JPH04106900U - Tube voltage control circuit for X-ray imaging equipment - Google Patents

Abstract

(57) [Summary] [Purpose] Differentially amplify the amount of feedback proportional to the X-ray tube voltage value and the target value of the tube voltage, and use the output of this first differential amplifier and the output of the switching regulator for tube voltage control. In an X-ray imaging apparatus equipped with a tube voltage control circuit that further differentially amplifies the feedback amount proportional to the Reduce rise time. [Configuration] Feedback amount H proportional to X-ray tube voltage value
Voltage limiting means 13 is provided to maintain the output value of the first differential amplifier OP1 at a value necessary to bring the X-ray tube voltage to a target value or a voltage close to this when FB is zero. [Effect] The rise time from turning on the X-ray switch until the tube voltage reaches the target value is shortened.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This idea is a tube that shortens the rise time of the X-ray tube voltage in an X-ray imaging device. This relates to voltage control circuits.

0002

[Conventional technology]

Figure 3 shows the configuration of a tube voltage control circuit in a conventional X-ray imaging device. Zuko's circuit will be explained. In the figure, 1 is an X-ray tube, 2 is a high voltage generation circuit, and 3 is a high voltage switching regulator. 4 is a rectifier circuit, 5 is an X-ray switch, 6 is a commercial power supply, 7 is a filament driver The X-ray tube 1 is equipped with a high-voltage inverter circuit 2a, a high-voltage transformer 2b, and a A high voltage tube voltage is generated from a high voltage generation circuit 2 consisting of a clockcroft Walton circuit 2c, etc. Supplied. 8 is a tube voltage fluctuation correction circuit, 9 is a power supply voltage fluctuation correction circuit, and 10 is a pulse voltage fluctuation correction circuit. This is a width modulation circuit.

0003 OP1 is the first differential amplifier provided in the tube voltage fluctuation correction circuit 8, and OP2 is the first differential amplifier provided in the tube voltage fluctuation correction circuit 8. This is a second differential amplifier provided in the power supply voltage fluctuation correction circuit 9. differential amplifier A reference voltage REF that determines the target value of the X-ray tube voltage is applied to the non-inverting terminal of OP1. Detection proportional to the X-ray tube voltage value taken out via resistor R10 is connected to the inverting terminal. Voltage HFB is given via impedance conversion circuit 11, and both are differentially amplified. The widened output is input to the non-inverting terminal of the differential amplifier OP2. Also, differential amplifier OP The switching regulator taken out via the photocoupler 12 is connected to the inverting terminal of 2. A detection voltage RFB proportional to the output of the motor 3 is input, and both are differentially amplified. The output is input to the pulse width modulation circuit 10, and a control signal with a pulse width proportional to the output is input to the pulse width modulation circuit 10. The signal is sent to the switching regulator 3 and its semiconductor element 3a is switched. Ru. This kind of feedback control ensures that it is not affected by fluctuations in power supply voltage. The X-ray tube voltage value corresponding to the voltage set by the reference voltage REF is stably maintained. It is.

0004 Now, when switch 5 is open and no X-rays are output, the voltage HFB = 0 (V), so the output of differential amplifier OP1 is saturated at the control circuit power supply voltage Vcc (V). are doing. Also, when the switching regulator output is 0 (V), the voltage RFB = 0 (V). Therefore, the output of the differential amplifier OP2 is also saturated at Vcc (V). follow Therefore, if this continues, the output pulse width of the pulse width modulation circuit 10 will reach the maximum, If you try to irradiate X-rays in this state and turn on switch 5, a transient effect will occur on the high voltage circuit. Excessive current flows and components such as switching regulator 3 and high voltage generation circuit 2 are damaged. In the worst case, the X-ray tube 1 will be damaged.

[0005] In order to prevent this, the circuit connected to the input side of the pulse width modulation circuit 10 is provided. This is the limiter LIM2 that is While pulling the input to 0 (V), the limiter LIM2 is turned on at the same time as the switch 5 is turned on. By slowly increasing the potential, the output pulse width of the circuit 10 gradually widens. That's what I do. This allows the X-ray tube voltage to rise without overshooting. As the detection voltage HFB begins to rise, the output of the differential amplifier OP1 gradually decreases, and the The back loop becomes stable. However, until the output of differential amplifier OP1 reaches a steady value, differential amplifier OP2 Since the input of O is still high, the voltage rise rate of limiter LIM2 is lower than that of differential amplifier O If the output of P1 is faster than the speed at which it reaches a steady value, the X-ray tube voltage will still be over. I end up shooting. Therefore, the voltage rise speed of limiter LIM2 is considerably slowed down. Therefore, it takes a long time for the X-ray tube voltage to stabilize.

