High-voltage generator for an X-ray device

Abstract

A high-voltage generator for an X-ray device includes an input-side inverter unit, an output-side rectifier unit and a transformer connected between the inverter unit and the rectifier unit. The inverter unit is configured to generate two inverter voltages that are phase-shifted with respect to each other. These inverter voltages are transformed by the transformer into two rectifier voltages that are fed to the rectifier unit such that in no-load operation, one of the two rectifier voltages is proportional to the sum of the inverter voltages while the other of the two rectifier voltages is proportional to the difference between the inverter voltages.

Claims

1. A high-voltage generator for an X-ray device, the high-voltage generator comprising: an input-side inverter unit, an output-side rectifier unit, and a transformer connected between the inverter unit and the rectifier unit, wherein the inverter is configured to generate two inverter voltages phase-shifted with respect to each other that in a normal operating mode have a phase offset of 90 and that are transformed by the transformer into two rectifier voltages that are fed to the rectifier unit such that in no-load operation one of the two rectifier voltages is proportional to the sum of the inverter voltages (u.sub.i1,u.sub.i2), while the other of the two rectifier voltages (u.sub.r2) is proportional to the difference between the inverter voltages (u.sub.i1,u.sub.i2).

2. The high-voltage generator as claimed in claim 1, wherein the inverter unit comprises two inverters, each of which feeds an assigned primary winding system with one of the two inverter voltages, wherein each of the two primary winding systems contains two series-connected primary windings, wherein the transformer has two transformer cores, each of which is wound with one primary winding of the two primary winding systems, and wherein the two primary windings in one of the two primary winding systems are connected in series in the same direction while the two primary windings in the other of the two primary winding systems are connected in series in opposing directions.

3. The high-voltage generator as claimed in claim 2, wherein the two inverters are connected in series across an input voltage (U.sub.i).

4. The high-voltage generator as claimed in claim 3, wherein the rectifier unit comprises a passive rectifier.

5. The high-voltage generator as claimed in claim 2, wherein the two inverters are connected in parallel in an input voltage, and wherein each of the two inverters has two half-bridges in each case that are connected in each case between two series-connected intermediate DC circuits.

6. The high-voltage generator as claimed in claim 5, wherein the rectifier unit comprises a passive rectifier.

7. The high-voltage generator as claimed in claim 2, wherein the rectifier unit comprises a passive rectifier.

8. The high-voltage generator as claimed in claim 1, wherein the rectifier unit comprises two rectifiers connected in series across an output voltage that are each fed with one of the two rectifier voltages via two secondary winding systems, wherein each of the two secondary winding systems contains two series-connected secondary windings, wherein the transformer has two transformer cores, each of which is wound with one secondary winding of the two secondary winding systems, and wherein the two secondary windings in one of the two secondary winding systems are connected in series in the same direction while the two secondary windings in the other of the two secondary winding systems are connected in series in opposing directions.

9. The high-voltage generator as claimed in claim 8, wherein the rectifier unit comprises a passive rectifier.

10. The high-voltage generator as claimed in claim 1, wherein the transformer comprises a transformer core with three parallel legs that are connected on both sides by yokes.

11. The high-voltage generator as claimed in claim 10, having a first primary winding system that contains two primary windings connected in series and is fed by the inverter unit with one of the two inverter voltages, and having a second primary winding system that contains a further primary winding and is fed by the inverter unit with the other of the two inverter voltages, wherein the central leg of the transformer core is wound with the primary winding of the second primary winding system, and wherein the outer legs or the adjacent sections of one of the two yokes are wound with the two primary windings of the first primary winding system such that one of the two primary windings of the first primary winding system is oriented in the same direction as the primary winding of the second primary winding system while the other of the two primary windings of the first primary winding system is oriented in opposing directions with the primary winding of the second primary winding system.

