JPH07313489A - Gradient magnetic field power source device - Google Patents

Abstract

PURPOSE:To make it possible to output waveforms of arbitrary shapes in spite of high voltages and to minimize energy loss even if the number of the series connecting states of an inverter is increased by changing the connecting states of plural high-voltage sources and a series circuit of a linear amplifier and a gradient magnetic field coil. CONSTITUTION:This gradient magnetic field power source device 1 has two pieces of series connected high-voltage sources HVS 1, HVS 2 which are capable of applying high voltages to the series circuit formed by connecting the linear amplifier Lin in series to the gradient magnetic field coil Lg, electronic switches SW 1 to SW 12 for on and off which are interposed between these high-voltage sources HVS 1, HVS 2 and the series circuit and a control circuit 10 as a control means for changing over the on and off of these electronic switches SW1 to SW12. The continuous arbitrary waveform voltages of, for example, 0 to + or -2100V are applied to the gradient magnetic field coil Lg by changing over the first electronic switches SW 1 to SW 8 by the on and off control signals of the control circuit 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradient magnetic field power supply device used in a magnetic resonance imaging (MRI) system, and more particularly to a gradient magnetic field power supply device suitable for high speed imaging.

[0002]

2. Description of the Related Art In imaging using a magnetic resonance phenomenon, in order to obtain an NMR signal having spatial position information,
It is necessary to apply a pulsed gradient magnetic field. This gradient magnetic field is generated by passing a current pulse through a gradient magnetic field coil that is large enough for a human body to enter. A device for supplying the current is a gradient magnetic field power supply, which is inserted between the gradient magnetic field sequencer and the gradient magnetic field coil.

The gradient magnetic field power source used in the conventional typical imaging has a current of about 100 [A] to 200 [A] and a voltage of about 200 [V] to 300 [V]. The MRI system equipped with is usually long in imaging time of about 10 to 15 minutes. Therefore, in recent years, research and development have been carried out in order to speed up shooting and shorten shooting time. In order to speed up imaging from the perspective of the gradient magnetic field, increase the strength of the pulsed gradient magnetic field and
The fall time should be shortened. However, for that purpose, it is necessary to supply a large current to the gradient magnetic field coil in a short rise / fall time, and it is necessary to prepare a large current / high voltage power source for the gradient magnetic field.

For example, in order to shorten the photographing time to about several seconds, the current is approximately 300 [A] to 400 [A] and the voltage is 200.
An amplifier of about 0 [V] to 3000 [V] is required, but it is extremely difficult to realize this with a current class AB or PWM linear amplifier using MOSFETs and transistors. Even if it is realized, the gradient magnetic field amplifier becomes very large, and there arises a problem that it cannot enter the imaging room of a hospital, for example.

Therefore, as a conventional gradient magnetic field power supply capable of overcoming this situation and achieving high-speed imaging, the one shown in FIG. 11 is known. This power supply is capable of generating a high voltage by adding a simple external circuit to a normal gradient magnetic field amplifier. In detail, as shown in the figure, four switches SW1 to SW4 are connected in a bridge.
And an inverter circuit composed of a high voltage source HVS are connected in series, and a gradient magnetic field coil Lg, which is a load, and a linear amplifier Lin are connected in series. A high voltage is generated by the two-stage series connection of the inverters, and a voltage of the linear amplifier Lin is applied to cause an arbitrary waveform current to flow through the gradient magnetic field coil Lg.

[0006]

However, in the above-mentioned gradient magnetic field power source of the multi-stage serial connection of inverters, the power efficiency when a constant current is passed through the gradient magnetic field coil is low, and due to these, continuous operation for a long time is caused. This caused the inconvenience of being difficult to shoot. The details of this problem are as follows.

In general MRI imaging, the waveform of the current flowing through the gradient magnetic field coil is often a trapezoidal waveform, and the time for which a constant current flows is longer than the time during which the current value changes. Figure 1
When a constant current is passed through the gradient magnetic field coil Lg in the first circuit, the coil current i _Lg passes through two of the semiconductor switches SW1 to SW8 (SW2 and SW6) and two diodes as shown in FIG.

