X-ray tube filament current control circuit with simple structure and stable performance

Abstract

The present invention relates to an X-ray tube filament current control circuit with a simple structure and stable performance, which includes a CPU control unit, a filament drive unit, and a high-voltage transformer assembly: The CPU control unit further includes an AC filament current DC voltage value sampling circuit and a filament current control circuit, the filament drive unit further includes a filament output inverter and a filament loop current sampling circuit, and the high-voltage transformer assembly further includes a small focus filament transformer and a large focus filament transformer. The AC filament current DC voltage value sampling circuit in the CPU control unit converts the sampled value of the AC filament current output by the filament drive unit into a DC voltage sampling value, and this voltage sampling value is compared with the filament current setting voltage value in the filament current control circuit of the CPU control unit to control the width of the filament trigger pulse output to the filament drive unit. It has a simplified circuit design, which reduces the cost and working stability of the X-ray tube filament closed-loop control loop.

Description

Technical Field

[0001] The present invention relates to the technical field of medical devices, and particularly to an X-ray tube filament current control circuit with a simple structure and stable performance. Background Art

[0002] With the continuous improvement of the living standards of the people in our country, the imaging quality requirements for X-ray diagnostic products in primary hospitals at the township level are constantly increasing, making it imperative to replace traditional power-frequency X-ray machines with high-frequency X-ray machines. However, most high-frequency X-ray machines at home and abroad currently use precision surface-mounted components. Due to the very close distance between the leads of precision surface-mounted components, the distance between the component pads and wires on the circuit board and between wires is very small, and the equipment is easily affected by the ambient temperature and humidity during operation. The equipment usage environment in primary hospitals at the township level is relatively poor, and it is very difficult to meet the requirements of national standards for the temperature and humidity of the usage environment. Using X-ray diagnostic products manufactured with relatively high-precision surface-mounted components in this environment is likely to cause damage.

[0003] For current foreign X-ray machines, the filament loop current sampling generally works by using a precision voltage RMS converter to sample the voltage value of the filament loop current. The set value of the filament loop current control is output by a 12-bit D / A converter. For the maximum output current control of the filament loop, a 12-bit A / D converter is used for analog value sampling, and software is used to control the maximum output current of the filament loop. Due to the application of these precision control components, the operating environment requirements for the product are relatively harsh. Generally, air conditioners and dehumidifiers are required to meet the usage environment requirements of the product, which is not very suitable for use in primary hospitals at the township level.

[0004] Currently, domestic X-ray machines generally adopt the method of imitating foreign products, and the control methods used are basically the same as those of the above-mentioned foreign X-ray machines, and the operating environment requirements for the products are also relatively harsh. It is very difficult for the usage environment in primary hospitals at the township level to meet the requirements of the equipment, and the equipment is prone to failures when used in primary hospitals at the township level, which is not conducive to the use of the product in primary hospitals at the township level. Therefore, we need an X-ray diagnostic product with a simple circuit structure, stable performance, reliable operation, easy maintenance, and low cost. Summary of the Invention

[0005] The purpose of the present invention is to provide an X-ray tube filament current control circuit with a simple structure and stable performance, aiming to solve the technical problems existing in the prior art that X-ray machines are greatly affected by the working environment, require relatively harsh operating environments for products, are prone to failures when used in primary hospitals at the township level, and are not conducive to the use of products in primary hospitals at the township level.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] An X-ray tube filament current control circuit with a simple structure and stable performance is adopted, which includes a CPU control unit, a filament drive unit, and a high-voltage transformer assembly: The CPU control unit further includes an AC filament current DC voltage value sampling circuit and a filament current control circuit, the filament drive unit further includes a filament output inverter and a filament loop current sampling circuit, and the high-voltage transformer assembly further includes a small focus filament transformer and a large focus filament transformer.

[0008] Its working process is as follows: The AC filament current DC voltage value sampling circuit in the CPU control unit converts the sampled value of the AC filament current output by the filament drive unit into a DC voltage sampled value. This voltage sampled value is compared with the filament current set voltage value in the filament current control circuit in the CPU control unit to control the width of the filament trigger pulse output to the filament drive unit. The trigger pulse input by the CPU control unit controls the output current of the filament output inverter in the filament drive unit. This current flows through the sampling coil of the filament current sampling mutual inductor and then outputs to the high-voltage transformer assembly. The sampled value of the AC filament current output by the secondary of the filament current sampling mutual inductor is output to the CPU control unit for closed-loop control of the filament loop current. The filament drive current output by the filament drive unit outputs to the primaries of the large focus filament transformer and the small focus filament transformer in the high-voltage transformer assembly. The secondary current isolated by the large focus filament transformer and the small focus filament transformer outputs to the large focus filament and the small focus filament of the X-ray tube to control the heating temperature of the filament. Under the high voltage between the cathode and the anode of the X-ray tube, the tube current output by the X-ray tube reaches the set value requirement of the filament current control circuit in the CPU control unit.

