Method and circuit arrangement for operating an x-ray tube and x-ray device

Abstract

The invention relates to a method for operating an X-ray tube having at least one grid electrode arranged between an anode electrode and a cathode electrode, wherein an electron flow from the cathode electrode to the anode electrode is focused by means of a focusing unit in such a way that the focusing unit loads the grid electrode with a first grid potential at least with a focusing operation in order to focus the electron flow, the focusing unit is supplied with electrical energy in a galvanically isolated manner by means of an energy converter, the first grid potential is provided by means of an adjustable voltage divider of the focusing unit, and the adjustable voltage divider is adjusted by means of a control circuit of the focusing unit in such a way that the control circuit is loaded with at least one galvanically isolated control signal of a control unit which is galvanically isolated from the X-ray tube, wherein the control signal is related to a preset value of the first grid potential. According to the invention, the electrical power of the energy converter is adjusted in dependence on the preset value of the first grid potential.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for operating an X-ray tube having at least one grid electrode arranged between an anode electrode and a cathode electrode, wherein an electron flow from the cathode electrode to the anode electrode is focused by means of a focusing unit in such a way that the focusing unit loads the grid electrode with a first grid potential at least in a focusing mode in order to focus the electron flow and the focusing unit is supplied with electrical energy by means of an energy converter in a galvanically isolated manner. Furthermore, the invention relates to a circuit arrangement for operating an X-ray tube having at least one grid electrode arranged between an anode electrode and a cathode electrode, having a focusing unit for focusing an electron flow from the cathode electrode to the anode electrode, wherein the focusing unit is designed to load the grid electrode with a first grid potential at least in a focusing mode in order to focus the electron flow, an energy converter for supplying the focusing unit with electrical energy in a galvanically isolated manner, and a control unit galvanically isolated from the X-ray tube for regulating the electrical power of the energy converter. Finally, the invention also relates to an X-ray device having an X-ray tube having at least one grid electrode arranged between an anode electrode and a cathode electrode and a circuit arrangement connected to the X-ray tube by means of a connection line for operating the X-ray tube. BACKGROUND

[0002] X-ray tubes, methods for operating them and also circuit arrangements for this are widely known in the prior art. An X-ray tube is a special type of vacuum electron tube which is currently used to be able to provide X-ray radiation for various different purposes in a conventional mode of operation. X-ray devices are often also components of imaging apparatuses, as they are used, for example, in medical diagnostics or also in quality assurance. X-ray tubes are usually used here with the following functional principle, wherein electrons are strongly accelerated depending on the type of electron flow by a suitable adjustment of the voltage between the cathode electrode and the anode electrode and, under preset conditions, impinge on the anode electrode. X-ray radiation is released here. The release of X-ray radiation is influenced, inter alia, by the impingement area on the anode, which can be at least partially adjusted by focusing the electron flow.

[0003] In the case of an X-ray tube of this type, the anode-cathode voltage applied between the anode electrode and the cathode electrode can be approximately 20 kV to approximately 150 kV if the X-ray tube is monopolarly designed. In the case of a bipolar design of the X-ray tube, the same anode / cathode voltage is still applied, however, the voltage from the anode electrode or the cathode electrode with respect to a reference potential, for example ground, is only half the acceleration voltage. This can be approximately 30 kV to approximately 75 kV.

[0004] It is common in the prior art to realize a focusing and / or a deflection of the electron flow by means of a magnetic field, which is provided by means of a corresponding magnetic field unit. In order to interrupt the provision of X-ray radiation, it has been common to date to load at least one grid electrode with a suitable potential, such that a grid-cathode voltage arises between the grid electrode and the cathode electrode, which can lie in the range of approximately several hundred volts to approximately 4 kV, for example. At such a grid-cathode voltage, it is possible to realize a pinching of the electron flow in the X-ray tube, such that substantially no more electrons can reach the anode electrode. The grid-cathode voltage at which this effect occurs is also referred to as pinching voltage. Usually, the potential of the grid electrode is negative with respect to the potential of the cathode electrode. Furthermore, usually the potential of the anode electrode is positive with respect to the cathode electrode.

[0005] The region of the anode electrode, which is substantially hit by the electrons during the generation of the X-ray radiation, also referred to as focal spot, is advantageously adapted to the respective type of operation, especially with respect to the corresponding imaging method. Thereby, it is possible to realize a corresponding image quality for the respective application. For this purpose, it is possible to adjust a suitable focusing, or it is also possible to adjust a compromise with respect to the image quality and the as small as possible load of the X-ray tube, for example.

[0006] In many X-ray devices, especially in angiography, this is usually only difficult to realize with the use of magnetic field units due to the required structural dimensions. Therefore, it is endeavored to realize the focusing at least partially no longer by means of a magnetic field, but by means of a concentration caused by means of an electric field. In this case, US 4,361,901 discloses a multi-voltage X-ray switching system. For this purpose, it is known to load at least one grid electrode, which is suitable for the focusing, with a potential, which is at least partially settable between the cathode electrode and the anode electrode and / or at least partially also settable next to the cathode electrode. In this regard, the term "between" preferably also includes the region in which the grid electrode is at least partially set next to the cathode electrode. Thus, the grid electrode can have a limiting metal plate next to the cathode electrode, a web between a section-wise constituted cathode electrode, etc. DE 10 2007 042 108 A1, which discloses an electron source, for example, shows this teaching.

[0007] Even if the teaching has been verified in principle in the prior art, at least the following problem remains: At a pinching voltage switching to a pre-settable grid-cathode voltage for focusing the electron flow, the usually comparatively long high-voltage cable for operating the X-ray tube is discharged.

[0008] In the above teaching, the function of pinching the electron current is realized, for example, by means of a voltage converter with galvanic isolation, in order to achieve the potential isolation, for which purpose, for example, a transformer of corresponding construction can be provided, and by means of which the required pinching voltage can be quickly provided. By means of a short-circuiting switching element, the gate-cathode voltage can be quickly reduced, for example, to approximately zero, whereby the discharge of the parasitic capacitances of the connection cables can also be realized. In this circuit design, due to the required technical expenditure, which is usually not realized for actual value feedback, only a small accuracy of the gate-cathode voltage can be provided. For pinching the electron current, it is sufficient to realize at least the pinching voltage and to maintain the insulation strength of the system at the same time. However, for the accurate regulation of the gate-cathode voltage, in particular for the regulation of the electron current in a focused X-ray tube, this is not feasible here.

[0009] With regard to the focusing by means of the electric field, the above-mentioned voltage converter has also been used. Since usually a passive rectifier circuit is provided at the output terminals of the voltage converter, the gate-cathode voltage can only be changed slowly. The time constant can be related, inter alia, to the gate-cathode capacitance and to the discharge resistance connected in parallel thereto. However, only an inaccurate regulation of the gate potential can be realized thereby. Furthermore, the discharge by means of the discharge resistance can cause a long time constant upon discharge, in particular in the case of a large resistance value of the discharge resistance, or a high loss power in the discharge resistance upon application of the pinching voltage. SUMMARY

[0010] The object underlying the present application is to improve the use of the gate electrode not only for pinching the electron current but also, in particular, for focusing the electron current.

[0011] As a solution, the method, the circuit arrangement and the X-ray device according to the embodiments of the present application are proposed by means of the present application.

[0012] The features described by means of the embodiments of the present application result in an advantageous improvement scheme.

[0013] With regard to this method, it is proposed by means of the present application, in particular, that the first gate potential is provided by means of an adjustable voltage divider of the focusing unit, which is adjusted by means of a control circuit of the focusing unit in such a way that the control circuit is loaded with at least one galvanically isolated control signal of a control unit, which is galvanically isolated from the X-ray tube current, wherein the control signal is related to a preset value of the first gate potential, and the electrical power of the energy converter is adjusted in accordance with the preset value of the first gate potential.

[0014] With regard to such a circuit arrangement, it is proposed in particular with the present application that the focusing unit has an adjustable voltage divider and a control circuit for controlling the adjustable voltage divider, wherein the control unit is designed to supply the control circuit with at least one galvanically isolated control signal, which is associated with a preset value of the first gate potential, wherein the control circuit is designed to adjust the adjustable voltage divider in accordance with the at least one control signal, wherein the control unit is further designed to adjust the electrical power of the energy converter in accordance with the preset value of the first gate potential.

[0015] With regard to such an X-ray device, it is proposed in particular that the X-ray device has a circuit arrangement according to the present application.

