DE102010027492A1 - Voltage converter i.e. alternating-current to direct-current converter, for e.g. electronic device, has flyback converter connected with alternating-current terminal, so that voltage is applied between primary side connection points - Google Patents

Abstract

The converter (1) has a flyback converter (13) comprising a primary-side port (13p) with two primary side connection points, and a secondary-side port (13s) with two secondary connection points. The primary-side port is connected with a primary winding of a storage transformer (14) over electronic switches (17, 18), which are controlled by a control device. The flyback converter is connected with an alternating-current (AC) terminal (12) in such a manner that alternating voltage (uN) is applied between the primary side connection points of the flyback converter.

Description

The invention relates to a voltage converter.

For power supply information processing facilities or general electronic devices from the single-phase AC power supply units are usually used with an input-side pulse rectifier circuit and a downstream potential-separating DC / DC converter. The pulse rectification circuit has by appropriate control a sinusoidal current consumption, d. H. ohmic network behavior and a regulated output voltage (DC link voltage), which is applied to the input of the DC / DC converter. About the turns ratio of the transformer and an output voltage-dependent control of the duty cycle, the DC link voltage is converted into a constant, adapted to the load voltage This concept is characterized by a clear functional classification and thus by simple feasibility. However, there are three converter stages, i. H. arranged a diode bridge rectification, a non-isolated DC / DC converter with boost converter function and the final DC / DC conversion with potential separation in the power flow, resulting in a relatively low efficiency and a relatively high implementation costs result.

In particular, at low output powers in the range up to several 100 W, therefore, only two-stage concepts are often used, which combine the functions power factor correction and potential separation and load voltage control, so integrate both DC / DC converter stages. Here, a bridge rectifier and subsequently, for example, a flyback converter is arranged on the input side, which i. a. is operated with a constant on-time over the mains period and at the boundary of continuous and discontinuous input current (Boundary Mode Control, "BMC") or with constant on-time and constant duration of the pulse period. For BMC, the electronic switch, for example a power transistor, of the flyback converter is always switched on again after the constant switch-on time, when the current which is transferred to the secondary side when the power transistor is switched off is completely dissipated. Thus, the input current of the bridge rectifier has a sawtooth shape with a sinusoidal envelope and a sinusoidal local mean. The switching-frequency harmonics of the input current are kept away from the mains by an EMC filter with a low-pass characteristic. This results in again a sinusoidal, lying in phase with the mains voltage mains current. Alternatively, the function of the rectifier bridge and the non-isolated boost converter DC / DC converter can be combined to form a so-called bridge less PFC boost rectifier. The Bridge less PFC Boost Rectifier has a two-stage design consisting of a Power Factor Correction ("PFC") rectifier to form a sinusoidal input current and a subsequent floating DC / DC converter.

However, in both cases there is still a relatively high implementation effort and there is no longer a three-stage, but still two-stage energy conversion with limited efficiency.

The object of the invention is therefore to provide a voltage converter with improved properties.

According to the invention, this object is achieved by the subject matter of claim 1. A voltage converter with a DC connection, an AC connection and a flyback converter is proposed, wherein the flyback converter comprises a storage transformer with galvanically separated primary and secondary winding, a primary-side connection comprising a first and a second primary side Connection point, a secondary-side terminal comprising a first and a second secondary-side connection point, at least one electronic switch, via which the primary side terminal of the flyback converter is connected to the primary winding of the memory transformer, and a control circuit for controlling the at least one electronic switch, wherein the flyback converter is connected to the AC power connection such that an AC voltage is applied between the first and second primary-side connection point of the flyback converter.

The voltage converter according to the invention does not require any additional elements to rectify the AC voltage applied to the AC connection. Depending on the configuration, rectifier diodes can be saved so that, on the one hand, the complexity of the components decreases and, on the other hand, less electrical losses occur, so that an improvement in efficiency is achieved.

It can be provided that the primary winding of the memory transformer has two terminals, a first and a second terminal, and a center tap, that the first primary-side connection point is connected via a first current path comprising a first electronic switch to the first terminal of the primary winding of the memory transformer, in that the second primary-side connection point is connected to the second connection of the primary winding of the memory transformer via a second current path comprising a second electronic switch, and the center tap is connected to the second primary-side connection point via a third current path.

It can further be provided that the control device is designed such that it controls the first and the second electronic switch during the positive AC half-wave with a different control signal than during the negative AC half-wave, so that the second current path during the positive half cycle locked is and the first current path is disabled during the negative half cycle. The control device may preferably be integrated in the voltage converter.

But it is also possible to extend it as an external module or to provide an interface for control via a computer.

Further, it is possible that the control device is designed such that it controls the first and the second electronic switch such that during the positive AC half-wave, the positive AC half-wave is modulated by the first electronic switch according to a high-frequency signal and during the negative AC half-wave the negative AC half-wave is modulated by the second electronic switch according to the high-frequency signal. The frequency of the high-frequency signal may be 10 to 100 times the value of the alternating voltage applied to the voltage converter. This value may also be preferred for the embodiments described below. Due to the high frequency, it is possible to make the memory transformer very small.

The electronic switch may consist of a series connection of a diode and a switching transistor. In this case, the diode may be provided to protect the switching transistor from excessive negative reverse voltages. In accordance with voltage-proof transistors, the diode is unnecessary.

It can be provided that the primary winding of the memory transformer has two terminals, a first terminal and a second terminal, that the first primary-side terminal is connected via a first current path comprising an electronic switch to the first terminal of the primary winding of the memory transformer, and that Weather may be provided that the primary winding of the memory transformer two terminals, a first terminal and a second terminal, that the first primary-side terminal point via a first current path comprising a first current path electronic switch and a second electronic switch is connected to the first terminal of the primary winding of the memory transformer, and that the second primary-side connection point via a second current path with the two Iten connection of the primary winding is connected.

It can be provided that the first electronic switch and the second electronic switch consist of a counter-series circuit of two switching transistors with respective antiparallel freewheeling diode or a counter-series circuit of second IGBTs or MOSFET transistors.

Further, it is possible that the first electronic switch and the second electronic switch consist of a counter-parallel connection of two bipolar blocking switching transistors.

The control device can be designed such that it controls the first and the second electronic switch such that during the positive AC half-wave, the positive AC half-wave is modulated by the first electronic switch according to a high-frequency signal and during the negative AC half-wave negative AC half-wool is modulated by the second electronic switch according to the high-frequency signal, wherein when using MOSFET transistors for the realization of the switch of each unmodulated switch for minimizing the conduction losses advantageously remains in the on state.

Other designs are directed to the formation of the secondary circuit.

It can be provided that the secondary winding of the memory transformer has two terminals, a first and a second terminal, that the first secondary-side connection point is connected to the first terminal of the secondary winding of the memory transformer via a first current path comprising a diode, and that the second secondary-side connection point is connected via a second current path to the second terminal of the secondary winding.

It can further be provided that the secondary winding of the memory transformer has two terminals, a first and a second terminal, that the first secondary-side connection point is connected via a first bridge current path of a diode bridge to the first terminal of the secondary winding of the memory transformer, and that the second secondary-side connection point is connected via a second bridge current path of the diode bridge to the second terminal of the secondary winding.

In a further advantageous embodiment it can be provided that the secondary winding of the memory transformer has two terminals, a first and a second terminal, and a center tap, that the first secondary-side connection point via a first current path comprising a first diode to the first terminal of the secondary winding of the memory transformer and is connected via a second current path comprising a second diode to the second terminal of the secondary winding of the memory transformer and that the second secondary-side connection point is connected via a third current path to the center tap, wherein in the center point connection or in the connection to the positive secondary side connection point Advantageously, a further switching transistor can be inserted, which is only turned on when the storage transformer is to deliver energy to the secondary side. By arranging this switch, the operating range of the system is increased with respect to the possible level of the output voltage. An analogous same device, d. H. a switch in the negative or positive connection with the secondary-side connection point can advantageously also be provided for the execution of the secondary-side rectification as a diode bridge.