12. The high-voltage generator as claimed in claim 11, wherein the rectifier unit comprises a passive rectifier.

13. The high-voltage generator as claimed in claim 10, having a first secondary winding system that contains two secondary windings connected in series and via which the rectifier unit is fed with one of the two rectifier voltages, and having a second secondary winding system that contains a further secondary winding and via which the rectifier unit is fed with the other of the two rectifier voltages, and wherein the central leg of the transformer core is wound with the secondary winding of the second secondary winding system, and wherein the outer legs or the adjacent sections of one of the two yokes are wound with the two secondary windings of the first secondary winding system such that one of the two secondary windings of the first secondary winding system is oriented in the same direction as the secondary winding of the second secondary winding system while the other of the two secondary windings of the first secondary winding system is oriented in opposing directions with the secondary winding of the second secondary winding system.

14. The high-voltage generator as claimed in claim 13, wherein the rectifier unit comprises a passive rectifier.

15. The high-voltage generator as claimed in claim 10, wherein the rectifier unit comprises a passive rectifier.

16. The high-voltage generator as claimed in claim 1, wherein the rectifier unit comprises a passive rectifier.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments are explained in greater detail below with reference to the drawingS, in which:

(2) FIG. 1 shows an electric circuit diagram of one embodiment of a high-voltage generator for an X-ray device having an input-side inverter unit, which has two inverters connected in series across an input voltage, having an output-side rectifier unit, which has two rectifiers connected in series across an output voltage, and having a transformer connected between the inverter unit and the rectifier unit, it being the case that the inverter unit feeds each of two primary winding systems of the transformer with an inverter voltage and that each of the primary winding systems contains two primary windings;

(3) FIG. 2 shows 16 diagrams arranged in a 44 matrix, each of which depicts an example of the relevant course over time of the two inverter voltages (first and second columns from the left) and an example of the course over time of the falling primary voltages in the primary windings of the transformer (third and fourth columns from the left) for different duty cycles (rows one to four);

(4) FIG. 3 shows an example output characteristic of the high-voltage generator for different duty cycles in a diagram of the normalized output voltage against the normalized output current;

(5) FIGS. 4 to 6 each show an example of the fundamental component vector for the inverter voltages and the primary voltages in a complex vector diagram;

(6) FIG. 7 shows an alternative embodiment of the high-voltage generator depicted in accordance with FIG. 1; and

(7) FIGS. 8 to 10 each show further embodiments of the high-voltage generator in a circuit diagram simplified as compared with FIG. 1.

(8) Corresponding parts and quantities are always marked with the same reference characters in all figures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(9) The high-voltage generator 1 shown in FIG. 1 has an input-side inverter unit 2, an output-side rectifier unit 3 and a transformer 4 connected between this inverter unit and rectifier unit.

(10) The inverter unit 2 is formed from two inverters 5 and 6 that are connected in series across a constant input voltage U.sub.i of, for example, 800 Volts.

(11) The inverter 5 is formed from two half-bridges 7 and 8 that are connected in parallel with each other in an intermediate (DC) circuit 9 with an (intermediate circuit) capacitor 10. In each of the two half-bridges 7 and 8, the inverter 5 has in each case two series-connected active semiconductor switches (e.g., in the form of insulated gate bipolar transistors or IGBT) with a freewheeling diode connected in parallel in each case.

(12) Similarly the inverter 6 also has two half-bridges 11 and 12 connected in parallel with each other in an intermediate (DC) circuit 13 with an (intermediate circuit) capacitor 14. The half-bridges 11 and 12 are also formed by a series circuit of in each case two active semiconductor switches (e.g., IGBT) with a freewheeling diode connected in parallel in each case.

(13) The rectifier unit 3 is formed from two rectifiers 15 and 16 that are connected in series across an output voltage U.sub.o.

(14) The rectifier 15 includes two half-bridges 17 and 18 that are connected in parallel with each other in an intermediate (DC) circuit 19 with an (intermediate circuit) capacitor 20. Each of the two half-bridges 17 and 18 in this instance contains a series circuit of two diodes.

