JPH0210560B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an X-ray generation circuit having an overcurrent protection circuit and a tube current measurement circuit.

(Prior technology) The X-ray generation method for X-ray CT generally uses continuous X-rays.
There are a line generation method and a pulsed X-ray generation method, which are selectively used depending on the scanning method of the object.

FIG. 1 shows a schematic configuration of a conventional continuous X-ray generating circuit. In this figure, 1 is an X-ray tube that generates X-rays. 2 is an AC stabilized power supply, and 3 is a cutoff circuit. 4 is a tube voltage boosting circuit for boosting the tube voltage supplied to the X-ray tube 1, and includes a tube voltage setting function. 5 is a full-wave rectifier circuit that converts the voltage supplied to the X-ray tube 1 into direct current. A tube current correction circuit 6 controls the filament heating current of the X-ray tube 1. 7 is a smoothing circuit that serves to reduce the pulsation of the high DC voltage supplied to the X-ray tube 1; 8
is a resistor connected in parallel with the X-ray tube. Reference numeral 9 denotes an overvoltage protection circuit that receives the divided voltage from the resistor 8, monitors the voltage supplied to the X-ray tube 1, and generates a signal to turn off the cutoff circuit in the case of overvoltage.
Reference numeral 10 denotes an overcurrent protection circuit that monitors the tube current flowing through the X-ray tube 1 and generates a signal to turn off a cutoff circuit in case of overcurrent.

With this configuration, stable high DC voltage and filament heating power are continuously supplied to the X-ray tube 1 to obtain continuous X-rays.

On the other hand, in the conventional pulsed X-ray generation method,
A switching circuit is provided in the DC high voltage section to supply intermittent voltage to the X-ray tube to obtain pulsed X-rays.

(Problems to be Solved by the Invention) However, the conventional X-ray generation circuits in the continuous X-ray generation system and the pulsed X-ray generation system have the following drawbacks.

First, in the continuous X-ray generation system, when the power is turned on, a charging current flows through the capacitor of the smoothing circuit, and is superimposed on the current that the overcurrent protection circuit monitors as the tube current of the X-ray tube. Therefore, unless measures are taken such as increasing the setting of the overcurrent protection circuit or temporarily stopping the function of the overcurrent protection circuit when the power is turned on, the overcurrent protection circuit will malfunction. On the other hand, in the pulsed X-ray generation method, since the sum of the tube current and the charging/discharging current of the smoothing circuit is observed, the waveform cannot be observed accurately.

The present invention has been made in view of the above points, and its purpose is to eliminate the influence of the charging and discharging current of the capacitor by utilizing the symmetry of the X-ray generating circuit and the load, thereby improving the overcurrent protection circuit. An object of the present invention is to provide an X-ray generation circuit that enables high sensitivity and duplication of protection circuits.

(Means for Solving the Problems) The present invention achieves the above object by rectifying the high voltage obtained by a step-up transformer with a full-wave rectifier circuit, smoothing it with a smoothing capacitor, and converting it into a DC high voltage. In an X-ray generation circuit configured to generate X-rays by applying the X-rays to the X-ray tube, an X-ray generator is inserted in series to the primary side of the step-up transformer 124 to turn the primary side current ON/OFF. first and second switches 122, 122', and anti-parallel connected first and second semiconductor switches 1 inserted into the primary side of the step-up transformer 124 and connected in series with the switches 122, 122'.
23, 123', and the first and second resistors 1 with the same resistance value connected in series and whose connection point is connected to the common line.
5, 15', and the first and second resistors 1 connected to the secondary low voltage side of the step-up transformer 124 and serving as a load.
A series circuit of 5 and 15' connects the first resistor 15.
A diode bridge 13 is connected to the positive side of the diode bridge 13, and a first smoothing capacitor 14 whose one end is connected to the positive side output of the full-wave rectifier circuit 125 is connected between the common line. A third resistor 16 having the same resistance value as the first resistor 15 is connected between the second smoothing capacitor 14', one end of which is connected to the negative output of the full-wave rectifier circuit 125, and the common line. , a fourth resistor 16' having the same resistance value as the first resistor 15, and the first resistor 15 and the third resistor 16.
A first differential amplifier 17 which takes the difference between the voltages generated between the
and the second resistor 15' and the fourth resistor 1
A second differential amplifier 17' which takes the difference in the voltage generated between Then, the first switch opens at least the first switch 122 and the second switch 122', respectively.
The output voltages of the second overcurrent protection relays 18, 18' and the first and second differential amplifiers 17, 17' are monitored, and when these exceed thresholds, the output voltages of the first and second semiconductors are switch 123, 12
3'.

