JPH0773993A - X-ray tube filament heating circuit - Google Patents

Abstract

PURPOSE:To reduce the influence of inductance by a heating transformer and a high tension cable, and thereby radiate X-rays stably at high speeds by forming a resonance circuit using a synthetic value of inductances of the heating transformer and the high tension cable and the like. CONSTITUTION:The DC voltage of a DC voltage power supply is converted into AC voltage by synthesizing the voltages of a switching element 3a and a switching element 3d, and a switching element 3b and a switching element 3c. The aforesaid AC voltage is formed into AC voltage in a sign wave shape by a resonance circuit made up of the electrostatic capacity of a capacitor for resonance, leakage inductance 7 at the primary side of a heating transformer 6, and of inductance 8 reduced at the primary side of the high tension cable 9. In this case, the inductance 7 of the transformer 6 is canceled by the inductance 8 of the high tension cable 9, delay in rise of filament current by inductance 7 is thereby reduced, and concurrently sufficient filament current can thereby be fed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray tube filament heating circuit capable of heating a filament with high efficiency, high performance and high speed by a high frequency resonance current.

[0002]

2. Description of the Related Art X-rays have a high voltage applied to both ends of an X-ray tube.
The thermoelectrons emitted from the filament, which is the cathode heated to a high temperature, are obtained by colliding with the anode. The power supply circuit for heating the filament to a high temperature is an X-ray tube filament heating circuit. As a method of heating the filament to a high temperature, there are AC heating for supplying a rectangular wave AC current and DC heating for supplying a DC current.

In the AC heating, the commercial AC voltage source is rectified into DC and the duty of the chopper circuit is changed to change the DC voltage value input to the power conversion inverter to control the output. The inverter is a voltage type inverter in which a switching element for power conversion is configured in a half bridge shape, and converts a DC voltage output from a chopper circuit into a rectangular wave AC current having a frequency higher than that of a commercial voltage source. The rectangular wave alternating current is insulated by the heating transformer, and the output of the heating transformer supplies the current to the filament of the X-ray tube through the high voltage cable to heat the filament to a high temperature. In the DC heating, a rectifier circuit provided at the output of the heating transformer converts the DC current into DC current, which is then supplied to the filament for heating.

[0004]

The AC heating of the prior art described above supplies a high frequency current to the filament, and therefore has the advantage that there are few pulsations appearing in the tube voltage or tube current waveform, but the inverter input voltage output is adjusted. The problem is that the chopper circuit that is used is large in size for handling a large current and that noise during switching is very large. Further, in order to further reduce the pulsation appearing in the tube voltage or tube current waveform and obtain a stable X-ray, it is necessary to increase the frequency to a higher level than at present. When the frequency is increased, the leakage inductance of the heating transformer becomes large and a sufficiently large current does not flow, and when the filament current is suddenly changed, a delay occurs and a sufficient response is not shown.
Further, there is a problem that the inductance of the high voltage cable cannot be ignored. Particularly in recent years, since a long high-voltage cable has been used, the inductance that increases in proportion to the high-voltage cable length increases, and the potential drop due to this increases the current supply to the filament. Since the rectangular-wave alternating current is distorted by the inductance of the high-voltage cable into a triangular-wave alternating current, the power supplied to the filament, which is the load, is reduced and sufficient output cannot be obtained, further increasing the frequency of the heating circuit. It is difficult to increase the frequency.

On the other hand, in the above DC heating, there is no potential drop due to the impedance of the high voltage cable, but as in the above AC heating, the response of the filament current due to the leakage inductance of the heating transformer becomes a problem.

According to the present invention, even when the frequency is further increased, the delay of the current response due to the leakage inductance of the heating transformer and the distortion of the current waveform due to the inductance of the high voltage cable are reduced, and stable X-rays are radiated at high speed. The purpose is to obtain a filament heating circuit for.

[0007]

The above object is to provide a direct current voltage source, an inverter connected to the direct current voltage source for converting direct current to high frequency alternating current, and a heating transformer for insulation connected to the output of the inverter. An X-ray tube filament heating circuit comprising a filament of an X-ray tube connected to a high voltage cable for supplying current, a combined value of the leakage inductance of the heating transformer and the inductance of the high voltage cable, and the inverter output. This is achieved by forming a resonance circuit with the capacitance of the resonance capacitor connected in series to the filament and supplying a high-frequency resonance current to the filament.

Further, the resonance circuit is formed by the leakage inductance of the heating transformer and the capacitance of the resonance capacitor, and a rectifying circuit is provided on the output side of the heating transformer, and the rectification circuit is connected to the filament through a high voltage cable. It is achieved by supplying a direct current.

[0009]

In the AC heating in the X-ray tube filament heating circuit according to the present invention, the chopper circuit which is inevitably increased in size and causes a large noise is removed, and the output is controlled only by the inverter for power exchange. A resonance type inverter with a resonance circuit connected to the output is used,
In the above resonance circuit, together with the capacitance of the resonance capacitor connected to the output of the inverter, a resonance phenomenon occurs due to the combined value of the leakage inductance of the heating transformer and the inductance of the high voltage cable, so even when the frequency is further increased, It is possible to reduce the current response delay due to the leakage inductance and the distortion of the current waveform due to the inductance of the high voltage cable, supply a sufficient current to the X-ray tube filament, and obtain stable X-rays.

Further, in the case of the X-ray tube filament heating circuit by DC heating, the resonance phenomenon of the resonance circuit is caused by the capacitance of the resonance capacitor and the leakage inductance of the heating transformer, so that the frequency is Even when it is further increased, the delay of the filament current due to the leakage inductance of the heating transformer can be significantly reduced, and a sufficient current can be supplied to the filament. A rectifier circuit is provided between the heating transformer and the high-voltage cable,
By passing a direct current, the impedance of the high-voltage cable is ignored, and the potential drop is only due to the minute resistance component existing in the high-voltage cable, which enables high-speed response of filament current and stable X-ray supply.

[0011]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a circuit diagram showing a first embodiment of an X-ray tube filament heating circuit according to the present invention, FIG. 2 is a diagram showing voltage and current waveforms at various portions of the embodiment, and FIG. 3 is an X-ray tube filament heating circuit according to the present invention. FIG. 4 is a circuit diagram showing the second embodiment of FIG. 4, FIG. 4 is a diagram showing the relationship between the length of the high voltage cable and the time until the steady current is reached, and FIG.
FIG. 6 is a diagram showing a single-end push-pull inverter.

First Embodiment FIG. 1 shows the first embodiment of the X-ray tube filament heating circuit according to the present invention.
It is a figure which shows the case of alternating current heating as an Example. The heating circuit is a power supply circuit that heats the filament 11 corresponding to the cathode of the X-ray tube 10 to a high temperature and controls the amount of thermoelectrons corresponding to the target that is the anode. The DC voltage source 1 supplies a DC voltage, and is constituted by, for example, a combination of a commercial AC power source and a diode bridge rectifier circuit. The inverter 2 is for converting the output voltage of the DC voltage source 1 into a high-frequency AC voltage, and is a combination of four switching elements 3a to 3d made of a MOS type field effect transistor (hereinafter abbreviated as MOSFET) in a bridge shape. The flywheel diodes 4a to 4d are incorporated corresponding to the switching elements 3a to 3d, respectively. The voltage waveforms of the DC voltage source 1 and the switching elements 3a to 3d of the inverter 2 are shown in FIG. 2. By combining the voltages of the switching element 3a and the switching element 3d, and the switching element 3b and the switching element 3c, the DC voltage is changed. The DC voltage of source 1 is converted to an AC voltage as shown in the inverter output voltage of FIG.

The AC voltage is represented by a resonance circuit constituted by the capacitance of the resonance capacitor 5, the primary side leakage inductance 7 of the heating transformer 6 and the primary side converted inductance 8 of the high voltage cable 9. A sinusoidal alternating current as shown in 2 is obtained. Due to the above resonance circuit, the primary side leakage inductance 7 of the heating transformer 6 and the high voltage cable 9
The inductance 8 is canceled out, and the delay of the filament current due to the primary side leakage inductance 7 can be reduced and a sufficient filament current can be supplied.

Conventionally, when a voltage-type inverter is used, a rectangular wave current is distorted into a triangular wave current due to the inductance of the high-voltage cable, but as described above, a sinusoidal current is formed by the resonance circuit. This eliminates waveform distortion. Moreover, the electromagnetic induction noise and the switching loss of the switching elements 3a to 3d are also reduced.

Second Embodiment FIG. 3 shows a second embodiment of the X-ray tube filament heating circuit according to the present invention.
It is a figure which shows the case of direct-current heating as an Example. The process of converting the DC voltage of the DC voltage source 1 into the AC output voltage as shown in FIG. 2 by the inverter 2 is the same as in the first embodiment. The AC voltage becomes a sinusoidal AC current as shown in FIG. 2 due to the resonance circuit constituted by the resonance capacitor 5 and the primary side leakage inductance 7 of the heating transformer 6. The resonance circuit cancels the primary side leakage inductance 7 of the heating transformer 6,
It is possible to reduce the delay of the filament current due to the secondary leakage inductance 7 and supply a sufficient filament current. Moreover, the electromagnetic induction noise and the switching loss of the switching elements 3a to 3d in the inverter 2 are reduced.

