JPH084050B2 - Magnetic field generation circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to tilting of, for example, a nuclear magnetic resonance CT for the purpose of deflecting or accelerating an ion beam or an electron beam, or scanning of a nuclear magnetic resonance CT (computer tomography). The present invention relates to a magnetic field generation circuit that excites a magnetic field generation coil such as a magnetic field coil to generate a magnetic field that changes into, for example, a trapezoidal shape.

In order to create a trapezoidally changing magnetic field generation pattern as described above, it is necessary to supply a trapezoidally changing exciting current to the magnetic field generating coil. In order to pass such a trapezoidal excitation current to the magnetic field generation coil, it is only necessary to apply a high voltage from the high voltage power supply to the magnetic field generation coil at the first rising portion of the excitation current, and the low voltage after that. It is only necessary to apply a low voltage from the power supply to the magnetic field generating coil.

Configuration of Conventional Example and Problems Thereof In the conventional magnetic field generating circuit of this type, as shown in FIG. 3, the difference between the output voltage of the command signal source 1 and the voltage of the current detection resistor 10 is taken out by the comparator 2. In addition to the control amplifier 3,
The output of the control amplifier 3 is applied to the control transistor 5, and the output of the switching signal source 13 is applied to the switching transistor 4. Further, the negative electrode of the high-voltage power supply 8 and the positive electrode of the low-voltage power supply 9 are connected, and the anode of the diode 7 is connected to the connection point of the high-voltage power supply 8 and the low-voltage power supply 9, and between the positive electrode of the high-voltage power supply 8 and the cathode of the diode 7. The switching transistor 4 is connected, and a series circuit of a control transistor 5, a magnetic field generating coil 6 and a current detection resistor 10 is connected between the cathode of the diode 7 and the negative electrode of the low voltage power source 9.

Next, the operation of this circuit will be described with reference to FIG. As shown in FIG. 4 (A), the command signal source 1 rises at a constant gradient (rapid excitation period T ₁ ) and maintains a constant state for a predetermined time (flat top period T ₂ ) and then falls at a constant gradient (rapid Degaussing period T ₃ ) When a command signal is given, comparator 2, control amplifier 3, control transistor 5 and current detection resistor
Due to the negative feedback action of the coil 10, a coil exciting current I having a waveform similar to the command signal as shown in FIG. 4B flows through the magnetic field generating coil 6.

This will be described in more detail. This circuit provides the command signal source 1 with the command signal of FIG. 4 (A) and the switching signal source 13 with the drive signal of FIG. 4 (F).

Before time t _0, both the command signal and the drive signal are at the zero level, so both the switching transistor 4 and the control transistor 5 are off, and therefore the coil exciting current I (FIG. 4 (B)) is zero. The voltage V ₀ of the magnetic field generating coil 6 (FIG. 4 (C)) is also zero, and the voltage V _CE of the control transistor 5 is the voltage V _L of the low voltage power supply 9.

During the rapid excitation period T ₁ after the time t ₀ , when the drive signal becomes high level and the command signal rises, the switch transistor 4 is turned on, the diode 7 is reversely applied, and the high voltage power source 8 is turned off. voltage V _H and the control transistor 5 obtained by adding the voltage V _L of the low-voltage power supply 9 is applied to the series circuit of the magnetic field generating coil 6 and the current detection resistor 10, magnetic field generated by the voltage V _H + V _L The impedance of the control transistor 5 is controlled to decrease so that the coil exciting current I (FIG. 4 (B)) flowing through the coil rises with the same gradient as the command signal (FIG. 4 (A)). Rapid excitation period
T ₁ in the energizing V _H + V _L of the high-voltage power supply 8 and the low-voltage power supply 9, for during a fast excitation period has a high impedance of the magnetic field generating coil, can not perform the current control only voltage V _L of the low voltage power supply 9 During this period, most of the voltage V _H + V _L is applied to the magnetic field generating coil 6.