(15) The rectifier 16 is likewise formed from two half-bridges 21 and 22 that are connected in parallel with each other in an intermediate (DC) circuit 23 with an (intermediate circuit) capacitor 24. The half-bridges 21 and 22 are also each formed by a series circuit of two diodes.

(16) The transformer 4 contains two transformer cores 25 and 26 (e.g., annular transformer cores with no air gap). The transformer core 25 is in this instance wound with two primary windings 27 and 28 and one secondary winding 29. The transformer core 26 is similarly wound with two primary windings 30 and 31 and one secondary winding 32. All of the primary windings 27,28,30,31 have the same number of windings N.sub.1 (e.g., where N.sub.1=6) and, in the example according to FIG. 1, the same direction of winding. The secondary windings 29 and 32 each have a greater number of windings N.sub.2 (for example N.sub.2=1600).

(17) The number of windings N.sub.2 is chosen such that the transformation ratio n (where n=N.sub.2/N.sub.1) of the transformer 4 is overdimensioned with respect to the desired maximum voltage transformation ratio U.sub.o/U.sub.i, for example by a factor of 1.4, in order to compensate for losses in the transformer 4.

(18) The two primary windings 27 and 31, each of which is assigned to a different one of the two transformer cores 25 and 26, are combined to form a primary winding system 33, while the other two primary windings 28 and 30, each of which is assigned to a different one of the two transformer cores 25 and 26, are combined to form a primary winding system 34. The primary winding system 33 formed by the primary windings 27 and 31 is connected between center taps (terminals) of the half-bridges 7 and 8 of the first inverter 5. The primary winding system 34 formed by the other primary windings 28 and 30 is connected between center taps (terminals) of the half-bridges 11 and 12 of the inverter 6. The primary windings 28 and 30 in the primary winding system 34 are connected in series in the same direction (in relation to their direction of winding), while the primary windings 27 and 31 in the primary winding system 33 are connected in series in opposing directions.

(19) Connected between center taps of the half-bridges 17 and 18 of the rectifier 15 is a secondary winding system 35 that in the exemplary embodiment according to FIG. 1 contains only the secondary winding 29. A further inductance is shown in series with the secondary winding 29 in FIG. 1. This is not, however, a physical component, but rather an equivalent circuit diagram that represents the stray inductance 36 of the transformer core 25 and the associated windings.

(20) Similarly, there is connected between center taps of the half-bridges 21 and 22 of the rectifier 16 a secondary winding system 37 that in the exemplary embodiment according to FIG. 1 contains just the secondary winding 32. Here too the stray inductance 38 of the transformer core 26 and the associated windings is indicated as an equivalent circuit diagram.

(21) When the high-voltage generator 1 is operating, the inverter 5 feeds the primary winding system 33 with an inverter voltage u.sub.i1 that causes a current with an (inverter) current strength i.sub.i1 to flow in the primary winding system 33. Primary voltages u.sub.p1 and u.sub.p2 fall here across the two primary windings 27 and 31 of the primary winding system 33. The inverter 6 similarly feeds the primary winding system 34 with an inverter voltage u.sub.i2 that causes a current with an (inverter) current strength i.sub.i2 to flow in the primary winding system 34, it being the case that the primary voltages u.sub.p1 and u.sub.p2 likewise fall across the two primary windings 28 and 30. The fact that the primary coils 27,28,30 and 31 have the same number of windings N.sub.1 means that the voltage fall for the two primary coils 27 and 28, and 30 and 31, respectively, coupled by a shared transformer core 25 or 26 are the same in each case due to the law of induction.

(22) The primary voltage u.sub.p1 causes a secondary voltage u.sub.s1 to be induced in the secondary coil 29 via the transformer core 25, which secondary voltage u.sub.s1 generates a current with a (rectifier) current strength i.sub.r1 in the secondary winding system 35 and a rectifier voltage u.sub.r1 between the half-bridges 17 and 18 of the rectifier 15.