[0009] Preferably, the AC filament current DC voltage value sampling circuit in the CPU control unit is used to convert the sampled value of the AC filament current output by the filament drive unit into a DC voltage sampled value for the filament current control circuit to perform closed-loop control of the filament output current. At the same time, the fluoroscopy X-ray tube filament loop current sampling compensation circuit in the sampling circuit is used to improve the feedback value of the filament current during fluoroscopy work, so that the sampled value of the filament current during fluoroscopy is in the same feedback voltage range as that during radiography, in order to make full use of the 256 voltage output gradients of the 8-bit D / A converter and improve the accuracy of the filament control voltage set value output by the D / A conversion for controlling the filament loop current. The filament current control circuit in the CPU control unit is used to compare the DC voltage sampled value of the filament current with the set voltage value output by the 8-bit D / A converter to control the width of the filament trigger pulse, so that the filament current of the X-ray tube reaches the set value requirement.

[0010] Preferably, the filament output inverter in the filament drive unit outputs an AC pulse voltage, which is output to the high-voltage transformer assembly through the sampling coil of the AC current transformer. The secondary sampling output of the AC current transformer is used to collect the current values of the filaments of the large focus and small focus of the X-ray tube in real time, for the closed-loop filament current control of the CPU control unit. When operating at the small focus, the small focus sampling compensation coil 2T is connected to boost and compensate the current sampling value of the small focus filament, so that the current sampling value ranges of the large focus and small focus filaments are the same, in order to make full use of the 256 voltage output gradients of the 8-bit D / A converter of the filament current control set value and improve the control accuracy of the D / A conversion of the filament circuit current control.

[0011] Preferably, the large focus filament transformer and the small focus filament transformer in the high-voltage transformer assembly are used for the isolation between the high-voltage cathode filament circuit of the X-ray tube and the low-voltage X-ray tube filament current control circuit. At the same time, by controlling the turns ratios of the large focus and small focus filament transformers, the primary limit output pulse widths of the large focus filament transformer and the small focus filament transformer are made to be the same, so as to simplify the overheat protection circuits of the large focus and small focus filaments of the X-ray tube.

[0012] Preferably, the large focus and small focus filament input power limiting circuit of the X-ray tube controls the maximum current output to the primaries of the large focus filament transformer and the small focus transformer in the high-voltage transformer assembly by controlling the maximum filament trigger pulse width limiting circuit in the CPU control unit, the maximum output current control circuit in the filament drive unit, and the turns ratios of the large focus filament transformer and the small focus filament transformer in the high-voltage transformer assembly, so as to prevent the X-ray tube filament current from overheating caused by the failure of the pulse width limiting circuit or the too high output voltage of the filament inverter regulated power supply, and to ensure that the examined patient is not exposed to excessive X-ray radiation and the safety of the X-ray tube filament.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1. The present invention avoids using the existing precise voltage RMS converter to work with the voltage value sampling method of the filament circuit current. Instead, it adopts the X-ray tube filament current control circuit with the AC filament current DC voltage sampling and the filament circuit current sampling method of the present invention. This circuit simplifies the design and reduces the cost of the X-ray tube filament closed-loop control circuit without reducing the working performance.

[0015] 2. Instead of using the output of a precise 12-bit D / A converter and a precise 12-bit A / D converter to sample the analog value of the filament current for the set value of the filament circuit current control in the present invention, the set values of the filament current and the sampled values of the filament current under various working conditions are overall designed. Under the condition of ensuring the accuracy requirement of the filament current control, the set value of the filament current and the sampled value of the filament current are controlled within 256 gradient ranges, which is suitable for the set value of the output current control of a common 8-bit D / A converter with a larger pin pitch and a common 8-bit A / D converter to sample the analog value of the filament current, reducing the requirements for the use environment, that is, not requiring the configuration of air conditioners and dehumidifiers. The present invention reduces the use cost of the product and improves the working stability of the filament closed-loop control circuit of the X-ray tube.