The voltage V ₀ (Fig. 4 (C)) of the magnetic field generating coil 6 rises at time t ₀ and then gradually rises further until time t ₁ . On the other hand, the voltage V of the control transistor 5
_CE (Fig. 4 (D)) appears as V _H + V _L minus V ₀ at this time.

Then, when the command signal becomes a constant level and the drive signal turns off in the flat top period T ₂ after the time t ₁ , the switch transistor 4 turns off, and the control transistor 5, the magnetic field generation coil 6 and the current detection resistor. Only the voltage V _L of the low voltage power supply 9 is applied to the series circuit of 10, and the impedance of the control transistor 5 is adjusted so that the coil excitation current I flowing in the magnetic field generating coil 6 corresponds to the level of the command signal by this voltage V _L. Is controlled. The current can be controlled only by the voltage V _L of the low-voltage power supply 9 during this flat top period because the impedance of the magnetic field generating coil 6 becomes only resistance when the current is constant, and most of the voltage V _L is controlled. For the transistor 5 for use.

The voltage V ₀ of the magnetic field generating coil 6 suddenly drops at time t ₁ ,
After that, the constant value is held until time t ₂ . On the other hand, the voltage V _CE of the control transistor 5 is the voltage V _L minus the voltage V ₀ .

Further, in the rapid demagnetization period T ₃ after time t ₂ , when the command signal falls, the coil exciting current also decreases, the voltage is induced in the magnetic field generating coil 6, and the voltage V _L and the magnetic field generating coil 6 start up. The voltage controls the impedance of the control transistor 5 so that the coil exciting current I flowing through the magnetic field generating coil 6 decreases at the same gradient as the command signal.

Voltage V ₀ is continued increase in the negative direction until time t ₃ sharply turned negative value at time t _2, the at time t ₃ becomes zero. The voltage V _CE surges in the positive direction at time t ₂ and continues to increase until time t ₃ ,
It becomes V _L at time t ₃ .

FIG. 4 (E) shows the loss of the control transistor during the above operation.

Such a conventional magnetic field generation circuit requires the switching transistor 4 for switching the connection / disconnection of the high-voltage power supply 8, and the switching transistor 4 requires the same breakdown voltage and the same current capacity as the control transistor 5. The capacity of the power control unit becomes large, and the switching signal source 13
However, there is a disadvantage that the cost becomes high, the size becomes large, and the weight becomes heavy.

More specifically, the switching transistor 4 needs to handle the rated current while having a high insulation capacity (high withstand voltage), and due to the withstand voltage and the current capacity, it cannot be configured with a single transistor. Since it is necessary to connect a large number of them in series and parallel, the size is increased as a whole, and also in terms of heat dissipation, the size is increased, further increasing the cost.

An object of the present invention is to provide a magnetic field generation circuit capable of achieving cost reduction and reduction in size and weight.

The magnetic field generating circuit of the present invention has a high voltage power supply and a low voltage power supply connected in series with the same polarity, and one end connected to the connection point of the high voltage power supply and the low voltage power supply so that the low voltage power supply has a forward polarity. And a high resistance resistor connected between the high voltage power supply side end of the series circuit of the high voltage power supply and the low voltage power supply and the other end of the diode, and the other end of the diode and the high voltage power supply and the low voltage power supply. , A series circuit of a control transistor, a magnetic field generating coil, and a current detection resistor connected between the series circuit and a low-voltage power supply side end, a command signal source for generating a command signal having a predetermined waveform, and this command A comparator for extracting the difference between the output of the signal source and the voltage of the current detection resistor and supplying it to the control transistor as a base signal, the other end of the diode, the high voltage power supply and the low voltage. And a capacitor connected between the low voltage power supply side end of the series circuit of the power supply and the capacitor.

