JP2738113B2 - X-ray equipment filament power supply - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a power supply for supplying a filament current to an X-ray tube of an X-ray imaging apparatus, and in particular, eliminates instability of the filament current due to voltage fluctuation of a DC source. Power supply device.

[Conventional technology]

FIG. 3 is a schematic configuration diagram showing the entire power supply device, and FIG. 4 is a connection diagram of main parts showing a conventional filament power supply. In the figure, a high-voltage power supply 11 is provided with a rectifier 12 that receives a supply of power from an AC power supply 19 and outputs a DC current, and a capacitor 13 that smoothes the output current and suppresses voltage fluctuations,
Inverter 14 that converts DC current to high-frequency current, step-up transformer 15 that boosts high-frequency voltage, and high-voltage rectifier that rectifies the output voltage and supplies it to X-ray tube as DC high-voltage tube voltage Vp of up to 100 KV to 150 KV 16 and a voltage dividing resistor 17 that is grounded at the middle point for detecting the tube voltage Vp, and receives a detection signal 17S of the tube voltage Vp.
By issuing the tube voltage control signal 14S for controlling the output current of the above, the tube voltage Vp is controlled to the command value.

On the other hand, the filament power supply 1 rectifies the AC current from the AC power supply 19 with the rectifier 2, smoothes and constant-voltages with the capacitor 3, and directs the DC current I 1 to the midpoint terminal 5 C of the primary winding 5 A of the insulating transformer 5. Supply. When the tube voltage Vp of the X-ray tube 10 is 100 to 150 KV, the filament is 50
The secondary winding 5B connected to the filament is insulated from the primary winding 5A so as to withstand a high voltage of 50 to 75 KV while maintaining a potential of 75 KV to 75 KV. The winding end of the primary winding 5A is connected to an inverter circuit 4 composed of a pair of semiconductor switches 4A and 4B.
The semiconductor switches 4A and 4B are alternately turned on and off at a predetermined timing by the inverter control unit 9 to convert the current I1 flowing through the primary winding 5A into a square wave pulse current. The pulse current I1 is detected by the shunt resistor 7 and the effective value detection unit 8 as an effective value signal of the pulse current I1 and supplied to the inverter control unit 9. The inverter control unit 9 controls the semiconductor switches 4A and 4A so that the difference between the filament current command signal 20C from the main control unit 20 and the effective value signal 8E approaches zero.
It outputs pulse width control signals 9A and 9B for controlling the conduction time width τ of B.

In the X-ray imaging using the conventional power supply device configured as described above, first, the tube voltage Vp and the tube current set in advance are set.
The filament current If determined by Ip is supplied from the filament power supply 1 to the filament of the X-ray tube, and the tube voltage Vp is applied from the high-voltage power supply 11 at the time when the filament current is preheated for about several seconds. X-rays are generated in proportion to the product.

FIG. 5 is a time chart showing the operation of the conventional filament power supply 1, and shows a semiconductor switch of the inverter circuit.
When the ON / OFF control of 4A and 4B is alternately performed with the conduction time width τ as shown in the figure, the primary winding current II having a substantially rectangular pulse shape flows through the primary winding of the insulating transformer 5. Since the pulse current flowing through the primary winding 5A alternately flows through half the windings symmetrical with respect to the midpoint terminal 5C, the filament current If electromagnetically induced in the secondary winding 5B alternately flows. Is supplied to the filament of the X-ray tube 10 as an alternating pulse current. Further, by controlling the conduction time width τ of the semiconductor switch with the effective value detection signal 8E, the effective value of the filament current If can be controlled to the current value indicated by the command signal 20C.

