JPS5814040B2 - Triode X-ray tube control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control circuit for controlling the emission and blocking of X-rays from a triode X-ray tube.

Generally, the lattice bias voltage (10) required to cut off a triode X-ray tube is 2 to 3 KV, and conventionally this voltage has been generated and controlled by an electron tube.

That is, it was common to have a configuration as shown in FIG.

In FIG. 1, a high voltage is applied between the anode A and cathode (filament) K of the triode X-ray tube 11 from a DC high voltage power supply 12, and the voltage generated in the resistor 14 is applied to the grid G. ing.

One end of this resistor 14 is connected to the anode of the triode 13, and another high voltage DC power source is connected between the other end of the resistor 14 and the cathode of the triode 13.

The voltage generated in the secondary winding of the isolation transformer 16 is applied to the grid of the triode 13 via a diode 17, and a capacitor 18 is connected between the grid and the cathode.
and a resistor 19 are connected.

With this configuration, if a high frequency signal is applied to the primary winding of the transformer 16 only during a period t, the triode 13 will be cut off during this period t, and as a result, no voltage will be generated across the resistor 14. X-ray radiation is performed from the triode X-ray tube 11.

During the period when high frequency signals are not being sent, the triode 13 is on, and high voltage is generated across the resistor 14, so the grid bias voltage necessary for cut-off is added to the grid G of the triode X-ray tube 11. X-ray radiation is blocked.

Incidentally, in recent years, electron tubes have gradually ceased to be produced, and there has been a shift towards the use of semiconductor devices in place of electron tubes, but semiconductor devices are less reliable than electron tubes in terms of withstand voltage, and as a result, it is difficult to handle such high voltages. There is great concern about voltage resistance, especially in the event of an abnormality such as when the X-ray tube generates glow discharge.

Furthermore, since there is stray capacitance (capacitor 20 shown by the base line) in the high voltage cable for sending high voltage to the grid G of the triode X-ray tube 11, it takes time to cut off the triode X-ray tube 11. There is an inconvenience that it takes.

In view of the above, this invention does not use any electron tubes or active semiconductor elements that have problems with withstand voltage, and has a simple circuit configuration.
It is an object of the present invention to provide a control circuit for a triode X-ray tube that can shorten the time required for cut-off of the polar X-ray tube.

An embodiment of the present invention will be described below with reference to FIG.

In FIG. 2, a series circuit of a capacitor 21 and a diode 22 is connected to both ends of the secondary winding of the transformer 16, and the anode of the diode 22 is connected to the grid G of the triode X-ray tube 11.
The cathodes of the diodes 22 are respectively connected to the cathodes K of the triode X-ray tube 11.

The voltage limiting element 23 connected in parallel to the capacitor 21 is a so-called surge absorber or the like having characteristics similar to a Zener diode.

In this configuration, the capacitor 21 is first charged until the voltage is limited by the voltage limiting element 23.

For this purpose, it is sufficient to apply a pulse to the primary winding of the transformer 16 in such a state that no DC voltage is applied between the anode A and the cathode K of the triode X-ray tube 11, or that the filament is not heated.

The characteristics of the voltage limiting element 23 are selected so that the voltage generated across the charged capacitor 21 becomes the grid bias voltage V0 necessary to cut off the triode X-ray tube 11.

After charging the capacitor 21 in this way, the triode X-ray tube 1
A DC voltage is applied between the anode A and the cathode K of No. 1, and the filament is heated to be in a standby state for X-ray radiation.

At this time, a pulse is applied to the primary winding of the transformer 16.

Then, a voltage is generated in the secondary winding, but as shown in Figure 3, when it is positive, the voltage generated across the capacitor 21 and the voltage generated in the secondary winding have opposite polarities, so they cancel each other out. Therefore, a voltage equivalent to the forward drop of the diode 22 is generated between the anode and cathode of the diode 22, and this voltage is applied to the grid G and cathode K of the triode X-ray tube 11.
It will be applied in between.

Therefore, the triode X-ray tube 11 emits X-rays.

Conversely, when a negative voltage occurs in the secondary winding, it is added to the voltage of the capacitor 21 and is generated between the anode and cathode of the diode 22, as shown in FIG.

Therefore, this added negative voltage is applied between the grid G and cathode K of the triode X-ray tube 11, so that
Block radiation.

By the way, when blocking X-ray radiation, a negative voltage is applied to the grid G, which is the sum of the voltage of the capacitor 21, that is, the grid cutoff voltage ■0, and the voltage generated in the secondary winding. As shown in FIG. 5, the voltage applied to G exceeds voltage 0 and is greatly biased to the negative side.

Therefore, the high voltage cable connected to grid G has a stray capacitance (
Even if a capacitor 20) were present, this stray capacitance would be rapidly charged, resulting in a three-pole
The cutoff time of the wire tube 11 is greatly shortened.

As mentioned above, it is possible to apply a pulse to the primary winding of the transformer 16 and emit X-rays only during the time that this pulse is occurring, but if the pulse is occurring for a long time, the transformer 16 The maximum time for X-ray emission is limited by saturation.

However, within this limit, it is possible to perform control with sufficiently high precision.

As described in the embodiments above, according to the present invention, a control circuit for a triode X-ray tube with an extremely simple circuit configuration is realized without using any electron tubes or active semiconductor elements with poor withstand voltage in the high voltage circuit. can.

Furthermore, since no active elements are used in the high voltage circuit, the power supply required for the active elements is not required.

Furthermore, the diode connected between the grid and the cathode of the triode X-ray tube also serves as a protective element in the event of glow discharge between the anode and the grid.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional example, FIG. 2 is a circuit diagram showing an embodiment of the present invention, FIGS. 3 and 4 are circuit diagrams for explaining each operating state of the embodiment, and FIG. FIG. 5 is a graph showing the transition of the grid bias voltage of the triode X-ray tube. 11...triode X-ray tube, 12,15...
DC high voltage power supply, 13...triode, 16...
...Transformer, 23... Voltage limiting element.

Claims (1)

[Claims] 1. Consists of a transformer, a diode and a capacitor connected in series between both ends of the secondary winding of this transformer, and the voltage generated between the anode and cathode of this diode is transferred to a triode X-ray tube. In addition to the lattice of The voltage applied to the grid causes the triode X-ray tube to emit X-rays, and when the voltage generated in the secondary winding is in the same direction as the charging voltage of the capacitor, the voltage that is the sum of both voltages is A control circuit for a triode X-ray tube in which X-ray radiation is blocked by adding 2. The control circuit for a triode X-ray tube according to claim 1, characterized in that a voltage limiting element for maintaining the charging voltage of the capacitor at a predetermined value is connected in parallel to the capacitor.