JPH0620792A - Inverter type x-ray high voltage device - Google Patents

Abstract

PURPOSE:To provide a large capacity X-ray high voltage device of inverter type constructed in a small size and at a low cost even in case three-phase AC 200V main is used. CONSTITUTION:Through thyristors 1, 2, at least two capacitors 3 are provided in series connection for charging the U-V, V-W, W-U inter-wire voltages of three-phase AC mains 7. These capacitors 3 are charged from one side by the thyristors 1, 2, and the inter-end voltages of the capacitors 3 are fed as the input voltage to an inverter circuit 10. When three-phase 200V AC main is used, the input voltage to the inverter circuit 10 can be heightened by a voltage doubling rectifier circuit 8 consisting of thyristors 1, 2 and capacitor 3 where no provision is required for any boosting chopper circuit or a booster transformer, so that the current of the inverter circuit 10 can be reduced, the ratio of turns in the windings of a high voltage transformer, and the device can be constructed in small size and with good economy.

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 circuit for boosting an input voltage of an inverter circuit.

[0002]

2. Description of the Related Art As a compact and high-performance X-ray high-voltage device,
In recent years, an inverter type X-ray high voltage device using a power semiconductor element has been used. It rectifies a single-phase or three-phase AC power supply voltage and converts it into a DC voltage, converts it into a high frequency AC voltage with an inverter circuit, boosts this voltage with a high voltage transformer and rectifies it into an X-ray tube. It is applied.
Further, in the inverter type X-ray high voltage device, downsizing of the device, that is, downsizing of the inverter circuit and the high voltage transformer is required, and therefore, the input voltage of the inverter circuit and the high voltage transformer is increased to increase the inverter circuit. It was necessary to reduce the current of and to reduce the turns ratio of the high voltage transformer.

In the conventional single-phase 200V power supply, the AC power supply voltage is doubled and rectified, and the inverter input voltage is boosted to about twice that in full-wave rectification. In addition, since there is no circuit system that boosts voltage with a rectifier circuit in a three-phase 200V power supply, the existing 2
The 00V power supply equipment is changed to a 400V power supply, or 200V to 400V is boosted by a step-up transformer and this voltage is full-wave rectified, or the input voltage of the inverter is boosted by a step-up chopper circuit.

[0004]

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention
In the case of a 00V power source, a step-up chopper circuit and a step-up transformer were separately provided. However, this boost chopper circuit requires large-capacity self-extinguishing semiconductor switching elements such as transistors and insulated gate bipolar transistors and their control circuits, and multiple large passive components such as reactors and capacitors. The step-up transformer was expensive and large in size because it required a transformer with the same capacity as the AC power supply. In addition, the 200V power supply is 400
When changing to a V power source, the cost of remodeling was enormous.

Therefore, an object of the present invention is to provide a three-phase AC 200V.
An object of the present invention is to provide a large-capacity inverter type X-ray high-voltage device that is small in size and inexpensive even when a power source is used.

[0006]

In order to achieve the above object, a first rectifier circuit for rectifying the output voltage of a three-phase AC power supply, and a smoothing circuit for smoothing the output voltage of the first rectifier circuit, An inverter circuit that converts the output voltage of the smoothing circuit into high-frequency AC, a high-voltage transformer that boosts the output voltage of the inverter circuit, a second rectifier circuit that rectifies the output voltage of the high-voltage transformer, An inverter type X-ray high-voltage device having an X-ray tube for applying an output voltage of a second rectifier circuit to irradiate X-rays, comprising:
At least two capacitors for respectively charging the V, VW, and WU line voltages are connected in series via the first rectifier circuit, and the plurality of capacitors are charged from a certain direction by the first rectifier circuit. Then, the voltage across the capacitor is used as the input voltage of the inverter circuit.

[0007]

The capacitor provided between the lines of the three-phase AC power supply via the rectifier circuit is charged with only the positive polarity voltage between the lines, so that the capacitor is charged with the DC voltage. Since two or three capacitors are connected in series, the input voltage of the inverter is 2 to the AC power supply voltage.
DC voltage is tripled. Thus, in the case of three-phase 200V, the input voltage can be boosted without providing a boosting transformer or the like, so that the entire device can be made small and inexpensive.

