Circuit with unipolar or bipolar power supply for controlling x-ray exposure by gate current

Abstract

The invention relates to a circuit for controlling X-ray exposure by means of an intermediate current or feedback current proportional to the gate current (IG), thereby controlling the tube anode current and ultimately taking charge of the emission of X-ray photons. The circuit comprises: an anode (A); a cathode (K) which is grounded; and a gate (G) connected to a gate current (IG) controller circuit comprising a DC-DC converter (CONV), to which a supply voltage (Vsup) is connected, or a "buck converter", the output of which is connected to an inverter (INV), which in turn is connected to a transformer (TR), where the output of the transformer (TR) is connected to a rectifier (RECT), the rectifier (RECT) being connected to the DC-DC converter (CONV). The output of the rectifier is connected to the gate (G) and to ground. Further, there is a control circuit (CONT) in the controller circuit.

Description

Technical Field

[0001] As the title of the invention indicates, the object of the present invention is a circuit for controlling X-ray exposure in a cold cathode X-ray tube by means of a grid current.

[0002] The present invention is characterized by the special design and configuration of each element that is part of the control circuit, which enables the X-ray exposure to be controlled by an intermediate current or "feedback" current that is proportional to the grid current, which in turn controls the tube anode current and is ultimately responsible for the emission of X-ray photons.

[0003] Due to the characteristics of the circuit, a more precise control is achieved: the voltage ripple between anode and cathode is smaller and thus the emission dose is more controlled, wherein the components that are part of the circuit do not have to be subjected to high voltages.

[0004] Therefore, the present invention belongs to the scope of X-ray devices, in particular cold cathode devices. Background Art

[0005] As is known in the art, the energy of X-ray radiation depends on the applied kV, while the amount of radiation depends on the current and exposure time. One way to control this radiation is to control the temperature of the filament, a method known as thermionic emission control.

[0006] Currently, cold cathode X-ray tubes are used in which the control of the electron emission is performed by a cold cathode consisting of a series of carbon nanotubes with a grid interposed between the cathode and the anode.

[0007] Figure 1 A schematic diagram of a cold cathode X-ray device is shown, which includes an anode (A) and a cathode (K), wherein the cathode (K) is formed by a series of carbon nanotubes and is arranged opposite to the anode (A), a grid (G) is placed between the anode (A) and the cathode (K), wherein there is a first loop formed by the anode (A), the cathode (K) and a voltage-controlled power supply, wherein the voltage-controlled power supply can be monopolar or bipolar. Configuration with bipolar power supply ( Figure 1a ) is grounded in the middle of the power supply to halve the insulation stress of the power supply itself and the X-ray tube relative to ground. There is also a second loop formed by the grid (G), cathode (K) and current control power supply. These two loops share a common part, so current IA flows through the first loop, current IG flows through the second loop, and current IA+IG flows through the common part.

[0008] Figure 2 shows a graph showing that the anode current (IA) is linearly related to the gate current (IG), while Figure 3It is shown that the relationship between the anode current (IA) and the gate current (IG) with respect to the gate voltage (VG) is exponential, so controlling the anode current (IA) by the gate voltage is very complicated.

[0009] Figure 4 A diagram of a circuit for controlling the anode current (IA) by voltage is shown, wherein the anode is grounded via a power supply (VAG), the gate (G) is directly grounded, and the cathode (K) is grounded via a power supply (Vsup) and a MOSFET switch, wherein in the MOSFET switch a voltage (Vcont) is dropped and a signal of the current demanded by the cathode is controlled.

[0010] exist Figure 4 In the control scheme shown, the following conditions are met:

[0011] VGK = Vsup - Vcont;

[0012] VAK=VAG+VGK;

[0013] VAK=VAG+Vsup-Vcont.

[0014] This control scheme performs linear control of the cathode current (IK) in a very complex manner. Furthermore, it requires a MOSFET capable of operating at several kilovolts, where the voltage drop between source and drain is very large.

[0015] Another major disadvantage of this type of control is that the voltage between the anode and cathode of the X-ray tube depends on the grid voltage (which varies as the X-ray tube ages), thus directly influencing the energy of the emitted radiation.

[0016] The object of the invention is therefore to develop a circuit for controlling the X-ray exposure in a separate and independent manner by means of a gate current, wherein a constant voltage VAK is established between the anode and the cathode which is independent of the gate control, and to develop a controller circuit, such as the one described below, the essence of which is contained in the first claim. Summary of the invention

[0017] The object of the invention is essentially contained in the independent claim, while different embodiments are contained in the dependent claims.

[0018] The purpose of the circuit is to control the X-ray exposure via the IFB current which is proportional to the grid current (IG), which in turn controls the tube anode current and is ultimately responsible for the emission of X-ray photons.

[0019] The circuit for controlling X-ray exposure can be configured for a unipolar or bipolar X-ray tube power supply. In a unipolar configuration, the circuit for controlling X-ray exposure includes an anode connected to a power supply connected to ground via a shunt for measuring the anode current; the circuit also includes a cathode, which is also connected to ground; and further, the circuit includes a gate having a gate current controller circuit in which the power supply voltage is connected to a DC-DC converter or "buck converter", the output of which is connected to an inverter, the output of which is connected to a transformer, wherein the output of the transformer is connected to a rectifier, the output of which is connected to the gate and to ground.

[0020] In a bipolar power supply configuration for an X-ray tube, an X-ray exposure control circuit comprises an anode connected to a power supply connected to ground via a shunt for measuring the anode current, a cathode connected to a power supply also connected to ground, and a gate provided with a gate current control circuit in which the supply voltage is connected to a DC-DC converter or "buck converter", the output of which is connected to an inverter, the output of which is connected to a transformer, and the output of said transformer is connected to a rectifier, the output of which is connected to the gate and to the cathode.

[0021] In addition, there is a control circuit in the controller circuit, which receives the feedback current (I FB ) signal, a signal from a demand current, a preload signal, and an exposure signal, and outputs a first signal toward a DC-DC converter and a second signal toward an inverter.

[0022] In a preferred but non-limiting embodiment, the DC-DC converter is formed by a capacitor connected in parallel with the first switch and the first diode, a coil, and a return diode connected in parallel with the assembly formed by the first switch and the coil.

[0023] The inverter is formed by a bridge including a second switch, a third switch, a fourth switch and a fifth switch, wherein the second switch and the fifth switch are connected in series to form a first branch, and the third switch and the fourth switch are connected in series to form a second branch, and the two branches are connected in parallel to each other.

[0024] Each branch is connected to a transformer in the middle, the output of the transformer is connected to a rectifier bridge, where the gate current is obtained, and the feedback current (I FB )Signal.

[0025] Due to the control circuit described, the gate is controlled via a current and not via a voltage, since the control of the gate voltage is very complex to implement. Furthermore, the control of the gate via the applied voltage requires an increase in the size of the components used, for example the size of the MOSFET switch, which must be able to withstand voltages of up to 15 kV if necessary. Furthermore, the voltage drop between the source and the drain is very large. This voltage varies with the aging state of the X-ray tube, which changes the total voltage applied between the anode and the cathode and has a direct effect on the X-ray exposure dose, since as this voltage (VAK) changes, the energy of the emitted photons also changes and thus the total emitted dose also changes.

[0026] All these disadvantages are overcome by means of a control circuit which controls the anode current by means of the gate current and is ultimately responsible for the emission of X-ray photons.

[0027] Unless otherwise specified, all technical and scientific elements used in this specification have the meanings commonly understood by those skilled in the art to which the invention belongs. In the practice of the present invention, methods and materials similar or equivalent to those described in this specification can be used.

[0028] In the specification and claims, the word "comprise" and its variations are not intended to exclude other technical features, additions, components or steps. For those skilled in the art, other purposes, advantages and features of the present invention will be inferred in part from the specification and in part from the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] To supplement the description herein, and to assist in a better understanding of the features of the invention, according to a preferred practical embodiment of the invention, said specification is accompanied as an integral part thereof by a set of drawings, in which the following is given in an illustrative and non-limiting manner.

[0030] Figure 1 A schematic diagram of a cold cathode X-ray device is shown with a unipolar power supply for the X-ray tube.

[0031] Figure 1a The same X-ray device is shown, in this case with a bipolar power supply.

[0032] Figure 2 A graph is shown showing that the anode current (IA) is linearly related to the gate current (IG).

[0033] Figure 3 The relationship between the anode current (IA) and the gate current (IG) and the gate voltage (VG) is shown.

[0034] Figure 4 A schematic diagram of a prior art circuit is shown for controlling the anode current (IA) via the cathode current (IK), which in turn influences the voltage (VAK) between anode and cathode (and therefore also the energy of the emitted radiation).

[0035] Figure 5 A circuit for controlling X-ray exposure by means of a gate current (IG) with a unipolar power supply for an X-ray tube is shown.

[0036] Figure 5a The same control circuit is shown, but with a bipolar power supply for the X-ray tube.

[0037] Figure 6 A possible embodiment of such a circuit is shown in .

[0038] Figure 7 The operating cycle of a first operating mode or preload and exposure mode is shown.

[0039] Figure 8 The operating cycle of the second operating mode or direct exposure mode is shown.

[0040] Fig. 9 A possible embodiment of a current control circuit is shown. DETAILED DESCRIPTION

[0041] In view of the accompanying drawings, preferred embodiments of the present invention are described below.

[0042] Figures 1 to 4 Corresponding to the description of the prior art of X-ray exposure control.

[0043] Figure 5 An X-ray exposure control circuit with a unipolar power supply for an X-ray tube is shown, in which the anode (A) is connected to a power supply (VAK), which is grounded through a shunt for measuring the anode current (IA), and the cathode (K) is also grounded; on the other hand, the gate (G) is connected to a gate current (IG) control circuit; in this gate current control circuit, the power supply (Vsup) is connected to a DC-DC converter (CONV) called a "buck converter", which is in turn connected to an inverter (INV), the output of the inverter is connected to a transformer (TR), and the output of the transformer (TR) is connected to a rectifier (RECT), and the output of the rectifier is connected to the gate (G) and grounded.

[0044] Figure 5aAn X-ray exposure control circuit with a bipolar power supply for an X-ray tube is shown, in which the anode (A) is connected to a power supply (VAK / 2) which is grounded through a shunt for measuring the anode current (IA), and the cathode (K) is connected to another power supply (VAK / 2) which is also grounded. In addition, the gate (G) is connected to a gate current (IG) control circuit; in the gate current control circuit, the power supply voltage (Vsup) is connected to a DC-DC converter (CONV) called a "buck converter", which in turn is connected to an inverter (Inv), the output of the inverter is connected to a transformer (TR), and the output of the transformer (TR) is connected to a rectifier (RECT), and the output of the rectifier is connected to the gate (G) and to the cathode (K).

[0045] Furthermore, in the controller circuit there is a control circuit (CONT) which receives a current (I FB ) signal, demand current (I dem ) as well as a preload signal (PRE) and an exposure signal (EXP), and outputs a first signal (S1) toward a DC-DC converter and a second signal (S2) toward an inverter (Inv). The circuit can have three states: disconnected, preloaded, and exposed, so two control signals are required: a preload signal (PRE) and an exposure signal (EXP).

[0046] Figure 6 A non-limiting preferred embodiment of the above-mentioned control circuit elements is shown, wherein a DC-DC converter is formed by a capacitor (C) connected in parallel with a first switch (Q1) and a diode (D1), a coil (L), and a return diode (D2) connected in parallel with the assembly formed by the first switch (Q1) and the coil (L).

[0047] The inverter is formed by a bridge including a second switch (Q2), a third switch (Q3), a fourth switch (Q4) and a fifth switch (Q5), wherein the second switch (Q2) and the fifth switch (Q5) are connected in series to form a first branch, and the third switch (Q3) and the fourth switch (Q4) are connected in series to form a second branch, and the two branches are connected in parallel to each other.

[0048] Each branch is connected to a transformer (TR1) in the middle, and the output of the transformer (TR1) is connected to a rectifier bridge, where the gate current (IG) is obtained, and the current (I FB )Signal.

[0049] Figure 7 A first operating mode of the circuit for controlling X-ray exposure is shown, which first operating mode corresponds to a preload mode.

[0050] The figure shows the states of different cycles (C1, C2, C3, C4, C5, C6, C7, C8) and different switches (Q1, Q2, Q3, Q4, Q5), as well as the current demand value (I dem ) and current (I FB ).

[0051] During the C1 cycle, all five transistors (Q1, Q2, Q3, Q4, Q5) are turned on. It can be seen that the current (I FB ) rises linearly – it is limited by the value of the inductor (L).

[0052] During the C2 cycle, everything remains unchanged because the current (IFB) has not yet reached the required value (IDEM).

[0053] In the third cycle C3, the current (I FB ) finally reaches the required value (I dem ), the transistor (Q1) stops conducting, causing the current (I FB ) starts to decrease. In the next cycle, the transistor (Q1) turns on again, and only when the current (I FB ) reaches the required value again (I dem ) before it turns off. This preload state can be maintained indefinitely, with the four inverter bridge transistors (Q2, Q3, Q4, Q5) turned on and the transistor (Q1) maintaining the current (I FB ).

[0054] At a certain moment, the system controller decides to start the exposure by means of a signal (EXP), transferring the current stored in the inductor (L) to the gate circuit. To start this new state, the inverter bridge transistors (Q2, Q3, Q4, Q5) open the short circuit and start operating as an inverter, i.e. as a DC-AC converter. To do this, transistors (Q2) and (Q4) are turned on, while transistors (Q3) and (Q5) are turned off. In the next cycle, transistors (Q2) and (Q4) are turned off, while transistors (Q3) and (Q5) are turned on, and this alternating cycle is maintained indefinitely as long as the X-ray exposure remains active. In each cycle and regardless of whether in the preload state or the exposure state, transistor (Q1) continues to pass the current (I FB ) is maintained at the required value (I DEM ).

[0055] When the system controller decides to terminate the X-ray exposure through the signal (EXP), the five transistors (Q1, Q2, Q3, Q4, Q5) are immediately turned off simultaneously. At this moment, the current stops flowing to the gate, thus immediately shutting down the X-ray exposure. The energy stored in the inductor (L) is transferred to the power supply (Vsup) through the diodes (D1) and (D2).

[0056] Another method of terminating the X-ray exposure is to turn on the four transistors (Q2, Q3, Q4, Q5) of the inverter bridge while maintaining the current (I FB ) control, which will enter preload mode so that new exposures can be performed at any time without delay.

[0057] Figure 8 A second operating mode of the circuit for controlling X-ray exposure is shown, which corresponds to the direct mode.

[0058] The purpose of direct mode is to start the X-ray exposure immediately without waiting for the gate to reach the optimal current. In this mode, the exposure time will be slightly longer than in preload mode.

[0059] exist Figure 8 As can be seen, the transistor (Q1) is in current controller mode, that is, when the current (I FB ) reaches the required value (I DEM ), transistor (Q1) turns off. Then, transistors (Q2, Q3, Q4, Q5) start to operate in inverter mode, transferring all current to the gate from the initial moment.

[0060] In cycle C1, transistor (Q1) is 100% on because the current (I FB ) has not yet reached the required value (I DEM ). Then transistors (Q2) and (Q4) are turned on, while transistors (Q3) and (Q5) remain off. In the next cycle C2, transistor (Q1) remains permanently turned on, because the required value (I dem ), while transistors (Q2) and (Q4) are turned off and transistors (Q3) and (Q5) are turned on to reverse the polarity of the magnetic field of the core of the transformer (TR1) to prevent it from saturating.

[0061] Repeat the same cycle until the current (I FB ) finally reaches the required value (I dem ), and the transistor (Q1) starts regulating the current.

[0062] exist Figure 8 As can be seen in the direct mode, the required value (I dem) is longer than in the preload mode. This is because in the direct mode, the energy of the inductor (L) is transferred from the very first moment, while in the preload mode, the energy is accumulated until it reaches the optimum value and is suddenly released at the time of X-ray exposure.

[0063] As in the preload mode, when the system controller decides to terminate the X-ray exposure, the five transistors (Q1, Q2, Q3, Q4, Q5) are immediately turned off simultaneously. At this moment, the current stops flowing to the gate, thereby immediately cutting off the X-ray exposure. The energy stored in the inductor (L) is transferred to the power supply (V) through diodes (D1) and (D2). sup ).

[0064] As in the preload mode, the current (I FB ) to cut off the X-ray exposure, thereby entering the preload mode, so that new exposure can be performed at any time without delay.

[0065] at last, Fig. 9 The current (I FB ) control circuit; it can be seen that the control circuit includes a trigger (FF1), which is preferably a D-type trigger triggered by a positive edge. When the inputs of the gate (AND1) are all "1", that is, when the request to start preloading (PRE) and the signal (Clock) is received, the output (Q) of the trigger will be activated to turn on the transistor (Q1).

[0066] When the current (I FB ) reaches the required value (I dem ), the comparator output becomes "0", thereby restarting the output Q of the flip-flop (FF1) and turning off the transistor (Q1) until the transistor is turned on again in the next clock cycle (Clock).

[0067] It is worth noting that although the grid current (IG) ripple is proportional to the anode current, it has no effect on the dose control of X-ray exposure, because the dose control of X-ray exposure depends on the amount of photons generated in the anode of the tube, that is, the integral of the anode current during the exposure time, internationally known as mAs. On the contrary, the ripple of the voltage (VAK) is very important because it produces photons of different energies, which has a very important direct impact on the emission dose.

