JPH04342997A - Inverter type x-ray device - Google Patents

Abstract

PURPOSE:To accomplish a small-sized X-ray device, which can operate with a high frequency even with an inverter using switching elements involving a turnoff delay time. CONSTITUTION:Each switching element 1-4 of an inverter 5 consists of IGBT, and inside of each driver circuit 6-9 a turnoff sensing circuit is furnished, which is to sense the voltage between emitter and gate of the IGBT to know that the current to the switching element 1-4 is shut off. These driver circuits 6-9 are connected with respective AND circuits 28-31, and in conformity to a current shutoff signal (Sto1 etc.) from one of the two switching elements belonging to the same string among the switching elements 1-4, the AND circuits produce a turnon signal (Sg2 etc.) for the other switching element in series connection thereto.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an inverter-type X-ray device that uses an inverter as an energy conversion means for electric power and is applied to devices with high power and high operating frequency, such as medical X-ray generators, and particularly relates to a turn-off X-ray device. The present invention relates to an inverter-type X-ray apparatus that can be operated at a high frequency even with an inverter using switching elements with a delay time, and that can reduce the size of the apparatus.

0002

2. Description of the Related Art Inverter circuits have recently been widely used as energy conversion means for electric power, and have many advantages such as easy control of output voltage and high efficiency. As shown in FIG. 7, the conventional inverter circuit is composed of a DC voltage source E and a plurality of switching elements 1, 2, 3, 4, and converts the output voltage of the DC voltage source E into an AC voltage. 5, drive circuits 6, 7, 8, and 9 for respectively operating the switching elements 1 to 4 of the inverter 5, and a load circuit 10 to which the output voltage from the inverter 5 is applied. . In addition, in FIG. 7, symbols 11, 12, 13, 14
2 shows flywheel diodes connected in antiparallel to each of the switching elements 1 to 4, respectively.

Since the operating frequency of such an inverter circuit can be changed arbitrarily, efforts are being made to increase the operating frequency for the purpose of downsizing circuit components. Therefore, as the plurality of switching elements 1 to 4 constituting the inverter 5, high-speed switching elements that turn on and turn off at high speed are desired. However, in applications requiring high power, for example, tens of kilowatts or more, there are few high-speed switching elements, and even if there are, they are often very expensive or require complicated driving methods.

In power conversion of this level of output, insulated gate bipolar transistors (hereinafter abbreviated as "IGBT"), which are faster than normal bipolar transistors (BJTs), can be used as the switching elements 1 to 4. However, IGBTs have a delay time during turn-off called fall time, and for this reason, the maximum operating frequency of high-power IGBTs is generally about 10 KHz.
It is said that This frequency band overlaps with the human audible frequency band and is the cause of noise phenomena.
Furthermore, this has been an obstacle to downsizing high-power devices.

[0005] Here, the reason why the operating frequency of the above-mentioned IGBT cannot be increased will be explained. As shown in FIG. 7, in a full-bridge inverter 5 configured by combining four switching elements 1 to 4 each consisting of an IGBT, a set of first and fourth switching elements 1 and 4 or a set of second and fourth switching elements 1 and 4 are used. AC power is supplied to the load circuit 10 by alternately conducting the third switching elements 2 and 3. However, the first and second switching elements 1 connected in series within the same string of inverters 5
and the second or third and fourth switching elements 3 and 4,
If there is a period of conduction at the same time, the DC voltage source E input to the inverter 5 will be connected to the two switching elements 1.
and 2, or 3 and 4, resulting in a short circuit state, and an excessive current that does not pass through the load circuit 10 flows through each switching element 1 to 4.
This could cause a so-called arm short-circuit phenomenon in which the metal flows into the components and destroys them.

In order to prevent this phenomenon, FIGS. 8(a) to (d)
As shown in FIG. 2, between the drive control signals Q1 and Q2 to the first switching element 1 and the second switching element 2, which should be given complementary to each other, the third switching element 3
A rest period Td is provided between the drive control signals Q3 and Q4 to the fourth switching element 4, respectively, so that none of the switching elements 1 to 4 is conductive. The length of this pause period Td corresponds to the storage time of the IGBTs used as switching elements 1 to 4, that is, as shown in FIG. 8(e),
As shown in (f), even if the drive control signals Q1 to Q4 are stopped, the collector currents Ic1 and Ic2 continue to flow for a certain period of time, which is determined by the turn-off delay time, that is, the length of the fall time Tf. And always Tf<Td
...The condition (1) must be satisfied.