With this configuration, the conventional switching transistor and its switching signal source can be omitted by simply adding a capacitor and a resistor, and the conventional switching transistor and its switching signal source are added instead. Capacitors and resistors are inexpensive and advantageous in terms of heat dissipation and withstand voltage, and those of large capacity are easy to obtain, so the number can be small, and cost reduction and miniaturization and weight reduction can be achieved.

Description of Embodiments An embodiment of the present invention will be described with reference to FIGS. 1 and 2. This magnetic field generating circuit, as shown in FIG.
The difference between the output of the command signal source 1 and the voltage of the current detection resistor 10 is taken out by the comparator 2 and added to the control amplifier 3, and the output of this control amplifier 3 is applied to the control transistor 5. Further, the negative electrode of the high voltage power source 8 and the negative electrode of the low voltage power source 9 are connected, the anode of the diode 7 is connected to the connection point of the high voltage power source 8 and the low voltage power source 9, and the positive electrode of the high voltage power source 8 and the cathode of the diode 7 are connected. Resistor with very high resistance
12 is connected, and between the cathode of the diode 7 and the negative electrode of the low voltage power source 9, the control transistor 5 and the magnetic field generating coil 6 are connected.
And a series circuit of current detection resistor 10 and diode 7
A capacitor 11 is connected between the cathode and the negative electrode of the low voltage power supply 9.

The operation of this circuit will be described below with reference to FIG. As shown in FIG. 2 (A), the command signal source 1 rises at a constant gradient (rapid excitation period T ₁ ), maintains a constant state for a predetermined time (flat top period T ₂ ), and then falls at a constant gradient ( Rapid demagnetization period T ₃ ) When a command signal is given, comparator 2, control amplifier 3, control transistor 5 and current detection resistor
The negative feedback action of 10 causes a coil exciting current I having a waveform similar to that of the command signal to flow through the magnetic field generating coil 6 as shown in FIG.

This will be described in more detail. This circuit supplies the command signal shown in FIG. 2 (A) from the command signal source 1, so that the coil exciting current I shown in FIG. 2 (B) having a waveform similar to the command signal is caused by the negative feedback action. Before time t _0, the command signal is at the zero level and the control transistor 5 is off.
Therefore, the coil exciting current I (FIG. 2 (B)) is zero, the voltage V ₀ of the magnetic field generating coil 6 (FIG. 2 (C)) is zero, and the voltage V _{C of the} capacitor 12 (FIG. 2 (C)). )) Is charged to V _H + V _L, and the voltage V _CE (FIG. 2D) of the control transistor 5 is the same as V _C.

In the rapid excitation period T ₁ after time t ₀ , the command signal rises, the voltage V _{C of the} capacitor 11 is applied to the series circuit of the control transistor 5, the magnetic field generation coil 6 and the current detection resistor 10, and this voltage V _C The impedance of the control transistor is controlled by _{C so} that the coil exciting current I flowing in the magnetic field generating coil 6 rises with the same gradient as the command signal.

At this time, the voltage V _{C of the} capacitor 11 drops as the charge is discharged, and the voltage V ₀ of the magnetic field generating coil 6 sharply increases at time t ₀ and gradually increases until time t ₁ . At this time, V _C -V ₀ appears as the voltage V _CE of the control transistor 5, and the voltage V _CE
Most of _C is added to the magnetic field generating coil 6.

In the flat top period T ₂ after the time t _1, the impedance of the control transistor 5 is controlled so that the command signal becomes a constant level and the coil exciting current I also becomes constant. In this case, the voltage V ₀ of the magnetic field generating coil 6 is determined only by the resistance component, and the control transistor 5 bears most of the voltage V ₀ . Also, the voltage of the capacitor 11
V _C continues to descend after becoming a flat top and then remains constant. The current I flows from the capacitor 11 while the voltage V _C is high, but when the voltage V _C becomes low, the current I automatically flows from the low voltage power supply 9 through the diode 7. Further, since the high-voltage power source 8 is limited by the resistor 12, only a minute current flows. On the other hand, the voltage V ₀ suddenly drops at time t ₁ and then becomes a constant value until time t ₂ . The voltage V _CE is V _C −V ₀ .

