JPH0696894A - Inverter type x-ray high-voltage device - Google Patents

Abstract

PURPOSE:To surely prevent the breakage of a switching element when an overcurrent is generated. CONSTITUTION:The inter-terminal voltage is inputted from driving circuits 3a-3d, the overcurrent by the arm short circuit is detected by a comparing circuit 11, the inverter output current is inputted from a sensor 10, and the overcurrent by a load circuit is detected by the second comparing circuit 12. The overcurrent is compared with the reference value by the comparing circuit 11 or the second comparing circuit 12 respectively, signals are outputted to driving circuits 3a-3d if the measured value is larger, and operations of gate insulation type bipolar transistors 2a-2d are stopped. Overcurrents by the arm short circuit and load short circuit are separately detected respectively, the overcurrents can be surely detected, and the breakage of IGBT2 can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter type X-ray high voltage device, and more particularly to a technique for preventing the destruction of switching elements due to overcurrent in a load circuit.

[0002]

2. Description of the Related Art An inverter type X-ray high voltage device includes an inverter circuit 4 for converting a DC power supply voltage into a high frequency AC as shown in FIG. 5, and a high voltage transformer 7 for boosting an output voltage of the inverter circuit 4. It comprises a high voltage rectifier 8 for rectifying the output voltage of the high voltage transformer 7 and an X-ray tube 9 to which the output voltage of the high voltage rectifier 8 is applied.

In recent years, this inverter circuit has tended to have higher power and higher frequency, and has been changed to a switching element having a large capacity and capable of switching at high speed. Along with this, the overcurrent has become a large current, and it has become essential to detect the overcurrent promptly, stop the switching element at high speed and safely, and protect the switching element.

In addition, this overcurrent is generated when the switching elements of the series connection body of the inverter circuit are simultaneously conducted (hereinafter referred to as arm short-circuit), and a slight discharge of the X-ray tube as a load circuit or a high voltage transformer. There is something that occurs due to a short circuit in the winding of the container (hereinafter referred to as load short circuit). Conventionally, in order to detect these overcurrents, the voltage across the terminals of the switching element is measured and indirectly obtained, and compared with a reference value in a comparison circuit, and the switching element operates when the measured value exceeds the reference value. To stop.

[0005]

In the above-mentioned conventional device,
Both the arm short circuit and the load short circuit were controlled by a single comparison circuit. However, although arm short-circuiting has a quick rise, overcurrent can be detected in a short time, but load short-circuiting takes a long time because the rate of change of overcurrent is small due to the impedance of the wiring. Therefore, an overcurrent may flow in the switching element during the detection due to the load short circuit, and the switching element may be destroyed.

Therefore, an object of the present invention is to prevent the switching element from being destroyed when an overcurrent occurs.

[0007]

In order to achieve the above object, a DC power supply, a series connection body of a first switching element and a second switching element, and a third switching device connected in parallel to the series connection body. An inverter circuit for converting the output from the DC power supply into high-frequency AC, which includes a series connection body of an element and a fourth switching element and a drive circuit provided in the first to fourth switching elements, and detection by the drive circuit Comparing circuit for inputting the current flowing through the switching element and comparing it with a reference value to output a signal for stopping the operation of the switching element, a high voltage transformer for boosting the high frequency alternating current, and an output of this high voltage transformer. In an inverter type X-ray high voltage device having a high-voltage rectifier for rectifying DC, and an X-ray tube for applying the rectified DC to generate X-rays, A detector for detecting the output current of the data circuit, and a second comparison circuit for comparing the current detected by the detector with a reference value and outputting a signal for stopping the operation of the switching element, The operation of the inverter circuit is controlled by the output of the comparison circuit or the output of the second comparison circuit.

[0008]

The comparator circuit detects the overcurrent due to the arm short circuit, and the second comparison circuit detects the overcurrent due to the load short circuit. Then, the comparison circuit or the second comparison circuit compares the reference value and the detected value, and if the measured value is larger, outputs a signal to the drive circuit to stop the operation of the switching element. As a result, the arm short circuit and the load short circuit can be detected separately, so that the switching element can be surely prevented from being damaged by the overcurrent.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 is a circuit diagram showing a configuration of the present invention, FIG. 2 is a diagram showing characteristics of an IGBT, FIG. 3 is a diagram showing an inverter drive voltage, an inverter current in a normal state and an arm short circuit, a terminal voltage, and FIG. It is a figure which shows the inverter output current at the time of normal and a load short circuit. Reference numeral 1 is a DC power source, 2 is a gate insulating bipolar transistor (hereinafter referred to as IGBT), and four IGBTs 2a to 2d are combined in a full bridge type and used, and diodes are respectively connected in antiparallel. Reference numeral 3 is a drive circuit for operating the IGBTs 2a to 2d, and one drive circuit is provided for each of the IGBTs 2a to 2d.
d is provided.

Reference numeral 4 is an inverter circuit composed of an IGBT 2 and a drive circuit 3 for converting the voltage from the DC power supply 1 into a high frequency AC voltage, and 5 is a load circuit to which the high frequency AC from the inverter circuit 4 is applied. In this embodiment, the load circuit 5 includes a resonance capacitor 6 connected in series with the output of the inverter circuit 4, a high-voltage transformer 7 that boosts the output voltage of the inverter circuit 4, and an output voltage of the high-voltage transformer 7. And a high-voltage rectifier 8 for converting DC into DC, and an X-ray tube 9 to which the output of the high-voltage rectifier 8 is applied and radiates X-rays.

