WO2009153675A2

WO2009153675A2 - Power supply comprising multiple outputs

Info

Publication number: WO2009153675A2
Application number: PCT/IB2009/051907
Authority: WO
Inventors: Markus Schmid; Thomas A. Duerbaum; Gian Hoogzaad; Peter Laro; Johan B. D. Kuebrich
Original assignee: Nxp B.V.
Priority date: 2008-06-20
Filing date: 2009-05-08
Publication date: 2009-12-23
Also published as: WO2009153675A3

Abstract

The present application relates to a power factor correction stage, and more particularly, to a switch mode power supply comprising the liquid crystal display device. Thepower factor correction stage comprises a rectifying circuit connectable to an alternating current energysupply. The power factor correction stage comprises a transformer circuit configured to galvanically insulate the alternating current energy 5 supply from atleast one load. The transformer circuit comprises at least one power factor correcting inductor. The transformer circuit comprises at least one primary inductor formed by a first inductor. The transformer circuit comprises a first secondary inductor coupled to the primary inductor via a core. The transformer circuit comprises at least a second secondaryinductor coupled to the primary inductor via the core, wherein 10 the secondaryinductors are formed such that at least one output voltage of the transformer circuit is adjusted according to requirements of the at least one load.

Description

Power supply comprising multiple outputs

FIELD OF THE INVENTION

The present application relates to a power factor correction stage comprising a rectifying circuit connectable to an alternating current energy supply, and more particularly, to a switch mode power supply comprising the power factor correction stage and a liquid crystal display (LCD) system.

BACKGROUND OF THE INVENTION

In general, electrical devices, such as television receivers, computers and the like, require a power supply. The power supply, for instance a switch mode power supply (SMPS), may be provided to connect these devices to an alternating current energy supply, like the mains. Normally, the devices and the loads implemented within the devices respectively are driven by direct current (DC) and DC voltage respectively. Thus, the alternate current (AC) and AC voltage respectively of the mains has to be converted to direct current and DC voltage respectively. Converting can be performed in two stages, wherein in a first stage AC/DC conversion is performed and in a second stage DC/DC conversion is performed. In the first stage, a power factor correction (PFC) is necessary due to undesired harmonics generated by required non-linear components, such as rectifiers together with bulky electrolytic capacitors. These disturbances cause a reduced power factor which can be corrected by an active and/or passive PFC. The second stage is necessary, since different loads, requiring different voltage levels, which are not directly obtainable from the mains via a boost-converter which is typically used as PFC, are implemented within an aforementioned device.

Furthermore, a galvanic insulation between loads and the mains is required for safety reasons. The galvanic insulation can be realised within the first or second stage. For reducing effort, the galvanic insulation can be realised preferably within the first stage, the AC/DC conversion stage, in particular, for systems comprising several independently regulated mains insulated outputs. From document US 5,894,412, an apparatus comprising a power factor correction stage and a subsequently arranged transverter stage is known. Thereby, the transverter stage may be implemented for galvanic insulation of the mains from the loads. Furthermore, this apparatus includes a single output of the transverter stage. The output is a single DC voltage bus comprising a particular voltage level. For supplying loads with required voltage levels, several DC/DC converters can be connected to the single DC voltage bus. However, the transverter stage and the power factor correction stage are two independent stages.

In addition, the DC/DC conversion may be inefficient in case the required voltage level of a load is significantly below or above the voltage level of the single DC voltage bus. In such a case, a DC/DC conversion is costly due to the essential use of additional transformers, since otherwise the efficiency of the power supply is low. Moreover, a stand-by power and stand-by voltage respectively is not provided.

The single DC voltage bus typically comprises a relatively high voltage level due to efficiency reasons. It may be advantageous to get the highest voltage level and use suitable down converters for the remaining lower voltage levels. Associated with a high voltage level are high voltage stress on the used components as well as the capacitor of the DC voltage bus must fulfil high voltage requirements.

