JPH0562789A - High-voltage generating device - Google Patents

Abstract

PURPOSE:To suppress the increase of loss and noise due to switching even when the load side impedance of an X-ray tube and the like is changed and the resonance mode of a voltage resonance type inverter circuit is changed. CONSTITUTION:A detecting transformer 18 is connected to both ends of the capacitor 17 of a voltage resonance type inverter circuit, and the resonance voltage is stepped down and extracted. The resonance detection voltage VR is outputted to a control circuit 24. The resonance voltage VR is full-wave- rectified by the control circuit 24, then it is fed to a comparator as one reference input via a peak hold circuit and a voltage dividing circuit. The full-wave- rectified output is fed to the comparator as the other input. When the full-wave- rectified output is lower than the reference input, the output of the comparator rises to drive a mono-stable multivibrator. Inverter/chopper control oscillators 25, 27 are operated synchronously with the output rise of the multivibrator.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an X-ray diagnostic apparatus and an X-ray C
The present invention relates to a high voltage generator suitable for supplying a high voltage to an X-ray tube in a T device, and more particularly to a high voltage generator using a voltage resonance type inverter.

[0002]

2. Description of the Related Art Conventionally, as a high voltage generator equipped with a voltage resonance type inverter, there is a structure shown in FIG. In FIG. 5, 100 is an air-core transformer, and the center tap of the primary coil 100a of this transformer 100 is connected to the plus side of a DC power supply 103 via a choke coil 101 and a chopper transistor 102. The negative side of the DC power supply 103 is connected to both ends of the primary coil 100a via switching transistors 104 and 105 in parallel, and the collectors of both switching transistors 104 and 105 are connected via a resonance capacitor 106. ing. 1 in the figure
Reference numeral 07 is a commutation diode. On the other hand, both ends of the secondary coil 100b of the transformer 100 are connected to an X-ray tube 109 which is a load via a bridge rectifier 108. The chopper transistor 102 and the switching transistors 104 and 105 are driven in synchronization with the chopper and the switching by a control signal from the control circuit 110 in consideration of the excitation balance in the primary coil 100a of the transformer 100. Is becoming

Therefore, a voltage resonance is generated between the primary and secondary coils 100a and 100b of the transformer 100 having a predetermined element constant and the resonance capacitor 106, and the resonance voltage is directly boosted by the transformer 100 to generate a response. It is possible to obtain a high-voltage output with good performance. At that time,
The output voltage can be adjusted by changing the duty ratio with respect to the transistor 102 and changing the magnitude of the current flowing through the choke coil 101.

Further, the switching transistor 10
With respect to Nos. 4 and 105, the sine wave arc of the resonance voltage is used to perform the switching operation in the phase region of low voltage value at or near zero volt, so that the transistor 1
It is possible to suppress the generation of switching loss and switching noise of 04 and 105.

[0005]

By the way, in a high voltage generator for X-ray, generally, a wide output variable range is taken and there is a special application that a capacitive load is connected to smooth the output voltage. There is a demand. Therefore, even if the optimum switching frequency is determined under a certain condition, when the impedance of the X-ray tube is changed by changing the setting of the tube voltage or the tube current of the X-ray tube, the transformer 100 and the capacitor are changed. The natural frequency of the resonance circuit composed of 106 changes, and the operation mode of the resonance circuit changes. That is, the description will be made with reference to the collector-emitter voltage Vce of one switching transistor 104 in FIG. 5, for example, from the proper state of FIG. 6A to that of FIG. 6B.
The phase shifts to the load fluctuation state of 1 and the switching of the transistor 104 must be performed at a phase angle where the resonance voltage is still high. In addition, even when a capacitive load is connected to smooth the secondary high voltage, the operation mode transiently greatly changes.