(23) The primary voltage u.sub.p2 similarly causes a secondary voltage u.sub.s2 to be induced in the secondary winding 32 via the transformer core 26, which secondary voltage u.sub.s2 generates a current with a rectifier current strength i.sub.r2 in the secondary winding system 37 and a rectifier voltage u.sub.r2 between the half-bridges 21 and 22 of the rectifier 16.

(24) The fact that the primary windings 27 and 31, and 28 and 30, are connected in the same direction and in opposite directions, respectively, means that the inverter voltages u.sub.i1 and u.sub.i2 correspond to the difference and sum, respectively, of the primary voltages u.sub.p1 and u.sub.p2:
u.sub.i1=u.sub.p1u.sub.p2Eq 1.1
u.sub.i2=u.sub.p1+u.sub.p2Eq 1.2

(25) Reversing this system of equations produces the following for the primary voltages:

(26) $\begin{array}{cc}{u}_{p1}=\frac{1}{2}.Math.\left(u_{i1}+u_{i2}\right)\mathrm{and}& \mathrm{Eq}2.1\\ u_{p2}=\frac{1}{2}.Math.\left(-u_{i1}+u_{i2}\right)& \mathrm{Eq}2.2\end{array}$
The primary voltage u.sub.p1 thus corresponds to half of the sum of the two inverter voltages u.sub.i1 and u.sub.i2 (i.e., the common mode portion of the two inverters 5,6), while the primary voltage u.sub.p2 corresponds to half of the difference between the two inverter voltages u.sub.i1 and u.sub.i2 (i.e., the differential mode portion of the two inverters 5,6).

(27) Both inverter voltages u.sub.i1, u.sub.i2 are generated in the normal operating mode of the high-voltage generator 1 as pulsed square wave voltages with the same duty cycle (pulse/pause ratio) d, which means that both inverter voltages u.sub.i1,u.sub.i2 have the same form, but with a phase offset of 90. The two primary voltages u.sub.p1 and u.sub.p2 thus also have the same form and a phase offset of 90. Eq 2.1 and 2.2 yield the form of the inverter voltages u.sub.i1 and u.sub.i2 and the primary voltages u.sub.p1 and u.sub.p2 as depicted in FIG. 2 as a function of the duty cycle d.

(28) When the duty cycle is 50% (d=0.5), each of the primary voltages u.sub.p1 and u.sub.p2 thus assumes the mean value of the two intermediate circuit voltages of the two inverters 5,6 for one quarter of the period duration in each period, followed by a zero interval lasting a further quarter of the period and an identical half-wave with the opposite leading sign.

(29) The peak value of the primary voltages u.sub.p1 and u.sub.p2 thus corresponds to the mean value of the two intermediate circuit voltages of the inverters 5,6. The maximum voltage-time area is only half as large as for the inverter voltages u.sub.i1 and u.sub.i2, however, so the number of windings of the primary and secondary windings may be halved in each case in the circuit according to FIG. 1 as compared with a transformer wound with a single primary coil at the same flux density in the transformer core. The stray inductance is proportional to the square of the number of windings, so halving the number of windings of the transformer 4 (relative to the comparative circuit described above) reduces the stray inductance to a quarter of the level in the comparative circuit described above.

(30) As with conventional topologies, the maximum value reached by the output voltage U.sub.o in no-load operation of the high-voltage generator 1 depends on the transformation ratio n of the transformer 4 and the input voltage U.sub.i. This no-load voltage U.sub.o,max is calculated thus:
U.sub.o,max=n.Math.U.sub.iEq 3
The maximum value that may be reached for the output current I.sub.o occurs with short-circuited output. This short-circuit current I.sub.o,max amounts to

(31) $\begin{array}{cc}{I}_{o,\max }=\frac{3.Math.{\mathrm{nU}}_i}{64.Math.f.Math.L_{}}& \mathrm{Eq}4\end{array}$
where f is the switching frequency of the inverters 5,6 and L.sub. is the stray inductance 36,38.

