Power demultiplexer for high efficiency multichannel LED driver

Abstract

The invention relates to a power stage for powering a first load, the first load being coupleable between a first output and a second output, the power stage comprises a first input for receiving a bus voltage, a first output coupled to the first input and arranged to be coupleable to a first load, a first capacitor coupled between a second output and a first further node and coupleable in series with the first load, a second power converter, the second power converter includes a controller for controlling the second power converter, a first inductive element and a first switching element coupled in series between the second input and the return node, a second inductive element inductively coupled to the first inductive element, and a first unidirectional device coupled in series between the second output and the first further node, wherein the second power converter is arranged to provide a current to the first capacitor, the current being opposite in polarity to a current provided to the first capacitor via the first load.

Description

Technical Field

[0001] The present invention relates to a power stage for supplying power to a load. The present invention also relates to a power supply system. Background Art

[0002] The power stage (also called a driver) typically regulates the power delivered to the load. The load may require a specific voltage to function properly. If the load or driver is replaced, damaged, or upgraded, the load and driver may no longer match in terms of supplied and required voltages. If the driver voltage is greater than the voltage required by the load, the voltage difference may cause parasitic losses. If the driver voltage is lower than the voltage required by the load, the load may not even start or function properly.

[0003] In the lighting sector, in particular, lighting loads can be replaced independently of their drivers. When replacing lighting loads and creating new combinations of drivers and lighting loads, the forward voltage of the lighting load may not fully match the voltage supplied by the driver. This can result in additional power loss in the driver or a non-functional combination of driver and lighting load. This is expected to provide greater design freedom by allowing a wider range of drivers to be combined with a wider variety of lighting loads. Summary of the Invention

[0004] It is an object of the present invention to provide a power efficient device which allows matching the supplied voltage from, for example, a driver to the voltage required by a load.

[0005] To achieve this effect, in a first aspect of the present invention, a power stage for powering a first load is provided, wherein the first load may be coupled between a first output and a second output. The power stage comprises:

[0006] - a first input for receiving a bus voltage;

[0007] - a first output coupled to the first input and arranged to be coupleable to a first load;

[0008] - a first capacitor coupled between the second output and the first further node and coupleable in series with the first load;

[0009] - a second power converter, the second power converter comprising:

[0010] - a controller for controlling the second power converter;

[0011] - a first inductive element and a first switching element coupled in series between the second input and a return node;

[0012] a second inductive element inductively coupled to the first inductive element, and a first unidirectional device coupled in series between the second output and the first further node,

[0013] The second power converter is arranged to provide a current to the capacitor that is opposite in polarity to a current provided to the first capacitor via the first load.

[0014] A power stage according to the present invention has a first input that can receive a bus voltage. The bus voltage can be any type of voltage, preferably a regulated voltage. The voltage can have ripple, so that the bus voltage is an average regulated voltage. A first output is provided to which a first load can be connected. The first output is also coupled to the first input.

[0015] A first capacitor is disposed between the second output and a first additional node, and a first load may also be coupled to the second output. When the first load is coupled between the first output and the second output, the first load and the first capacitor are connected in series. A second power converter is provided. The second power converter includes a controller for controlling the second power converter. A first inductive element and a first switching element are coupled in series with each other between the second input and a return node. The first inductive element is inductively coupled to the second inductive element. A first unidirectional device is coupled in series between the second output and the first additional node.

[0016] The second power converter is arranged to provide a current to the first capacitor that is of opposite polarity to a current provided to the capacitor via the first load.

[0017] The power stage according to the present invention allows the voltage of the first load to match the bus voltage. In this example, the sum of the voltages across the first load and the first capacitor equals the bus voltage. The voltage across the first load is not easily regulated, but the voltage across the first capacitor can be regulated using a second power converter. The second power converter uses a first switching element to allow current to flow through a first inductor. The inductive coupling between the first and second inductors effectively forms a flyback transformer. Therefore, current flowing through the first inductor is reflected to the second inductor. A first unidirectional device is coupled to the second inductor such that when the first switching element is closed, no current flows through the second inductor. Conversely, when the first switching element is open, current through the first inductor is reflected to the second inductor, causing this current to supply a current to the first capacitor of opposite polarity to the current flowing through the first load. For example, the current flowing through the first load also flows through the first capacitor. This current can discharge the first capacitor. The polarity of the current supplied to the capacitor via the second inductor causes it to charge the first capacitor. The balance between charging and discharging of the capacitor allows the voltage across the first capacitor, and thereby also the current flowing through the first load, to be regulated.The duration of the on-time of the first switching element may be used to provide a regulated amount of energy to the first capacitor.

