another example, the voltage fluctuation of the fluctuating voltage is greater than the voltage fluctuation of the further fluctuating voltage. Preferably, the fluctuating voltage may be a mains voltage and may have a voltage fluctuation of 0V to, for example, 325V. The voltage fluctuation of the further fluctuating voltage is significantly lower and may depend on the operating window of the driver. The operating window is defined as the voltage range that can be generated by the driver. This is also the range of the further fluctuating voltage. For example, the range may be a window between 40V and 100V. Nevertheless, the desired effect of the present invention is still achieved.

[0022] In another example, the first ceramic capacitor and the second ceramic capacitor are multilayer ceramic capacitors (MLCC) capacitors.

[0023] The use of MLCC capacitors allows the use of capacitors that are very suitable for filtering high frequency noise. In addition, these types of capacitors have a large deviation capacitance value that strongly depends on and varies with the changing voltage across the capacitor.

[0024] In another example, the first ceramic capacitor and the second ceramic capacitor are of X7R type.

[0025] Using X7R type provides a cost-effective solution. Using another material as NP0 may be too expensive in the application, in the present invention, X7R becomes a suitable substitute. X5R material can be cheaper, but results in very poor performance.

[0026] In a further example, the switch mode power converter is arranged to provide power factor correction.

[0027] Preferably, the switch mode power converter can provide power factor correction. This improves the power factor of the driver. The mains voltage provided to the driver can be rectified and provided to the switch mode power converter. In order to provide good power factor correction, the rectified mains voltage may not be buffered by (e.g., electrolytic capacitor). Therefore, the voltage fluctuation of the fluctuating voltage is as high as possible. The voltage at both ends of the first ceramic capacitor changes between 0V and the peak voltage of the mains voltage.

[0028] In further examples, the switch mode power converter is a synchronous switch mode power converter.

[0029] The switch mode power converter being a synchronous switch mode power converter is more energy efficient. It also allows the switch mode power converter to use negative current to achieve soft switching, thereby reducing EMI levels.

[0030] In further examples, the first ceramic capacitor and the second ceramic capacitor have substantially the same capacitance.

[0031] Using capacitors of the same type and / or same value for the first ceramic capacitor and the second ceramic capacitor allows the same components to be used, and thus a cheaper driver can be manufactured, since twice as many of one component are needed, resulting in a cheaper unit price of the components.

[0032] Alternatively, the first ceramic capacitor and the second ceramic capacitor have capacitances that are significantly different from each other.

[0033] In a further example, the driver includes a rectifier circuit adapted to rectify an alternating current (AC) voltage into a rectified voltage, wherein the rectified voltage is a fluctuating voltage.

[0034] Rectifying the AC voltage using a rectifier circuit provides a DC voltage with a similar fluctuation to the AC voltage, but rectified. This voltage can be used for effective power factor correction. The rectified voltage is then provided to the first node so that the fluctuating voltage is the same as the rectified voltage.

[0035] In another example, a system is provided, which includes a driver according to the present invention and a load.

[0036] In another example, the load is a semiconductor lighting load and the system is a lamp or a light.

[0037] Preferably, the load is a semiconductor lighting load, such as an LED or laser diode load.Preferably, the system is a luminaire or a lamp. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Examples of the present invention will now be described with reference to the accompanying drawings, in which:

[0039] Figure 1 An example of the relationship between the voltage across a capacitor and the capacitance of the capacitor is shown.

[0040] Figure 2 An example of a circuit of a driver is shown.

[0041] Figure 3 An example of the relationship between the voltage across the capacitor and the capacitance of the capacitor having the improved configuration is shown.

[0042] Figure 4 Another example of a circuit for a driver is shown.

[0043] Figure 5 A further example of a circuit for a driver is shown. DETAILED DESCRIPTION

[0044] The present invention will be described with reference to the accompanying drawings.

