JPH02131364A - Resonance-type dc-dc converter - Google Patents

Abstract

PURPOSE:To reduce the loss of switches of an inverter by suppressing the rise of a voltage to be applied to arms only by means of capacitance through making the initial current of the arms of the inverter negative. CONSTITUTION:A frequency and a phase difference capable of making the initial current negative at the time of turning-ON of four arms (52, 56), (53, 57), (54, 58), (55, 59) of an inverter 40 are generated by combination of output voltage and load current. Then, the inverter 40 is operated according to the frequency and phase difference generated in the manner of corresponding to the set output voltage and load current. Thus, it is possible to reduce the loss of switches 52-55 of the inverter 40.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a power converter, and particularly to a low-loss resonant DC converter.
-Regarding a DC converter.

[Conventional technology]

Switching power supplies are widely used to make power supplies smaller, lighter, and more efficient. However, switching power supplies that are currently widely used are basically PWM controlled. Therefore, the voltage and current waveforms handled are square waves, which causes the following problem.

(1) The loss in the switching element during switching is large.

(2) The upper limit of the converter's operating frequency largely depends on the switching time of the switching element. (3) Switching noise is likely to occur.

As a solution to these problems, resonant converters are being developed that insert a resonant element into a part of the converter to make the voltage or current waveform sinusoidal, thereby reducing the load on the switching element during switching.

There is a phase difference control method as a method of controlling the output voltage of this resonant converter. The operation of this system is described in detail in Japanese Patent Laid-Open No. 190556/1983, but the operation will be briefly explained below using the time charts of FIGS. 3 and 4.

FIG. 3 shows the main circuit configuration of the resonant converter. 1 is a DC voltage source, 2 to 5 are switches 2a, 3a, 4a, 5a
and an arm consisting of diodes 2b, 3b, 4b, and 5b connected in antiparallel to each switch, and
5 constitutes an inverter. 10 is an inductance, 11 is a capacitance, 13 is an aftereffect rectifier circuit consisting of diodes 13a to 13d, and 14 is a full wave rectifier circuit 1.
3 is a capacitance for smoothing the output, and 15 is a load.

In FIG. 4, (a), (b), (c), and (d) indicate on/off periods of the switches 2a, 5a, 3a, and 4a, respectively. As shown in the figure, switch 2a and switch 5
a is turned on with a phase difference α, and the on periods of the switches 3a and 4a also have a phase difference α. Also, switch 2
a and switch 3a, and switch 4a and switch 5a
are turned on alternately with a phase of 180''.

In the above operation, the period (tb3 to tb4) during which the switches 2a and 58 are on simultaneously. and switch 3a
Since power is supplied from the power supply only during the period (tb6 to tb7) in which inverters and 48 are simultaneously on, the output voltage waveform of the inverter becomes a square wave with positive and negative peak values only during the above period.

Therefore, the phase difference α between switch 2a and switch 5a,
Alternatively, by changing the phase difference α between the switch 3a and the switch 4a, the period during which each switch is simultaneously turned on can be changed, and the power supplied to the load can be controlled.

Figure 5 shows the relationship between phase difference and output voltage. [Problems to be Solved by the Invention] First, if the turn-on is not delayed, the first arm consisting of the switch 2a and the anti-parallel diode 2b and the switch 3a
Attention will be paid to the operation of the second arm consisting of the anti-parallel diode 3b and the anti-parallel diode 3b. As shown in FIG. 4, the current flowing in the first arm starts at the time tb when the ON signal is input to the switch 2a.
It is negative in l. Therefore, in this case, switch 2
The voltage applied to a is only the on-voltage of the diode 2b and is approximately zero. When the current changes from negative to positive and the current starts flowing through the switch 2a, the loss of the switch 2a is zero because it is the product of the voltage and current at that time.

However, at tb4 when switch 2a turns off, the current in switch 2a is positive. Figure 6 shows the operation from when switch 2a starts turning off until the current becomes zero.As shown in the figure, the voltage of the switch begins to increase before the current becomes zero, so this current and voltage Switch 2a causes loss. The above operation is the same for the second arm.

In order to reduce this loss, for example, as shown in FIG.
2 or a circuit called a snubber circuit consisting of a capacitance 21, a resistor 22, and a diode 23 as shown in FIG. When these snubber circuits are used, the voltage rise when the switch is turned off is suppressed, and the switch loss at the time of turn-off can be reduced.

However, in the snubber circuit as described above, the charge accumulated in the capacitance 21 when the switch is off is discharged through the switch 20 and the resistor 22 when the switch 20 is turned on, so the resistor 22 causes a loss. occurs. Since the resistor 22 suppresses the maximum value of the current at this time, if the resistor 22 is not present, an excessive current will flow and destroy the switch.