[0018] In another example, the second input is directly coupled to the first input.

[0019] Preferably, a direct coupling is provided between the second input and the first input so that energy losses can be kept as low as possible.However, if required, electronic components may be placed between the second input and the first input, for example to provide additional functionality.

[0020] In another example, the first further node is coupled to the return node.

[0021] Preferably, the first capacitor, and the series combination of the first inductive element and the first switching element are both directly coupled to the return node. This enables a simple and energy-efficient design of the power stage.

[0022] In another example, the power stage includes a linear current regulator connected in series between the first further node and the return node.

[0023] A linear current regulator may be provided between the further node and the return node. The linear current regulator may then be effectively connected in series with the first load and the first capacitor. The linear current regulator may be used to further reduce current ripple of the current passing through the first load.

[0024] In another example, the current provided via the first load is arranged to discharge the first capacitor.

[0025] In another example, the current provided via the first load is arranged to charge the first capacitor.

[0026] In another example, the current provided via the second inductive element is arranged to charge the first capacitor.

[0027] In another example, the current provided via the second inductive element is arranged to discharge the first capacitor.

[0028] In another example, the second power converter is a flyback converter.

[0029] Using a flyback converter for the second power converter allows for a simple design of the inductive coupling between the first inductive element and the second inductive element.

[0030] In another example, a power supply system is provided. The power supply system includes:

[0031] - a power level according to any of the preceding examples;

[0032] a third output coupled to the first input and arranged to be coupleable to a second load, the second load being coupleable between the third output and the fourth output;

[0033] - a second capacitor coupled between the fourth output and the second further node and coupleable in series with the second load;

[0034] - a third power converter, the third power converter comprising:

[0035] a third inductive element inductively coupled to the first inductive element, a third switching element, and a second unidirectional device coupled in series between the fourth output and the second further node,

[0036] The second power converter further includes a second switching element connected in series with the first unidirectional device,

[0037] The third power converter is arranged to provide a current to the second capacitor, the current having a polarity opposite to that of a current provided to the second capacitor via the second load.

[0038] Another independent second load can be powered by the same power supply system. The second load can be coupled in series with the second capacitor. A third power supply can receive power from the first inductive element. The third power supply includes a third inductive element inductively coupled to the first inductive element, a third switching element coupled in series between the fourth output and the second further node, and a second unidirectional device. The third power supply can operate in the same manner as the second power supply. When the first switching element is open, the second unidirectional device allows the third inductive element to supply current to the second capacitor. Furthermore, the third power converter is arranged to supply a current to the second capacitor that is opposite in polarity to the current supplied to the capacitor via the second load. This means that when the current supplied by the load charges the capacitor, the current supplied by the third inductive element discharges the capacitor, and vice versa. The first inductive element supplies current to the second and third inductive elements. To determine the power distribution between the second and third inductive elements, the second power converter includes a second switching element coupled in series with the first unidirectional device, and the third power converter includes a third switching element coupled in series with the second unidirectional device. Control of the second and third switches allows for regulation of the current flowing to the first and second capacitors, respectively.

[0039] In another example, the first load and the second load are included in a power supply system.

[0040] In another example, the first load and / or the second load is a lighting load.

[0041] Preferably, at least one load is a lighting load. Another load may also be a lighting load, but may also be another type of load, such as a sensor.

[0042] In another example, the lighting load is a semiconductor lighting load.

[0043] Examples of semiconductor lighting loads may be LEDs or lasers, such as laser diodes or vertical cavity surface emitting lasers (VCSELs).

[0044] In another example, the forward voltage of the first load is different from the forward voltage of the second load.

[0045] The power supply system according to the example allows compensating for a difference between forward voltages of a load by providing different voltages across a first capacitor and a second capacitor.

[0046] In another example, the power supply system further includes a mains power converter adapted to convert the mains input voltage into a bus voltage.

[0047] The bus voltage may be an unregulated voltage, but preferably the bus voltage is a regulated voltage.The mains power converter may regulate an unregulated voltage, such as a rectified mains voltage, to a regulated bus voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Examples of the present invention will now be described with reference to the accompanying drawings, in which:

[0049] Figure 1 An example of a circuit diagram of a power stage is shown.

[0050] Figure 2 Another example of a circuit diagram of a power stage is shown.

[0051] Figure 3 Another example of a circuit diagram of a power supply system is shown.

[0052] Figure 4 Another example of a circuit diagram of a power supply system is shown.

[0053] Figure 5 An example of a power supply system is shown.

[0054] Figure 6 Another example of a power supply system is shown. DETAILED DESCRIPTION

[0055] The present invention will be described with reference to the accompanying drawings.

[0056] It should be understood that the detailed description and specific examples, while 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 be better understood through the following description, the appended claims, and the accompanying drawings. It should also be understood that the drawings are merely schematic and not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings to indicate the same or similar parts.

[0057] Figure 1 An example of a power stage is shown. The power stage has a first input Input arranged to receive a bus voltage. The power stage also has a ground node for providing a return path for current provided via the input Input. This node is shown as ground. In this example, it may also be referred to as a return node or a first further node. A first inductive element L1 and a first switching element M1 are coupled in series between a second input Input2, which in this example is directly coupled to the first input Input1, and the return node.

[0058] A first load LED1 and a first capacitor C1 are coupled in series between the first input Input and a first additional node. In this example, the first additional node is directly coupled to a return node. The first load LED1 can form part of a power stage. Thus, the power stage has a first output 1 and a second output 2, to which the first load LED1 is coupled. In this example, the first output 1 is directly coupled to the first input Input 1. In this example, the second output 2 is directly coupled to the anode of a first unidirectional device D1 and the first capacitor C1. The unidirectional device D1 and a second inductive element L2 are coupled in series between the second output 2 and the first additional node. In this example, the second power converter includes a first inductive element L1, a first switching element M1, the first unidirectional device D1, and a second inductive element L2. The first and second inductive elements L1 and L2 are inductively coupled, such that the second power converter forms a flyback converter. The second power converter can be controlled by a controller. The first capacitor C1 is considered the load of the second power converter. The second power converter supplies current to the first capacitor C1 in the positive direction of the polarity of the first capacitor C1. The current flowing through the first load, LED1, flows through the first capacitor, C1, in the negative direction of the first capacitor's polarity. The present invention recognizes that the voltage across the first load, LED1, needs to match the bus voltage in order to regulate the current through the first load, LED1. In this example, the bus voltage is lower than the voltage required by the first load, LED1. Compared to the voltage across the first load, LED1, the voltage across the first capacitor has a negative polarity, effectively "boosting" the bus voltage relative to the required load voltage. Therefore, the second power converter is used to increase the bus voltage level so that the voltage across the first load, LED1, is sufficiently high to allow the desired, regulated current amplitude to flow through the first load, LED1.

[0059] For example, the bus voltage may be 20V, and the required voltage of the first load LED1 may be 25V.

[0060] The bus voltage is equal to the sum of the voltage of the first load LED1 and the voltage of the first capacitor C1. Then, the second power converter is controlled to generate a voltage of -5V on the first capacitor, and V bus =V load +V c , and we get 20V=25V-5V.

[0061] To provide a more stable bus voltage, the bus voltage may be buffered by a buffer capacitor C10. The bus voltage may have a considerable two-line frequency voltage ripple, as the second power converter will compensate for the ripple and keep the load voltage constant.