[0016] The present application is based in particular on the idea that a rapid adjustment of the gate potential can be achieved in particular when adjusting with regard to the focusing operation. The present application makes use in particular of the knowledge that the parasitic capacitance of the connection cable, which electrically couples the focusing unit to the X-ray tube, can be recharged or discharged. The focusing unit should assist the active recharging or discharging of the gate capacitance or the gate-cathode capacitance and also of the capacitance of the connection cable by its construction, so that the time constant can be reduced in the course of a potential transformation, in particular in the course of the focusing operation. For this purpose, the focusing unit makes use of an adjustable voltage divider, by means of which the desired advantageous effects can be achieved. Namely, the adjustable voltage divider can achieve an improved, in particular accelerated, recharging or discharging of the parasitic capacitance as described above. For example, the time constant when transforming from a pinched-off electron flow to a focused electron flow can be reduced, in turn reducing the influence of the potential transformation on the properties of the focal spot. It is further possible to couple the focusing unit to the potential of the cathode electrode in particular with regard to the regulation of the gate-cathode voltage or the gate potential, whereby a more precise focusing of the electrode flow in the X-ray tube can be achieved. The use of magnetic deflection and the disadvantages that arise with it can be largely avoided. In particular, the structural length required for the magnetic deflection can be reduced, since the electrons no longer need to fly through a magnetic field. Capacitive focusing can be carried out by means of focusing elements present in the cathode region, for example a Wehnelt cylinder, so that the structural length can be shortened. Here, the present application takes into account the construction and / or properties mentioned at the outset, for example.

[0017] Furthermore, the regulation can also be achieved in the blocked operation or the pinched-off electron flow, wherein the voltage can remain limited in order to limit the voltage load of the components.

[0018] In order to be able to achieve a stable operation of the adjustable voltage divider in combination with the energy converter, the electrical power of the energy converter is adjusted by means of the control unit in accordance with the preset value of the first gate potential.

[0019] It is preferably proposed that the pinch potential or the pinch voltage is provided directly by means of the energy converter. In contrast, the focusing potential or the focusing voltage can be provided by means of the focusing unit, which for this purpose can utilize an adjustable voltage divider. For this purpose, the focusing unit can be supplied with electrical energy by the energy converter. Furthermore, it is preferably proposed that the energy converter does not regulate the gate potential or the gate voltage in the focusing mode in order to avoid positive feedback. With regard to the power to be provided, the energy converter can be adjusted in accordance with the gate potential currently to be provided, so that reliable operation of the focusing unit in the respective operating state can be reliably ensured. Thereby, for example, the power loss of the focusing unit, in particular of the voltage divider, can be kept low. The adjustment of the power can also at least partially comprise an adjustment of the voltage provided by the energy converter. Thus, the energy converter only needs to provide electrical power to such an extent that the focusing unit can also reliably adjust the gate potential to be adjusted. This can comprise an adjustment margin.

[0020] The energy converter is preferably an electrical energy converter which is coupled in terms of energy between at least two electrical networks. The energy converter, which is also sometimes referred to as energy transformer, can be designed for coupling the electrical networks in a galvanically isolated manner. The energy converter serves to convert electrical energy of a first form into electrical energy of at least one second form. The energy converter can be designed for realizing the energy conversion only in one direction. However, the energy converter can also be designed for realizing the energy conversion at least partially or sometimes in both directions.

[0021] The focusing unit is currently supplied with electrical energy by means of the energy converter in a galvanically isolated manner. Thereby, the focusing unit, which is electrically coupled to the gate electrode and to the cathode electrode for the normal operation, can be supplied with electrical energy by means of the energy converter in a potential-free manner. The focusing unit can thus be part of a first electrical network. The energy source which provides the required electrical energy can thus be part of a second electrical network. The first and the second electrical network can be coupled by means of the energy converter. It is thereby possible that the first reference potential of the first electrical network is different from the second reference potential of the second electrical network. This is advantageous in the case that the anode electrode is coupled to a ground potential, wherein the cathode electrode is normally loaded with a comparatively low potential in the normal operation. Thereby, an advantageous energy supply can be realized for the focusing unit, in particular. By means of the galvanic isolation, the energy converter can supply electrical energy for the focusing unit at least in a potential-free manner. The power of the energy converter is preferably not directly controlled by the focusing unit. Rather, the power adjustment of the energy converter is preferably carried out by means of a control unit. Herein, the control unit can take into account, in particular, the power currently required for the normal operation of the focusing unit and adjust the power of the energy converter in accordance therewith. In particular, the power of the energy converter can be directly adjusted by means of the control unit.

[0022] In principle, this naturally also applies with preference to a possible separate heating energy source, which can be used to supply the heating device of the cathode electrode with electrical energy. The heating energy source is thus preferably also configured without an electrical potential. For this purpose, the heating energy source can have a heating electrical energy converter which is configured with galvanic isolation. One or more energy converters can obtain electrical energy, for example, from a public power grid or an electrical energy store. At present, without an electrical potential means, in particular, that there is no need for an electrical connection to other electrical potentials of the circuit device.

[0023] The control signals can be transmitted in a galvanically isolated manner using an isolated converter, an isolated transformer, an optocoupler or the like. Thereby, the coupling in terms of signals between a signal source, for example a control unit, and a signal receiver, for example a focusing unit, can be realized in a manner without an electrical potential.

[0024] The electrical potential of the X-ray tube is preferably electrically isolated from the electrical potential of the control unit in order to achieve galvanic isolation.

[0025] The adjustable voltage regulator can have, for example, a series circuit composed of a resistance and an electronic component whose electrical conductivity is adjustable, wherein the gate electrode of the X-ray tube is electrically coupled to the intermediate terminal of the series circuit. The resistance can in principle naturally also be supplemented or replaced by a constant current circuit. The adjustable voltage regulator can in principle have, for example, at least one adjustable resistive element, in particular the above-mentioned electronic component, for example a transistor or the like which operates in linear operation. It is thereby possible to provide the desired gate-cathode voltage or the desired gate potential for the focusing of the electron flow using the electrical energy provided by the energy converter. It proves to be particularly advantageous to regulate the focusing of the electron flow by means of the focusing unit, in particular the control circuit. Thereby, an essentially constant regulation for generating X-ray radiation can be achieved even if the operating conditions change.

[0026] For this purpose, the control circuit can have a corresponding regulating circuit which is coupled to suitable measuring sensors. The measuring sensors can detect, for example, the emitted X-ray radiation and provide suitable sensor signals for the control circuit or the circuit device. The control circuit or the circuit device can evaluate the sensor signals and adjust the gate potential in accordance therewith. In this case, the control signal can be, for example, a desired value of the first gate potential. A high reliability can be achieved by means of the series circuit, since the desired function can be achieved by means of only a small number of electrical or electronic components. The focusing unit, in particular its control circuit, can be coupled in terms of communication or signals to the control unit and can obtain at least one control signal therefrom.

[0027] The value of the preset first gate potential can be provided by a control device of a superior of the X-ray device. The value can be related to an object to be examined which is loaded with X-ray radiation released by the X-ray tube.

[0028] The focusing unit preferably has a series resistor or shunt for electrical coupling to the energy converter. The series resistor can be the resistance of the above-mentioned adjustable voltage regulator, which is connected in series with the transistor of the focusing unit, for example. The series resistor makes it possible to bring the focusing unit into a defined operating state that can be preset, so that the gate potential of the gate electrode can be precisely regulated in the case of high reliability.

[0029] The focusing unit therefore comprises at least an adjustable voltage divider and a control circuit for adjusting the adjustable voltage divider. As a rule, the focusing unit is at least partially galvanically coupled to the electrical potential of the X-ray tube. This applies in particular to the gate electrode that is electrically coupled thereto, in order to be able to adjust the desired gate potential.

[0030] The control circuit is preferably an electronic hardware circuit, which can also at least partially have a program-controlled computer unit. The control circuit provides the desired functionality in order to adjust the adjustable voltage divider, so that at least the first gate potential can be adjusted, preferably in accordance with a value of the first gate potential that is transmitted together with a control signal. This adjustment can particularly preferably also comprise a regulation, which can have a detection of the gate potential, for example. This detected gate potential can be compared with a preset value of the first gate potential in accordance with the control signal. In accordance with the comparison, the adjustable voltage divider can then be adjusted. However, in principle, a control of the adjustable voltage divider without regulation can also be provided. In this case, the following possibility can additionally be proposed: the regulation functionality is achieved by detecting the focal point by means of suitable sensors and corresponding preset comparison values, wherein the control signal is then determined in accordance with the comparison. Further design variants and combinations are conceivable.

[0031] The electrical power of the energy converter is adjusted in accordance with the preset value of the first gate potential. Thereby, the focusing unit can be provided with the required electrical energy, so that the focusing unit can achieve the required adjustment on the adjustable voltage divider and, in particular, can ensure that the gate potential on the gate electrode substantially corresponds to the preset value of the first gate potential. For this purpose, it can be proposed that the value of the first gate potential is evaluated by the control unit and a corresponding energy converter signal is provided, which can be used to adjust the power to be converted of the energy converter. The energy converter is correspondingly designed, so that it adjusts the converted power in accordance with the energy converter signal.

[0032] Overall, the application makes it possible to significantly improve the functionality of the circuit arrangement and, in turn, also of the X-ray device, more precisely in particular with regard to the focusing of the electron flow using the electric field that is induced by means of the at least one gate electrode. The costly use of magnetic fields can therefore be significantly reduced, if not completely avoided.

[0033] It is further proposed that the electrical power of the energy converter is additionally selected in accordance with at least one electrical power, voltage or current of the focusing unit required by the focusing unit for providing the first gate potential. Thereby, the energy can be supplied to the focusing unit as required. It proves to be particularly advantageous if the electrical power of the energy converter is selected in accordance with the current of the focusing unit. Thereby, it is possible, inter alia, to largely avoid an over- and / or under-supply of the focusing unit with electrical energy. In particular, the use of an adjustable voltage divider can lead, in the case of a regulation of the adjustable voltage divider and the energy converter independently of one another, to a large dissipation power due to a positive feedback, for example, to an upper limit of the voltage for providing the gate potential, or in particular in the region of the adjustable voltage divider. Conversely, in the case of an output voltage for the potential of the gate electrode being too low, it can lead to the gate potential no longer reaching the preset value. With the improvement, the problem can be better reduced. From the variables on the side of the focusing unit, the current energy requirement or the current power can be determined, so that the energy converter can be controlled accordingly. Thereby, a good, reliable coordination between the energy supply of the focusing unit and the energy requirement for the regular operation can be achieved. The respective power requirement of the focusing unit can be determined in accordance with a data table, a measurement value, at least one preset value of the first gate potential, etc.

[0034] According to one improvement, it is proposed that the electrical power of the energy converter is determined using a characteristic diagram. The energy converter is therefore not operated, as is common in the prior art, such that the energy converter provides an adjustable constant voltage on the output side, but rather more precisely, is operated such that, in accordance with the operation of the focusing unit, a desired value of the voltage provided by the energy converter, inter alia, is extracted, which can ensure a reliable operation of the focusing unit in consideration of a regulation margin of the focusing unit. The desired value can be extracted from a characteristic diagram, for example, from a characteristic curve, etc. The characteristic diagram can exist, for example, in the form of a file, in which the required operating values of the energy converter, for example, the output voltage provided by the energy converter, etc., can be stored in an associated manner in accordance with the respective discrete operating states of the focusing unit. Overall, the method control according to the invention can thereby be further improved.

[0035] Furthermore, it is proposed that the electrical power of the energy converter is determined also in accordance with a regulation margin preset for the regulatable voltage divider. The regulation margin serves to indicate an excess value of the electrical power or of the electrical energy which should be provided in order to be able to regulate the regulatable voltage divider in a high dynamic as required without leaving the normal operating state of the regulatable voltage divider. In this connection, the improvement takes into account that the regulatable voltage divider can be regulated at a very high speed compared to the adjustment of the energy converter. It is thereby possible to largely decouple the time constant associated with the regulation of the regulatable voltage divider from the time constant of the power regulation of the energy converter. The regulation margin can be preset as a percentage supplement or also as a tolerance band in relation to a preset value.

[0036] Furthermore, it is proposed that the energy converter is operated in an operating mode in which the energy converter provides a regulatable constant current on the side of the focusing unit. In this way, the positive feedback effect set out at the beginning can be suppressed in an improved manner. The operating mode can correspond to a current source mode in which the provided current is regulated by the control unit. In this way, a good decoupling of the function of the control circuit in terms of regulation can be achieved.

[0037] It is also proposed that the energy converter has a voltage converter coupled to the electrical energy source and a galvanically isolated resonant converter, wherein the resonant converter is electrically coupled on the input side to the voltage converter and on the output side to at least the focusing unit, wherein the input current of the resonant converter is regulated in accordance with a preset value of the first gate potential. By this measure, the focusing and / or pinching of the electron flow can be further improved. The voltage converter can be designed as a DC / DC converter. Depending on the requirements, the voltage converter can be designed, for example, as a step-up converter (booster) or also as a step-down converter (buck). Combinations thereof can of course also be envisaged, for example in order to be able to achieve a wide input voltage range by means of the voltage converter. Furthermore, in some cases, a rectification can also be provided on the input side in addition, in order to be able to achieve a supply of energy from an alternating voltage source, for example the public power grid. The control or regulation on the side of the energy converter is thus no longer based on a voltage, but advantageously at least partially on a current. For the purpose of control or regulation, it can be proposed that the input current of the resonant converter is detected by means of a suitable current sensor, which provides a corresponding current sensor signal to the control unit. The control unit can evaluate this current sensor signal and control the energy converter accordingly, more precisely in particular the voltage converter. Basically, the resonant converter can also be formed by another galvanically isolated energy converter.

[0038] The current-isolated energy converter is supplied with electrical energy by the voltage converter in such a manner that the voltage converter provides a direct voltage for this purpose. Both the voltage converter and the current-isolated energy converter are preferably controlled by means of a control unit. For example, the direct voltage provided by the voltage converter can be regulated, in particular controlled, by means of the control unit. For this purpose, the provided direct voltage can be detected by means of a voltage sensor and a corresponding voltage signal can be transmitted to the control unit. The current-isolated energy converter is preferably designed as a current-isolated resonant converter. If the current-isolated energy converter is formed by a resonant converter, at least a part of the resonant inductance can be provided by a transformer designed as an isolation transformer for this purpose. The resonant circuit is connected, for example, to at least one half-bridge circuit by means of which a conventional resonant operation can be achieved. The function of the voltage converter and the current-isolated energy converter, in particular the resonant converter, is known to the person skilled in the art, so that a further detailed explanation thereof is currently omitted.

[0039] By combining the voltage converter with the resonant converter, a number of different operating modes are possible which allow the function of the circuit arrangement to be adapted to the respective specific operating situation in accordance with the requirements. It is thus possible, for example, to control the respective converter in the converter not only with respect to the voltage provided but also with respect to the current provided. This can be achieved, for example, by means of a control unit.

[0040] It is furthermore proposed that a minimum current value and a maximum current value are preset for the input current, the input current is detected and compared with at least the minimum or maximum current value and the voltage provided by the voltage converter for the resonant converter is regulated in accordance with the comparison. By means of this improved solution, it is possible to achieve a tolerance band control. The deviation of the minimum current value or the maximum current value from a preset average value can be selected to be the same for the minimum current value and the maximum current value. Of course, the application is not limited thereto and different deviations from the average value can also be provided. This design also makes it possible to achieve a tolerance band control. If too low a supply voltage is to be provided for the focusing unit, in particular for the adjustable voltage divider, the current through the voltage divider can become zero. The input current of the resonant converter would then also be zero. However, the cascade control can now be designed in such a manner that the voltage provided by the voltage converter is made larger. Thus, instead of regulating the voltage provided by the voltage converter, the current is more precisely regulated. If the voltage is increased as a result of the above-mentioned positive feedback, the input current is also increased, the maximum input current will be limited in a corresponding manner by the cascade control. Overall, it is thus possible to achieve a reliable regulation or control with little outlay.

[0041] It is further proposed that the frequency of the control signal is related to the preset value of the first gate potential and that the control circuit determines the preset value of the first gate potential from the frequency of the control signal. With this design, the value of the first gate potential can be transmitted from the control unit to the control circuit in a simple manner, so that the control circuit can adjust the adjustable voltage divider accordingly. In this case, the control signal is preferably an alternating voltage signal, the frequency of which can be adjusted by the control unit. Since the control signal is an alternating voltage signal, the alternating voltage signal can be transmitted to the control circuit or the focusing unit in a galvanically isolated manner by means of a galvanically isolated converter or transformer. It is thus possible in a simple manner to adjust the gate potential in accordance with the preset value of the first gate potential.

[0042] It is further proposed that the focusing unit is deactivated in the case of a preset, in particular preset minimum or maximum, frequency. Deactivation of the focusing unit in particular comprises at least the state in which the gate potential is negative compared to the potential of the cathode electrode, so that the electron flow is pinched off. In this operating state of the X-ray tube, essentially no X-ray radiation is emitted. For this purpose, it is proposed that, in addition to the focusing unit, a switching unit is provided, which, like the focusing unit, is supplied with electrical energy by the energy converter. It is proposed, for example, that the switching unit and the focusing unit are connected in series, so that the desired functionality can be achieved. It is further proposed, for example, that in the case of a frequency of the control signal that is less than a preset minimum frequency, the switching unit can achieve deactivation of the focusing unit and loading of the gate electrode with a gate potential as described above. Essentially similar embodiments can also be provided in duplicate for the maximum frequency. For this purpose, the control characteristic can be provided, for example, reversibly. Of course, this gate potential can also be achieved by the joint action of the focusing unit and the switching unit. The switching unit can also be included at least partially by the focusing unit. Overall, the operation of the X-ray tube can be further improved.