Furthermore, when a large number of inverter circuits are connected in series to generate a high voltage, the current passes through as many semiconductor switches. For example, in the circuit of FIG. 13 in which four inverter circuits are connected in series, as shown in FIG. 14, the coil current i _Lg is four semiconductor switches SW2 and S2.
It passes through W6, SW10, SW14 and four diodes. Generally, a semiconductor switch has a large loss because it has an on-resistance, and the larger the number of switches through which a current passes, the larger the loss.

For example, an IGB transistor (In which an electric current of about 300 A to 400 A can flow and a withstand voltage of about 1000 V (In
In the case of a simulated gate bipolar transistor (IGBT), the on-state voltage is about 3 [V], so a loss of 900 W occurs when a current of 300 A flows. Therefore, this IGB
At least 360 if it has four transistors
A loss of 0 W will occur.

When the number of stages connected in series is large and the power loss is large as described above, the heat radiating portion is inevitably large and the system becomes large. This enlargement is not preferable in view of current needs, and even if the enlargement is allowed, there is a physical limitation and it can be limited to a certain limit. Therefore, if the heat is not sufficiently dissipated, the duty ratio cannot be made large, and the above-described inconvenience that continuous shooting for a long time is difficult occurs.

The present invention has been made in view of the above situation, and can output an arbitrarily shaped waveform at high voltage.
It is an object of the present invention to provide a gradient magnetic field power supply device which has a small energy loss even when the number of serially connected imperator is increased and is suitable for continuous imaging for a long time.

[0012]

In order to achieve the above object, a gradient magnetic field power supply device according to the invention of claims 1 to 6 supplies a coil current for generating a gradient magnetic field to a gradient magnetic field coil according to a command signal. Is a power supply device mounted on a magnetic resonance imaging system, which is connected in series to the gradient magnetic field coil and linearly amplifies the command signal to form the coil current, which is generated by the gradient magnetic field. A linear amplifier that can be supplied to the coil, a power supply unit that can apply a high voltage to the gradient magnetic field coil and that is connected in series with a plurality of high voltage sources, and a full bridge for the series circuit of the linear amplifier and the gradient magnetic field coil. Four sets of switching means connected to each other and each connected in series, a series connection point between the plurality of high voltage sources and each switching The second electronic switches respectively inserted between the plurality of first electronic switches of the stages and the series connection point, and the plurality of first electronic switches are turned on / off in accordance with the waveform of the command signal. The main part is to have a control means.

The gradient magnetic field power supply device according to the present invention is mounted in a magnetic resonance imaging system for supplying a gradient magnetic field coil current to a gradient magnetic field coil in response to a command signal. Power supply,
A linear amplifier connected in series to the gradient magnetic field coil, capable of linearly amplifying the command signal to form the coil current and supplying the current to the gradient magnetic field coil, and applying a high voltage to the gradient magnetic field coil. A power supply means composed of a plurality of possible high voltage sources, a short circuit means connected in parallel to a series circuit of the linear amplifier and the gradient magnetic field coil, and using an electronic switch unit capable of short-circuiting the series circuit; Connection control means including a plurality of electronic switches for controlling the connection state between the voltage source and the series circuit of the linear amplifier and the gradient magnetic field coil and the on / off state of the electronic switch of the short-circuit means according to the waveform of the command signal. The main part is to have.

[0014]

In the gradient magnetic field power supply device according to the present invention, the control means causes the first electronic switches of the four switching means in full bridge connection to respond to the waveform of the command signal. It is turned on / off to switch the electrical connection state between the plurality of high voltage sources and the series circuit of the linear amplifier and the gradient magnetic field coil. As a result, a higher voltage arbitrary waveform can be applied to the gradient magnetic field coil by the sum and difference of the output voltages of the plurality of high voltage sources and the voltages of the linear amplifier. Furthermore, when a constant current is supplied to the gradient magnetic field coil, even if the number of stages of the inverter circuit formed by the high voltage source and the first electronic switch is increased, the number of elements through which the current passes is always the first electron. Since only two switches and two second electronic switches are required, the power loss can be small for the number of stages of the inverter circuit.

Further, in the gradient magnetic field power supply device according to the present invention, the connection control means switches the connection means between the plurality of high voltage sources and the linear amplifier and the series circuit of the gradient magnetic field coils. Therefore, a higher voltage arbitrary waveform can be applied to the gradient coil. In particular, when a constant value of coil current is supplied, the series circuit of the linear amplifier and the gradient magnetic field coil is short-circuited by the short-circuiting means, and the number of electronic switch elements through which the current supplied by the linear amplifier when supplying a constant current passes is further reduced. However, the power loss is further reduced.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS.

The gradient magnetic field power supply device 1 shown in FIG. 1 supplies a pulse current to a gradient magnetic field coil Lg provided in a diagnostic space of a magnet (not shown) for generating a static magnetic field. Specifically, in the gradient magnetic field power supply device 1, as shown in the figure, a linear amplifier Lin is connected in series to the gradient magnetic field coil Lg, and two serially connected high-voltage-applyable series circuits are connected. High voltage sources HVS1 and HVS2 (output voltages are VH1 = 600 [V], respectively in this embodiment)
VH2 = 1200 [V]) and this high voltage source HVS1,
The electronic switch SW1 to SW12 for on / off interposed between the HVS2 and the series circuit and the control circuit 10 as a control means for switching on / off of the electronic switch SW1 to SW12 are provided.

Of these, the linear amplifier Lin is adapted to generate a current obtained by linearly amplifying the input command current Ip. The voltage V of this linear amplifier Lin
L is VL = ± 300 [V]. The electronic switches SW1 to SW12 are the first electronic switches SW1 to SW8.
And second electronic switches SW9 to SW12. Of the first electronic switches SW1 to SW8, the switch S
W1 and SW3, switches SW2 and SW4, switches SW5 and SW7, and switches SW6 and SW8 are respectively connected in series to configure respective switching means, and these four sets of switching means include linear amplifier Lin and gradient magnetic field coil Lg. A full bridge connection is made to the series circuit as shown.

On the other hand, the second electronic switch SW9-
Each SW12 has two high voltage sources, HVS1 and HVS2.
Intermediate connection point a and switching means "SW1, SW3"
To "SW6, SW8" are connected between the intermediate connection points b1 to b4.

As a more specific configuration, as shown in FIG. 2, the first electronic switches SW1 to SW8 are respectively
IGB transistor T1 (to T8) and diode D1
(To D8) are connected in anti-parallel. Also,
Each of the second electronic switches SW9 to SW12 is formed by a diode D9 (to D12) as shown in FIG.

Further, the control circuit 10 includes a linear amplifier Li.
IGB transistors T1 to T of the first electronic switches SW1 to SW8 according to the waveform of the command current ip given to n.
Control signals for switching ON / OFF of 8 are output respectively.

Next, the operation when a current having an arbitrary waveform is passed through the gradient magnetic field coil Lg will be described with reference to FIGS.

First, 0 to ± 300 is applied to the gradient magnetic field coil Lg.
To apply the voltage of [V], the first electronic switch SW
The transistors SW3, SW6 or SW4, SW5 are turned on by the control circuit 10. As a result, only the linear amplifier Lin is electrically connected to the gradient magnetic field coil Lg, and a voltage of 0 to ± 300 [V] is applied. At this time, the gradient magnetic field coil current (hereinafter, referred to as “coil current”) i _Lg flows through the path indicated by the alternate long and short dash line or the broken line in FIG.

The gradient magnetic field coil Lg has ± 300
When a voltage of [V] to ± 900 [V] is applied, the first electronic switches SW1, SW3, SW4, SW6 or SW
The transistors 2, 2, SW4, SW3 and SW5 are switched on, whereby the linear amplifier Lin is connected in series to the first high voltage source HVS1. Therefore, the gradient magnetic field coil Lg has ± 300 due to the sum or difference of the output voltages of the linear amplifier Lin and the first high voltage source HVS1.
A voltage of [V] to ± 900 [V] is applied. Now, for example, the first electronic switches SW1, SW3, SW4, SW
6 is turned on, the coil current i _Lg flows as shown by the alternate long and short dash line or the broken line in FIG. 4 (the alternate long and short dash line indicates a state in which the current is supplied from the first high voltage source HVS1 to the gradient magnetic field coil Lg. On the other hand, the broken line indicates the state in which the current is regenerated from the gradient magnetic field coil Lg to the first high voltage source HVS1).

Further, the gradient magnetic field coil Lg has ± 900
When a voltage of [V] to ± 1500 [V] is applied, the first
Electronic switch SW3, SW5, SW6, SW8 or S
Each of the transistors W4, SW6, SW5 and SW7 is turned on, which causes the linear amplifier Lin to become the second transistor.
Of the high voltage source HVS2. Therefore, the gradient magnetic field coil Lg has ± 900 due to the sum or difference of the output voltages of the linear amplifier Lin and the second high voltage source HVS2.
A voltage of [V] to ± 1500 [V] is applied. Now
For example, the first electronic switches SW3, SW5, SW6, S
If W8 is turned on, the coil current i _Lg is as shown in FIG.
Flows as indicated by the alternate long and short dash line or dashed line (the alternate long and short dash line indicates the second
The current is being supplied from the high voltage source HVS2 to the gradient magnetic field coil Lg, while the broken line shows the current being regenerated from the gradient magnetic field coil Lg to the second high voltage source HVS2).

Further, the gradient coil Lg has ± 1500.
When a voltage of [V] to ± 2100 [V] is applied, the first
Electronic switch SW1, SW3, SW6, SW8 or S
The transistors W2, SW4, SW5 and SW7 are turned on, whereby the linear amplifier Lin is connected in series to the first and second high voltage sources HVS1 and HVS2. Therefore, the gradient magnetic field coil Lg has ± 1500 [V] to ± 210 depending on the sum or difference of the output voltages of the linear amplifier Lin and the first and second high voltage sources HVS1 and HVS2.
A voltage of 0 [V] is applied. If, for example, the first electronic switches SW1, SW3, SW6 and SW8 are turned on, the coil current i _Lg flows as shown by the one-dot chain line or the broken line in FIG. 6 (the one-dot chain line indicates the first and second dashed lines). While the current is being supplied from the high voltage sources HVS1 and HVS2 to the gradient magnetic field coil Lg, the broken line indicates that the current is regenerated from the gradient magnetic field coil Lg to the first and second high voltage sources HVS1 and HVS2. Showing the state).

As described above, the first electronic switches SW1 to S
By switching W8 by the ON / OFF control signal of the control circuit 10, 0 to ± 2100 is applied to the gradient magnetic field coil Lg.
A continuous arbitrary waveform voltage up to [V] can be applied, and a coil current i _Lg having an arbitrary waveform can be passed through the gradient magnetic field coil Lg.

Next, a second embodiment of the present invention will be described with reference to FIG. The gradient magnetic field power supply device according to the first embodiment described above has a configuration in which two high voltage sources are provided.
It has been added to the table.

The output voltages of the three first to third high voltage sources HVS1 to HVS3 in the second embodiment are 1200 V for the first high voltage source HVS1 and the second high voltage source HVS2.
Is 600 [V], and the third high voltage source HVS3 is 210
0 [V] is selected and connected in series. The voltage of the linear amplifier Lin is set to ± 300 [V], and the linear amplifier Lin and the gradient magnetic field coil Lg are connected in series. For this series circuit, switching means "SW1, SW3, SW5", "SW2, S" each consisting of three first electronic switches connected in series are provided.
"W4, SW6", "SW7, SW9, SW11" and "SW8, SW10, SW12" are full-bridge connected. Each of the first electronic switches SW1 to SW12 is formed by an anti-parallel connection of an IGB transistor and a diode as in the first embodiment, and is turned on / off by a control signal from the control circuit 10.