[0062] Figure 2 Shown Figure 1An improved example of a power stage is shown. The power stage has a first input Input1 arranged to receive a bus voltage. The power stage also has a ground node for providing a return path for current provided via the input Input. This node is shown as ground. In this example, it can also be referred to as a return node. A first inductive element L1 and a first switching element M1 are coupled in series between a second input Input2 and the return node. In this example, the second input is directly coupled to the first input Input1. A first load LED1 and a first capacitor C1 are coupled in series between the first input Input1 and a first further node. The first load LED1 can form part of the power stage. Therefore, the power stage has a first output 1 and a second output 2, to which the first load LED1 is coupled. In this example, the first output 1 is directly coupled to the first input Input1. In this example, the second output 2 is directly coupled to the anode of a first unidirectional device D1 and the first capacitor C1. The unidirectional device D1 and the second inductive element L2 are coupled in series between the second output 2 and the first further node. In this example, the second power converter includes a first inductive element L1, a first switching element M1, a first unidirectional device D1, and a second inductive element L2. The first and second inductive elements L1 and L2 are inductively coupled, forming a flyback converter. The second power converter can be controlled by a controller. The first capacitor C1 is considered the load of the second power converter. The second power converter supplies current to the first capacitor C1 in the positive direction of the first capacitor C1. The current flowing through the first load LED1 flows through the first capacitor C1 in the negative direction of the first capacitor C1. The present invention recognizes that the voltage across the first load LED1 needs to match the bus voltage in order to regulate the current through the first load LED1. In this example, the bus voltage is lower than the voltage required by the first load LED1. Compared to the voltage across the first load LED1, the voltage across the first capacitor has a negative polarity, effectively "boosting" the bus voltage relative to the required load voltage. Therefore, the second power converter acts to increase the bus voltage level so that the voltage across the first load LED1 is large enough to regulate the desired current amplitude through the first load LED1.

[0063] For example, the bus voltage may be 20V, and the required voltage of the first load LED1 may be 25V.

[0064] The bus voltage is equal to the sum of the voltage of the first load LED1 and the voltage of the first capacitor C1. Then, the second power converter is controlled to generate a voltage of -5V on the first capacitor, and V bus =V load +V c , and we get 20V=25V-5V.

[0065] To provide a more stable bus voltage, the bus voltage can be buffered by a buffer capacitor C10. An additional circuit is provided to reduce the ripple of the current flowing through the first load LED1. This is a linear current regulator. A transistor Q1 having a current sensing circuit R1 can be arranged in series between the first additional node and the return node. The feedback circuit 5 can receive a signal from the current sensing circuit R1 that represents the current flowing through the transistor Q1. In this example, the current sensing circuit R1 is a resistor. The feedback circuit 5 uses this signal to control the base of the transistor Q1 so that the desired current flows through the transistor Q1. The feedback circuit 5 can also receive an additional signal for setting the desired current amplitude. This can be a dimming signal, such as a PWM dimming signal, which can be provided by a controller controlled by an external device (such as a remote control).

[0066] It is important to note that the linear current regulator can be implemented in any of the examples provided, not just in Figure 2 Each capacitor connected in series with a corresponding load may also be coupled in series with a corresponding linear current regulator. In this case, since the linear current regulator is placed between the additional nodes, the additional nodes are not directly coupled to the return node.

[0067] Figure 3 An example of a power supply system is shown. According to this example of the present invention, the power supply system may include a power stage. The power supply system has a first input Input1 arranged to receive a bus voltage. The power supply system also has a ground node for providing a return path for current provided via the input Input. This node is shown as ground. In this example, it may also be referred to as a return node or a first additional node. A first inductive element L1 and a first switching element M1 are coupled in series between a second input Input2 and the return node. In this example, the second input is directly coupled to the first input Input1. A first load LED1 and a first capacitor C1 are coupled in series between the first input Input1 and a first additional node. In this example, the first additional node is directly coupled to the return node. The first load LED1 may form part of the power supply system. Therefore, the power supply system has a first output 1 and a second output 2, to which the first load LED1 is coupled. In this example, the first output 1 is directly coupled to the first input Input1. In this example, the second output 2 is directly coupled to the anode of the first capacitor C1 and the first unidirectional device D1. The first unidirectional device D1, the second switching element M2 and the second inductive element L2 are coupled in series between the second output 2 and the first further node. In this example, the second power converter comprises a first inductive element L1, a first switching element M1, a first unidirectional device D1, a second switching element M2 and a second inductive element L2.