[0043] According to one refinement, it is proposed that the focusing unit is controlled in the case of a preset frequency, in particular a preset minimum or maximum frequency, so that both the switching unit and the transistor are operated in an on switching state to provide a gate short circuit. Thereby, a third operating state can be achieved in which the gate electrode can be short-circuited. Thereby, the pinching off of the electron flow and the focusing of the electron flow can be deactivated. For this purpose, the transistor is preferably operated in a switching operation that is different from the linear operation.

[0044] It is further proposed that the output current of the voltage converter is adjusted in accordance with a preset value of the first gate potential. This refinement uses the current source characteristic for the operation of the energy converter. This can in particular be adjusted separately for the focusing operation. The general control of the energy converter can take place outside the focusing operation, in particular by providing a preset voltage. Furthermore, of course, the possibility exists of changing the clock frequency of the resonant converter in order to operate the resonant converter in a corresponding resonance, in particular in the case of an LLCC resonant converter. At this resonant frequency, the output current is generally independent of the load, in particular is essentially determined only by the input voltage of the resonant converter and the tank inductance. As a result, the voltage converter and the resonant converter can be operated in a controlled manner, since, due to the current source characteristic, an appropriate, sufficiently large output voltage is always adjusted for the focusing unit. As a result, sufficient regulation margins can also be achieved for the adjustable voltage divider up to the maximum load.

[0045] It is further proposed that the resonant converter has a full bridge circuit with two half bridge circuits, wherein one of the two half bridge circuits is at least temporarily activated during the focusing operation, while the other of the two half bridge circuits is deactivated. As a result, for example, the transformer primary voltage can be roughly halved, which is particularly advantageous with regard to a significantly smaller focusing voltage. Deactivating a half bridge circuit means in particular that this half bridge circuit does not actively participate in the energy conversion. Preferably, it is completely switched off. However, it can be proposed that the deactivated half bridge circuit provides a current path, for example, for freewheeling current, etc., however, without intervention by means of a clock here. That is, the switching elements of this deactivated half bridge circuit are not loaded with a corresponding switching signal.

[0046] The half bridge circuits each have two series-connected switching elements, in particular semiconductor switches, by means of which a direct voltage provided by the voltage converter can be converted into an alternating voltage. This circuit topology is also referred to as full bridge circuit. The half bridge circuits are connected in parallel at the terminals and are operated in antiphase.

[0047] In the sense of the present disclosure, a semiconductor switch is a preferably controllable electronic switching element, for example a transistor, a thyristor, a combination circuit thereof, in particular with a parallel-connected freewheeling diode, for example a metal-oxide-semiconductor field-effect transistor (MOSFET), an insulated-gate bipolar transistor (IGBT), preferably with an integrated freewheeling diode, etc.

[0048] The intermediate terminal of the half bridge circuit is a terminal which is conductively connected to the connection point of the series-connected semiconductor switches. In the inverter operation, the converted alternating voltage is generally provided at this intermediate terminal.

[0049] The switching operation of a semiconductor switch in the form of a transistor means that in the on state a very low resistance is provided between the terminals forming the switching section, so that a high current flow at a very small residual voltage is possible. In the off state, the switching section of the semiconductor switch is high ohmic, i.e. it provides a high resistance, so that even in the case of a high voltage applied across the switching section, there is essentially no or only a very small, in particular negligible, current flow. This is different in the linear operation.

[0050] Furthermore, it is proposed that the circuit arrangement has a switching unit which is designed to load at least one gate electrode in a first switching state with a first gate potential of the focused electron flow and in a second switching state with a second gate potential for pinching off the electron flow between the anode electrode and the cathode electrode. Furthermore, the improvement is based on the idea that it is possible by a suitable combination of the switching unit and the focusing unit to provide the possibility of quickly switching the gate-cathode voltage or the gate potential of the gate electrode from the pinch-off voltage or the pinch-off potential to a predefinable focusing voltage or a predefinable focusing potential and / or vice versa. Here, it is added that the focusing unit can be used to recharge or discharge the parasitic capacitances of the connection cable and / or the gate electrode. By actively recharging the gate capacitance or the gate-cathode capacitance and the capacitance of the connection cable by the switching unit and the focusing unit, it is possible to reduce the time constant when switching from the pinch-off electron flow to the focused electron flow or vice versa, and thus to reduce the influence of the switching transition on the focal spot properties. Furthermore, it is possible to couple the focusing unit to the potential of the cathode electrode, in particular with regard to the regulation of the gate-cathode voltage or the gate potential, whereby it is possible to achieve a more precise focusing of the electron flow in the X-ray tube. Furthermore, the improvement makes it possible to integrate the circuit arrangement into the X-ray device in a simple manner. By the circuit arrangement according to the invention, it is possible to save construction space and costs.

[0051] Basically, the switch unit can have one or more suitable electromechanical switching elements in order to realize the desired switching function. However, the switch unit usually has one or more electronic switching elements, in particular semiconductor switching elements, for example for reasons of switching speed, by means of which the desired switching function of the switch unit can be realized. The switching elements can be formed, for example, by transistors, thyristors, combinations thereof or the like. It can be particularly advantageous for the proposed application to essentially operate a plurality of electronic switching elements in a series connection in a substantially synchronized manner. It is thereby also possible to realize an operation at a significantly greater maximum permissible operating voltage of the respective switching element by means of an electronic switching element which is constituted only for a part of the occurring voltage. The switch unit provides at least one first switching state in which the grid electrode is loaded with a first grid potential which releases an electron current, more precisely preferably a grid potential which is provided by the focusing unit. In a second switching state of the switch unit, at least one grid electrode can be loaded with a second grid potential for pinching off the electron current between the anode electrode and the cathode electrode. For this purpose, the switch unit can be electrically coupled with the energy converter, wherein the switch unit couples the energy converter with the X-ray tube such that the energy converter provides at least a pinch-off voltage between the grid electrode and the cathode electrode. This can be realized by a series circuit of the switch unit and the focusing unit.

[0052] Since the switch unit and the focusing unit are preferably connected in series, the second grid potential can be provided at least by the focusing unit. Thereby, the focusing unit can assist the respective switching transformation of the switch unit, whereby the function can be realized more reliably.

[0053] For the focusing, a grid-cathode voltage in the range from approximately zero V to approximately 500 V can be provided. The voltage can likewise be provided by the energy converter which acts as an operating voltage source. For this purpose, the focusing unit can adjust the voltage provided by the energy converter, for example, accordingly.

[0054] The control circuit is preferably connected to at least one switching element of the switch unit, in particular to at least one semiconductor switching element. The switch unit does not need to have a communication interface by means of which the switch unit is communicatively connected with the control unit. Thereby, the switching transformation of the switch unit can also be controlled by means of the control circuit.

[0055] The control unit can assume or provide other functions, in particular with regard to the focusing voltage, the pinch-off voltage, the provision of the operating voltage by the energy converter or the like. The control unit can be constituted electrically insulated from the circuit arrangement and is preferably connected to the circuit arrangement in a galvanically isolated manner. The control unit itself can be provided as a separate structural unit. However, it is preferably an integral part of the circuit arrangement and is particularly preferably integrated therein.

[0056] It is further proposed that at least two of the three operating states mentioned above are provided at least partially statically. This enables particularly fast switching between two successive operating states. This improvement proves particularly advantageous in the case of a switch between the focus operating state and the pinch operating state. The problem of an undefined focus spot with regard to the electron flow that occurs during the switch in the prior art can be largely reduced, if not completely avoided.

[0057] The advantages and effects given for the method according to the application also apply to the circuit arrangement according to the application and to the X-ray device equipped with the circuit arrangement according to the application, and vice versa. Thus, features stated according to the method can also be stated according to the device, and vice versa. BRIEF DESCRIPTION OF DRAWINGS

[0058] The embodiments set forth below relate to preferred embodiments of the present application. Features, combinations of features, and also features and feature combinations mentioned in the present description and / or shown in the attached drawings can not only be used in the respective stated combinations, but also in other combinations, i.e. also in combinations which are not explicitly stated. The application is therefore also to be considered as comprising all features and feature combinations mentioned in the present description and / or shown in the attached drawings, even if not explicitly stated in or with respect to a combination. Features, functions and / or effects stated in the embodiments can be self- contained and can be realized independently of other features, functions and / or effects described in the present application. Such independent features, functions and / or effects realize self- contained embodiments of the present application. A combination of features, functions and / or effects referred to in at least one of the embodiments is to be considered as self- contained embodiment of the present application, independently of combinations of other features, functions and / or effects referred to in at least one of the embodiments. The application is therefore also to be considered as comprising all features, combinations of features, functions and / or effects referred to in at least one of the embodiments, even if not explicitly stated in the combinations.

