JPH03127497A - Power source circuit for x-ray equipment - Google Patents

Abstract

PURPOSE:To detect and protect an overcurrent with a simple structure by comparing the terminal voltage of a switching element in an inverter circuit supplying an AC power to a load with the output voltage of a reference voltage generating circuit in an overcurrent detecting section. CONSTITUTION:A DC power of a DC power source 1 is converted to an AC power in an inverter circuit 2 provided with pairs of switching elements 4a and 4d, 4c and 4b to supply to a load 5. The terminal voltage of the element 4d connected to the negative side of the power source 1 is detected in a detector circuit 9 in an overcurrent detecting section 8, and compared with the output voltage of a reference voltage generating circuit 10 outputted synchronously to the operation of the element 4d in a comparison circuit 12, to supply comparison signals to a driving circuit 3d. That is similar as to the element 4b too, then with a simple structure consisting of a small number of elements, the detection of an overcurrent and the protection against an overcurrent can be carried out.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a power supply circuit for an X-ray apparatus that uses an inverter circuit to supply alternating current power to a load such as an The present invention relates to a power supply circuit for an X-ray apparatus that can simplify and reduce the number of means for detecting and protecting overcurrent flowing through multiple pairs of switching elements.

[Conventional technology]

As shown in FIG. 2, the power supply circuit of a conventional X-ray apparatus includes a DC power supply and multiple pairs of switching elements 4a, 4b, 4.
an inverter circuit 2 which has AC power from the DC power supply 1 and converts the DC power from the DC power supply 1 into AC power and supplies AC power to the load 5;
and multiple pairs of switching elements 4a, 4b of this inverter circuit 2.

Drive circuits 3a and 3 that respectively drive or cut off 4c and 4d
b, 3c, and 3d. A plurality of pairs of switching elements 4 constituting the inverter circuit 2
To detect overcurrent flowing to a:4b, 4c:4d,
Although not shown, each switching element 4a, 4b, 4c
, 4d were all equipped with an overcurrent detection section. Each overcurrent detection section detects the voltage applied to each of the switching elements 4a to 4d, and the applied voltage during the period when the switching element is in a conductive state is set in advance according to the voltage-current characteristics of the switching element. When the current level exceeds a certain reference value, it is determined that the current level has reached an abnormal value, and a signal is sent to the drive circuit 3a, 3b, 3c, or 3d of the switching element. Thereby, a cutoff signal is sent from the drive circuit to the switching element, the switching element is cut off, and the circuit is protected.

[Problem to be solved by the invention]

In the power supply circuit of such a conventional X-ray apparatus, an overcurrent detection section was provided for all of the switching elements 48 to 4d that were intended to detect and protect overcurrent, so that each switching element 48 to 4d could be reliably detected. However, the number of overcurrent detection sections increases, the number of parts increases, the circuit configuration becomes complicated, and the cost increases. Furthermore, when applied to a bridge-type inverter circuit, for example, three or more isolated power supply systems are required for the overcurrent detection section, which also complicates the circuit configuration and increases costs. Therefore, the present invention solves these problems.

It is an object of the present invention to provide a power supply circuit for an X-ray apparatus that can simplify and reduce the number of means for detecting and protecting overcurrent flowing through a plurality of pairs of switching elements constituting an inverter circuit.

[Means to solve the problem]

In order to achieve the above object, a power supply circuit of an X-ray apparatus according to the present invention includes a DC power supply and a plurality of pairs of switching elements, converts DC power from the DC power supply into AC power, and supplies AC power to a load. In a power supply circuit for an X-ray apparatus, the power supply circuit includes an inverter circuit that drives or cuts off a plurality of pairs of switching elements of the inverter circuit, and switching elements in symmetrical positions connected to the negative side of the DC power supply. includes a detection circuit that detects the terminal voltage when the switching element connected to the negative side is conducting or non-conducting, and a reference voltage generating circuit that generates reference voltages when conducting and non-conducting, respectively. and a comparison circuit that compares the detected terminal voltage with the reference voltage and sends a comparison signal to the drive circuit. It was established.

[For production]

The power supply circuit of the X-ray apparatus configured in this way detects whether the switching elements are conductive or non-conductive by overcurrent detection units provided in symmetrically positioned switching elements connected to the negative side of the DC power supply. The unit generates reference voltages, switches each reference voltage in synchronization with the operation of the switching element, and detects the terminal voltage when the switching element connected to the negative side is conductive or non-conductive.

The detected terminal voltage is compared with the reference voltage at that time, and a comparison signal is sent to the switching element drive circuit. Thereby, it is possible to detect that an overcurrent flows through each switching element, cut off the switching element, and protect the circuit.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing an embodiment of a power supply circuit of an XvA device according to the present invention. This power supply circuit supplies AC power to a load such as an X-ray tube device, and as shown in FIG. 1, it includes a DC power supply 1, an inverter circuit 2, a drive circuit 3a,
3b, 3c, and 3d.

The DC power supply 1 supplies DC power.