It is one object of the present application to provide a power supply comprising an increased efficiency. Another object is to provide such power supply in a compact design. A further object is to provide a power supply comprising a stand-by voltage for high efficient stand-by operation. Another object is to reduce high voltage stress on components of the system. A further object is to reduce high voltage requirements of the capacitor of a DC voltage bus. A further object is to reduce power consumption.

SUMMARY OF THE INVENTION

These and other objects are solved by a power factor correction stage, comprising a rectifying circuit connectable to an alternating current energy supply. The power factor correction stage comprises a transformer circuit configured to galvanically insulate the alternating current energy supply from at least one load. The transformer circuit comprises at least one power factor correcting inductor. The transformer circuit comprises at least one primary inductor formed by a first inductor. The transformer circuit comprises a first secondary inductor coupled to the primary inductor via a core. The transformer circuit comprises at least a second secondary inductor coupled to the primary inductor via the core, wherein the secondary inductors are formed such that at least one output voltage of the transformer circuit is adjusted according to requirements of the at least one load.

The power factor correction stage according to the present application can be employed in several applications. Furthermore, the power factor correction stage can be connected to the alternating current energy supply. More particularly, an arranged rectifying circuit can be connected to an alternating current energy supply. The energy supply may generate an AC voltage or current. According to an embodiment of the present application, the alternating current energy supply may be the mains supplying an AC voltage and/or AC current.

The AC voltage or current may be converted to a rectified mains or pulsating DC voltage or current using a suitable rectifying circuit. For instance, the rectifying circuit may be a full wave rectifier comprising diodes. It shall be understood that other rectifying circuits are also possible. Furthermore, the power factor correction stage may serve for correcting a power factor. In a power supply, disturbances, like harmonics, can occur. In particular, nonlinear components, like the rectifying circuit and/or a rectifying circuit together with bulky electrolytic capacitors can generate undesired harmonics. These disturbances may reduce the power factor. Contrary to expectations, it is found according to the present application that at least one part of the transformer circuit can be used for power factor correction. A transformer circuit can be also called a topology. The transformer circuit comprises at least one power factor correcting inductor. More particularly, the transformer circuit may comprise a number of inductors, wherein at least one of the inductors is responsible for power factor correction. It shall be understood that more than one inductor can be responsible for power factor correction. The actual inductor of the number of inductors acting for power factor correction may depend on the particular realization, especially the topology of the transformer circuit. The transformer circuit according to the present application improves the power factor to at least comply with regulations. It may be also possible that further components are arranged for power factor correction.

For safety reasons, loads of an application and the alternating current energy supply must be galvanically separated from each other. According to the present application, the transformer circuit can be also used to realize the required galvanic insulation. An additional stage for galvanic insulation can be omitted. A transformer circuit may be particularly suitable for a galvanic insulation, since the energy may be transferred magnetically. It is found, according to a preferred application that a compact design can be achieved by using at least one inductor not only for power factor correction but also as an inductor of the transformer circuit, like a primary inductor or at least one inductor arranged at the secondary side of the transformer circuit. The arrangement of additional inductors can be avoided. The costs of construction as well as required space can be reduced without limiting the performance of the present voltage source.

It is further found according to the application that the already required transformer circuit can be also used to improve the efficiency of the power factor correction stage and/or an overall power conversion system significantly by reconfiguration of the transformer circuit. The primary inductor of the transformer circuit can be coupled to at least two secondary inductors of the transformer circuit via a common core. As a core, any suitable medium can be used. Such a voltage transformation is low- loss and can be implemented without great effort. More particularly, it is found according to the application that the efficiency of the power factor correction stage and/or the overall power conversion system can be significantly increased in case the primary inductor is coupled to the secondary inductors such that at least one output voltage of the transformer circuit is adjusted according to requirements of at least one load. Applications may comprise several loads, which may require different voltage levels. The at least one output voltage can be adjusted according to at least the voltage level of one load. This means that the voltage difference between the required voltage level and the generated voltage level may be small. According to the present application the voltage of every multiple output can be optimized to at least one of the loads and/or dc-dc converters and the load connected to it.

