JP3053920B2 - High voltage generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 configuration shown in FIG. In FIG. 5, reference numeral 100 denotes an air-core transformer. The center tap of the primary coil 100a of the transformer 100 is connected to the positive 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. In the figure, 1
Reference numeral 07 denotes 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 as a load via a bridge rectifier 108. The chopper transistor 102 and the switching transistors 104 and 105 are driven such that the chopper and the switching are driven in synchronization by a control signal from the control circuit 110 in consideration of the excitation balance in the primary coil 100a of the transformer 100. Has become.

For this reason, voltage resonance is caused 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, and the response is increased. A good high-voltage output can be obtained. At that time, the chopper
The output voltage can be adjusted by changing the duty ratio for the transistor 102 and changing the magnitude of the current flowing through the choke coil 101.

Further, the switching transistor 10
Regarding the transistors 4 and 105, by using a sine-wave arc of the resonance voltage and performing a switching operation in a phase region of a low voltage value at or near zero volt, the transistor 1
It is possible to suppress the occurrence of switching loss and switching noise of the switches 04 and 105.

[0005]

In general, a high-voltage generator for X-rays has a special purpose in that it has a wide output variable range and a capacitive load connection for smoothing the output voltage. Requests. For this reason, even if the optimum switching frequency is determined under certain conditions, for example, when the impedance of the X-ray tube is changed by changing the tube voltage or tube current setting of the X-ray tube, the transformer 100 and the capacitor The natural frequency of the resonance circuit composed of 106 changes, and the operation mode of the resonance circuit changes. In other words, the voltage Vce between the collector and the emitter of one switching transistor 104 in FIG. 5 will be described, for example, from the proper state in FIG.
In this case, the phase shifts to the load variation state, and the transistor 104 must be switched at a phase angle at which the resonance voltage is still high. Also, when a capacitive load is connected to smooth the secondary-side high voltage, the above-mentioned operation mode is greatly changed transiently.

In such a situation, the conventional device does not consider the change in the operation mode of the resonance circuit due to the load fluctuation. Therefore, when the load impedance changes greatly, the resonance mode shifts and the resonance mode shifts as shown in FIG. Thus, the switching timing is shifted. For this reason, there is a problem that the cross-sectional area between the current flowing during conduction and the voltage applied during disconnection increases, and switching loss and noise increase. In addition, miniaturization is hindered due to the necessity of heat radiation measures, high output becomes difficult, and
There was a problem that the ratio decreased. On the other hand, if the load impedance is fixed to a predetermined value or a capacitive load is not connected, the above-mentioned problem does not occur, but the above-mentioned demands for the high voltage generator for X-rays are satisfied. This makes the device less versatile.

The present invention has been made in view of such a problem of the prior art. Even when the impedance of an X-ray tube or the like as a load changes, the switching timing shift due to the change of the resonance mode is automatically performed. Accordingly, it is an object to prevent an increase in switching loss and generation of switching noise.

[0008]

In order to achieve the above object, according to the present invention, a transformer for voltage transformation inserted between a load side and a power supply side, and a supply current to a primary coil of the transformer is intermittently connected. A resonance element detecting means for detecting a voltage value of the voltage resonance state, and an inverter circuit having a switching element for performing the voltage resonance at a predetermined natural frequency between the coil of the transformer and the capacitor. A reference voltage setting unit that sets a reference voltage corresponding to a preset reference phase angle based on a detection value of the resonance state detection unit; and a setting value of the reference voltage setting unit matches a detection value of the resonance state detection unit. Timing signal forming means for forming a timing signal indicating that the switching has been performed, and controlling the switching of the switching element in synchronization with the forming signal of the timing signal forming means. That includes a switching control unit.

[0009]

The switching element interrupts the current supplied from the power supply to the primary coil of the transformer at a predetermined period to increase the frequency, thereby causing voltage resonance between the coil of the transformer and the capacitor. This resonance voltage is directly boosted by a transformer, and then converted into a high DC voltage and supplied to a load. At this time, the resonance voltage that draws a sine wave arc is detected by the resonance state detection means, and a 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 set value with the resonance voltage detection value,
A timing signal indicating that they match is formed. That is, when the timing signal is formed, the observation phase angle of the resonance voltage reaches the reference phase angle. Therefore, the switching element of the inverter circuit is intermittently controlled by the switching control means in synchronization with the timing signal.