For example, it consists of a battery that is not grounded, or a power supply device that combines an AC power source, a rectifying circuit, and a smoothing circuit. The inverter circuit 2 converts the DC power supplied from the DC power supply 1 into AC power and supplies the AC power to a load 5 such as a high voltage generator or an X-ray tube device, and is, for example, a bridge type inverter circuit. It has two pairs (4a:4b, 4c:4d) of switching elements made of semiconductor elements such as transistors and thyristors. Note that symbols 6a, 6b, 6c, and 6d are free wheel diodes provided in each of the switching elements 4a, 4b, 4c, and 4d. Active circuits 3a, 3b.

3c and 3d are for driving or cutting off the two pairs of switching elements 4a:4b, 4c:4d of the inverter circuit 2, respectively, and are 0N10 input from a control device not shown.
Each of the above switching elements 48 to 4 according to the FF control signal
d is turned ON and OFF. In addition, the first
In the figure, numeral 7 is a fuse.

Here, in the present invention, an overcurrent detection section 8 is provided in the fourth switching element 4d and the second switching element 4b, which are connected to the negative side of the DC power supply 1 and are located symmetrically.
．． 8' is provided.

The overcurrent detection units 8 and 8' detect the terminal voltage of each switching element 4d and 4b when the switching element 4d and 4b are conductive or nonconductive.
It detects the overcurrent of a r 4 b t 4 c * 4 d, and as shown in FIG. and a comparison circuit 12.

The detection circuit 9 detects the terminal voltage when the fourth switching element 4d of the inverter circuit 2 is conductive or non-conductive, and detects the terminal voltage between the collector C and emitter E of the transistor. ing. The reference voltage generation circuit 10 generates reference voltages V□ and -2 when the fourth switching element 4d is conductive and non-conductive, respectively.

The switching circuit 11 inputs the respective reference voltages V, , V, generated by the reference voltage generating circuit 10, and switches them in synchronization with the conduction or non-conduction operation of the fourth switching element 4d. It outputs and can be switched by an 0N10FF control signal input to the fourth drive circuit 3d. The comparison circuit @12 compares the terminal voltage V of the fourth switching element 4d detected by the detection circuit 9 with the reference voltage v1 or v2 output from the switching circuit 11, and generates the comparison signal S. This signal is sent to the fourth drive circuit 3d. Note that the other overcurrent detection section 8' provided in the second switching element 4b in FIG.

The operating principle of the overcurrent detection sections 8, 8' configured in this way will be explained. First, in the switching elements 4d and 4b made of semiconductor elements such as transistors and thyristors, the value of forward voltage drop changes depending on the flowing current due to its voltage-current characteristics. Therefore, by monitoring this voltage value, it is possible to detect overcurrent during the conduction period of the switching elements 4d and 4b. On the other hand, during the period when the semiconductor element should be non-conductive, the semiconductor element blocks current flow, so a voltage appears between its terminals. At this time, if the switching elements 4d and 4b become conductive for some reason (that is, if a malfunction occurs), the voltage appearing between their terminals decreases. The voltage appearing between these terminals also changes depending on the characteristics of the load 5, so
By setting an appropriate detection level according to the characteristics of the load 5, it is possible to detect overcurrent during the non-conducting period of the switching cables 4d and 4b.

Next, the operation of the power supply circuit of the X-ray apparatus configured as described above will be explained. First, in the inverter circuit 2,
When the first and second switching elements 4a and 4b are in a conductive state under the control of the drive circuits 3a and 3b, the load 5
A current flows in the direction of 4a→5→4b. Next, under the control of the drive circuits 3a and 3b, the first and second switching elements 4a and 4b are rendered non-conductive, and under the control of the other drive circuits 3c and '3d, the third and fourth switching elements 4c, 4d becomes conductive. In this case, current flows through the load 5 in the direction 4c→5→4d. Then, by repeating the above operations under the control of the drive circuits 3a to 3d, alternating current power is supplied to the load 5.

In such a state, there are three primary cases in which overcurrent may occur in the inverter circuit 2. The first is a case where the load 5 is short-circuited or in a state close to it. Second, when the switching element 4a (or 4c) is conductive, the switching element 4d (or 4
This is the case when b) becomes conductive for some reason or the free wheel diode 6d (or 6b) is short-circuited.

The third case is when the switching element 4a (or 4c) becomes conductive for some reason while the switching element 4d (or 4b) is conductive, or the freewheeling diode 6a (or 6c) is short-circuited. .

For the first state above, the -
Current flows through the load 5 in the direction 4a → 5 → 4b and in the direction 4G → 5 → 4d by the second switching elements 4a, 4b and the third and fourth switching elements 4c, 4d. , when an overcurrent occurs in the load 5, the abnormal current flows through the fourth switching element 4d which is in a conductive state at that time.
or the second switching element 4b.

For example, regarding the fourth switching element 4d.