[0045] It should be understood that the detailed description and specific examples, although indicating exemplary embodiments of the apparatus, system and method, 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 apparatus, system and method of the present invention will become better understood based on the following description, the appended claims and the accompanying drawings. It should also be understood that the drawings are merely schematic and are not drawn to scale. It should also be understood that in all drawings, the same reference numerals are used to indicate the same or similar parts.

[0046] Figure 2An example of a driver is shown. The driver has a switch mode power converter 2. In the example provided, the switch mode power converter 2 is a boost converter. The first node N1 is coupled to the input of the switch mode power converter 2. The second node N2 is coupled to the output of the switch mode power converter 2. The switch mode power converter 2 may have an inductor L1, a switch M1, and another switch M2. A controller 1 is used to control the switch M1. The other switch M2 may be a diode. If the other switch M2 is a switch such as a transistor or a MOSFET, the other switch may also be controlled by the controller 1. If the other switch M2 is a transistor or a MOSFET, the switch mode power converter 2 may be operated as a synchronous converter. The first ceramic capacitor C1 is coupled to the first node N1 at one end. The other end of the first ceramic capacitor C1 is preferably coupled to a return path, such as a ground reference. The second ceramic capacitor C2 is coupled between the first node N1 and the second node N2. The second ceramic capacitor C2 is arranged to provide a main capacitance between the first node N1 and the second node N2, and the first ceramic capacitor C1 is arranged to provide a main capacitance to the first node N1. The rectifier circuit RECT can be configured to rectify the input voltage V1. The input voltage can be any type of voltage, preferably a commonly used mains voltage, such as 230V at 50Hz or 120V at 60Hz. The optional capacitor C3 can be used to buffer the output of the switch mode power converter 2, so that a stable voltage can be provided more reliably and easily. The optional capacitor C3 can be an electrolytic capacitor. The boost converter provides a stable voltage to the second node N2 and the load LED. The first ceramic capacitor C1 is exposed to the fluctuating voltage appearing at the first node N1. An example is now provided to explain the relationship between the voltage at the first node N1 and the second node N2 and the capacitance value of the first ceramic capacitor C1 and the second ceramic capacitor C2. If the fluctuating voltage is low, for example 0V, the capacitance of the first ceramic capacitor C1 is the largest, such as Figure 1 As shown, on the Y axis, point C / C0 is 1. The stable voltage at the second node N2 is adjusted to a stable voltage of, for example, 400V. The differential voltage across the second ceramic capacitor C2 is 400V, i.e., 400V relative to 0V. This means that the capacitance of the second ceramic capacitor C2 is at its lowest value. Figure 1As shown, the C / C0 value is Cmin / C0. In this example, vCmax is 400V, and now the fluctuating voltage increases. If the fluctuating voltage reaches, for example, 200V, the voltage across the first ceramic capacitor C1 is 200V. The voltage across the second ceramic capacitor C2 is 400V-200V=200V. In the example provided, the polarity of the voltage across the capacitor is irrelevant to determining the capacitance value. The amplitude is considered to be the determining factor of the voltage. The voltage across the first ceramic capacitor C1 and the second ceramic capacitor C2 is the same. This causes the capacitance to be the same. The fluctuating voltage is even further increased to a maximum voltage of, for example, 325V. The voltage across the first ceramic capacitor C1 is 325V. The voltage across the second ceramic capacitor C2 is 400V-325V=75V. The voltage across the first ceramic capacitor C1 is relatively large, resulting in a low capacitance value. The voltage across the second ceramic capacitor C2 is at a relatively low value, resulting in a relatively large capacitance value. The total capacitance available for filtering noise generated by the switch mode power converter 2 is greater than the capacitance when the capacitors C1 and C2 are coupled in parallel at the first node N1. This means that using the same capacitors, a higher total minimum capacitance can be obtained, effectively improving the utilization of the capacitors.

