JPS5811080B2 - Tube voltage adjustment device for X-ray equipment - Google Patents

Description

[Detailed description of the invention] The present invention relates to a tube voltage adjustment device for an X-ray apparatus.

In an X-ray apparatus, it is necessary to adjust the X-ray tube voltage during fluoroscopy.

Conventional tube voltage regulators are comprised of slide-type single-turn transformers, but they are large in size and suffer from mechanical wear.

It also has drawbacks such as slow response.

Therefore, especially when automatic brightness adjustment is performed by changing the tube voltage in an X-ray television set, the response is slow, which is extremely inconvenient.

An object of the present invention is to provide a tube voltage adjustment device for an X-ray apparatus that improves the above-mentioned conventional drawbacks.

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

In FIG. 1, both ends of the primary winding of a power transformer 1 are connected to an AC power source.

The transformer 20 is for high voltage generation, and its secondary winding is connected to a high voltage generation circuit 21 to supply high voltage to the X-ray tube 22.

Transistors 12 and 13 are Darlington connected and resistor 9
, 10, 14 and the diode 11 constitute a switching circuit.

Amplifier 5 constitutes a comparison circuit together with resistors 6 and 7.

A power supply voltage that has passed through a transformer 2 and a full-wave rectifier circuit 3 is applied to one input of this comparison circuit, and a reference voltage is applied to the other input.

The variable resistor 8 is for changing this reference voltage and is for setting the tube voltage.

The switching circuit controls energization to the primary winding of the high voltage transformer 20 via the full-wave rectifier circuit 19.

A Zener diode 15 and a resistor 16 are connected to one end of the resistor 14.
The other end of this series circuit is connected to the base of a transistor 17 whose collector is connected to the connection point of the resistors 9 and 10.

This transistor 17 acts as a gate for the comparator circuit output, and when the transistor 17 is off, the comparator circuit output is sent to the base of the transistor 12, and when the transistor 17 is on, the comparator circuit output is short-circuited through this transistor 17, and the transistor Not sent to 12 bases.

When switch 4 is OFF, the reference voltage is as shown in Figure 2 A.
As shown in FIG. 2, it is zero, and the output C of the comparator circuit is negative (see FIG. 2C).

Therefore, the transistors 12 and 13 are non-conductive and the high voltage transformer 20 is not energized.

When the switch 4 is turned on at time T0, a reference voltage is applied as shown in FIG. 2A.

Then, this reference voltage and the power supply voltage are compared, and as shown in Fig. 2B, at time T0, the output C of the comparator circuit becomes positive at a phase lower than the power supply voltage S (see Fig. 2C). )
.

However, since transistors 12 and 13 were off until this time T1, the emitter of transistor 13 and D
The full-wave rectified power supply voltage is generated as is between the point and the point D, and the potential at point D as seen from the emitter of the transistor 13 exceeds the threshold Z of the Zener diode 15, as shown in the second diagram. Therefore, current flows from the Zener diode 15 to the base of the transistor 17, turning the transistor 17 ON.

Therefore, even if a comparison circuit output occurs at time T1, it is short-circuited by transistor 17 and does not reach the base of transistor 12, and transistors 12 and 13 remain OFF.

When the phase advances further and the potential at point D falls below the threshold Z at time T2, the transistor 17 turns OFF.
Since it becomes F, the comparison circuit output is sent to the base of transistor 12, and transistors 12 and 13 are turned on.
become.

When transistors 12 and 13 turn on, transistor 1
The potential between the collector and emitter of the transistor 3 becomes almost zero, and the potential at point D is equal to the voltage drop generated in the resistor 14 due to the current flowing between the collector and emitter of the transistor 13 and through the resistor 14.

The voltage drop across this resistor 14 is normally small and the potential at point D does not exceed the threshold Z, so even if the phase advances further and the power supply voltage rises, the transistor 17 remains off.

