An x-ray tube filament heating current control circuit

Abstract

The application relates to an X-ray tube filament heating current control circuit which comprises a rectification filtering module, a conversion module, a current collection module, an error module and a PWM controller; the rectification filtering module is used for connecting an alternating current power supply; the conversion module is connected with the rectification filtering module and is used for receiving two-way pulse control signals output by the PWM controller, and outputs alternating current under the driving of the two-way pulse control signals, and the alternating current is used for output to a filament transformer; the current collection module is used for accurately collecting the current flowing into the filament transformer and outputting a current detection signal; the error module is connected with the current collection module and is used for calculating the error between the current value reflected by the current detection signal and a current correction value and outputting a current error signal; the PWM controller is connected with the error module and is used for adjusting the pulse width of the pulse control signal according to the current error signal and outputting two-way pulse control signals. The application has the effect of more accurately controlling the filament heating current.

Description

Technical Field

[0001] This application relates to the field of X-ray tubes, and more particularly to an X-ray tube filament heating current control circuit. Background Technology

[0002] Currently, X-ray generators are widely used in medical, security inspection, industrial flaw detection, food and packaging inspection and other fields.

[0003] As we understand it, the working principle of an X-ray tube is as follows: the filament, acting as the cathode, emits thermionic electrons under heating conditions. These thermionic electrons, under the influence of a high-voltage electric field applied between the anode and cathode of the X-ray tube, strike the anode target at high speed, thereby generating X-rays. In this process, the intensity of the X-rays is closely related to the electric field strength and the number of high-speed electrons striking the anode target. The process of striking the anode target generates the tube current. Therefore, the intensity of X-rays can be controlled by controlling the magnitude of the tube current. Since the filament of an X-ray tube is generally made of tungsten wire wound in a spiral, the heating intensity of the filament can be controlled by controlling the heating current of the filament, thereby controlling the magnitude of the tube current.

[0004] In practice, X-ray tube manufacturers typically provide emission characteristic curves. These curves show the relationship between the heating current of the filament and the final tube current under a given electric field strength. Due to environmental limitations, the available electric field strength may vary for different users. This necessitates that the heating circuit of the X-ray tube filament provide a controllable current source to deliver a precise tube current, allowing the X-ray tube to be better suited for various environments. Summary of the Invention

[0005] In order to accurately control the tube current, this application provides an X-ray tube filament heating current control circuit.

[0006] This application provides an X-ray tube filament heating current control circuit, which adopts the following technical solution: An X-ray tube filament heating current control circuit includes a rectifier and filter module, a converter module, a current acquisition module, an error module, and a PWM controller; The rectifier and filter module is used to connect to an AC power source and to rectify and filter the AC voltage when it is applied, and output DC voltage to supply power. The conversion module is connected to the rectifier and filter module and is used to receive a set of control signals output by the PWM controller. The control signals include two pulse control signals with a phase difference of 180°. The conversion module is also used to output an AC current under the drive of the two pulse control signals. The AC current is used to output to the filament transformer. The amplitude of the AC current depends on the pulse width of the pulse control signal. The current acquisition module is used to accurately acquire the current flowing into the filament transformer and output a current detection signal; The error module is connected to the current acquisition module and is used to calculate the error between the current value reflected by the current detection signal and the current correction value when the current detection signal is received, and output the current error signal. The current correction value is the algebraic sum of the error between the actual tube current value and the preset tube current value and the preset current value. The PWM controller is connected to an error module, which is used to adjust the pulse width of the pulse control signal according to the current error signal when a current error signal is received, and output a set of adjusted control signals.

[0007] By adopting the above technical solution, the current acquisition module can acquire accurate filament heating current, and the error module can calculate the difference between the real-time filament heating current and the current correction value, and feed it back to the PWM controller. The PWM controller can adjust the pulse width of the two pulse control signals based on the current error signal, thereby adjusting the amplitude of the filament heating current to achieve closed-loop control of the filament heating current. Although the filament heating current can be accurately controlled, due to other factors, when the filament heating current reaches the current preset value, there may still be a deviation between the tube current and the tube current preset value. Therefore, taking into account the deviation between the tube current and the tube current preset value when determining the current correction value can make the filament heating current control more accurate.

[0008] Optionally, the error module includes a preset value input unit, a first comparison unit, a calculation unit, and a second comparison unit; The preset value input unit is used to set a first preset signal and output it, wherein the value reflected by the first preset signal is a current preset value. The first comparison unit is used to calculate the error between the actual tube current value and the preset tube current value, and output the tube current error signal; The calculation unit is connected to the preset value input unit and the first comparison unit respectively, and is used to calculate the algebraic sum of the current difference reflected by the tube current error signal and the current preset value, and output a current reference signal reflecting the current correction value. The second comparison unit is connected to the current acquisition module and the calculation unit respectively, and is used to calculate the error between the current value reflected by the current detection signal and the current correction value, and output the current error signal.

[0009] Optionally, the first comparison unit includes a preset value input subunit and an error comparison subunit; The preset value input subunit is used to set a second preset signal and output it, wherein the value reflected by the second preset signal is a preset value of tube current. The error comparison subunit includes a first operational amplifier, a first resistor, a second resistor, a third resistor, a first capacitor, and a second capacitor; The non-inverting input of the first operational amplifier is grounded through a first resistor. The inverting input of the first operational amplifier is connected to a preset value input subunit and a signal input terminal. The signal input terminal is used to receive a tube current detection signal, which reflects the actual tube current value. One end of the second resistor is connected to the inverting input of the first operational amplifier, and the other end is connected to the output of the first operational amplifier. The third resistor and the first capacitor are connected in series, and the third resistor and the first capacitor are connected in parallel to a second resistor. The second capacitor is connected in parallel to the second resistor. The first operational amplifier is used to calculate the error between the actual tube current value reflected by the tube current detection signal and the preset tube current value, and outputs a tube current error signal.

[0010] Optionally, the computing unit includes a second operational amplifier, a fourth resistor, a fifth resistor, and a third capacitor; The non-inverting input of the second operational amplifier is grounded through the fourth resistor. The inverting input of the second operational amplifier is connected to the preset value input unit and the first comparison unit, respectively. One end of the fifth resistor is connected to the inverting input of the second operational amplifier, and the other end is connected to the output of the second operational amplifier. The third capacitor is connected in parallel with the fifth resistor. The second operational amplifier is used to calculate the algebraic sum of the current difference reflected by the tube current error signal and the current preset value, and outputs a current reference signal reflecting the current correction value.

[0011] Optionally, a jumper device is also provided on the line connecting the inverting input terminal of the second operational amplifier to the first comparator unit; The first comparison unit further includes a sixth resistor and a switching device; The sixth resistor is connected in series with the switching device, and the sixth resistor and the switching device are connected in parallel with the second resistor. The control terminal of the switching device is connected to the seventh resistor and the command input terminal respectively. The free end of the seventh resistor is grounded. The switching device is used to close when a control command is received.

[0012] By adopting the above technical solution, the first comparison unit is connected to the calculation unit via a jumper device. This means that the operator can choose to connect the first comparison unit to the calculation unit or not. When the first comparison unit is connected to the calculation unit, if the X-ray tube filament heating current control circuit is used for a short period of time, there will be no error between the actual tube current value and the preset tube current value. In this case, there is no need to activate the first comparison unit, and the calculation unit will amplify the preset current value. However, if the X-ray tube filament heating current control circuit is used for a longer period of time, an error will occur between the actual tube current value and the preset tube current value. The operator can then add control commands to activate the first comparison unit, thereby achieving more precise control of the filament heating current.