[0016] 3. The maximum pulse limit circuit for filament triggering in the CPU control unit of the present invention and the maximum output current limit circuit of the filament inverter regulated power supply in the filament drive unit cooperate with the control of the turns ratio of the large-focus filament transformer and the small-focus filament transformer in the high-voltage transformer assembly to achieve precise limitation of the input limit power of the filaments of the large and small foci of the X-ray tube, protecting the filaments of the X-ray tube and enabling the product to meet the use requirements of primary hospitals with poor power supply, temperature and humidity conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the circuit block diagram of the present invention;

[0018] Figure 2 is the circuit diagram of the AC filament current DC voltage sampling circuit in the present invention;

[0019] Figure 3 is the circuit diagram of the filament circuit current sampling circuit in the present invention;

[0020] Figure 4 is the circuit diagram of the maximum output current limit circuit of the filament inverter regulated power supply in the present invention;

[0021] Figure 5 is the circuit diagram of the filament input power limit circuit of the X-ray tube in the present invention;

[0022] Markings in the figure:

[0023] M1, CPU control unit; M11, filament current control circuit; M111, filament trigger pulse width control circuit; M112, filament current setting circuit; M12, AC filament current DC voltage sampling circuit;

[0024] M2, filament drive unit; M21, filament output inverter; M211, filament inverter circuit; M212, filament inverter regulated power supply; M213, maximum output current limit circuit of the filament inverter regulated power supply; M22, filament circuit current sampling circuit;

[0025] M3, high-voltage transformer assembly; M31, small-focus filament transformer; M32, large-focus filament transformer;

[0026] M4, X-ray tube. Specific embodiments

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] In the description of the present invention, it should be noted that, unless otherwise clearly defined and limited, the terms "installation", "connection", and "connection" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the internal communication of two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0029] Refer to Figure 1 , an X-ray tube filament current control circuit with a simple structure and stable performance, including a CPU control unit M1, a filament drive unit M2, and a high-voltage transformer assembly M3;

[0030] The input end of the CPU control unit M1 is connected to the filament loop current sampling signal output ends FILASAMP1 and FILA SAMP2 of the filament drive unit M2. The input end of the filament drive unit M2 is connected to the filament trigger pulse signal output ends FILA DR1 and FILA DR2 of the CPU control unit M1. The input end of the high-voltage transformer assembly M3 is connected to the output ends FS-out, FL-out, and FC-out of the filament drive unit M2. The output end of the high-voltage transformer assembly M3 is connected to the filament input ends S, L, and C of the X-ray tube assembly.

[0031] The CPU control unit M1 consists of a filament current control M11 and an AC filament current DC voltage value sampling circuit M12. The filament current control M12 consists of a filament current setting circuit M112 and a filament trigger pulse width control circuit M111. The CPU control unit M1 is used to generate a pulse width modulation signal for driving the filament drive unit M2. The AC filament current DC voltage value sampling circuit M12 is used to convert the AC filament current sampling value output by the filament loop current sampling circuit M22 in the filament drive unit M2 into a DC voltage signal. The filament trigger pulse width control circuit in the filament current control circuit M11 is used to compare the sampling voltage output by the AC filament current DC voltage value sampling circuit with the voltage output by the filament current setting circuit, and to close-loop control the output pulse width of the filament trigger pulse width modulation signal, so as to control the current value of the X-ray tube filament.

[0032] The filament drive unit M2 consists of a filament output inverter M21 and a filament loop current sampling circuit M22. The filament output inverter M21 consists of a filament inverter regulated power supply maximum output current limiting circuit M213, a filament inverter regulated power supply M212, and a filament inverter circuit M211. The filament drive unit M2 is used to generate a pulse width modulated AC voltage for driving the high voltage transformer assembly M3. The filament regulated power supply in the filament output inverter M21 is used to generate a 40V stable DC voltage, and the filament inverter circuit is used to generate a 40V AC pulse width modulated voltage. The filament loop current sampling circuit M22 in the filament output inverter is used to collect the filament current output to the high voltage transformer assembly.

[0033] The high voltage transformer assembly M3 includes a small focus filament transformer M31 and a large focus filament transformer M32. Function 1: It is used to isolate the X-ray tube high voltage cathode filament circuit from the low voltage X-ray tube filament current control circuit. Function 2: It is used to match the working currents of the X-ray tube small focus filament and large focus filament.

[0034] The high voltage transformer assembly M3 outputs the current set by the CPU control unit to the X-ray tube M4, which meets the requirements of various X-ray diagnoses.

[0035] Refer to Figure 2 , the AC filament current DC voltage sampling circuit M12 in the CPU control unit M1; which consists of a full wave rectifier bridge V47, V48, V49 and V50 (1N4148), a sampling resistor R78 (3×10 3 Ω) and an operational amplifier N4A to form a filament AC sampling current to filament DC voltage sampling circuit. The fluoroscopy filament current sampling compensation circuit is composed of a MOS field effect transistor V51, resistors R107, R108 and an operational amplifier N4B.