The loss due to the resistor 22 occurs each time the switch 20 is repeatedly turned on and off, so in an inverter like the one shown in FIG. 3, the loss of the switch increases in proportion to the frequency of the inverter. Particularly in resonant converters, it is common to increase the frequency in order to make the device smaller and lighter, resulting in very large switching losses.

On the other hand, the operation of the third arm consisting of the switch 4a and the anti-parallel diode 4b whose turn-on is delayed, and the fourth arm consisting of the switch 5a and the anti-parallel diode 5b will be considered.

In the example shown in FIG. 4, the current in the switch becomes zero at tbs while the on signal of the switch 5a is being output (tb3 to tb6), and a negative current flows after tb5. In other words, current flows through the anti-parallel diode 5b.

Next, at time tb6, the on signal to the switch 5a disappears, and the switch 4a starts turning on. Then, the current that had been flowing through the anti-parallel diode 5b is commutated to the switch 4a, and the anti-parallel diode 5b is reverse biased and turned off. However, at this time, the diode cannot be turned off instantaneously, and a current called a recovery current flows through the diode until the junction capacitance of the PN junction is charged. Therefore, while this recovery current is flowing, the third arm and the fourth arm are in the same state as being short-circuited, and an excessive current flows, not only increasing the loss of the switch but also potentially destroying the switch. be. This operation is similar when the switch 4a is turned off.

As mentioned above, the operations of the first arm and the second arm and the operations of the third arm and the fourth arm are different. (a) First and second arms: Increase in loss due to snubber circuit ( Mouth) Third and fourth arms: There is a problem of arm short circuit due to diode recovery current.

[Purpose of the invention]

The present invention was made in view of the above-mentioned problems, and its objectives are: (1) to reduce loss in switching elements of an inverter;
Highly efficient resonant DC-DC converter.

■ A highly reliable resonant DC-DC converter that sets the initial current at turn-on of the inverter arm to be negative, prevents arm short circuits, eliminates overcurrent to the switching elements, and does not damage the switching elements.

■ In addition to the above ■ and ■, there is also a resonant DC-DC converter with good output voltage stability.

Our goal is to provide the following.

[Means to achieve the purpose]

The above object is achieved by the following inventions, objects (■) and (■) are achieved by the following first and second inventions, and object (■) is achieved by the following first and second inventions.
This is achieved by the following third and fourth inventions.

The first invention has a first series connection body consisting of a DC power supply, a first switch connected to the positive pole of the DC power supply, and a second switch connected to the negative pole of the DC power supply, and a second switch connected to the positive pole. A third switch and a fourth switch connected to the negative electrode have a second series connection body connected in parallel to the first series connection body, and further have an opposite connection body connected to the first to fourth switches, respectively. an inverter having first to fourth diodes connected in parallel, receiving direct current from the direct current power source and converting it to alternating current; an inductance connected to the output of the inverter; and a capacitance connected in series with the inductance. A resonant DC-DC converter comprising: a transformer connected in series with the inductance and capacitance to insulate the output; a rectifier that converts the output of the transformer into direct current; and a load connected to the output of the rectifier.
In the converter, capacitances are connected in parallel to the first to fourth switches of the inverter, and operating phases of the first to fourth switches are determined according to setting signals for a voltage to be applied to the load and a current to be passed to the load. a frequency determining circuit that controls the operating frequencies of the first to fourth switches in accordance with setting signals for the voltage applied to the load and the current flowing through the load; a frequency phase control circuit that controls the operating phase and frequency of the first to fourth switches of the inverter according to the output signal from the frequency determining circuit;
The third and fourth switches are turned on alternately with a phase difference of 80°, and the third and fourth switches are similarly turned on with a phase difference of 1800 degrees. By changing the phase difference between when the first switch is turned on and the third switch is turned on, the power supplied to the load is controlled, and an on signal is input to the first to fourth switches of the inverter. The second invention is characterized in that the inverter is operated at a frequency and a phase difference such that current flows through the first to fourth diodes, The first series connection body includes a first switch connected to the negative electrode thereof and a second switch connected to the negative electrode thereof, and a third switch connected to the positive electrode and a fourth switch connected to the negative electrode. a second series connection body connected in parallel to the first series connection body; further comprising first to fourth diodes connected in antiparallel to the first to fourth switches, respectively; an inverter that receives direct current from a power source and converts it into alternating current; an inductance connected to the output of the inverter; a capacitance connected in series to the inductance; and a transformer connected in series to the inductance and capacitance to isolate the output. , a resonant DC-DC having a rectifier that converts the output of the transformer into direct current, and a load connected to the output of the rectifier.
The converter includes capacitances connected in parallel to the first to fourth switches of the inverter, a current detector that detects the output current of the inverter, and a frequency of the output current of the inverter based on the output signal of the current detector. a frequency detector that outputs a synchronized signal; a phase determining circuit that controls the operating phases of the first to fourth switches according to setting signals for the voltage applied to the load and the current flowing through the load; a frequency phase control circuit for controlling the operating frequency of the inverter and the operating phases of the first to fourth switches of the inverter according to the output signal from the circuit and the output signal from the frequency detector; 1 switch and 2nd switch are 1
The third and fourth switches are turned on alternately with a phase difference of 80", and the third and fourth switches are similarly turned on with a phase difference of 180". The power supplied to the load is controlled by changing the phase difference between when the second switch is turned on and the third switch is turned on.