[0013] Optionally, the second comparison unit includes a third operational amplifier, an eighth resistor, a ninth resistor, a tenth resistor, a fourth capacitor, and a fifth capacitor; The non-inverting input of the third operational amplifier is grounded through the eighth resistor. The inverting input of the third operational amplifier is connected to the calculation unit and the current acquisition module, respectively. One end of the ninth resistor is connected to the inverting input of the third operational amplifier, and the other end is connected to the output of the third operational amplifier. The tenth resistor and the fourth capacitor are connected in series, and the tenth resistor and the fourth capacitor are connected in parallel to the ninth resistor. The fifth capacitor is connected in parallel to the ninth resistor. The third operational amplifier is used to calculate the error between the current value reflected by the current detection signal and the current correction value, and outputs a current error signal.

[0014] Optionally, the conversion module includes a half-bridge conversion unit and a resonant output unit; The half-bridge converter unit includes a pulse transformer, a first NMOS transistor, a second NMOS transistor, a first voltage divider resistor, a second voltage divider resistor, a third voltage divider resistor, and a fourth voltage divider resistor. Both ends of the primary winding of the pulse transformer are connected to the output terminal of the PWM controller. The first winding on the side of the pulse transformer is connected in series with the first and second voltage divider resistors to form a loop. The same-name terminal of the first winding is connected to the first voltage divider resistor. The gate of the first NMOS transistor is connected to the common terminal of the first and second voltage divider resistors. The drain of the first NMOS transistor is connected to the positive terminal of the DC voltage. The source of the first NMOS transistor is connected to the common terminal of the second voltage divider resistor and the first winding. The second winding on the side of the pulse transformer is connected in series with the third and fourth voltage divider resistors to form a loop. The same-name terminal of the second winding is connected to the fourth voltage divider resistor. The gate of the second NMOS transistor is connected to the common terminal of the third and fourth voltage divider resistors. The drain of the second NMOS transistor is connected to the source of the first NMOS transistor. The source of the second NMOS transistor is connected to the common terminal of the fourth voltage divider resistor and the second winding. The source of the second NMOS transistor is also connected to the negative terminal of the DC voltage. The common terminal of the first and second NMOS transistors outputs AC current. The resonant output unit is connected to the common terminal of the first NMOS transistor and the second NMOS transistor, and is used to shape the waveform of the alternating current into a sine wave.

[0015] Optionally, the current acquisition module includes a current sampling unit, a rectification unit, a conversion unit, a voltage divider unit, a high-precision true RMS converter, and a first-stage amplification unit; The current sampling unit is connected to the resonant output unit and is used to collect the magnitude of the current flowing into the filament transformer and output the current sampling signal. The rectifier unit is connected to the current sampling unit and is used to rectify the received current sampling signal and output a DC pulsating current sampling signal. The conversion unit is connected to the rectifier unit and is used to convert the received DC pulsating current sampling signal into a first voltage sampling signal and output it. The voltage divider unit is connected to the conversion unit and is used to divide the voltage value reflected by the received first voltage sampling signal and output the second voltage sampling signal. The high-precision true RMS converter is connected to the voltage divider unit and is used to perform high-precision conversion on the second voltage sampling signal in the form of DC pulsation, so as to obtain and output the true RMS value of the second voltage sampling signal. The first-stage amplification unit is connected to a high-precision true RMS converter, which amplifies the voltage value reflected by the true RMS value of the second voltage sampling signal according to a preset ratio when the true RMS value of the second voltage sampling signal is received, so as to obtain a voltage-form current detection signal and output it.

[0016] By adopting the above technical solutions, the high-precision true RMS converter can improve sampling accuracy.

[0017] Optionally, a protection module may also be included, which includes an overcurrent detection unit, a temperature detection unit, a triggering unit, and a first relay. The overcurrent detection unit is connected to the current acquisition module and is used to output an overcurrent detection signal when the current value reflected by the received current detection signal reaches a preset upper limit value. The temperature detection unit is used to detect the temperature of the X-ray tube assembly and to output a temperature detection signal when the temperature of the X-ray tube assembly reaches a preset temperature threshold. The triggering unit is connected to the overcurrent detection unit and the temperature detection unit respectively, and is used to output a power failure trigger signal when an overcurrent detection signal or a temperature detection signal is received; The power supply circuit containing the coil of the first relay is connected to the trigger unit. The normally open contact of the first relay is located on the line connecting the rectifier filter module and the AC power supply. The power failure trigger signal is used to control the power supply circuit to disconnect.

[0018] By adopting the above technical solution, the AC power supply can be automatically cut off when the filament heating current is too high or the X-ray tube assembly temperature is too high, so as to protect the circuit.

[0019] Optionally, the triggering unit includes a first NAND gate, a second NAND gate, a third NAND gate, a PNP transistor, a fifth voltage divider resistor, and a sixth voltage divider resistor; One input terminal of the first NAND gate is connected to the temperature detection unit and the overcurrent detection unit, respectively. One input terminal of the second NAND gate is connected to the output terminal of the first NAND gate. The other input terminal of the second NAND gate is connected to a reset signal input terminal. The output terminal of the second NAND gate is connected to the other input terminal of the first NAND gate. One input terminal of the third NAND gate is connected to the output terminal of the second NAND gate. The other input terminal of the third NAND gate is connected to the reset signal input terminal. The base of the PNP transistor is connected to the output terminal of the third NAND gate. The emitter is connected to the first amplitude power supply voltage. The collector is connected to the fifth voltage divider resistor and the sixth voltage divider resistor in sequence. The free end of the sixth voltage divider resistor is grounded.

[0020] In summary, this application includes at least one of the following beneficial technical effects: 1. In this application, the current acquisition module can acquire accurate filament heating current, and the error module can calculate the difference between the real-time filament heating current and the current correction value, and feed it back to the PWM controller. The PWM controller can adjust the pulse width of the two pulse control signals according to the current error signal, thereby adjusting the amplitude of the filament heating current to achieve closed-loop control of the filament heating current. Although the filament heating current can be accurately controlled, due to other factors, when the filament heating current reaches the current preset value, there may be a deviation between the tube current and the tube current preset value. Therefore, taking into account the deviation between the tube current and the tube current preset value when determining the current correction value can make the filament heating current more accurately controlled. 2. The first comparison unit is connected to the calculation unit via a jumper, meaning the operator can choose to connect the first comparison unit to the calculation unit or not. When the first comparison unit is connected to the calculation unit, if the X-ray tube filament heating current control circuit has a short usage time, there will be no error between the actual tube current value and the preset tube current value. In this case, there is no need to activate the first comparison unit, and the calculation unit will amplify the preset current value. However, if the X-ray tube filament heating current control circuit has a long usage time, an error will occur between the actual tube current value and the preset tube current value. The operator can then add control commands to activate the first comparison unit, thereby achieving more precise control of the filament heating current. 3. The protection module can automatically cut off the AC power supply to protect the circuit when the filament heating current is too high or the X-ray tube assembly temperature is too high. Attached Figure Description

[0021] Figure 1 This is a system schematic diagram of the X-ray tube filament heating current control circuit according to an embodiment of this application.

[0022] Figure 2 This is a circuit diagram of the EMI filter module and the rectifier filter module according to an embodiment of this application.

[0023] Figure 3 This is a circuit diagram of the transformation module according to an embodiment of this application.

[0024] Figure 4 This is a circuit diagram of the current sampling unit according to an embodiment of this application.