According an embodiment of the present application, it may be advantageously to adjust both output voltage levels of the transformer circuit according to different requirements of the at least two loads. It should be denoted that the term loads could also mean a group of loads comprising at least similar voltage requirements. An output voltage of the transformer circuit can be adjusted by using turn ratios between primary and secondary inductors. More particularly, the second inductors may comprise a different number of turns, and thus, the turn ratios may differ from each other.

The efficiency of the present power factor correction stage and/or the overall power conversion system can be increased meanwhile the power loss of the power factor correction stage and/or the overall power conversion system can be reduced. Furthermore, high voltage stress on the components can be avoided as well as the voltage requirements of at least one bus capacitor, preferably all bus capacitors, can be reduced. Additionally, loads can be connected with a high efficiency and without high effort.

According to a further embodiment of the present application, at least one part of the transformer circuit may be formed in a flyback converter topology, forward converter topology, half-bridge converter topology and/or resonant converter topology. By way of example, in a flyback converter topology, the secondary side may comprise a diode for avoiding a negative current and a capacitor for storing energy transferred by the transformer and for smoothing the voltage. On the primary side, a switching element, like a suitable transistor or the like can be implemented. An adequate signal, like a pulse width modulated (PWM) signal can be used for driving the switching element. By activating and deactivating the switching unit, a pulsating current can be created for transferring energy. According to the different topologies, different inductors of the transformer circuit may be the power factor correcting inductor and may be provided for power factor correction. The PWM signal can be generated in order to improve the power factor at least according to the regulation/standards. By way of example, in case a flyback converter topology is implemented, the primary inductor may be provided for power factor correction. In contrary, in a forward converter topology or half-bridge converter topology, inductors on the secondary side, like the additional inductors, may be responsible for power factor correction. It may be advantageously to implement the total transformer circuit in a same topology. It shall be understood that according to other variants of the present application, further topologies which serve the purpose can also be employed. A smoothed DC voltage particular suitable for further processing can be generated.

Furthermore, according to another embodiment of the present application, at least one output voltage may be connected to a DC/DC converter. The DC/DC converter may be configured to connect at least one load to the transformer circuit. For supplying loads with required voltage levels, DC/DC converters can be implemented between DC voltage busses and the loads. Different voltage output levels may cause that the arranged DC/DC converters can be dimensioned to work efficiently. More particularly, great voltage differences between voltage levels requirements of the loads and the supplied voltages, which can cause high power losses, can be avoided due to the generation of two or more voltage levels, since these voltage levels are adjusted to the voltage requirements of the loads. A DC/DC converter may be configured such that it may resemble a DC current source. Such a DC/DC converter may be in particular suitable as LED drivers or the like. In a further embodiment of the application, the power factor correction stage may comprise at least a third secondary inductor, which may be coupled via the core to the primary inductor of the transformer circuit. In addition, it is also possible to use further secondary inductors. The number of secondary inductors can be adapted according to the range of voltage requirements of implemented loads. The respective output voltage levels can be used for a plurality of functions.

It is found, according to the present application that the efficiency of a stand-by supply can be significantly increased, in case the stand-by voltage comprises a suitable voltage level. According to an embodiment, the third secondary inductor may be arranged for generating such a suitable stand-by voltage. The stand-by terminal can be integrated within the power factor correction stage. As mentioned above, the voltage applied at the output of a secondary inductor can be generated by using a suitable turn ratio of the number of turns of the primary and secondary inductor. The voltage level can be set such that stand-by operation can be performed as efficient as possible. The use of a DC voltage provided for supplying several loads as well as stand-by voltage can be avoided. According to further embodiments of the present application, the power factor correction stage may comprise at least one output voltage, which may be connectable to at least one linear regulator. The stand-by voltage can be used in combination with further components, like the linear regulator. A linear regulator may be provided for regulating at least one output voltage meanwhile further output voltages can be cross- regulated. A high flexibility can be achieved. It shall be understood that according to other variants of the present application, additional uncritical loads can be also directly supplied from one or more outputs of the AC to DC conversion stage.