A third invention has a first series connection body consisting of a DC power supply, a first switch connected to the positive pole of the DC power supply, and a second switch connected to the negative pole of the DC power supply, and a second switch connected to the positive pole. A third switch and a fourth switch connected to the negative electrode have a second series connection body connected in parallel to the first series connection body, and further have an opposite connection body connected to the first to fourth switches, respectively. an inverter having first to fourth diodes connected in parallel, receiving direct current from the direct current power source and converting it to alternating current; an inductance connected to the output of the inverter; and a capacitance connected in series with the inductance. A resonant DC-DC converter comprising: a transformer connected in series with the inductance and capacitance to insulate the output; a rectifier that converts the output of the transformer into direct current; and a load connected to the output of the rectifier.
In the converter, the operating frequency of the first to fourth switches is determined according to capacitances connected in parallel to the first to fourth switches of the inverter, and setting signals for the voltage applied to the load and the current applied to the load. a frequency determining circuit that controls the load; a voltage divider that detects the voltage applied to the load;
An error amplification circuit which inputs the detection signal from this voltage divider and a preset target voltage signal, amplifies the difference between them, and determines the operating phase of the first to fourth switches of the inverter based on this error; and this error amplification circuit. The operating frequency of the inverter and the first frequency of the inverter depend on the output signal from the circuit and the output signal from the frequency determining circuit.
and a frequency phase control circuit for controlling the operating phase of the fourth switch, and the first switch and the second switch of the inverter are connected to one another.
The third and fourth switches are turned on alternately with a phase difference of 8o6, and the third and fourth switches are similarly turned on with a phase difference of 1800 degrees. The power supplied to the load is controlled by changing the phase difference between when the switch is turned on and when the third switch is turned on, and when an on signal is input to the first to fourth switches of the inverter. The invention is characterized in that the inverter is operated at a frequency such that current flows through the first to fourth diodes.

And, the fourth invention has a first series connection body consisting of a DC power supply, a first switch connected to the positive pole of the DC power supply, and a second switch connected to the negative pole thereof, and connected to the positive pole. a third switch connected to the negative electrode and a fourth switch connected to the negative electrode, and a second series connection body connected in parallel to the first series connection body, and further connected to the first to fourth switches. an inverter having first to fourth diodes connected in antiparallel to each other, receiving DC from the DC power source and converting it to AC; an inductance connected to the output of the inverter; and an inductance connected in series with the inductance. a resonant DC-type DC-DC, which has a capacitance connected to the inductance and the capacitance, a transformer connected in series to the inductance and the capacitance and insulated from the output, a rectifier that converts the output of the transformer to direct current, and a load connected to the output of the rectifier. D.C.
The converter includes capacitances connected in parallel to the first to fourth switches of the inverter, a current detector that detects the output current of the inverter, and a frequency of the output current of the inverter based on the output signal of the current detector. A frequency detector that outputs a synchronized signal, a voltage divider that detects the voltage applied to the load, and a detection signal from this voltage divider and a preset target voltage signal are input and the difference is amplified and this error is an error amplification phase determining circuit that determines the operating phases of the first to fourth switches of the inverter; and an operating frequency of the inverter according to the output signal from the error amplification phase determining circuit and the output signal from the frequency detector. and a frequency phase control circuit for controlling the operating phases of the first to fourth switches of the inverter, the first switch and the second switch of the inverter being one
The third and fourth switches are turned on alternately with a phase difference of 806 degrees, and the third and fourth switches are similarly turned on with a phase difference of 180 degrees. The power supplied to the load is controlled by changing the phase difference between when the first switch is turned on and the third switch is turned on.

[Technical principle of the present invention]

The present invention is based on a technical principle that solves the problems (a) and (g) above. Therefore, the principle will be explained first.

First, (1) first arm and second arm: the increase in loss due to the snubber circuit is solved. In the snubber circuits shown in FIGS. 7 and 8, loss occurs due to the resistance when discharging the charge of the capacitance.

Here, we will consider the operation of the first arm and the second arm again. As mentioned above, as shown in FIG. 4, when the ON signal to the first arm is input, current flows through the anti-parallel diodes before current flows through each switch. Therefore, when current flows through the anti-parallel diode, the voltage applied to that arm becomes zero. therefore,
It can be seen that when such an operation is performed, there is no need for a resistor to consume the charge of the capacitance as shown in Figures 7 and 8. In other words, even with a configuration in which a capacitor is connected in parallel with the switch as shown in Figure 10, the voltage rise at turn-off can be suppressed, and the charge in the capacitance can be discharged together with the load current before current starts flowing to the anti-parallel diode. becomes possible.

Next, consider (2) third arm and fourth arm: arm short circuit due to diode recovery current.

FIG. 11 shows the relationship between the frequency of the inverter and the value of the initial current when the ON signal is input to the third or fourth arm (hereinafter simply referred to as the initial arm current). As shown in the figure, as the frequency of the inverter increases, the initial current in the arm shifts from positive to negative. In other words, since the initial current of the arm becomes negative, the operation is the same as that of the first arm and the second arm, so the snubber circuit similar to the first arm and the second arm is used without causing an arm short circuit. , loss can be reduced.

As mentioned above, when performing phase difference control for power control,
By changing the operating frequency of the inverter, the initial current at turn-on of the four arms of the inverter can be made negative. (1) At turn-on, the applied voltage to the switch is zero and the current is also zero. Therefore, switching loss can be reduced to zero.

(2) With the arm at turn-off. The charge of the capacitance connected in parallel can be discharged together with the load current, and the loss of the snubber circuit can be reduced to zero.

(3) At turn-off, the capacitance connected in parallel with the arm allows the rise of the voltage applied to the switch to be delayed, resulting in low switch loss. It can be reduced.

Therefore, it is possible to construct a converter with low loss and less burden on the switching elements.

FIG. 12 shows the relationship between the phase difference, the output voltage, and the frequency at which the initial current at turn-on of the arm can be made negative. Note that the frequency is expressed as the ratio F i /F o between the inverter frequency Fi and the resonance frequency FO.

[Effect]

The operation of the present invention will be explained below. The first invention uses a combination of output voltage and load current to
A device that generates a frequency and phase difference that can make the initial current at turn-on of two arms negative, and operates an inverter according to the frequency and phase difference in response to a set output voltage and load current. It is.

The second invention generates a phase difference of the inverter by a combination of an output voltage and a load current, and operates the inverter according to the phase difference corresponding to the set output voltage and load current. Furthermore, by detecting the point in time when the output current of the inverter becomes zero and operating the inverter in synchronization with that point, the initial current when the four arms of the inverter are turned on is made negative.

The third invention generates a frequency that can make the initial current at turn-on of the four arms of the inverter negative even if the phase difference changes depending on the combination of the output voltage and load current, and maintains the set output voltage and load current. The inverter is operated according to the frequency according to the load current. The output voltage is stabilized by detecting the output voltage and changing the phase difference using feedback control.

The fourth invention is a combination of the second invention and the third invention. In other words, the output voltage is stabilized using feedback control, which detects the inverter's output current and operates the inverter in synchronization with the zero point, making the initial current at turn-on of the four arms of the inverter negative. This is how it was done.

〔Example〕

FIG. 1 shows a first embodiment of the present invention. 51 is a DC power supply, 52 to 55 are transistors that are turned on by flowing a base current, 56 to 59 are diodes connected in antiparallel to the transistors 52 to 55, respectively;
2 and 56 are the first arm, 53 and 57 are the second arm,
54 and 58 constitute a third arm, 55 and 59 constitute a fourth arm, and the first to fourth arms constitute an inverter 4.
Configure 0. 67 is a capacitor, and 68 is an inductance, which together with the capacitor 67 forms a resonant circuit.

60 is a high voltage transformer, and 61 to 64 are diodes, which constitute a rectifier 41 that rectifies the output voltage of the high voltage transformer 60. 65 is the capacitance of a high voltage cable for applying the output voltage of the rectifier 41 to the X-ray tube 66, which is a load. The capacitance 65 has a smoothing effect on the output voltage of the rectifier 41.

Reference numeral 70 determines the operating phase of the transistors 52 to 55 by signals corresponding to the voltage applied to the X-ray tube 66 (hereinafter referred to as tube voltage) and the current flowing through the X-ray tube 66 (hereinafter referred to as tube current). A phase determining circuit 76 determines the operating frequency of the transistors 52 to 55 based on signals corresponding to the tube voltage and tube current. Frequency phase control circuits 72 to 75 output signals for operating phases and frequencies using X-ray exposure signals, and are drive circuits that drive transistors 52 to 55 in accordance with signals from the phase control circuits, respectively.

The operation of FIG. 1 is as follows.

Once the tube voltage and tube current are determined, a tube voltage setting signal S1. corresponding to the tube voltage is generated. The 6-phase determining circuit 70 inputs the tube current setting signal S2 corresponding to the tube current to the phase determining circuit 70 and the frequency determining circuit 76, and calculates the load resistance value from the tube voltage signal Sl and the tube current signal S2. The operating phase difference α (hereinafter abbreviated as inverter phase) of the transistors of the inverter 40 is determined from the tube voltage using the relationship shown in FIG. Further, the frequency determining circuit 76 uses the relationship shown in FIG. 12 from the tube voltage signal S1 to convert the inverter 4
0 transistor operating frequency Fi/Fo (hereinafter abbreviated as inverter frequency) is determined. A signal corresponding to the above operating phase and operating frequency is input to the frequency phase control circuit 71, and the frequency phase control circuit 71 generates a signal for turning on and turning off each of the transistors 52 to 55 from this signal. When the X-ray exposure signal S4 is input to the frequency phase control circuit 71, the transistor 5
A signal for turning on and turning off transistors 2 to 55 is output to drive circuits 72 to 75, and drive circuits 72 to 75 drive transistors 52 to 55 in accordance with a signal from frequency phase control circuit 71. When the transistors 52 to 55 start operating, a resonant current as shown in FIG. 2 flows through the high voltage transformer 6o, a set tube voltage is applied to the X-ray tube 66, and a tube current flows. In Figure 2, looking at the time point and current when the on signal is input to each arm, 1) Start of the on signal to the first arm: Tal...Switch 5 of the first arm
2 turn-on: Ta3 2) Start of on-signal to the fourth arm: Ta2... Turn-on of switch 55 of the fourth arm: Ta3 3) Start of on-signal to the second arm: Ta4... Turn-on of the switch 53 of the second arm: Ta6 4) Start of the on-signal to the third arm: Ta5... Turn-on of the switch 54 of the third arm: Ta6 All are negative so that .

In this example, by combining the output voltage and load current, it is possible to generate a frequency and a phase difference that can make the initial current at turn-on of the four arms of the inverter negative. Since the inverter is operated according to the frequency and phase difference corresponding to the current, the loss of the inverter switches can be reduced, and a low-loss converter can be constructed.

Note that the phase determining circuit 70 and the frequency determining circuit 76 can be easily constituted by a memory in which the relationships are tabulated as shown in FIGS. 5 and 12, a function generator, an operational amplifier, etc., so a detailed explanation will be omitted.

FIG. 13 shows a second embodiment of the present invention. In the figure, 40,
41.51 to 68.70 to 75 are the same as those shown in FIG. 1, so their explanation will be omitted. 100 is a current detector that detects the output current of the inverter 40; 101 is a current detector 10;
This is a frequency detector that outputs a square wave synchronized with a zero output signal. 102 is a transistor 5 in response to the phase difference signal from the phase determining circuit 70 and the output signal of the frequency detector 101.
X signal for operating phase and frequency from 2 to 55
This is a frequency phase control circuit that outputs according to the radiation exposure signal S4.

Further, FIG. 14 is a configuration diagram of the frequency phase control circuit 102. 110 and 116 are phase comparators that detect the phase difference between two input square waves, 111 is a low-pass filter (hereinafter referred to as LPF) that smoothes the output of the phase comparator 110, and 117 is a low-pass filter that smoothes the output of the phase comparator 116. ,112,118
is a voltage controlled oscillator (hereinafter referred to as VC○) whose oscillation frequency changes depending on the input voltage. 113 and 119 are buffers that output the output of the VCO as they are; 114 and 120 are inverters that output the negative of the input signal; and 115 is a delay circuit that delays the signal. 130 and 131 are AND
It is a circuit.

The operation of the frequency phase control circuit 102 shown in FIG. 14 is as follows. A signal X obtained by delaying the square wave signal f input from the outside of the phase comparator 110 and the output signals of VCO 1 1 2
are compared and smoothed with LPFIII to obtain vCO112
is input. V C 0112 oscillates according to the output voltage of LPFIII. Such a configuration is vC○11
2 is a so-called P L that oscillates at the same frequency in synchronization with the square wave signal input from the outside to the phase comparator 110.
L (PhaseLock Loop). Also,
In the PLL composed of the phase comparator 116, LPF 117 and vCO 118, the output signal of vC○118 is directly compared with the other input signal of the phase comparator 116, and the LP
A phase control signal P is inputted to F117 from the outside. With this configuration, the VCO 1 1 8 can oscillate at the same frequency as the signal X and output a signal with a phase difference according to the signal X and the phase control signal p.

When the X-ray exposure signal s4 is input, ON signals to the four arms of the inverter are output, and solar radiation starts.

With the above configuration, the operation of FIG. 13 is as follows.

Once the tube voltage and tube current are determined, a tube voltage setting signal S1 corresponding to the tube voltage and a tube current setting signal S2 corresponding to the tube current are input to the phase determining circuit 70. Phase determining circuit 7
0, the load resistance value is determined from the tube voltage signal and the tube current signal, and the operating phase α of the inverter 40 is determined from the load resistance value and the tube voltage using the relationship shown in FIG. This operating phase α
The phase control signal p corresponding to the frequency phase control circuit 102
is input.

When the X-ray exposure signal No. S is input to the frequency phase control circuit 102, signals a to d for turning on and off the transistors 52 to 55 are output to the drive circuits 72 to 75, and the drive circuits 72 to 75 control the frequency phase. Control circuit 10
Transistors 52-55 are driven according to the signal from 2. When transistors 52 to 55 start operating,
A resonant current as shown in FIG. 2 flows through the high voltage transformer 60. Then, the current detector 100 detects this inverter current, and a square wave signal f synchronized with the inverter current is input to the frequency phase control circuit 102, and the inverter starts operating in synchronization with the frequency. A set tube voltage is applied to the X-ray tube 66, and a tube current flows. In the embodiment of the present invention, the phase difference of the inverter can be generated in advance by a combination of the output voltage and the load current, so the inverter is operated according to the phase difference corresponding to the set output voltage and load current. In addition, a frequency detector detects the point in time when the output current of the inverter becomes zero, and the inverter is operated in synchronization with that point, thereby making the initial current at turn-on of the four arms of the inverter negative. It is. Therefore, even if there is a change in the resonant frequency due to a load change or the like, the inverter frequency can be changed accordingly, and the inverter switch can always operate optimally.

FIG. 15 shows a third embodiment of the present invention. 51-68.
71 to 76 are of the same type as those shown in FIG. 1, so their explanation will be omitted.

80 is a voltage divider for detecting the tube voltage applied to the X-ray tube 66, 81 is a signal converter that converts the signal detected by the voltage divider into a signal suitable for use in the control circuit, and 82 is a signal converter. This is a phase determining circuit that determines the phase of the inverter 40 based on the difference between the signal from the inverter 40 and the tube voltage setting signal corresponding to the set tube voltage.

The operation of FIG. 15 is as follows.

Once the tube voltage is determined, the tube voltage setting signal S corresponding to that voltage is
1 is input to the phase determining circuit 82. On the other hand, a tube voltage detection signal from the signal converter 81 corresponding to the tube voltage detected by the voltage divider 80 is input to the phase determining circuit 82 . The phase determining circuit 82 determines the phase α of the inverter 40 in accordance with the difference between these two signals. Before the start of X-ray exposure, the tube voltage detection signal is zero with respect to the tube voltage setting signal Sz, so the phase α of the inverter 40 is zero so that the maximum power can be supplied.

In the frequency determining circuit 76, the tube voltage setting signal S1 to the 12th
Using the relationship shown in the figure, the operating frequency Fi of the transistors of the inverter (hereinafter abbreviated as inverter frequency) is determined. When the X-ray exposure signal S4 corresponding to the above operating frequency is input to the frequency phase control circuit 71, the frequency phase control circuit 71 turns on and turns off the transistors 52 to 55 according to the signal from the phase determination circuit 82. The signal is output to the drive circuits 72 to 75, and the drive circuits 72 to 75
drives the transistors 52 to 55 in accordance with the signal from the frequency phase control circuit 71.

When the transistors 52 to 55 start operating, a resonant current as shown in FIG. 2 flows through the high voltage transformer, a tube voltage starts to be applied to the X-ray tube 66, and a tube current flows. As the tube voltage approaches the set value, the difference between the tube voltage setting signal and the tube voltage detection signal becomes smaller.
, and reduces the power supply from the DC power supply 51. When the tube voltage becomes approximately equal to the set value, the inverter operates in a phase that allows the DC power supply 51 to supply power equal to the power generated by the set tube voltage and tube current.

In this example, even if the phase difference changes depending on the combination of output voltage and load current, it is possible to generate a frequency that can make the initial current at turn-on of the four arms of the inverter negative. The inverter can operate according to the frequency corresponding to the voltage and load current, and the output voltage is stabilized by detecting the output voltage and changing the phase difference using feedback control, which allows for more accurate tube voltage. Obtainable.

FIG. 16 shows a fourth embodiment of the present invention. 51-68.
71 to 75 are of the same type as those shown in FIG. 1, so their explanation will be omitted. Further, 80 to 82 are of the same type as in FIG. 15, and 100 to 102 are of the same type as in FIG. 13.

The present invention is a combination of FIG. 13 and FIG. 15, and detailed explanation of the operation will be omitted. The tube voltage is controlled by feeding back the detected actual value, and the frequency is determined by detecting the inverter current and operating at a frequency that makes the initial current in the inverter arm negative. Stable and accurate control is possible even when parameters change.

It goes without saying that the present invention is not limited to the above embodiments, but can be applied within the scope of the invention. For example, GTO can be used as a transistor for the switching element used in the inverter, and to further increase the frequency, M(IsFET, IGBT, SI transistor, SI thyristor, etc.) can be used.

Needless to say, the DC voltage of the inverter can be obtained from a rectified commercial power source, a battery, etc.

Furthermore, although the frequency phase control circuits 71 and 102 of the embodiments shown in FIGS. 1 to 16 generally perform normal proportional-integral control, it is possible to convert them into digital values once and apply control by software. is also possible.

It is also effective to apply the load target not only to an X-ray tube but also to a general DC-DC converter.

〔Effect of the invention〕

According to the present invention, by making the initial current of the arm of the inverter negative, a snubber circuit is configured that suppresses the rise of the voltage applied to the arm using only capacitance, thereby reducing the loss of the switching elements of the inverter to almost zero. Since it is possible to reduce the loss of the snare/< circuit to zero, it is possible to realize an efficient DC-DC converter.

In addition, since the operating frequency and operating phase difference of the inverter are set so that the initial current at turn-on of each arm of the inverter is negative, arm short circuits will not occur, and therefore excessive current will not flow to the switching elements. Therefore, a highly reliable 51 resonance type DC-DC converter without damage to switching elements can be realized.

Furthermore, since the voltage actually applied to the load is detected and used as a feed A to determine the operating phase of the inverter, a resonant DC-DC converter with improved tube voltage accuracy and stability can be realized.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of the first embodiment of the present invention, FIG. 2 is a time chart explaining the operation of the present invention, FIG. 3 is a configuration diagram of a conventional resonant DC-DC converter, and FIG. 4 is a time chart diagram explaining the operation of Figure 3, Figure 5 is a diagram showing the relationship between phase difference and output voltage in the phase difference control method using load resistance as a parameter, and Figure 6 is when a snubber circuit is not used. Fig. 7 is an example of a snubber circuit, Fig. 8 is an example of a snubber circuit, Fig. 9 is a turn-off waveform when using a snubber circuit, and Fig. 10 is a snubber circuit diagram used in the present invention. , FIG. 11 is a diagram of the relationship between the inverter frequency and the initial current of the inverter arm, FIG. 12 is a diagram of the relationship between the phase difference and the inverter frequency that makes the output voltage and initial current negative, and FIG. 13 is the relationship diagram of the second embodiment of the present invention. FIG. 14 is a block diagram showing a configuration example of a frequency phase control circuit, FIG. 15 is a third embodiment of the present invention, and FIG. 16 is a fourth embodiment of the present invention. 40... Inverter, 51... DC power supply, 52-5
5...Transistor, 56-59...Diode,
60...Transformer, 61-64...Diode, 65
．． 67... Capacitance, 68... Inductance, 70, 82... Phase determining circuit, 71, 102...
・Frequency phase control circuit, 76...frequency determination circuit, 1
00...Current detector, 101...Frequency detector. Chaguchi & Shunsai〆kyo 7 Fig. 7 Cha Otsu Kasumi 7-n Sai Fukan Ai 7-n Sai Fuoka Hajime I Prisoner

Claims (1)

[Claims] 1. A DC power source and a first electrode connected to the positive terminal of the DC power source.
and a second switch connected to the negative electrode thereof, and a third switch connected to the positive electrode and a fourth switch connected to the negative electrode. It has a second series connection body connected in parallel to the series connection body, and further has first to fourth diodes connected in antiparallel to the first to fourth switches, respectively, and receives DC from the DC power supply. an inverter that receives power and converts it into alternating current; an inductance connected to the output of the inverter; a capacitance connected in series to the inductance; a transformer connected in series to the inductance and capacitance to isolate it from the output; A resonant type DC-DC having a rectifier that converts the output of the device into direct current, and a load connected to the output of the rectifier.
In the converter, capacitances are connected in parallel to the first to fourth switches of the inverter, and operating phases of the first to fourth switches are determined according to setting signals for a voltage to be applied to the load and a current to be passed to the load. a frequency determining circuit that controls the operating frequencies of the first to fourth switches in accordance with setting signals for the voltage applied to the load and the current flowing through the load; a frequency phase control circuit that controls the operating phase and frequency of the first to fourth switches of the inverter according to the output signal from the frequency determining circuit;
The third and fourth switches are turned on alternately with a phase difference of 80°, and the third and fourth switches are similarly turned on with a phase difference of 180°. By changing the phase difference between when the second switch is turned on and the third switch is turned on, the power supplied to the load is controlled, and an on signal is sent to the first to fourth switches of the inverter. A resonant DC-DC converter, characterized in that the inverter is operated at a frequency and a phase difference such that current flows through the first to fourth diodes at the time of input. 2. The resonant DC-DC converter according to claim 1, wherein the load is an X-ray tube. 3. A DC power supply and a first terminal connected to the positive terminal of this DC power supply.
and a second switch connected to the negative electrode thereof, and a third switch connected to the positive electrode and a fourth switch connected to the negative electrode. It has a second series connection body connected in parallel to the series connection body, and further has first to fourth diodes connected in antiparallel to the first to fourth switches, respectively, and receives DC from the DC power supply. an inverter that receives power and converts it into alternating current; an inductance connected to the output of the inverter; a capacitance connected in series to the inductance; a transformer connected in series to the inductance-capacitance and insulated from the output; A resonant DC-DC having a rectifier that converts the output of the rectifier into direct current, and a load connected to the output of the rectifier.
The converter includes capacitances connected in parallel to the first to fourth switches of the inverter, a current detector that detects the output current of the inverter, and a frequency of the output current of the inverter based on the output signal of the current detector. a frequency detector that outputs a synchronized signal; a phase determining circuit that controls the operating phases of the first to fourth switches according to setting signals for the voltage applied to the load and the current flowing through the load; and the phase determining circuit. a frequency phase control circuit for controlling the operating frequency of the inverter and the operating phases of the first to fourth switches of the inverter according to the output signal from the circuit and the output signal from the frequency detector; 1 switch and 2nd switch are 1
The third and fourth switches are turned on alternately with a phase difference of 80°, and the third and fourth switches are similarly turned on with a phase difference of 180°. A resonant DC-DC converter characterized in that the power supplied to the load is controlled by changing the phase difference between when the second switch is turned on and the third switch is turned on. 4. The resonant DC-DC converter according to claim 3, wherein the load is an X-ray tube. 5. A DC power supply and a first terminal connected to the positive terminal of this DC power supply.
and a second switch connected to the negative electrode thereof, and a third switch connected to the positive electrode and a fourth switch connected to the negative electrode. It has a second series connection body connected in parallel to the series connection body, and further has first to fourth diodes connected in antiparallel to the first to fourth switches, respectively, and receives DC from the DC power supply. an inverter that receives power and converts it into alternating current; an inductance connected to the output of the inverter; a capacitance connected in series to the inductance; a transformer connected in series to the inductance and capacitance to isolate it from the output; A resonant type DC-DC having a rectifier that converts the output of the device into direct current, and a load connected to the output of the rectifier.
In the converter, the operating frequency of the first to fourth switches is determined according to capacitances connected in parallel to the first to fourth switches of the inverter, and setting signals for the voltage applied to the load and the current applied to the load. a frequency determining circuit that controls the voltage, a voltage divider that detects the voltage applied to the load, and a voltage divider that inputs the detection signal from the voltage divider and a preset target voltage signal, amplifies the difference between them, and uses this error to an error amplification circuit that determines the operating phase of the first to fourth switches of the inverter; and a frequency phase control circuit for controlling the operating phase of the first to fourth switches, the first switch and the second switch of the inverter are
The third and fourth switches are turned on alternately with a phase difference of 80°, and the third and fourth switches are similarly turned on with a phase difference of 180°. By changing the phase difference between when the second switch is turned on and the third switch is turned on, the power supplied to the load is controlled, and an on signal is sent to the first to fourth switches of the inverter. A resonant type DC-DC characterized in that the inverter is operated at a frequency such that current flows through the first to fourth diodes at the time of input.
converter. 6. The resonant DC-DC converter according to claim 5, wherein the load is an X-ray tube. 7. A DC power supply and a first terminal connected to the positive terminal of this DC power supply.
and a second switch connected to the negative electrode thereof, and a third switch connected to the positive electrode and a fourth switch connected to the negative electrode. It has a second series connection body connected in parallel to the series connection body, and further has first to fourth diodes connected in antiparallel to the first to fourth switches, respectively, and receives DC from the DC power supply. an inverter that receives power and converts it into alternating current; an inductance connected to the output of the inverter; a capacitance connected in series to the inductance; a transformer connected in series to the inductance and capacitance and insulated from the output; A resonant DC-DC having a rectifier that converts the output of a transformer into direct current, and a load connected to the output of this rectifier.
The converter includes capacitances connected in parallel to the first to fourth switches of the inverter, a current detector that detects the output current of the inverter, and a frequency of the output current of the inverter based on the output signal of the current detector. A frequency detector that outputs a synchronized signal, a voltage divider that detects the voltage applied to the load, and a detection signal from this voltage divider and a preset target voltage signal are input and the difference is amplified and this error is an error amplification phase determining circuit that determines the operating phases of the first to fourth switches of the inverter according to the above; and a frequency phase control circuit for controlling the operating frequency and the operating phase of the first to fourth switches of the inverter, the first switch and the second switch of the inverter being one
The third and fourth switches are turned on alternately with a phase difference of 80°, and the third and fourth switches are similarly turned on with a phase difference of 180°. A resonant DC-DC converter characterized in that the power supplied to the load is controlled by changing the phase difference between when the second switch is turned on and the third switch is turned on. 8. The resonant DC-DC converter according to claim 7, wherein the load is an X-ray tube.