The secondary winding of the memory transformer may also have two terminals, a first and a second terminal, and it may be provided that the first secondary-side connection point is connected to the first terminal of the secondary winding of the memory transformer via a first current path comprising a third electronic switch The control unit may be equipped to control the third electronic switch to turn on and off in accordance with a high-frequency signal.

In a further advantageous embodiment it can be provided that the secondary winding of the memory transformer has two terminals, a harvesting and a second connection, that the first secondary-side connection point via a first bridge current path formed with a fourth electronic switches bridge with the first terminal of the secondary winding of the memory transformer is connected, and that the second secondary-side connection point is connected via a second bridge current path of the formed with the fourth electronic switches bridge to the second terminal of the secondary winding.

It can further be provided that the fourth electronic switch consist of a switching transistor with antiparallel freewheeling diode or an IGBT or MOSFET transistor.

The secondary winding of the memory transformer may also have two terminals, a first and a second terminal, and a center tap, wherein it may further be provided that the first secondary-side connection point via a first current path comprising a fifth electronic switch connected to the first terminal of the secondary winding of the memory transformer is connected via a second current path comprising a sixth electronic switch to the second terminal of the secondary winding of the memory transformer and the center tap is connected via a third current path to the second secondary-side connection point.

The control device can be designed such that it controls the fourth or fifth and sixth electronic switches in such a way that during the positive AC half-wave a first group of the fourth electronic switches or the fifth electronic switches are switched on and off in accordance with a high-frequency signal and during the negative AC half cycle, a second group of the fourth electronic switch or the sixth electronic switch are turned on and off.

The control device can further be designed such that, after filtering switching-frequency components of the input current through an EMC filter, a mains voltage-proportional or sinusoidal input current at the AC connection results. The EMC filter, which may be an LC element, is provided to eliminate the input current of the flyback converter, which may have a pulse shape with a sinusoidal envelope, from harmonics, so that no disturbing effects on the network enter.

The voltage converter according to the invention enables a multiplicity of embodiments by combining the designs provided for the primary side and the secondary side. If electronic switches are used instead of the diodes on the secondary side, as described above, it is possible to use the voltage transformers not only as AC / DC converters but also as DC / AC converters with appropriate control. Thus, it is possible to feed on the DC side energy accumulating, for example, braking energy in an AC mains.

The invention will now be explained in more detail with reference to exemplary embodiments. Show it

1 A first embodiment of a voltage converter according to the invention;

2 Diagrams for controlling the voltage transformer in 1 ;

3 A second embodiment of a voltage converter according to the invention;

4 A third embodiment of a voltage converter according to the invention;

5 Diagrams for controlling the voltage transformers in 3 and 4 ;

8th A fourth embodiment of a voltage converter according to the invention;

7 Diagrams for controlling the voltage transformer in 6 ;

8th A fifth embodiment of a voltage converter according to the invention;

9 A sixth embodiment of a voltage converter according to the invention;

10 Diagrams for controlling the voltage transformers in 8th and 9 ;

11 a seventh embodiment of a voltage converter according to the invention;

12 an eighth embodiment of a voltage converter according to the invention;

13 A ninth embodiment of a voltage converter according to the invention.

1 shows a voltage converter 1 with a DC connection 11 , an AC power connection 12 and a flyback converter 13 , The voltage converter works as an AC / DC converter.

The flyback converter 13 has a storage transformer 14 with a primary winding and a galvanically isolated secondary winding. A primary-side connection 13p of the flyback converter 13 has a first and a second primary-side connection point. A secondary-side connection 13s has a first and second secondary-side connection point.