[0006] In order to make this as short as possible, conventionally a limiter LI is installed on the output side of the differential amplifier OP1. M1 is provided, and the non-inverting input of differential amplifier OP2 is set to a constant potential VS (V) in advance. If the switch 5 is turned on in this state, the X-ray tube voltage will be the detection voltage HF. The photovoltaic voltage is set by resistor R9 so that the voltage HS (kV) remains constant without being affected by B. The conversion efficiency of the tocoupler 12 is set. This reduces the X-ray tube voltage to voltage HS(k It quickly rises to V) and then reaches the target X-ray tube voltage value HT (kV). Since the X-ray tube voltage is automatically controlled, the time required for the X-ray tube voltage to reach a steady state is The time is shortened.

[0007] Figure 4 shows the rise of the X-ray tube voltage during the above operation until it reaches a steady state. This is a timing chart of the X-ray tube voltage corresponding to the inverting input of the differential amplifier OP1. voltage, the output voltage of differential amplifier OP1, and the time variation of the non-inverting input of differential amplifier OP2. It shows that

[0008] When switch 5 is turned on at time T1, the X-ray tube voltage is independent of the value of voltage HFB. The voltage rises to HS (kV) at time T2 a short time later. Along with this, the voltage HFB Since the amount of feedback increases, the output of differential amplifier OP1 becomes lower than the voltage Vcc (V). The feedback loop stabilizes when it reaches the target potential VT(V) at time T3. However, the X-ray tube voltage rises from HS (kV) to HT (kV) and enters a steady state. Here, in an attempt to shorten the time to steady state, the voltage rise speed of limiter LIM1 is The potential of the non-inverting input of the differential amplifier OP2 is changed to the time T4 as shown by the broken line in the figure. , the output of the differential amplifier OP1 still reaches the potential VT(V). V) is larger than VT(V) from time T4 to T3, and the X-ray tube voltage is as shown by the broken line. I end up overshooting.

[0009]

[Problem that the idea aims to solve]

Therefore, the non-inverting input of the differential amplifier OP2 is applied at the shortest time from time T1 to time T3. It is necessary to make the X-ray tube voltage reach the steady state by applying The time required for the power supply voltage fluctuation correction circuit 9 to become It will take even longer due to operation delays. This is true for example in dentistry. When the X-ray irradiation time is relatively long, such as with a panoramic X-ray imaging device, This is not a major problem, but when the irradiation time is short, such as in cephalometric standard imaging, The timer expires before the X-ray tube voltage reaches a steady state, and a proper X-ray image cannot be obtained. The problem of not being able to do so is more likely to occur. This idea was made with the aim of improving this problem, and it is a simple The circuit configuration allows the X-ray tube voltage to rise quickly without overshooting. The purpose is to

0010

[Means to solve the problem]

In order to achieve the above purpose, this invention uses a circuit configuration as shown in Figure 3. In the X-ray imaging device equipped with If the output value of the first differential amplifier is not saturated and the X-ray tube voltage is set to the target value or A voltage limiting means is provided to maintain the above output value at the value necessary to obtain a voltage close to Ru.

[0011]

[Effect]

A first differential increase is made to a value necessary to bring the X-ray tube voltage to or near the target value. Since the output value of the width transducer is maintained, the tube voltage will reach the target value after turning on the X-ray switch. The rise time to reach the target is shortened.

0012

【Example】

The embodiment shown in FIGS. 1 and 2 will be described below. In this embodiment, a limiter 13 is provided as a voltage limiting means, as shown in FIG. 1(a). This is connected in parallel to the feedback resistor R3 of the first differential amplifier OP1, and a certain Alternatively, it is inserted between the output side and the reference voltage REF as shown in (b). In addition, other circuits The configuration is the same as that in FIG. As shown by the chain line in Figure 4, X-rays are output. When in standby mode, set the output of differential amplifier OP1 to potential VL (V) and set the limit. This potential VL(V) is kept in the control circuit so that it does not exceed this potential. The voltage is selected to be considerably lower than the power supply voltage Vcc (V) and slightly higher than the target potential VT (V). (Vcc≫VL>VT).

