Method and circuit arrangement for controlling an X-ray tube and X-ray apparatus

Abstract

The present invention relates to a method for controlling an X-ray tube (12), the X-ray tube 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), and the at least one grid electrode (18) is loaded in a first switching state with a first grid potential for clamping off the electron flow (26) between the anode electrode (14) and the cathode electrode (16) and in a second switching state with a second grid potential for releasing the electron flow (26). According to the invention, the second grid potential is provided at least by the focusing unit (24).

Description

Field of the Invention

[0001] The present invention relates to a method for controlling an X-ray tube having at least one grid electrode disposed 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, and at least one grid electrode is loaded with a first grid potential for clamping off the electron flow between the anode electrode and the cathode electrode in a first switching state and with a second grid potential for releasing the electron flow in a second switching state by means of a switching unit. The present invention also relates to a circuit arrangement for controlling an X-ray tube having at least one grid electrode disposed between an anode electrode and a cathode electrode, the circuit arrangement having: a focusing unit for focusing an electron flow from the cathode electrode to the anode electrode; and a switching unit configured to load at least one grid electrode with a first grid potential for clamping off the electron flow between the anode electrode and the cathode electrode in a first switching state and with a second grid potential for releasing the electron flow in a second switching state. Finally, the present invention also relates to an X-ray device having: an X-ray tube having at least one grid electrode disposed between an anode electrode and a cathode electrode; and a circuit arrangement for controlling the X-ray tube connected to the X-ray tube by means of a connecting line. Background Art

[0002] X-ray tubes, methods for their operation, and control devices therefor are widely known in the prior art. An X-ray tube is a special type of vacuum electron tube that is currently used to generate X-ray radiation for different purposes in a regulated operation. X-ray devices are usually also part of imaging devices, such as those used, for example, in medical diagnostics or also in quality assurance. X-ray tubes generally use the following principle: electrons are strongly accelerated according to the type of electron flow by appropriately setting the voltage between the cathode electrode and the anode electrode, and under preset conditions, the electrons impinge on the anode electrode. Here, X-ray radiation is released. The release of X-ray radiation can in particular be influenced by the impact area on the anode, which can be set at least in part by focusing the electron flow.

[0003] In such an X-ray tube, if the X-ray tube is of a monopolar configuration, the anode-cathode voltage applied between the anode electrode and the cathode electrode can be from about 60 kV to about 150 kV. In a bipolar X-ray tube, the voltage can be from about 30 kV to about 75 kV.

[0004] In the prior art, it is common to focus an electron beam by means of a magnetic field, which is provided by a corresponding magnetic field unit. In order to interrupt the provision of X-ray radiation, it has hitherto been common to apply a suitable electric potential to at least one grid electrode such that a grid-cathode voltage occurs between the grid electrode and the cathode electrode, which grid-cathode voltage can, for example, be in the range of approximately a few hundred volts to approximately 4 kV. At such a grid-cathode voltage, it is possible to pinch off the electron beam in an X-ray tube such that substantially no electrons can reach the anode electrode. The grid-cathode voltage at which this effect occurs is sometimes also referred to as the pinch-off voltage.

[0005] The region of the anode electrode, also known as the focal spot, which the electrons essentially strike during the generation of X-ray radiation, is advantageously matched to the respective operating type, in particular with respect to the respective imaging method. Thereby, the respective image quality can be achieved for the respective application. For this purpose, a suitable focusing can be set, or, for example, a compromise with respect to the image quality and the smallest possible load on the X-ray tube can also be set.

[0006] In many X-ray devices, especially in angiography, this is usually difficult to achieve with a magnetic field unit due to the required structural dimensions. Therefore, efforts are made to achieve focusing by means of a magnetic field by means of focusing by means of an electric field. For this purpose, it is known to apply a suitable electric potential for focusing to at least one grid electrode which is arranged, for example, at least partially between the cathode electrode and the anode electrode and / or at least partially also beside the cathode electrode. In this context, the term "between" also includes the region in which the grid electrode is arranged at least partially beside the cathode electrode. Thus, the grid electrode can have a bounding metal plate beside the cathode electrode, a tab between segmented cathode electrodes, etc. Such teachings are known, for example, from DE 10 2013219 173 A1, which discloses a voltage supply device for the electric focusing of an electron beam. In addition, DE 10 2009035 547 A1 discloses a voltage regulating element which is supposed to be suitable for setting the cathode voltage of an X-ray tube.