What is more, the power factor correction stage may comprise at least one switching device according to another embodiment. The switching device may be configured to disconnect the loads from the transformer circuit and alternating current energy supply respectively. In case of the stand-by operation, the further loads can be disconnected from the alternating current energy supply by the at least one switching device. In particular, for avoiding unnecessary power consumption the further components, like loads and DC/DC converters respectively can be disconnected by a suitable switching device. By way of example, for each load one switching device can be arranged.

Another possibility for switching off the loads in case of stand-by operation is to use a high voltage winding, which can be switched to the low voltage stand-by output. By doing this the voltage of all outputs can be reduced by the factor of the high voltage winding to the output voltage used for stand-by, e.g. if the high voltage winding supplies 30V and stand-by is at 5 V, all voltages would be reduced by a factor of 6. This reduction may be sufficiently large to deactivate the other loads, especially in case of dc-dc converters the under- voltage lock-out of those will disable their operation. According to a further embodiment, the power factor correction stage may comprise a driving unit, which may be arranged for driving the power factor correction stage in a burst mode, a frequency reduced mode, Ipeak control or a combination of burst mode and frequency reduced mode. These modes may increase the efficiency. Another aspect of the application is a switch mode power supply wherein the switch mode power supply uses an AC to DC conversion stage that provides for power factor correction, galvanic insulation and multiple different output voltages as well. Thereby, the switch mode power supply may be configured for supplying different loads. The switch mode power supply may comprise an integrated stand-by power supply. A further aspect of the present application is a liquid crystal system (LCD) device comprising an AC to DC conversion stage that provides for power factor correction, galvanic insulation and multiple different output voltages. By way of example, the device may be an LCD television, monitor or the like. In particular, the power factor correction stage according to the application can be employed into an LCD television comprising light emitting diodes (LED) as backlights. The required voltage levels of the LED drivers may be low. Thus, using at least a second DC voltage bus comprising a small voltage level according to embodiments of the present application may be advantageously. More particularly, the LCD device according to an embodiment of the present application may comprise several voltage busses comprising different voltage levels. The voltage bus comprising a different voltage level may be arranged for the lighting of the LCD, the logic of the LCD and/or other functions. Employing the power factor correction stage into an LCD device may cause an easily handling with high voltage level differences between different loads. According to a further embodiment, the liquid crystal display system may further comprise a backlight unit comprising at least two LEDs, which may comprise different colors, wherein for each color a different voltage level may be provided.

Furthermore, the liquid crystal system according to another embodiment may comprise a backlight unit comprising at least two LED strings, which may comprise different colors, wherein for each LED string a different voltage level may be provided. These and other aspects of the present patent application become apparent from and will be elucidated with reference to the following figures. The features of the present application and of its exemplary embodiments as presented above are understood to be disclosed also in all possible combinations with each other.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Figures show:

Fig. 1 a first embodiment of the switch mode power supply comprising the power factor correction stage according to the present application;

Fig. 2 a second embodiment of the switch mode power supply comprising the power factor correction stage according to the present application.

Like reference numerals in different Figures indicate like elements.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following detailed description of the present application, exemplary embodiments of the present application will describe and point out the increased efficiency, compact design and simple construction of a power factor correction stage according to the application. Fig. 1 shows a first simplified embodiment of the switch mode power supply comprising the power factor correction stage according to the present application. The shown power factor correction stage comprises an alternating current energy supply 10, like the mains. The alternating current energy supply 10 may generate an AC voltage and/or AC current. The frequency and the voltage level supplied by the alternating current energy supply 10 may depend on the particular mains, like 50 Hz mains or 60 Hz mains.