[0047] Preferably, the first ceramic capacitor C1 is the only capacitor coupled to the first node N1. Preferably, the second ceramic capacitor C2 is the only capacitor coupled between the first node N1 and the second node N2. Preferably, the coupling of the first ceramic capacitor C1 is completed between the first node N1 and the return path. By having only ceramic capacitors, the total capacitance at the input of the driver is relatively low. This is mainly because the capacitance value of ceramic capacitors is significantly lower than the capacitance value of electrolytic capacitors or film capacitors. Since the lower the capacitance at the input of the driver, the better the power factor can be corrected, the power factor correction can be performed in an efficient manner. This further allows the driver to operate at high frequencies, because ceramic capacitors are very suitable for high frequency operation. Preferably, the driver can operate at frequencies above 500kHz.

[0048] Figure 3An example of a graph is shown, which shows the relationship between the capacitance value of the combined capacitance of the first ceramic capacitor C1 and the second ceramic capacitor C2 and the fluctuating voltage (e.g., the mains input voltage or the rectified mains input voltage). On the X-axis, the fluctuating voltage at the first node N1 is defined as from 0V to the maximum voltage vCmax. On the Y-axis, the relative capacitance of the capacitor is defined. Cin defines the actual capacitance, and C0 defines the absolute capacitance of the capacitor. The maximum relative capacitance is 2 because there are two capacitors, where Cin of both capacitors is equal to C0. In conventional applications, the minimum capacitance that can be achieved is a capacitance value of 2Cmin. Therefore, the relative minimum capacitance is defined as 2Cmin / C0. 2Cmin / C0 is defined as the maximum voltage vCmax. Preferably, the voltage across the capacitor does not exceed this voltage. In the example provided, for simplicity, it is assumed that the first ceramic capacitor C1 and the second ceramic capacitor C2 are the same. If the second ceramic capacitor C2 is placed in parallel with the first ceramic capacitor C1, rather than between the first node N1 and the second node N2, the relationship shown by the dotted line is also as shown Figure 1 As shown. The capacitance at the lowest voltage level is twice the capacitance value of one capacitor, because the sum of the capacitances of the first ceramic capacitor C1 and the second ceramic capacitor C2 is equal to twice the capacitance of a single capacitor. Based on the increase in the voltage level across the capacitor, the capacitance decreases almost exponentially. At the maximum provided voltage vCmax, the total capacitance is reduced to 2Cmin / C0. However, the solid line shows the total capacitance of the first ceramic capacitor C1 and the second ceramic capacitor C2 according to the present invention. The capacitance at the lowest voltage is lower than the conventional setting, i.e., 1+Cmin / C0. The increase in the fluctuating voltage level almost exponentially reduces the capacitance of the first ceramic capacitor C1, and also almost exponentially increases the capacitance of the second ceramic capacitor C2. First, the capacitance of the first ceramic capacitor C1 decreases faster than the capacitance of the second ceramic capacitor C2 increases, so the total capacitance decreases as the voltage increases. This happens until the voltage level reaches a threshold of 1 / 2vCmax, at which time the capacitance of the first ceramic capacitor C1 decreases less, while the capacitance of the second ceramic capacitor C2 increases more as the voltage increases. In this example, the threshold of 1 / 2vCmax is an example of a threshold level. The skilled person understands that this threshold may be different when different designs are selected. When the voltage increases and is above the voltage threshold vCmax, the total capacitance increases.

[0049] In the example provided, at the maximum available voltage vCmax, the total capacitance is 1+Cmin / C0. Depending on the design choices of the driver, the total capacitance can also be larger or smaller. The minimum capacitance value will always be greater than 2Cmin / C0, and in this example, the minimum capacitance value is 4Cmin / C0. Therefore, in the example provided, the minimum capacitance value is twice that of conventional solutions. The minimum capacitance value achieved by the present invention, defined as 4Cmin / C0, is preferably between 50% and 20% of the maximum possible voltage defined as C0. More preferably, the minimum capacitance value is between 40% and 30%.