[0007] Even if the teachings have in principle proven in the prior art, there is at least one problem when switching the pinch-off voltage to a presettable grid-cathode voltage for focusing the electron beam during the discharge of the usually relatively long high-voltage cable used for controlling the X-ray tube.

[0008] In the above teachings, for example, current isolation for achieving electrical isolation is used through a voltage converter to implement the function of clamping off the electron flow. For this purpose, a correspondingly configured transformer can be used, for example, and the required clamping voltage can be provided quickly with the aid of the transformer. The gate-cathode voltage can be quickly reduced with the aid of a short-circuit switching element, for example, reduced to approximately zero V, whereby the parasitic capacitance of the connecting cable can also be discharged. In this circuit concept, due to the usually required technical effort, a feedback of the actual value is not implemented, and thus the gate-cathode voltage can only be provided with a small accuracy. For clamping off the electron flow, it is basically sufficient to at least achieve the clamping voltage and at the same time maintain the insulation strength of the system.

[0009] An improvement of the above structure proposes a jointly controlled transistor cascade connected in series with the X-ray tube on the cathode side. If the transistor is operated in a high-resistance operating state, a corresponding voltage can be formed due to the current through the X-ray tube according to the type of negative feedback. Thus, the clamping voltage can also be at least partially provided in such a way that the corresponding electrical potential of the voltage is applied to the gate electrode of the X-ray tube. However, the adjustment or precise setting of the gate-cathode voltage is not possible thereby.

[0010] Regarding the focusing by means of an electric field, the above voltage converter has also been used. Since a passive rectifier circuit is usually provided at the output terminals of the voltage converter, the gate-cathode voltage can only be changed slowly. The time constant can be related in particular to the gate-cathode capacitance and also to the discharge resistor connected in parallel with the gate-cathode capacitance. However, only an imprecise setting of the gate potential can be achieved thereby. In addition, the discharge through the discharge resistor can either cause a long time constant during discharge, especially at a high resistance value of the discharge resistor, or cause a high power loss in the discharge resistor when the clamping voltage is applied. Summary of the Invention

[0011] The object on which the present invention is based is to improve the use of the gate electrode for clamping off the electron flow and also for focusing the electron flow.

[0012] As a solution, the present invention proposes a method, a circuit arrangement, and an X-ray device according to embodiments.

[0013] Advantageous improvements result from the features of the embodiments.

[0014] Regarding such a method, the present invention particularly proposes that at least a second gate potential is provided by a focusing unit.

[0015] Regarding such a circuit arrangement, it is particularly proposed that the switching unit and the focusing unit are connected in series.

[0016] Regarding such an X-ray device, it is particularly proposed that the X-ray device has a circuit arrangement according to the present invention.

[0017] The present invention is also based on the following concept: It is feasible that through a suitable combination of a switching unit and a focusing unit, the following feasibility can be achieved: quickly switching the gate-cathode voltage or the gate potential from the pinch-off voltage or the pinch-off potential to a preset focusing voltage or a preset focusing potential. Here, the focusing unit can be additionally used to recharge or discharge the parasitic capacitance of the connecting cable. By actively recharging the gate capacitance or the gate-cathode capacitance and the capacitance of the connecting cable by the switching unit and the focusing unit, the time constant when switching from the pinched-off electron flow to the focused electron flow can be reduced, and thus the influence of the switching on the characteristics of the focal spot can be reduced. In addition, it is feasible that, especially with regard to the regulation of the gate-cathode voltage or the gate potential, the focusing unit is coupled to the potential of the cathode electrode, whereby more precise focusing of the electron flow in the X-ray tube can be achieved. Here, a one-way transmission of the desired value may be sufficient for the regulation. Therefore, especially when considering the high potential difference in the specified operation, the actual value transmission can be saved.

[0018] In addition, the present invention enables the circuit device to be integrated into the X-ray device in a simple manner. The structural space and cost can be saved by the circuit device according to the present invention.

[0019] The switching unit may have one or more suitable electromechanical switching elements for the above reasons to achieve the desired switching function. Preferably, however, the switching unit has one or more electronic switching elements, especially semiconductor switching elements, by means of which the desired switching function of the switching unit can be achieved. The switching elements can be formed, for example, by transistors, thyristors, their combinations, etc. For the proposed application, it can be particularly advantageous to operate a plurality of electronic switching elements in a substantially synchronous manner in a series connection. Thus, it is also possible to operate with an electronic switching element that can withstand only a small part of the occurring voltage at a voltage significantly higher than the maximum allowable operating voltage of the corresponding switching element. The switching unit provides at least a first switching state, in which at least one gate electrode is loaded with a first gate potential for pinching off the electron flow between the anode electrode and the cathode electrode. For this purpose, the switching unit can be connected to a corresponding operating voltage source, where the switching unit couples the operating voltage source to the X-ray tube such that the operating voltage source provides at least the pinch-off voltage between the gate electrode and the cathode electrode. In the second switching state of the switching unit, the gate electrode can be loaded with a second gate potential for releasing the electron flow, more precisely, preferably the gate potential provided by the focusing unit. This can be achieved by a series circuit of the switching unit and the focusing unit.

[0020] By connecting the switching unit and the focusing unit in series, the focusing unit can at least provide the second gate potential. Thus, the focusing unit can support the corresponding switching of the switching unit, whereby the function can be realized more reliably.

[0021] A grid-cathode voltage in a range of approximately zero V to approximately 500 V may be provided for focusing. The voltage may also be provided by operating a voltage source. For this purpose, the focusing unit may correspondingly adjust the voltage provided by the operating voltage source, for example.

[0022] Generally, the potential of the grid electrode is negative with respect to the potential of the cathode electrode. In addition, the potential of the anode electrode is generally positive with respect to the potential of the cathode electrode.

[0023] The switching unit may have one or more switching elements. Among multiple switching elements, it may be proposed that the multiple switching elements are at least partially connected in series so that a preset cut-off performance can be ensured in the off switching state of the switching unit. The switching element may be formed by one or more semiconductor switching elements. In addition, the switching element may also include electromechanical switching elements, such as relays, contactors, etc. For this reason, the semiconductor switching element may also be formed by an electromechanical switching element or any other suitable switching element.

[0024] The switching element, especially the semiconductor switching element, may be formed by a transistor, especially a field effect transistor, preferably a metal oxide field effect transistor (MOSFET), an insulated gate bipolar transistor (IGBT), but also by a gate turn-off thyristor (GTO), etc. or any other type of switching element.

[0025] To provide the desired switching state of the switching unit, the semiconductor switching element is operated during switching operation. Regarding the semiconductor switching element in the case of using a transistor, the switching operation means that a very small resistance is provided between the terminals forming the switching section of the transistor in the on switching state, so that a high current is possible with a very small residual voltage. Conversely, in the off switching state, the switching section of the transistor is highly ohmic, that is, the switching section provides a high resistance, so that even with a high voltage applied to the switching section, basically no or only a very small, especially negligible current exists. This is different from the linear operation in the case of a transistor.

[0026] The control unit is at least connected to at least one switching element of the switching unit, especially at least one semiconductor switching element. Preferably, the switching unit has its own communication interface, by means of which the switching unit is communicatively connected to the control device. Thereby, the switching of the switching unit can also be controlled by means of the control device. The control unit may also assume or provide other functions, especially regarding the provision of the focusing voltage, pinch-off voltage, operating voltage by the operating voltage source, etc. The control unit may be configured to be electrically insulated from the circuit device and preferably connected to the circuit device in an electrically isolated manner.

[0027] The control unit itself can be set as an independent structural unit. Preferably, however, it is a component of the circuit device and is particularly preferably integrated into the circuit device.

[0028] The focusing unit can, for example, have at least one adjustable resistive element, such as a transistor operating in linear operation, etc. Thus, it is feasible to provide the desired gate-cathode voltage for focusing in the case of using an operating voltage source or the operating supply voltage provided by the operating voltage source.

[0029] Therefore, through the series circuit of the switching unit and the focusing unit, it can be achieved that the focusing unit can be deactivated in the first switching state by means of the switching unit, and conversely, the focusing unit can be activated in the second switching state of the switching unit. Here, the focusing unit can at least partially support the switching between the first switching state and the second switching state.

[0030] According to an advantageous improvement, it is proposed to set the first grid potential and / or the second grid potential according to the preset anode-cathode voltage between the anode electrode and the cathode electrode. This design can consider that not only the pinch-off voltage or pinch-off potential but also the gate-cathode voltage or focusing voltage or focusing potential for focusing can be related to the anode-cathode voltage. Therefore, it can be proposed that the pinch-off voltage also increases as the anode-cathode voltage increases. In principle, this can also be set for the focusing voltage. Thus, the function of the present invention can be further improved overall.