[0036] Large focus current sampling signal source impedance:

[0037] Z1 / Z2 = (N1 / N2) 2

[0038] Z2 = (N2 / N1) 2 ×Z1

[0039] = (3000÷3) 2 ×10

[0040] = 1×10 7 Ω

[0041] Note: Z1 and Z2 are the primary and secondary impedances of the large focus transformer respectively, and N1 and N2 are the primary and secondary turns of the large focus transformer respectively. The primary impedance Z1 of the large focus transformer = 10Ω.

[0042] Small focus current sampling signal source impedance:

[0043] Z1 / Z2 = (N1 / N2) 2

[0044] Z2 = (N2 / N1) 2 ×Z1

[0045] = (3000÷5) 2 ×10

[0046] = 3.6×10 6 Ω

[0047] Note: Z1 and Z2 are the primary and secondary impedances of the small focus transformer respectively, and N1 and N2 are the primary and secondary turns of the small focus transformer respectively. The primary impedance Z1 of the small focus transformer = 10Ω.

[0048] According to the 1N4148 voltage-current working curve, it can be seen that when 1N4148 works at 0mA - 20mA, the VF working range is 0.6V - 0.8V. Based on this, the dynamic resistance value within this working range can be calculated.

[0049] r = ΔV / ΔI

[0050] = (0.8 - 0.6)÷(0.02 - 0)

[0051] = 10Ω

[0052] Where: r is the dynamic resistance of 1N4148, ΔV is the input voltage change range of 1N4148, and ΔI is the input current change range of 1N4148.

[0053] From the above calculated values, it can be seen that the internal resistance of the large focus current sampling signal source is 1×10 7Ω, the internal resistance of the small focus current sampling signal source is 3.6×10 6 Ω, which is much larger than the dynamic impedance of 10Ω of the switching diode 1N4148. The on-resistance of the switching diode 1N4148 does not affect the normal operation of the rectifier circuit.

[0054] AC average value sampling circuit current-voltage conversion rate:

[0055] Vout = I × R78

[0056] = 1×10 -3 ×3×10 3

[0057] = 3

[0058] It can be seen from the above calculation that the current-voltage conversion rate is 3V / 1mA.

[0059] It can be seen from the large focus filament curve of the E7833X type X-ray tube that the maximum driving power of the large focus fluoroscopy filament is at 40kV 75mA, that is, the driving voltage is 8.5V and the driving current is 4.3A.

[0060] Maximum driving power of the fluoroscopy large focus filament:

[0061] P FL = I FL × U FL

[0062] = 4.3×8.5

[0063] = 36.55W

[0064] Among them: I FL is the working current at 40kV 75mA, and U FL is the working voltage at 40kV 75mA.

[0065] In order to ensure that the sampling value ranges of the large focus fluoroscopy and photography are consistent, it is necessary to satisfy that the ratio of the maximum driving powers of the photography and fluoroscopy large focus filaments is consistent with the ratio of the gains of the fluoroscopy and photography. The ratio of the maximum driving powers of the photography and fluoroscopy large focus filaments (57.96÷36.55) is 1.59.

[0066] It can be seen from the small focus filament curve of the E7833X type X-ray tube that the maximum driving power of the small focus fluoroscopy filament is at 40kV 40mA, that is, the driving voltage is 6.0V and the driving current is 3.7A.

[0067] Maximum driving power of the fluoroscopy small focus filament:

[0068] P FS = I FS × U FS

[0069] = 3.7 × 6.0

[0070] = 22.2 W

[0071] Note: I FS is the working current at 40 kV 40 mA, and U FS is the working voltage at 40 kV 40 mA.

[0072] To ensure that the sampling value ranges of small focus fluoroscopy and photography are consistent, it is necessary to satisfy that the ratio of the maximum driving power of the small focus filaments for photography and fluoroscopy is consistent with the ratio of the gains for fluoroscopy and photography. The ratio of the maximum driving power of the large focus filaments for photography and fluoroscopy (36.18 ÷ 22.2) is 1.63.

[0073] Gain of the photography current sampling circuit:

[0074] 1 + R f ÷ R i

[0075] = 1 + R108 ÷ (R107 + R V51 )

[0076] = 1 + (3 × 10 3 ) ÷ (5.1 × 10 3 + ∞)

[0077] = 1.0

[0078] Where: When photographing, the V51 MOS field effect transistor is turned off, and RV51 is ∞.

[0079] Gain of the fluoroscopy current sampling circuit:

[0080] 1 + R f ÷ R i

[0081] = 1 + R108 ÷ (R107 + RV51)

[0082] = 1 + (3 × 10 3 ) ÷ (5.1 × 10 3 + 0)

[0083] = 1.59

[0084] Where: When fluoroscoping, the MOS field effect transistor V51 is turned on, and RV51 is 0.

[0085] The in - phase discharger circuit has a photography gain of 1 times and a fluoroscopy gain of 1.59 times. The ratio of the gains of the large - focus fluoroscopy and photography circuits is the same as the ratio of the powers of the large - focus photography and fluoroscopy, which is 1.59. The ratio of the gains of the small - focus fluoroscopy and photography circuits is basically the same as the ratio of the powers of the small - focus photography and fluoroscopy, which is 1.563, meeting the requirement that the feedback value ranges of photography and fluoroscopy are basically the same.

[0086] Reference Figure 3 , the filament drive unit M2 includes a filament output inverter M21 and a filament loop current sampling circuit M22. Among them, the filament loop current sampling circuit M22 is composed of a precision current transformer T1 (TVA1421 - 01), a large - focus sampling coil 3T, a small - focus additional sampling coil 2T, and a K1 large / small - focus switching relay. The secondary turns N2 of the current transformer: 3000 turns, supporting the X - ray tube E7833X. In order to make full use of all 256 gradients of the 8 - bit D / A converter, the filament current sampling value ranges in various working states should be consistent.

[0087] According to the large - focus filament curve graph of the E7833X type X - ray tube, it can be seen that the maximum drive power point of the large - focus filament is at 40 kV 250 mA, that is, the filament drive voltage is 12 V and the filament drive current is 4.83 A.

[0088] The maximum drive power of the large - focus filament for photography:

[0089] P RL =I×U

[0090] =4.83×12

[0091] =57.96 W

[0092] According to the small - focus filament curve graph of the E7833X type X - ray tube, it can be seen that the maximum drive power point of the small - focus filament is at 40 kV 100 mA, that is, the filament drive voltage is 9 V and the filament drive current is 4.02 A.

[0093] The maximum drive power of the small - focus filament for photography:

[0094] P RS =I×U

[0095] =4.02×9

[0096] =36.18 W

[0097] To ensure that the sampling value ranges of the large and small foci are consistent, it is necessary to meet the requirement that the ratio of the input currents is inversely proportional to the ratio of the sampling transformer turns. Since the output voltage of the filament drive circuit is constant, the ratio of the output currents is equal to the ratio of the output powers. Since the secondary of the sampling transformer is shared, the sampling ratio of the sampling transformer is the ratio of the primary turns. The primary turns of the large - focus sampling transformer are 3 turns:

[0098] P RL / P RS =N S / N L

[0099] N S =(P RL / P RS )N L

[0100] =(57.96÷36.18)×3

[0101] =4.81

[0102] Where: P RL 、P RS are the maximum driving powers of the large and small focus filaments, and N L 、N S are the turns of the current sampling coils of the large and small focus filaments.

[0103] The primary turns of the small focus sampling transformer should be 4.81 turns. Selecting the integer as 5 turns, so the small focus sampling compensation coil is 5 minus 3, which is 2 turns, meeting the requirements of theoretical calculation.

[0104] Referring to Figure 4 , the filament drive unit M2 includes a maximum output current limiting circuit M213 of the filament inverter regulated power supply. This maximum output current limiting circuit of the filament inverter regulated power supply is composed of components such as the output control triode V1, the current limiting thyristor V2, the current sampling resistor R7, the anti-interference threshold control diode D4, the alarm time control resistor R11 (100Ω), the capacitor C9 (47μF), and the current overlimit indicator LD1.

[0105] τ=R11×C9

[0106] =100×47×10 -6

[0107] =4.7×10 -3 s

[0108] When the maximum output current of the filament inverter power supply exceeds the limit value for 4.7ms, thyristor V2 is triggered, causing V2 to conduct and lock the conduction state. The current limit locking thyristor V2 is used to pull down the base potential of V1 when the maximum output current of the filament inverter power supply exceeds the limit value, shutting down the output of the filament inverter power supply and maintaining the shutdown state. The current overlimit indicator LD1 is used to indicate the current overlimit state, facilitating fault diagnosis. The output control transistor V1 is used to shut down the filament inverter power supply when the maximum output current exceeds the limit value. This ensures that the X-ray tube filament heating current is cut off when the pulse width limiting circuit fails or the output voltage of the filament inverter power supply is too high, thereby protecting the examinee from excessive X-ray radiation and damage to the X-ray tube filament.