[0068] After fully describing the characteristics of the present invention, in addition to the way of putting it into practice, it should be noted that, in essence, the present invention can also be put into practice in other embodiments that are different in details from those shown in the examples, and the scope of protection is equally applicable to these embodiments, as long as the main principles thereof are not changed, varied or modified.

Claims

1. An X-ray exposure control circuit by means of a gate current, wherein: The X-ray exposure control circuit comprises an anode (A) connected to a power supply (VAK) or (VAK / 2), which in turn is grounded; the X-ray exposure control circuit also comprises a cathode (K), which is also grounded, and on the other hand, the X-ray exposure control circuit has a gate (G), which is connected to a gate current (IG) controller circuit, the gate current controller circuit comprising a DC-DC converter (CONV) or "buck converter", to which a power supply voltage (Vsup) is connected, the output of the DC-DC converter (CONV) is connected to an inverter (INV), the output of the inverter is connected to a transformer (TR), and the output of the transformer (TR) is connected to a rectifier (RECT), the output of the rectifier is connected to the gate (G) and to ground; in addition, there is a control circuit (CONT) in the gate current controller circuit, the control circuit (CONT) receives a current (I FB ) signal, demand current (I DEM ) signal as well as a preload signal (PRE) and an exposure signal (EXP), and outputs a first signal (S1) toward the DC-DC converter and a second signal (S2) toward the inverter (INV).

2. The X-ray exposure control circuit using gate current according to claim 1, wherein: The DC-DC converter is formed by a capacitor (C) connected in parallel with a first switch (Q1) and a diode (D1), a coil (L), and a return diode (D2) connected in parallel with the assembly formed by the first switch (Q1) and the coil (L).

3. The X-ray exposure control circuit using gate current according to claim 1 or 2, wherein: The inverter (INV) is formed by a bridge including a second switch (Q2), a third switch (Q3), a fourth switch (Q4) and a fifth switch (Q5), wherein the second switch (Q2) and the fifth switch (Q5) are connected in series to form a first branch, and the third switch (Q3) and the fourth switch (Q4) are connected in series to form a second branch, the two branches are connected in parallel to each other, and each branch is connected to a transformer (TR1) at a midpoint, the output of the transformer is connected to a rectifier bridge, the gate current (IG) is obtained from the rectifier bridge, and the current (I I) is obtained from the lower ends of the two branches of the inverter and the DC-DC converter. FB )Signal.

4. The X-ray exposure control circuit using gate current according to claim 3, wherein: The controller circuit operates in a preload mode, wherein in the preload mode, in a first cycle, five transistors (Q1, Q2, Q3, Q4, Q5) are turned on and the current (I FB ) rises and is limited by the inductance (L).

5. The X-ray exposure control circuit using gate current according to claim 3, wherein: The controller circuit operates in a direct mode in which X-ray exposure starts immediately without waiting for the gate to reach an optimal current.

6. The X-ray exposure control circuit according to any one of the preceding claims by means of a gate current, wherein: Current (I FB ) The control circuit includes a trigger (FF1), which is preferably a D-type trigger triggered by a positive edge, wherein when the inputs (AND1) of the gate are all "1", that is, when the request to start preloading (PRE) is received and the (Clock) signal is received, the output (Q) of the trigger will be activated to turn on the transistor (Q1); the current control circuit also includes a comparator (COMP1), which converts the required current (I dem ) and the inverter current (I FB ) as input, so that when the current (I FB ) reaches the required value (I dem ), the output of the comparator will become "0", thereby restarting the output (Q) of the flip-flop (FF1) and turning off the transistor (Q1) until the transistor (Q1) is turned on again in the next clock cycle (Clock).

7. The X-ray exposure control circuit according to any one of the preceding claims by means of a gate current, wherein: The power supply is a unipolar power supply from a power source (VAK), wherein the anode (A) is connected to the power source (VAK) which is grounded via a shunt for measuring the anode current (IA), while the cathode (K) is also grounded.

8. The X-ray exposure control circuit using gate current according to any one of claims 1 to 6, wherein: The power supply is a bipolar power supply, where the anode (A) is connected to a power supply (VAK / 2) connected to ground via a shunt for measuring the anode current (IA), while the cathode (K) is connected to another power supply (VAK / 2) also connected to ground.

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