[0025] Figure 5 This is a circuit diagram of the rectifier unit, conversion unit, voltage divider unit, and analog-to-digital converter according to an embodiment of this application.

[0026] Figure 6 This is a circuit diagram of the first-stage amplification unit and the second-stage amplification unit in an embodiment of this application.

[0027] Figure 7 This is a circuit diagram of the preset value input unit, the calculation unit, and the second comparison unit in an embodiment of this application.

[0028] Figure 8 This is a circuit diagram of the first comparison unit in an embodiment of this application.

[0029] Figure 9 This is a circuit diagram of the PWM controller according to an embodiment of this application.

[0030] Figure 10 This is a circuit diagram of the temperature detection unit according to an embodiment of this application.

[0031] Figure 11 This is a circuit diagram of the upper limit value preset subunit in an embodiment of this application.

[0032] Figure 12 This is a circuit diagram of the protection module in an embodiment of this application.

[0033] Figure 13 This is a circuit diagram of the control circuit for switching between large and small filaments according to an embodiment of this application.

[0034] Explanation of reference numerals in the attached diagram: 1. Rectifier and filter module; 2. Conversion module; 21. Half-bridge converter unit; 22. Resonant output unit; 3. Current acquisition module; 31. Current sampling unit; 32. Rectifier unit; 33. Conversion unit; 34. Voltage divider unit; 35. High-precision true RMS converter; 36. First-stage amplifier unit; 37. Second-stage amplifier unit; 4. Error module; 41. Preset value input unit; 42. First comparison unit; 421. Preset value input subunit; 422. Error comparison subunit; 43. Calculation unit; 44. Second comparison unit; 5. PWM controller; 6. Protection module; 61. Overcurrent detection unit; 611. Upper limit preset subunit; 62. Temperature detection unit; 63. Trigger unit; 64. Undercurrent detection unit; 7. EMI filter module; 8. Coil of the first relay; 9. Coil of the second relay. Detailed Implementation

[0035] To make the purpose, technical solution, and advantages of this application clearer, the following description is provided in conjunction with the appendix. Figure 1-13 The present application will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the application.

[0036] This application discloses an X-ray tube filament heating current control circuit.

[0037] Reference Figure 1The X-ray tube filament heating current control circuit includes an EMI filter module 7, a rectification filter module 1, a conversion module 2, a current acquisition module 3, an error module 4, a PWM controller 5, and a protection module 6. The current acquisition module 3, the error module 4, and the PWM controller 5 form a closed-loop control circuit, enabling precise control of the filament heating current.

[0038] Reference Figure 1 and Figure 2 The rectifier and filter module 1 is connected to the AC power supply through the EMI filter module 7. It is used to rectify and filter the AC voltage when it is connected, and output DC voltage to supply power.

[0039] The rectifier-filter module 1 includes a bridge rectifier circuit and a filter circuit. Specifically, the two input terminals of the bridge rectifier circuit are connected to the EMI filter module 7 to receive the AC voltage that has been filtered out for electromagnetic interference by the EMI filter module 7. The bridge rectifier circuit is used to rectify the AC voltage, and its output terminal outputs a DC voltage.

[0040] The filter circuit includes a first filter capacitor C1, a second filter capacitor C7, a first filter resistor R1, a second filter resistor R2, a third filter resistor R5, and a fourth filter resistor R6. The first filter capacitor C1 and the second filter capacitor C7 are connected in series, and the free ends of the first filter capacitor C1 and the second filter capacitor C7 are respectively connected to the two output terminals of the bridge rectifier circuit. The first filter resistor R1 and the second filter resistor R2 are connected in series, and the first filter resistor R1 and the second filter resistor R2 are connected in parallel with the first filter capacitor C1. The third filter resistor R5 and the fourth filter resistor R6 are connected in series, and the third filter resistor R5 and the fourth filter resistor R6 are connected in parallel with the second filter capacitor C7.

[0041] It is worth noting that one output terminal of the EMI filter module 7 is also connected to a power jumper device. The free end of the power jumper device is connected to the common terminal of the first filter capacitor C1 and the second filter capacitor C7. In actual use, if the AC voltage amplitude is 230V, the power jumper device is in the open state, and the bridge rectifier circuit performs full-wave rectification. If the AC voltage amplitude is 115V, the power jumper device can be closed, causing the two diodes in the bridge rectifier circuit to be short-circuited, and the bridge rectifier circuit performs half-wave rectification. By adding the power jumper device, the X-ray tube filament heating current control circuit can adapt to AC power supplies of different magnitudes. The EMI filter module 7 is a mature technology in related fields, and this application does not improve upon it; therefore, it will not be described in detail here.

[0042] Reference Figure 1 and Figure 3The conversion module 2 is connected to the rectifier and filter module 1. It is used to receive a set of control signals output by the PWM controller and output AC current under the drive of the control signals. The AC current is used to output to the filament transformer to supply power to the filament transformer.

[0043] The conversion module 2 includes a half-bridge conversion unit 21 and a resonant output unit 22.

[0044] The half-bridge converter unit 21 is connected to the rectifier and filter module 1, and is used to receive a set of control signals output by the PWM controller 5, and output AC current under the drive of the control signals. Specifically, the half-bridge converter unit 21 includes a pulse transformer T2, a first NMOS transistor Q1, a second NMOS transistor Q2, a first voltage divider resistor R8, a second voltage divider resistor R9, a third voltage divider resistor R13, a fourth voltage divider resistor R14, and multiple resistors. The two ends of the primary winding of the pulse transformer T2 are connected to the output terminal of the PWM controller 5 through a resistor to receive a set of control signals. The control signals include two pulse control signals with a phase difference of 180°. The first winding on the pulse transformer T2 is connected in series with the first voltage divider resistor R8 and the second voltage divider resistor R9 to form a loop. The same-name terminal of the first winding is connected to the first voltage divider resistor R8. The gate of the first NMOS transistor Q1 is connected to the common terminal of the first voltage divider resistor R8 and the second voltage divider resistor R9. Its drain is connected to the positive terminal of the DC voltage, and its source is connected to the common terminal of the second voltage divider resistor R9 and the first coil. The second coil on the pulse transformer T2 is connected in series with the third voltage divider resistor R13 and the fourth voltage divider resistor R14, forming a loop. The corresponding terminal of the second coil is connected to the fourth voltage divider resistor R14. The gate of the second NMOS transistor Q2 is connected to the common terminal of the third voltage divider resistor R13 and the fourth voltage divider resistor R14. Its drain is connected to the source of the first NMOS transistor Q1. The source is connected to the common terminal of the fourth voltage divider resistor R14 and the second coil, and the negative terminal of the DC voltage. The common terminal of the first NMOS transistor Q1 and the second NMOS transistor Q2 outputs AC current. It can be understood that the two pulse control signals are 180° out of phase. The PWM controller 5 controls the two pulse control signals to work alternately, causing the first NMOS transistor Q1 and the second NMOS transistor Q2 to conduct alternately. When the pulse control signal current flows into the same-named terminal of the primary winding of pulse transformer T2, the first NMOS transistor Q1 is turned off and the second NMOS transistor Q2 is turned on. When the pulse control signal current flows into the other terminal of the primary winding of pulse transformer T2, the first NMOS transistor Q1 is turned on and the second NMOS transistor Q2 is turned off. At this time, the common terminal of the first NMOS transistor Q1 and the second NMOS transistor Q2 outputs AC current. Considering that the current of the two pulse control signals is bidirectional, a diode is also provided to prevent current backflow.