[0007]

[Problem to be solved by the invention] However, FIG.
As is clear from (f), according to the conditions of the above equation (1), there is a time Td0 during which all switching elements 1 to 4 are actually cut off, and Td0 = Td - Tf
...(2) There is a relationship. And this time Td
0 is equal to the time during which the inverter 5 is stopped, and no power is supplied to the load circuit 10, which causes a reduction in the efficiency of the inverter 5. Therefore, the time Td0 needs to be as small as possible. In addition, when trying to control the output voltage by changing the conduction ratio or operating frequency of the inverter 5, the above time Td0 becomes an uncontrollable period, so if this value is too large, it will cause a decrease in control performance. there were. It is clear that these problems occur more easily as the proportion of time Td0 that occupies within one period of inverter 5 increases.

FIG. 9 shows one of the characteristics of the turn-off delay time Tf of a general IGBT. In the figure, the turn-off delay time Tf is
It has characteristics that vary significantly depending on the collector current Ic flowing in the IGBT, the junction temperature Tj within the IGBT, etc. For this reason, the idle period Td must satisfy Tfmax<Td according to the equation (1), where Tfmax is the longest turn-off delay time Tf. However, in the pause period Td determined in this way, when the turn-off delay time Tf is Tfmin, which is the shortest condition, the second
) The value of time Td0 given by the equation becomes very large, causing the above-mentioned problem.

From the above, in a switching element with a large turn-off delay time Tf, in order to secure the time Td0 necessary to prevent the arm short-circuit phenomenon, the rest period Td should be longer than the turn-off delay time Tf and as long as possible. Small values are preferred. And this time Td0
In order to reduce the ratio, the inverter period Ti shown in FIG. 8(a) must be made long. From this,
In conventional inverter circuits, the operating frequency of the inverter cannot be increased. Therefore, it has been difficult to downsize the device.

SUMMARY OF THE INVENTION Therefore, the present invention aims to provide an inverter-type X-ray apparatus that can be operated at a high frequency even with an inverter using a switching element with a turn-off delay time, and that can reduce the size of the apparatus. purpose.

[0011]

[Means for Solving the Problems] In order to achieve the above object, an inverter type X-ray apparatus according to the present invention is constructed of a DC voltage source and a plurality of switching elements, and converts the output voltage of the DC voltage source into an AC voltage. An inverter for converting, a drive circuit for operating each switching element of this inverter, a high voltage generator for boosting the output AC voltage of the inverter and converting this output into DC, and a high voltage generator for converting the output from the high voltage generator. In an inverter-type X-ray apparatus comprising an X-ray tube to which a DC high voltage is applied, and an inverter control circuit that sends control signals to each of the drive circuits, each switching element of the inverter is an insulated gate bipolar Each of the drive circuits described above includes turn-off detection means for detecting the voltage between the emitter and gate of an insulated gate bipolar transistor as a switching element and detecting that the current of the switching element has been cut off. are provided, and their drive circuits generate a turn-on signal for the other switching element connected in series with the current cutoff signal from one of the two switching elements in the same string among the plurality of switching elements. These means are connected to each other.

Further, the turn-off detection means sets a detection level based on the Zener voltage of a Zener diode inserted between the emitter and gate of an insulated gate bipolar transistor as a switching element, and The voltage is
Higher than the voltage generated at the emitter seen from the gate during the conduction time or fall time of the insulated gate bipolar transistor, but lower than the voltage at the emitter seen from the gate when the insulated gate bipolar transistor reverse recovers. It is effective if you do it.

[0013]

[Operation] The inverter-type X-ray apparatus configured as described above uses turn-off detection means provided inside each drive circuit of the inverter, in which each switching element is composed of an insulated gate bipolar transistor, to detect insulation as each switching element. The voltage between the emitter and gate of the gated bipolar transistor is detected to detect that the current of each switching element is cut off, and the turn-on signal generating means connected to each of the drive circuits turns on the plurality of switching elements. It operates to generate a turn-on signal for the other switching element connected in series with the current cutoff signal from one of the two switching elements in the same string. As a result, in an inverter-type X-ray device equipped with an inverter that uses a switching element with a turn-off delay time, it is possible to shorten the inverter's rest period, increase the operating frequency, and make the device more compact. can.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a circuit diagram showing an embodiment of an inverter type X-ray apparatus according to the present invention. This inverter type
The ray device uses an inverter as an energy conversion means for electric power, and is applied to devices with high power and high operating frequency, such as medical X-ray generators, as shown in the figure.
DC voltage source E, inverter 5, and drive circuits 6, 7, 8
, 9, a high voltage generator 15, an X-ray tube 19, and an inverter control circuit 16.

The DC voltage source E supplies a DC voltage, and is formed by combining a commercial AC power source and a thyristor rectifier circuit, for example. The inverter 5 includes the DC voltage source E
It converts the output voltage of ，
12, 13, and 14 are connected in antiparallel. Drive circuit 6
-9 are respective switching elements 1-4 of the inverter 5
Each switching element 1 to
There are four in total, one for each.

The high voltage generator 15 is connected to the inverter 5.
a high-voltage transformer 17 that serves as a load supplied with the voltage output from the inverter 5 and boosts the output AC voltage of the inverter 5;
The high voltage rectifier 18 converts the output of the high voltage transformer 17 into direct current. The X-ray tube 19 also serves as a load, and the output DC high voltage of the high voltage rectifier 18 is applied thereto. In this case, the AC output of the inverter 5 is supplied to a series circuit consisting of a high voltage transformer 17 and a capacitor 20, and the leakage reactance of the high voltage transformer 17 and the capacitance of the capacitor 20 are connected in series. A resonant circuit is configured, and the current waveform flowing through the inverter 5 is made into a sine wave, and electromagnetic induction noise and each switching element 1 to 4 are
The aim is to reduce switching loss. The input voltage to the X-ray tube 19 is detected by a detector 21 and fed back to the inverter control circuit 16 as a feedback voltage Vf.

The inverter control circuit 16 sends a drive control signal Q to each of the drive circuits 6 to 9 of the inverter 5.
1, Q2, Q3, and Q4, and an operational amplifier 22 that compares the feedback voltage Vf with a predetermined set voltage Vset, and an error voltage Ve output from this operational amplifier 22 that is input and converted into a digital quantity. A/D
A converter 23, a clock signal oscillator 24 that outputs a clock signal CK, a first flip-flop 25 that creates a complementary signal synchronized with the clock signal CK from the clock signal oscillator 24, and a first flip-flop 25 that generates a complementary signal synchronized with the clock signal CK from the clock signal CK. A down counter 26 that is synchronized and outputs a delayed clock signal CKd delayed at a timing corresponding to the error voltage digital amount from the A/D converter 23, and a complementary clock signal CKd that is synchronized with the delayed clock signal CKd from the down counter 26. a second flip-flop 27 that creates a signal
It consists of And the first flip-flop 25
drive control signals Q1 and Q2 are sent from the second flip-flop 27 to the first and second drive circuits 6 and 7, respectively, and drive control signals are sent from the second flip-flop 27 to the third and fourth drive circuits 8 and 9, respectively. Signals Q3 and Q4 are sent out. These four drive control signals Q1 to Q4 are sent out at the timing shown in FIG.
4, or drive control signal Q3 for drive control signal Q2
This delay is called a phase difference φ, and the conduction ratio of the inverter 5 to the load is determined by this phase difference φ. For this reason,
Tube voltage control of the X-ray tube 19 as a load in this embodiment is called a phase difference control (PWM) method. In this case, since the tube voltage is adjusted by the phase difference φ without controlling the operating frequency of the inverter 5, the ripple frequency of the tube voltage does not change depending on the load conditions, and the There is little variation in concentration and good linearity.

The inverter control circuit 16 and
The drive circuits 6 to 9 connected to the four switching elements 1 to 4 respectively create a set of the first switching element 1 and the fourth switching element 4, or a set of the second switching element 2 and the third switching element 3. An AC voltage is generated by operating the two pairs in a complementary manner to each other and applied to the X-ray tube 19 as a load.

In the present invention, each of the switching elements 1 to 4 of the inverter 5 is composed of an IGBT (insulated gate bipolar transistor), and each of the drive circuits 6 to 9 has the IGBT Turn-off detection means is provided for detecting that the current in the switching elements 1 to 4 consisting of the following is cut off. Note that the drive circuits 6 to 9 include AND circuits 28, 29, 3, which will be described later.
Gate voltage control signals Sg1 and Sg1 output from 0 and 31
g2, Sg3, and Sg4 output gate voltages for driving the first to fourth switching elements 1 to 4, each of which is an IGBT. Each of the drive circuits 6 to 9 includes a circuit for detecting a cutoff of the collector current flowing through each of the switching elements 1 to 4, that is, a turn-off, and each receives a turn-off detection signal S.
To1, Sto2, Sto3, and Sto4 are output.

Now, to explain the internal configuration of the first drive circuit 6 as an example, as shown in FIG.
2 and 33, a PNP transistor 34, an NPN transistor 35, a resistor 36, a photocoupler 37,
Resistor 38, another PNP transistor 39, and resistor 40
and a turn-off detection circuit 41.

[0021] The DC voltage sources 32 and 33 are IGBTs.
This is a power supply for supplying forward and reverse gate voltages to the first switching element 1 consisting of the following. In addition, apart from these, a common power supply Vs is supplied to each of the drive circuits 6 to 9 together with the ground potential GND. The PNP transistor 34 and the NPN transistor 35 are elements that selectively switch the forward gate voltage or the reverse gate voltage with respect to the first switching element 1. The resistor 36 connected to the PNP transistor 34 and the NPN transistor 35 is a limiting resistor for setting the gate current to an optimal value for the first switching element 1.

When the gate voltage control signal Sg1 is supplied to the input side of the photocoupler 37, it converts it into light and transmits the signal while electrically insulating it. The signal on the output side connected to the DC voltage source 32 becomes logic L (low). Other PNPs
The transistor 39 inverts the logic of the output signal of the photocoupler 37.
When the base connected to is at logic L, the collector connected to DC voltage source 32 through resistor 40 is at logic H (high).

When the collector of the transistor 39 is at logic H, the PNP transistor 34 becomes conductive, and at the same time the NPN transistor 35 becomes non-conductive, so that the voltage of the DC voltage source 32 is applied between the gate and emitter of the first switching element 1. By applying the forward gate voltage, the first switching element 1 becomes conductive. Conversely, when the collector of the transistor 39 is at logic L, the NPN
The transistor 35 becomes conductive, and at the same time the PNP transistor 34 becomes non-conductive, and the voltage of the DC voltage source 33 is applied between the emitter gate of the first switching element 1, and a reverse gate voltage is applied, whereby the first switching Element 1 becomes non-conductive. With this configuration, the first switching element 1 is driven by the gate voltage control signal Sg1.

Further, the turn-off detection circuit 41
It is connected between the emitter gate of the first switching element 1 consisting of a resistor 42 and a resistor 42, as shown in FIG.
It consists of a Zener diode 43, a photocoupler 44, another resistor 45, and a logic inverter 46. The Zener diode 43 has a characteristic that when a voltage of a certain value or more is applied from the anode to the cathode, a breakdown phenomenon occurs and a current flows in the opposite direction. The voltage at which the Zener diode breaks down is called the Zener voltage, and this Zener voltage is a value specific to each Zener diode, and can be selected within the range of about 2V to 40V.

The operation of the turn-off detection circuit 41 will now be described with reference to FIG. 4, which shows waveforms of various parts of the first switching element 1. Note that the transmission delay times in the transistors 34, 35, 39 and the photocoupler 37 used in the first drive circuit 6 are very short compared to the first switching element 1, so they are ignored here. First, the gate voltage control signal Sg1 input to the first drive circuit 6 has a waveform as shown in FIG. The waveform will be as shown in (b). Then, as shown in FIG. 4(a), the gate voltage control signal S
Even if g1 becomes logic L and a reverse gate voltage is applied, the same figure (
As shown in b), for a while the collector current Ic1
continues to flow, and the collector current Ic1 becomes zero after a fall time, that is, a turn-off delay time Tf. Gate-emitter voltage Vg of first switching element 1
As shown in FIG. 4(c), when the gate voltage control signal Sg1 shown in FIG. 4(a) becomes logic H, e1 similarly enters the forward bias state, and when it becomes logic L, the turn-off delay time T
The state of zero voltage continues for only a period of f, and then the collector current Ic1 shown in FIG. 3(b) becomes zero and at the same time the state becomes reverse biased.

At this time, as shown in FIG. 4(a), the gate voltage control signal Sg1 becomes logic L, and the voltage of the DC voltage source 33 shown in FIG. The reason why no voltage is generated between the gate and emitter during the turn-off delay time Tf as shown in FIG. 4(c) even though it is applied as a reverse bias is because the IGB
This is because, as a characteristic of T, during the turn-off delay time Tf, charges remain in the junction between the gate and emitter, and the impedance between the gate and emitter is in a low state. Then, as shown in FIG. 4(b), the reverse recovery between the gate and emitter is completed when the collector current Ic1 stops flowing.
Impedance becomes high and reverse bias appears. Therefore, as shown in FIG. 4(c), if the gate-emitter voltage Vge1 is set to a negative threshold voltage Vth that is lower than the voltage during the turn-off delay time Tf and higher than the voltage during reverse bias, the above It can be detected that when the gate-emitter voltage Vge1 is higher than Vth, it is in a conductive state, and conversely, when it is lower than Vth, it is in a non-conductive state.

Turn-off detection circuit 4 shown in FIG.
1, if the forward voltage drop in the photocoupler 44 is made small, the above-mentioned detection function can be realized by selecting the Zener voltage of the Zener diode 43 to be equal to the threshold voltage Vth. That is, when the gate-emitter voltage Vge1 becomes a reverse bias state at turn-off and becomes a negative voltage lower than the Zener voltage, a reverse current flows through the Zener diode 43, is limited to an appropriate current value by the resistor 42, and is applied to the photocoupler 44. Enter. At this time,
The output of the photocoupler 44, which is pulled up by the resistor 45, becomes logic L, and the output of the logic inverter 46 becomes logic H, so that the turn-off detection signal Sto1 is generated as shown in FIG. 4(e). Become.

Further, in the present invention, for each of the drive circuits 6 to 9 shown in FIG.
AND circuits 28, 29, 30, and 31 are used as means for generating a turn-on signal for the other switching element connected in series with the current cutoff signal from one of the two switching elements in the same string among 4 to 4. each connected. These AND circuits 28 to 31 receive drive control signals Q for the respective switching elements 1 to 4.
1, Q2, Q3, Q4, and turn-off detection signals Sto1, Sto2 of adjacent switching elements in the same string.
, Sto3, and Sto4 are generated and outputted to the drive circuits 6, 7, 8, and 9 as gate voltage control signals Sg1, Sg2, Sg3, and Sg4, respectively.

Next, the operation of the inverter 5 in the inverter type X-ray apparatus configured as described above will be explained with reference to FIG. First, the collector current Ic1 flowing through the first switching element 1 in FIG. 1 is as shown in FIG. 5(a).
It has a waveform as shown in . FIG. 5(b) shows the turn-off detection signal Sto1 output from the turn-off detection circuit 41 (see FIG. 3) built in the drive circuit 6 of the first switching element 1. This turn-off detection signal Sto1 is determined by the turn-off detection circuit 41 to have a logic L level while the collector current Ic1 shown in FIG. 5(a) is flowing, and becomes a logic H level when the collector current Ic1 is cut off. FIG. 5(c) shows the first flip-flop 25 shown in FIG.
The drive control signal Q2 to the second switching element 2 outputted from the drive control signal Q2 is shown. This drive control signal Q2 is Du
ty50%, and also the first flip-flop 25
There is a complementary relationship with the drive control signal Q1 (see FIG. 5(g)) outputted from the first switching element 1. In this state, the drive control signal Q2 and the turn-off detection signal Sto1 output from the first drive circuit 6 are input to the second AND circuit 29 shown in FIG.
D is taken, and as shown in FIG. 5(d), a gate voltage control signal Sg2 is generated and sent to the second drive circuit 7. This second drive circuit 7 receives the gate voltage control signal S
When g2 is logic H, a forward gate voltage is supplied to the second switching element 2, and as a result, the second switching element 2 is turned on, as shown in FIG. 5(e).
Collector current Ic2 flows.

That is, the turn-on of the second switching element 2 is determined only by the rise of the turn-off detection signal Sto1 that occurs when the collector current Ic1 of the first switching element 1 is turned off, regardless of its drive control signal Q2. The Rukoto. For this reason, Figure 8
As is clear from FIGS. 5A and 5E, even if the pause period Td is not provided before the drive control signal Q2 as in the conventional case shown in FIG. 5B, the collector current Ic2 of the second switching element 2 is the collector current I of the first switching element 1
It can be turned on without overlapping with c1. The same thing is done when turning on the first switching element 1 shown in FIGS. 5(e) to 5(h), and neither of the switching elements 1 and 2 becomes conductive redundantly.

In the above explanation, for simplicity, FIG.
Although only the left string of the inverter 5 has been described, the same operation is performed in the right string, that is, the third and fourth switching elements 3 and 4.
Each of the switching elements 3 and 4 does not become conductive redundantly. Since the operations of the left and right strings are performed independently, they are completely unaffected by the phase difference between the left and right strings. It can be done in the same way as the method. It is also effective in a so-called AM method in which the output voltage is controlled using an inverter input voltage.

FIG. 6 is a circuit diagram showing a second example of the internal configuration of the drive circuit 6 and the like. In this example, P
A Pch field effect transistor 47 is used instead of the NP transistor 34, and the NPN transistor 3
In this embodiment, an Nch field effect transistor 48 is used in place of the inverter 5 shown in FIG. 1, and since high-speed switching operation is possible, the inverter 5 shown in FIG. Furthermore, since each of the elements 47 and 48 is of a voltage-driven type and has a high gate threshold voltage, it is characterized by less malfunction due to noise. In the turn-off detection circuit 41' in this example, the emitter voltage of the first switching element 1 is supplied to the Zener diode 43 via the diode 49. Generally, it is considered undesirable to flow current from the anode side to the cathode side of a Zener diode due to its characteristics. Therefore, the diode 49 is connected to the first switching element 1
Current flowing through the Zener diode 43 during forward bias is blocked. And Zener diode 43
A resistor 50 connected to the cathode side of the Zener diode 43 is provided to stabilize the cathode potential of the Zener diode 43 when the diode 49 is turned off. Further, the capacitor 51 connected to the anode side of the Zener diode 43 is connected to the gate-emitter voltage V of the first switching element 1.
This is provided to absorb high frequency noise when it occurs in ge1. Furthermore, the resistor 52 is a discharge resistance of the capacitor 51.

Here, when the first switching element 1 is cut off and reverse bias is applied to the gate-emitter voltage Vge1, and this voltage exceeds the Zener voltage, a current flows to the base of the transistor 54 via the base current limiting resistor 53a. is supplied, and the transistor 54 becomes conductive. As a result, a current is supplied to the photocoupler 44 via the collector current limiting resistor 53b, and the turn-off detection signal Sto1 becomes logic L and is output. At this time, the capacitor 55
is charged while the first switching element 1 is reverse-biased, and even when the first switching element 1 is then forward-biased, it is not discharged by the discharge blocking diode 56 and continues to hold the voltage. This voltage stabilizes the current supplied to the photocoupler 44 and prevents erroneous detection of the turn-off detection signal Sto1 even if the gate-emitter voltage Vge1 decreases. According to the drive circuit 6 and the like having the configuration shown in FIG. 6, even when the reverse bias is low and there is a risk of malfunction due to noise, a stable turn-off detection operation can be performed.
It can support even higher inverter operating frequencies.

In a medical X-ray generator to which an inverter-type X-ray device having such a configuration is applied, the load conditions and imaging time vary depending on the part of the patient to be imaged, and the loss generated in the inverter 5 varies in magnitude. Furthermore, the load range is approximately 10 to the fourth power, and therefore the current flowing through the inverter 5 also changes greatly. Furthermore, in a resonant type inverter, the collector current of each of the switching elements 1 to 4 is often sinusoidal, and when used in a phase difference control method, the cutoff current varies depending on the phase difference. That is, it is inevitable that the turn-off delay time Tf of the switching element changes depending on the collector current Ic and the junction temperature Tj of the transistor as shown in FIG. According to the embodiment shown in FIG. 1, the optimum idle period Td is automatically determined according to the length of the turn-off delay time Tf, and each switching element 1 to 4
It is equivalent to being added to the drive control signals Q1 to Q4. Therefore, even if the turn-off delay time Tf changes depending on the collector current Ic or the transistor junction temperature Tj,
The so-called arm short circuit phenomenon does not occur. Further, since the inverter 5 operates so that the actual cut-off time Td0 is always the minimum, the efficiency of the inverter does not decrease. Furthermore, even if the operating frequency of the inverter 5 is increased, these effects do not change, and even if high-power transistors are used as the switching elements 1 to 4, the frequency can be increased to higher than the audible frequency.

In the above description, the DC voltage source E is a commercial AC power source converted by a thyristor rectifier circuit, but the present invention is not limited to this, and a fixed voltage type such as a battery may be used. Further, the inverter 5 is not limited to a full bridge type, and can be similarly applied to a configuration such as a half bridge type or a push-pull type as long as the inverter 5 uses the rest period Td.

[0036]

[Effects of the Invention] Since the present invention is configured as described above,
The turn-off detection means (41) provided inside each drive circuit 6-9 of the inverter 5, in which each switching element 1-4 is an IGBT, detects the
Turn-on signal generating means (28 ~31), a current cutoff signal (
Sto1 to Sto4) can generate a turn-on signal for the other switching element connected in series. As a result, in an inverter type X-ray apparatus equipped with an inverter 5 using a switching element with a turn-off delay time Tf, the inverter 5 has a rest period Td.
The operating frequency can be increased by shortening the length, and the device can be made more compact. Further, since the inverter 5 operates so that the actual cut-off time Td0 is always the minimum, the efficiency of the inverter does not decrease.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of an inverter-type X-ray apparatus according to the present invention,

[Figure 2] A timing diagram showing the timing of drive control signals sent from the inverter control circuit to each drive circuit of the inverter,

[Figure 3] A circuit diagram showing the internal configuration of the inverter drive circuit,

[Figure 4] Timing diagram for explaining the operation of the turn-off detection circuit,

[Fig. 5] Timing diagram for explaining the operation of the inverter in the present invention,

[Fig. 6] A circuit diagram showing a second example of the internal configuration of the inverter drive circuit,

[Fig. 7] A circuit diagram showing an inverter circuit in a conventional inverter type X-ray device,

FIG. 8 is a timing diagram showing the timing of drive control signals sent to each drive circuit in order to prevent arm short-circuiting in the conventional example;

FIG. 9 is a graph showing one of the characteristics of turn-off delay time of IGBT.

[Explanation of symbols]

1 to 4...Switching element, 5...Inverter,
6-9... Drive circuit, 11-14... Flywheel diode, 15... High voltage generator, 16... Inverter control circuit, 19... X-ray tube, 21... Detector, 28-31... AND circuit, 41, 41' ...Turn-off detection circuit, 43...Zener diode,
E...DC voltage source.

Claims (2)

[Claims] 1. A DC voltage source, an inverter configured with a plurality of switching elements and converting the output voltage of the DC voltage source into an AC voltage, a drive circuit that operates each switching element of the inverter, and a drive circuit for operating each switching element of the inverter. A high voltage generator that boosts the output AC voltage and converts this output into DC, an X-ray tube to which the high DC voltage output from the high voltage generator is applied, and sends control signals to each of the above drive circuits. In the inverter-type X-ray apparatus, each switching element of the inverter is composed of an insulated gate type bipolar transistor, and each of the drive circuits includes an insulated gate type bipolar transistor as a switching element. A turn-off detection means is provided for detecting the voltage between the emitter and gate of the bipolar transistor to detect that the current of the switching element has been cut off, and the drive circuit thereof is provided with An inverter-type X-ray apparatus characterized in that means for generating a turn-on signal for the other switching element connected in series with the current cutoff signal from one of the two switching elements is connected to each of the switching elements. 2. The turn-off detection means sets a detection level based on the Zener voltage of a Zener diode inserted between the emitter and gate of an insulated gate bipolar transistor as a switching element, and The voltage is higher than the voltage generated at the emitter as seen from the gate during the conduction time or fall time of the insulated gate bipolar transistor, and the voltage at the emitter as seen from the gate when the insulated gate bipolar transistor recovers reversely. 2. The inverter type X-ray apparatus according to claim 1, wherein the inverter type X-ray apparatus is lower than .