[0059] The drawings show:

[0060] Figure 1 a schematic circuit diagram of an X-ray device with an X-ray tube connected to a circuit arrangement, wherein a section of the gate control of the X-ray tube of the circuit arrangement is shown;

[0061] Figure 2 a schematic block diagram of a circuit arrangement comprising a section according to Figure 1 ;

[0062] Figure 3 a schematic block diagram of a circuit arrangement according to Figure 2 in a first operating state;

[0063] Figure 4 a schematic block diagram of a circuit arrangement according to Figure 2 in a first operating state;

[0064] Figure 5 a schematic graph view of the voltage of the circuit arrangement in the first operating state;

[0065] Figure 6 a schematic graph view of the supply current provided by the energy converter of the circuit arrangement according to Figure 2 in the first operating state;

[0066] Figure 7 a schematic graph view of the voltage of the circuit arrangement according to Figure 5 in the first operating state;

[0067] Figure 8 a schematic graph view of the supply current of the circuit arrangement according to Figure 6 in the first operating state;

[0068] Figure 9 a schematic graph view of the voltage of the circuit arrangement according to Figure 4 in the first operating state; and

[0069] Figure 10 a schematic graph view of the supply current of the circuit arrangement according to Figure 6 in the first operating state. DETAILED DESCRIPTION

[0070] Figure 1 A part of an X-ray device 10 with an X-ray tube 12 is shown in a schematic circuit diagram, the X-ray tube having an anode electrode 14 and a cathode electrode 16 arranged in a vacuum vessel. A gate electrode 18 is arranged between the anode electrode 14 and the cathode electrode 16. The anode electrode 14 is electrically connected with a terminal 52, the gate electrode is electrically connected with a terminal 50, and the cathode electrode 16 is electrically connected with two terminals 46, 48. The cathode electrode 16 has two terminals, namely the terminals 46 and 48, for heating purposes, via which the cathode electrode 16 can be supplied with electrical energy in order to heat the cathode electrode 16 in a regular operation to a predefinable temperature in order to enable a desired electron emission. For this purpose, the terminals 46, 48 are electrically connected with an electrical heating energy source 54.

[0071] The terminals 48, 52 are also electrically connected with a voltage source 56, which provides an anode-cathode voltage 72, which is also substantially applied between the cathode electrode 16 and the anode electrode 14. The anode potential of the anode electrode 14 is generally greater than the cathode potential of the cathode electrode 16.

[0072] In relation to the gate potential at the gate electrode 18, the electrons emitted from the cathode material of the cathode electrode 16 are accelerated to the anode electrode 14 in such a way that an electron flow 26 is formed. Upon the electrons hitting the anode electrode 14, which is generally constructed as a rotating electrode, X-ray radiation is generated and emitted by the X-ray tube 12.

[0073] The function of the X-ray tube 12 can be influenced by the gate potential at the gate electrode 18. It is thus possible, in one aspect, for the gate electrode 18 to be loaded with a second gate potential by means of which the electron current 26 between the anode electrode 14 and the cathode electrode 16 can be pinched off. The second gate potential is also referred to as the pinch-off potential. A corresponding gate-cathode voltage is thus referred to as the pinch-off voltage. The pinch-off voltage can be in the range of approximately zero kV to approximately 4 kV in the X-ray tube, for example. In the present design, the pinch-off voltage is higher than approximately 500 V, for example approximately 3.5 kV or even higher. The transition region between focusing and pinching off is undesirable, since it can cause undefined focal spots and undefined electron currents in the X-ray tube 12.

[0074] In general, the gate potential for at least pinching off the electron current 26 is negative with respect to the cathode potential of the cathode electrode 16.

[0075] The second gate potential is generally selected such that a safe and reliable pinching off of the electron current 26 is possible without impairing the electrical insulation in the X-ray device 10. In many cases, the maximum permissible gate-cathode voltage is approximately 4 kV, so the X-ray device 10, together with its components, is correspondingly constructed for said voltage.

[0076] During pinching off of the electron current 26, substantially no X-ray radiation is generated, since the electron current 26 is substantially suppressed.

[0077] In addition, the gate electrode 18 can be loaded with a first gate potential which allows the electron current 26 to be released, in particular focused. The corresponding gate-cathode voltage is also referred to as the focusing voltage. By means of the focusing voltage, it is possible not only for the electron current 26 to be released, preferably controlled, but also for the focusing of the electron current 26 with respect to impingement on the anode electrode 14 to be controlled at the same time. A focal spot 58 on the anode electrode 14 can thus be realized in a predefinable manner, for example. The generation of X-ray radiation can thus be influenced via another region.

[0078] The first terminal of the connection line 20 is connected to the electrical terminals 46, 48, 50. The opposite terminal of the connection line 20 is connected to the electrical terminals 60, 62, 64. The connection line 20 comprises a high-voltage cable, in particular, which influences the line capacitance 66 of the gate voltage. The electrical terminals 46, 48, 50, 52 are currently tube-side terminals. The electrical terminals 60, 62, 64 are currently generator-side terminals.

[0079] The heating energy source 54 is connected to the electrical terminals 60, 62. The circuit arrangement 22 is connected to the electrical terminals 62, 64, by means of which a gate potential for the gate electrode 18 can be provided in a predefinable manner. In Figure 1In the middle only a part of the circuit arrangement 22 is shown. From the following it will also be set out that Figures 2 to 4 In the middle a schematic block diagram of the circuit arrangement 22 is derived.

[0080] Furthermore, from Figure 1 It can be seen in the middle that the connection line 20 has a line capacitance, which in Figure 1 is shown symbolically by a capacitor 66. The capacitor 66 also comprises a grid-cathode capacitance of the X-ray tube 12, which, however, is not further shown in the middle. The capacitor 66 furthermore is related to the length of the cable and can for example have a capacitance value of approximately 4 nF. This is relevant for controlling the X-ray tube with regard to pinching the electron flow 26 and focusing the electron flow 26 only via the grid electrode 18, as will also be set out below. Figure 1

[0081] For the focusing, a grid-cathode voltage of approximately zero V to approximately 500 V is currently required. Depending on the configuration of the X-ray tube 12, the voltage can also be different, as is the pinching voltage.

[0082] For providing the grid potential, the circuit arrangement 22 has an energy supply device, which will also be set out in the following and which is only schematically identified with 28 in the middle. The energy supply device 38 has an internal resistance 68 via which the elements and components of the circuit arrangement 22 are supplied with electrical energy for the regular operation. Figure 1

[0083] The circuit arrangement 22 also has a focusing unit 24 connected in series with the switching unit 28. This series circuit, which is composed of the focusing unit 24 and the switching unit 28, is connected via the internal resistance 68 to the energy supply device 38 and is loaded with an operating voltage by the energy supply device.

[0084] The switching unit 28 currently provides two switching states, namely an on switching state as a first switching state and an off switching state as a second switching state. The on switching state corresponds to the focusing function and corresponds to the first operating state in the above. In the on switching state, the operating voltage is essentially applied to the focusing unit 24. As will also be set out below, the focusing unit 24 provides a grid-cathode voltage, which allows the electron flow 26 to be focused in a predefinable manner.

[0085] ​​In the second switching state of the switching unit 28, in which the switching unit 28 is in the switched-off switching state, the focusing unit 24 is substantially deactivated, such that substantially the operating voltage of the energy supply device 38 is provided between the grid electrode 18 and the cathode electrode 16. It is noted here that in the described operating state substantially no current flows at least in the steady state. Thus, if the operating voltage is approximately 3.5 kV, the described operating voltage is also applied between the grid electrode 18 and the cathode electrode 16 in the switched-off switching state of the switching unit 28. The voltage is currently negative with respect to the cathode electrode, so that the grid potential is less than the cathode potential. Thus, in this switching state the pinch-off of the electron stream 26 is achieved, so that substantially no more electrons reach the anode electrode 14, and in turn the generation of X-ray radiation is substantially interrupted.

[0086] In the first switching state, i.e. the switched-on switching state, of the switching unit 28, the focusing unit 24 is loaded with the operating voltage. The focusing unit 24 then provides a corresponding first grid potential, so that not only the electron stream 26 is released, but also a corresponding predefinable focusing of the electron stream 26 upon impingement on the anode electrode 14 can be achieved.

[0087] For this purpose, the focusing unit 24 comprises at least one series circuit composed of a resistor 30, which can also be used as a series resistor with respect to the connection of the energy supply device 38, and a transistor 32, which is currently formed by a field effect transistor, more precisely a self- blocking n-channel MOSFET. Thereby, an adjustable voltage divider is provided. However, depending on the design variant, other transistors can also be used here, in particular also bipolar transistors.