[0068] A second load LED2 and a second capacitor C2 are coupled in series between the first input Input1 and a second further node. In this example, the second further node is directly coupled to the return node. The second load LED1 can form part of a power supply system. Therefore, the power supply system has a third output 3 and a fourth output 4, to which the second load LED2 is coupled. In this example, the third output 3 is directly coupled to the first input Input1. In this example, the fourth output 4 is directly coupled to the anode of the second unidirectional device D2 and the second capacitor C2. The second unidirectional device D2, the third switching element M3, and the third inductive element L3 are coupled in series between the fourth output 4 and the second further node. In this example, the third power converter includes the second unidirectional device D2, the third switching element M3, and the third inductive element L3. A controller can also be used to control the third power converter. This means that the controller can, for example, be used to control the third switching element M3. The first inductive element L1, the second inductive element L2, and the third inductive element are inductively coupled, such that the second power converter forms a flyback converter. The main difference from a conventional flyback converter is that on the second and third sides, namely, on the second and third inductor elements L2 and L3, switching elements are positioned to allow or prevent current from flowing to the corresponding first capacitor C1 or second capacitor C2. The current passing through the first inductor element L1 is reflected to the second and third inductor elements L2 and L3. The second and third switching elements M2 and M3 can be controlled to control the current flowing from the second and third inductor elements L2 and L3 to the first and second capacitors C1 and C2, respectively.

[0069] and Figure 1 and Figure 2 Similar to the example provided in , the current through the load discharges the series capacitor, and the current provided by the inductive element charges the capacitor. In this example, the current through the first load LED1 discharges the first capacitor C1, and the current provided by the second inductive element L2 charges the first capacitor C1. The current through the second load LED2 discharges the second capacitor C2, and the current provided by the third inductive element L3 charges the second capacitor C2. Figure 1 and Figure 2 Similar to the example, the voltages across capacitors C1 and C2 are negative, while the voltages required by loads LED1 and LED2 are greater than the bus voltage. By controlling switching elements M1, M2, and M3, the voltages across capacitors C1 and C2 can also be controlled independently of each other. This allows the voltage required by load LED1 to differ from the voltage required by load LED2. The advantage of this scenario is that a single bus voltage can be provided to multiple loads, even if the bus voltage does not match the voltage of the loads.

[0070] Preferably, the first switching element M1 , the second switching element M2 and the third switching element M3 are controlled by a single controller. In order to provide a more stable bus voltage, the bus voltage may be buffered by a buffer capacitor C10 .

[0071] Figure 4 Another example of a power supply system is shown. Figure 3 The power supply systems are nearly identical. The main difference is that the polarities of the first capacitor C1 and the second capacitor C2 are opposite. This means that the currents provided by the second inductor L2 and the third inductor discharge the first capacitor C1 and the second capacitor C2, respectively. The currents flowing through the first load LED1 and the second load LED2 charge the first capacitor C1 and the second capacitor C2, respectively. In this example, the capacitor voltage can be positive. Therefore, the bus voltage can be greater than the required load voltage.

[0072] For example, for simplicity, considering only the first load LED1 , the bus voltage may be 25V, and the required voltage of the first load LED1 may be 20V.

[0073] The bus voltage is equal to the sum of the voltage of the first load LED1 and the voltage of the first capacitor C1. Then, the second power converter is controlled to generate a voltage of 5V on the first capacitor, resulting in V bus =V load +V c , and we get 25V=20V+5V.

[0074] In order to provide a more stable bus voltage, the bus voltage may be buffered by a buffer capacitor C10.

[0075] Figure 5 Another example of a power supply system is shown. The power supply system has a first input Input1 arranged to receive a bus voltage. The power supply system also has a ground node for providing a return path for current provided via the input Input. This node is shown as ground. In this example, it can also be referred to as a return node or a first additional node.

[0076] In this example, the bus voltage is provided by a mains power converter. The mains power converter can be configured to rectify the mains input voltage. Common mains voltage is 230V at 50Hz and 120V at 60Hz. The rectified mains voltage is converted to a bus voltage by the mains power converter. In this example, the mains power converter has an inductor L10, a switching element M10 and a unidirectional device D10, and is configured to operate as a boost converter. The mains power converter can be configured as any other type of switching mode power converter, such as a boost converter, a buck converter, a buck-boost converter, a flyback converter or an LLC converter. The main purpose of the mains power converter is to convert the input voltage (in this case, the mains voltage) into a regulated bus voltage at the input Input1.