The above sinusoidal resonance current is insulated by the heating transformer 6, but in the present embodiment, two of the heating transformer 6 are isolated.
The secondary output is guided to a rectifier circuit 12 composed of four diodes 12a to 12d configured in a bridge shape, rectified into a direct current like the current of the filament shown in FIG. It is fed to the filament 11 of the tube 10 and heats it to a high temperature.

By providing the resonance circuit as described above, it is possible to further increase the frequency even when a heating transformer having a large leakage inductance is used, and the current flowing through the high voltage cable 9 is a direct current. Therefore, the inductance of the high-voltage cable 9 can be neglected, and the time from preheating to reaching a steady current can be shortened as shown in FIG. 4, especially when the length of the high-voltage cable becomes long. The effect is remarkable.

In each of the above embodiments, the inverter 2 is of the full bridge type, the phase difference control type is used, the switching elements 3a to 3d are MOSFETs, and the resonance circuit is the series resonance type. The structure may be a half bridge type as shown in FIG. 5 or a single end push-pull type as shown in FIG. However, in the case of the DC heating shown in the second embodiment, the primary side equivalent inductance 8 of the high voltage cable shown in FIGS. 5 and 6 does not exist. The circuit system of the inverter may be a frequency modulation type, a bipolar transistor or an insulated gate bipolar transistor may be used as the switching element, and the same effect can be obtained even if the resonance circuit is a parallel resonance type.

[0019]

As described above, the X-ray tube filament heating circuit according to the present invention includes a DC voltage source, an inverter connected to the DC voltage source for converting DC to high frequency AC, and an insulation connected to the output of the inverter. In a heating filament for an X-ray tube comprising a heating transformer for heating and a filament of an X-ray tube connected to a high voltage cable for supplying an electric current, the leakage inductance of the heating transformer and the inductance of the high voltage cable. A resonance circuit is formed by the combined value and the capacitance of the resonance capacitor connected in series with the output of the inverter, and a high-frequency resonance current is supplied to the filament. And the capacitance of the resonance capacitor, and a rectifier circuit is provided on the output side of the heating transformer. By supplying a DC current to the filament via a high-voltage cable, the frequency can be further increased even when using a heating transformer with a large leakage inductance, and the resonant circuit converts the output of the inverter into a sinusoidal AC current. By doing so, the delay of the filament current can be reduced, and the distortion of the current waveform due to the inductance of the high-voltage cable can be reduced, or by converting the sinusoidal AC current into DC current by the rectifier circuit provided in the preceding stage of the high-voltage cable Since the voltage drop due to the inductance of the high voltage cable can be reduced, it is possible to obtain an X-ray tube filament heating circuit which can respond at high speed and can supply a stable filament current.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of an X-ray tube filament heating circuit according to the present invention.

FIG. 2 is a diagram showing voltage and current waveforms of various portions of the embodiment.

FIG. 3 is a circuit diagram showing a second embodiment of the X-ray tube filament heating circuit according to the present invention.

FIG. 4 is a diagram showing the relationship between the length of a high voltage cable and the time required to reach a steady current.

FIG. 5 is a diagram showing a half-bridge inverter.

FIG. 6 is a diagram showing a single-end push-pull inverter.

[Explanation of symbols]

 1 DC voltage source 2 Inverter 5 Resonant capacitor 6 Heating transformer 7 Leakage inductance of heating transformer 8 High-voltage cable inductance primary conversion value 9 High-voltage cable 10 X-ray tube 11 Filament 12 Rectifier circuit

Claims (2)

[Claims] 1. A DC voltage source, an inverter connected to the DC voltage source for converting DC to high frequency AC, a heating transformer for insulation connected to the output of the inverter, and a high voltage for supplying current. In an X-ray tube filament heating circuit comprising a filament of an X-ray tube connected to a cable, a combined value of the leakage inductance of the heating transformer and the inductance of the high-voltage cable, and a resonance capacitor connected in series to the output of the inverter. An X-ray tube filament heating circuit, characterized in that a resonance circuit is formed by the electrostatic capacity of and the high frequency resonance current is supplied to the filament. 2. A DC voltage source, an inverter connected to the DC voltage source for converting DC into high frequency AC, a heating transformer for insulation connected to the output of the inverter, and a high voltage for supplying current. In an X-ray tube filament heating circuit composed of a filament of an X-ray tube connected to a cable, a resonance circuit is formed by the leakage inductance of the heating transformer and the capacitance of a resonance capacitor connected in series with the output of the inverter. An X-ray tube filament heating circuit, characterized in that a rectifying circuit is provided on the output side of the heating transformer and a DC current is supplied to the filament via a high voltage cable.