In such a situation, since the above-mentioned conventional device does not consider the change of the operation mode of the resonance circuit due to the load change, when the load impedance is largely changed, the resonance mode is deviated and the resonance mode of FIG. As you can see, the switching timing is off. For this reason, there is a problem in that a crossing area between a current flowing when conducting and a voltage applied when disconnecting becomes large, and switching loss and noise increase. In addition, downsizing is hindered due to the need for heat dissipation measures, high output is difficult, and S / N
There was a problem that the ratio decreased. On the other hand, if the load impedance is fixed to a predetermined value or the capacitive load is not connected, the above-mentioned problem does not occur, but the above-mentioned demand for an X-ray high-voltage generator is satisfied. It is impossible to do so, and the device has low versatility.

The present invention has been made in view of the problems of the prior art described above. Even when the impedance of the X-ray tube, which is a load, changes, the shift of the switching timing due to the change of the resonance mode is automatically made. The purpose is to prevent increase of switching loss and generation of switching noise.

[0008]

In order to achieve the above object, in the present invention, a transformer for transformation inserted between a load side and a power source side and a supply current to a primary coil of this transformer are intermittently connected. And a resonance state detecting means for detecting a voltage value in the voltage resonance state, and an inverter circuit having a switching element and a capacitor for generating voltage resonance of a predetermined natural frequency between the coil of the transformer. Reference voltage setting means for setting a reference voltage corresponding to a preset reference phase angle based on the detection value of the resonance state detecting means, and the set value of the reference voltage setting means and the detection value of the resonance state detecting means match. Timing signal forming means for forming a timing signal indicating that the switching signal is formed, and the switching of the switching element is controlled in synchronization with the forming signal of the timing signal forming means. That includes a switching control unit.

[0009]

The current supplied from the power supply to the primary coil of the transformer is intermittently oscillated by the switching element in a predetermined cycle to generate a high frequency, so that voltage resonance occurs between the coil of the transformer and the capacitor. This resonance voltage is directly boosted by the transformer, then converted into a high DC voltage and supplied to the load. At this time, the resonance voltage that draws the arc of the sine wave is detected by the resonance state detecting means, and the reference voltage corresponding to the reference phase angle is set by the reference voltage setting means based on the detected value. At the same time, the timing signal forming means compares the reference voltage setting value with the resonance voltage detection value,
A timing signal is formed which indicates that the two match. That is, when the timing signal is formed, the observed phase angle of the resonance voltage reaches the reference phase angle. Therefore, the switching control means intermittently controls the switching element of the inverter circuit in synchronization with the timing signal.

As a result, for example, when an X-ray tube is used as the load and the setting of the tube voltage or the tube current is changed to change the load impedance on the secondary side of the transformer and the resonance frequency is deviated, the switching timing of the inverter circuit is changed. The (operating period) is always forcibly synchronized with the reference phase angle in the changed resonance mode voltage waveform. For this reason,
By presetting the reference phase angle to an appropriate value near the resonance voltage of 0 volt, it is possible to reliably avoid the state where switching is performed when the resonance voltage reaches a high value, and to avoid load fluctuations. However, increase in switching loss and noise generation can be suppressed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. This embodiment is a high voltage generator for an X-ray tube using a push-pull type voltage resonance inverter.

The high voltage generator shown in FIG. 1 comprises a voltage converter 1a and a switching controller 1b. The voltage conversion unit 1a includes a DC power supply 10 for commercial voltage, a boosting transformer 11, a chopper transistor (MOS type) 12 connected between the DC power supply 10 and the boosting transformer 11,
The choke coil 13, the commutation diode 14, the switching transistors (MOS type) 15 and 16, the resonance capacitor 17 and the detection transformer 18 connected to the primary side of the step-up transformer 11, and the step-up transformer 11. The bridge rectifier 19 is provided on the secondary side (load side).

Of these, the positive side of the DC power supply 10 is connected to the center tap of the primary coil 11a of the step-up transformer 11 via a chopper transistor 12 and a choke coil 13. Both ends of the primary coil 11a are connected to the drains of the switching transistors 15 and 16 as shown, and the sources of the transistors 15 and 16 reach the negative side of the DC power supply 10. A commutation diode 14 is inserted between the intermediate point between the choke coil 13 and the transistor 12 and the negative side of the DC power supply 10. Furthermore, both switching transistors 1
The drains 5 and 16, that is, both ends of the primary coil 11 a of the boosting transformer 11 are connected to each other via a capacitor 17.