[0109] Reference Figure 5 The filament trigger pulse width control circuit M111 in the CPU control unit M1, the filament inverter regulated power supply M212 in the filament drive unit M2, and the large-focus filament transformer and small-focus filament transformer in the high-voltage transformer assembly M3 form the filament input power limiting circuit of the X-ray tube. The filament input power limiting circuit of the X-ray tube limits the maximum operating current of the focus filament and small-focus filament of the X-ray tube M4; the current output pulse width modulator D16 on the filament trigger pulse width control circuit M111 and the peripheral resistors, capacitors, and potentiometers form an output pulse width limiting circuit, wherein the potentiometer RP6 controls the minimum trigger interval of the pulse width modulator. When the trigger period is constant, the maximum output pulse width is limited. Since the output voltage is constant, the maximum output power of the filament inverter circuit on the filament drive unit is limited. By controlling the ratio of the secondary output voltages of the large-focus and small-focus filament transformers in the high-voltage transformer assembly, the purpose of taking into account the protection of the large-focus and small-focus filaments of the X-ray tube is achieved.

[0110] It can be seen from the large-focus filament curve of the E7833X X-ray tube that the maximum filament operating point during large-focus photography is: 40kV, 250mA, the operating voltage is 12V, the operating current is 4.83A, and its driving power PFL = 57.96W.

[0111] Filament resistance at the maximum filament operating point during wide focus photography:

[0112] R RL =U RL ÷I RL

[0113] =12÷4.83

[0114] =2.48Ω

[0115] Filament pulse voltage at the maximum filament operating point during wide focus photography:

[0116] Output impedance of large focus filament transformer (internal resistance Ri of filament inverter circuit = 1.0 Ω)

[0117] Rio = (N2 ÷ N1) 2 × Ri

[0118] = (12 ÷ 24) 2 × 1

[0119] = 0.25 Ω

[0120] Where: N1 and N2 are the number of turns of the primary and secondary windings of the large focus filament transformer.

[0121] No-load output voltage of large focus filament transformer

[0122] Uo = N2 ÷ N1 × 40

[0123] = 12 ÷ 24 × 40

[0124] = 20 V

[0125] Large focus filament voltage:

[0126] U FL = Uo × R RL ÷ (R RL + R io )

[0127] = 20 × 2.48 ÷ (2.48 + 0.25)

[0128] = 18.17 V

[0129] Where: R io is the internal resistance of the large focus filament transformer, and R RL is the large focus filament resistance in this state.

[0130] Maximum filament operating point during large focus photography. Pulse width τ of large focus filament drive RL :

[0131] P O = U FL 2 ÷ R RL

[0132] = 18.17 2 ÷ 2.48

[0133] = 133.12 W

[0134] τ RL ÷ τ = P RL ÷ P O

[0135] τ RL = (P RL÷P O )×τ

[0136] =(57.96÷133.12)×50

[0137] =21.77 μS

[0138] Wherein: The operating frequency of the filament drive inverter circuit is 10 kHz, and the period of the positive pulse and the negative pulse: τ = 50 μS.

[0139] It can be seen from the above calculation results that when taking a large focal spot radiograph, the maximum filament operating point of the large focal spot has a filament drive pulse width of 21.77 μS. Considering reserving an adjustment margin of about 10%, adjusting the potentiometer RP6 can control the minimum trigger interval of the pulse width modulator, so that the maximum drive pulse width is limited to 24 μs. In this way, it can meet the working requirements of the large focal spot and ensure the safety of the large focal spot filament when the filament closed-loop control circuit fails.

[0140] The filament drive pulse width τ of the small focal spot at the maximum filament operating point when taking a small focal spot radiograph RS , is designed according to the filament drive pulse width of 21.77 μs of the large focal spot.

[0141] The filament resistance at the maximum filament operating point when taking a small focal spot radiograph:

[0142] R RS =U RS ÷I RS

[0143] =9÷4.02

[0144] =2.24 Ω

[0145] The filament pulse voltage at the maximum filament operating point when taking a small focal spot radiograph:

[0146] The output impedance of the small focal spot filament transformer (the internal resistance of the filament inverter circuit Ri = 1.0 Ω)

[0147] Rio=(N2÷N1) 2 ×Ri

[0148] =(9÷24) 2 ×1

[0149] =0.14 Ω

[0150] The no-load output voltage of the small focal spot filament transformer

[0151] Uo=N2÷N1×40

[0152] =9÷24×40

[0153] =15 V

[0154] Small focus filament voltage:

[0155] U FS = Uo × R RS ÷ (R RS + R io )

[0156] = 15 × 2.24 ÷ (2.24 + 0.14)

[0157] = 14.12V

[0158] Where: R io is the internal resistance of the small focus filament transformer, and R RS is the small focus filament resistance in this state.