[0031] In addition, this design allows the present invention to be specifically matched to many different X-ray devices or X-ray tubes and can also be specifically matched to the application. It can also be matched to a specific operating state in this way, so that, for example, the desired X-ray radiation can be provided. The present invention is further improved especially in terms of flexibility.

[0032] In addition, it is proposed to adjust the focusing of the electron flow by means of the focusing unit. Thus, a substantially constant setting for generating X-ray radiation can be achieved even under changing operating conditions. For this purpose, the circuit device can include a corresponding adjustment circuit coupled to a suitable measurement sensor. The measurement sensor can, for example, detect the emitted X-ray radiation and provide a suitable sensor signal for the circuit device. The circuit device can evaluate the sensor signal and set the grid potential accordingly.

[0033] According to an advantageous improvement, the operating voltage for the switching unit and / or the focusing unit is adjusted when switching between the first switching state and the second switching state. This design has proven to be particularly advantageous in the following case: the same operating voltage of the operating voltage source is used for the switching unit and the focusing unit. It can be determined here that the value of the pinch-off voltage is generally significantly greater than the value of the focusing voltage. Therefore, with the switching of the operating voltage or with the adjustment of the operating voltage, it is possible to reduce the switching losses, especially considering the high voltages present here. At the same time, the switching between the first switching state and the second switching state can be supported thereby, such that the switching can be performed faster.

[0034] Furthermore, it is proposed that the focusing unit has a series circuit composed of a resistor and a transistor, and the intermediate terminal of the series circuit is electrically coupled to at least one gate electrode. In this way, a settable gate potential can be provided particularly simply. In addition, high reliability can be achieved through this circuit structure, because the desired function can be provided with a small number of components. In addition, the switching between the first switching state and the second switching state can also be supported by correspondingly controlling the transistor. This is particularly simple and feasible in this design. The focusing unit can be connected to the control unit and obtain a setting signal for the gate potential from the control unit.

[0035] According to an advantageous improvement, the gate electrode is electrically coupled to the intermediate terminal via an attenuation resistor connected to the intermediate terminal. This design takes into account that unwanted capacitive effects, such as the capacitance of the connecting line, may not only play a role when setting the potential of the gate electrode, but also unwanted capacitive effects may act unfavorably on the circuit device. By means of the attenuation resistor, it is possible to attenuate the current pulses that occur especially when switching between the first switching state and the second switching state. Thereby, the operating safety can be further improved and also the reliability can be further increased. However, this design has also proven to be particularly advantageous for reducing the problem of electromagnetic compatibility, especially with regard to the emission of radio interference that can be reduced thereby. By appropriately selecting the resistance value of the resistor, a high switching speed during switching and / or also a high setting speed during focusing can be achieved simultaneously.

[0036] It has proven to be particularly advantageous that the operating voltage source is configured to provide the operating voltage for supplying the focusing unit in relation to the switching state of the switching unit. Exactly in the series circuit of the switching unit and the focusing unit, not only can the switching be supported thereby, but especially in the operating state of the second switching state in which the focusing of the electron flow is activated, the loss power of the focusing unit can be reduced during proper operation. This allows not only to save electrical energy, but also to reduce the structural size at the same time, because the components especially with regard to the focusing unit can be reduced, and also the structural volume especially with regard to the cooling function can be reduced.

[0037] Preferably, the focusing unit has a series resistor for connection to an operating voltage source. The series resistor can be a resistor connected in series with respect to the transistor of the focusing unit. The series resistor can be configured to place the focusing unit in a predefined defined operating state such that precise adjustment of the gate potential of the gate electrode can be achieved with high reliability.

[0038] Furthermore, it is proposed to connect a reverse diode in parallel with the series resistor. By means of the reverse diode, it is possible to include the operating voltage source at least subsidiarily during the switching between the first and the second switching states. Thereby, the operating voltage source can be used to supplementarily assist the recharge of the parasitic capacitance of the connecting cable and / or the gate-cathode capacitance.

[0039] Furthermore, it can be proposed to connect a capacitor in parallel with respect to the focusing unit and / or with respect to the switching unit. Thereby, the switching between the first and the second switching states can also be supported. In particular, if not only the focusing unit but also the switching unit each have a capacitor connected in parallel, the switching process from the first switching state to the second switching state can be significantly supported. Then it is feasible that the capacitor receives or provides a part of the charge required for the respective switching. This design, in combination with the reverse diode, has proven to be particularly advantageous, whereby it is possible to transfer the charge from the connecting line and / or the gate electrode to at least one capacitor particularly quickly. The switching can thereby be further accelerated.

[0040] Regarding the X-ray device, it is further proposed that the X-ray device has a voltage sensor for detecting the anode-cathode voltage and for providing a voltage sensor signal for the circuit arrangement. By means of the voltage sensor, it is possible to configure the circuit arrangement in relation to the detected anode-cathode voltage and thereby further improve or optimize the function of the circuit arrangement. For example, the pinch-off voltage and / or the focusing voltage can be set and / or even adjusted in relation to the voltage sensor signal.

[0041] Furthermore, it is proposed that the X-ray device has a focusing sensor for detecting the focusing of the electron flow from the cathode electrode to the anode electrode and for providing a focusing sensor signal for the circuit arrangement. This enables the provision of an adjustment for the focusing voltage such that the circuit arrangement can provide a preferably substantially optimal respective focusing voltage or focusing potential. Thereby, the function of the present invention can be further improved. For this purpose, the focusing sensor can, for example, detect the emitted X-ray radiation. For this purpose, the circuit arrangement can also be configured to correspondingly evaluate the focusing sensor signal.

[0042] The advantages and effects described for the method according to the invention also apply to the circuit arrangement according to the invention and to the X-ray device equipped with the circuit arrangement according to the invention, and vice versa. Thus, the features described in terms of the method can also be described in terms of the device, and vice versa.

[0043] The embodiments described below relate to preferred embodiments of the present invention. Features, combinations of features that have been described previously in the specification, and features and combinations of features that are also mentioned in the following description of the embodiments and / or shown separately in the drawings can be used not only in the separately described combinations, but also in other combinations. Thus, the following embodiments of the present invention or what is considered to be disclosed thereby are also included, which embodiments are not explicitly shown and described in the drawings, but are known from and can be produced by the separately described embodiments through separate combinations of features. The features, functions, and / or actions shown according to the embodiments can each separately show individual, independently observable features, functions, and / or actions of the present invention, which also independently improve the present invention with respect to each other. Thus, the embodiments should also include combinations different from those in the described embodiments. In addition, the described embodiments can also be supplemented by other features, functions, and / or actions among the features, functions, and / or actions of the present invention that have already been described. Description of the Drawings

[0044] Only Figure 1 Shows:

[0045] A schematic circuit diagram of an X-ray device having an X-ray tube connected to a circuit arrangement. Detailed Description of the Invention

[0046] Figure 1 An X-ray device 10 having an X-ray tube 12 is shown in a schematic circuit diagram. The X-ray tube has an anode electrode 14 and a cathode electrode 16 arranged in a evacuated container. A grid electrode 18 is arranged between the anode electrode 14 and the cathode electrode 16. The anode electrode 14 is electrically connected to a terminal 52, the grid electrode to a terminal 50, and the cathode electrode 16 to two terminals 46, 48. The cathode electrode 16 has two terminals for heating purposes, namely terminals 46 and 48, via which the cathode electrode 16 can be supplied with electrical energy so that the cathode electrode 16 is heated to a preset temperature during proper operation in order to enable the desired electron emission. For this purpose, the terminals 46, 48 are electrically connected to an electrical heating energy source 54.

[0047] The terminals 48, 52 are also electrically connected to a voltage source 56 which provides an anode-cathode voltage 72 which is essentially also 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.

[0048] Depending on the grid potential at the grid electrode 18, electrons emitted from the cathode material of the cathode electrode 16 are accelerated to form an electron stream 26 towards the anode electrode 14. When the electrons impinge on the anode electrode 14 which is generally configured as a rotating electrode, X-ray radiation is generated and the X-ray radiation is emitted through the X-ray tube 12.

[0049] The function of the X-ray tube 12 can be influenced by the grid potential at the grid electrode 18. Thus, on the one hand, it is feasible that by applying a first grid potential to the grid electrode 18, the electron flow 26 between the anode electrode 14 and the cathode electrode 16 can be pinched off by means of the first grid potential. The first grid potential is also referred to as the pinch-off potential. Correspondingly, the grid-cathode voltage is obtained, and the grid-cathode voltage is thus referred to as the pinch-off voltage. The pinch-off voltage can be in the range of, for example, approximately zero kV to approximately 4 kV in an X-ray tube. In the current design, the pinch-off voltage is higher than approximately 500 V, for example, approximately 3.5 kV or even higher. Generally, at least the grid potential for pinching off the electron flow 26 is negative with respect to the cathode potential of the cathode electrode 16.

[0050] The first grid potential is usually selected such that the electron flow 26 can be pinched off safely and reliably without damaging the electrical insulation in the X-ray device 10. In many cases, the maximum allowable grid-cathode voltage is approximately 4 kV, and thus the X-ray device 10 and its components are correspondingly configured for this voltage.

[0051] During the pinching off of the electron flow 26, basically no X-ray radiation is generated because the electron flow 26 is basically suppressed.

[0052] In addition, the grid electrode 18 can be applied with a second grid potential, which allows the release, especially the focusing, of the electron flow 26. The corresponding grid-cathode voltage is also referred to as the focusing voltage. With the focusing voltage, it is feasible to not only preferably release the electron flow 26 in a controlled manner but also simultaneously control the focusing of the electron flow 26 hitting the anode electrode 14. Thus, for example, a focal spot 58 can be achieved on the anode electrode 14 in a preset manner. Thereby, the generation of X-ray radiation can be influenced via another region.

[0053] The first terminal at 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.

[0054] The heating energy source 54 is connected to the electrical terminals 60, 62. The circuit device 22 is connected to the electrical terminals 62, 64, by means of which the grid potential for the grid electrode 18 can be provided in a preset manner. In addition, it can be seen from Figure 1 that the connection line 20 has a line capacitance, which is symbolically shown by the capacitor 66 in Figure 1 The capacitor 66 also includes the grid-cathode capacitance of the X-ray tube 12, which is in Figure 1This is not shown further herein. The capacitor 66 may for example have a capacitance of approximately 4 nF. As will also be explained below, this is important for controlling the X-ray tube with respect to the pinch-off electron flow 26 and for focusing the electron flow 26 only via the grid electrode 18.

[0055] For focusing, a grid-cathode voltage of approximately zero V to approximately 500 V is currently required. Depending on the structure of the X-ray tube 12, this voltage may also be different, as is the case with the pinch-off voltage.

[0056] To provide the grid potential, the circuit arrangement 22 has an operating voltage source 38 which has an internal resistance 68 via which the components and assemblies of the circuit arrangement 22 are supplied with electrical energy for proper operation.

[0057] The circuit arrangement 22 also includes a focusing unit 24 connected in series with a switching unit 28. The series circuit formed by the focusing unit 24 and the switching unit 28 is connected to the operating voltage source 38 via the internal resistance 68 and is loaded with the operating voltage by the operating voltage source.

[0058] The switching unit 28 currently provides two switching states, namely the off switching state as the first switching state and the on switching state as the second switching state. In the on switching state, the operating voltage is essentially applied to the focusing unit 24. As will also be explained below, the focusing unit 24 provides a grid-cathode voltage which allows the electron flow 26 to be focused in a presettable manner.

[0059] In the first switching state of the switching unit 28, in which the switching unit 28 is in the off switching state, the focusing unit 24 is essentially deactivated, such that the operating voltage of the operating voltage source 38 is essentially provided between the grid electrode 18 and the cathode electrode 16. It is noted here that in this operating state there is essentially no current flow at least in the steady state. Thus, if the operating voltage is approximately 3.5 kV, this operating voltage is also applied between the grid electrode 18 and the cathode electrode 16 in the off switching state of the switching unit 28. This voltage is currently negative so that the grid potential is less than the cathode potential. Thus, in this switching state, the pinch-off of the electron flow 26 is achieved such that essentially no more electrons reach the anode electrode 18 and thus the generation of X-ray radiation is essentially interrupted.

[0060] In the second switching state of the switching unit 28, i.e., the on switching state, the focusing unit 24 is loaded with the operating voltage. Then, the focusing unit 24 provides the corresponding grid potential in order to not only release the electron flow 26 but also to enable a corresponding presettable focusing of the electron flow 26 upon impact on the anode electrode 14.

[0061] For this purpose, the focusing unit 24 includes at least one series circuit composed of a resistor 30 and a transistor 32. The resistor 30 can also be used as a series resistor for connecting the operating voltage source 38. The transistor 32 is currently formed by a field effect transistor, more precisely a self-cutoff n-channel MOSFET. However, according to the design, other transistors can also be used here, especially bipolar transistors.

[0062] The transistor 32 currently has a gate terminal, which is not drawn and is connected to a driver circuit that is also not shown. The driver circuit loads the gate terminal with a preset gate potential so that a preset gate potential can be provided substantially at the intermediate terminal 34 of the series circuit. For this purpose, the transistor 32 is operated in linear operation so that a corresponding gate potential is set at the intermediate terminal 34 in relation to the corresponding setting of the gate potential at the transistor 32. As can be seen from the diagrams in Figure 1 the focusing unit 24 is activated by turning on the switch unit 28 and deactivated by turning off.

[0063] When switching between the first and second switch states of the switch unit 28 or between the on and off switch states, a significant potential jump will occur at the intermediate terminal 34. Considering the capacitance 66, this can be at least problematic or require a high-cost structure in the focusing unit 24.

[0064] To reduce the effect of the capacitance 66, the circuit device 22 thus has a damping resistor 36, which is connected in the middle between the intermediate terminal 34 and the electrical terminal 62. By appropriately selecting the resistance value, the effect of the capacitance 66 can thus be reduced without significantly affecting the switching characteristics.

[0065] Even if the resistor 36 is currently arranged between the intermediate terminal 34 and the electrical terminal 62, the resistor 36 can alternatively or additionally also be arranged between the terminal of the switch unit 28 to the reference potential 70 and the terminal 64, without substantially impairing the function.

[0066] If the switch state changes from the off switch state of the switch unit 28 to the on switch state, this can cause the operating voltage of the operating voltage source 38 to be applied substantially to the transistor 32 during the switching. However, through rapid adjustment, the conductivity of the transistor 32 almost suddenly increases, so that the potential at the intermediate terminal 34 rises to the value for focusing the electron flow 26. This also requires the discharge of the capacitance 66.

[0067] For the support of the switching, capacitors 42, 44 are connected in parallel not only with respect to the focusing unit 24 but also with respect to the switching unit 28, respectively. In combination with the antiparallel diode 40 connected in parallel with the resistor 30, an additional effect can thus be achieved during the switching, such that the electrical load on the transistor 32 can be reduced. Thus, switching on the switching unit 28 enables the provision of a voltage divider function in the switched-off switching state by means of the capacitors 42, 44, which voltage divider function can be used to support the discharging of the capacitor 66 when the switching unit 28 is switched on. The antiparallel diode 40 also serves this purpose, and the antiparallel diode 41 can also be used as a series resistor for the resistor 30 in this case.

[0068] When the switching unit 28 is switched off, the focusing unit 24 is deactivated and the capacitor 44 is charged via the transistor 32. At the same time, the capacitor 66 is also charged via the damping resistor 36. The capacitor 42 serves as an additional energy source in this case and supports the charging of the capacitor 44 and the capacitor 66.

[0069] In the current design, it is also proposed that the operating voltage source 38 for providing the operating voltage can be switched. The switching of the operating voltage can be carried out together with the switching of the switching unit 28. This allows, in particular with respect to the focusing unit 24, a reduction in the switching losses. Thus, for the switched-on switching state of the switching unit 28, it can be provided that the operating voltage source 38 provides an operating voltage in the range of approximately 500 V, whereas the operating voltage source 38 provides an operating voltage of approximately 3.5 kV in the switched-off switching state of the switching unit 28.

[0070] In the current design, it is also proposed that an (not shown) driver unit for the transistor 32 is electrically coupled to the reference potential 70. Since the potential of the source terminal of the transistor 32 is currently related to the switching state of the switching unit 28, the gate terminal of the transistor 32 can be decoupled via a corresponding diode decoupling circuit. Thereby, an overload of the gate terminal with respect to voltage loading can be avoided. However, this is not shown in Figure 1 it.

[0071] With the capacitive voltage divider formed by the capacitors 42, 44, a voltage distribution with respect to the focusing unit 24, in particular the transistor 32 and the switching unit 28, can be achieved. In addition, the voltage rise at the transistor 32 can be better limited when the switching unit 28 is switched on. The voltage change process at the capacitor 42 is substantially continuous.

[0072] Even if the current switching unit 28 is electrically coupled to the reference potential 70, the series circuit formed by the focusing unit 24 and the switching unit 28 can in principle be exchanged, without thereby impairing the function of the invention. In this arrangement, for example, the antiparallel diode 40 can also be saved.

[0073] Furthermore, in the current design, the reference potential 70 is relative to the negative potential of the operating voltage source 38. However, for the reasons stated, the reference potential is also connected to the positive potential of the operating voltage source 38. However, in this design, it is expedient that the transistors 32 and the switching unit 28 can be controlled in a potential-separated manner or in a potential-free manner.

[0074] The circuit arrangement 22 can be used to adjust the grid focusing potential to be precisely set. Only the expected values are transmitted via potential-separated transmission.