[Problems to be solved by the invention]

In the filament power supply, since the secondary winding 5B side of the insulating transformer 5 has a high potential, it is difficult to directly measure the filament current If. Therefore, the effective value of the pulse current If flowing through the primary winding 5A of the insulating transformer is calculated as follows. The effective value of the filament current If is measured by multiplying the measured value by the transformation ratio of the insulating transformer 5. Further, since the effective value of the filament current If is controlled by controlling the pulse width of the primary winding current I1, when the high voltage power supply 11 connected to the same AC power supply 19 is driven, the AC input voltage decreases. The DC voltage Vc of the filament power supply decreases. When a common storage battery is used instead of the rectifier, the DC voltage Vc is further reduced because the internal resistance of the storage battery is large. The inverter control unit 9 of the filament power supply that detects this voltage drop as a decrease in the effective value of the current I1 performs control to increase the pulse width of the current I1 and keep the effective value of I1 constant.

However, the insulating transformer 5 has an LC filter action on the square wave pulse determined by the leakage inductance and the stray capacitance, and this causes the rising and falling waveforms of the square wave pulse currents I1 and If to be distorted. However, there is a problem that the degree of influence of the distortion of the waveform on the effective value of each of the currents I1 and If varies depending on the change of the pulse width τ, and the linear relationship between the effective values of I1 and If is lost. Accordingly, there arises a problem that an error between the filament current If and its command value increases.

By the way, an example of the tube voltage-tube current characteristics of the X-ray tube is shown in FIG.
For example, if the tube voltage Vp is 50 KV, the filament current If
Has a characteristic that when the current changes by 10%, the tube current Ip changes by 100% or more. Therefore, for example, the pulse width τ of the current I1 becomes
Assuming that the control for expanding the 15% to 20% is performed and the effective value of the current I1 is kept constant, a control error of about 4% occurs in the effective value of the filament current If. Is reduced by as much as 20 to 40%, which has a serious adverse effect on radiography.

In addition, the primary winding current I1 includes the exciting current of the insulating transformer 5 which is not included in the filament current If on the secondary winding side. When the pulse width τ changes, the exciting current occupies the effective value of the current I1. , The control error of the filament current further increases.

An object of the present invention is to provide a filament power supply that can supply a stable filament current with little fluctuation even when the input voltage of the filament power supply fluctuates.

[Means for solving the problem]

In order to solve the above-mentioned problems, according to the present invention, a filament current controlled to a predetermined value based on a command signal from a high-voltage power supply for supplying a tube voltage and a tube current to an X-ray tube is supplied via an insulating transformer. A step-down chopper circuit that is provided between a DC power supply unit and a midpoint terminal of the insulating transformer primary winding and that performs a high-speed switching operation; A 180 ° conduction-type inverter circuit comprising a pair of semiconductor switches which are alternately connected to the DC power supply unit and perform low-speed switching operation, an average value detection unit for a current flowing through the primary winding, and an average value detection unit And a chopper control unit that controls the pulse width of the step-down chopper circuit so as to eliminate the difference between the detection signal of the unit and the command signal.

[Action]

According to the configuration of the present invention, the primary winding current of the insulating transformer
The inverter that turns on and off I1 alternately consists of a pair of semiconductor switches that conduct 180 °, and the current detector detects the average value of the primary winding current, and consists of either a rectifier or a storage battery. A step-down chopper circuit is provided between the DC power supply unit and the center terminal of the primary winding, which switches the output current of the DC power supply at high speed in a cycle much shorter than that of the inverter, and then returns to the DC current. By configuring the chopper current to be pulse width controlled so that the average value of I1 matches the command signal, the charging current contained in the primary winding current I1 is first eliminated by detecting the average value, and the filament current control error One cause of can be eliminated. In addition, the change in the input voltage is detected as a change in the instantaneous value of the average current, and the pulse voltage of the chopper current is immediately compensated, so that the DC voltage Vc of the DC intermediate circuit is maintained at a constant value, and the rise of the inverter current is increased. In addition, since the distortion of the falling waveform is also corrected in the same manner, the linearity between the primary current and the secondary current of the insulating transformer is greatly improved. A small filament current If can be stably supplied to the filament of the X-ray tube.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

FIG. 1 is a connection diagram of a main part showing a filament power supply of an X-ray imaging apparatus according to an embodiment of the present invention, and FIG. 2 is a waveform diagram showing an operation of the embodiment. The same reference numerals are given and detailed description is omitted. In FIG. 1, a semiconductor switch 22, a choke coil 23A, and a diode are provided on the DC output side of a DC power supply unit 30 (which may be replaced by a storage battery) composed of a rectifier 2 and a capacitor 3 for a smoothing and constant voltage source. A step-down chopper circuit 21 comprising a capacitor 23C and a capacitor 23C is provided, and the output current
I ₃ is a midpoint terminal 5C provided on the primary winding 5A of the insulating transformer 5
Supplied to An inverter circuit 24 including a pair of semiconductor switches 24A and 24B is connected to both winding terminals of the primary winding 5A. The inverter circuit 24 operates so that the inverter circuit 24 operates as a 180-degree conducting square wave inverter. Are turned on / off by the on / off control signals 29A and 29B generated by the controller. Primary winding current I ₃ is the average value is detected by a detector consisting of shunt resistor 7 and the average value detecting unit 28.. For example, when the average value detection unit 28 is a circuit including a T-type RC filter, it is possible to detect an average current in which the exciting current of the insulating transformer 5 is canceled. Average value detection signal 28E
Is supplied to the chopper control unit 31 together with the filament current command new issue 20C from the main control unit 20, and the chopper control unit 31 issues a pulse width control signal 31C issued to the semiconductor switch 22.
The pulse width of the chopper current is thereby controlled.

Next, the operation of the filament power supply will be described with reference to the waveform diagram of FIG. First, the on / off control of the semiconductor switch 22 of the chopper circuit 21 is generally changed by controlling the pulse width τ ₀ at a high frequency of 50 KHz to 100 KHz by a pulse width control signal 31 C generated by the chopper control unit 31. Suppresses the voltage fluctuation of the DC power supply unit 30 which is slow. As a result, the DC voltage Vc of the DC intermediate circuit on the primary winding side of the tuke coil 23A can be kept at a constant value, and therefore, the influence of the fluctuation of the power supply voltage, which has been a problem in the prior art, can be eliminated. Further, the primary winding current I ₃ flowing into the primary winding 5A from the midpoint terminal 5C is applied to a pair of semiconductor switches 24 operating as a 180 ° conducting rectangular wave inverter.
A and 24B make each conduction time width τ half of the period T,
That is 180 DEG one alternately on-off control, thus current I ₃ is a DC current including a serrated excitation current I ₃ b. Further, since the inverter current flowing through the pair of semiconductor switches 24A and 24B alternately flows through the half of the primary winding 5B in different directions, the filament current If flowing through the secondary winding 5B
Is a normal wave alternating current and supplied to the filament of the X-ray tube 10. Further, the exciting current component I ₃ b in the primary winding current I ₃
Is the average value I ₃ m by the shunt resistance 7 and the average value detection unit 28.
Is canceled by detecting the average current detection signal
28E is a DC current equivalent to the effective value of the filament current If. Accordingly, by controlling the conduction time width τ ₀ of the semiconductor switch 22 so that the chopper control unit 31 maintains the average current I ₃ m of the primary winding current at the command value of the command signal 20C, the filament current If becomes the command value. It is possible to maintain the filament current by eliminating the factor that impairs the linearity between the primary and secondary windings of the insulating transformer, which is a problem in the prior art.
If can be controlled as instructed. Therefore, a large change in the tube current caused by a slight change in the filament current If is suppressed, and the X-ray dose determined by the time product of the tube current can be controlled faithfully to the command value.

In addition, in the case of the configuration described above, the fluctuation of the exciting current I ₃ b due to the manufacturing error of the insulating transformer can be automatically canceled by the average value detection unit, and the calculation accuracy of the effective value in the effective value detection unit can be reduced. Since the average value detection unit can be configured using an inexpensive T-type RC filter without using a dedicated IC required for improvement, the advantage that the manufacturing cost can be reduced to about 1/100 of that of the related art is obtained. Further, in the embodiment, the example in which the inverter circuit is constituted by the voltage type inverter is shown, but the same function as described above can be obtained by using the current type inverter.