[0013] During the transition period of the rise of the X-ray tube voltage, the differential amplifier O is controlled by the limiter LIM1. Increase the potential of the non-inverting input of P2 from VL (V) to VT (V) in the time (T5 - T1) Therefore, the X-ray tube voltage value is controlled by the feedback control of the power supply voltage fluctuation correction circuit 9. The voltage increases to the target voltage HT (kV) as shown by the chain line. and exceeds HT(kV) Then, the output of the differential amplifier OP1 becomes lower than VL(V), and the tube voltage fluctuation correction circuit 8 is controlled. A steady state is reached under control. T5 in Figure 4 indicates that the X-ray tube voltage increases due to this operation. This is the time when the steady state is reached, and by providing the limiter 13, the limiter LIM1 Since the voltage rise speed can be increased, it is much faster than the conventional time T3. This allows the X-ray tube voltage to rise without overshooting.

[0014] The limiter 13 may be configured as appropriate so as to obtain the above-mentioned operation. Specifically, it is configured as shown in FIG. 2, for example. This is an example of case (a) in Figure 1. The transistor Tr is connected in parallel to the feedback resistor R3 as shown in FIG. child According to the circuit, in the steady state, the output of the differential amplifier OP1 is equal to the reference voltage REF. Therefore, the potential VL (V) is set slightly higher than the reference voltage REF. Considering the voltage drop between the emitter and base of the transistor Tr, It is selected to be approximately VL=REF+Vbe(V). Vbe is emitter base The voltage between

[0015]

[Effect of the idea]

As is clear from the above explanation, the tube voltage control circuit of this invention can control the X-ray tube voltage value When the feedback amount proportional to is zero, the output value of the first differential amplifier is saturated. First, set the voltage limiter to the value necessary to bring the X-ray tube voltage to the target value or a voltage close to it. It was designed to be maintained in stages. Therefore, by simply adding a simple circuit, the tube voltage can be adjusted to the target value after turning on the X-ray switch. It is possible to shorten the rise time to reach the It is said that proper X-ray pictures cannot be obtained with X-ray imaging equipment used for short irradiation times. problem is resolved. Furthermore, even if the detection voltage HFB becomes zero during X-ray irradiation, the tube voltage remains Since the target HT (kV) is never exceeded, if some accident occurs during X-ray irradiation, Even if the feedback loop were to break, excessive current would flow and high voltage would occur. This also has the effect of not damaging the circuit or the X-ray tube.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a main part of an embodiment of this invention.

FIG. 2 is a specific circuit diagram of main parts of the same embodiment.

FIG. 3 is a circuit diagram of a tube voltage control circuit in a conventional X-ray imaging apparatus.

FIG. 4 is a timing chart for explaining the operation.

[Explanation of symbols]

1 X-ray tube 2 High pressure generation circuit 3 High voltage switching regulator 5 X-ray switch 8 Tube voltage fluctuation correction circuit 9 Power supply voltage fluctuation correction circuit 10 Pulse width modulation circuit 13 Limiter OP1 First differential amplifier OP2 Second differential amplifier Tr Transistor HT Target value of X-ray tube voltage HFB Feedback amount of X-ray tube voltage RFB Feedback amount of switching regulator output REF Reference voltage

Claims (1)

[Scope of utility model registration request] 1. A first differential amplifier that differentially amplifies a feedback amount proportional to an X-ray tube voltage value and a target value of tube voltage, and a switching regulator that controls the output of this differential amplifier and the tube voltage. and a second differential amplifier that further differentially amplifies the amount of feedback proportional to the output, and is configured to increase or decrease the output of the switching regulator according to the output value of the second differential amplifier. A tube voltage control circuit of the apparatus that does not saturate the output value of the first differential amplifier when the feedback amount proportional to the X-ray tube voltage value is zero, and keeps the X-ray tube voltage at or close to the target value. 1. A tube voltage control circuit for an X-ray imaging apparatus, characterized in that a voltage limiting means is provided for maintaining the output value at a value required for the voltage.