[0077] A first inductor L1 and a first switch M1 are coupled in series between a second input, Input2, and a return node. In this example, the second input is directly coupled to the first input, Input1. A first load LED1 and a first capacitor C1 are coupled in series between the first input, Input1, and a first further node. In this example, the first further node is directly coupled to the return node. The first load LED1 can form part of a power supply system. Thus, the power supply system has a first output 1 and a second output 2, to which the first load LED1 is coupled. In this example, the first output 1 is directly coupled to the first input, Input1. In this example, the second output 2 is directly coupled to the anode of a first unidirectional device D1 and the first capacitor C1. The first unidirectional device D1, the second switch M2, and the second inductor L2 are coupled in series between the second output 2 and the first further node. In this example, the second power converter includes a first inductor L1, a first switch M1, the first unidirectional device D1, the second switch M2, and the second inductor L2.

[0078] A second load LED2 and a second capacitor C2 are coupled in series between the first input Input1 and a second further node. In this example, the second further node is directly coupled to the return node. The second load LED2 can form part of a power supply system. Therefore, the power supply system has a third output 3 and a fourth output 4, to which the second load LED2 is coupled. In this example, the third output 3 is directly coupled to the first input Input1. In this example, the fourth output 4 is directly coupled to the anode of the second unidirectional device D2 and the second capacitor C2. The second unidirectional device D2, the third switching element M3, and the third inductive element L3 are coupled in series between the fourth output 4 and the second further node. In this example, the third power converter includes the second unidirectional device D2, the third switching element M3, and the third inductive element L3. The controller can also be used to control the third power converter. This means that the controller can, for example, be used to control the third switching element M3. The first inductive element L1, the second inductive element L2, and the third inductive element are inductively coupled, so that the second power converter forms a flyback converter. The main difference from a conventional flyback converter is that on the second and third sides, namely, on the second and third inductor elements L2 and L3, switching elements are positioned to allow or prevent current from flowing to the corresponding first capacitor C1 or second capacitor C2. The current passing through the first inductor element L1 is reflected to the second and third inductor elements L2 and L3. The second and third switching elements M2 and M3 can be controlled to independently control the current flowing from the second and third inductor elements L2 and L3 to the first and second capacitors C1 and C2, respectively.

[0079] By coupling the series combination of the first inductive element L1 and the first switching element M1 between the first input and return nodes, control of the first switching element M1 can be simplified because a regulated bus voltage can be provided. When the bus voltage is lower than the voltage provided to the mains power converter, components can have lower voltage requirements, thereby allowing the selection of smaller and / or less expensive components.

[0080] In this example, the mains power converter is combined with two loads. It should be understood that the mains power converter can be combined with any number of loads. Figure 1 or Figure 2 Power supply systems that supply a single load with a power stage can also benefit from a mains power converter.

[0081] Figure 6 An example of another power supply system is shown. Figure 5 The same configuration is used to control the voltage across the first capacitor C1 and the second capacitor C2. Figure 5The difference in the power supply system is that the series combination of the first inductive element L1 and the first switching device M1 is placed at the second input Input2 and the return node. In the previous example, the second input Input2 was directly coupled to the first input Input1. In this example, the second input Input2 is coupled to the outputs of rectifiers D11, D12, D13, and D14. Therefore, the mains power converter does not need to provide the power conversion required by the second power converter or the power conversion required by the second power converter and the third power converter. Instead, electricity can be obtained directly from the mains. This can make the power conversion of the power supply system more energy-efficient.

[0082] The terms positive voltage and negative voltage are based on reference to ground (i.e., the return node). This means that the voltage on a capacitor can be considered positive or negative with respect to ground.

[0083] In the examples provided, the charging and discharging of a capacitor can also be understood as providing a positive voltage across the capacitor or providing a negative voltage across the capacitor. For example, when the average current provided by the load is greater than the current provided by the inductive element, the capacitor will effectively charge over time, and the voltage across the capacitor will increase and become positive. When the average current provided by the load is less than the current provided by the inductive element, the capacitor will effectively discharge over time, and the voltage across the capacitor will decrease and may even become negative.