Its terminal voltage increases. This terminal voltage V is detected by a detection circuit 9 of one overcurrent detection section 8. At this time, the switching circuit 11 switches to and outputs the reference voltage v1 generated from the reference voltage generating circuit 10 during conduction. The comparison circuit 12 inputs and compares the terminal voltage (2) and the reference voltage v1, detects that the terminal voltage V has increased, and sends a comparison signal S1 to the opening circuit 3d. Then, this open circuit 3d generates an active/cutoff signal S2 by inputting the comparison signal S1, and the fourth switching element 4d
As a result, the fourth switching element 4d is cut off and the circuit is protected.

Next, regarding the second state, if the fourth switching element 4d, which is in the OFF state, malfunctions and becomes conductive while the first switching element 4a is normally conducting, the abnormal current will flow to the load. The current flows from 4a to 4d via a fourth switching element 4d whose impedance is lower than that of 5. At this time, the fourth switching element 4・d
Since the non-conducting state becomes conductive, the terminal voltage decreases. This terminal voltage V is detected by a detection circuit 9 of one overcurrent detection section 8. At this time, the switching circuit 11 switches to and outputs the non-conducting reference voltage v2 generated by the reference voltage generating circuit 10. The comparison circuit 12 inputs and compares the terminal voltage V and the reference voltage v2, detects that the terminal voltage V has decreased, and sends a comparison signal S□ to the drive circuit 3d. Then, this drive circuit 3d generates a drive/cutoff signal S2 in response to the input of the comparison signal S, and outputs the drive/cutoff signal S2 to the fourth switching element 4d.
Send to. As a result, the fourth switching element 4d
is shut off and the circuit is protected.

Next, regarding the third state, if the first switching element 4a, which is in the OFF state, malfunctions and becomes conductive while the fourth switching element 4d is normally conducting, the abnormal current will be applied to the load. The current flows from 4a to 4d via the first switching element 4a whose impedance is lower than that of 5. At this time, the fourth switching element 4d is in a conductive state, so its terminal voltage increases. Then, this terminal voltage (2) is detected by the detection circuit 9 of one of the overcurrent detection sections 8. The following operation proceeds in exactly the same manner as the operation in the first state described above, and the fourth switching element 4
d is cut off and one circuit is protected.

In this way, one overcurrent detection section 8 detects an overcurrent for the first switching element 4a and the fourth switching element 4d, regardless of whether they are in a conductive state or a non-conductive state, and one circuit is protected. be able to.

In addition, regarding the second switching element 4b and the third switching element 4C, the overcurrent can be detected by the other overcurrent detecting section 8' in exactly the same manner as described above, and the circuit can be protected.

〔Effect of the invention〕

Since the present invention is configured as described above, the switching elements 4d and 4b in symmetrical positions connected to the negative side of the DC type i1
The overcurrent detecting sections 8, 8' provided respectively in the switching elements 4d and 4b generate respective base voltages when the switching elements 4d and 4b are conductive and non-conductive, and the respective base '$ lightning voltages of the switching elements 4d and 4b are generated. , 4b.

The terminal voltage V when the switching elements 4d and 4b connected to the negative side are conductive or non-conductive is detected, and the detected terminal voltage V and the reference voltage V□ or v2 at that time are detected.
The comparison signal S is compared with the switching element 4d.
, 4b drive circuit 3d.

It can be sent to 3b. Thereby, it is possible to detect that an overcurrent has flowed through each switching element, cut off the switching elements 4d and 4b, and protect the circuit. Therefore, the number of overcurrent detection sections 8,8' is reduced (for example, by half) compared to the conventional one, and the number of components can be reduced by five, thereby simplifying the circuit configuration and reducing costs. Furthermore, when applied to a bridge-type inverter circuit, for example, there is no need to particularly insulate the power supplies of the overcurrent detection sections 8 and 8', and only one power supply system is required.
After all, the circuit configuration can be simplified and costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a power supply circuit of an XI@ device according to the present invention, and FIG. 2 is a circuit diagram showing a main part of a power supply circuit of a conventional Xm device. 1... DC power supply, 2... Inverter circuit,
38-3d... Drive circuit, 4a-4d... Switching element, 5... Load, 68-6d... Freewheeling diode, 8, 8'... Overcurrent detection section, 9...
Detection circuit, 10... Reference voltage generation circuit, 11...
Switching circuit, 12... Comparison circuit, VL, V2...
Reference voltage, ■. ...Terminal voltage, S□...Comparison signal, S2...
Drive/cutoff signal.

Claims (1)

[Claims] A DC power supply, an inverter circuit having multiple pairs of switching elements that converts DC power from the DC power supply into AC power and supplies AC power to a load, and driving or cutting off each of the multiple pairs of switching elements of this inverter circuit. In the power supply circuit for an X-ray apparatus, the switching element connected to the negative side of the DC power supply at a symmetrical position has a power supply circuit when the switching element connected to the negative side is conductive or non-conductive. a detection circuit that detects the terminal voltage of the terminal; a reference voltage generation circuit that generates reference voltages for conduction and non-conduction; a switching circuit that switches each reference voltage in synchronization with the operation of the switching element; What is claimed is: 1. A power supply circuit for an X-ray apparatus, comprising an overcurrent detection section each having a comparison circuit that compares the terminal voltage and a reference voltage and sends a comparison signal to the drive circuit.