Thus, even when an X-ray tube is used as a load and the tube voltage and tube current are changed to change the load impedance on the secondary side of the transformer and the resonance frequency is shifted, the switching timing of the inverter circuit is changed. The (operating cycle) is always forcibly synchronized with the reference phase angle in the changed resonance mode voltage waveform. For this reason,
By preliminarily setting the reference phase angle to an appropriate value near zero volt of the resonance voltage, a state in which switching is performed at the time when the resonance voltage becomes a high value is reliably avoided, and a load fluctuation may occur. However, an increase in switching loss and noise generation can be suppressed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One 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 includes a voltage converter 1a and a switching controller 1b. The voltage converter 1a includes a DC power supply 10 of commercial voltage, a transformer 11 for boosting, a chopper transistor (MOS type) 12 connected between the DC power supply 10 and the transformer 11 for boosting,
A choke coil 13, a commutation diode 14, and switching transistors (MOS type) 15 and 16; a resonance capacitor 17 and a detection transformer 18 connected to the primary side of the step-up transformer 11; A bridge rectifier 19 provided on the secondary side (load side).

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 the chopper transistor 12 and the 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 minus side of the DC power supply 10. A commutation diode 14 is inserted between an intermediate point between the choke coil 13 and the transistor 12 and a minus 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 step-up 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 and the 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, 16 and the capacitor 17 form a voltage resonance type inverter circuit. Step-up transformer 11
Is connected via a bridge rectifier 19 to
The load reaches the X-ray tube 20.

The detecting transformer 18 is a step-down transformer, and its primary coil 18a is connected to the resonance capacitor 1
7 are connected in parallel. Thereby, the capacitor 1
The secondary coil 18b reduces the resonance voltage of several hundred V at both ends to an AC voltage of several V, and supplies the AC voltage to the switching control unit 1b.

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

As shown in FIG. 2, the control circuit 24 includes a full-wave rectifier 30 for inputting a resonance voltage across the resonance capacitor 17.
And a peak hold circuit 31 for holding the peak value of the rectified voltage of the full-wave rectifier 30, and a voltage divider 32 for dividing the output voltage of the peak hold circuit 31, while the output voltage of the voltage divider 32 is Is used as a reference input and the rectified voltage of the full-wave rectifier 30 is used as a comparison input.
And a monostable multivibrator 34 which is energized to the rising edge of the output voltage of the comparator 33 and outputs a rectangular pulse having a fixed time width. The voltage dividing circuit 32 performs voltage division by multiplying the input voltage by a predetermined coefficient (<1). In addition, the monostable multivibrator 34 is connected with an inverter control oscillator 25 and a chopper control oscillator 27 in parallel. Note that the output signal of the monostable multivibrator 34 is also a reset signal of the peak hold circuit 31.

The inverter control oscillator 25 and the chopper control oscillator 27 output a control pulse signal synchronized with the rise of the input voltage to the inverter control circuit 26 and the chopper drive circuit 28, respectively. Among them, the inverter drive circuit 26 drives in synchronization with the control pulse signal of the oscillator 25, and turns on and off the switching transistors 15 and 16 alternately. The chopper drive circuit 28 is driven in synchronization with a control pulse signal of the oscillator 27 to turn on and off the chopper transistor 12.

In this embodiment, the detecting transformer 18 and the full-wave rectifier 30 constitute the resonance state detecting means of the present invention, the peak hold circuit 31 and the voltage dividing circuit 32 constitute the reference voltage setting means, and the comparator 33 And monostable multivibrator 3
Reference numeral 4 denotes 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 specified value set in advance. In this state, the inverter control oscillator 25 and the chopper control oscillator 27
4 oscillates at the same frequency based on the square wave pulse signal, and drives the inverter drive circuit 26 and the chopper drive circuit 28, respectively. As a result, the inverter drive circuit 26 turns on (conducts) and turns off (non-conducts) the switching transistors 15 and 16 alternately at the same cycle Ta / 2, as shown by the solid lines in FIGS. 3 (a) and 3 (b). . The chopper drive circuit 27 sets the chopper transistor 12 to the cycle Tb as shown by the solid line in FIG.
On (period Tb1) and off (period Tb2) are repeated every time. At this time, the ON period Tb1 of the chopper transistor 12 is evenly overlapped with the ON periods of both the switching transistors 15 and 16. From this transformer 11
The excitation balance of the primary coil 11a is well maintained.

For this reason, the power supply voltage of the DC power supply 10 is chopper-converted 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, the on and off of the switching transistors 15 and 16 are switched in accordance with the natural frequency. Therefore, the sine shown by the solid line in FIG. Voltage resonance of the wave waveform 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 and noise generation are minimized. This 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 power energy stored in the voltage resonance type inverter circuit gradually decreases. Therefore, the energy of this reduced amount is used as the switching transistor 1
At the time of conduction of 5 and 16, the conduction period and the chopper
Since the DC power is supplied from the DC power supply 10 via the smoothing coil 13 during the overlapping of the conduction periods of the transistor 12, the resonance state is maintained. Current I _L flowing through the smoothing coil 13,
It becomes like the solid line of FIG.3 (d).

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 power supply state, the resonance voltage v oscillating sinusoidally across both ends of the resonance capacitor 17.
_R is generated as shown in FIG. The resonance voltage v _R is stepped down at a predetermined ratio by the detecting transformer 17, and the stepped down resonance voltage v _R is input to the control circuit 24.

In the control circuit 24, first, the full-wave rectifier 30 performs full-wave rectification of the resonance voltage v _R and converts it into a voltage waveform shown in FIG. When this rectified waveform is peak-held by the peak hold circuit 31, after reaching the peak value, it is converted into a waveform in which the peak value is held, as shown in the voltage waveform of FIG. The reason why the peak value is held in this way is to set a 90-degree phase (that is, the phase of the peak value) in the sinusoidal resonance voltage waveform.

Next, the peak hold voltage waveform is multiplied by a predetermined coefficient in a voltage dividing circuit 32 to obtain a divided voltage waveform shown in FIG.
It is converted as shown in (d). Thereby, a reference voltage value (waveform) having a peak value corresponding to a reference phase angle of 90 degrees or less.
Is formed. The peak value of the reference voltage waveform can be appropriately changed 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 shown by, when the full-wave rectified waveform becomes smaller than the reference voltage waveform, the output of the comparator 33 rises to the logic H level (see FIG. 4E). Energized at the rise of the comparator 33, the monostable multivibrator 34 at the next stage rises its output for a fixed time TB as shown in FIG.
The square-wave pulse signal generated by the start-up is supplied to the inverter control oscillator 25 and the chopper control oscillator 27.
The oscillation timing of the oscillators 25 and 27 is 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 the rising, and becomes a trigger pulse.

Therefore, since the tube voltage and the tube current of the X-ray tube 20 as the load need to be changed, the load side impedance Z changes, and the phase of the resonance voltage is changed, for example, as shown in FIG.
It is assumed that the specified mode shown by the solid line in (e) changes to the phase mode shown by the virtual line. Even in the case where the phase of the resonance voltage is shifted in this way, the control circuit 24 determines the timing of the reference phase angle θ (see FIG. 4) for the shifted resonance voltage waveform by performing the above-described monitoring control. Inverter and chopper control oscillators 25 and 27 at phase angle θ
Oscillating frequency is forcibly and automatically synchronized. 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 dividing 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, and the X-ray dose is increased with high efficiency.
S / N ratio can be improved by suppressing generation of switching noise. In addition, since a capacitive load is provided on the load side of the rectifier 19 to smooth the secondary high voltage and suppress the voltage ripple, the resolution of the CT image,
Resolution also improves. Further, according to the device 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 device can be provided.
Further, it is possible to reduce the size of the device by reducing the capacity of the power supply filter.

In the high voltage generator of the above embodiment, the chopper circuit is mounted before the inverter circuit. However, the chopper circuit does not always need to be mounted.

[0033]

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

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a detailed configuration of a control circuit in FIG. 1;

3 (a) to 3 (e) are waveform diagrams showing timings of a chopper operation and an inverter operation according to one embodiment of the present invention.

4 (a) to 4 (f) are waveform diagrams showing a state of inverter synchronous control according to one embodiment of the present invention.

FIG. 5 is a circuit block diagram showing a configuration of a conventional example, which is partially divided into blocks.

FIGS. 6A and 6B are waveform diagrams for explaining a shift of a resonance mode (phase).

[Explanation of symbols]

 Reference Signs List 10 DC power supply 11 Step-up transformer 15, 16 Switching transistor 17 Resonant 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)

(57) [Claims] A transformer for voltage transformation inserted between a load side and a power supply side, a switching element for intermittently supplying current to a primary coil of the transformer, and a predetermined characteristic between a coil of the transformer. A resonance state detecting means for detecting a voltage value of the voltage resonance state, comprising: an inverter circuit having a capacitor for generating voltage resonance at a frequency;
A reference voltage setting unit that sets a reference voltage corresponding to a preset reference phase angle based on a detection value of the resonance state detection unit; and a setting value of the reference voltage setting unit and a detection value of the resonance state detection unit. A high-voltage circuit comprising: a timing signal forming unit that forms a timing signal indicating that the two signals coincide with each other; and a switching control unit that controls intermittent switching of the switching element in synchronization with the forming signal of the timing signal forming unit. Generator.