Further, in the rapid demagnetization period T ₃ after time t ₂ , when the command signal falls, the coil exciting current also decreases, the voltage is induced in the magnetic field generating coil 6, and the voltage V _L and the electromotive voltage of the magnetic field generating coil 6 are induced. Thus, the impedance of the control transistor 5 is controlled so that the coil exciting current I flowing through the magnetic field generating coil 6 decreases with the same gradient as the command signal.

The voltage V _C continues to rise after time t ₂ , and the voltage V ₀
It suddenly becomes negative at t ₂ and continues to increase until time t ₃ ,
It becomes zero at t ₃ . Voltage V _CE is continued to increase until time t ₃ soaring at time t ₂ in the positive direction, the V _C at time t _3.

FIG. 2 (E) shows the loss of the control transistor 5 when the above operation is performed.

The capacitor 11 needs to be set to a capacity that can supply sufficient current to the magnetic field generating coil 6 during the rapid excitation period T ₁ .

As described above, in this embodiment, since the high voltage for rapid excitation is given by the charged capacitor 11, the high voltage is applied only during the rapid excitation period, and in the flat top state. Only a minute current flows from the high-voltage power supply 8 through the resistor 12, and a switch transistor for shutting off the high-voltage power supply 8 as in the conventional example is not required, so that cost reduction and reduction in size and weight can be achieved. However, the loss of the control transistor 5 increases to some extent.

According to the magnetic field generating circuit of this embodiment, the conventional switching transistor and its switching signal source can be omitted by simply adding the capacitor 11 and the resistor 12, and the conventional switching transistor and its driving signal can be omitted. Capacitor 11 to be added instead of the switching signal source of
Also, the resistor 12 is inexpensive and advantageous in terms of heat dissipation and pressure resistance, and the number thereof can be small, and cost reduction and downsizing and weight reduction can be achieved.

EFFECTS OF THE INVENTION According to the magnetic field generation circuit of the present invention, the conventional switching transistor and the switching signal source for driving the switching transistor can be omitted simply by adding the capacitor and the resistor.
Capacitors and resistors added in place of conventional switching transistors and switching signal sources for driving them are inexpensive, advantageous in terms of heat dissipation and withstand voltage, and can be reduced in number, cost reduction, and size and weight reduction. can do.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a waveform diagram of each part thereof, FIG. 3 is a circuit diagram of a conventional example, and FIG. 4 is a waveform diagram of each part thereof. 5 ... Control transistor, 6 ... Magnetic field generating coil,
7 ... Diode, 8 ... High-voltage power supply, 9 ... Low-voltage power supply,
11 ... Capacitor, 12 ... Resistor

Claims (2)

[Claims] 1. A high-voltage power supply and a low-voltage power supply connected in series with the same polarity, a diode whose one end is connected to the connection point of the high-voltage power supply and the low-voltage power supply so as to have a forward polarity with respect to the low-voltage power supply, and the high-voltage power supply. A high resistance resistor connected between the high voltage power supply side end of the series circuit of the power supply and the low voltage power supply and the other end of the diode, and the low voltage power supply of the series circuit of the other end of the diode and the high voltage power supply and the low voltage power supply. A series circuit of a control transistor, a magnetic field generation coil and a current detection resistor connected between the side end, a command signal source for generating a command signal having a predetermined waveform, the output of this command signal source and the above A comparator for extracting the difference from the voltage of the current detection resistor and supplying it as a base signal to the control transistor, and a low voltage power supply of the series circuit of the other end of the diode and the high voltage power supply and the low voltage power supply. Magnetic field generation circuit that includes a capacitor connected between an end. 2. The magnetic field generation circuit according to claim 1, wherein the waveform of the command signal is a trapezoidal wave.