Further, a series connection point of switches in each switching means and the first to third high voltage sources HVS1 to HVS.
Diodes D13 to D20 as second electronic switches are connected between the series connection point of VS3 and as shown in the drawing. For example, switching means "SW1, SW3, SW
5 ”, the connection point between the switches SW1 and SW3 is the second and third high voltage sources HVS2 and HVS2 via the diode D13.
It reaches the connection point of HVS3, and that of the switches SW3 and SW5 reaches that of the first and second high voltage sources HVS1 and HVS2 via another diode D17. The same applies to other switching means.

With this structure, the same effect as that of the first embodiment can be obtained, and 0 to ± 4200 can be obtained.
An arbitrary waveform voltage of [V] and a higher voltage can be generated and applied to the gradient magnetic field coil Lg.

Further, in the gradient magnetic field power supply device 1 according to the second embodiment, even if the number of serially connected stages of the inverter circuit is increased (here, three stages) so that a higher voltage can be generated, the gradient magnetic field coil is provided. There is a special advantage that the loss in the switch element is relatively small when a constant current is passed through Lg. The reason for this is as follows. In order to flow a constant current, in the case of the first embodiment, the electronic switches SW3, SW
6 (or SW4, SW5) should be turned on, and the coil current i _Lg was passing through the two switches at this time (see FIG. 3). On the other hand, even in the case of the second embodiment in which the number of connection stages is increased so that a higher voltage can be generated, a constant current can be supplied by turning on the two electronic switches SW5, SW8 (or SW6, SW7). That is, also in the case of the gradient magnetic field power supply device of the second embodiment, the power loss caused by the electronic switch when a constant current is passed is the same as that of the first embodiment. As described above, in MRI imaging, a trapezoidal wave current is often passed through the gradient magnetic field coil Lg. Therefore, in such a situation, the proportion of the period during which a constant current is inevitably increased,
Since the power loss during this period is less than before,
You can increase efficiency. The degree of improvement in energy efficiency becomes more remarkable as the number of serially connected inverter circuits increases. Therefore, the heat dissipation mechanism can be made smaller, the duty ratio can be increased, and continuous shooting for a long time becomes easy.

Further, a third embodiment will be described with reference to FIGS. 8 and 9. The gradient magnetic field power supply device of the third embodiment is configured to further reduce power loss when a constant current is supplied to the gradient magnetic field coil.

Specifically, as shown in FIG. 8, the short circuit as a short circuit means capable of short-circuiting the series circuit of the linear amplifier Lin and the gradient magnetic field coil Lg in the circuit shown in FIG. 2 described in the first embodiment. 11 is added. This short circuit 11 connects electronic switches SW21 and SW22, which are composed of an anti-parallel connection circuit of an IGB transistor T21 (T22) and a diode D21 (D22) in series, and is connected in parallel to a series circuit of a linear amplifier Lin and a gradient magnetic field coil Lg. It is connected.

In a mode in which a constant current is supplied as the coil current i _Lg , the electronic switch SW21 of this short circuit 11 is used.
Alternatively, the SW 22 is turned on by the control circuit 10 as the connection control means. As a result, the coil current i _Lg flows through the path shown by the alternate long and short dash line in FIG. 9, so the number of current passing switches in this constant current supply mode is reduced to one. Therefore, it is possible to further reduce the power loss when a constant current is supplied.

Further, a fourth embodiment will be described with reference to FIG. In the fourth embodiment, the short-circuit circuit at the time of supplying the constant current described in the third embodiment has the same structure as the conventional circuit shown in FIGS.
It is applied to the gradient magnetic field power supply device shown in FIG.

The gradient magnetic field power supply device 1 shown in FIG.
Electronic switches SW1 to SW4 and first high voltage source HVS
1st inverter circuit INV1 by 1 and electronic switch S
Second inverter circuit INV2 by W5-SW8 and second high voltage source HVS2, electronic switches SW9-SW12
And the third inverter circuit INV3 by the third high voltage source HVS3 and the fourth inverter circuit INV by the electronic switches SW13 to SW16 and the fourth high voltage source HVS4.
4 are connected in series as shown in the figure, and the linear amplifier Lin and the gradient magnetic field coil Lg are inserted in series as shown in the figure. Further, the linear amplifier Lin and the gradient magnetic field coil Lg are provided with first and second short-circuiting circuits 12 and 13 as short-circuiting means capable of short-circuiting each other on both sides thereof. Each of the first and second short circuits 12 and 13 has an electronic switch SW23 or SW24 formed in the same manner as in the third embodiment.
It is constituted by a series circuit of (SW25, SW26), and is set to a coil current i _Lg, and is turned on / off from the control circuit 10 as a connection control means when a constant current is passed.

In the case of the conventional configuration shown in FIG. 13 corresponding to the fourth embodiment, the number of switches through which the coil current i _Lg having a constant value passes is four as shown in FIG. However, in the fourth embodiment, the electronic switches SW23, SW26 or S
A constant coil current i _Lg can be passed through W24 and SW25, and the number of switches is reduced to two. Therefore, the power loss in the mode in which a constant value is supplied as the coil current i _Lg can be significantly reduced as compared with the conventional case.

In each of the above embodiments, the IGB transistor is used as the semiconductor switching element used for the electronic switch, but the present invention is not necessarily limited to such an element, and may be, for example, a power transistor, a GTO thyristor or a MOSFET. Good.

[0040]

As described above, according to the gradient magnetic field power supply device of the present invention, by changing the connection state between the plurality of high voltage sources and the series circuit of the linear amplifier and the gradient magnetic field coil, multi-levels can be obtained. The inverter configuration can be realized and a high voltage arbitrary waveform can be output.On the other hand, even if the number of inverter stages is increased, the circuit loss due to the passing current when supplying a constant value as the coil current can be relatively reduced, and the heat dissipation can be improved. The part can be downsized and the duty ratio can be increased, which is suitable for continuous shooting for a long time.

[Brief description of drawings]

FIG. 1 is a block diagram showing the basic configuration of a gradient magnetic field power supply device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a more specific configuration of the gradient magnetic field power supply device according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing one mode of a coil current flow.

FIG. 4 is an explanatory view showing one mode of a coil current flow.

FIG. 5 is an explanatory diagram showing one mode of a coil current flow.

FIG. 6 is an explanatory view showing one mode of a coil current flow.

FIG. 7 is a block diagram showing a configuration of a gradient magnetic field power supply device according to a second embodiment of the present invention.

FIG. 8 is a block diagram showing the configuration of a gradient magnetic field power supply device according to a third embodiment of the present invention.

FIG. 9 is an explanatory diagram showing a current path when supplying a constant coil current in the gradient magnetic field power supply device according to the third embodiment of the present invention.

FIG. 10 is a block diagram showing a configuration of a gradient magnetic field power supply device according to a fourth embodiment of the present invention.

FIG. 11 is a block diagram showing an example of a conventional gradient magnetic field power supply device.

FIG. 12 is an explanatory diagram showing a current path when a constant value coil current is supplied in the conventional device.

FIG. 13 is a block diagram showing another example of a conventional gradient magnetic field power supply device.

FIG. 14 is an explanatory diagram showing a current path when a constant value coil current is supplied in the conventional device.

