JPH0491660A - Inverter circuit and inverter type x-ray device using same - Google Patents

Abstract

PURPOSE:To achieve operation at a high frequency and enable a device to be compact by generating a turn-on signal of other switching element which is connected in series with one switching element out of two switching elements within a same string among the switching elements by current interruption signal. CONSTITUTION:A drive control signal Q2 and a turn-off detection signal o1 which is output from a drive circuit 6 are fed to an AND circuit 24 and logic AND operation is calculated, thus enabling a base current control signal Sb2 to be generated and to be sent to a drive circuit 7. The drive circuit 7 allows base current to be flown to a switching element 2 when a base current control signal Sb2 is in logic H and the switching element 2 to be turned on for enabling collector current to flow. Thus, even if no pause period is provided before the drive control signal Q2, a collector current Ic2 of the switching element 2 can be turned on without overlapping with a collector current Ic1.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an inverter circuit as an energy conversion means for electric power and an inverter-type Xa device using the same, and particularly to an inverter-type Xa device using the inverter circuit as an energy conversion means for electric power. The present invention relates to an inverter circuit that can operate at a high frequency even in an inverter circuit, and which can reduce the size of the apparatus, and an inverter-type X-ray apparatus using the inverter circuit.

[Prior 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. 11, the conventional inverter circuit includes a DC voltage source E and a plurality of switching elements 1 and 2.
, 3.4, which converts the output voltage of the DC voltage source E into an AC voltage; and drive circuits 6, 7, 8.9, which respectively operate 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. 11, reference numerals 11, 12, 13, and 14 indicate 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, bipolar junction transistors (hereinafter abbreviated as rBJTJ) are usually used as the switching elements 1 to 4. However, BJTs have a turn-off delay time called storage time, and for this reason, the maximum operating frequency of BJTs for high power applications is generally said to be several kHz. Since this frequency band overlaps with the human audible frequency band, it causes the Ii sound phenomenon to occur, and also poses an obstacle in downsizing high-power devices.

Here, the inside of the ring in which the operating frequency of the BJT cannot be increased will be explained. As shown in FIG. 11, in a full-bridge inverter 5 constructed by combining four switching elements 1 to 4 each made of a BJT,
AC power is supplied to the load circuit 10 by alternately conducting the fourth set of switching elements 1 and 4 or the set of second and third switching elements 2 and 3. However, if there is a period in which the first and second switching elements 1 and 2 or the third and fourth switching elements 3 and 4 connected in series in the same string of inverters 5 conduct at the same time, the inverter 5, the DC voltage source E input to the switching elements 1 and 2 or 3 and 4 becomes short-circuited, and an excessive current that does not pass through the load circuit 10 flows into each of the switching elements 1 to 4. This sometimes causes a so-called arm short-circuit phenomenon that results in destruction. To prevent this phenomenon, Figure 12 (
As shown in a) to (d), 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 and A pause 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 accumulation time of the BJTs used as switching elements 1 to 4, that is, as shown in FIGS. The collector currents I cl and I C2 continue to flow for a certain period of time even if the motor stops for a short period of time, which is determined by the length of the turn-off delay time Ts. Then, the condition Ts < Td (1) must always hold.

[Problem to be solved by the invention]

However, as is clear from FIGS. 12(a) to (f),
According to the condition of the above equation (1), there is a time Td during which all the switching elements 1 to 4 are actually cut off, and the relationship TdO=Td-Ts-(2) exists. And this time Tdo is the inverter 5
Since no power is supplied to the load circuit 10 for a period equal to the time when the inverter 5 is stopped, the efficiency of the inverter 5 is reduced. Therefore, the above time Td. must be set to a value as small as possible. Furthermore, when trying to control the output voltage by changing the conduction ratio or operating frequency of the inverter 5, the above-mentioned time Tdo becomes an uncontrollable period, so if this value is too large, it will cause a decline in control performance. there were. It is clear that these problems occur more easily as the ratio of time Td that occupies within one period of inverter 5 increases.