[0088] The transistor 32 currently has a gate terminal, which is not depicted and which is connected to a control circuit 40, which is schematically shown in Figure 1 , loads the gate terminal with a predefinable grid potential, so that on the intermediate terminal 34 of the series circuit a grid potential can be provided substantially in accordance with the predefinable value of the first grid potential. For this purpose, the transistor 32 is operated in linear operation, so that on the intermediate terminal 34 the corresponding grid potential can be adjusted in relation to the corresponding adjustment of the grid potential at the transistor 32. As can be seen in the diagram in Figure 1 , the focusing unit 24 is activated by switching on the switching unit 28 and deactivated by switching off. In the deactivated operating state of the focusing unit 24, the pinch-off potential thus corresponds to the predefinable value for the second grid potential.

[0089] Figure 2 The circuit arrangement 22 is now shown in a schematic block diagram. As can be seen in Figure 2 , the circuit arrangement 22 comprises, in addition to the already described focusing unit 24, a switching unit 28, which is connected to the focusing unit 24 and which is designed to switch the focusing unit 24 between a first, switched-on switching state and a second, switched-off switching state. The switching unit 28 is designed to be controlled by a control unit 36, which is connected to the switching unit 28 and which is designed to control the switching unit 28 in a corresponding manner. Figure 1In addition to the components and assemblies described, an energy converter 38 is provided for supplying energy, in particular to the focusing unit 24. For this purpose, the energy converter 38 is designed as a galvanically isolated energy converter in order to be able to supply energy to the focusing unit 24 and the switching unit 28, which are electrically coupled to the grid potential and the cathode potential of the X-ray tube 12. For this purpose, the energy converter 38 is connected to a DC voltage source 80. The DC voltage source 80 can in turn be supplied with electrical energy from the public power grid.

[0090] The energy converter 38 is connected to a control unit 74, which provides corresponding control signals for the regular operation of the energy converter 38. The control unit 74 is also communicatively coupled to a superior controller 90 via which operating values, in particular values of the first grid potential, can be preset.

[0091] In addition, an auxiliary converter 82 is provided, which is likewise supplied with electrical energy from the DC voltage source 80. The auxiliary converter 82 is likewise connected to the control unit 74 and is supplied with corresponding, not shown control signals for the regular operation by the control unit. The auxiliary converter 82 serves to provide two control signals 42, 44 in a galvanically isolated manner for controlling the control circuit 40. One of the control signals 42 serves to supply the control circuit 40 with electrical energy, while a second one of the control signals, more precisely the control signal 44, serves to control at least one operating value of the control circuit 40 and the units controlled by the control circuit 40, i.e. the focusing unit 24 and the switching unit 28. This will be explained further below.

[0092] The energy converter 38 currently has a voltage converter 76, which is electrically connected on the input side to the DC voltage source 80. On the output side, a resonant converter 78 is connected to the voltage converter 76, which provides an energy supply for the focusing unit 24 and the switching unit 28 in a galvanically isolated manner. For this purpose, the resonant converter 38 has an inverter 96, which is currently formed by two half-bridge circuits, which operate a resonant circuit, the inductance of which is formed at least partially by a primary side of a transformer 98 designed as an isolation transformer. On the secondary side, the transformer 98 is connected to a rectifier 100, which provides a corresponding DC voltage for the focusing unit 24 and the switching unit 28. A voltage detection unit 84 detects the converted voltage provided by the voltage converter 76 and provides a corresponding voltage signal to the control unit 74. The control unit 74 likewise provides corresponding control signals for the inverter 96, so that a desired converter operation of the resonant converter 78 can be achieved.

[0093] The transformer 98 also comprises an auxiliary winding, not further shown, which is connected to a transformer detection unit 86, which provides a corresponding transformer signal to the control unit 74.

[0094] The auxiliary converter 82 currently comprises an auxiliary inverter 88, which is connected to the DC voltage source 80, and an auxiliary transformer 92, which is connected to the auxiliary inverter 88. The auxiliary transformer 92 is likewise configured as an isolation transformer and is connected to the auxiliary inverter 88 by means of its primary winding. The secondary winding of the auxiliary transformer 92 is connected to a rectifier 94, which provides the control signals 42, 44 for the control circuit 40. As already explained, the control signal 42 serves to supply the control circuit 40 with energy, while the control signal 44 provides a corresponding control value, for example a preset value for the first gate potential of the gate electrode 18. It is currently proposed that the preset value of the first gate potential is related to the frequency of the control signal 44. As soon as the frequency of the control signal 44 is greater than a preset minimum frequency value, the switching unit 28 is switched into the switched-on switching state by the control circuit 40. At the same time, the transistor 32 is adjusted by the control circuit 40 in terms of its conductivity depending on the frequency, so that a gate-cathode voltage is provided at the terminals 62, 64 depending on the value of the first gate potential. The auxiliary inverter 88 is thus controlled correspondingly by the control unit 74, so that the corresponding control signals 42, 44 can be provided by means of the rectifier 94. The auxiliary converter 82 thus serves not only as an energy converter for the control circuit 40, in turn especially as an energy converter for the focusing unit for providing an energy supply which is free of potentials, but the auxiliary converter 82 at the same time also serves as a galvanically isolated signal converter. By means of the control of the auxiliary inverter 88 by the control unit 74, for example by applying a suitable modulation, a signal function for transmitting data or signals can thus be realized at the same time, whereby it is possible to realize that data or signals are transmitted depending on the control signal 44. The control unit 74 is thus galvanically isolated from the control circuit 40, especially the focusing unit. At the same time, it is possible to transmit control signals to the control circuit 40 in a galvanically isolated manner. The control signal 42 is thus an energy signal, which serves essentially to supply the control circuit 40 with energy here.

[0095] In Figure 2 A galvanic isolation 102 is shown in

[0096] The resonant converter 78 is currently configured as an LLCC resonant converter. In alternative design variants, another resonant converter type or galvanically isolated energy converter can of course also be provided here. The invention is not limited thereto.

[0097] Figure 2 A configuration according to Figure 1The control circuit 40 obtains the desired value of the gate potential and the switching state of the switching unit 28 from the control unit 74. The units currently operate independently of one another. Both realize a corresponding regulation function. The control unit 74 controls or regulates the energy converter 38, wherein the control unit 74 obtains corresponding control commands and data from a superior controller 90. The communication connection between the superior controller 90 and the control unit 74 is currently embodied as a one-way communication connection. However, the application is not necessarily limited thereto. Rather, the communication connection can also be embodied bidirectionally.

[0098] The control circuit 40 assumes the function of regulating the adjustable voltage divider 36 and accordingly actuates the transistor 32. The corresponding desired value and switching state are transmitted from the control unit 74 to the control circuit 40 via the auxiliary converter 82. Here, basically two operating states can be distinguished, more precisely the first operating state, in which the switching unit 28 is currently in the on switching state, and the circuit arrangement 22 is in the focusing operation, in which the gate potential of the gate electrode 18 is regulated by means of the focusing unit 24 according to a preset value of the first gate potential, which is transmitted as a desired value by the control unit 74 to the control circuit 40. In this regard, the control circuit 40 provides a regulation function and accordingly regulates the gate potential of the gate electrode 18. At the same time, in the present design, the gate potential also serves as a reference potential for the focusing unit. In alternative designs, this can change, and for example the cathode potential can also be selected as a reference potential. However, the function of the application is independent thereof.

[0099] In the second operating state, also referred to as gate cut-off, the switching unit 28 is switched by the control circuit 40 into the off switching state, so that a pinch-off potential is applied to the gate electrode 18. The operating state is regulated by the control circuit 40 by means of the control signal 44.

[0100] In the second operating state, the focusing unit 24 is also deactivated, as is shown in accordance with Figure 3 the drawing, and the switching unit 28 is in the off switching state. No gate potential is generated on the high-voltage side. In this operating state, the gate-cathode voltage is related to the voltage provided by the energy converter 38, which is related to the output voltage of the voltage converter 76. In this operating state, the voltage converter 76 can be operated unregulated. In contrast, regulation can be carried out taking into account the voltage provided by the auxiliary winding of the transformer 98 via the transformer detection unit 86. This variable can provide an actual variable compared to the actuating variable provided by the output voltage of the voltage converter 76.

[0101] In this operating state, the resonant converter 78 operates at a fixed frequency at the LLCC operating point with an invariant output voltage. The actual value of the gate potential used for regulation in this operating state is detected by measuring the voltage at the auxiliary winding on the primary side of the transformer 98. The gate-cathode voltage can be mapped by means of evaluation through the magnetic coupling between the secondary winding and the auxiliary winding of the transformer 98. Therefore, it is feasible to regulate the gate-cathode voltage on the primary side without direct electrical coupling to the high-voltage side.