(Example) Hereinafter, an example of the present invention will be described in detail using the drawings.

FIG. 2 is a schematic configuration diagram showing an embodiment of the X-ray generating circuit of the present invention. In this figure, 11 is
An X-ray tube that generates radiation, 12 is a high-voltage transformer section,
An alternating current voltage source 121 is boosted by a step-up transformer 124, and then converted to direct current by a full-wave rectifier circuit 125 and output. Note that the primary line of the step-up transformer 124 includes switches 122, 122' and semiconductor switches 123, 1, which are normally closed.
23' is inserted, and the primary side input current is
It can be turned on/off. These switches 122, 122' are connected in series, and are turned ON/OFF by protective relays 18, 18', which will be described later.
The semiconductor switches 123 and 123' are connected in antiparallel, and are turned on and off by gate control. The gate control is performed by protection relays 18 and 18' or as will be described later. This is performed by any of the overcurrent protection circuits 20. 13 is a step-up transformer 124
A diode bridge that performs full-wave rectification is connected to the secondary low-voltage side of the converter, and consists of four bridge-connected diodes. 14, 14' are full wave rectifier circuit 1
This is a smoothing capacitor that suppresses the pulsation of the tube voltage output from 25 and supplied to the X-ray tube, and one end is connected to the positive side and negative side outputs of the full-wave rectifier circuit 125, respectively. 15, 15' are diode bridge 1
Resistors 16 and 16' are connected in series between the positive and negative outputs of 3, and resistors 16 and 16' are connected in series between the other ends of the smoothing capacitors 14 and 14'. Note that the connection point of resistors 15 and 15' and the connection point of resistors 16 and 1
The connection points 6' are both connected to the common line, and the resistance values of the resistors 15, 15', 16, and 16' are selected to be equal. 17, 17' are the voltages generated across resistors 15, 15', and resistor 1, respectively.
This is a differential amplifier that calculates the difference between the voltages generated at terminals 6 and 16'. 18, 18' are differential amplifiers 17, 1
This is an overcurrent protection relay with a control terminal connected between the inputs of switch 7', and switches 122 and 122' are turned on and off using the opening and closing of the contacts of relays 18 and 18'.
It performs ON/OFF control of the input current by controlling the OFF control and the gates of the semiconductor switches 123 and 123'. That is, when a current exceeding a predetermined value flows through the excitation coil of the protective relay 18, 18', this relay 1
8 and 18' operate to switch the open/closed state of the contact, so use this to turn the switches 122 and 1.
22' and semiconductor switches 123, 123'.
Turn ON/OFF. If only the switches 122, 122' are to be ON/OFF controlled by the protective relays 18, 18', a normally closed contact relay should be used as the protective relays 18, 18', and this contact should be used as the switches 122, 122'. Bye. 19 is 2
This is an adder that adds the output voltages of two differential amplifiers 17 and 17'. 20 is two differential amplifiers 17,
17' is monitored, and when the output voltage of the differential amplifiers 17, 17' exceeds a preset threshold,
These are overcurrent protection circuits that control the gates of semiconductor switches 123 and 123', respectively, and turn off the semiconductor switches.

The operation in such a configuration will be explained next.

First, a stable AC power supply voltage is boosted in the high-voltage transformer section 12, and then converted into DC. Pulsations are removed by smoothing capacitors 14 and 14', and the DC high voltage necessary for generating X-rays is transferred to the X-ray tube. supply to.

On the other hand, the secondary current of the step-up transformer 124 is converted to direct current by the diode bridge 13 connected to the secondary low voltage side of the high voltage transformer section 12, and the resistor connected to the output side of the diode bridge 13 15, 15' convert it into voltage. Now, the voltage obtained by these resistors 15 and 15' is V ₁ ,
Let V ₁ ′. On the other hand, the charging/discharging current flowing through the smoothing capacitors is converted into voltage by resistors 16, 16' connected in series with the smoothing capacitors 14, 14'. Now, let these voltages be V ₂ and V ₂ '. The potential difference between the voltages V ₁ and V ₂ is input to the differential amplifier 17 . Similarly, the differential amplifier 17' receives the voltages V ₁ ',
A potential difference of V ₂ ' is input. The output voltages of these two differential amplifiers 17 and 17' have amplification factors of A and A, respectively.
If A', then A( _V1 - _V2 ) and A'( _V1' - _V2 '). These output voltages are supplied to the overcurrent protection circuit 20 and also to the adder 19 at the same time.

Here, the current flowing through the protective relays 18, 18' will be described. In the above configuration, the positive side and the negative side are symmetrical, so if we consider the operation only on the positive side, the equivalent circuit around the protective relay 18 is shown in FIG.

Note that the symbols in FIGS. 2 and 4 are as follows.

i1; Current i2 flowing through the smoothing capacitors 14, 14'; Tube current il flowing through the X-ray tube 11; Current R1 flowing through the excitation coil of the protective relay 18; Resistance value R2 of the resistor 15; Resistance value Rl of the resistor 16 ;Resistance value of the protective relay 18 Therefore, the current il flowing through the protective relay 18 is expressed by the following equation.

il=(i1+i2)・R1/(R1+Rl+R2)−il・
R2/(R1+Rl+R2) = {(i1+i2)・R1−i1・R2}/(R1+Rl
+R2)...(1) Here, if we set R1=R2=R, equation (1) becomes as follows.

il=i2・R/(2R+Rl) ……(2) This equation (2) is expressed as the current il flowing through the protective relay 18.
is proportional to the tube current i2 flowing through the X-ray tube 11, and is unrelated to the charging/discharging current i1 flowing through the smoothing capacitor 14, and the protective relay 18 is not affected by the charging/discharging i1 and is proportional to the value of the tube current i2 only. It is shown that it is operated by.

Since the voltages Rl and il are input to the differential amplifier 17, this input voltage is also applied to the smoothing capacitor 14.
The signal is independent of the charging/discharging current i1 and is proportional only to the tube current i2.

The same applies to the current flowing through the protection relay 18' and the input voltage to the differential amplifier 17'.

The adder 19 includes the two differential amplifiers 17,
Since the sum (corresponding to the average) of the output voltages of 17' is determined, it is possible to measure the tube current excluding the influence of the charging/discharging current flowing through the smoothing capacitor.

This situation is shown in FIG. In this figure, A is the secondary low voltage side current waveform of the high voltage transformer section 12. B shows the waveform of the charging/discharging current flowing through the smoothing capacitors 14, 14'. C is the output waveform of the adder 19, which corresponds to the tube current from which the influence of the charging and discharging currents of the smoothing capacitors 14 and 14' has been removed. In this way, the smooth capacitor 14,1
It can be seen that the influence of the charge/discharge current of 4' has been successfully eliminated. As a result, it is possible to accurately measure the tube current, and furthermore, it is possible to perform measurements that are not affected by power-on.

On the other hand, in the overcurrent protection circuit 20 that receives the output voltages of the two differential amplifiers 17 and 17' as input, the influence of the smoothing capacitors 14 and 14' that may cause malfunction of the overcurrent protection circuit 20 is removed from the input signal. Therefore, the threshold value for protection can be set low, and a highly sensitive overcurrent protection circuit can be achieved. When the tube current exceeds this threshold,
Immediately, the semiconductor switches 123 and 123' are energized and turned OFF by the output of the overcurrent protection circuit 20, and the current on the primary side of the step-up transformer 124 is cut off to prevent overcurrent from flowing into the X-ray tube 11. .
In addition, the protection relays 18 and 18' are also activated at the same time or one after the other, and the switches 122 and 122' are turned OFF.
It also acts to turn off the semiconductor switches 123 and 123', and turns off the step-up transformer 1.
Cut off the next-side current.