[0050] Figure 4 Another example of a driver is shown. The driver has a switch mode power converter 2 configured as a buck converter. The buck converter has an input terminal coupled to a second node N2. The switch mode power converter 2 may have an inductor L1, a switch M1, and another switch M2. A controller 1 is used to control the switch M1. Another switch M2 may be a diode. If another switch M2 is a switch such as a transistor or a MOSFET, the other switch may also be controlled by the controller 1. If another switch M2 is a transistor or a MOSFET, the switch mode power converter 2 may be operated as a synchronous converter. A second ceramic capacitor C2 is coupled to the second node N2. Preferably, the second node N2 is coupled to an optional capacitor C3, which provides a buffer to maintain the voltage stability at the second node N2. A rectifier circuit RECT may be configured to rectify an input voltage V1. The input voltage may be any type of voltage, preferably a commonly used mains voltage, such as 230V at 50Hz or 120V at 60Hz. The first node N1 is coupled to the output terminal of the buck converter. The first ceramic capacitor C1 is coupled to the first node N1. The buck converter provides a fluctuating voltage to the first node N1 and the load LED, and the fluctuating voltage can be defined as the operating window of the buck converter. The fluctuating voltage does not have to fluctuate in a short time. Over time, the voltage can remain constant. A configuration setting can be provided to the controller 1 of the buck converter, which allows the voltage provided by the buck converter to change. The voltage can increase or decrease within the operating window of the buck converter. This can be identified as another fluctuating voltage. The capacitance value must be guaranteed within the entire operating window. Therefore, the second ceramic capacitor C2 is coupled between the first node N1 and the second node N2. Figure 3 The effects described in the description of are achieved in a similar manner. The effective minimum capacitance value has been increased.

[0051] Figure 5 Another example of a driver is shown. The driver has a switch mode power converter 2 configured as a two-stage converter. The first stage is shown as a boost converter. The boost converter has Figure 2The same features as the boost converter shown. A fluctuating voltage such as a mains voltage is provided to the input of the driver. The fluctuating voltage is rectified by a rectifier circuit RECT. The rectifier circuit RECT provides a rectified voltage as a fluctuating voltage provided to the first node N1. The boost converter provides a stable voltage to the second node N2. The voltage can be buffered by an optional capacitor C3. The stable voltage is provided to the second stage, i.e., the buck converter. The buck converter receives a stable voltage at the second node N2. The buck converter provides an additional fluctuating voltage to the third node N3 and the load LED. The load LED is also coupled to the third node. Capacitor C5 can be provided to stabilize the voltage at the output of the buck converter, allowing the buck converter to operate with a voltage window under a stable voltage. The second ceramic capacitor C2 is coupled between the first node N1 and the second node N2. The third capacitor C4 can be placed between the second node N2 and the third node N3. The total minimum capacitance at the input of the boost converter and the total minimum capacitance at the output of the buck converter are subsequently improved. Optionally, only one of the second ceramic capacitor C2 and the third capacitor C4 is used. In one example, the second ceramic capacitor C2 is placed, but the third capacitor C4 is not placed.

[0052] In the example provided, the total fluctuation of the capacitance value is now reduced. The maximum capacitance value has been reduced, but this is not a problem for the design of the driver. Instead, the absolute minimum value of the capacitance value is a crucial parameter. Since the absolute minimum value of the capacitance value has been increased by the present invention, which in the example provided is twice as large, the overall design of the driver can be improved.

[0053] In the example provided, it is assumed that the capacitance values ​​of the first ceramic capacitor C1 and the second ceramic capacitor C2 are substantially the same. Additionally, it is assumed that the value of the third capacitor C4 is substantially the same.

[0054] The driver according to any example may be used in many applications where regulated power is to be provided to a load. An example of a load that may be powered by the driver may be a load that may be powered by USB-C. An example of a load that may be powered by the driver may be, but is not limited to, any of a laptop, a mobile phone, a lighting load such as an LED or laser diode, a monitor, or a television.

[0055] Preferably, the switch mode power converter is of non-isolated type. Buck converter or boost converter is the preferred topology. Therefore, no isolation transformer is used, making the design of the switch mode power converter simpler.