(32) The short-circuit current I.sub.o,max is thus higher by a factor of three than with a conventional topology in which the transformer cores 25 and 26 are wound with just a single primary winding and are each fed from a single inverter 5 and 6, respectively. The high-voltage generator 1 shown in FIG. 1 also allows higher output currents than the conventional topology at other operating points.

(33) The use of two primary windings 27,28 and 30,31, respectively, per transformer core 25 and 26, respectively, means that in each case both inverter currents i.sub.i1 and i.sub.i2 contribute to the formation of the rectifier currents i.sub.r1 and i.sub.r2, so that for the latter the relationships:
n.Math.i.sub.r1=i.sub.i1+i.sub.i2Eq 5.1
n.Math.i.sub.r2=i.sub.r1+i.sub.i2Eq 5.2
apply.

(34) Reversing this system of equations produces the following for the inverter currents:

(35) $\begin{array}{cc}{i}_{i1}=\frac{n}{2}.Math.\left(i_{r1}-i_{r2}\right)& \mathrm{Eq}6.1\\ i_{i2}=\frac{n}{2}.Math.\left(i_{r1}+i_{r2}\right)& \mathrm{Eq}6.2\end{array}$
The rms value i.sub.i,eff of the inverter currents i.sub.i1 or i.sub.i2 corresponds to:

(36) $\begin{array}{cc}{i}_{i,\mathrm{eff}}=\frac{n}{\sqrt{2}}.Math.i_{r,\mathrm{eff}},& \mathrm{Eq}7\end{array}$
where i.sub.r,eff denotes the rms value of the rectifier currents i.sub.r1 or i.sub.r2.

(37) The rms value i.sub.i,eff of the inverter currents is thus smaller by a factor of {square root over (2)} than in a conventional circuit of the type described above, which significantly reduces the conduction losses in the semiconductors.

(38) The proposed arrangement of the primary windings 27,28,30 and 31 enables significantly reduced inverter currents throughout the operating range. The relative increase in the rms value i.sub.r,eff for low output currents is also smaller, which is observable primarily with output currents of less than 25% of the maximum short-circuit current and average output voltages.

(39) The output voltage U.sub.o is controlled for the high-voltage generator 1 according to FIG. 1 by a voltage controller (not shown) via the duty cycle d of the inverter voltages u.sub.i1,u.sub.i2. The switching frequency (and thus the period length) is maintained at a constant level. The semiconductor switches of the inverters 5,6 in this case undergo soft switching (i.e., the switches are switched on in the voltage-free state). The voltage controller is preferably realized as an integral or integrated controller.

(40) FIG. 3 shows the output characteristic of the high-voltage generator 1 according to FIG. 1 for different duty cycles d (namely for d=0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 and 0.5). The output characteristic is defined in this instance by the course of the output current I.sub.o, normalized for the short-circuit current I.sub.o,max, plotted against the output voltage U.sub.o, normalized for the no-load voltage U.sub.o,max (I.sub.o/I.sub.o,max=I.sub.o/I.sub.o,max (U.sub.o/U.sub.o,max,d)).

(41) It can be seen from FIG. 3 that the output current I.sub.o falls as the output voltage U.sub.o rises, which acts to counter an overshoot of the output voltage U.sub.o and allows a high gain for the voltage controller and thus a high dynamic level for the output voltage control.