Here, one of the characteristics of the turn-off delay time Ts of a commonly used BJT is shown in FIG. 13. In the figure, the turn-off delay time Ts is B
It has characteristics that vary significantly depending on the collector current Ic flowing through the JT, the junction temperature Tj within the BJT, etc. Therefore, the pause period Td is the turn-off delay time Ts
is the longest condition, T smax.
), it must be established that Tsold<Td. However, in the pause period Td determined in this manner, when the turn-off delay time Ts is Tsmin, which is the shortest condition, the (second
) The value of time Td 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 Ts, in order to secure the time Td0 necessary to prevent the arm short circuit phenomenon.

It is desirable that the idle period Td is longer than the turn-off delay time Ts and is as small as possible by 71%. In order to reduce the ratio of this time Td, as shown in Fig. 12(a)
It is necessary to take a long inverter period Ti shown in FIG. For this reason, 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 provides an inverter circuit that can be operated at a high frequency even in an inverter circuit using switching elements with a turn-off delay time, and that can reduce the size of the device, and an inverter-type X-ray apparatus using the inverter circuit. The purpose is to provide

[Means to solve the problem]

In order to achieve the above object, an inverter circuit according to the present invention includes a DC voltage source, an inverter that is configured with a plurality of switching elements and converts the output voltage of the DC voltage source into an AC voltage, and each switching element of the inverter. In an inverter circuit having a drive circuit to be operated and a load circuit to which an output voltage from the inverter is applied, turn-off detection is provided inside each of the drive circuits to detect that the current of each of the switching elements is interrupted. means are provided, and their drive circuits are configured to receive 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. The generation means are connected to each other.

Further, each of the switching elements may be a bipolar junction transistor, and the turn-off detection means may detect a voltage between an emitter and a base of the bipolar junction transistor.

Furthermore, the turn-off detection means sets the detection level by the Zener voltage of the Zener diode, and the Zener voltage of the Zener diode is generated at the emitter of the bipolar junction transistor as a switching element when viewed from the base during the storage time. The voltage may be higher than that of the bipolar junction transistor, but lower than the emitter voltage seen from the base when the bipolar junction transistor recovers reversely.

The inverter-type X-ray apparatus according to the present invention includes a DC voltage source, an inverter that includes a plurality of switching elements and converts the output voltage of the DC voltage source into an AC voltage, and operates each switching element of the inverter. an inverter circuit having a drive circuit; an inverter control circuit that sends control signals to each of the drive circuits; a high-voltage transformer that boosts the output AC voltage of the inverter circuit; and a high-voltage transformer that converts the output of the high-voltage transformer into DC. In an inverter-type X-ray apparatus comprising a rectifier and an X-ray tube to which the output DC voltage of the high-voltage rectifier is applied, the inverter circuit configured as described above is used as the inverter circuit.

[For production]

The inverter circuit configured as described above detects that the current of each switching element is cut off by the turn-off detection means provided inside each drive circuit,
The turn-on signal generation means connected to each of the drive circuits generates a current cutoff signal from one of the two switching elements in the same string among the plurality of switching elements to turn on the other switching element connected in series with it. Operates to generate a turn-on signal. As a result, in an inverter circuit using a switching element with a turn-off delay time, the inverter's rest period can be shortened and the operating frequency can be increased.

Further, an inverter-type X-ray apparatus using the inverter circuit configured as described above can increase the operating frequency and downsize the apparatus through the operation of the inverter circuit.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing an embodiment of an inverter circuit according to the present invention. This inverter circuit serves as an energy conversion means for electric power, and as shown in FIG. It consists of

The DC voltage source E supplies a DC voltage, and the inverter 5, which is a combination of a commercial AC power source and a thyristor rectifier circuit, converts the output voltage of the DC voltage source E into an AC voltage, For example, four switching elements 1゜2.3.4 consisting of BJTs (bipolar junction transistors) are combined to form a full bridge type, and these switching elements 1
~4 have flywheel diodes 11 and 12, respectively.
．． 13 and 14 are connected in antiparallel. Drive circuit 6-9
The inverter 5 operates each of the switching elements 1 to 4 of the inverter 5, and a total of four switching elements are provided, one for each of the switching elements 1 to 4. The load circuit 1o is supplied with the voltage output from the inverter 5, and is, for example, a motor or an X-ray tube device.The input voltage is detected by the detector 15 and fed back to the control circuit 16 as a feedback voltage Vf. It is now possible to do so.

This control circuit 16 includes each drive circuit 6 of the inverter 5.
~9 respectively drive control signals Q1HQ2+Q, , Q,
an operational amplifier 17 that compares the feedback voltage Vf with a predetermined set voltage Vset, and an A/D converter 18 that inputs the error voltage Ve output from the operational amplifier 17 and converts it into a digital quantity. , a clock signal oscillator 19 that outputs a clock signal CK, and a first flip-flop 2 that creates a complementary signal synchronized with the clock signal CK from the clock signal oscillator 19.
0, and in synchronization with the clock signal GK, the A/
A down counter 21 outputs a delayed clock signal CKd delayed at a timing corresponding to the error voltage digital amount from the D converter 18, and a complementary signal synchronized with the delayed clock signal CKd from the down counter 21 is created. and a second flip-flop 22. and,
A drive control signal Q□lQ2 is sent from the first flip-flop 20 to the second and second drive circuits 6 and 7, respectively.
is sent out from the second flip-flop 22 to the third and fourth drive circuits 8 and 9, respectively.
3. Q is sent. These four drive control signals Q1
~Q4 is sent out at the timing shown in FIG. 2, and the delay of the drive control signal Q with respect to the drive control signal Q□ or the drive control signal Q with respect to the drive control signal Q2 is called a phase difference φ.

The conduction ratio of the inverter 5 to the load is determined by this phase difference φ.

The drive circuits 6 to 9 connected to the control circuit 16 and the four switching elements 1 to 4, respectively, control the pair of the first switching element 1 and the fourth switching element 4, or the second switching element 2. An alternating current voltage is generated and applied to the load circuit 10 by operating the two pairs of third switching elements 3 in a complementary manner to each other.

Here, in the present invention, each of the above drive circuits 6
-9 is provided with turn-off detection means for detecting that the current of each of the switching elements 1-4 is cut off. Each of the drive circuits 6 to 9 is an AND circuit 2 which will be described later.
3, 24, 25, 26 output base current control signals sb, sb2°Sb3. sb4, first to fourth switching elements 1 to 4 each made of a BJT.
It outputs the base current that drives the. and,
These drive circuits 6 to 9 are connected to each switching element 1 described above.
-4 has an internal circuit that detects the cutoff of the collector current, that is, turn-off, and generates turn-off detection signals S tol, S to □, and 5 to 3° 5t, respectively.
04 is output.

Now, to explain the internal configuration of the first drive circuit 6 as an example, as shown in FIG.
, PNP)-transistor 29, NPN transistor 30, resistor 31, photocoupler 32, and resistor 33
, another PNP transistor 34, a resistor 35, and a turn-off detection circuit 36. The DC voltage sources 27 and 28 are power sources for supplying forward and reverse base currents to the first switching element 1 made of a BJT. 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. P
NP) - transistor 29 and NPN transistor 3o
is an element that selects and switches a forward base current or a reverse base current with respect to the first switching element 1. A resistor 31 connected to the collector side of the PNP transistor 29 is a limiting resistor for setting the forward base current to an optimal value for the first switching element 1.

The photocoupler 32 has a base current control signal S on the input side.
When b1 is supplied, it is converted into - starlight and electrically isolated to transmit the signal.At this time, the signal on the output side connected to the DC voltage source 27 via the resistor 33 is , becomes logic L (low). The other PNP)-transistor 34 is for inverting the logic of the 8-power signal of the photocoupler 32, and when the base connected to the photocoupler 32 is logic, it outputs a DC voltage source via the resistor 35. The collector connected to 27 is a logic H (high)
becomes. When the collector of the transistor 34 is at logic H, the PNP transistor 29 becomes conductive, and at the same time, the NPN transistor 30 becomes non-conductive, and the DC voltage source 29 becomes conductive.
7 is applied between the base and emitter of the first switching element 1, and a forward hess current flows, thereby making the first switching element 1 conductive. Conversely, when the collector of the transistor 34 is in logic state, the NPN transistor 30 becomes conductive, and at the same time the PNP transistor 29 becomes non-conductive, and the voltage of the DC voltage source 28 is applied between the emitter and base of the first switching element 1. , the reverse base current flows, so that the first switching element 1
becomes non-conductive. With this configuration, the first switching element 1 is driven by the base current control signal sb.

The turn-off detection circuit 36 is connected between the emitter and base of the first switching element 1 made of a BJT, and as shown in FIG. It consists of a resistor 40 and a logic inverter 41. The Zener diode 38 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 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 2V to 40V.

Here, the operation of the turn-off detection circuit 36 will be explained 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 29, 30, 34 and the photocoupler 32 used in the first drive circuit 6 are very short compared to the first switching element 1, so they are ignored here. First, the base current control signal Sb1 input to the first drive circuit 6 is
It has a waveform as shown in FIG. 4(a), and the collector current Ic flowing through the first switching element l according to this waveform.
The result is a waveform as shown in Figure (b). As shown in FIG. 4(a), even if the base current control signal Sb1 becomes logical and a reverse base current flows, the collector current Icm continues to flow for a while as shown in FIG. 4(b). , after the turn-off delay time Ts, the collector current I
cm becomes zero current. As shown in FIG. 4(C), the pace emitter voltage Vbe of the first switching element 1 becomes forward biased at the same time as the base current control signal sb shown in FIG. 4(a) becomes logic H. If the logic holds true, the voltage state will continue to be zero for the turn-off delay time Ts, and then the collector current Ic shown in FIG. 4(b) will become zero and at the same time it will be in a reverse bias state.At this time, as shown in FIG. 4(a). As shown in FIG. 3, the base current control signal sb becomes logical and the DC voltage source 28 shown in FIG.
Although the voltage is applied as a reverse bias to the first switching element 1 through the NPN)-transistor 30, a voltage is generated between the base and emitter during the turn-off delay time Ts, as shown in FIG. This is because, as a characteristic of the BJT, during the turn-off delay time Ts, charges remain at the junction between the pace emitters, and the impedance between the pace emitters is low. Then, as shown in FIG. 4(b), when the collector current Ic stops flowing, the reverse recovery between the pace emitters is completed, the impedance becomes high, and a reverse bias appears. From this, as shown in FIG. 4(C), if a negative threshold voltage vth is set for the pace emitter voltage Vbe, which is lower than the voltage during the turn-off delay time Ts and higher than the voltage during reverse bias. , when the pace emitter voltage vbe1 is higher than vth, it is in a conductive state.

Conversely, when it is lower than vth, it can be detected that it is in a non-conductive state.

In the turn-off detection circuit 36 shown in FIG. 3, if the forward voltage drop in the photocoupler 39 is made small, the Zener voltage of the Zener diode 38 is selected to be equal to the threshold voltage vth, and the detection function can be realized. That is, when the pace emitter voltage V be 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 38 and is limited to an appropriate current value by the resistor 37, so that the photo Input to coupler 39. At this time, the resistance is 40
The output of the photocoupler 39, which is pulled up by Become.

Further, in the present invention, each of the drive circuits 6 to 6 shown in FIG.
9, as a 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 the plurality of switching elements 1 to 4. , AND circuits 23, 24, and 25, 26 are connected, respectively. These AND circuits 23 to 26 generate drive control signals Q□ for the respective switching elements 1 to 4.

Q2. Q3. Q, and turn-off detection signals Sto□ and Sto□ of adjacent switching elements in the same string.

S to3. Create an AND signal with Sto4 and output the pace current control signals sb2, sb2. sb...
It is designed to be outputted as sb4 to each drive circuit 6, 7, 8.9.

Next, the operation of the inverter circuit of the present invention configured as above will be explained with reference to FIG. First, the collector current IC1 flowing through the first switching element 1 in FIG. 1 has a waveform as shown in FIG. 5 (,). FIG. 5(b) shows the turn-off detection signal S tol output from the turn-off detection circuit 36 (see FIG. 3) built in the drive circuit 6 of the first switching element 1.

This turn-off detection signal S tol is determined by the turn-off detection circuit 36 to be logical while the collector current Ic shown in FIG. 5(a) is flowing, and becomes logical H when the collector current Icm is cut off.

FIG. 5(c) shows the drive control signal Q2 to the second switching element 2 output from the first flip-flop 20 shown in FIG. This drive control signal Q2 is
The duty is 50%, and there is a complementary relationship with the drive control signal Q to the first switching element 1, which is also output from the first flip-flop 20 (see FIG. 5(g)). In this state, the drive control signal Q2 and the turn-off detection signal Sto output from the first drive circuit 6
□ is input to the second AND circuit 24 shown in FIG. 1 and logical AND is taken, and as shown in FIG. 5(d), the base current control signal Sb2 is generated and the second drive circuit 7. This second drive circuit 7 causes a base current to flow through the second switching element 2 when the base current control signal Sb2 is at logic H, and as a result, the second switching element 2 turns on and the fifth As shown in Figure (e), collector current IC2 flows.

That is, the turn-on of the second switching element 2 is
Regardless of the drive control signal Q2, it is determined only by the rise of the turn-off detection signal Sto which occurs when the collector current Ic1 of the first switching element 1 is turned off.

Therefore, even if the pause period Td is not provided before the drive control signal Q2 as in the conventional case shown in FIG. 12(b), FIG.
As is clear from a) and (e'), the collector current Ic2 of the second switching element 2 can be turned on without overlapping with the collector current Ic of the first switching element 1. The same thing can be seen in Figures 5(e) to 5(e).
It is also performed when the first switching element 1 is turned on as shown in (h), and both switching elements 1 and 2 are turned on.
There will be no redundant conduction.

In addition, in the above explanation, only the string on the left side of the inverter 5 in FIG. 1 was described for the sake of simplicity.
A similar operation is performed in the right string, that is, the third and fourth switching elements 3 and 4, and the switching elements 3 and 4 do not become conductive redundantly. Since the operations of the left and right strings are performed independently, the method of controlling the phase difference is completely unaffected by the phase difference relationship between the left and right strings.

This can be done in the same way as the normal rest period Td setting 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, a Pch field effect transistor 42 is used in place of the PNP transistor 29 shown in FIG. 3, and an Nch field effect transistor 43 is used in place of the NPN transistor 30, resulting in high-speed switching. The first because it is possible to operate
The inverter 5 shown in the figure can be operated at a high frequency. Furthermore, since each element 42, 43 is of a voltage-driven type and has a high gate threshold voltage, it has the characteristic that malfunctions due to noise are small. In the turn-off detection circuit 36' in this example, the emitter voltage of the first switching element 1 is supplied to the Zener diode 38 via the diode 44. 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 44 blocks current flowing through the Zener diode 38 when the first switching element 1 is forward biased. A resistor 45 connected to the cathode side of the Zener diode 38 is provided to stabilize the cathode potential of the Zener diode 38 when the diode 44 is turned off. Further, a capacitor 46 connected to the anode side of the Zener diode 38 is connected to the pace emitter voltage Vbe1 of the first switching element 1.
This is to absorb high frequency noise when it occurs. Furthermore, the resistor 47 is connected to the capacitor 46
discharge resistance.

Here, when the first switching element 1 is cut off and reverse bias is applied to the pace emitter voltage Vbe□, and this voltage exceeds the Zener voltage, the base current limiting resistor 48a
A current is supplied to the base of the transistor 49 through
The transistor 49 becomes conductive. As a result, a current is supplied to the photocoupler 39 via the collector current limiting resistor 48b, and the turn-off detection signal Sto□ is output as a logical logic. At this time, the capacitor 50 is charged while the first switching element 1 is reverse biased, and even if it is then forward biased, the capacitor 50 is not discharged by the discharge blocking diode 51 and continues to hold the voltage. This voltage stabilizes the current supplied to the photocoupler 39 and prevents erroneous detection of the turn-off detection signal Sto even if the pace emitter voltage Vbe decreases. According to the drive circuit 6 etc. having the configuration shown in FIG.
Even when the reverse bias is low and there is concern about malfunction due to noise, stable turn-off detection operation can be performed and even higher inverter operating frequencies can be supported.

Other examples of the internal configuration of the drive circuit 6 etc. include one configured to detect the collector-emitter voltage vCe1 of the first switching element 1 shown in FIG. 7, and one configured to detect the collector-emitter voltage vCe1 of the first switching element 1 shown in FIG. BJT as the first switching element 1 shown in FIG.
There is one in which the collector current of the JT is detected by a current transformer 53.

In the above explanation, it is assumed that the DC voltage source E is a commercial AC power source converted by a thyristor rectifier circuit.
The present invention is not limited to this, and may be of a voltage fixed type such as a battery. 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.

Next, an embodiment of an inverter-type X-ray apparatus using the inverter circuit configured as described above will be described with reference to FIG. This inverter-type X-ray device supplies high voltage to the X-ray tube as a load using an inverter circuit, and as shown in the figure, a DC voltage source E and a plurality of switching elements 1.2, 3.4 an inverter circuit comprising an inverter 5 configured to convert the output voltage of the DC voltage source E into an AC voltage, and drive circuits 6, 7, 8.9 respectively operating the switching elements 1 to 4 of the inverter 5; An inverter control circuit 16 that sends control signals to each of the drive circuits 6 to 9, a high voltage transformer 54 that steps up the output AC voltage of the inverter circuit, and a high voltage rectifier 55 that converts the output of the high voltage transformer 54 into DC. , an X-ray tube 5 to which the output DC voltage of this high voltage rectifier 55 is applied.
6. The inverter circuit in FIG. 10 is constructed in exactly the same way as the inverter circuit shown in FIG. 1, and the load circuit 10 in FIG. It was replaced with a circuit. In the example shown in FIG. 10, the AC output of the inverter circuit is supplied to a series circuit consisting of the high-voltage transformer 54 and the capacitor 57, and the leakage reactance of the high-voltage transformer 54 and A series resonant circuit is configured with the capacitance of the capacitor 57, and the current waveform flowing through the inverter 5 is set to be a sine wave.

Each switching element 1 consists of electromagnetic induction noise and BJT
-4 switching losses are being reduced.

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. In addition, the load range is about 10 to the 4th power,
Therefore, the current flowing through the inverter 5 also changes greatly.

Furthermore, in a resonant type inverter, each switching element 1
The collector current of ~4 is often sinusoidal, and when used in a 1-phase difference control force type, the interrupting current differs depending on the phase difference. That is, it is inevitable that the turn-off delay time Ts 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. 10, the optimum idle period T is determined according to the length of the turn-off delay time Ts
This is equivalent to automatically determining d and adding it to the drive control signals Q, -Q4 to each switching element 1-4.

Therefore, even if the turn-off delay time Ts 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 Td is always minimized, 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.

〔Effect of the invention〕

Since the present invention is configured as described above, the inverter circuit detects each switching element 1 by the turn-off detection means (36) provided inside each of the drive circuits 6 to 9.
Turn-on signal generating means (23 to 4) detecting that the currents of 4 to 4 are interrupted and connected to each of the drive circuits 6 to 9.
26), a current cutoff signal (Sto~5t04) from one of the two switching elements in the same string among the plurality of switching elements 1 to 4 causes a turn-on signal for the other switching element connected in series thereto. can be generated. Thereby, in an inverter circuit using a switching element with a turn-off delay time Ts, the idle period Td of the inverter 5 can be shortened and the operating frequency can be increased.

Further, an inverter-type X-ray apparatus using the inverter circuit configured as described above can increase the operating frequency and downsize the apparatus through the operation of the inverter circuit. Also, the actual shutoff time Tdo
Since the inverter 5 operates so that
There is no reduction in inverter efficiency.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the inverter circuit according to the present invention, Fig. 2 is a timing diagram showing the timing of drive control signals sent from the control circuit to each drive circuit, and Fig. 3 is the internal configuration of the drive circuit. FIG. 4 is a timing diagram for explaining the operation of the turn-off detection circuit, and FIG.
The figure is a timing diagram for explaining the operation of the inverter circuit of the present invention, Figures 6 to 9 are circuit diagrams showing other examples of the internal configuration of the drive circuit, and Figure 10 is a timing diagram for explaining the operation of the inverter circuit of the present invention. A block diagram showing an example of the inverter type X-ray apparatus used, FIG. 11 is a circuit diagram showing a conventional inverter circuit,
FIG. 12 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, and FIG. 13 is a graph showing one of the characteristics of the turn-off delay time of the BJT. . 1-4...Switching element, 5...Inverter,
6-9... Drive circuit, 10... Load circuit,
11-14...Flywheel diode, 16
...control circuit, 23-26...AND circuit,
36... Turn-off detection circuit, 54... High voltage transformer, 55... High voltage rectifier, 56... X-ray tube.

Claims (4)

[Claims] (1) A DC voltage source, an inverter that is composed of a plurality of switching elements and converts the output voltage of the DC voltage source into AC voltage, a drive circuit that operates each switching element of this inverter, and an output from the inverter. In an inverter circuit having a load circuit to which a voltage is applied, turn-off detection means for detecting that the current of each of the switching elements is cut off is provided inside each of the drive circuits, and the drive circuits include: A means is connected to each of the plurality of switching elements 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. inverter circuit. (2) The inverter circuit according to claim 1, wherein each of the switching elements is a bipolar junction transistor, and the turn-off detection means detects a voltage between an emitter and a base of the bipolar junction transistor. (3) The turn-off detection means sets the detection level by the Zener voltage of the Zener diode,
In addition, the Zener voltage of the Zener diode is higher than the voltage generated at the emitter of the bipolar junction transistor as a switching element as seen from the base during the storage time, and the voltage of the emitter as seen from the base when the bipolar junction transistor recovers reversely. 3. The inverter circuit according to claim 2, wherein the voltage is lower than that of the inverter circuit. (4) an inverter circuit comprising a DC voltage source, an inverter configured to convert the output voltage of the DC voltage source into an AC voltage, and a drive circuit configured to operate each switching element of the inverter; An inverter control circuit that sends control signals to each drive circuit, a high-voltage transformer that boosts the output AC voltage of the inverter circuit, a high-voltage rectifier that converts the output of this high-voltage transformer into DC, and an output DC of this high-voltage rectifier. An inverter-type X-ray apparatus comprising an X-ray tube to which a voltage is applied, wherein the inverter circuit is as claimed in claim 1, 2 or 3.
An inverter-type X-ray apparatus characterized by using the inverter circuit described above.