Reference numeral 10 is a sensor for detecting the current flowing in the load circuit 5, 11 is a comparison circuit for comparing the current of the IGBT 2 detected by the drive circuit 3 with a reference value, and 12 is a comparison of the current of the sensor 10 with the reference value. A comparison circuit, 13 is a comparison circuit 11
Alternatively, it is an OR circuit that outputs a control signal to the drive circuit 3 when either of the output signals of the comparison circuit 12 is input.

Next, the operation of this embodiment will be described with reference to FIG. First, the DC voltage from the DC power supply 1 is converted into the inverter circuit 4
When input to, it is converted into a high frequency AC voltage. In this inverter circuit 4, first, the IGBTs 2a and 2d are operated, and at the next timing, the IGBTs 2b and 2c are operated to convert direct current into alternating current. And
The high-frequency AC voltage from the inverter circuit 4 resonates with the leakage inductance of the capacitor 6 and the high-voltage transformer 7, and is boosted by the high-voltage transformer 7. The boosted voltage is converted into a DC voltage by the high-voltage rectifier 8 and the X-ray tube 9 Apply to.

The detection when the arm is short-circuited and when the load is short-circuited will be described with reference to FIGS. To detect the arm short circuit, the current of the IGBT 2 is detected by the drive circuit 3, and the detected value is input to the comparison circuit 11 to be compared with the arbitrarily set reference value. Actually, the driving circuit 3 does not directly detect the current Ic of the IGBT 2 but measures the inter-terminal voltage Vce. As shown in FIG. 2, the current Ic and the inter-terminal voltage Vce have a relationship in which the inter-terminal voltage Vce rapidly increases when the current Ic increases above the normal operating range, and therefore the inter-terminal voltage Vce is changed. Measure the current Ic
Is deciding how much is flowing.

Looking at the operation of the IGBT 2a, the drive signal Vge from the drive circuit 3 as shown in FIG.
a is input to the IGBT 2a. During normal operation, the terminal voltage Vcea becomes an operating voltage of several V, and the current Ica becomes a sinusoidal current flowing through the IGBT 2a in the positive direction and through the diode in the negative direction due to the series resonance circuit including the leakage inductance of the capacitor 6 and the high-voltage transformer 7. . When the arm is short-circuited, the inter-terminal voltage V'cea is initially applied with the operating voltage, but gradually increases. Since the current I'ca does not flow through the resonance circuit such as the capacitor 6 because the arm is short-circuited, it does not become a sinusoidal current and further does not flow into the load, so that the current rapidly increases.

The inter-terminal voltage V'cea measured by the drive circuit 3 is input to the comparison circuit 11 and compared with a preset reference value. If the measured value is larger, the IGBT2
A signal for stopping the operation of a is output. IGBT2b ~
Similarly for 2d, the arm short circuit is detected.

When the load is short-circuited, the current is directly detected by the sensor 10 provided in series on the output side of the inverter circuit 4. The output current Iinv of the inverter circuit 4 at the normal time is a sinusoidal alternating current as shown in FIG. 4, but the output current I′inv at the time of load short circuit is larger than that at the normal time. Then, the detected output current is input to the comparison circuit 12 and compared with a preset reference value, and when the detected value is larger, a signal for stopping the operation of the IGBT 2 is output.

An OR circuit 13 is provided on the output terminal side of the comparison circuit 11 and the comparison circuit 12, and the comparison circuit 11,
When either of the output signals of 12 is input, I is input to drive signal 3.
The stop signal of GBT2 is output.

This makes it possible to reliably stop the operation of the IGBT 2 when an arm short circuit and a load short circuit occur.

[0019]

According to the present invention, when an arm short circuit occurs, a drive circuit attached to each switching element detects a current flowing through the switching element, and this current is compared by a first comparison circuit to detect an overcurrent. it can. In the case of load short circuit, an overcurrent can be detected by detecting an output current with a detector provided on the output side of the inverter and comparing this current with a second comparison circuit. As a result, the arm short circuit and the load short circuit can be detected separately, so that it is possible to reliably detect the overcurrent and prevent the switching element from being destroyed.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of the present invention.

FIG. 2 is a diagram showing the characteristics of an IGBT.

FIG. 3 is a diagram showing a drive voltage of the inverter, a voltage between terminals at a normal time and an arm short circuit, and an inverter current.

FIG. 4 is a diagram showing inverter output current under normal conditions and under load short circuit

FIG. 5 is a circuit diagram showing a conventional inverter type X-ray high voltage device.

[Explanation of symbols]

 2 IGBT 3 Drive circuit 4 Inverter circuit 6 Capacitor 7 High voltage transformer 8 High voltage rectifier 9 X-ray tube 10 Sensor 11 Comparison circuit 12 Comparison circuit 13 OR circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideki Uemura Inventor Hideki Ueno 2-1 No. 2 Shinjuyo, Kashiwa City, Chiba Prefecture

Claims (1)

[Claims] 1. A DC power supply, a series connection body of a first switching element and a second switching element, and a series connection body of a third switching element and a fourth switching element connected in parallel to the series connection body. An inverter circuit that includes a drive circuit provided in each of the first to fourth switching elements and that converts an output from the DC power supply into a high frequency AC, and a reference value by inputting a current flowing in the switching element detected by the drive circuit. A comparator circuit that outputs a signal that stops the operation of the switching element, a high-voltage transformer that steps up the high-frequency alternating current, a high-voltage rectifier that rectifies the output of the high-voltage transformer into direct current, and the rectified In an inverter type X-ray high-voltage device having an X-ray tube for applying a direct current to generate an X-ray, a detector for detecting an output current of the inverter circuit, A second comparison circuit that compares the current detected by the detector with a reference value and outputs a signal that stops the operation of the switching element, and outputs the output of the comparison circuit or the output of the second comparison circuit. Inverter type X characterized by controlling the operation of an inverter circuit
Line high voltage equipment.