[0045] The resonant output unit 22 is connected to the half-bridge converter unit 21 and is used to shape the waveform of the alternating current into a sine wave. The resonant output unit 22 includes a resonant inductor L2 and a resonant capacitor C9. The resonant inductor L2 and the resonant capacitor C9 are connected in series with the common terminal of the first NMOS transistor Q1 and the second NMOS transistor Q2.

[0046] Reference Figure 2 , Figure 3 and Figure 4 In this application, the common terminal of the first filter capacitor C1 and the second filter capacitor C7, together with the output terminal of the resonant output unit 22, serves as the output terminal connected to the filament transformer to supply power to the filament transformer.

[0047] Refer to 1 and Figure 4 The current acquisition module 3 is used to accurately acquire the current flowing into the filament transformer and output a current detection signal.

[0048] The current acquisition module 3 includes a current acquisition unit, a rectification unit 32, a conversion unit 33, a voltage divider unit 34, a high-precision true RMS converter 35, and a first-stage amplification unit 36.

[0049] The current sampling unit 31 is connected to the resonant output unit 22 and is used to collect the magnitude of the current flowing into the filament transformer and output a current sampling signal. Preferably, the current sampling unit 31 is a current transformer. The primary winding of the current transformer T1 is located on the line connecting the resonant output unit 22 and the filament transformer, and the two ends of the secondary winding output current sampling signals. The ratio of the current value reflected by the current sampling signal to the magnitude of the filament heating current flowing through the filament transformer is the ratio of the number of turns of the primary winding to the number of turns of the secondary winding. In this application, the current value reflected by the current sampling signal is 1 / 100 of the filament heating current flowing through the filament transformer. Of course, in other specific embodiments, the current sampling unit 31 can also be other detection instruments with current detection functions.

[0050] Reference Figure 4 , Figure 5 and Figure 6 The rectifier unit 32 is connected to the current sampling unit 31 and is used to receive the current sampling signal and rectify the received current sampling signal to output a DC pulsating current sampling signal. Since the current sampling signal is an AC signal, it needs to be rectified by the rectifier unit 32 to more accurately measure its effective value. Preferably, the rectifier unit 32 is a full-bridge rectifier circuit.

[0051] Conversion unit 33 is connected to rectifier unit 32 and is used to receive a DC pulsating current sampling signal, convert the received DC pulsating current sampling signal into a first voltage sampling signal, and output it. Conversion unit 33 includes resistors R49 and R50. Resistor R49 is connected to the output terminal of rectifier unit 32, that is, one end is connected to the positive output terminal of rectifier unit 32, the other end is connected to the negative output terminal of rectifier unit 32, and grounded. Resistor R50 is connected in parallel with resistor R49.

[0052] Voltage divider unit 34 is connected to conversion unit 33. It receives a first voltage sampling signal, divides the voltage value reflected by the received first voltage sampling signal, and outputs a second voltage sampling signal. Specifically, voltage divider unit 34 includes resistors R45 and R53. Resistor R45 and resistor R53 are connected in series. The free end of resistor R45 is connected to the output terminal of conversion unit 33, and the free end of resistor R53 is grounded. By dividing the voltage value reflected by the first voltage sampling signal through resistors R45 and R53, the second voltage sampling signal is obtained to protect the high-precision true RMS converter 35.

[0053] A high-precision true RMS converter 35 is connected to a voltage divider unit 34 to receive the second voltage sampling signal and to perform high-precision conversion on the DC pulsating second voltage sampling signal to obtain and output the true RMS value of the second voltage sampling signal. In this application, the high-precision true RMS converter 35 uses an AD736 true RMS converter chip. This true RMS converter chip enables more accurate measurement of the filament heating current, facilitating precise control of the filament heating current.

[0054] Specifically, the VIN pin of the true RMS converter chip is connected to the common terminal of resistors R45 and R53 to receive the second voltage sampling signal. A capacitor C28 is also connected to the VIN pin to filter the second voltage sampling signal. The OUT pin of the true RMS converter chip serves as the output terminal, outputting the true RMS value of the second voltage sampling signal.

[0055] The first-stage amplification unit 36 ​​is connected to the high-precision true RMS converter 35, which is used to receive the true RMS value of the second voltage sampling signal, and to amplify the voltage value reflected by the true RMS value of the second voltage sampling signal according to a preset ratio when the true RMS value of the second voltage sampling signal is received, so as to obtain a voltage-form current detection signal and output it.

[0056] The first-stage amplification unit 36 ​​includes an operational amplifier U6A, multiple resistors, and multiple capacitors. Specifically, the non-inverting input of operational amplifier U6A is connected to the output of the true RMS converter chip via resistor R54 to receive the true RMS value of the second voltage sampling signal. The non-inverting input of operational amplifier U6A is also connected to capacitor C32. The free end of capacitor C32 is grounded to filter the true RMS value of the second voltage sampling signal. One end of resistor R46 is connected to the inverting input of operational amplifier U6A, and the other end is connected to the output of operational amplifier U6A. The inverting input of operational amplifier U6A is also connected to resistors R94 and R47 in series, with the free end of resistor R47 grounded. Resistor TR4 is connected in parallel with resistor R94. Capacitor C26 is connected in parallel with resistor R46. The output of operational amplifier U6A outputs a voltage-form current detection signal. Resistor TR4 is a variable resistor; the signal amplification ratio of the first-stage amplification unit 36 ​​can be adjusted by changing its resistance value.

[0057] Reference Figure 1 , Figure 7 and Figure 8 Error module 4 is connected to current acquisition module 3. It is used to receive current detection signals and, when the current detection signal is received, to calculate the error between the current value reflected by the current detection signal and the current correction value, and output a current error signal.

[0058] Error module 4 includes a preset value input unit 41, a first comparison unit 42, a calculation unit 43, and a second comparison unit 44.

[0059] The preset value input unit 41 is used to set and output a first preset signal. The value reflected by the first preset signal is a current preset value. In this application, the current preset value can be a value input through a port or manually adjusted and set by the operator. Specifically, the preset value input unit 41 includes a preset value input terminal. The preset value input terminal is used to connect to and output the first preset signal. In some specific embodiments, the preset value input terminal can be connected to a control device such as a controller that can output control commands. In addition, to facilitate manual setting of the current preset value by the operator, the preset value input unit 41 also includes an input jumper device, an NPN transistor Q3, a resistor R25, and a resistor TR1. Resistors R25 and TR1 are connected in series, and the free end of resistor R25 is connected to the first amplitude power supply voltage, while the free end of resistor TR1 is grounded. Resistor TR1 is a sliding rheostat, and its resistance value can be adjusted by the operator. The base of the NPN transistor Q3 is connected to the movable end of resistor TR1, the collector is connected to the first amplitude power supply voltage, and the emitter is connected to the preset value input terminal through the input jumper device. That is, when manufacturing the X-ray tube filament heating current control circuit, the operator can choose whether to include a function for manually setting the preset current value, depending on the actual situation. When the NPN transistor Q3, resistor R25, and resistor RT1 are connected to the X-ray tube filament heating current control circuit, the operator can choose to input the preset current value from the preset value input terminal or manually set the preset current value. The power supply voltage for the first amplitude is +15V, which can be provided by the controller or power chip.

[0060] It is understood that this application mainly aims to control the tube current by precisely controlling the filament heating current. However, in reality, after the X-ray tube filament heating current control circuit has been used for a long time, there will be a deviation between the actual tube current value and the preset tube current value. Therefore, in order to ensure that both the filament heating current and the actual tube current value reach the expected value, it is necessary to consider the error between the actual tube current value and the preset tube current value before adjusting according to the error between the filament heating current and the current preset.

[0061] The first comparison unit 42 is used to calculate the error between the actual tube current value and the preset tube current value, and outputs the tube current error signal. The first comparison unit 42 includes a preset value input subunit 421 and an error comparison subunit 422.

[0062] The preset value input subunit 421 is used to set and output a second preset signal. The value reflected by the second preset signal is the preset value of the tube current. Similarly, a preset value input terminal can also be set to input the preset value of the tube current.

[0063] Furthermore, the preset value of the tube current reflected by the second preset signal needs to be amplified before being compared with the actual tube current value. Specifically, the first comparison unit 42 also includes an operational amplifier U2A, resistors R23, R19, R16, and capacitor C10. The non-inverting input terminal of the operational amplifier U2A is grounded through resistor R23, and the inverting input terminal is connected to the preset value input terminal through resistor R19. One end of resistor R16 is connected to the inverting input terminal of the operational amplifier U2A, and the other end is connected to the output terminal of the operational amplifier U2A. Capacitor C10 is connected in parallel with resistor R16. The operational amplifier U2A is used to receive the second preset signal and amplify the second preset signal to output the amplified second preset signal.

[0064] The error comparison subunit 422 includes a first operational amplifier U2B, a first resistor R24, a second resistor R20, a third resistor R18, a first capacitor C11, and a second capacitor C50. Specifically, the non-inverting input terminal of the first operational amplifier U2B is grounded through resistor R24, and the inverting input terminal is connected to the preset value input subunit 421 and a signal input terminal. The signal input terminal is used to input the tube current detection signal. The value reflected by the tube current detection signal is the actual tube current value. One end of the second resistor R20 is connected to the inverting input terminal of the first operational amplifier U2B, and the other end is connected to the output terminal of the first operational amplifier U2B. The third resistor R18 and the first capacitor C11 are connected in series, and the third resistor R18 and the first capacitor C11 are connected in parallel with the second resistor R20. The second capacitor C50 is connected in parallel with the second resistor R20. The first operational amplifier U2B is used to receive the second preset signal and the tube current detection signal, and when the second preset signal and the tube current detection signal are received, it is used to calculate the error between the actual tube current value reflected by the tube current detection signal and the preset tube current value, so as to output the tube current error signal.

[0065] The calculation unit 43 is connected to the preset value input unit 41 and the first comparison unit 42 respectively. It is used to receive the first preset signal and the tube current error signal, and when the first preset signal and the tube current error signal are received, it calculates the algebraic sum of the current difference reflected by the tube current error signal and the current preset value, and outputs a current reference signal reflecting the current correction value.

[0066] Specifically, the calculation unit 43 includes a second operational amplifier U4A, a fourth resistor R40, a fifth resistor R32, and a third capacitor C16. The non-inverting input of the second operational amplifier U4A is grounded through the fourth resistor R40, and the inverting input is connected to the preset value input unit 41 and the first comparison unit 42, respectively. One end of the fifth resistor R32 is connected to the inverting input of the second operational amplifier U4A, and the other end is connected to the output of the second operational amplifier U4A. The third capacitor C16 is connected in parallel with the fifth resistor R32. The second operational amplifier U4A is used to receive a first preset signal and a tube current error signal, and when it receives the first preset signal and the tube current error signal, it is used to calculate the algebraic sum of the current difference reflected by the tube current error signal and the current preset value, so as to output a current reference signal.

[0067] It is worth noting that a jumper device is also provided on the line connecting the inverting input terminal of the second operational amplifier U4A to the first comparator unit 42. The first comparator unit 42 also includes a sixth resistor R17 and a switching device. Specifically, the sixth resistor R17 is connected in series with the switching device, and the sixth resistor R17 is connected in parallel with the switching device to the second resistor R20. The control terminal of the switching device is connected to a seventh resistor R15 and a command input terminal. The free end of the seventh resistor R15 is grounded. The switching device is used to close when a control command is received. The first comparator unit 42 is connected to the calculation unit 43 via the jumper device, meaning that the operator can choose to connect the first comparator unit 42 to the calculation unit 43 or not. When the first comparator unit 42 is connected to the calculation unit 43, if the X-ray tube filament heating current control circuit is used for a short time, there will be no error between the actual tube current value and the preset tube current value. In this case, it is not necessary to activate the first comparator unit 42, and the calculation unit 43 performs the amplification function of the preset current value. When the X-ray tube filament heating current control circuit has been in use for a long time, an error will occur between the actual tube current value and the preset tube current value. Operators can add control commands to activate the first comparison unit 42, thereby achieving more precise control of the filament heating current. The current correction value is the algebraic sum of the error between the actual tube current and the preset tube current value and the preset current value.

[0068] The second comparison unit 44 is connected to the current acquisition module 3 and the calculation unit 43 respectively. It is used to receive the current detection signal and the current reference signal, and to calculate the error between the current value reflected by the current detection signal and the current correction value when the current detection signal and the current reference signal are received, and to output the current error signal.

[0069] The second comparison unit 44 includes a third operational amplifier U4B, an eighth resistor R42, a ninth resistor R31, a tenth resistor R30, a fourth capacitor C15, and a fifth capacitor C14. The non-inverting input of the third operational amplifier U4B is grounded through the eighth resistor R42, and the inverting input is connected to the calculation unit 43 and the current acquisition module 3, respectively. One end of the ninth resistor R31 is connected to the inverting input of the third operational amplifier U4B, and the other end is connected to the output of the third operational amplifier U4B. The tenth resistor R30 and the fourth capacitor C15 are connected in series, and the tenth resistor R30 and the fourth capacitor C15 are connected in parallel with the ninth resistor R31. The fifth capacitor R14 is connected in parallel with the ninth resistor R31. The third operational amplifier U4B is used to receive the current detection signal and the current reference signal, and when the current detection signal and the current reference signal are received, it is used to calculate the error between the current value reflected by the current detection signal and the current correction value, and output the current error signal.

[0070] It should be noted that when sampling the filament heating current using a current transformer, the current sampling signal reflects a value of 1 / 100 of the filament heating current. Furthermore, the current sampling signal is amplified. Therefore, to accurately calculate the current error signal, the inverting input of the third operational amplifier U4B needs to be connected to both the calculation unit 43 and the current detection module via resistors. Specifically, the resistance of the resistor connected to the calculation unit 43 is 10 times that of the resistor connected to the current detection module.

[0071] Reference Figure 1 and Figure 9The PWM controller 5 is connected to the error module 4 to receive the current error signal and, upon receiving the current error signal, adjusts the pulse width of the pulse control signal to output an adjusted set of control signals. Preferably, the PWM controller 5 is a controller chip of model UC3525ADW. The +IN pin of the controller chip is connected to the output terminal of the second comparator unit 44 to receive the current error signal. The VCC pin is connected to capacitor C20, capacitor C19, and resistor R28. The free ends of capacitors C19 and C20 are grounded, and the free end of resistor R28 is connected to the power supply voltage of the first amplitude. The VC pin is connected to capacitors C18 and C21, and resistor R29. The free ends of capacitors C18 and C21 are grounded, and the free end of resistor R29 is connected to the power supply voltage of the first amplitude. The OUTA and OUTB pins are used to output one pulse control signal, and each of the two output pins is connected to two Zener diodes. In this configuration, the anode of one Zener diode is connected to the output pin, and the cathode is connected to the common terminal of resistor R29 and capacitor C18. The cathode of the other Zener diode is connected to the output pin, and the anode is grounded. The CT, RT, and DIS pins determine the pulse frequency of the two pulse control signals. Specifically, the DIS pin is connected in sequence to resistor R38 and capacitor C22, with the free end of capacitor C22 grounded. The CT pin is connected to the common terminal of resistor R38 and capacitor C22. The RT pin is connected in sequence to resistor R39 and resistor R43, with the free end of resistor R43 grounded.

[0072] It is understood that the X-ray tube filament heating current control circuit of this application can adjust the magnitude of the filament heating current through a closed-loop control circuit composed of the current acquisition module 3, the error module 4, and the PWM controller 5. The main method for adjusting the magnitude of the filament heating current is to adjust the pulse width and pulse frequency of the pulse control signal. However, X-ray tube manufacturers typically recommend that the frequency of the filament heating current should not exceed 20kHz. Since a higher frequency of the filament heating current makes it easier to achieve precise control, the frequency of the filament heating current in this application is 17kHz. Furthermore, since the frequency of the filament heating current is a fixed value, adjusting the magnitude of the filament heating current can only be achieved by adjusting the pulse width of the pulse control signal.

[0073] Reference Figure 1 The protection module 6 can protect the above circuit. The protection module 6 includes an overcurrent detection unit 61, an undercurrent detection unit 64, a temperature detection unit 62, a trigger unit 63, and a first relay.

[0074] Reference Figure 10The temperature detection unit 62 is used to detect the temperature of the X-ray tube assembly and to output a temperature detection signal when the temperature of the X-ray tube assembly reaches a preset temperature threshold. In some specific embodiments, a temperature switch, a temperature sensor, and a controller can be used to achieve the above functions. In this application, the temperature detection signal is a low-level signal. If the temperature of the X-ray tube assembly does not reach the preset temperature threshold, a high-level signal is output, that is, no temperature detection signal is output.

[0075] Reference Figure 11 and Figure 12 The overcurrent detection unit 61 is connected to the current acquisition module 3, and is used to receive the current detection signal and output the overcurrent detection signal when the current value reflected by the received current detection signal reaches the preset upper limit of the current value.

[0076] Specifically, the overcurrent detection unit 61 includes an upper limit preset subunit 611 and a comparator U8B.

[0077] The upper limit preset subunit 611 includes an NPN transistor Q6, two switching switches, and multiple resistors. Resistors R65, TR2, and R70 are connected in series. The free end of resistor R65 is connected to the power supply voltage of the first amplitude. Resistor TR2 is a variable resistor. The free end of resistor R70 is grounded. One end of switching switch U1C is connected to the movable end of resistor TR2, and the other end is connected to the non-inverting input of comparator U8B. Resistors R76, TR3, and R80 are connected in series. The free end of resistor R76 is connected to the power supply voltage of the first amplitude. Resistor TR3 is a variable resistor. The free end of resistor R80 is grounded. One end of switching switch U1B is connected to the movable end of resistor TR3, and the other end is connected to the non-inverting input of comparator U8B. The control terminal of switching switch U1C is connected to resistor R69, and the free end of resistor R69 is connected to the power supply voltage of the first amplitude. The control terminal of switch U1B is connected to resistor R81, with the free end of resistor R81 grounded. The base of NPN transistor Q6 is connected to the control terminal of switch U1B via resistor R75, its emitter is grounded, and its collector is connected to the control terminal of switch U1C. This circuit can set two upper current limits, corresponding to the upper current limits of the large filament and the small filament, respectively. When the X-ray tube is connected to the large filament, the upper current limit needs to be switched to the large filament's current limit; when the X-ray tube is connected to the small filament, the upper current limit needs to be switched to the small filament's current limit. If a high-level control signal is applied to the control terminal of switch U1B, the upper current limit is the small filament's current limit; if a low-level control signal is applied, the upper current limit is the large filament's current limit.

[0078] The inverting input of comparator U8B is connected to the current detection module. When a current detection signal is received, it compares the current value reflected by the current detection signal with the upper limit of the current. If the current value reflected by the current detection signal reaches the upper limit of the current, it outputs a low-level signal, i.e., an overcurrent detection signal. If the current value reflected by the overcurrent detection signal does not reach the upper limit of the current, it outputs a high-level signal, i.e., no overcurrent detection signal is output.

[0079] Reference Figure 6 It should be noted that since the current value reflected by the current detection signal output by the first-stage amplification unit 36 ​​is of a different order of magnitude from the upper limit of the current, it still needs to be amplified by the second-stage amplification unit 37 in the current acquisition module 3.

[0080] Specifically, the secondary amplification unit 37 includes operational amplifier U6B, resistors R52, R55, and R56. The inverting input of operational amplifier U6B is grounded through resistor R56, and the non-inverting input is connected to the output of the primary amplification unit 36. One end of resistor R55 is connected to the inverting input of operational amplifier U6B, and the other end is connected to its output. Operational amplifier U6B is used to amplify the received current detection signal according to a preset ratio and output it.

[0081] Reference Figure 11 and Figure 12 The trigger unit 63 is connected to the overcurrent detection unit 61 and the temperature detection unit 62 respectively, and is used to receive the overcurrent detection signal and the temperature detection signal, and to output the power failure trigger signal when the overcurrent detection signal or the temperature detection signal is received.

[0082] Specifically, the trigger unit 63 includes a first NAND gate U7B, a second NAND gate U7A, a third NAND gate U7D, a PNP transistor Q4, a fifth voltage divider resistor R61, and a sixth voltage divider resistor R64. One input terminal of the first NAND gate U7B is connected to both the temperature detection unit 62 and the overcurrent detection unit 61. One input terminal of the second NAND gate U7A is connected to the output terminal of the first NAND gate U7B. The other input terminal of the second NAND gate U7A is connected to a reset signal input terminal, and the output terminal of the second NAND gate U7A is connected to the other input terminal of the first NAND gate U7B. One input terminal of the third NAND gate U7D is connected to the output terminal of the second NAND gate U7A, and the other input terminal of the third NAND gate U7D is connected to the reset signal input terminal. The base of the PNP transistor Q4 is connected to the output terminal of the third NAND gate U7D, the emitter is connected to the first amplitude power supply voltage, and the collector is connected sequentially to the fifth voltage divider resistor R61 and the sixth voltage divider resistor R64. The free end of the sixth voltage divider resistor R64 is grounded. The reset signal input terminal is used to receive the reset signal. The reset signal can also be output by a controller or other device. The circuit operates as follows: Upon power-up, the reset signal input terminal is low, and the output of the third NAND gate U7D is high, preventing the PNP transistor Q4 from conducting. Simultaneously, the output of the second NAND gate U7A is high. In the absence of overcurrent, comparator U8B outputs a high signal, and the output of the second NAND gate U7B is low. When the reset signal input terminal is high, the output of the third NAND gate U7D is low, turning on the PNP transistor Q4. At this time, the common terminal of the fifth and sixth voltage divider resistors R61 and R64 outputs a high-level signal, meaning no power-off trigger signal is output. In the event of overcurrent or excessive temperature, the output of the first NAND gate U7B is high, the output of the second NAND gate U7A is low, and the output of the third NAND gate U7D is high. At this time, the common terminal of the fifth voltage divider resistor R61 and the sixth voltage divider resistor R64 outputs a low-level signal, which is the power-off trigger signal.

[0083] The power supply circuit containing the coil 8 of the first relay is connected to the trigger unit 63, and the normally open contact of the first relay is located on the connection line between the rectifier filter module 1 and the EMI filter module 7.

[0084] Specifically, the power supply circuit includes an opto-isolator OP2, a PNP transistor Q5, and multiple resistors. The input anode of opto-isolator OP2 is connected to the common terminal of the fifth voltage divider resistor R61 and the sixth voltage divider resistor R64, while the input cathode is grounded. The output anode is connected to the second amplitude power supply voltage via resistor R63, and the output cathode is connected in sequence to resistors R96 and R95, and to the coil 8 of the first relay. The free end of the coil 8 of the first relay is grounded. The base of the PNP transistor Q5 is connected to the output anode of opto-isolator OP2, the emitter is connected to the second amplitude power supply voltage, and the collector is connected to the common terminal of opto-isolator OP2 and resistor R96. When the input anode of opto-isolator OP2 receives a power-off trigger signal, opto-isolator OP2 and PNP transistor Q5 also de-energize, thus de-energizing the coil 8 of the first relay and causing the normally open contact to open, thereby protecting the X-ray tube filament heating current control circuit. Conversely, when the input anode of opto-isolator OP2 does not receive a power-off trigger signal, opto-isolator OP2 is in the conducting state, and PNP transistor Q5 is also in the conducting state. At this time, the coil 8 of the first relay is energized, its normally open contact closes, and the X-ray tube filament heating current control circuit can work normally. The second amplitude power supply voltage can also be provided by the controller or power chip.

[0085] Meanwhile, in the event of overcurrent or overheating, the X-ray tube filament heating current control circuit can report an error, and the indicator light will illuminate.

[0086] The undercurrent detection unit 64 is connected to the current acquisition module 3, and is used to receive the current detection signal and output the undercurrent detection signal when the current value reflected by the received current detection signal is lower than the current lower limit.

[0087] The undercurrent detection unit 64 includes a comparator U8A, an opto-isolator OP4, and multiple resistors. The inverting input of comparator U8A is connected to the secondary amplifier unit 37, and the non-inverting input is connected to resistors R73 and R77. The free end of resistor R73 is connected to the power supply voltage of the first amplitude, and the free end of resistor R77 is grounded to set the lower current limit. Comparator U8A outputs a high-level signal (undercurrent detection signal) when the current value reflected by the received current detection signal is lower than the lower current limit; conversely, it outputs a low-level signal (no undercurrent detection signal) when the current value reflected by the current detection signal is not lower than the lower current limit. The input anode of opto-isolator OP4 is connected to the common terminal of PNP transistor Q4 and the fifth voltage divider resistor R61 via resistor R71, and the input cathode is connected to the output of comparator U8A. One end of resistor R78 is connected to the output of comparator U8A, and the other end is connected to the input anode of opto-isolator OP4. The output anode of opto-isolator OP4 is connected to the second amplitude power supply voltage, and the output cathode serves as the output terminal to output an error signal. That is, when an undercurrent condition occurs, the output cathode of opto-isolator OP4 outputs a low-level signal to provide an error warning.

[0088] Reference Figure 13 The X-ray tube filament heating current control circuit of this application, in addition to adjusting the corresponding upper limit value of the current according to the size of the connected filament, also has the function of switching between large and small filaments. Specifically, a second relay contact is also provided on the line connecting the filament transformer and the resonant output unit 22. When a control command for switching between large and small filaments is input, the level of the control command can affect the energization state of the coil 9 of the second relay, and at the same time, it can also affect the level of the control signal input to the switching switch U1B, thereby realizing the switching of the upper limit value of the current corresponding to the size of the filament while switching between large and small filaments.

[0089] In this application, all externally input control signals and control commands can be transmitted to the corresponding signal input terminal or command input terminal through opto-isolation or other isolation methods.

[0090] The implementation principle of an X-ray tube filament heating current control circuit according to an embodiment of this application is as follows: the current acquisition module 3 can acquire accurate filament heating current, the error module 4 can calculate the difference between the real-time filament heating current and the current correction value, and feed it back to the PWM controller 5. The PWM controller 5 can adjust the pulse width of the two pulse control signals according to the current error signal, thereby adjusting the amplitude of the filament heating current to achieve closed-loop control of the filament heating current. Although the filament heating current can be accurately controlled, due to the influence of other factors, when the filament heating current reaches the current preset value, there may be a deviation between the tube current and the tube current preset value. Therefore, taking into account the deviation between the tube current and the tube current preset value when determining the current correction value can make the filament heating current more accurately controlled.

[0091] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Any feature disclosed in this specification (including the abstract and drawings) may be replaced by other equivalent or similar features unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is only one example of a series of equivalent or similar features.

Claims

1. A circuit for controlling the heating current of an X-ray tube filament, characterized in that: It includes a rectifier and filter module (1), a conversion module (2), a current acquisition module (3), an error module (4), and a PWM controller (5); The rectifier and filter module (1) is used to connect to an AC power source and to rectify and filter the AC voltage when it is connected, and output DC voltage to supply power. The conversion module (2) is connected to the rectifier and filter module (1) and is used to receive a set of control signals output by the PWM controller (5). The control signals include two pulse control signals with a phase difference of 180°. The conversion module (2) is also used to output AC current under the drive of the two pulse control signals. The AC current is used to output to the filament transformer. The amplitude of the AC current depends on the pulse width of the pulse control signal. The current acquisition module (3) is used to accurately acquire the current flowing into the filament transformer and output a current detection signal; The error module (4) is connected to the current acquisition module (3) and is used to calculate the error between the current value reflected by the current detection signal and the current correction value when the current detection signal is received, and output the current error signal. The current correction value is the algebraic sum of the error between the actual tube current value and the preset tube current value and the preset current value. The PWM controller (5) is connected to the error module (4) and is used to adjust the pulse width of the pulse control signal according to the current error signal when the current error signal is received, and output a set of adjusted control signals.

2. The X-ray tube filament heating current control circuit according to claim 1, characterized in that: The error module (4) includes a preset value input unit (41), a first comparison unit (42), a calculation unit (43), and a second comparison unit (44); The preset value input unit (41) is used to set a first preset signal and output it, wherein the value reflected by the first preset signal is a current preset value. The first comparison unit (42) is used to calculate the error between the actual tube current value and the preset tube current value, and output the tube current error signal; The calculation unit (43) is connected to the preset value input unit (41) and the first comparison unit (42) respectively, and is used to calculate the algebraic sum of the current difference reflected by the tube current error signal and the current preset value, and output the current reference signal reflecting the current correction value. The second comparison unit (44) is connected to the current acquisition module (3) and the calculation unit (43) respectively, and is used to calculate the error between the current value reflected by the current detection signal and the current correction value, and output the current error signal.

3. The X-ray tube filament heating current control circuit according to claim 2, characterized in that: The first comparison unit (42) includes a preset value input subunit (421) and an error comparison subunit (422); The preset value input subunit (421) is used to set a second preset signal and output it. The value reflected by the second preset signal is the preset value of the tube current. The error comparison subunit (422) includes a first operational amplifier, a first resistor, a second resistor, a third resistor, a first capacitor, and a second capacitor; The non-inverting input of the first operational amplifier is grounded through a first resistor. The inverting input of the first operational amplifier is connected to a preset value input subunit (421) and a signal input terminal is connected thereto. The signal input terminal is used to receive a tube current detection signal. The value reflected by the tube current detection signal is the actual tube current value. One end of the second resistor is connected to the inverting input of the first operational amplifier, and the other end is connected to the output of the first operational amplifier. The third resistor and the first capacitor are connected in series. The third resistor and the first capacitor are connected in parallel to a second resistor. The second capacitor is connected in parallel to a second resistor. The first operational amplifier is used to calculate the error between the actual tube current value reflected by the tube current detection signal and the preset tube current value, and outputs a tube current error signal.

4. The X-ray tube filament heating current control circuit according to claim 3, characterized in that: The computing unit (43) includes a second operational amplifier, a fourth resistor, a fifth resistor, and a third capacitor; The non-inverting input of the second operational amplifier is grounded through the fourth resistor. The inverting input of the second operational amplifier is connected to the preset value input unit (41) and the first comparison unit (42) respectively. One end of the fifth resistor is connected to the inverting input of the second operational amplifier, and the other end is connected to the output of the second operational amplifier. The third capacitor is connected in parallel with the fifth resistor. The second operational amplifier is used to calculate the algebraic sum of the current difference reflected by the tube current error signal and the current preset value, and outputs a current reference signal reflecting the current correction value.

5. The X-ray tube filament heating current control circuit according to claim 4, characterized in that: A jumper device is also provided on the line connecting the inverting input terminal of the second operational amplifier to the first comparator unit (42); The first comparison unit (42) further includes a sixth resistor and a switching device; The sixth resistor is connected in series with the switching device, and the sixth resistor and the switching device are connected in parallel with the second resistor. The control terminal of the switching device is connected to the seventh resistor and the command input terminal respectively. The free end of the seventh resistor is grounded. The switching device is used to close when a control command is received.

6. The X-ray tube filament heating current control circuit according to claim 5, characterized in that: The second comparison unit (44) includes a third operational amplifier, an eighth resistor, a ninth resistor, a tenth resistor, a fourth capacitor, and a fifth capacitor; The non-inverting input of the third operational amplifier is grounded through the eighth resistor. The inverting input of the third operational amplifier is connected to the calculation unit (43) and the current acquisition module (3) respectively. One end of the ninth resistor is connected to the inverting input of the third operational amplifier, and the other end is connected to the output of the third operational amplifier. The tenth resistor and the fourth capacitor are connected in series. The tenth resistor and the fourth capacitor are connected in parallel to the ninth resistor. The fifth capacitor is connected in parallel to the ninth resistor. The third operational amplifier is used to calculate the error between the current value reflected by the current detection signal and the current correction value, and outputs the current error signal.

7. The X-ray tube filament heating current control circuit according to claim 6, characterized in that: The conversion module (2) includes a half-bridge conversion unit (21) and a resonant output unit (22); The half-bridge converter unit (21) includes a pulse transformer, a first NMOS transistor, a second NMOS transistor, a first voltage divider resistor, a second voltage divider resistor, a third voltage divider resistor, and a fourth voltage divider resistor; Both ends of the primary coil of the pulse transformer are connected to the output terminal of the PWM controller (5). The first coil on the side of the pulse transformer is connected in series with the first voltage divider resistor and the second voltage divider resistor to form a loop. The same-name terminal of the first coil is connected to the first voltage divider resistor. The gate of the first NMOS transistor is connected to the common terminal of the first voltage divider resistor and the second voltage divider resistor. The drain of the first NMOS transistor is connected to the positive terminal of the DC voltage. The source of the first NMOS transistor is connected to the common terminal of the second voltage divider resistor and the first coil. The second coil on the side of the pulse transformer is connected in series with the third voltage divider resistor and the fourth voltage divider resistor to form a loop. The same-name terminal of the second coil is connected to the fourth voltage divider resistor. The gate of the second NMOS transistor is connected to the common terminal of the third voltage divider resistor and the fourth voltage divider resistor. The drain of the second NMOS transistor is connected to the source of the first NMOS transistor. The source of the second NMOS transistor is connected to the common terminal of the fourth voltage divider resistor and the second coil. The source of the second NMOS transistor is also connected to the negative terminal of the DC voltage. The common terminal of the first NMOS transistor and the second NMOS transistor outputs AC current. The resonant output unit (22) is connected to the common terminal of the first NMOS transistor and the second NMOS transistor, and is used to shape the waveform of the alternating current into a sine wave.

8. The X-ray tube filament heating current control circuit according to claim 7, characterized in that: The current acquisition module (3) includes a current sampling unit (31), a rectification unit (32), a conversion unit (33), a voltage divider unit (34), a high-precision true RMS converter (35), and a first-stage amplification unit (36); The current sampling unit (31) is connected to the resonant output unit (22) and is used to collect the magnitude of the current flowing into the filament transformer and output the current sampling signal; The rectifier unit (32) is connected to the current sampling unit (31) and is used to rectify the received current sampling signal and output a DC pulsating current sampling signal. The conversion unit (33) is connected to the rectifier unit (32) and is used to convert the received DC pulsating current sampling signal into a first voltage sampling signal and output it. The voltage divider unit (34) is connected to the conversion unit (33) and is used to divide the voltage value reflected by the received first voltage sampling signal and output the second voltage sampling signal. The high-precision true RMS converter (35) is connected to the voltage divider unit (34) and is used to perform high-precision conversion on the second voltage sampling signal in the form of DC pulsation, so as to obtain and output the true RMS value of the second voltage sampling signal; The first-stage amplification unit (36) is connected to a high-precision true RMS converter (35), which amplifies the voltage value reflected by the true RMS value of the second voltage sampling signal according to a preset ratio when the true RMS value of the second voltage sampling signal is received, so as to obtain a voltage-form current detection signal and output it.

9. The X-ray tube filament heating current control circuit according to claim 8, characterized in that: It also includes a protection module (6), which comprises an overcurrent detection unit (61), a temperature detection unit (62), a trigger unit (63), and a first relay. The overcurrent detection unit (61) is connected to the current acquisition module (3) and is used to output an overcurrent detection signal when the current value reflected by the received current detection signal reaches the preset upper limit of current. The temperature detection unit (62) is used to detect the temperature of the X-ray tube assembly and to output a temperature detection signal when the temperature of the X-ray tube assembly reaches a preset temperature threshold. The triggering unit (63) is connected to the overcurrent detection unit (61) and the temperature detection unit (62) respectively, and is used to output a power failure trigger signal when receiving an overcurrent detection signal or a temperature detection signal; The power supply circuit where the coil (8) of the first relay is located is connected to the trigger unit (63). The normally open contact of the first relay is set on the line connecting the rectifier filter module (1) and the AC power supply. The power failure trigger signal is used to control the power supply circuit to disconnect.

10. The X-ray tube filament heating current control circuit according to claim 9, characterized in that: The trigger unit (63) includes a first NAND gate, a second NAND gate, a third NAND gate, a PNP transistor, a fifth voltage divider resistor, and a sixth voltage divider resistor; One input terminal of the first NAND gate is connected to the temperature detection unit (62) and the overcurrent detection unit (61) respectively. One input terminal of the second NAND gate is connected to the output terminal of the first NAND gate. The other input terminal of the second NAND gate is connected to a reset signal input terminal. The output terminal of the second NAND gate is connected to the other input terminal of the first NAND gate. One input terminal of the third NAND gate is connected to the output terminal of the second NAND gate. The other input terminal of the third NAND gate is connected to the reset signal input terminal. The base of the PNP transistor is connected to the output terminal of the third NAND gate. The emitter is connected to the power supply voltage of the first amplitude. The collector is connected to the fifth voltage divider resistor and the sixth voltage divider resistor in sequence. The free end of the sixth voltage divider resistor is grounded.

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