[0159] The maximum filament operating point during small focus photography. The small focus filament drive pulse width τ RS :

[0160] τ RS ÷ τ = P RS ÷ P OS

[0161] τ RS = (P RS ÷ P OS ) × τ

[0162] = P RS ÷ (U FS 2 ÷ R RS ) × τ

[0163] = 36.18 ÷ (14.12 2 ÷ 2.24) × 50

[0164] = 20.32μS

[0165] Where: The operating frequency of the filament drive inverter circuit is 10kHz, and the period of the positive and negative pulses: τ = 50μS.

[0166] From the above calculations, it can be seen that when the secondary windings of the large and small focus filament transformers are designed with 12 and 9 turns respectively, the pulse width at the maximum filament output power point required for the small focus is 20.32μS, slightly less than the pulse width of 21.77μs at the maximum filament output power point of the large focus. With such a configuration of large and small focus transformers, it can not only meet the filament drive requirements of the large and small foci but also take into account the overload protection of the large and small focus filaments of the X-ray tube, thus achieving the protection of the X-ray tube M4.

[0167] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention, and all such changes, modifications, substitutions, and variations should be included within the protection scope of the present invention.

Claims

1. An X-ray tube filament current control circuit with a simple structure and stable performance mainly includes: A CPU control unit, a filament drive unit, and a high-voltage transformer assembly, characterized in that: The CPU control unit includes a filament current control circuit and an AC filament current DC voltage sampling circuit. The filament current control circuit further includes a filament current setting circuit and a filament trigger pulse width control circuit. The input end of the CPU control unit is connected to the filament loop current sampling signals FILA SAMP1 and FILA SAMP2 output by the filament drive unit. The output ends FILA DR1 and FILA DR2 of the CPU control unit are connected to the input end of the filament output inverter. The filament drive unit includes a filament output inverter and a filament loop current sampling circuit. The filament output inverter further includes a filament inverter regulated power supply maximum output current limiting circuit, a filament inverter regulated power supply, and a filament inverter circuit. The input end of the filament drive unit is connected to the pulse width modulation signals FILA DR1 and FILA DR2 output by the CPU control unit. One group of output ends FS-out, FL-out, and FC-out of the filament drive unit are connected to the input end of the high-voltage transformer assembly. The other group of output current sampling signals FILA SAMP1 and FILA SAMP2 of the filament drive unit are connected to the input end of the CPU control unit. The high-voltage transformer assembly includes a small focus filament transformer and a large focus filament transformer. The input end of the high-voltage transformer assembly is connected to the output ends FS-out, FL-out, and FC-out of the filament drive unit. The output ends TS-out, TL-out, and TC-out of the high-voltage transformer assembly are connected to the small focus filament and the large focus filament of the X-ray tube. The AC filament current DC voltage sampling circuit converts the filament loop current sampling signals FILA SAMP1 and FILA SAMP2 into a DC voltage sampling value FILA SAMP. The voltage FILA-SET output by the filament current setting circuit serves as the set input value of the filament trigger pulse width control circuit. The DC voltage sampling value FILA SAMP of the filament loop current serves as the feedback value of the filament trigger pulse width control circuit to perform closed-loop adjustment of the modulation signal pulse width of the filament trigger pulse width control circuit. This pulse width modulation signal serves as the input control signal of the filament drive unit to control the output current of the filament drive unit, so that the current value output by the X-ray tube filament current control circuit meets the requirements for the X-ray output of the X-ray tube. The AC filament current DC voltage sampling circuit includes a DC voltage sampling circuit and a fluoroscopy gain compensation control circuit. The DC voltage sampling circuit includes a full-wave rectifier bridge composed of diodes V47, V48, V49, and V50, an operational amplifier N4A, and a current / voltage conversion resistor R78. The fluoroscopy gain compensation control circuit includes an operational amplifier N4B, an insulated gate field effect transistor V51, and compensation control resistors R107 and R108. The diode full-wave rectifier bridge, operational amplifier N4A, and current / voltage conversion resistor R78 form a simple sampling circuit for converting the AC current sampling value into a DC voltage sampling value, which is used as the feedback value for closed-loop filament current control. The fluoroscopy gain compensation control circuit is used to keep the sampling ranges of the DC voltage values of the filament currents for X-ray radiography and fluoroscopy consistent, so as to make full use of the 256 output voltage gradients of the simple 8-bit D / A converter in the filament current control circuit, and ensure that the accuracy of the output currents for X-ray radiography and fluoroscopy meets the requirements of national standards.