The step-up transformer 11 is an air-core transformer, and the total inductance L thereof and the electrostatic capacitance C of the resonance capacitor 17 constitute a voltage resonance circuit having a predetermined natural frequency. Here, the step-up transformer 11, the switching transistors 15 and 16, and the capacitor 17 form a voltage resonance type inverter circuit. Step-up transformer 11
The secondary coil 11b of the
The load reaches the X-ray tube 20.

Further, the detection transformer 18 is a step-down transformer, and its primary coil 18a has a resonance capacitor 1
7 are connected in parallel. This allows the capacitor 1
The resonance voltage of several hundreds of volts across 7 is stepped down to an alternating voltage of several volts by the secondary coil 18b, and the alternating voltage is supplied to the switching controller 1b.

The switching control unit 1b includes a control circuit 24 connected to the secondary coil 18b of the detection transformer 18.
And an inverter control oscillator 25, an inverter drive circuit 26, a chopper control oscillator 27, and a chopper drive circuit 28 connected to the output side of the control circuit 24.

The control circuit 24, as shown in FIG. 2, is a full-wave rectifier 30 for inputting the resonance voltage across the resonance capacitor 17.
And a peak hold circuit 31 that holds the peak value of the rectified voltage of the full-wave rectifier 30, and a voltage divider circuit 32 that divides the output voltage of the peak hold circuit 31, while the output voltage of the voltage divider circuit 32. Is a reference input and the rectified voltage of the full-wave rectifier 30 is a comparison input.
And a monostable multivibrator 34 which is urged to rise by the output voltage of the comparator 33 and outputs a rectangular pulse having a constant time width. The voltage dividing circuit 32 divides the input voltage by multiplying it by a predetermined coefficient (<1). Further, an inverter control oscillator 25 and a chopper control oscillator 27 are connected in parallel to the monostable multivibrator 34. The output signal of the monostable multivibrator 34 also serves as a reset signal for the peak hold circuit 31.

The inverter control oscillator 25 and the chopper control oscillator 27 output control pulse signals synchronized with the rising of the input voltage to the inverter control circuit 26 and the chopper drive circuit 28, respectively. Of these, the inverter drive circuit 26 is driven in synchronization with the control pulse signal of the oscillator 25 to alternately turn on and off the switching transistors 15 and 16. The chopper drive circuit 28 is driven in synchronization with the control pulse signal of the oscillator 27 to turn on and off the chopper transistor 12.

In this embodiment, the detection transformer 18 and the full-wave rectifier 30 form the resonance state detecting means of the present invention, the peak hold circuit 31 and the voltage dividing circuit 32 form the reference voltage setting means, and the comparator 33. And monostable multivibrator 3
4 constitutes a timing signal forming means. Further, the inverter control oscillator 25 and the inverter drive circuit 26 form a switching control means.

Next, the operation of this embodiment will be described with reference to FIGS.

Now, the impedance Z of the X-ray tube 20 is a preset specified value, and in this state, the inverter controlling oscillator 25 and the chopper controlling oscillator 27 are controlled by the control circuit 2.
It is assumed that the inverter drive circuit 26 and the chopper drive circuit 28 are respectively driven by oscillating at the same frequency based on the square wave pulse signal from 4. As a result, the inverter drive circuit 26 alternately turns on (conducts) and off (non-conducts) the switching transistors 15 and 16 in the same cycle Ta / 2 as shown by the solid lines in FIGS. 3 (a) and 3 (b). .. In addition, the chopper drive circuit 27 sets the chopper transistor 12 to the cycle Tb as shown by the solid line in FIG.
The ON (period Tb1) and the OFF (period Tb2) are repeated every time. At this time, the ON period Tb1 of the chopper transistor 12 is equally divided into the ON periods of both the switching transistors 15 and 16. Trance 11
The excitation balance of the primary coil 11a is maintained well.