[0075] The invention allows the operating voltage source 38 to be provided in the X-ray apparatus 10 together with the circuit arrangement 22. The operating voltage source 38 can for example comprise a rectified transistor, which is provided in the X-ray apparatus 10. Furthermore, other combinations are technically feasible. If the circuit arrangement 22 is integrally provided in the X-ray apparatus 10, the line capacitance, in particular the capacitance 66, can thereby also be reduced.

[0076] The embodiments are merely used to illustrate the invention and should not limit the invention.

Claims

1. A method for controlling an X-ray tube (12), the X-ray tube (12) having at least one grid electrode (18) disposed between an anode electrode (14) and a cathode electrode (16), wherein - focusing an electron flow (26) from the cathode electrode (16) to the anode electrode (14) by means of a focusing unit (24), and - loading the at least one grid electrode (18) with a first grid potential in a first switching state and with a second grid potential releasing the electron flow (26) in a second switching state by means of a switching unit (28), the first grid potential being for clamping off the electron flow (26) between the anode electrode (14) and the cathode electrode (16), characterized in that the switching unit (28) and the focusing unit (24) are connected in series, the second grid potential is provided at least by the focusing unit (24), and the switching unit is connected to a corresponding operating voltage source, wherein the switching unit couples the operating voltage source to the X-ray tube such that the operating voltage source provides at least the clamping voltage between the grid electrode and the cathode electrode.

2. The method according to claim 1, wherein The first grid potential and / or the second grid potential are provided in relation to a preset anode-cathode voltage (72) between the anode electrode (14) and the cathode electrode (16).

3. The method according to claim 1 or 2, characterized in that, Adjusting the focusing of the electron flow (26) by means of the focusing unit (24).

4. The method according to claim 1 or 2, characterized in that, Adjusting the operating voltage for the switching unit (28) and / or the focusing unit (24) when switching between the first switching state and the second switching state.

5. A circuit arrangement (22) for controlling an X-ray tube (12), the X-ray tube (12) having at least one grid electrode (18) disposed 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), and - a switching unit (28) configured to load the at least one grid electrode (18) with a first grid potential in a first switching state and with a second grid potential releasing the electron flow (26) in a second switching state, the first grid potential being for clamping off the electron flow (26) between the anode electrode (14) and the cathode electrode (16), characterized in that the switching unit (28) and the focusing unit (24) are connected in series, and the switching unit is connected to a corresponding operating voltage source, wherein the switching unit couples the operating voltage source to the X-ray tube such that the operating voltage source provides at least the clamping voltage between the grid electrode and the cathode electrode.

6. The circuit device according to claim 5, characterized in that, The focusing unit (24) has a series circuit composed of a resistor (30) and a transistor (32), and an intermediate terminal (34) of the series circuit is electrically coupled to the at least one grid electrode (18).

7. The circuit device according to claim 6, characterized in that, The grid electrode (18) is electrically coupled to the intermediate terminal (34) via an attenuation resistor (36) connected to the intermediate terminal (34).

8. The circuit device according to any one of claims 5 to 7, characterized in that, The operating voltage source (38) is configured to provide an operating voltage for supplying the focusing unit (24) in relation to the switching state of the switching unit (28).

9. The circuit device according to claim 8, characterized in that, The focusing unit (24) has a series resistor (30) for connection to the operating voltage source (38).

10. The circuit device according to claim 9, characterized in that, A reverse diode (40) is connected in parallel on the series resistor (30).

11. The circuit device according to claim 9, characterized in that, The focusing unit (24) has a transistor connected in series with the series resistor (30).

12. The circuit device according to any one of claims 5 to 7, characterized in that, Capacitors (42, 44) are connected in parallel with the focusing unit (24) and / or with the switching unit (28).

13. An X-ray device (10) having: an X-ray tube (12) having at least one grid electrode (18) disposed between an anode electrode (14) and a cathode electrode (16), and circuit means (22) connected to the X-ray tube (12) by means of a connection line (20) for controlling the X-ray tube (12), characterized in that the circuit means (22) is configured according to any one of claims 5 to 12.

14. The X-ray device according to claim 13, characterized in that, A voltage sensor is provided for detecting the anode-cathode voltage (72) and for providing a voltage sensor signal for the circuit means (22).

15. The X-ray device according to claim 13 or 14, characterized in that, A focusing sensor is provided for detecting the focusing of the electron flow from the cathode electrode (16) to the anode electrode (14) and for providing a focusing sensor signal for the circuit means (22).

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