[0102] In focused operation or the first operating state, the difference lies in that the adjustable voltage divider 36 now loads the transformer 98 on the secondary side. As already explained, the gate potential is regulated by the adjustable voltage divider 36 as follows: the current passing through the adjustable voltage divider 36 is changed by the transistor 32 by altering its conductivity. As the current increases, the voltage drop across the resistor 30 and the internal resistor 68 increases. The greater this voltage drop, the lower the gate-cathode voltage at the output or intermediate terminal 34 of the adjustable voltage divider. Because the auxiliary winding approximately maps the voltage on the secondary side of the energy converter 38, this voltage drop is detected. This is adjusted by the control unit 74, where the voltage supplied by the energy converter 38 is boosted again. The control circuit 40 reacts by correspondingly controlling the transistor 32 to adjust the boosted voltage. This creates an undesirable positive feedback, which not only causes high power loss, especially in the adjustable voltage divider 36, but also overloads, eventually leading to component failure. A similar situation occurs in the reverse regulation case.

[0103] This feature is based on Figure 5 and 6 The schematic diagram is shown schematically. Figure 5 A schematic graphical view showing the voltage of circuit device 22 in this first operating state, while Figure 6 Shown in the first operating state Figure 1 The diagram shows a schematic view of a portion of the supply section of the circuit device 22. Figure 5 In the graph, the vertical axis is related to voltage, while the horizontal axis is related to time. Figure 6 In the graph, the vertical axis is related to the current, while the horizontal axis is related to time. Figure 5 and 6 Their timelines correspond to each other. Figure 5 and Figure 6 Related.

[0104] Figure 5 The voltage variation curve is shown, while Figure 6 The corresponding current change curves are shown. This invention is not applied here. The output voltage of the regulating transformer 98 (curve 106), more precisely, in the case of...Figure 1 The voltage at the element marked 68 in the attached figure. Here, the current focus is on the element with transformer 98 ( Figure 2 The leakage inductance of the line resistance. Reduce the desired value of the gate voltage. Therefore, according to... Figure 1 The control unit improves the penetration Figure 1 The current in transistor 32 is increased to improve the voltage drop at component 68. This results in an increase in input current ( Figure 6 Therefore, the input voltage of transformer 98 (corresponding to) Figure 1 The transformed voltage (or figure 38) increases, thereby generating positive feedback.

[0105] As from Figure 5 and Figure 6 As can be seen, the operating state is adjusted over a period of approximately 3ms to approximately 4ms, during which the gate-cathode voltage is approximately 250V, and the gate-cathode voltage is... Figure 5 The curve 108 is shown in the figure. The voltage supplied upstream of the internal resistor 68 of the energy converter 38 is approximately 500V, as shown in the curve 104. The voltage across the focusing unit 24, which is connected in series with the switching unit 28, which is currently in the on state, is approximately 300V, as shown in the curve 106. According to... Figure 6 In the graph, approximately 40 mA of current is supplied for this time period, and this current flows through the adjustable voltage divider 36. This is shown in graph 110.

[0106] At time t = 4 ms, the desired value for the gate-cathode voltage or the first gate potential is changed by means of control signal 44, more precisely, the gate-cathode voltage is changed to approximately 150 V, as per this... Figure 5 As can be seen in graph 108. Due to the aforementioned positive feedback, control unit 74 now controls energy converter 38 such that the voltage provided by said energy converter compensates for the higher load, resulting in a substantially constant voltage according to graph 106. For this purpose, the voltage provided by energy converter 38 is correspondingly increased, more precisely, increased to a value of approximately 1000V. From approximately t = 6.5ms, the value of the first gate potential then returns to the value given before time point t = 4ms. The voltage changes accordingly according to graphs 104 and 108. Figure 6 As can be seen, a current of approximately 150mA exists in the range from t = 4ms to t = 6.5ms. During this time period, this causes considerable power loss, which must be supplied not only through the energy converter 38 but also simultaneously on the high-voltage side, particularly through the adjustable voltage divider 36. This can also cause malfunctions or interference. Scenarios for reducing or avoiding this problem are described below.

[0107] Furthermore, a third operating state can be provided, in which the switching unit 28 is in the on-switching state and the transistor 32 is operated in the on-switching state in the switching operation. As a result, a short circuit of the gate electrode can be possible.

[0108] Figure 7 and 8 relate to the same schematic diagram views as Figure 5 and 6 , likewise for the first operating state, more precisely in the case of application of the application, in which the voltage provided by the energy converter 38 is fixedly adjusted by the voltage converter 76. The two figures are also related to each other. The graph again relates to the same variables as previously explained with regard to Figure 5 and Figure 6 . As can be seen from Figure 7 and Figure 8 , here the voltage provided by the energy converter 38 is now fixedly adjusted by the control unit 74 to a fixed value of approximately 500 V. At the time point t = 4 ms, the change state explained with regard to Figure 5 and Figure 6 is again induced. It results from the view that the gate-cathode voltage is adjusted accordingly. At the same time, here the supply voltage for the adjustable voltage divider 36 is also reduced by a small value. At the time point of approximately t = 6.5 ms, the change is again resumed. As can be seen from Figure 8 , the current likewise increases slightly. As can be seen from Figure 7 and Figure 8 , in the case of application of the application, a stable operating behavior can be achieved without large loss power compared to the application in the first operating state shown in Figure 5 and Figure 6 .

[0109] The value of the first gate potential is preset by the superior controller 90. The control unit 74 provides the output voltage accordingly by the energy converter 38. Furthermore, the preset value for the first gate potential is transmitted to the control circuit 40 via the auxiliary converter 82. Depending on the frequency of the control signal 44, the control circuit 40 recognizes the switching state for the switching unit 28 and switches said switching unit into the on-switching state. The control circuit 40 recognizes that the frequency is greater than a preset minimum frequency below which the switching unit 28 should be switched in the off-switching state. Furthermore, a preset maximum frequency can be proposed, at which, upon detection by the control circuit 40, a direct coupling to the cathode potential via the switching unit 28 and the transistor 32 is effected, whereby a short circuit between the gate electrode 18 and the cathode 16 can almost be achieved. An intermediate value with regard to the frequency can then be used in order to determine the corresponding value for the first gate potential in such a way that the corresponding value is associated with the corresponding frequency.

[0110] The function of the circuit principle can also be seen in the following Figure 3 The schematic circuit diagram of the circuit arrangement 22 according to Figure 2 is used for the first operating state. While the unit 86 is used for the second operating state.

[0111] In an alternative design with respect to the second operating state, it can be proposed to utilize the output current of the voltage converter 76 in order to simplify the characteristic map for the control or regulation. In this case, the control or regulation can be carried out in accordance with the output current.

[0112] In a further alternative with respect to the second operating state, a minimum value and a maximum value of the input current of the resonant converter 78 can be preset. A tolerance band regulation can then be realized on the basis thereof. In this case, for example, the voltage provided by the energy converter 38 is too small for the preset value of the first gate potential regulated by the adjustable voltage divider 36, as a result of which the current through the transistor 32 can become zero as a result of the regulating function of the control circuit 40. As a result of this, the input current of the resonant converter 78 can also fall below the minimum value. It is proposed in this case that the control unit 74 carries out a regulation such that the voltage provided by the voltage converter 76 is increased. The regulation of the voltage is then no longer carried out, but instead a regulation of the current is carried out instead. If the positive feedback described above increases the voltage provided by the energy converter and thus also the current for the adjustable voltage divider 36, then the maximum current will also be able to be limited in the same way. It is generally possible to achieve that, when applying the present application, the input voltage of the transformer 98 remains substantially constant at least in the second operating state.

[0113] Figure 9 and Figure 10 The first operating state of a further design according to the application is illustrated in a similar manner to the schematic diagram Figure 5 and Figure 6 as will be set out hereinafter. Figure 9 and Figure 10 The reference numerals of the graphs in Figure 5 and Figure 6 correspond to the reference numerals of the corresponding graphs in Figure 5 and Figure 6The axes of the graphs already explained. The two figures are also interrelated. In this design of the application, for the first operating state it is proposed that, at least in the focusing operation, the voltage provided by the energy converter 38 is based on the current source characteristic. This can be achieved by means of a suitable regulation by the control unit 74. Furthermore, the possibility exists of increasing the operating frequency or clock frequency of the resonant converter 78 in order to have it operate in actual resonance, in particular in LLCC resonance. At this frequency, the output current of the resonant converter 78 is essentially independent of the load and is determined only by the input voltage of the resonant converter 78 and the oscillation loop inductance. Thereby, both the regulation by the controller 74 and the resonant converter itself can be operated in a controlled manner, since due to the current source characteristic an appropriate, sufficiently high voltage can always be formed at the output of the energy converter 38. Here, a regulation margin can be achieved which is sufficient for the regular operation of the focusing unit 24, in particular of the adjustable voltage divider 36. This is achieved by means of a suitable control of the energy converter 38, in particular of the voltage divider 36, in order to have the voltage at the output of the energy converter 38 be in the range of the focusing voltage, in particular in the range of the focusing voltage of the focusing unit 24. The voltage divider 36 can be controlled in a manner known per se, in particular by means of a control signal from the control unit 74. The control unit 74 can be designed in a manner known per se, in particular as a microcontroller or microprocessor. Figure 4 The schematic block diagram according to Fig. 11 shows that, in the third operating state, the voltage provided by the energy converter 38 is even lower than in the time period before t = 4 ms. Thereby, a regular operation with particularly low power can be achieved. This is advantageous for the construction of the circuit arrangement, in particular of the X-ray device 10, since, on the one hand, significantly less power is required compared to the first operating state, and, on the other hand, components can be constructed more cost-effectively and more compactly due to the significantly lower power in the regular operation.