Between the first and second primary-side connection point of the primary-side connection 13p is an AC voltage. The connection 13p is in the in 1 illustrated embodiment by a capacitor 15 of an LC element, which is bridged out of the capacitor 15 and a throttle 16 is formed. The throttle 16 lies in a first current path between the first primary-side connection point of the primary-side connection 13 and a first connection point of the AC power connection 12 , A second current path connects the second primary-side connection point of the primary-side connection 13 with a second connection point of the AC power connection 12 , At the AC connection 12 is a mains voltage U _N on. The LC element from throttle 16 and capacitor 15 is intended to protect against EMC radiation.

The primary winding of the storage transformer 14 has a first and a second port and a center tap. The first primary-side connection point of the flyback converter 13 is via a first power path, which has a first electronic switch 17 comprising, with the first terminal of the primary winding of the memory transformer 14 connected. The first primary-side connection point is further connected via a second current path, which is a second electronic switch 18 comprising, with the second terminal of the primary winding of the storage transformer 14 connected. The second electronic switch 19 is in the opposite direction to the first electronic switch 18 connected. The second primary-side connection point of the flyback converter 13 is via a third current path with the center tap of the primary winding of the memory transformer 14 connected. The electronic switches 17 and 18 are in the in 1 illustrated embodiment of the series connection of a diode and a switching transistor formed. The switching transistor has a control terminal 17s respectively. 18s on. On the diode can also be with appropriate design of the switching transistor after 2 be waived.

The secondary winding of the storage transformer 14 has a first and a second connection. The first secondary-side connection point of the flyback converter 13 is via a first current path, which is a diode 19 includes, connected to the first port. The second secondary-side connection point of the flyback converter 13 is connected to the second terminal via a second current path. The first and the second secondary-side connection point of the flyback converter 13 form the DC connection 11 of the flyback converter 13 and are with a capacitor 20 bridged. The capacitor 20 is provided as a storage capacitor and advantageously designed as an electrolytic capacitor.

To protect against overvoltages, the two partial windings of the primary winding of the memory transformer 14 through a voltage limiter 21 be bridged, which is formed in the illustrated embodiments of an opposite series circuit of a diode and a zener diode.

In a flyback converter, in a conducting phase in which the electronic switch is closed, a small amount of energy is stored in the magnetic field of the storage transformer and removed in a blocking phase, in which the electronic switch is opened, from an electrical load arranged at the DC connection. Thereby energy is in the condenser 20 cached, so that even in the conducting phase, in which the magnetic field is built, electrical energy can be removed at the DC connection.

The described cycle will run through a few thousand times per second, so that a quasi-continuous flow of energy from the primary side to the secondary side of the flyback converter is formed.

2 Using diagrams to illustrate the operation of the in 1 shown voltage converter 1 ,

The upper diagram shows the lateral profile of the AC voltage u _N in the course of an AC voltage period. The alternating voltage U _N has a sinusoidal profile with a positive and a negative half-wave.

The two diagrams below show the timing of the at the control terminals 17s and 18s applied control voltages u _17s and u _18s , which by an in 1 not shown control device can be provided. The controller is configured to include the first and second electronic switches 17 . 18 such that during the positive AC half-wave, the positive AC half-wave from the first electronic switch 17 is modulated according to a high-frequency signal and during the negative AC half-wave, the negative AC half-wave from the second electronic switch 18 is modulated according to the high-frequency signal. The frequency of the high-frequency signal can be, for example, 10 to 100 times the mains frequency.

The lower diagram illustrates the pulsed current flow in the primary circuit, which is represented as a sequence i _S (t) of triangular pulses whose amplitudes show a sinusoidal characteristic that is in phase with the voltage profile. The above in 1 described LC element from the throttle 16 and the capacitor 15 smoothes the alternating current waveform represented by the curve i _N (t).

3 and 4 show a second and a third embodiment of the voltage converter according to the invention. The two voltage transformers have the same design on the primary side.

3 shows a voltage converter 2 with a direct current connection, an ac connection and a flyback converter 13 , The voltage converter works as an AC / DC converter.

The primary winding of the storage transformer 14 has two ports, a first port and a second port. The first primary-side connection point of the flyback converter 13 is a first current path comprising a first electronic switch 17 and a second electronic switch 18 with the first terminal of the primary winding of the memory transformer 14 connected. The second primary-side connection point of the flyback converter 13 is connected via a second current path to the second primary-side connection point.

The voltage converter 2 continues like the one in 1 described voltage converter 1 an LC element from choke 18 and capacitor 15 on, and optionally a voltage limiter 18 , which is the primary winding of the memory transformer 14 Bridged.

The secondary winding of the storage transformer 14 has two ports, a first and a second port. The first secondary-side connection point of the flyback converter 13 is across a first bridge current path of a diode bridge formed by four diodes 9 , with the first connection of the secondary winding of the storage transformer 14 connected. The second secondary-side connection point of the flyback converter 13 is via a second bridge current path of the diode bridge to the second terminal of the secondary winding of the memory transformer 14 connected.

The in 4 shown voltage converter 2 is like the one in 3 described voltage transformer, with the difference that the secondary winding of the memory transformer 14 two terminals, a first and a second terminal, and a center tap, that the first secondary-side terminal of the flyback converter 13 via a first current path comprising a first diode 19 with the first terminal of the secondary winding of the memory transformer 14 is connected and via a second current path comprising a second diode 19 is connected to the second terminal of the secondary winding of the memory transformer and that the center tap via a third current path with the second secondary-side connection point of the flyback converter 13 connected is.

The electronic switches 17 and 18 exist in the in 3 and 4 illustrated embodiments of a switching transistor with antiparallel freewheeling diode or an IGBT or MOSFET transistor. The electronic switches 17 and 18 are arranged in a counter series circuit. It is also possible that the first electronic switch 17 and the second electronic switch 18 consist of a counter-parallel connection of two bipolar blocking switching transistors.

5 Using diagrams to illustrate the operation of the in 3 and 4 shown voltage converter 2 ,

The upper diagram shows the time course of the AC voltage U _N in the course of a period of oscillation. The alternating voltage u _N has a sinusoidal course with a positive and a negative half-wave.

The two diagrams below show the timing of the at the control terminals 17s and 18s applied control voltages u _17s and u _18s . The in the in 3 and 4 not shown control device is designed such that it controls the first and the second electronic switch such that during the positive AC half-wave, the positive AC half-wave from the first electronic switch 17 is modulated according to a high-frequency signal and the second switch 18 is closed and during the negative AC half wave the negative AC half wave from the second electronic switch 18 is modulated according to the high-frequency signal and the switch 17 closed is.

The lower diagram illustrates the pulsed current flow in the primary circuit, which is represented as a sequence i _S (t) of triangular pulses whose amplitudes show a sinusoidal profile. The value above in 1 described LC element from the throttle 16 and the capacitor 15 smoothes the current curve, represented by the curve i _N (t).

6 shows a fourth embodiment of the voltage converter according to the invention.

A voltage transformer 4 is like the one up in 1 described voltage converter 1 formed, with the difference that in the secondary circuit instead of the diode 19 an electronic switch 22 with a control connection 22s is arranged The electronic switch 22 is like the electronic switch 17 and 18 formed from the series connection of a diode and a switching transistor. The switching transistor has the control terminal 22s on.

7 Using diagrams to illustrate the operation of the in 6 shown voltage converter 3 ,

The upper diagram shows the time course of the alternating voltage u _N in the course of a period of oscillation. The alternating voltage u _N has a sinusoidal profile with a positive and a negative half-wave.

The three diagrams below show the timing of the at the control terminals 21s . 17s and 18s applied control voltages u _21s , u _17s and u _18s . During both half cycles of the AC voltage u _N is located on the secondary side control input 21s a pulse-shaped control voltage u _21s . At the control entrance 17s the control voltage u _{17s is} permanently present during the positive half wave, while the control voltage is zero during the negative half wave. The two electronic switches act like a diode. At the negative half wave is at the control input 18s the control voltage u _18s continuously on, the control voltage u _17s is zero. The two switches 17 and 18 now act as oppositely poled diode, which lets through the negative half-wave of the alternating current.

The lower diagram illustrates the pulsed current flow in the primary circuit, which is represented as a sequence i _S (t) of triangular pulses whose amplitudes show a sinusoidal profile. The value above in 1 described LC element from the throttle 12 and the capacitor 13 smoothes the current curve, represented by the curve i _N (t).

The 8th shows an embodiment in which a voltage converter 4 like the one above in 3 described voltage converter 2 is formed, with the difference that in the secondary circuit instead of the diode 19 formed bridge rectifier circuit one of electronic switches 22 to 25 trained bridge rectifier circuit is provided, wherein the electronic switch 22 and 23 the upper bridge branch and the electronic switches 24 and 25 form the lower brocken branch.

The 9 shows a sixth embodiment in which a voltage converter 4 like the one above in 4 described voltage converter 2 is formed, with the difference that in the secondary circuit instead of the diodes 19 electronic switches 22 and 23 with control connections 22s and 23s are provided.

In the 8th and 9 shown voltage transformers allow because of the provided in the secondary circuit electronic switch, the return of electrical energy from the secondary circuit in the primary circuit of the voltage converter 13 , wherein at the same time the conversion of DC voltage in AC voltage including voltage adjustment is possible.

10 clarifies the relationships for the embodiment in 9 ,

The upper diagram shows the time course of the alternating voltage u _N in the course of a period of oscillation. The alternating voltage u _N has a sinusoidal course with a positive and a negative half-wave.

The four middle diagrams show the time-dependent curves of the control voltages u _20as , u _20bs , u _21bs / u _19bs and u _21as / u _19as .

The curves of u _22s and u _23s are alternating in the two half waves of the alternating voltage, ie if u _{22s is} pulsed, u _23s = 0 and vice versa.

Likewise, the curves of u _26s / u _18s and u _24s / u _{17s are} alternating in the two half-waves of the alternating voltage, ie when _{μ 25s} / u _18s is applied, u _24s / u _17s = 0 and vice versa. The said voltages are constant in each case for the duration of a half-wave.

The 6 to 10 describe voltage transformers of the type of DC / AC converter.

The in the 11 to 13 illustrated embodiment allow depending on the control operation in both directions. Depending on the type of control, these voltage transformers can therefore be used as AC / DC or DC / AC converters.

Such an operation is basically also by antiparallel arrangement of one of the AC / DC systems after 1 . 3 , or 4 and a DC / AC system 6 . 8th , or 9 feasible, the integrated design after 11 . 12 , or 13 However, it has a much lower implementation effort.

This in 11 illustrated embodiment shows a voltage converter 5 , the primary side like the one above 1 described voltage transformer is formed, with the difference that the electronic switch as in the 3 . 4 . 8th and 9 are formed.

Secondary, the voltage converter 5 the structure out 1 on, with the difference that instead of the diode 19 an electronic switch 22 with a control connection 22s is provided.

Depending on the control, the following operating modes result: operating mode switch 17 switch 18 switch 17 ' switch 18 ' AC / DC at clocked out clocked DC / AC clocked out clocked out

This in 12 illustrated embodiment is as in the above in 3 described embodiment, with the difference that in a voltage converter 6 a secondary circuit is provided, which is like the one above 8th is formed described secondary circuit.

Depending on the control, the following operating modes result: operating mode switch 22 - 25 AC / DC blocked DC / AC controlled as in Fig. 10

This in 13 From embodiment shown is like that in 4 described embodiment, with the difference that in the secondary circuit instead of the diodes 19 electronic switches 22 and 23 with control connections 22s and 23s are provided.

Depending on the control, the following operating modes result: operating mode switch 22 and 23 AC / DC blocked DC / AC controlled as in Fig. 10

LIST OF REFERENCE NUMBERS

1-6

DC converter

11

DC power connector

12

AC connection

13

flyback converter

13p

primary-side connection

13s

secondary side connection

14

flyback transformer

15

capacitor

16

throttle

17, 18

electronic switch

17s, 18s

control connection

19

diode

20

capacitor

21

voltage limiter

22-25

electronic switch

22s-25s

control connection

Claims (20)

Voltage transformer ( 1 - 6 ) with a DC connection ( 11 ), an AC power connection ( 12 ) and a flyback converter ( 13 ), wherein the flyback converter ( 13 ) a storage transformer ( 14 ) with galvanically separated primary and secondary winding, a primary-side connection ( 13p ) comprising a first and a second primary-side connection point, a secondary-side connection ( 13s ), comprising a first and a second secondary-side connection point, at least one electronic switch ( 17 . 18 . 17 . 18 ' ), through which the primary-side connection ( 13p ) of the flyback converter ( 13 ) with the primary winding of the memory transformer ( 14 ), and a control device for controlling the at least one electronic switch ( 17 . 18 . 17 ' . 18 ' ), wherein the flyback converter ( 13 ) in such a way with the AC connection ( 12 ), that between the first and second primary-side connection point of the flyback converter ( 13 ) an alternating voltage (u _N ) is applied. Voltage transformer according to claim 1, characterized in that the primary winding of the memory transformer ( 14 ) has two terminals, a first and a second terminal, and a center tap, that the first primary-side connection point via a first current path comprising a first electronic switch ( 17 ) to the first terminal of the primary winding of the memory transformer ( 14 ) that the second primary-side connection point via a second current path comprising a second electronic switch ( 18 ) to the second terminal of the primary winding of the memory transformer ( 14 ) and the center tap is connected to the second primary-side terminal via a third current path Voltage transformer according to claim 2, characterized in that the control device is designed such that it the first and the second electronic switch ( 17 . 18 ) during the positive AC half-wave with a different control signal than during the negative AC half cycle, so that the second current path is disabled during the positive half cycle and the first current path is disabled during the negative half cycle. Voltage transformer according to claim 2 or 3, characterized in that the control device is equipped so that it the first and the second electronic switch ( 17 . 18 ) in such a way that during the positive AC half-wave the positive AC half-wave from the first electronic switch ( 17 ) is modulated according to a high-frequency signal and during the negative AC half-wave, the negative AC half-wave from the second electronic switch ( 18 ) is modulated according to the high-frequency signal. Voltage transformer according to one of claims 2 to 4, characterized in that the electronic switch ( 17 . 18 ) consists of a series connection of a diode and a switching transistor. Voltage transformer according to claim 1, characterized in that the primary winding of the memory transformer ( 14 ) has two terminals, a first terminal and a second terminal, that the first primary-side connection point via a first current path comprising an electronic switch ( 17 . 18 ) to the first terminal of the primary winding of the memory transformer ( 14 ), and that the second primary-side connection point is connected via a second current path to the second terminal of the primary winding. Voltage transformer according to claim 1, characterized in that the primary winding of the memory transformer ( 14 ) has two terminals, a first terminal and a second terminal, that the first primary-side connection point via a first current path comprising a first electronic switch ( 17 ) and a second electronic switch ( 18 ) to the first terminal of the primary winding of the memory transformer ( 14 ), and in that the second primary-side connection point is connected via a second current path to the second connection of the primary winding of the memory transformer ( 14 ) connected is. Voltage transformer according to claim 7, characterized in that the first electronic switch ( 17 ) and the second electronic switch ( 18 ) from a counter-series circuit of two switching transistors with respective antiparallel freewheeling diode or a counter-series circuit of second IGBTs or MOSFET transistors. Voltage transformer according to claim 7, characterized in that the first electronic switch ( 17 ) and the second electronic switch ( 18 ) consist of a counter-parallel connection of two bipolar blocking switching transistors. Voltage converter according to one of claims 7 to 9, characterized in that the control device is designed such that it the first and the second electronic switch ( 17 . 18 ) in such a way that during the positive AC half-wave the positive AC half-wave from the first electronic switch ( 17 ) is modulated according to a high-frequency signal and during the negative AC half-wave, the negative AC half-wave from the second electronic switch ( 18 ) is modulated according to the high-frequency signal. Voltage converter according to one of claims 1 to 5, characterized in that the secondary winding of the storage transformer ( 14 ) has two terminals, a first and a second terminal, that the first secondary-side connection point via a first current path, the a diode ( 19 ), with the first terminal of the secondary winding of the memory transformer ( 14 ), and that the second secondary connection point is connected to the second connection of the secondary winding via a second current path. Voltage transformer according to one of claims 1 to 10, characterized in that the secondary winding of the storage transformer ( 14 ) has two terminals, a first and a second terminal, that the first secondary-side connection point via a first bridge current path of a diode bridge with the first terminal of the secondary winding of the memory transformer ( 14 ), and in that the second secondary-side connection point is connected to the second terminal of the secondary winding via a second bridge current path of the diode bridge Voltage transformer according to one of claims 1 to 10, characterized in that the secondary winding of the storage transformer ( 14 ) has two terminals, a first and a second terminal, and a center tap, that the first secondary-side terminal point via a first current path comprising a first diode ( 19 ) to the first terminal of the secondary winding of the memory transformer ( 14 ) and via a second current path comprising a second diode ( 19 ) to the second terminal of the secondary winding of the memory transformer ( 14 ) and that the second secondary-side connection point is connected to the center tap via a third current path. Voltage converter according to one of claims 1 to 5, characterized in that the secondary winding of the storage transformer ( 14 ) has two terminals, a first and a second terminal, that the first secondary-side connection point via a first current path, the third electronic switch ( 22 ), with the first terminal of the secondary winding of the memory transformer ( 14 ), and that the second secondary-side connection point is connected via a second current path to the second terminal of the secondary winding. Voltage converter according to claim 14, characterized in that the control device is designed such that it the third electronic switch ( 22 ) such that it turns on and off according to a high-frequency signal. Voltage transformer according to one of claims 1 to 10, characterized in that the secondary winding of the storage transformer ( 14 ) has two terminals, a first and a second terminal, that the first secondary-side connection point via a first bridge current path with a fourth electronic failure ( 22 - 25 ) formed bridge with the first terminal of the secondary winding of the memory transformer ( 14 ), and in that the second secondary-side connection point is connected via a second bridge current path to that of the fourth electronic switches ( 22 - 25 ) formed bridge is connected to the second terminal of the secondary winding. Voltage transformer according to claim 16, characterized in that the fourth electronic switch ( 22 - 25 ) consist of a switching transistor with antiparallel freewheeling diode or an IGBT or MOSFET transistor. Voltage transformer according to one of claims 1 to 10, characterized in that the secondary winding of the storage transformer ( 14 ) has two terminals, a first and a second terminal, and a center tap, that the first secondary-side connection point via a first current path comprising a fifth electronic switch ( 22 ) to the first terminal of the secondary winding of the memory transformer ( 14 ) and via a second current path comprising a sixth electronic switch ( 23 ) to the second terminal of the secondary winding of the memory transformer ( 14 ) and the center tapping is connected to the second secondary side terminal via a third current path. Voltage transformer according to claim 16 to 18, characterized in that the control device is designed so that they the fourth and fifth and sixth electronic switches ( 22 - 25 ) such that during the positive AC half-wave a first group of the fourth electronic switch or the fifth electronic switch according to a high-frequency signal on and off and during the negative AC half-wave, a second group of the fourth electronic switch or the sixth electronic switch on or off. Voltage transformer according to one of the preceding claims, characterized in that the control device is designed so that after filtering switching frequency components of the input current through an EMC filter, a mains voltage proportional or sinusoidal input current i _N at the AC power connector ( 12 ) results.

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