[0008]

Embodiments of the present invention will be described below with reference to FIGS. 1 is a circuit diagram showing an embodiment of the present invention, FIG.
FIG. 2 is a waveform diagram showing input and output voltages of the voltage doubler rectifier circuit in FIG. 1. Reference numerals 1 and 2 denote thyristors for charging the capacitor 3 from the three-phase AC power supply 7 only when the line voltage is positive, and the voltage from the three-phase AC power supply 7 is charged through the thyristor 1, the capacitor 3, and the thyristor 2. Reference numeral 3 is a capacitor for charging a positive line voltage, 8 is a voltage doubler rectifying circuit formed by the thyristors 1 and 2, and 9 is a smoothing circuit for smoothing the output voltage from the voltage doubler rectifying circuit 8. 10 is a smoothing circuit. An inverter circuit for converting the output voltage from the circuit 9 into a high-frequency alternating current. Transistors 11a to 11d and a diode 1 connected in antiparallel to the transistors 11a to 11d.
2a to 12d are full bridge inverter circuits.

Reference numeral 19 is a resonance capacitor connected in series with the inverter circuit 10, 20 is a high voltage transformer, 21 is a rectifying circuit for converting the AC voltage from the high voltage transformer 20 into DC, 2
Reference numeral 2 is a tube voltage detection resistor for feeding back the tube voltage to the inverter circuit 10, 23 is an X-ray tube, 24 is a voltage control circuit for operating the inverter circuit 10 constantly, and 25 is a base drive for operating the transistor 11 of the inverter circuit 10. Circuit.

First, the operation of the inverter type X-ray high voltage device will be described. First, the X-ray conditions for irradiating the subject are set, but in this embodiment, only the tube voltage is set and controlled.
Then, when a desired tube voltage is set and an X-ray exposure signal is given, the voltage control circuit 24 sends a signal for controlling the inverter circuit 10 to the base drive circuit 25 by the tube voltage setting signal, and the base drive circuit 25 amplifies the signal. Output to the base of the transistor 11 of the inverter circuit 10.

Then, the inverter circuit 10 starts a switching operation for alternately turning on and off the transistors 11a and 11d and the transistors 11b and 11c at a predetermined cycle to set the tube voltage, and is determined by the capacitor and the inductance. A current (resonance current) having a vibration cycle flows through the high voltage transformer 20. Here, of the capacitor and the inductance that determine the vibration period, the capacitor is the resonant capacitor 19 connected in series to the primary winding of the high-voltage transformer 20.
And the stray capacitance existing between the layers of the secondary winding of the high voltage transformer 20, and the inductance is the leakage inductance of the high voltage transformer 20 and the wiring inductance.

Within the half cycle of the predetermined cycle in which the transistors 11a and 11d are driven, the resonance current first becomes the transistor 11a → the resonance capacitor 19 → the high voltage transformer 20.
The primary winding of the transistor 11d flows through the circuit of the transistor 11d in an arc of the resonance frequency and becomes zero after 1/2 hour of the half cycle. This time, the diode 12d → the primary winding of the high voltage transformer 20 → the resonance capacitor 19 → Flows through the circuit of the diode 12a. Then, the transistors 11a and 11d are turned off, the transistors 11b and 11c are turned on in the next cycle, and the resonance current flows in the same manner as described above.

An AC current obtained by subtracting the exciting current of the high voltage transformer 20 and the current flowing in the stray capacitance of the secondary winding from the primary current flowing through the primary winding of the high voltage transformer 20 is rectified by the rectifier circuit 21. It is smoothed by the stray capacitance of the high voltage cable and applied to the X-ray tube 23. And the tube voltage detection resistor 2
2, the actual tube voltage is detected, and a signal corresponding to the detected tube voltage is input to the voltage control circuit 24 so that the difference between the set tube voltage signal and the detected tube voltage signal becomes zero. The width is controlled, and this control signal is input to the transistor 11 via the base drive circuit 25. As a result, the operating frequency of the inverter circuit 10 in the next cycle is corrected and the tube voltage setting value is accurately controlled.