[0114] As can be seen from the graphs 110 and 112, the current according to the graph 110, independently of the implementation of the change in the value of the first gate potential, is almost independent of the value of approximately 10 mA. From this it follows that the corresponding voltage changes. As can be seen in comparison with the graph 112, in the third operating state the voltage provided by the energy converter 38 is even lower in the time period of approximately 4 ms to approximately 6.5 ms than in the time period before t = 4 ms. Thereby, a regular operation with particularly low power can be achieved. This is advantageous for the construction of the circuit arrangement, in particular of the X-ray device 10, since, on the one hand, significantly less power is required compared to the first operating state, and, on the other hand, components can be constructed more cost-effectively and more compactly due to the significantly lower power in the regular operation. Figure 9 Figure 10 As can be seen from the graphs 110 and 112, the current according to the graph 110, independently of the implementation of the change in the value of the first gate potential, is almost independent of the value of approximately 10 mA. From this it follows that the corresponding voltage changes. As can be seen in comparison with the graph 112, in the third operating state the voltage provided by the energy converter 38 is even lower in the time period of approximately 4 ms to approximately 6.5 ms than in the time period before t = 4 ms. Thereby, a regular operation with particularly low power can be achieved. This is advantageous for the construction of the circuit arrangement, in particular of the X-ray device 10, since, on the one hand, significantly less power is required compared to the first operating state, and, on the other hand, components can be constructed more cost-effectively and more compactly due to the significantly lower power in the regular operation. Figure 9 Figure 5

[0115] In order to be able to achieve further advantages with regard to the regular operation it can be proposed that, in particular, the inverter 96 can be operated dynamically with regard to its operating mode. Here, it can be taken into account that the blocking voltage is usually in the range of several thousand volts. In contrast, the focusing voltage in the focusing operation is usually only a few 100 V. It can therefore be advantageous to deactivate one of the half-bridge circuits of the inverter 96 in the focusing operation. Thereby, the voltage transfer ratio of the resonant converter 78 can be reduced accordingly, essentially halved.

[0116] ​​​It is also possible in an alternative design to provide two separate converters. When switching between the provision of pinch voltage and focus voltage, it is possible to switch between the outputs of the converters. Thereby, for example, a short switching time, in particular a large edge steepness, can be achieved, for example when switching from focusing to cutting off or pinching off the electron stream. The switching time for cutting off or pinching off the electron stream after focusing can be determined by the focusing unit. Each of the converters can be optimally configured with respect to its output voltage range.

[0117] The embodiments are merely illustrative of the present application and are not restrictive thereof.

Claims

1. Method for operating an X-ray tube (12) having at least one grid electrode (18) arranged between an anode electrode (14) and a cathode electrode (16), wherein - an electron flow (26) from the cathode electrode (16) to the anode electrode (14) is focused by means of a focusing unit (24) in such a way that the focusing unit (24) loads the grid electrode (18) with a first grid potential at least in a focusing mode in order to focus the electron flow (26), - the focusing unit (24) is supplied with electrical energy in a galvanically isolated manner by means of an energy converter (38), - the first grid potential is provided by means of an adjustable voltage divider (36) of the focusing unit (24), and - the adjustable voltage divider (36) is adjusted by means of a control circuit (40) of the focusing unit (24) in such a way that the control circuit (40) is loaded with at least one galvanically isolated control signal (42, 44) of a control unit (74) which is galvanically isolated from the X-ray tube (12), wherein the control signal (42, 44) is related to a preset value of the first grid potential, characterized in that - an electrical power of the energy converter (38) is adjusted in accordance with the preset value of the first grid potential. The electrical power of the energy converter (38) is also selected in accordance with at least one electrical power, voltage or current of the focusing unit (24) which is required by the focusing unit (24) in order to provide the first grid potential. The electrical power of the energy converter (38) is determined using a characteristic map, wherein the characteristic map can be present in the form of a file in which required operating values of the energy converter can be stored in accordance with corresponding discrete operating states of the focusing unit. The energy converter (38) is operated in an operating mode in which the energy converter (38) provides an adjustable constant current on the focusing unit side. The electrical power of the energy converter (38) is furthermore determined in accordance with an adjustment margin which is preset for the adjustable voltage divider (36). The energy converter (38) has a voltage converter (76) which is coupled to an electrical energy source (80) and a galvanically isolated resonant converter (78), wherein the resonant converter (78) is electrically coupled on the input side to the voltage converter (76) and on the output side to at least the focusing unit (24), wherein an input current of the resonant converter (78) is adjusted in accordance with the preset value of the first grid potential. A minimum current value and a maximum current value are preset for the input current, the input current is detected and compared to at least the minimum current value or the maximum current value, and a voltage which is provided by the voltage converter (76) for the resonant converter (78) is adjusted in accordance with the comparison.

2. The method of claim 1, wherein, A frequency of the control signal (44) is related to the preset value of the first grid potential, and the control circuit (40) determines the preset value of the first grid potential from the frequency of the control signal (44).

3. The method according to claim 1 or 2, characterized in that, The focusing unit (24) is deactivated in the event of a preset frequency.

4. The method according to claim 1 or 2, characterized in that, ​ 5. The method according to claim 1 or 2, characterized in that, ​ 6. The method of claim 1 or 2, wherein, ​ 7. The method of claim 6, wherein, ​ 8. The method of claim 1 or 2, wherein, ​ 9. The method of claim 8, wherein, ​ 10. The method of claim 6, wherein, The frequency of the control signal (44) is related to a preset value of the first gate potential, and the control circuit (40) determines the preset value of the first gate potential from the frequency of the control signal (44).

11. The method of claim 10, wherein, The output current of the voltage converter (76) is adjusted in accordance with the preset value of the first gate potential.

12. The method of claim 6, wherein, The resonant converter (78) is operated in a resonant mode at least throughout the focusing operation.

13. The method of claim 6, wherein, The resonant converter (78) has a full bridge circuit with two half bridge circuits, wherein one of the two half bridge circuits is activated at least temporarily during the focusing operation, while the other one of the two half bridge circuits is deactivated.

14. The method of claim 9, wherein, The preset frequency is a preset minimum or maximum frequency.

15. Circuit arrangement (22) for operating an X-ray tube (12), the X-ray tube (12) having at least one gate electrode (18) arranged between an anode electrode (14) and a cathode electrode (16), the circuit arrangement (22) having: - a focusing unit (24) for focusing an electron flow (26) from the cathode electrode (16) to the anode electrode (14), wherein the focusing unit (24) is designed for loading the gate electrode (18) with a first gate potential at least in a focusing operation in order to focus the electron flow; - an energy converter (38) for supplying the focusing unit (24) in a galvanically isolated manner with electrical energy; and - a control unit (74) galvanically isolated from the X-ray tube (12) for adjusting the electrical power of the energy converter (38), wherein the focusing unit (24) has an adjustable voltage divider (36) and a control circuit (40) for controlling the adjustable voltage divider (36), wherein the control unit (74) is designed for providing at least one galvanically isolated control signal (42, 44) for the control circuit (40), the control signal (42, 44) being related to a preset value of the first gate potential, wherein the control circuit (40) is designed for adjusting the adjustable voltage divider (36) in accordance with the at least one control signal (42, 44), characterized in that the control unit (74) is further designed for adjusting the electrical power of the energy converter (38) in accordance with the preset value of the first gate potential.

16. The circuit arrangement of claim 15, characterized by There is provided a switching unit (28) designed for loading at least one gate electrode (18) with a first gate potential for focusing the electron flow (26) in a first switching state and with a second gate potential for pinching off the electron flow (26) between the anode electrode (14) and the cathode electrode (16) in a second switching state.

17. An X-ray apparatus (10) having an X-ray tube (12), the X-ray tube (12) having at least one grid electrode (18) arranged between an anode electrode (14) and a cathode electrode (16), and a circuit arrangement (22) connected to the X-ray tube (12) by means of a connection line (20) for operating the X-ray tube (12), characterized in that the circuit arrangement (22) according to claim 15 or 16 is formed.

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