[0056] Preferably, the driver is integrated in the luminaire or lamp, but the driver may also be a separate driver.

[0057] In the examples, the capacitor is shown as a single capacitor. It should be understood that more capacitors of the same type are used in different configurations to achieve, for example, a desired capacitance value or rated voltage. Thus, the capacitor may consist of multiple capacitors connected in series and / or in parallel.

[0058] Other variations to the disclosed embodiments may be understood and effected by those skilled in the art in practicing the claimed invention, by studying the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A driver for driving a load, the driver comprising: a first node (N1) adapted to be coupled to a fluctuating voltage; a second node (N2) adapted to be coupled to a stable voltage; A switch mode power converter (2) configured to convert the fluctuating voltage into the stable voltage or to convert the stable voltage into the fluctuating voltage; a first ceramic capacitor (C1) coupled to the first node (N1); A second ceramic capacitor (C2) is coupled between the first node (N1) and the second node (N2), wherein the second ceramic capacitor (C2) is arranged to provide a main capacitance between the first node (N1) and the second node (N2), and the first ceramic capacitor (C1) is arranged to provide a main capacitance to the first node (N1).

2. The driver according to claim 1, wherein a ratio between a capacitance of the first ceramic capacitor (C1) and a capacitance of the second ceramic capacitor (C2) is based on a ratio between a peak voltage of the fluctuating voltage and a magnitude of the stable voltage.

3. A driver according to any one of the preceding claims, wherein the switch mode power converter (2) is a boost converter, wherein the first node (N1) is coupled to the input of the switch mode power converter (2), and wherein the second node (N2) is coupled to the output of the switch mode power converter (2) and the load (LED).

4. A driver according to claim 1 or 2, wherein the switch mode power converter (2) is a buck converter, wherein the second node (N2) is coupled to the input of the switch mode power converter (2), and wherein the first node (N1) is coupled to the output of the switch mode power converter (2) and the load (LED).

5. A driver according to claim 1 or 2, wherein the driver includes a third node (N3), which is suitable for being coupled to an additional fluctuating voltage, wherein the switch-mode power converter (2) is a two-stage converter, wherein the first stage is a boost converter and the second stage is a buck converter, wherein the output of the boost converter is coupled to the input of the buck converter, wherein the first node (N1) is coupled to the input of the boost converter, the second node (N2) is coupled to the output of the boost converter and the input of the buck converter, and the third node (N3) is coupled to the output of the buck converter and the load (LED), wherein the boost converter is suitable for providing the regulated voltage to the second node (N2), and the buck converter is suitable for providing the additional fluctuating voltage to the third node (N3).

6. The driver of claim 5, further comprising a third capacitor (C3) coupled between the second node (N2) and the third node (N3).

7. The driver according to any one of claims 5 or 6, wherein the voltage fluctuation of the fluctuating voltage is greater than the voltage fluctuation of the further fluctuating voltage.

8. Driver according to any of the preceding claims, wherein the first ceramic capacitor (C1) and the second ceramic capacitor (C2) are multi-layer ceramic capacitors (MLCC) capacitors.

9. Driver according to any of the preceding claims, wherein the first ceramic capacitor (C1) and the second ceramic capacitor (C2) are of X7R type.

10. A drive according to any one of the preceding claims, wherein the switch mode power converter (2) is arranged to provide power factor correction.

11. A drive according to any one of the preceding claims, wherein the switch mode power converter (2) is a synchronous switch mode power converter.

12. Driver according to any of the preceding claims, wherein the first ceramic capacitor (C1) and the second ceramic capacitor (C2) have substantially the same capacitance.

13. Driver according to any of the preceding claims, further comprising a rectifier circuit (RECT) adapted to rectify an alternating AC voltage into a rectified voltage, wherein the rectified voltage is the fluctuating voltage.

14. A system comprising a driver according to any one of the preceding claims and the load (LED).

15. The system of claim 14, wherein the load (LED) is a semiconductor lighting load, and wherein the system is a lamp or a light.

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