Next, the operation of the voltage doubler rectifier circuit 8 of this embodiment will be described. Two-phase AC power as shown in FIG. 2A is supplied to the voltage doubler rectifier circuit 8 from each phase of the three-phase AC power supplies 7u, 7v, and 7w. Then, when the line voltage between the three-phase AC power supplies 7u and 7v is positive, the thyristors 1u and 2v are ignited and the thyristors 1u and 2v are ignited as shown in FIG.
The capacitor 3u is charged like
When the line voltage between 7 and 7w is positive, the thyristor 1v is ignited by 2w to charge the capacitor 3v as shown in FIG. 2C, and when the line voltage between the three-phase AC power supplies 7w and 7u is positive. Then, the thyristors 1w and 2u are ignited and the capacitor 3w is charged as shown in FIG. 2 (d). These capacitors 3
Are connected in series, and when the voltage across this is smoothed by the smoothing circuit 9 consisting of a reactor and a capacitor as the input voltage e _dc of the inverter circuit 10, as shown in FIG. It becomes a voltage. This input voltage e _dc can be varied by controlling the gate phase angle of each phase thyristor 1 or 2, or both thyristors.

Further, in order to lower the tube voltage in the region where the tube current is small as in the case of fluoroscopy, the inverter input voltage e _dc may be decreased. For example, by setting the v-phase thyristors 1v and 2v to be non-conductive and performing full-wave rectification of the line voltage of the three-phase AC power supplies 7u and 7w by the thyristors 1u and 2w and 1w and 2u, fine voltage setting is possible. When not used in this way, the inverter input voltage can be boosted even if the thyristor on the input side to the capacitor 3 is replaced with the diode 4 as shown in FIG.

Next, an embodiment in which two capacitors are used will be described with reference to FIGS. 4 and 5. This is because capacitors 6u and 6w are provided between the lines of the three-phase AC power supplies 7u and 7v and 7v and 7w, respectively, and between the three-phase AC power supply 7u and the capacitor 6u and between the three-phase AC power supply 7w and the capacitor 6w. Thyristors 5u and 5w are provided respectively. Then, the line voltage of the three-phase AC power supplies 7u and 7v is applied to the thyristor 5
5b is charged in the capacitor 6u by half-wave rectification, and the line voltage between the three-phase AC power supplies 7v and 7w is half-wave rectified by the thyristor 5w and is converted into the capacitor 6w in FIG.
Charge the voltage as shown in (c) and use the capacitors 6u, 6
The voltage e ₀ across w is used as the inverter input voltage.

As a result, when the three-phase 200V power supply is used, the input voltage of the inverter circuit 10 can be increased by the voltage doubler rectifier circuit 8 without using the step-up chopper circuit or the step-up transformer. The current can be reduced and the turns ratio of the high-voltage transformer can be halved, and the device can be made compact and economical.

[0018]

According to the present invention, the line voltage of the three-phase AC power supply is charged by the capacitors, and the voltage across these capacitors is used as the input voltage of the inverter circuit. The pressure can be increased about 2-3 times. As a result, the current of the inverter circuit can be reduced, and the turns ratio of the high-voltage transformer can be halved, so that the overall size of the device can be reduced and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment using three capacitors of the present invention.

FIG. 2 is a waveform diagram showing input and output voltages of the voltage doubler rectifier circuit in FIG.

FIG. 3 is a circuit diagram showing another embodiment using three capacitors.

FIG. 4 is a circuit diagram showing an embodiment using two capacitors.

5 is a waveform diagram showing input and output voltages in FIG.

[Explanation of symbols]

 1 Thyristor 2 Thyristor 3 Capacitor 4 Diode 5 Thyristor 6 Capacitor 7 Three-phase AC power supply 8 Double voltage rectifier circuit 9 Smoothing circuit 10 Inverter circuit 19 Resonant capacitor 20 High voltage transformer 21 Rectifier circuit 22 Tube voltage detection resistor 23 X-ray tube 24 Voltage Control circuit 25 Base drive circuit

Claims (1)

[Claims] 1. A first rectifier circuit for rectifying an output voltage of a three-phase AC power supply, a smoothing circuit for smoothing an output voltage of the first rectifier circuit, and an output voltage of the smoothing circuit for converting into a high frequency AC. An inverter circuit, a high-voltage transformer that boosts the output voltage of this inverter circuit, a second rectifier circuit that rectifies the output voltage of this high-voltage transformer, and an output voltage of this second rectifier circuit that is applied. In an inverter type X-ray high-voltage device having an X-ray tube for irradiating X-rays, capacitors for respectively charging the U-V, V-W, and W-U line voltages of the three-phase AC power source are provided in the first. At least two are connected in series via a rectifier circuit, the plurality of capacitors are charged from a certain direction by the first rectifier circuit, and the voltage across the capacitors is used as the input voltage of the inverter circuit. X High voltage equipment.