JPH0159718B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply device for an X-ray imaging apparatus, and more particularly to a current supply circuit for an X-ray tube filament having a control circuit function suitable for heating the filament of an X-ray tube. It is.

As a method of heating the filament of an X-ray tube,
There are AC heating methods and DC heating methods. In the AC heating method, fluctuations due to changes in the temperature of the filament have a large effect on the tube current of the X-ray tube.In particular, since fluctuations (pulsations) in the tube current are synchronized with the power frequency, this affects the tube voltage waveform and reduces the output dose. Similarly, it causes fluctuations in the film, and has an adverse effect on the degree of blackening of the film.

On the other hand, the direct current heating method is a good heating method because it can eliminate tube current fluctuations by rectifying the output of the heating transformer to make it direct current. However, this direct current heating method requires a rectifier circuit and a smoothing circuit on the secondary side of the heating transformer, resulting in large size and high cost.

Therefore, the present applicant has developed an alternating current heating method that uses the thermal inertia of the filament to achieve the same effect as the direct current heating method by increasing the frequency to a high frequency, and that is also compact and inexpensive. this is,
By feeding back the signal corresponding to the filament current that heats the filament of the X-ray tube and comparing it with the set voltage, losses in the voltage control transistor are reduced, and the rectifier circuit and smoothing circuit on the secondary side of the heating transformer are eliminated. It is a smaller version.

FIG. 1 is an X-ray filament current supply circuit diagram using the AC heating method previously developed by the present applicant. The circuit rectifies and smoothes an AC power supply 1 using a rectifier circuit 2 and a capacitor 3, and converts it into a DC voltage. is converted to By controlling the on/off state of the voltage control transistor 4, the capacitor 3 is connected to the smoothing circuit composed of the reactor 6 and the capacitor 7.
voltage. The diode 5 is a flywheel diode in a switching circuit composed of a smoothing circuit including a transistor 4, a capacitor 7, and a resistor 8. Reference numeral 6 indicates a reactor, and the voltage of a capacitor 7 connected in parallel with the diode 5 through the reactor 6 is converted from DC voltage to a high frequency AC voltage by a switching circuit composed of transistors 9a and 9b. It is input to the primary side of. The output voltage of the heating transformer 11 is made high frequency and heats the filament of the X-ray tube 12. In addition, since the tube current depends on the filament current, the set voltage of the voltage comparator 20 obtained from the filament current-filament voltage characteristic
Vpat ₁ and the voltage of smoothing capacitor 7 are divided by voltage dividing resistor 8
Comparison circuit 1 compares the voltage V _C2 with more feedback.
4, and the output of the drive circuit 13
By operating the transistor 4 and controlling the switching of the transistor 4, the voltage of the capacitor 7 is controlled to be constant, that is, the input voltage of the heating transformer 11 is controlled to be constant.

Note that 10a and 10b are transistors 9a and 9
15 is a space charge compensation circuit, and 16 is a tube current setting circuit, which is arbitrarily set according to the filament characteristics of the X-ray tube used.
Further, 17 is an abnormality detection circuit, 19 is a DC high voltage power supply, and 20 is an adder that adds the outputs of the space charge compensation circuit 15 and the tube current setting circuit 16 to provide the set voltage Vpat ₁ to the comparison circuit 14. According to the filament current supply circuit described above, since the tube current depends on the filament voltage, the set voltage V _pat1 that sets the input voltage of the heating transformer 11 is compared with the voltage V _C2 of the smoothing capacitor 7 divided by the voltage dividing resistor 8. By feeding back the amount of deviation to the drive circuit 13 and controlling the switching of the transistor 4, the control voltage which is the input to the heating transformer 11 is kept constant at a voltage corresponding to the set voltage _Vpat1 . Note that the DC high-voltage power supply 19 is shown as a DC power supply to simplify the explanation, but in reality, the AC power is obtained through a high-voltage transformer and a rectifier circuit, and the DC high-voltage power supply 19 is High voltage transformer 2
This means the output power source of the rectifier circuit provided on the next side.

The initial problem of pulsating tube current in the AC heating system configured as shown in FIG. 1 can be solved, and the control voltage that is input to the heating transformer 11 can be kept constant, but Due to the temperature characteristics of the X-ray tube during irradiation, the characteristics shown in FIG. 3a decrease over time as the X-ray irradiation time increases, as shown in FIG. 3b.

SUMMARY OF THE INVENTION An object of the present invention is to provide a filament current supply circuit that eliminates the above-mentioned problems and can make the tube current more constant.

In order to control the X-ray tube current to be constant, the present invention detects the tube current of the X-ray tube, compares the tube current with a set tube current, and feeds back the amount of error. The input voltage of the heating transformer is controlled. The present invention will be described in detail below with reference to FIGS. 2 to 5.

FIG. 2 is a circuit diagram showing a specific example,
Components denoted by the same reference numerals as in FIG. 1 indicate the same components. In Fig. 2, 101 is a high voltage power supply 19
This is a tube current detection circuit connected in series to the 102
103 is a tube current-to-voltage conversion circuit that converts the detection tube current into a feedback voltage Vp, and 103 is a reference voltage V _S corresponding to the feedback voltage Vp and a tube current that is arbitrarily set according to the installed X-ray tube.
SW ₁ is a changeover switch that works with an X-ray exposure start switch (not shown), and is normally connected to the contact B side. Sometimes it is switched to the contact A side. Reference numeral 104 denotes an adder for the reference voltage V _S itself, which outputs a reference signal to the adder 21 as there is no error amount in the reference voltage V _S system when the switch SW ₁ is switched to the B contact side. This adder 21 connects the output of adder 20 and adder 103 or 104.
This is to compare and add the output of . 105 is
For example, in a voltage control circuit configured as shown in FIG. 5, the voltage from the adder 21 is
Its main function is to control the operating frequency and pulse width (conduction width) for on/off switching control of the transistor 4 according to the deviation amount δ between V _pat2 and the detected voltage V _C2 .

Now, when X-ray exposure is started by a switch (not shown), a tube current detection circuit 101 detects the tube current, and a tube current-voltage conversion circuit 102 converts the detected tube current into a feedback voltage Vp. At the start of X-ray exposure, the switch SW ₁ is switched to the contact A side, and by switching the switch, the feedback voltage Vp is compared with the reference voltage V _S set corresponding to the tube current of the X-ray tube 12 used. are added, and the error amount ΔV is output. This error amount ΔV
In the adder 21, the space charge compensation circuit 15
and the set voltage output from the voltage setting circuit composed of the tube current setting circuit 16 and the adder 20.
It is compared and added to V _Pat1 to obtain a new set voltage V _pat2 . This set voltage V _pat2 changes, for example, as shown in FIG. 3c, if the tube current decreases with the X-ray exposure, as shown in FIG. 3b. This set voltage V _pat2 is compared with the detected voltage V _c2 of the input voltage of the heating transformer 11 in the voltage control circuit 105, and is made into a pulse control signal according to the deviation amount δ.

Voltage control circuit 105 that obtains this pulse control signal
As shown in FIG. 5, the circuit is comprised of a voltage-frequency conversion circuit 201, a voltage-pulse width conversion circuit 202, a transistor control circuit 203, and an adder 204. Of these, the adder 204 obtains the deviation amount δ by comparing and adding the detected voltage V _C2 and the voltage V _pat2 . Conversion circuit 20
1,202, depending on this deviation amount δ, Fig. 4a,
As shown in b, the transistor control circuit 2 outputs a voltage control signal for changing the operating frequency and pulse width of the transistor 4 and controlling the output voltage to a constant level.
03 to the drive circuit 13.

