JPH0412640Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention is used in the field of protecting X-ray high voltage equipment and switching elements.

TECHNICAL FIELD The present invention relates to an X-ray high-voltage device, and more particularly to protection of switching elements of the X-ray high-voltage device.

(b) Prior art An inverter-based X-ray high-voltage device converts a constant primary voltage from DC to AC using a switching element, then inputs it to a high-voltage transformer, rectifies the output, and applies it to the X-ray tube. are doing.

Such a conventional device is shown in FIG.

Here, 1 is a commercial power supply, 2 is a rectifier circuit, 3 is a power supply smoothing capacitor, 4 is a switching element, 5 is a flywheel diode, 6 is a switching element drive circuit, 7 is a switching element control pulse generator, and 8 is a transformer. , 9 is a high voltage rectifier circuit, 10 is X
Line tube 11 is the floating capacitance of the high voltage cable.

(c) Problems to be solved by the invention However, since the high-voltage transformer and high-voltage cable have stray capacitance 11, it is necessary to flow a large current for charging when the X-ray tube voltage 10 rises.

This large current can exceed 1000A and may destroy the switching element.

For this reason, a means is required to suppress the charging current at the time of rising for an appropriate period of time using an appropriate resistor.

However, this has problems such as the resistance value or suppression time must be set depending on conditions such as output KW and high voltage cable length, and the rise time becomes long.

In view of the above, an object of the present invention is to provide an X-ray apparatus that can protect the switching elements used from excessive current and at the same time shorten the rise time of the tube voltage.

(d) Means for solving the problem The above purpose is to provide a detection circuit for the current flowing in the switching element or a current proportional to it in an X-ray high voltage apparatus using an inverter system, and to detect a current close to the rated value of the switching element. This can be achieved by having a circuit that compares detected currents using the value as a reference value, and a switching element control circuit that turns off switching elements that exceed the reference value and turns on switching elements in the opposite direction.

(E) Effect The current of the switching element is detected and the detected current value is compared with a value close to its rated value. If a current larger than the reference value is detected, the relevant switching element is turned off and the switching element is turned off in the opposite direction. Add a control system to turn on the switching element.

(F) Embodiment A preferred embodiment of the present invention will be described with reference to FIGS. 1 and 2.

For convenience, the conventional example shown in FIG. 4 will be explained.

A voltage that has been rectified and smoothed to a constant voltage by the rectifier circuit 2 and the power supply smoothing capacitor 3 is input to the DC-AC converter. The DC-AC converter is a full bridge circuit including switching elements 4a, 4b, 4c, 4d and flywheel diodes 5a, 5b, 5c, 5d.

Here, it is converted into an alternating current voltage with a constant period and inputted to the high voltage transformer 8. After this output is rectified by the rectifier circuit 9, it is applied to the X-ray tube 10.

As mentioned above, since the high voltage transformer and the high voltage cable have stray capacitance 11, it is necessary to flow a large current for charging to the primary side when the tube voltage rises. This large current may exceed 1000A and may destroy the switching elements 4 and 5.

The waveforms of the current flowing through the switching element 4 and the tube voltage at this time are shown in FIG. 3a.

A resistance method has been conventionally used to solve this charging current problem. As shown in FIG. 5, this is a method in which a resistor is inserted in series on the primary side, and the charging current at the time of rising is controlled for an appropriate time by an appropriate resistance value.

The waveforms of the current flowing through the switching element 4 and the tube voltage at this time are shown in FIG. 3b. A control resistor is inserted until time to, and the resistor is short-circuited after time to.

In this way, the charging radio waves are controlled and there is no risk of damaging the switching element. However, with the resistance method, it is necessary to set the resistance value or control time depending on conditions such as tube voltage, tube current, and high-voltage cable length, and there are also steps in the rise of the tube voltage, resulting in a longer rise time. There are other problems.

A circuit diagram of one embodiment of the present invention is shown in FIG. 1, and its corresponding characteristics are shown in FIG. 3C.
Current detection circuit 12, comparator 13 and OR
A circuit 14 is added.

The maximum current value Is is set in advance, taking into consideration the current rating of the switching element. When the tube voltage rises, a large current flows to charge the stray capacitance of the high voltage transformer and high voltage cable, but the current is monitored by the current detection circuit 12, and when it exceeds the previously set +Is, the output of the comparator 13a goes high. The signal is inverted and input to the switching element control pulse generator 7 via the OR circuit 14.

Upon receiving this signal, the controller 7 turns off the switching elements 4a and 4d that had been on. When the current value decreases and reaches +Is, comparator 13
The output of a is inverted to L, and upon receiving this signal, the controller 7 turns on the switching elements 4b and 4c in the opposite direction.

By repeating this operation, the stray capacitance is charged. After charging the stray capacitance is completed, the inverter operates in a normal fixed cycle.

According to the present invention, the switching element can be protected from excessive current, and at the same time, as shown in FIG. 3C, the rise time t3 of the tube voltage can be shortened compared to t2 when using the resistance method.

In addition, in this invention, the current on the primary side is detected,
It can also be controlled. A circuit diagram of such an embodiment is shown in FIG.

Note that the switching element is not limited to a transistor as in the illustrated embodiment, but other elements can also be used in the present invention.

(g) Effects According to the present invention, the switching element is protected from excessive current, and the rise time of the tube voltage can be shortened.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, Fig. 2 is a similar diagram showing another embodiment, Fig. 3 is a diagram illustrating a comparison of characteristics between the conventional example and the present invention, and Fig. 4 is a circuit diagram showing one embodiment of the present invention. Conventional Example Circuit Diagram FIG. 5 is a partial circuit diagram of another conventional example. 4 is a switching element, 8 is a transformer, 10 is X
Ray tube, 11 is stray capacitance, 12 is radio wave detector, 13
a is a negative side comparator, 13b is a positive side comparator, and 14 is a negative side comparator.
It is an OR circuit.

Claims (1)

[Scope of utility model registration request] In an X-ray high voltage device using an inverter system, there is a circuit for detecting the current flowing through the switching element or a current proportional to it, a circuit for comparing the detected current with a current value close to the rating of the switching element as a reference value, and a circuit for comparing the detected current with a current value close to the rating of the switching element as a reference value. 1. An X-ray apparatus comprising a switching element control circuit configured to turn off a switching element in the opposite direction and turn on a switching element in the opposite direction.