Therefore, the power supply voltage of the DC power supply 10 is choppered by the chopper transistor 12 to have a high frequency and is supplied to the inverter circuit of the load. At this time,
In the inverter circuit, since the switching transistors 15 and 16 are switched on and off according to the natural frequency, the total inductance of the transformer 11 and the electrostatic capacitance of the resonance capacitor 17 cause the sine shown in the solid line in FIG. Waveform voltage resonance occurs. Now, since the load impedance Z (tube current and tube voltage of the X-ray tube) is a specified value, the voltage resonance mode is also a specified state in which preset switching loss, noise generation, etc. are minimized. The resonance voltage is directly boosted by the transformer 11, rectified by the rectifier 19 and supplied to the X-ray tube 20.

When power is supplied to the X-ray tube 20 in this manner, the electric power energy stored in the voltage resonance type inverter circuit gradually decreases. Therefore, the energy reduced by the switching transistor 1
When conducting 5 and 16, the conduction period and chopper
Since the DC power supply 10 supplies power via the smoothing coil 13 during the overlap of the conduction periods of the transistor 12, the resonance state continues. The current I _L flowing through the smoothing coil 13 is
It becomes like the solid line in FIG.

The secondary output voltage of the transformer 11 is
By changing the duty ratio of the chopper transistor 12, it is changed in a state independent of the resonance mode.

On the other hand, in the above-mentioned power supply state, the resonance voltage v which oscillates in a sinusoidal shape is applied across the resonance capacitor 17.
_R is generated as shown in FIG. The resonance voltage v _R is stepped down by the detection transformer 17 at a predetermined ratio, and the stepped down resonance voltage v _R is input to the control circuit 24.

In the control circuit 24, the full-wave rectifier 30 first full-wave rectifies the resonance voltage v _R and converts it into the voltage waveform shown in FIG. 4B. When this rectified waveform is peak-held by the peak-hold circuit 31, after the peak value is reached, the peak value is converted into a held waveform as in the voltage waveform of FIG. The reason for holding the peak value in this way is to set the phase of 90 degrees (that is, the phase of the peak value) in the sinusoidal resonance voltage waveform.

Next, this peak hold voltage waveform is multiplied by a predetermined coefficient in the voltage dividing circuit 32, and the divided voltage waveform is shown in FIG.
It is converted as shown in (d). As a result, the reference voltage value (waveform) having the peak value corresponding to the reference phase angle of 90 degrees or less
Is formed. The peak value of the reference voltage waveform can be changed as appropriate by changing the coefficient value of the voltage dividing circuit 32.

The reference voltage value thus formed is compared with the full-wave rectified value in the comparator 33. While the full-wave rectified waveform exceeds the reference voltage waveform, the output of the comparator 33 maintains the logic L level, but the timing t _{3 in} FIG.
As indicated by, when the full-wave rectified waveform becomes smaller than the reference voltage waveform, the output of the comparator 33 rises to the logical H level (see FIG. 4 (e)). As the comparator 33 is urged to rise, the monostable multivibrator 34 in the next stage raises the output for a certain time TB as shown in FIG. 4 (f).
The square wave pulse signal generated by this rise is supplied to the inverter control oscillator 25 and the chopper control oscillator 27,
The oscillation timings of the oscillators 25 and 27 are forcibly synchronized with the input pulse signal.

Since the peak hold circuit 31 is reset by the output of the monostable multivibrator 34, the rising signal of the comparator 33 falls immediately after rising and becomes a trigger pulse.