Directly attached to the alternating current energy supply 10 is a power factor correction stage 12. This device 12 may serve to convert the input AC voltage to a DC voltage and to correct the power factor. Furthermore, the power factor correction stage 12 may provide for a galvanic insulation between the alternating current energy supply 10 and at least one further component, preferably all further components. In further power processing stages, a galvanic insulation can be omitted. A galvanic insulation may be required for safety reasons. For reducing effort and costs, it is preferred to implement the galvanic insulation within the power factor correction stage 12. The power factor correction stage 12 comprises a transformer circuit including at least one power factor correcting inductor. A possible and detailed implementation of the power factor correction stage 12 is elucidated subsequently.

As can be seen from Fig. 1, two DC voltage busses 14a and 14b and a further port 18 comprising a DC voltage are provided as outputs of the power factor correction stage 12. The power factor correction stage 12 may provide several output voltage levels. In the shown embodiment, each output 14a, 14b and 18 may comprise another voltage level suitable for further processing. It may be also possible, according to other variants of the present application that more than the depicted outputs are provided. The output voltage applied at port 18 may serve as a stand-by voltage. This stand-by voltage can be generated such that it may be particular suitable for stand-by operation. The stand-by output port 18 can be integrated within the power factor correction stage 12 without the need for further converting, which may reduce effort of implementation and increase efficiency during stand-by operation of the presented power conversion system significantly.

Furthermore, a first DC/DC converter 16a is connected to the first voltage bus 14a and a second DC/DC converter 16b is connected to the second voltage bus 14b. It shall be understood that, according to other variants of the present application, a plurality of DC/DC converter can be connected to the DC voltage busses 14a, 14b. In addition, loads 20a, 20b comprise a connection to the respective DC/DC converters 16a, 16b. These loads 20a, 20b may differ in their voltage requirements. More particularly, the required voltage level of the respective loads 20a, 20b may be different.

The difference between the voltage level required by a particular load 20, 20b and the voltage level provided by the respective voltage bus 14a, 14b can be reduced, since the output voltage can be adjusted according to the particular requirements of the load 20a, 20b. Large voltage differences between requirements of the loads and the respective voltage busses may be avoided. The efficiency of the DC/DC conversion is particular considerable. It shall be understood that more than one DC/DC converter can be attached to each voltage bus 14a, 14b in case the loads being supplied require similar voltage levels. It is also possible, according to other embodiments of the present application that further voltage busses comprising different voltage levels are arranged. Moreover, according to further embodiments of the application, the third output voltage can be connected to further circuits, such as a linear regulator. Such a linear regulator may be employed for regulating a particular output voltage It shall be understood that one or more outputs can be directly used, e.g. for driving a fan or the like. In Fig. 2, a second simplified embodiment of the switch mode power supply comprising the power factor correction stage according to the present application is depicted. One possible implementation of the power factor correction stage 12 is shown. As can be seen from Fig. 2, the alternating current energy supply 10 is connected to a rectifying circuit 22. The rectifying circuit 22 may be a full wave rectifier comprising diodes or the like.

Furthermore, the power factor correction stage 12 comprises a filtering unit 24. The filtering unit 24 may be attached for EMI filtering. In the shown embodiment, merely a capacitive element is arranged. However, it shall be understood that further components can be additionally arranged for filtering. A filtering unit 24 is needed for fulfilling EMI requirements.

Furthermore, a transformer circuit 26 is arranged within the power factor correction stage 12. The shown transformer circuit 26 is formed in a flyback converter topology. However, according to further variants of the application, other topologies, such as a forward converter topology, a half-bridge converter topology, resonant converter topology, combined topologies or the like, can also be implemented.

The depicted transformer circuit 26 comprises a primary inductor 28 and three secondary inductors 32a to 32c. Thereby, the primary inductor 28 is formed by the inductor 28. It is found according to the present application that a transformer circuit 26, in particular at least one power factor correcting circuit included within the transformer circuit 26, can be used for power factor correction. More particularly, according to the shown embodiment, the primary inductor 28 may be the power factor correcting inductor. However, it shall be understood that according to other topologies of the system according to the present application, inductors at the secondary side may also serve for power factor correction. Moreover, each of these inductors 28 and 32a to 32c may comprise a particular number of turns Np, Ns₁, Ns2 and Ns3. Furthermore, the transformer circuit 26 encompasses a common core 30, which can be formed of any suitable material. The secondary inductors 32a to 32c may be magnetically coupled to the primary inductor 28 and the energy can be transmitted by the magnetic flux. What is more, the secondary inductors 32a to 32c and the primary inductor 28 are galvanically separated to each other. Thus, the power factor correction stage 12 is not only provided for power factor correction but also for providing a galvanic insulation between the mains and the further power processing stages. In series to the primary inductor 28, a switching element 34 is arranged. The switching element 34 may be a semiconductor switch, for instance a bipolar transistor or a field effect transistor. Other switching elements are also possible. A controlling unit for driving the switching element 34 by a suitable signal, like a PWM signal, is not shown in Fig. 2 for lucidity reasons. On the secondary side of the transformer circuit 26, diodes 36a to 36c and capacitors 38a to 38c are arranged, wherein the capacitors 38a to 38c may provide for storing energy and the diodes 36a to 36c for rectifying the voltage. The diodes 36a to 36c may serve to avoid a negative current. According to other variants of the present application, synchronous rectifiers as well as a bi-directional flyback topology can be also implemented. At each output of the transformer circuit 26, a different output voltage level may be obtained. Further arranged components are already known from Fig. 1.

In the following, the functioning of the switch mode power supplies according to Fig. 1 and 2 is pointed out in depth. The AC voltage generated by the alternating current energy supply 10 can be rectified by the rectifying circuit 22. The power factor correction needed according to regulations and standards can be obtained due to correspondingly chosen PWM pattern driving the power switch at the primary side. When the switching element 34 is conductive, a current flows through the primary inductor 28 of the transformer circuit 26 and may induce an increased magnetic flux. In other words, energy is stored into the transformer circuit 26 during the conductive stage. At the same time, each diode 36a, to 36c connected to the respective secondary inductor 32a to 32c may avoid a current flow since the voltages across secondary inductors 32a to 32c of the transformer circuit 26 are negative. Moreover, at the same time the capacitors 38a to 38c may supply their stored energy to the further components, such as the DC/DC converters 16a, 16b. When the switching element 34 is not conductive, a current cannot flow through the primary inductor 28. However, the primary inductor 28 tries to maintain a current flow and respectively it tries to act against the changing of the magnetic flux. Thus, a current flow starts through the diode 32a to 32c, which are no longer reversed-bias and the stored energy is transferred to the further components and to the capacitor 38a to 38c. The capacitors 38a to 38c are reloaded.

As stated above, each secondary inductor 32a to 32c comprises a particular number of turns Ns₁, Ns2 and Ns3, which may be different resulting in different turn ratios ni= Np/Nsi, n₂ ⁼ Np /Ns₂ and n3= Np /Ns₃. The DC voltage obtained at the outputs of the transformer circuit 26 can be adjusted by the turn ratios n_{l s} n₂ and n₃. In case, the turn ratios n_{l s} n₂ and n₃ are different, different DC voltage levels are provided at the outputs of the transformer circuit 26. The turn ratios n_{l s} n₂ and n₃ are adjusted corresponding to voltage levels required by the loads 20a and 20b. The employed DC/DC converters 16a, 16b may comprise a high efficiency, and high voltage stress on the components can be avoided as well as the voltage requirements of the bus capacitors can be reduced.

One of the average values of the voltage obtained at the outputs of the transformer circuit 26 can be controlled via a feedback loop adapting the PWM pattern. The other output voltages can be cross-regulated due to the coupling of the transformer to produce voltages according to the chosen turn ratios. Alternatively, a weighted sum of the deviation from two or more outputs can be used for the feedback.