That is, the voltage control circuit 1 having the configuration as shown in FIG.
05, the operating frequency and pulse width of the transistor 4 are changed as shown in Fig. 4a and b, and the voltage of the capacitor 7 is controlled so that the tube current is constant at the set value as shown in Fig. 3d. Then, X
Due to the temperature characteristics of the ray tube 12, etc., the problem that the X-ray tube current decreases over time with the X-ray exposure time is eliminated.

As is clear from the above embodiments, according to the present invention, the tube current of a high voltage transformer is detected during X-ray exposure, the detected signal is compared with a reference signal, and the error amount ΔV is also fed back. Since the filament heating voltage is controlled by
Current fluctuations in which the tube current decreases with the start of radiation exposure can be corrected, and highly accurate tube current settings can be made. Moreover _, in this case, in the present invention, the adder V pat2, which combines the error amount ΔV between the tube current and the reference tube current and the set voltage V _pat1 for setting the tube current, is used as the detection voltage V _C2 on the input side of the heating transformer. Compare and add deviation amount δ
The capacitor output voltage is controlled to be constant by changing the operating frequency and pulse width of the voltage control transistor accordingly.

Here, if the voltage of the capacitor 3 is E _C1 , the voltage of the capacitor 7 (heating transformer input side voltage) is E _C2 , the operating frequency of the voltage control transistor 4 is f ₁ , and the pulse width is D, then E _C2 is E _C2 ] D・f ₁・E Represented by _C1 .

Therefore, when the voltage on the input side of the heating transformer is made constant only by the pulse width D (for example,
55-50597, etc.), the control width for the deviation amount δ can be increased, and the control response can be made faster.

[Brief explanation of drawings]

FIG. 1 shows an X-ray tube filament current supply circuit developed earlier by the applicant, FIG. 2 shows an X-ray tube filament current supply circuit showing an embodiment of the present invention, and FIG.
4A and 4B are diagrams for explaining the circuit operation of FIG. 2, and FIG. 5 is a diagram specifically showing a part of the circuit of FIG. 2. 1... AC power supply, 2... Rectifier circuit, 3, 7... Capacitor, 4, 9a, 9b... Transistor, 5, 10
a, 10b...diode, 6...reactor, 8...
Resistor, 11...Heating transformer, 12...X-ray tube, 13,
18... Drive circuit, 15... Space charge compensation circuit,
16...Tube current setting circuit, 17...Abnormality detection circuit, 1
9...High voltage power supply, 20, 21, 103, 104,
204... Adder, 105... Voltage control circuit, SW ₁ ...
Changeover switch, 201...voltage-frequency conversion circuit,
202... Voltage-pulse width conversion circuit, 203... Transistor control circuit.

Claims (1)

[Claims] 1 DC voltage is input and the first switching element 4
and a voltage main control circuit that variably sets the output voltage using a smoothing circuit, and second switching elements 9a and 9b.
A DC/AC conversion circuit that converts the output voltage of the voltage main control circuit from direct current to alternating current by on/off control, and a heating transformer 11 to which the output voltage of the DC/AC conversion circuit is applied. The X-ray tube filament current supply circuit includes a tube current setting means for outputting a tube current setting symbol (V _pat1 ) of the X-ray tube 12, and a tube current detection circuit 10 for detecting the tube current.
1 and the tube current detection signal from this tube current detection circuit
A first adder 103 that obtains an error signal ΔV between Vp and the reference tube current signal Vs, a second adder 21 that adds the error signal from this first adder and the tube current setting signal, and the voltage The frequency is determined according to the deviation signal δ between the output voltage detection signal 8 that detects the output voltage of the main control circuit, the output voltage detection signal V _C2 from this output voltage detection means, and the output signal V _pat2 from the second adder. An X-ray tube filament current supply comprising: a voltage control circuit 105 that performs conversion and pulse width conversion to generate a pulse control signal, and controls the first switching element on and off using the pulse control signal. circuit.