When the phase advances further and the power supply voltage exceeds the reference voltage S at time T3, as shown in FIG. 2C, the comparator circuit output becomes negative and the base current of the transistor 12 disappears. .13 is T at this point
3 turns it off.

When transistors 12 and 13 are turned off in this way,
The full-wave rectified voltage of the power supply voltage is again generated between the emitter of transistor 13 and point D, which exceeds the threshold value Z, so transistor 1
7 is turned on.

Then, when the phase advances further and the power supply voltage falls again, the comparator circuit output occurs first, but the transistor 17
remains ON, transistors 12 and 13 are OFF, and when the potential at point D falls to the threshold Z, transistor 17 is turned OFF and transistors 12 and 13 are turned ON, and so on. Repeated every half cycle of AC power.

Power is supplied to the primary side of the high voltage transformer 20 during the phase in which the transistors 12 and 13 are ON for each half cycle (between times T1 and T3), and thus phase control is performed. Start phase (time T1
) is determined by the threshold value Z of the Zener diode 15, and the conduction end phase (time T3) is determined by the reference voltage S.

Therefore, conduction always starts in the phase when the power supply voltage is low, and in what phase is the switch 4 turned OFF?
Even if the power supply voltage is N, energization of the high voltage transformer 20 is started from the phase where the power supply voltage is small.

Therefore, various transient problems at the initial stage of power-on can be avoided, and there are no inconveniences such as an increase in discharge current to the high-voltage cable or an excessive current flowing through the transistor 13.

Then, if the reference voltage S is changed by repeatedly adjusting the variable resistor 8, the conduction end phase (time T3) changes,
Since the conduction angle is controlled, the peak value of the voltage applied to the primary winding of the high voltage transformer 20 changes.

The tube voltage of the X-ray tube 22 can be adjusted in this way.

The above operation is a normal operation, but if an excessive current flows through the transistor 13 and the resistor 14 due to an accident on the load side, the voltage drop across the resistor 14 increases, and the voltage at point D increases.

When the voltage at point D exceeds threshold Z, Zener diode 15 becomes conductive and current flows to the base of transistor 17, turning on transistor 17.

Therefore, the transistors 12 and 13 are turned off, preventing excessive current from flowing, and protecting the transistor 13, the load, etc.

By the way, if there is no circuit such as this resistor 14, Zener diode 15, transistor 17, etc., when a large current flows, the voltage at point B will drop, so the conduction angle will be controlled in the direction of expanding, and the current will increase. Tilt in the direction of flow,
Although the transistor 13 and the like would be destroyed, this can be avoided according to the present invention.

As described above with respect to the embodiments, according to the present invention,
It is possible to realize a tube voltage adjustment device for an X-ray apparatus that solves problems when turning on the power and has a protection function against overcurrent.

In the above embodiment, the transistors 12 and 13 are used as elements constituting the switching circuit, but it is also possible to construct the switching circuit using Cyrisk.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram for explaining one embodiment of the present invention, and FIGS. 2A to 2D are time charts showing potentials at points A to D in FIG. 1. 1...Power transformer, 5...Amplifier,
8... Variable resistor for tube voltage setting, 20...
...High voltage transformer, 21...High voltage generation circuit,
22...X-ray tube.

Claims (1)

[Claims] 1 A comparator that compares the power supply voltage applied to the primary side of the high voltage transformer with a reference voltage and produces an output when the power supply voltage is smaller than the reference voltage is connected to the power line of the primary side of the high voltage transformer. a switching means that becomes conductive when the output of the comparator is sent, a variable means that changes the reference voltage, a resistor connected in series with the switching means, and a voltage generated across a series circuit of the switching means. Voltage detection means that detects that the voltage has exceeded a predetermined threshold voltage and generates an output; and gate means that responds to the output of the voltage detection means to cut off the output of the comparator and make the switching means non-conductive. A tube voltage adjustment device for an X-ray apparatus, comprising: