JP2020078102A - Electric power supply and medical image diagnostic device - Google Patents

Abstract

To provide an electric power supply and a medical image diagnostic device that can properly determine the occurrence of latchup.SOLUTION: An electric power supply 2 comprises a latchup determination circuit 241. The electric power supply 2 also comprises a controller 21, a primary-side gate drive circuit 22, an isolation transformer 23, a secondary-side gate drive circuit 24, and an inverter circuit 25. The latchup determination circuit 241 determines occurrence of latchup of the gate drive circuit, through which a gate signal flows for driving the inverter circuit, by examining presence or absence of a known periodic pulse overlapped with the gate signal.SELECTED DRAWING: Figure 2

Description

  Embodiments of the present invention relate to a power supply device and a medical image diagnostic apparatus.

  In a medical image diagnostic apparatus such as a magnetic resonance imaging apparatus, an X-ray CT apparatus, an X-ray diagnostic apparatus, and a phototherapy apparatus, a power supply device having a built-in inverter circuit is often used. In this type of power supply device, noise caused by the switching operation of the power device of the inverter circuit may cause an abnormality in the gate drive circuit that relays the gate signal for driving the inverter circuit. Noise caused by the switching operation includes common mode current, surge voltage, and the like.

  A major abnormality is latch-up due to a parasitic thyristor existing in a CMOS (Complementary Metal Oxide Semiconductor) element that constitutes a gate drive circuit. When latch-up occurs, the output of the gate drive circuit clings to a high potential or a low potential, and the inverter circuit cannot be driven normally. Therefore, it is necessary to determine latchup in the gate drive circuit early and stop the inverter circuit promptly.

JP, 2000-235405, A JP-A-1-246642

  However, in the conventional power supply device, there may be a case where the determination of the occurrence of latch-up may be omitted.

  The problem to be solved by the present invention is to appropriately determine the occurrence of latch-up.

  The power supply device according to the embodiment includes a determination circuit. The determination circuit determines the occurrence of latch-up in a gate drive circuit that relays a gate signal for driving an inverter circuit based on the presence or absence of a known periodic pulse superimposed on the gate signal.

FIG. 1 is a diagram showing an example of a medical image diagnostic apparatus according to an embodiment and a power supply apparatus inside thereof. FIG. 2 is a block diagram showing a configuration example of the power supply device. FIG. 3 is a diagram (1) showing an example of a signal change of each unit in the power supply device. FIG. 4 is a diagram (2) showing an example of a signal change of each unit in the power supply device. FIG. 5 is a diagram (1) showing a comparative example. FIG. 6 is a diagram (2) showing a comparative example.

  Hereinafter, embodiments of a power supply device and a medical image diagnostic apparatus will be described with reference to the drawings. The embodiment is not limited to the following contents. Moreover, the content described in one embodiment or the modification is similarly applied to other embodiments or the modification in principle.

  FIG. 1 is a diagram showing an example of a medical image diagnostic apparatus 1 according to one embodiment and a power supply apparatus 2 inside thereof. In FIG. 1, the medical image diagnostic apparatus 1 is, for example, a magnetic resonance imaging apparatus, an X-ray CT apparatus, an X-ray diagnostic apparatus, a phototherapy apparatus, or the like.

  Inside the medical image diagnostic apparatus 1, a power supply device 2 for supplying power to each unit of the medical image diagnostic apparatus 1 is provided. The power supply device 2 has a built-in inverter circuit, and the power supply device 2 supplies power of a desired voltage or current to each unit of the medical image diagnostic apparatus 1. The power supply device 2 may supply a voltage or current having a predetermined waveform, or may supply a DC voltage or current. When supplying a voltage or current having a predetermined waveform, for example, as a gradient magnetic field power supply of a magnetic resonance imaging apparatus, a voltage or current according to the waveform of the gradient magnetic field applied to the imaging space is output to the gradient magnetic field coil. Used for. Further, in the case of supplying a DC voltage or current, for example, it is used to generate a high voltage to be applied to the X-ray tube of the X-ray CT apparatus.

  FIG. 2 is a block diagram showing a configuration example of the power supply device 2. 2, the power supply device 2 includes a controller 21, a primary side gate drive circuit 22, an insulating transformer 23, a secondary side gate drive circuit 24, and an inverter circuit 25. The controller 21, the primary-side gate drive circuit 22, the insulating transformer 23, the secondary-side gate drive circuit 24, and the inverter circuit 25 may be provided in one housing, or may be divided into a plurality of housings for medical images. It may be provided in the diagnostic device 1.

  The controller 21 has a function of generating a gate signal for controlling the inverter circuit 25 and outputting it to the primary side gate drive circuit 22 of the next stage. The controller 21 compares, for example, a feedback signal such as an output current or an output voltage obtained from the final-stage inverter circuit 25 with an internal reference voltage or the like, and the output current or output voltage or the like of the final-stage inverter circuit 25 is desired. The ON period and the OFF period of the gate signal are changed so that the value becomes. The controller 21 may also serve as part of the control of the medical image diagnostic apparatus 1 other than the control of the power supply device 2.

  The primary-side gate drive circuit 22 has a function of relaying the gate signal output from the controller 21, and is provided at a position close to the controller 21 side, apart from the inverter circuit 25 that is a noise generation source. .. The primary side gate drive circuit 22 includes a periodic pulse superposition circuit 221 and a periodic pulse generation circuit 222. The periodic pulse superposition circuit 221 is an example of a superposition circuit.

  The periodic pulse generation circuit 222 has a function of generating a known periodic pulse for latch-up detection. The periodic pulse superposition circuit 221 has a function of superposing the periodic pulse generated by the periodic pulse generation circuit 222 on the gate signal input from the controller 21. The superposition of the periodic pulse may be performed by simply adding or subtracting the periodic pulse to or from the gate signal, or by modulating the gate signal with the periodic pulse. The modulation includes amplitude modulation (AM: Amplitude Modulation) and frequency modulation (FM: Frequency Modulation).

  The isolation transformer 23 is a transformer in which the primary winding and the secondary winding are insulated, and is upstream of the primary side gate drive circuit 22 and from the secondary side gate drive circuit 24 in which the influence of noise should be eliminated. It has the function of separating the downstream from the direct current. Since the DC component is blocked by the insulating transformer 23, there is no hindrance to passage of the gate signal on which the periodic pulse is superimposed.

  The secondary side gate drive circuit 24 has a function of relaying the gate signal that has passed through the insulating transformer 23 and supplying the gate signal to the inverter circuit 25. The secondary side gate drive circuit 24 includes a latch-up determination circuit 241, a periodic pulse removal circuit 242 in the latch-up determination circuit 241, a gate signal cutoff circuit 243, and a back gate bias generation circuit 244. The latch-up determination circuit 241 is an example of a determination circuit. The periodic pulse removing circuit 242 is an example of a removing circuit. The gate signal cutoff circuit 243 is an example of a cutoff circuit.

  The periodic pulse removal circuit 242 of the latch-up determination circuit 241 removes the periodic pulse from the gate signal on which the periodic pulse is superimposed, which is input through the insulating transformer 23, and determines whether or not the periodic pulse is superimposed. And has a function of outputting a periodic pulse presence / absence signal indicating whether or not the periodic pulse is superimposed. The generation of the periodic pulse presence / absence signal indicating whether or not the periodic pulse is superimposed is performed by, for example, a monostable multivibrator or a high pass filter. The removal of the periodic pulse is performed by, for example, a low pass filter or the like that allows the frequency band of the pulse of the gate signal to pass but does not pass by attenuating the frequency band of the periodic pulse.

  In the case of the monostable multivibrator, the periodic pulse triggers the monostable multivibrator to shift to the unstable state, and the recovery time from the unstable state to the stable state of the monostable multivibrator is longer than the period of the periodic pulse. The output of the monostable multivibrator becomes constant when the periodic pulse arrives continuously, and the output of the monostable multivibrator reverses when the periodic pulse is interrupted. Then, a periodic pulse existence / nonexistence signal indicating whether or not the periodic pulse is superimposed is generated. When using a high-pass filter, the frequency band of the gate signal pulse is attenuated and the frequency band of the periodic pulse is allowed to pass.When the level of the passed signal is high, it indicates that there is a periodic pulse. A low level of can be indicative of the absence of periodic pulses.

  The gate signal cutoff circuit 243 is input from the periodic pulse removal circuit 242 when the periodic pulse presence / absence signal from the periodic pulse removal circuit 242 of the latch-up determination circuit 241 indicates the presence of a periodic pulse. It has a function of outputting the gate signal after the periodic pulse is removed to the subsequent inverter circuit 25. Further, the gate signal cutoff circuit 243 uses the periodic pulse removal circuit when the periodic pulse presence / absence signal does not indicate the presence of the periodic pulse, that is, when the periodic pulse disappears due to the occurrence of latch-up. It has a function of stopping the supply of the gate signal from the inverter 242 to the inverter circuit 25 and outputting the back gate bias input from the back gate bias generation circuit 244 to the inverter circuit 25. In addition, when the periodic pulse disappears due to the occurrence of latch-up, the basic pulse of the gate signal also disappears, and in most cases, it sticks to the high potential or the low potential.

  The back gate bias generation circuit 244 has a function of outputting a back gate bias for promoting the stop of the power device 251 of the inverter circuit 25 when latch-up occurs. For example, when the power device 251 of the inverter circuit 25 is driven by a positive voltage, the back gate bias stays at the gate or base of the power device 251 by setting the back gate bias to a negative voltage. The electric charges that are generated are rapidly lost, and the switching operation is rapidly stopped.

  Note that, depending on the configuration of the power device 251 or the like in the inverter circuit 25, inconvenience may occur if the power device 251 or the like is immediately stopped at the time when the latch-up is detected. Therefore, the back gate bias generation circuit 244 is required. Acquires a timing signal indicating an internal operation state from the inverter circuit 25 and outputs a back gate bias at a desired timing. For example, it is not preferable to suddenly stop the power device 251 or the like in the inverter circuit 25 while a transient current is flowing when the power device 251 is turned on or off. Further, when the power devices 251 and the like in the inverter circuit 25 form an inverter bridge, the operation of turning off the power device 251 at the input stage is also the operation of turning on the other power devices inside, and therefore, simply The operation in the direction of turning off the power device 251 in the input stage cannot be said to be safe. Further, due to the delay of the operation in the inverter circuit 25, it cannot be said that the operation in the direction of simply turning off the power device 251 in the input stage is safe. Therefore, the inverter circuit 25 can be stopped in a safe state by outputting a timing signal indicating a period during which it can be safely stopped in the internal processing.

  The inverter circuit 25 has a power device 251 which is driven by receiving a gate signal from the gate signal cutoff circuit 243 of the secondary side gate drive circuit 24. The power device 251 is a switching element and has an IGBT (Insulated Gate Bipolar Transistor), an FWD (Free Wheeling Diode), or the like. The inverter circuit 25 also has functions such as transformation, rectification, and smoothing when supplying a DC voltage or current.

  FIG. 3 is a diagram showing an example of a signal change of each part in the power supply device 2, and shows a waveform at a normal time when latch-up does not occur. In FIG. 3, from the top, the gate signal output from the controller 21, the periodic pulse output from the periodic pulse generation circuit 222 of the primary side gate drive circuit 22, and the periodic pulse superposition of the primary side gate drive circuit 22 are superimposed. The gate signal output from the circuit 221 on which the periodic pulse is superimposed is output from the periodic pulse removal circuit 242 of the secondary side gate drive circuit 24, and the power device 251 of the inverter circuit 25 via the gate signal cutoff circuit 243. , The gate signal with the periodic pulse removed, respectively. In addition, although the period of the periodic pulse is exaggerated in the figure, the pulse of the gate signal is on the order of several tens of kHz, whereas the periodic pulse is on the order of several MHz. On the other hand, the periodic pulse has a short period of about two digits.

  In the state shown in FIG. 3, the gate signal from which the periodic pulse has been removed is supplied to the power device 251 of the inverter circuit 25, and the power is normally supplied.

  FIG. 4 is a diagram showing an example of a signal change of each part in the power supply device 2, and shows a waveform when a latch-up occurs from a normal state to an abnormal state. 4, the gate signal output from the controller 21 from the upper stage, the periodic pulse output from the periodic pulse generation circuit 222 of the primary side gate drive circuit 22 and the periodic pulse superposition of the primary side gate drive circuit 22 are superimposed. The gate signal output from the circuit 221 on which the periodic pulse is superimposed is output from the periodic pulse removal circuit 242 of the secondary side gate drive circuit 24, and the power device 251 of the inverter circuit 25 via the gate signal cutoff circuit 243. , The gate signal with the periodic pulse removed, respectively.

  Here, if latch-up occurs at time t1 entered for the waveform of the gate signal on which the periodic pulse is superimposed, the gate signal on which the periodic pulse is superimposed is, for example, at a high potential as shown in the figure. Fixed to the side. Therefore, the level does not change at time t2 when the level should originally change depending on the period of the periodic pulse, so that the periodic pulse removing circuit 242 determines that the periodic pulse does not exist and determines latch-up. As a result, at the subsequent time t3, the gate signal cutoff circuit 243 stops the supply of the gate signal to the power device 251 of the inverter circuit 25. The back gate bias from the back gate bias generation circuit 244 is applied to the power device 251 of the inverter circuit 25.

  In this way, after the latch-up occurs, the latch-up is determined within the time period of the periodic pulse, the supply of the gate signal to the inverter circuit 25 is stopped, and the back gate bias causes the power device 251 or the like to operate. Stopping is promoted, and damage to the inverter circuit 25 can be prevented. The occurrence of latch-up is also notified to the medical image diagnostic apparatus 1 accommodating the power supply device 2 from the latch-up determination circuit 241, and post-processing such as a reset operation of the power supply device 2 is performed.

  5 and 6 are diagrams showing a comparative example. In FIG. 5, a gate drive circuit 31, an abnormality detection circuit 32, a gate signal cutoff circuit 33, and an inverter circuit 34 are provided. An abnormality detection circuit 32 is provided independently of the gate drive circuit 31 that relays the gate signal. The abnormality detection circuit 32 controls the gate signal cutoff circuit 33, and the gate signal from the gate drive circuit 31 to the inverter circuit 34 is detected when the abnormality is detected. I'm trying to shut off.

  The abnormality detection circuit 32 inputs the same gate signal as that input to the gate drive circuit 31, and detects an abnormality when an abnormality occurs in the gate signal. The abnormality is also detected when the gate drive circuit 31 and the abnormality detection circuit 32 simultaneously latch up. That is, the abnormality detection circuit 32 is configured to detect an abnormality even when the latch-up itself occurs.

  FIG. 6 shows a specific configuration example of the gate drive circuit 31 and the abnormality detection circuit 32 in FIG. 5. A part of the gate drive circuit 31 is configured by the circuit element 36 of the CMOS IC 35, and the abnormality detection circuit 32 includes A part is configured by the circuit element 37 of the same CMOS IC 35. Since the latch-up is caused by the noise applied from the inverter circuit 34, it is highly possible that the circuit element 36 and the circuit element 37 in the same CMOS IC 35 simultaneously latch up. It should be noted that the abnormality detection circuit 32 does not have a configuration for directly detecting the output signal of the gate drive circuit 31 or the like to detect an abnormality, because the gate drive circuit 31 is independent of another circuit as seen from the abnormality detection circuit 32. This is because carelessly connecting the circuit element to the output signal or the like may cause signal interference, delicately affect the operation, and cause a malfunction.

  However, in FIGS. 5 and 6, even if latch-up occurs in the gate drive circuit 31 or the circuit element 36, the latch-up does not necessarily occur in the abnormality detection circuit 32 or the circuit element 37. In such a case, Latch-up detection may be missed.

  In contrast to the above comparative example, in the embodiment shown in FIG. 2, the presence / absence of a periodic pulse is determined in the periodic pulse removal circuit 242 of the latch-up determination circuit 241 that processes the gate signal. Therefore, the omission of the determination of the occurrence of latch-up does not occur. That is, since the processing of the gate signal and the determination of latch-up can be processed by the circuit of the same signal system, it is not necessary to consider the interference as in the case of adding another circuit, and the original processing function of the circuit can be achieved. As a result, the determination of the occurrence of latch-up can be realized. Further, the presence or absence of latch-up is determined by the presence or absence of the periodic pulse in the gate signal in the secondary side gate drive circuit 24 immediately before the inverter circuit 25. Latch-up in the part can be monitored. In addition, since it is possible to determine the occurrence of latch-up within a time period equivalent to the cycle of the periodic pulse, it is possible to quickly shut off the power device 251 of the inverter circuit 25 and effectively prevent damage to the power device 251. Can be prevented. As described above, the pulse of the gate signal is on the order of several tens of kHz, whereas the periodic pulse is on the order of several MHz, and the determination can be made in an extremely short time after the occurrence of latch-up.

  According to at least one embodiment described above, it is possible to appropriately determine the occurrence of latch-up.

  Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. The embodiments and their modifications are included in the scope of the invention and the scope thereof, and are included in the invention described in the claims and the scope of equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Medical image diagnostic apparatus 2 Power supply device 21 Controller 22 Primary side gate drive circuit 221 Periodic pulse superposition circuit 222 Periodic pulse generation circuit 23 Isolation transformer 24 Secondary side gate drive circuit 241 Latch-up determination circuit 242 Periodic pulse removal circuit 243 Gate signal cutoff circuit 244 Back gate bias generation circuit 25 Inverter circuit 251 Power device

Claims (8)

A determination circuit that determines the occurrence of latch-up in a gate drive circuit that relays a gate signal for driving an inverter circuit, based on the presence or absence of a known periodic pulse superimposed on the gate signal,
A power supply device. A superimposing circuit for superimposing the periodic pulse on the gate signal,
A removal circuit that determines whether or not the periodic pulse is superimposed on the gate signal on which the periodic pulse is superimposed, and generates a gate signal from which the periodic pulse is removed,
The power supply device according to claim 1, further comprising: When the periodic pulse is superposed, the gate signal from which the periodic pulse is removed is supplied to the inverter circuit, and when the periodic pulse is not superposed, the gate signal to the inverter circuit is supplied. Shutoff circuit to stop the supply,
The power supply device according to claim 1 or 2, further comprising: The cutoff circuit outputs a predetermined bias to the inverter circuit when the periodic pulse is not superimposed,
The power supply device according to claim 3. A primary side gate drive circuit and a secondary side gate drive circuit connected via an isolation transformer,
The superposition circuit is provided in the primary side gate drive circuit,
The removal circuit and the cutoff circuit are provided in the secondary side gate drive circuit,
The power supply device according to claim 3. The periodic pulse is superimposed by being added to the gate signal,
The power supply device according to claim 1. The periodic pulse is superimposed on the gate signal,
The power supply device according to claim 1. Medical image including a power supply device having a circuit for determining the occurrence of latch-up in a gate drive circuit that relays a gate signal for driving an inverter circuit, based on the presence or absence of a known periodic pulse superimposed on the gate signal Diagnostic device.

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