[0084] In the example provided, one load may require a voltage greater than the bus voltage, while another load may require a voltage less than the bus voltage. The polarity of the corresponding capacitors can be adjusted so that the greater and lower voltages can match the bus voltage.

[0085] In the examples provided, the switching elements may be any type of semiconductor switches, such as transistors and MOSFETs.

[0086] In the examples provided, the inductive element may be a coil of a transformer. In a preferred example, a single transformer is used so that all inductive elements of the second power converter or the second and third power converters form a single inductor and are therefore inductively coupled to each other.

[0087] In the example provided, the unidirectional device can be, for example, a diode.It is also possible to use a transistor that is controlled to allow conduction in one direction and prevent conduction in the other direction.

[0088] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the present 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 power stage for powering a first load (LED 1), the first load (LED 1) being coupleable between a first output (1) and a second output (2), the power stage comprising: - a second output (2), a first further node, a second input (Input2), and a return node; - a first input (Input 1), for receiving a bus voltage; - said first output (1) coupled to said first input (input1) and arranged to be coupleable to said first load (LED1); - a first capacitor (C1) coupled between the second output (2) and the first further node and capable of being coupled in series with the first load (LED1); - A second power converter comprising: - a controller for controlling the second power converter; - a first inductive element (L1) and a first switching element (M1) coupled in series between the second input (Input2) and the return node; a second inductive element (L2) inductively coupled to the first inductive element (L1) and a first unidirectional component (D1) coupled in series between the second output (2) and the first further node, wherein the second power converter is arranged to supply power to the first capacitor (C1) A current having a polarity opposite to that of a current supplied to the first capacitor (C1) via the first load (LED1) is supplied.

2. The power stage of claim 1, wherein the second input (Input2) is directly coupled to the first input (Input1).

3. The power stage according to any of the preceding claims, wherein the first further node is coupled to the return node.

4. A power stage according to any one of claims 1 or 2, further comprising a linear current regulator connected in series between the first further node and the return node.

5. The power stage according to any of the preceding claims, wherein the current provided via the first load (LED1) is arranged for discharging the first capacitor (C1).

6. A power stage according to any of claims 1 to 4, wherein the current provided via the first load (LED1) is arranged for charging the first capacitor (C1).

7. The power stage according to any of claims 1 to 5, wherein the current provided via the second inductive element (L2) is arranged for charging the first capacitor (C1).

8. A power stage according to any one of claims 1 to 4 or claim 6, wherein the current provided via the second inductive element (L2) is arranged for discharging the first capacitor (C1).

9. A power stage according to any preceding claim, wherein the second power converter is a flyback converter.

10. A power supply system comprising: - A power stage according to any one of the preceding claims; a third output (3) coupled to the first input (Input 1) and arranged to be coupleable to a second load (LED 2), the second load (LED 2) being coupleable between the third output (3) and a fourth output (4); - a second capacitor (C2) coupled between the fourth output (4) and a second further node and capable of being coupled in series with the second load (LED2); - A third power converter comprising: a third inductive element (L3), a third switching element (M3), and a second unidirectional device (D2), the third inductive element (L3) being inductively coupled to the first inductive element (L1), the second unidirectional device (D2) being coupled in series between the fourth output (4) and the second further node, The second power converter further comprises a second switching element (M2) connected in series with the first unidirectional device (D1), The third power converter is arranged to provide a current to the second capacitor (C2), the current having a polarity opposite to that of a current provided to the second capacitor (C2) via the second load (LED2).

11. The power supply system according to claim 10, further comprising the first load (LED1) and the second load (LED2).

12. The power supply system according to any one of claims 10 to 11, wherein the first load (LED1) and / or the second load (LED2) is a lighting load. 13 . The power supply system according to claim 10 , wherein the lighting load is a semiconductor lighting load.

14. The power supply system according to claim 13, wherein a forward voltage of the first load (LED1) is different from a forward voltage of the second load (LED2).

15. The power supply system according to any one of claims 10 to 14, further comprising a mains power converter adapted to convert a mains input voltage into the bus voltage.

Images