[Explanation of symbols]

 1 Gradient magnetic field power supply device 10 Control circuit 11-13 Short circuit D9-D20 Diode HVS1-HVS4 High voltage source Lg Gradient coil Lin Linear amplifier SW1-SW16, SW21-SW26 Electronic switch

Claims (10)

[Claims] 1. A gradient magnetic field power supply device mounted on a magnetic resonance imaging system for supplying a gradient magnetic field coil current to a gradient magnetic field coil according to a command signal, the gradient magnetic field power supply device being connected in series to the gradient magnetic field coil. And a linear amplifier capable of linearly amplifying the command signal to form the coil current and supplying the current to the gradient coil.
A power supply means capable of applying a high voltage to the gradient magnetic field coil, which is connected in series with a plurality of high voltage sources, and a full bridge connection to the series circuit of the linear amplifier and the gradient magnetic field coil, and each of which is connected in series. Four sets of switching means each including a plurality of first electronic switches, and a series connection point between the plurality of high voltage sources and a series connection point between the plurality of first electronic switches of the switching means, respectively. A gradient magnetic field power supply device comprising: an inserted second electronic switch; and a control means for turning on / off the plurality of first electronic switches according to the waveform of the command signal. 2. The power supply means is composed of two high voltage sources having different output voltage values, and each of the four sets of switching means is composed of two first electronic switches. The described gradient magnetic field power supply device. 3. The power supply means is composed of three high voltage sources having different output voltage values, and each of the four sets of switching means is composed of three first electronic switches. 1. The gradient magnetic field power supply device according to 1. 4. The two series connection points between the first, second, and third first electronic switches in each of the switching means are connected to the first, second, and third high voltage sources via a second electronic switch. 2nd of the 3rd and 3rd high voltage source
The gradient magnetic field power supply device according to claim 3, wherein the gradient magnetic field power supply device is individually connected to two series connection points. 5. The gradient magnetic field power supply device according to claim 2, wherein the first electronic switch is formed of an antiparallel connection circuit of a semiconductor switching element and a rectifying element. 6. The gradient magnetic field power supply device according to claim 2, wherein the second electronic switch is formed of a rectifying element. 7. A gradient magnetic field power supply device mounted in a magnetic resonance imaging system for supplying a coil current for generating a gradient magnetic field to a gradient magnetic field coil according to a command signal, the gradient magnetic field power supply device being connected in series to the gradient magnetic field coil. And a linear amplifier capable of linearly amplifying the command signal to form the coil current and supplying the current to the gradient coil.
A power supply unit composed of a plurality of high voltage sources capable of applying a high voltage to the gradient magnetic field coil, and an electronic switch unit connected in parallel to the series circuit of the linear amplifier and the gradient magnetic field coil and capable of short-circuiting the series circuit. A plurality of short-circuit means, a plurality of high-voltage sources connected to the series circuit of the linear amplifier and the gradient magnetic field coil, and an on / off state of an electronic switch of the short-circuit means according to the waveform of the command signal. And a connection control means including an electronic switch of the gradient magnetic field power supply device. 8. A plurality of high voltage sources of the power supply means are connected in series, and a plurality of electronic switches of the connection control means are full-bridged with respect to a series circuit of the linear amplifier and gradient magnetic field coil. A plurality of serially connected first electronic switches forming four sets of switching means and forming each of the switching means; a series connection point between the plurality of high voltage sources and a plurality of the switching means. 8. The gradient magnetic field power supply device according to claim 7, further comprising a second electronic switch interposed between the first electronic switch and a series connection point. 9. The gradient magnetic field power supply device according to claim 8, wherein the electronic switching section of the short-circuit means has a configuration in which a semiconductor switching element and a rectifying element are connected in antiparallel, and the parallel circuits are connected in series in directions opposite to each other. 10. The plurality of high voltage sources are provided side by side with each other, and the plurality of electronic switches of the connection control means form a plurality of inverter circuits with each of the plurality of high voltage sources, and the plurality of inverter circuits. 8. The gradient magnetic field power supply device according to claim 7, wherein the linear magnetic field power supply device is connected in multiple stages in series to the linear amplifier and the gradient magnetic field coil.