(42) FIG. 4 illustrates, in a vector diagram, the relative phase angle of the respective fundamental component of the inverter voltages u.sub.i1 and u.sub.i2 in the normal operating mode and the primary voltages u.sub.p1 and u.sub.p2 resulting from this according to Eq 2.1 and 2.2 in the normal operating mode of the high-voltage generator 1. The labels Re and Im here denote the real and imaginary axes of the vector diagram. As already mentioned, the inverter voltages u.sub.i1,u.sub.i2 are generated with a phase offset of 90 so that the fundamental components of the inverter voltages u.sub.i1,u.sub.i2 are orthogonal. The primary voltages u.sub.p1,u.sub.p2 are thus likewise orthogonal, but are phase-shifted with respect to the inverter voltages u.sub.i1,u.sub.i2 by a phase angle of 45.

(43) The secondary voltages u.sub.s1 and use and the resulting rectifier voltages u.sub.r1 and u.sub.r2 each have the same phase angle as the corresponding primary voltage u.sub.p1 and u.sub.p2, respectively, in no-load operation. This means that in no-load operation, the rectifier voltages u.sub.r1 and u.sub.r2 too are orthogonal and shifted with respect to the inverter voltages u.sub.i1 and u.sub.i2 by a phase angle of 45. Specifically, the rectifier voltages u.sub.r1 and u.sub.r2 in no-load operation are determined from the inverter voltages u.sub.i1 and u.sub.i2 in accordance with

(44) $\begin{array}{cc}{u}_{r1}=\frac{n}{2}.Math.\left(u_{i1}+u_{i2}\right)& \mathrm{Eq}8.1\\ u_{r2}=\frac{n}{2}.Math.\left(-u_{i1}+u_{i2}\right)& \mathrm{Eq}8.2\end{array}$

(45) If the two series-connected rectifiers 15 and 16 are loaded asymmetrically, this also produces an asymmetric distribution of the proportions in which the rectifiers 15,16 contribute to the output voltage U.sub.o. Such asymmetry is undesirable due to the limited withstand voltage of the semiconductor components used. If such asymmetry occurs, the intermediate circuit voltages of the two rectifiers 15,16 are therefore rendered symmetrical by actively increasing or reducing the phase offset between the inverter voltages u.sub.i1 and u.sub.i2 with respect to the normal value of 90 on the inverter side. This is illustrated in a vector diagram in FIG. 5 and FIG. 6.

(46) It can be seen from FIG. 5 and FIG. 6 that with a phase offset other than 90, the fundamental components of the primary voltages u.sub.p1 and u.sub.p2 differ in size, which causes the rectifier currents i.sub.r1 and i.sub.r2 to differ as well. A further controller is used to set the phase offset between the inverter voltages u.sub.i1 and u.sub.i2 to balance out the rectifiers 15,16 by applying different rectifier currents i.sub.r1 and i.sub.r2 to them where applicable.

(47) If the rectifiers 15,16 are loaded asymmetrically, however, this also leads in the exemplary embodiment according to FIG. 1 to asymmetric loading of the two inverters 5,6, which results in an uneven voltage distribution in the series circuit of the inverters 5,6.

(48) This is avoided in a variant of the high-voltage generator 1 shown in FIG. 7 by connecting one of the two half-bridges 7,11 of the inverters 5 and 6 to the intermediate circuit capacitor 10 and the other half-bridges 8,12 of the inverters 5 and 6 to the intermediate circuit capacitor 14. This means, in other words, that the two inverters 5,6 are each shared between the intermediate circuits 9 and 13, which are connected in series. The primary winding systems 33 and 34 are connected here, as already established, between the half-bridges 7 and 8 of the inverter 5 and between the half-bridges 11 and 12 of the inverter 6.

(49) Each of the two primary winding systems 33 and 34 in a high-voltage generator 1 according to FIG. 7 has connected between the primary windings 27 and 31, and 28 and 30, respectively, a capacitor 39 and 40 that accepts half of the input voltage U.sub.i. The capacitance of this capacitor 39,40 is dimensioned to be large enough that the resonant frequency of the oscillator circuits formed from the capacitors 39,40 and the stray inductance 36 and 38 is well below the switching frequency with which the semiconductor switches in the inverters 5 and 6 are switched.