In this way, a double protection function is activated in the event of an overcurrent.

(Effects of the Invention) As explained above, according to the present invention, the following effects can be obtained.

(1) The overcurrent protection circuit of the X-ray generation circuit is configured so that it is not affected by the charging and discharging current of the smoothing capacitor, so the setting of the protection circuit can be lowered, improving safety. .

(2) Due to the circuit configuration, dual protection is achieved using relays and electronic circuits (differential amplifier and overcurrent protection circuit), making it possible to realize a highly safe X-ray generation circuit in this respect as well. .

(3) Since it is possible to measure the waveform of the tube current with the influence of the charging and discharging current of the smoothing capacitor removed, it is possible to perform protection at the peak value of the tube current, and it is also possible to observe the accurate waveform of the tube current.

(4) The overcurrent protection according to the present invention is applicable to both continuous X-ray generation systems and pulsed X-ray generation systems.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a conventional continuous X-ray generation circuit, FIG. 2 is a schematic configuration diagram showing an embodiment of the X-ray generation circuit of the present invention, and FIG. 3 is a schematic configuration diagram of an X-ray generation circuit according to the present invention. An explanatory diagram showing operating waveforms of the generating circuit, and FIG. 4 is an equivalent circuit diagram around the protective relay. 11...X-ray tube, 12...High voltage transformer section, 1
22,122'...Switch, 123,123'...
...Semiconductor switch, 124...Step-up transformer, 1
25...Full wave rectifier circuit, 13...Diode bridge, 14,14'...Smoothing capacitor, 15,
15', 16, 16'...Resistor, 17, 17'...
...Differential amplifier, 18, 18'... Overcurrent protection relay, 19... Adder, 20... Overcurrent protection circuit.

Claims (1)

[Claims] 1. A high voltage obtained by a step-up transformer is rectified by a full-wave rectifier circuit and then smoothed by a smoothing capacitor to obtain a DC high voltage, which is applied to an X-ray tube to generate X-rays. An X-ray generation circuit configured as follows: first and second switches 122, 122' inserted in series on the primary side of a step-up transformer 124 to turn on/off the primary side current; and the step-up transformer. 124 and connected in series with the switches 122, 122', the first and second semiconductor switches 1 are connected in antiparallel.
23, 123', and the first and second resistors 1 with the same resistance value connected in series and whose connection point is connected to the common line.
5, 15', and the first and second resistors 1 connected to the secondary low voltage side of the step-up transformer 124 and serving as a load.
A series circuit of 5 and 15' connects the first resistor 15.
A diode bridge 13 is connected to the positive side of the diode bridge 13, and a first smoothing capacitor 14 whose one end is connected to the positive side output of the full-wave rectifier circuit 125 is connected between the common line. A third resistor 16 having the same resistance value as the first resistor 15 is connected between the second smoothing capacitor 14', one end of which is connected to the negative output of the full-wave rectifier circuit 125, and the common line. , a fourth resistor 16' having the same resistance value as the first resistor 15, and the first resistor 15 and the third resistor 16.
A first differential amplifier 17 which takes the difference between the voltages generated between the
and the second resistor 15' and the fourth resistor 1
A second differential amplifier 17' that takes the difference in the voltage generated between Then, the first switch opens at least the first switch 122 and the second switch 122', respectively.
The output voltages of the second overcurrent protection relays 18, 18' and the first and second differential amplifiers 17, 17' are monitored, and when these exceed thresholds, the output voltages of the first and second semiconductors are monitored. switch 123, 12
An X-ray generation circuit characterized by comprising an overcurrent protection circuit 20 for opening 3'.