2. The X-ray tube filament current control circuit with simple structure and stable performance according to claim 1, characterized in that: The filament output inverter inversely converts the 15V DC pulse width modulation signal input by the CPU control unit into a 40V AC pulse width modulation voltage, and this modulation voltage is output to the small-focus filament transformer and the large-focus filament transformer in the high-voltage transformer assembly. The filament loop current sampling current collected by the filament loop current sampling circuit is output to the CPU control unit for closed-loop control of the pulse width of the filament trigger pulse.

3. The X-ray tube filament current control circuit with simple structure and stable performance according to claim 1, characterized in that: The 40V AC pulse width modulation voltage output by the filament drive unit is output to the X-ray tube after being isolated from the low-voltage circuit and the cathode high-voltage circuit by the small-focus filament transformer and the large-focus filament transformer, to heat the small-focus filament and the large-focus filament of the X-ray tube.

4. The X-ray tube filament current control circuit with simple structure and stable performance according to claim 1, characterized in that: The filament loop current sampling circuit includes a precision AC current transformer T1, a large-focus filament current sampling coil 3T, a small-focus filament current sampling auxiliary coil 2T, and an X-ray tube large / small focus switching relay K1; The filament loop current sampling circuit with X-ray tube small-focus filament current sampling compensation makes the sampling value ranges of the filament currents of the large focus and the small focus of the X-ray tube consistent, so as to make full use of the 256 output voltage gradients of the 8-bit D / A converter in the filament current control circuits for the large focus and the small focus of the X-ray tube, and ensure that the accuracy of the output currents of the large focus and the small focus of the X-ray tube meets the requirements of national standards.

5. The X-ray tube filament current control circuit with simple structure and stable performance according to claim 1, characterized in that: The maximum output current limit circuit of the filament inverter regulated power supply includes an output control triode V1, a current limit locking thyristor V2, a current sampling resistor R7, a trigger threshold control diode D4, a trigger integration resistor R11, a trigger integration capacitor C9, and a current overlimit indicator light LD1; The current sampling circuit R7 and D4 are used to collect the output current of the filament inverter regulated power supply. R11 and C9 are used to control the overcurrent trigger delay integration of the thyristor V2. When the maximum output current of the filament inverter regulated power supply exceeds the set limit and the duration exceeds the delay integration time, the thyristor V2 is turned on and the on state is locked. The current limit locking thyristor V2 is used to pull down the base potential of the triode V1 when the maximum output current of the filament inverter regulated power supply exceeds the set limit, turn off the output of the triode V1 and lock the off state. The overcurrent indicator LD1 is used to indicate the overcurrent state for easy fault judgment. The output control triode V1 is used to turn off the output of the regulated power supply when the maximum output current of the filament inverter regulated power supply exceeds the set limit, ensuring that the pulse width limiting circuit fails or the output voltage of the filament inverter regulated power supply is too high, causing the output current to exceed the set limit, and turning off the X-ray tube filament heating circuit to prevent the examined patient from receiving excessive X-ray radiation and damage to the X-ray tube filament.

6. The simple-structured and stable-performance X-ray tube filament current control circuit according to claim 1, characterized in that: The filament input power limiting circuit of the X-ray tube is composed of a filament trigger pulse width control circuit, a filament drive unit, a high-voltage transformer assembly and an X-ray tube; The filament trigger pulse width control circuit includes a pulse width modulation controller D16 and a maximum pulse width limit adjustment potentiometer RP6, which are used to limit the maximum output pulse width of the filament drive when the filament drive closed-loop control circuit fails; The filament inverter regulated power supply and the filament inverter circuit of the filament drive unit are used to generate a pulse width modulation voltage of an alternating current constant pulse voltage to drive the small focus filament transformer and the large focus filament transformer in the high-voltage transformer assembly; The high-voltage transformer assembly includes a small focus filament transformer and a large focus filament transformer, which are used to control the filament input power of the large focus and small focus of the X-ray tube and isolate the high-voltage cathode filament circuit of the X-ray tube from the low-voltage filament inverter control circuit; By limiting the maximum output pulse width of the filament drive, the pulse width modulation voltage of the output alternating current constant pulse voltage, and controlling the turns ratio of the large focus filament transformer and the small focus filament transformer, the current output from the small focus filament transformer and the large focus filament transformer to the small focus filament and the large focus filament of the X-ray tube is limited to ensure that the filament of the X-ray tube does not overheat.

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