(50) FIGS. 8 to 10 show variants of the topologies described above in simplified form.

(51) The primary winding systems 33 and 34 in the variant according to FIG. 8 contain just the primary windings 27 and 30, respectively. The secondary winding systems 35 and 37 accordingly each include a further secondary winding 50 and 51, respectively, in addition to the secondary windings 29 and 32. The secondary winding 50 in this instance is connected in series in opposing directions with the secondary winding 29 in the secondary winding system 35 and wound on the transformer core 26. The secondary winding 51, on the other hand, is arranged in series in the same direction with the secondary winding 32 in the secondary winding system 37 and wound on the transformer core 25.

(52) The circuit topology according to FIG. 8 thus represents the quasi-mirror-image of the topology according to FIG. 1 in that the winding of the transformer cores 25 and 26 is mirrored between its primary side and its secondary side. The high-frequency generator 1 according to FIG. 8 otherwise corresponds to its mirror image shown in FIG. 1 with regard to design and function except that the rectifier voltages u.sub.r1 and u.sub.r2 in this instance are phase-shifted with respect to the inverter voltages u.sub.i1 and u.sub.i2 not by 45 but by 45.

(53) The variant of the high-voltage generator 1 shown in FIG. 9 has in place of the two independent transformer cores 25 and 26 what is known as an E core 60 (i.e., a transformer core with three parallel legs 61,62 and 63 that are connected on both sides by yokes 64 and 65). The E core 60 is designed with no air gap.

(54) The primary winding system 34 in this instance contains only the primary winding 30, which here is wound on the central leg 62 of the E core 60. The two primary windings 27 and 31 of the primary winding system 33 are in this instance connected in series in the same direction with each other and wound on the outer legs 61 and 63, respectively, of the E core 60. Alternatively, the primary windings 27 and 31as shown in FIG. 8are wound on the adjacent sections of the yoke 64 in each case.

(55) The secondary windings 29 and 32 of the secondary winding systems 35 and 37, respectively, are likewise wound on the outer legs 61 and 63, respectively, or alternatively on the adjacent sections of the yoke 65 in each case.

(56) The primary winding 30 is here wound on the E core 60 in the same direction as the primary winding 27 and in opposing directions with the primary winding 31 in terms of direction of winding and magnetic flux in the E core 60.

(57) FIG. 10, in turn, shows the mirror-image variant of the topology according to FIG. 9. In this instance, the primary winding system 33 contains just the primary winding 27 and the primary winding system 34 contains just the primary winding 30. The outer legs 61 and 63, respectively, of the E core 60 or, alternatively, the adjacent sections of the yoke 64 in each case, are here wound with these primary windings 27 and 30, respectively.

(58) The secondary winding 32, which in this instance constitutes the only winding of the secondary winding system 37, is wound on the central leg 62 of the E core 60. The secondary winding system 35, on the other hand, includes the two secondary windings 29 and 50, which in this instance are connected in series in the same direction with each other and are wound on the outer legs 61 and 63, respectively, or alternatively on the adjacent sections of the yoke 65 in each case.

(59) The secondary winding 32 is here wound on the E core 60 in the same direction as the secondary winding 29 and in opposing directions with the secondary winding 50 in terms of direction of winding and magnetic flux in the E core 60.

(60) The exemplary embodiments of FIG. 9 and FIG. 10 correspond to the high-frequency generator 1 shown in FIG. 1 with regard to their functioning except that the rectifier voltages u.sub.r1 and u.sub.r2 in this instance are phase-shifted with respect to the inverter voltages u.sub.i1 and u.sub.i2 not by 45 but by 135 and 135 respectively.

(61) The invention is rendered particularly clear by the exemplary embodiments described above. It is not, however, limited to these exemplary embodiments; indeed further embodiments of the invention can be derived from the claims and the foregoing description.

(62) It is intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.

(63) It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims can, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.