In case of using the stand-by voltage, the further loads 20a, 20b can be disconnected from the transformer circuit 26 and input voltage 10 respectively by a switching device. For lucidity reasons, the switching device is not shown in Fig. 2. Any suitable switching device can be implemented, which provides that a current flow through the loads 20a, 20b can be avoided. For each load, a switching device can be arranged. Another possibility is to couple at least one of the higher output voltage windings to the low output voltage winding required during stand-by operation. Then the other output voltages may drop to a value, which is low enough to deactivate the connected loads or, to deactivate the connected DC/DC converters, as shown in the present embodiment. In case the highest output voltage may not comprise enough turns, a separate winding could be also used for this purpose.

In addition, a driving unit (not shown) can be implemented for driving the power supply in case of a stand-by operation in a suitable mode. Such modes may be a burst mode, a frequency reduced mode or a combination of both. These modes are particular suitable to increase the efficiency of the power supply. According to further variants of the application, other modes can also be used.

The present power factor correction stage provides for power factor correction, galvanic insulation and multiple different output voltages as well.

Claims

CLAIMS:

1. A power factor correction stage, comprising: a rectifying circuit (22) connectable to an alternating current energy supply (10), a transformer circuit (26) configured to galvanically insulate the alternating current energy supply (10) from at least one load (20a, 20b), and - wherein the transformer circuit (26) comprises at least one power factor correcting inductor (28, 32a, 32b, 32c), wherein the transformer circuit (26) comprises at least one primary inductor (28) formed by a first inductor (28), wherein the transformer circuit (26) comprises a first secondary inductor (32a) coupled to the primary inductor (28) via a core (30), wherein the transformer circuit (26) comprises at least a second secondary inductor (32b) coupled to the primary inductor (28) via the core (30), and wherein the secondary inductors (32a, 32b) are formed such that at least one output voltage of the transformer circuit (26) is adjusted according to requirements of the at least one load (20a, 20b).

2. The power factor correction stage according to claim 1, wherein at least one part of the transformer circuit (26) is formed in at least one of:

A) flyback converter topology, B) forward converter topology,

C) half-bridge converter topology,

D) resonant converter topology.

3. The power factor correction stage according to claim 1, wherein at least one output voltage is connectable to a DC/DC converter (16a, 16b) configured to connect at least one load (20a, 20b) to the transformer circuit (26).

4. The power factor correction stage according to claim 1, wherein at least one output voltage is connectable to at least one linear regulator.

5. The power factor correction stage according to claim 1, further comprising: at least a third secondary inductor (32c) coupled via the core (30) to the primary inductor (28), - wherein the third secondary inductor (32c) is arranged for generating a standby voltage.

6. The power factor correction stage according to claim 5, further comprising at least one switching device configured to disconnect the loads (20a, 20b) from the transformer circuit (26).

7. The power factor correction stage according to claim 5, wherein the third secondary inductor (32c) is coupled to at least one further secondary inductor (32a, 32b) comprising a higher voltage level.

8. The power factor correction stage according to claim 5, further comprising a driving unit arranged for driving the power supply in at least one of:

A) burst mode,

B) frequency reduced mode, C) combination of burst mode and frequency reduced mode,

D) Ipeak control.

9. The power factor correction stage according to claim 1, wherein the alternating current energy supply (10) is mains supplying an AC voltage and/or AC current.

10. A switch mode power supply supplying different loads wherein the switch mode power supply uses an AC to DC conversion stage that provides for power factor correction, galvanic insulation and multiple different output voltages.

11. A switch mode power supply according to claim 10 with an integrated stand-by power supply.

12. A liquid crystal display system comprising an AC to DC conversion stage that provides for power factor correction, galvanic insulation and multiple different output voltages.

13. The liquid crystal display system according to claim 12, further comprising at least one voltage bus having a different voltage level for at least one of:

A) lighting,

B) logic.

14. The liquid crystal display system according to claim 12, further comprising a backlight unit comprising at least two LEDs being different in color, wherein for each color a different voltage level is provided.

15. The liquid crystal system according to claim 12, further comprising: - a backlight unit comprising at least two LED strings being different in color, wherein for each LED string a different voltage level is provided