JPS58160B2 - X-ray tube current stabilizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for stabilizing the x-ray tube current in an x-ray apparatus.

It is found that the X-ray tube current changes over time, but as the capacity of the X-ray device increases and the tube current increases, this change (which usually decreases) becomes non-negligible.

The purpose of this invention is to elucidate the mechanism of changes in X-ray tube current and to determine the tube current.

When a constant heating power is applied to the filament of an X-ray tube, an equilibrium state is maintained between the heating caused by the heating power and the heat loss due to thermal radiation, thermal conduction, and thermionic emission, and the filament maintains a constant temperature.

In this case, the thermoelectrons emitted from the filament receive a force that returns to the filament due to the space charge caused by this group of electrons, so they do not contribute much to heat radiation.

However, when a tube voltage is applied to the anode of the X-ray tube, these thermoelectrons are emitted and the filament temperature decreases.

As a result, the tube current decreases as shown in FIG. 1a.

Furthermore, in the filament heating circuit used in conventional X-ray apparatuses, a portion of the power flowing from the anode flows as a DC bias current to the secondary coil of the filament transformer.

As a result, due to the characteristics of the filament transformer, this state cannot be maintained, and the heating power is reduced in order to shift to an equilibrium state with the primary side voltage.

The synergistic effect of the above two mechanisms causes the tube current to drop sharply, as shown in Figure 1.

Normally, filament heating circuits have a constant voltage source or constant current source to keep the heating state constant, but the above two mechanisms work in these as well, and similar phenomena occur.

For example, a heating circuit using a constant voltage source connects an AC constant voltage source 31 to the primary coil 11 of a filament transformer through a heating adjustment resistor 32 as shown in FIG.
is connected to the filament 21 of the X-ray tube 2.

If a part of the tube current i flowing from the anode 22 to the filament 21 (temporarily assumed to be 1/2 as shown in the figure) flows to the secondary coil 12 of the filament transformer 1, then this i
/2 becomes a DC bias current, and as shown in FIG. 3, during AC cycles, this DC bias is added at one side (positive potential) and subtracted at the other side (negative potential), resulting in a positive/negative asymmetric waveform.

Next, embodiments of the present invention will be described.

4 to 6 show first to third embodiments applied to a constant voltage control system having an AC constant voltage source.

In FIG. 4, a diode bridge is constructed with four diodes 51 to 54, and the output of the secondary coil 12 of the filament transformer 1 is full-wave rectified to connect the filament 2 of the X-ray tube 2.
I am trying to send it to 1.

The anode 22 is connected to the negative output terminal (or the positive output terminal as shown by the dotted line) of the diode bridge.

In FIG. 4, the tube current is blocked or bypassed by the diode bridge so that it does not flow to the secondary coil 12, thereby improving the adverse effects of the tube current.

In Figure 5, the secondary coil 12 of the filament transformer 1
In addition to a diode bridge of diodes 51 to 54, a series circuit of resistors 61 and 62 is connected to the diodes 51 to 54.

The anode 22 of the X-ray tube 2 is connected to the connection point between the two resistors 61 and 62.

By doing so, the adverse effects caused by the tube current are alleviated.

In Figure 6, the secondary coil 12 of the filament transformer 1
A series circuit of resistors 61 and 62 is connected to the resistors 6 and 6.
The anode 22 is connected to the connection point 1.62.

If these resistors 61 and 62 are made to have the same resistance value, the tube current is completely divided into two by these resistors 61 and 62, and the influence on the primary coil 11 of the transformer 1 can be completely prevented.

Figures 7 to 9 show the fourth to sixth embodiments in which the present invention is applied to a constant current control type heating circuit. A DC power supply 41 is connected to the tap, and transistors 41 and 42 are alternately turned on at both ends to perform constant current control.
is connected.

First, in FIG. 7, an intermediate tap 13 is provided on the secondary coil 12 of the filament transformer 10, and this intermediate tap 13 is connected to the anode 22 of the X-ray tube 2, so that the tube current flows through the intermediate tap 13.
As a result, the tube currents flow in opposite directions in the secondary coil 12, canceling each other out and causing 2
Direct current bias current is not generated in the secondary coil 12.

In FIG. 8, a series circuit of resistors 61 and 62 is connected to the secondary coil 12, and the anode 22 is connected to the connection point of both resistors 61 and 62.

By setting the values of the resistors 61 and 62 to be the same, the influence of the tube current on the primary coil 11 side of the transformer 1 can be completely eliminated.

In FIG. 9, a series circuit of a diode bridge of diodes 51 to 54 and resistors 61 and 62 is connected to the secondary coil 12.

If the ratio of resistors 61.degree. and 62 in FIG. 9 is appropriately selected in accordance with the actual device, the tube current can be kept completely uniform.

In other words, in FIG. 9, when the value of the resistor 62 is decreased, the heating current flowing through the filament 21 and the tube current flowing in the same direction become larger, and the filament 21 is heated up by the amount of blue current, causing the tube to heat up. The current continues to rise.

Conversely, if the resistor 61 is made smaller, the tube current flowing through the filament in the opposite direction to the heating current increases, the heating current is canceled out, and as a result, the tube current decreases.

Therefore, by appropriately setting the ratio of the resistors 61 and 62, it is possible to maintain a completely uniform tube current in the intermediate state described above.

As described above with respect to the embodiments, according to the present invention, the influence of the tube current on the filament heating circuit can be removed, thereby eliminating changes in the tube current over time and providing a highly accurate X-ray apparatus.

[Brief explanation of the drawing]

Figures 1a and b are graphs showing changes in tube current over time, Figure 2 is a circuit diagram to explain the mechanism of tube current change, Figure 3 is a waveform diagram showing the current flowing through the filament, Figure 4, FIG. 5, FIG. 6, FIG. 7, FIG. 8, and FIG. 9 are circuit diagrams showing each of the first to sixth embodiments of the present invention. 1... Filament transformer, 11... Primary coil, 12... Secondary coil, 2... X-ray tube, 21...
- Filament, 22... Anode, 31... AC constant voltage source.

Claims (1)

[Claims] 1. A DC bias for blocking a DC bias current flowing to the secondary coil on the secondary coil side of a filament transformer whose secondary coil is connected to the filament of an X-ray tube and supplies heating current. An X-ray tube current stabilizer comprising a blocking circuit. 2. The X-ray tube current stabilizer according to claim 1, wherein the DC bias blocking circuit comprises a diode bridge. 3. X according to claim 1 or 2, characterized in that the DC bias blocking circuit has two resistors connected in series, and the connection point of both resistors is connected to an anode.
Line tube current stabilizer.