Therefore, since the tube voltage and the tube current of the X-ray tube 20 as a load are required and changed, the impedance Z on the load side changes and the phase of the resonance voltage is, for example, as shown in FIG.
It is assumed that the specified mode shown by the solid line in (e) is changed to the phase mode shown by the phantom line. Even when the phase of the resonance voltage is deviated in this way, the control circuit 24 performs the above-described monitoring control to determine the timing of the reference phase angle θ (see FIG. 4) with respect to the deviated resonance voltage waveform, and to determine the reference. Inverter, chopper control oscillator 25, 27 at phase angle θ
Forcibly and automatically synchronize the oscillation frequency of. As a result, the switch timings of the chopper circuit and the inverter circuit are respectively changed as shown by the phantom lines in FIG.
The same power supply operation as described above is performed. By changing the voltage division ratio of the voltage dividing circuit 32, the reference phase angle θ,
That is, the forced synchronization timing can be easily changed.

As described above, since the switching timing of the inverter circuit always matches the reference phase angle θ of the resonance voltage, it is possible to always return to a suitable resonance mode even if the resonance frequency changes. As a result, the switching loss is reduced, the X-ray dose is increased with high efficiency, and
It is possible to suppress the generation of switching noise and improve the S / N ratio. Further, a capacitive load is provided on the load side of the rectifier 19 to smooth the secondary high voltage and easily suppress the voltage ripple. Therefore, the resolution of the CT image,
The resolution is also improved. Further, according to the apparatus of this embodiment, the variable range of the output current and the output voltage of the X-ray tube can be widened while suppressing the switching loss and the switching noise, so that a highly versatile apparatus can be provided.
Further, the capacity of the power supply filter can be reduced to promote downsizing of the device.

In the high voltage generator of the above embodiment, the chopper circuit is mounted in the preceding stage of the inverter circuit, but this chopper circuit does not necessarily have to be mounted.

[0033]

According to the present invention, the voltage resonance type inverter circuit is provided between the load side and the power supply side, and the reference voltage corresponding to the reference phase angle is set based on the resonance voltage detection value of the inverter circuit. A timing signal indicating that the reference voltage setting value and the resonance voltage detection value match is formed, and the switching of the switching element of the inverter circuit is controlled in synchronization with this timing signal. Therefore, even if the resonance mode is shifted due to the phase shift of the resonance voltage due to the impedance change on the load side, the switching timing of the inverter circuit is automatically synchronized with the reference voltage setting value, that is, the phase suitable for switching. Therefore, it is possible to provide a highly versatile device capable of suppressing an increase in switching loss of the inverter circuit and the occurrence of switching noise, and changing the impedance on the load side without adversely affecting the operation of the inverter.

[Brief description of drawings]

FIG. 1 is a partially block circuit diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a detailed configuration of a control circuit in FIG.

3A to 3E are waveform charts showing timings of a chopper operation and an inverter operation according to an embodiment of the present invention.

FIGS. 4A to 4F are waveform charts showing a state of inverter synchronous control according to an embodiment of the present invention.

FIG. 5 is a partially block circuit configuration diagram showing a configuration of a conventional example.

6 (a) and 6 (b) are waveform diagrams for explaining the shift of the resonance mode (phase).

[Explanation of symbols]

 10 DC power supply 11 Boosting transformer 15, 16 Switching transistor 17 Resonance capacitor 18 Detection transformer 20 X-ray tube 30 Full-wave rectifier 31 Peak hold circuit 32 Voltage dividing circuit 33 Comparator 34 Monostable multivibrator 35 Inverter control oscillator 36 Inverter drive circuit

Claims (1)

[Claims] 1. A transformer for transformation inserted between a load side and a power source side, a switching element for connecting and disconnecting a current supplied to a primary coil of the transformer, and a coil specific to the transformer. A resonance state detecting means for detecting a voltage value of the voltage resonance state, which is provided with an inverter circuit having a capacitor for generating voltage resonance of a frequency,
Based on the detection value of the resonance state detecting means, a reference voltage setting means for setting a reference voltage corresponding to a preset reference phase angle, a set value of the reference voltage setting means and a detection value of the resonance state detecting means A high voltage, comprising: a timing signal forming means for forming a timing signal indicating the coincidence; and a switching control means for controlling on / off of the switching element in synchronization with a forming signal of the timing signal forming means. Generator.