〔The invention's effect〕

As described above, according to the present invention, the output side of the DC power supply unit is connected to the midpoint terminal of the primary winding of the insulating transformer via a step-down chopper circuit that performs high-speed switching operation, and both terminals of the primary winding are connected.
A closed circuit for returning to the DC power supply section through a 180 ° conduction type inverter is formed, and the pulse width of the chopper is controlled based on the difference between the primary winding current flowing through the closed circuit and the average value signal. As a result, voltage fluctuations in the DC power supply can be compensated for without delay by controlling the pulse width of the chopper that performs high-speed switching, and the DC voltage applied to the primary winding can be controlled at a constant voltage. The filament current changes due to the voltage fluctuation of the DC power supply unit, which is a problem in the device described above, and the phenomenon that the tube current of the X-ray tube further largely changes due to this can be almost completely prevented. Also, by alternately switching the direction of the current flowing through the primary winding with a 180 ° conduction type inverter, the filament current flowing through the secondary winding becomes a square wave alternating current with a fixed period, and the pulse width of the conventional filament current changes. In addition to eliminating the control error of the filament current caused by the above, the exciting current of the insulating transformer base can be automatically canceled by detecting the average value of the primary winding current. By controlling the conduction time width of the transformer, the factor of nonlinearity between the primary and secondary of the insulating transformer is almost completely eliminated, and the command value indicates the effective value of the filament current without being affected by the fluctuation of the input voltage. To provide an X-ray imaging apparatus equipped with a filament power supply capable of faithfully controlling the current value to be controlled and having high X-ray dose control accuracy, economically and advantageously. Can.

[Brief description of the drawings]

1 is a connection diagram showing a filament power supply according to an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of the embodiment, and FIG. 3 is a configuration showing a conventional filament power supply including a high-voltage power supply. FIG. 4, FIG. 4 is a connection diagram showing a conventional filament power supply, FIG. 5 is a waveform diagram showing the operation of the conventional filament power supply, and FIG. 6 is a characteristic line showing an example of tube voltage-tube current characteristics of an X-ray tube. FIG. 1: Filament power supply, 2: Rectifier, 3, 13, 23C: Capacitor, 4, 24: Inverter circuit, 5: Insulation transformer, 5A: Primary winding, 5B: Secondary winding, 5C: Midpoint terminal, 7 : Shunt resistance, 8: Effective value detector, 9, 29: Inverter controller, 10: X-ray tube, 11: High voltage power, 19: AC power, 20: Main controller, 21: Step-down chopper circuit, 22, 24A , 24B: semiconductor switch, 23A: choke coil, 28: mean value detecting portion, 31: chopper control unit, I1, I _3: primary winding current, the If: filament current (secondary winding current), Vc:
DC (intermediate circuit) voltage, 20C: command signal, 28E: average value detection signal, 30: DC power supply.

Claims (1)

(57) [Claims] 1. A filament current controlled to a predetermined value based on a command signal from a high voltage power supply for supplying a tube voltage and a tube current to an X-ray tube is supplied to a filament of the X-ray tube via an insulating transformer. A step-down chopper circuit that is provided between a DC power supply unit and a midpoint terminal of the insulating transformer primary winding and that performs high-speed switching operation, and that is connected between both terminals of the primary winding and the DC power supply unit. 18 consisting of a pair of semiconductor switches that alternately perform a low-speed switching operation
0 ゜ a conduction type inverter circuit, an average value detection unit for the current flowing through the primary winding, and pulse width control of the step-down chopper circuit so as to eliminate the difference between the detection signal of the average value detection unit and the command signal. A filament power supply for an X-ray imaging apparatus, comprising: