WO2016189768A1

WO2016189768A1 - Dc/ac inverter

Info

Publication number: WO2016189768A1
Application number: PCT/JP2015/085542
Authority: WO
Inventors: 静夫森岡; 鶴谷　守; 彰水谷
Original assignee: 東芝デジタルメディアエンジニアリング株式会社
Priority date: 2015-05-25
Filing date: 2015-12-18
Publication date: 2016-12-01
Also published as: JP6554324B2; JP2016220468A

Abstract

The present invention reduces the recovery current in a body diode of the main transistor of a DC/AC inverter. In an embodiment, the DC/AC inverter includes a normally-off switching transistor, a voltage source, and a drive circuit. The normally-off switching transistor is provided with a first terminal, a second terminal, and a control terminal, and is serially connected to a normally-off main transistor via the first terminal. The voltage source fixes the potential difference between the control terminal of the normally-off main transistor and the second terminal of the normally-off switching transistor. The drive circuit turns the normally-off switching transistor on and off. The withstand voltage of the normally-off switching transistor is lower than the withstand voltage of the normally-off main transistor.

Description

DC / AC inverter

Embodiment relates to a DC / AC inverter.

In order to generate AC power from DC power, a DC (Direct Current) / AC (Alternative Current) inverter is used. In the DC / AC inverter, a recovery current may be generated in the body (parasitic) diode of the main FET in accordance with the ON / OFF operation of the main FET (Field Effect Transistor). This recovery current increases switching loss and noise and may cause damage to the main FET.

Conventionally, for example, a first diode that blocks forward current of a body diode of a main FET is connected in series to the main FET, and a second diode that bypasses the current is connected to the anode of the first diode and the source of the main FET There is known a technique for preventing the generation of a recovery current in the body diode by connecting between the terminal and the terminal. However, such a technique has problems such as an increase in cost due to an increase in the number of elements, a loss due to the forward voltage of the first diode (that is, a reduction in efficiency of the DC / AC inverter), and the like.

As a further measure against the recovery current, an SRB (Synchronous Reverse Blocking) circuit is known. However, since the SRB circuit requires a high breakdown voltage / high-speed free-wheeling diode, loss remains a problem.

Furthermore, a technique for reducing the recovery current by realizing the main FET with a normally-on transistor is also known. However, in such a technique, when the drain-source voltage V _ds of the main FET changes during the OFF period of the main FET due to the action of the external circuit, the gate is connected via the feedback capacitance C _dg (or C _rss ) of the main FET. There is a possibility that the source-to-source voltage _Vgs rises and the main FET is erroneously turned on. If the main FET is erroneously turned on in spite of the OFF period, not only the loss increases, but the main FET may be damaged. Although it is possible to suppress the increase in V _gs by lowering the resonance frequency of the external circuit and gradually changing V _ds , there is an increase in the size of the external circuit, a decrease in efficiency due to a longer dead time, and the like. It becomes a problem.

JP 2011-067051 A

Embodiment aims at reducing the recovery current in the body diode of the main transistor of the DC / AC inverter.

According to the embodiment, the DC / AC inverter inputs a DC voltage via the first input terminal and the second input terminal and converts the DC voltage generated by converting the DC voltage to the first output terminal. And output via the second output terminal. The DC / AC inverter includes a first normally-off transistor, a second normally-off transistor, a third normally-off transistor, a fourth normally-off transistor, a fifth normally-off transistor, a sixth normally-off transistor, a seventh Normally-off transistor, eighth normally-off transistor, first voltage source, second voltage source, third voltage source, fourth voltage source, first drive circuit, second drive circuit, third Drive circuit and a fourth drive circuit. The first normally-off transistor is inserted between the first input terminal and the first output terminal. The second normally-off transistor is inserted between the second input terminal and the first output terminal. The third normally-off transistor is inserted between the first input terminal and the second output terminal. The fourth normally-off transistor is inserted between the second input terminal and the second output terminal. The fifth normally-off transistor includes a first terminal, a second terminal, and a control terminal, and is connected in series to the first normally-off transistor via the first terminal. The sixth normally-off transistor includes a first terminal, a second terminal, and a control terminal, and is connected in series to the second normally-off transistor via the first terminal. The seventh normally-off transistor includes a first terminal, a second terminal, and a control terminal, and is connected in series to the third normally-off transistor via the first terminal. The eighth normally-off transistor includes a first terminal, a second terminal, and a control terminal, and is connected in series to the fourth normally-off transistor via the first terminal. The first voltage source fixes a potential difference between the control terminal of the first normally-off transistor and the second terminal of the fifth normally-off transistor. The second voltage source fixes a potential difference between the control terminal of the second normally-off transistor and the second terminal of the sixth normally-off transistor. The third voltage source fixes a potential difference between the control terminal of the third normally-off transistor and the second terminal of the seventh normally-off transistor. The fourth voltage source fixes a potential difference between the control terminal of the fourth normally-off transistor and the second terminal of the eighth normally-off transistor. The first drive circuit drives the fifth normally-off transistor ON / OFF. The second drive circuit drives the sixth normally-off transistor ON / OFF. The third drive circuit drives the seventh normally-off transistor ON / OFF. The fourth drive circuit drives the eighth normally-off transistor ON / OFF. The breakdown voltage of the fifth normally-off transistor, the sixth normally-off transistor, the seventh normally-off transistor, and the eighth normally-off transistor is the same as that of the first normally-off transistor, the second normally-off transistor, and the third normally-off transistor. It is lower than the breakdown voltage of the transistor and the fourth normally-off transistor.

According to the embodiment, the DC / AC inverter inputs a DC voltage via the first input terminal and the second input terminal and converts the DC voltage generated by converting the DC voltage to the first output terminal. And output via the second output terminal. The DC / AC inverter includes a first normally-off transistor, a second normally-off transistor, a third normally-off transistor, a fourth normally-off transistor, a first normally-off transistor pair, a second normally-off transistor pair, Third normally-off transistor pair, fourth normally-off transistor pair, first voltage source, second voltage source, third voltage source, fourth voltage source, first drive circuit, second drive A circuit, a third drive circuit, and a fourth drive circuit. The first normally-off transistor is inserted between the first input terminal and the first output terminal. The second normally-off transistor is inserted between the second input terminal and the first output terminal. The third normally-off transistor is inserted between the first input terminal and the second output terminal. The fourth normally-off transistor is inserted between the second input terminal and the second output terminal. The first normally-off transistor pair is connected in series to the first normally-off transistor. The second normally-off transistor pair is connected in series to the second normally-off transistor. The third normally-off transistor pair is connected in series to the third normally-off transistor. The fourth normally-off transistor pair is connected in series to the fourth normally-off transistor. The first voltage source fixes a potential difference between the control terminal of the first normally-off transistor and the common terminal of the first normally-off transistor pair. The second voltage source fixes a potential difference between the control terminal of the second normally-off transistor and the common terminal of the second normally-off transistor pair. The third voltage source fixes a potential difference between the control terminal of the third normally-off transistor and the common terminal of the third normally-off transistor pair. The fourth voltage source fixes a potential difference between the control terminal of the fourth normally-off transistor and the common terminal of the fourth normally-off transistor pair. The first drive circuit drives the first normally-off transistor pair ON / OFF. The second drive circuit drives the second normally-off transistor pair ON / OFF. The third drive circuit drives the third normally-off transistor pair ON / OFF. The fourth drive circuit drives the fourth normally-off transistor pair ON / OFF. The breakdown voltages of the first normally-off transistor pair, the second normally-off transistor pair, the third normally-off transistor pair, and the fourth normally-off transistor pair are the first normally-off transistor, the second normally-off transistor, This is lower than the breakdown voltage of the normally-off transistor 3 and the normally-off transistor 4.

1 is a circuit diagram illustrating a DC / AC inverter according to a first embodiment. The circuit diagram which illustrates the basic circuit of a DC / AC inverter. Explanatory drawing of the recovery electric current which generate | occur | produces in the DC / AC inverter of FIG. The circuit diagram which illustrates the DC / AC inverter concerning a comparative example. Explanatory drawing of the effect of the DC / AC inverter of FIG. Explanatory drawing of the effect of the DC / AC inverter of FIG. The circuit diagram which illustrates the DC / AC inverter concerning a 2nd embodiment.

Hereinafter, embodiments will be described with reference to the drawings. Hereinafter, the same or similar elements as those already described are denoted by the same or similar reference numerals, and redundant description is basically omitted. In the following description, the FET may be replaced with various normally-off transistors such as a nitrogen gallium (GaN) transistor and a silicon carbide (SiC) transistor.

(First embodiment)
FIG. 2 illustrates a basic circuit of a DC / AC inverter. The DC / AC inverter of FIG. 2 is common to the DC / AC inverter according to the first embodiment in the basic operation principle, although no measures against recovery current are taken.

The DC / AC inverter of FIG. 2 receives a DC voltage (V _in ) via a first input terminal and a second input terminal (ground), and converts an AC voltage generated by converting the DC voltage into a first voltage. 1 is output via the first output terminal OUT1 and the second output terminal OUT2.

The DC / AC inverter of FIG. 2 includes a main FET Q205, a main FET Q206, a main FET Q207, a main FET Q208, a voltage source E201, a voltage source E202, a voltage source E203, a drive circuit Drive201, and a drive. A circuit Drive 202, a drive circuit Drive 203, and a drive circuit Drive 204 are included.

The drain terminal of the main FET Q205 is connected to the first input terminal of the DC / AC inverter, the gate terminal is connected to the output terminal (Out) of the drive circuit Drive201 via the resistor R202, and the source terminal is connected The inductor L1 is connected to the first output terminal of the DC / AC inverter. FIG. 2 also shows the body diode D201 of the main FET Q205. The drive circuit Drive 201 generates a control signal for controlling ON / OFF of the main FET Q205 using the voltage source E201 as a power source, and outputs the control signal via the output terminal.

The main FET Q206 has its drain terminal connected to the first output terminal of the DC / AC inverter via the inductor L1, and its gate terminal connected to the output terminal (Out) of the drive circuit Drive 202 via the resistor R205. , Its source terminal is connected to the second input terminal of the DC / AC inverter (ie, grounded). FIG. 2 also shows the body diode D202 of the main FET Q206. The drive circuit Drive 202 generates a control signal for controlling ON / OFF of the main FET Q206 using the voltage source E202 as a power source, and outputs the control signal via the output terminal.

The main FET Q207 has its drain terminal connected to the first input terminal of the DC / AC inverter, its gate terminal connected to the output terminal (Out) of the drive circuit Drive 203 via the resistor R208, and its source terminal The inductor is connected to the second output terminal of the DC / AC inverter via the inductor L2. FIG. 2 also shows the body diode D203 of the main FET Q207. The drive circuit Drive 203 generates a control signal for controlling ON / OFF of the main FET Q207 using the voltage source E203 as a power source, and outputs the control signal via an output terminal.

The drain terminal of the main FET Q208 is connected to the second output terminal of the DC / AC inverter via the inductor L2, and the gate terminal is connected to the output terminal (Out) of the drive circuit Drive204 via the resistor R211. , Its source terminal is connected to the second input terminal of the DC / AC inverter (ie, grounded). FIG. 2 also shows the body diode D204 of the main FET Q208. The drive circuit Drive 204 generates a control signal for controlling ON / OFF of the main FET Q208 using the voltage source E202 as a power source, and outputs the control signal via the output terminal.

The drive circuit Drive 201, the drive circuit Drive 202, the drive circuit Drive 203, and the drive circuit Drive 204 drive the main FET Q205, the main FET Q206, the main FET Q207, and the main FET Q208 on / off, respectively, to thereby turn on the first DC / AC inverter. AC power is supplied to the output terminal OUT1 and the second output terminal OUT2.

In the DC / AC inverter of FIG. 2, there is a possibility that a recovery current is generated in the body diode of each main FET. For example, if the main FET Q208 is switched from the ON state to the OFF state while the drain current of the main FET Q208 is flowing from the source terminal to the drain terminal, the main FET Q208 is forwarded to the body diode D204 over the subsequent dead time. Directional current will flow. Therefore, when the main FET Q207 switches from the OFF state to the ON state at the end of the dead time, as illustrated in FIG. 3, a recovery current is instantaneously generated in the body diode D204, and the switching loss of the DC / AC inverter is reduced. Increase.

FIG. 4 illustrates a DC / AC inverter according to a comparative example. Although the DC / AC inverter of FIG. 4 differs in the recovery current countermeasure mechanism as compared with the DC / AC inverter according to the first embodiment, it is common in the basic operation principle. Specifically, in the DC / AC inverter of FIG. 4, a diode D205, a diode D206, a diode D207, a diode D208, a diode D209, a diode D210, a diode D211 and a diode D212 are added to the DC / AC inverter of FIG. Corresponds to the configuration.

The diode D205 is inserted between the first input terminal of the DC / AC inverter and the main FET Q205 to block the forward current of the body diode D201 of the main FET Q205.

The diode D206 is inserted between the first output terminal of the DC / AC inverter and the main FET Q206 to block the forward current of the body diode D202 of the main FET Q206.

The diode D207 is inserted between the first input terminal of the DC / AC inverter and the main FET Q207 to block the forward current of the body diode D203 of the main FET Q207.

The diode D208 is inserted between the second output terminal of the DC / AC inverter and the main FET Q208 to block the forward current of the body diode D204 of the main FET Q208.

The diode D209 connects between the source terminal of the main FET Q205 and the anode of the diode D205 to form a current bypass. As the diode D209, a type of diode whose recovery current is small (compared to each body diode) or does not cause a problem is employed. Specifically, the diode D209 may be a Schottky barrier diode.

The diode D210 connects between the source terminal of the main FET Q206 and the anode of the diode D206 to form a current bypass. As the diode D210, a diode whose recovery current is small (compared to each body diode) or does not cause a problem is employed. Specifically, the diode D210 may be a Schottky barrier diode.

The diode D211 connects the source terminal of the main FET Q207 and the anode of the diode D207 to form a current bypass. As the diode D211, a diode whose recovery current is small (compared to each body diode) or does not cause a problem is employed. Specifically, the diode D211 may be a Schottky barrier diode.

The diode D212 connects the source terminal of the main FET Q208 and the anode of the diode D208 to form a current bypass. As the diode D212, a type of diode whose recovery current is small (compared to each body diode) or does not cause a problem is employed. Specifically, the diode D212 may be a Schottky barrier diode.

4, the recovery current is effectively reduced as compared with the DC / AC inverter of FIG. 2. For example, since the current from the source terminal to the drain terminal of the main FET Q208 is blocked by the diode D208, a forward current flows through the body diode D204 even when the main FET Q208 is switched from the ON state to the OFF state. Absent. On the other hand, as illustrated in FIG. 5, although the drain current bypassing the main FET Q208 flows through the diode D212 as a forward current, the influence of the recovery current by the diode D212 is small as described above. Therefore, according to the DC / AC inverter of FIG. 4, the recovery current can be effectively reduced. On the other hand, in the DC / AC inverter of FIG. 4, the cost increases as the number of elements increases, and the loss due to the forward voltage of the diode D205, the diode D206, the diode D207, and the diode D208 (ie, the efficiency of the DC / AC inverter decreases). Etc. becomes a problem.

In the DC / AC inverter according to the first embodiment, the gate terminal of each main FET is connected to a bias voltage source, and ON / OFF of the main FET is connected in series to the main FET (compared to the main FET). And) Control through a low breakdown voltage switching FET. A DC / AC inverter according to this embodiment is illustrated in FIG.

The DC / AC inverter of FIG. 1 receives a DC voltage (V _in ) via a first input terminal and a second input terminal (ground) and converts an AC voltage generated by converting the DC voltage into a first voltage. 1 is output via the first output terminal OUT1 and the second output terminal OUT2.

The DC / AC inverter of FIG. 1 includes a main FET Q101, a main FET Q102, a main FET Q103, a main FET Q104, a switching FET Q105, a switching FET Q106, a switching FET Q107, a switching FET Q108, and a voltage. A source E101, a voltage source E102, a voltage source E103, a drive circuit Drive101, a drive circuit Drive102, a drive circuit Drive103, a drive circuit Drive104, a diode D101, a diode D102, a diode D103, and a diode D104 Including. In FIG. 1, the body diode of each FET is not drawn.

Main FET Q101 has its drain terminal connected to the first input terminal of the DC / AC inverter, its gate terminal connected to the positive terminal of voltage source E101, and its source terminal connected to the drain terminal of switching FET Q105 and diode D101. Are commonly connected to the cathodes. Since the potential difference between the gate terminal of the main FET Q101 and the source terminal of the switching FET Q105 is fixed by the voltage source E101, the main FET Q101 can be switched on / off by controlling the switching FET Q105. The electromotive force of the voltage source E101 exceeds the threshold voltage of the main FET Q101.

The main FET Q102 has its drain terminal connected to the first output terminal of the DC / AC inverter via the inductor L1, its gate terminal connected to the positive terminal of the voltage source E102, and its source terminal connected to the switching FET Q106. Commonly connected to the drain terminal and the cathode of the diode D102. Since the potential difference between the gate terminal of the main FET Q102 and the source terminal of the switching FET Q106 is fixed by the voltage source E102, the main FET Q102 can be switched ON / OFF by controlling the switching FET Q106. The electromotive force of the voltage source E102 exceeds the threshold voltage of the main FET Q102 and the main FET Q104.

The main FET Q103 has its drain terminal connected to the first input terminal of the DC / AC inverter, its gate terminal connected to the positive terminal of the voltage source E103, and its source terminal connected to the drain terminal of the switching FET Q107 and the diode D103. Are commonly connected to the cathodes. Since the potential difference between the gate terminal of the main FET Q103 and the source terminal of the switching FET Q107 is fixed by the voltage source E103, the main FET Q103 can be switched on / off by controlling the switching FET Q107. The electromotive force of the voltage source E103 exceeds the threshold voltage of the main FET Q103.

Main FET Q104 has its drain terminal connected to the second output terminal of the DC / AC inverter via inductor L2, its gate terminal connected to the positive terminal of voltage source E102, and its source terminal connected to switching FET Q108. Commonly connected to the drain terminal and the cathode of the diode D104. Since the potential difference between the gate terminal of the main FET Q104 and the source terminal of the switching FET Q108 is fixed by the voltage source E102, the main FET Q104 can be switched on / off by controlling the switching FET Q108.

The auxiliary power source for driving the main FET Q104 and the switching FET Q108 can be provided independently of the auxiliary power source for driving the main FET Q102 and the switching FET Q106. The configuration can be simplified by sharing both as in E102.

The switching FET Q105 has its drain terminal connected in common to the source terminal of the main FET Q101 and the cathode of the diode D101, and its gate terminal connected to the output terminal (Out) of the drive circuit Drive101 via the resistor R102. The source terminal is connected to the first output terminal of the DC / AC inverter via the inductor L1, and further connected to the anode of the diode D101. The drive circuit Drive 101 generates a control signal for controlling ON / OFF of the switching FET Q105 using the voltage source E101 as a power source, and outputs the control signal via the output terminal.

The switching FET Q106 has its drain terminal connected in common to the source terminal of the main FET Q102 and the cathode of the diode D102, and its gate terminal connected to the output terminal (Out) of the drive circuit Drive102 via the resistor R105. The source terminal is commonly connected to the anode of the diode D102 and the second input terminal of the DC / AC inverter (ie, grounded). The drive circuit Drive 102 generates a control signal for controlling ON / OFF of the switching FET Q106 using the voltage source E102 as a power source, and outputs the control signal via the output terminal.

The switching FET Q107 has its drain terminal connected in common to the source terminal of the main FET Q103 and the cathode of the diode D103, and its gate terminal connected to the output terminal (Out) of the drive circuit Drive103 via the resistor R108. The source terminal is connected to the second output terminal of the DC / AC inverter via the inductor L2, and further connected in common to the anode of the diode D103 and the drain terminal of the main FET Q104. The drive circuit Drive 103 generates a control signal for controlling ON / OFF of the switching FET Q107 using the voltage source E103 as a power source, and outputs the control signal via an output terminal.

The switching FET Q108 has its drain terminal connected in common to the source terminal of the main FET Q104 and the cathode of the diode D104, and its gate terminal connected to the output terminal (Out) of the drive circuit Drive104 via the resistor R111. The source terminal is commonly connected to the anode of the diode D104 and the second input terminal of the DC / AC inverter (ie, grounded). The drive circuit Drive 104 generates a control signal for controlling ON / OFF of the switching FET Q108 using the voltage source E102 as a power source, and outputs the control signal via an output terminal.

The diode D101 connects the drain and source of the switching FET Q105. As the diode D101, a diode whose recovery current is small (compared to the body diode of each main FET) or does not cause a problem is employed. Specifically, the diode D101 may be a Schottky barrier diode.

The diode D102 connects between the drain and source of the switching FET Q106. As the diode D102, a diode whose recovery current is small (compared to the body diode of each main FET) or does not cause a problem is employed. Specifically, the diode D102 may be a Schottky barrier diode.

The diode D103 connects between the drain and source of the switching FET Q107. As the diode D103, a diode whose recovery current is small (compared to the body diode of each main FET) or does not cause a problem is employed. Specifically, the diode D103 may be a Schottky barrier diode.

The diode D104 connects the drain and source of the switching FET Q108. As the diode D104, a diode whose recovery current is small (compared to the body diode of each main FET) or does not cause a problem is employed. Specifically, the diode D104 may be a Schottky barrier diode.

The drive circuit Drive101, the drive circuit Drive102, the drive circuit Drive103, and the drive circuit Drive104 drive the switching FET Q105, the switching FET Q106, the switching FET Q107, and the switching FET Q108, respectively, and the main FET Q101, the main FET in conjunction with them. By turning ON / OFF the FET Q102, the main FET Q103, and the main FET Q104, AC power is supplied to the first output terminal OUT1 and the second output terminal OUT2 of the DC / AC inverter.

The charge for charging the parasitic capacitance (not shown) of the main FET Q101, the main FET Q102, the main FET Q103, and the main FET Q104 passes through the resistor R101, the resistor R104, the resistor R107, and the resistor R110. , Capacitor C102, capacitor C103 and capacitor C104 are charged. Therefore, part or all of the power consumption of the drive circuit Drive 101, the drive circuit Drive 102, the drive circuit Drive 103, and the drive circuit Drive 104 can be covered by such charge movement. With such an action, the efficiency of the DC / AC inverter can be improved.

In the DC / AC inverter of FIG. 1, the recovery current is effectively reduced as compared with the DC / AC inverter of FIG. For example, when the switching FET Q108 switches from the OFF state to the ON state, the gate-source voltage V _gs of the main FET Q104 substantially matches the electromotive force of the voltage source E102 (> the threshold voltage of the main FET Q104). The FET Q104 is turned on.

On the other hand, even if the switching FET Q108 is switched from the ON state to the OFF state while the drain current of the switching FET Q108 flows from the source terminal to the drain terminal, the diode D104 is forward biased ( That is, the source potential of the main FET Q104 is substantially maintained, and the main FET Q104 continues to be in the ON state. Therefore, the forward current of the diode D104 is supplied to the load through the channel of the main FET Q104. More precisely, if the voltage drop due to the channel resistance of the main FET Q104 is smaller than the forward voltage of the body diode of the main FET Q104, the body diode is cut off while the current flows through the channel of the main FET Q104. State (ie, forward current does not flow). Therefore, as illustrated in FIG. 6, even if the switching FET Q107 and the main FET Q103 are switched from the OFF state to the ON state after the dead time is over, the main FET Q104 is in the OFF state without a recovery current flowing through its body diode. Can be switched to.

If the switching FET Q108 is switched from the ON state to the OFF state with the drain current of the switching FET Q108 flowing from the drain terminal to the source terminal, the diode D104 is reverse-biased. The source potential of the main FET Q104 substantially matches the gate potential, and the main FET Q104 also switches from the ON state to the OFF state. In the dead time, since the body diode of the main FET Q104 is reverse-biased, no forward current flows. Therefore, even if the switching FET Q107 and the main FET Q103 are switched from the OFF state to the ON state after the dead time is over, the main FET Q104 can be switched to the OFF state without a recovery current flowing through the body diode.

As described above, the DC / AC inverter according to the first embodiment drives the switching FET connected in series to the main FET on / off without directly driving the main FET. Since the gate terminal of the main FET is connected to the bias voltage source, the switching FET is switched from the ON state to the OFF state with the drain current of the corresponding switching FET flowing from the source terminal to the drain terminal. Even when switching to, the ON state is maintained, and the drain current can flow through the channel instead of the body diode. Therefore, according to this DC / AC inverter, it is possible to prevent (at least reduce) the generation of a recovery current in the body diode of the main FET. According to this DC / AC inverter, since the gate terminal of the main FET is connected to the bias voltage source, even if the drain-source voltage _Vds is changed by an external circuit, the gate-source voltage is changed. V _gs does not increase, and the main FET is not erroneously turned on and is not damaged.

Further, according to this DC / AC inverter, it is only necessary to drive a low withstand voltage (small) switching FET instead of a high withstand voltage (large) main FET. And the efficiency of the DC / AC inverter can be improved. In addition, since this DC / AC inverter does not require a high breakdown voltage / high-speed free-wheeling diode, it can be realized on a small scale (low cost) and low loss.

Further, according to this DC / AC inverter, a diode having a low forward voltage such as a Schottky barrier diode is employed as the diode connecting the drain and source of the switching FET, so that loss (ie, DC / (Decrease in efficiency of the AC inverter) can be suppressed. Even if the diode is omitted, the body diode of the switching FET plays a role of the diode, so that the recovery current generated in the body diode of the main FET can be reduced.

(Second Embodiment)
If the voltage drop due to the channel resistance of the main FET is smaller than the forward voltage of the body diode of the main FET, the DC / AC inverter according to the first embodiment described above can prevent the generation of the recovery current. On the other hand, when the voltage drop due to the channel resistance of the main FET is the same as the forward voltage of the body diode of the main FET, this DC / AC inverter recovers because some forward current flows through the body diode. An electric current will be generated. The DC / AC inverter according to the second embodiment prevents a forward current from flowing through the body diode of the main FET and prevents the generation of a recovery current regardless of the channel resistance of the main FET.

In the DC / AC inverter according to the second embodiment, the gate terminal of each main FET is connected to a bias voltage source, and ON / OFF of the main FET is connected in series to the main FET (compared to the main FET). And control through a pair of switching FETs with low breakdown voltage (common source). A DC / AC inverter according to this embodiment is illustrated in FIG.

The DC / AC inverter of FIG. 7 inputs a DC voltage (V _in ) via a first input terminal and a second input terminal (ground) and converts an AC voltage generated by converting the DC voltage into a first voltage. 1 is output via the first output terminal OUT1 and the second output terminal OUT2.

The DC / AC inverter of FIG. 7 includes a main FET Q101, a main FET Q102, a main FET Q103, a main FET Q104, a switching FET Q305, a switching FET Q306, a switching FET Q307, and a switching FET Q308. FET Q309, switching FET Q310, switching FET Q311, switching FET Q312, voltage source E101, voltage source E102, voltage source E103, voltage source E304, drive circuit Drive 301, drive circuit Drive 302, and drive Circuit Drive 303, drive circuit Drive 304, diode D301, diode D302, diode D303, and diode D304. . In FIG. 7, the body diode of each FET is not drawn.

The main FET Q101 has a drain terminal connected to the cathode of the diode D301 in addition to the first input terminal of the DC / AC inverter, a gate terminal connected to the positive terminal of the voltage source E101, and a source terminal connected to the switching FET. Connected to the drain terminal of Q305. Since the potential difference between the gate terminal of the main FET Q101 and the source terminal of the switching FET Q305 and the switching FET Q306 is fixed by the voltage source E101, the main FET Q101 can be turned ON / OFF by controlling the switching FET Q305 and the switching FET Q306. Can be switched. As described above, the electromotive force of the voltage source E101 exceeds the threshold voltage of the main FET Q101.

Main FET Q102 has its drain terminal connected to the first output terminal of the DC / AC inverter via inductor L1, further connected to the cathode of diode D302, and its gate terminal connected to the positive terminal of voltage source E102. The source terminal is connected to the drain terminal of the switching FET Q307. Since the potential difference between the gate terminal of the main FET Q102 and the source terminal of the switching FET Q307 and the switching FET Q308 is fixed by the voltage source E102, the main FET Q102 can be turned ON / OFF by controlling the switching FET Q307 and the switching FET Q308. Can be switched. As described above, the electromotive force of the voltage source E102 exceeds the threshold voltage of the main FET Q102.

The main FET Q103 has a drain terminal connected to the cathode of the diode D303 in addition to the first input terminal of the DC / AC inverter, a gate terminal connected to the positive terminal of the voltage source E103, and a source terminal connected to the switching FET. Connected to the drain terminal of Q309. Since the potential difference between the gate terminal of the main FET Q103 and the source terminal of the switching FET Q309 and the switching FET Q310 is fixed by the voltage source E103, if the switching FET Q309 and the switching FET Q310 are controlled, the main FET Q103 is turned on / off. Can be switched. As described above, the electromotive force of the voltage source E103 exceeds the threshold voltage of the main FET Q103.

Main FET Q104 has its drain terminal connected to the second output terminal of the DC / AC inverter via inductor L2, further connected to the cathode of diode D304, and its gate terminal connected to the positive terminal of voltage source E304. The source terminal is connected to the drain terminal of the switching FET Q311. Since the potential difference between the gate terminal of the main FET Q104 and the source terminal of the switching FET Q311 and the switching FET Q312 is fixed by the voltage source E304, the main FET Q104 can be turned ON / OFF by controlling the switching FET Q311 and the switching FET Q312. Can be switched. The electromotive force of the voltage source E304 exceeds the threshold voltage of the main FET Q104.

The switching FET Q305 has its drain terminal connected to the source terminal of the main FET Q101, its gate terminal connected to the output terminal (Out) of the drive circuit Drive 301 via the resistor R102, and its source terminal connected to the switching FET Q306. Connected to the source terminal.

The switching FET Q306 has its drain terminal connected to the first output terminal of the DC / AC inverter via the inductor L1, further connected to the anode of the diode D301, and its gate terminal connected to the drive circuit Drive301 via the resistor R301. The output terminal (Out) of the switching FET Q305 is connected to the source terminal of the switching FET Q305.

The drive circuit Drive 301 generates a control signal for controlling ON / OFF of the switching FET Q305 and the switching FET Q306 using the voltage source E101 as a power source, and outputs the control signal via the output terminal. Since the switching FET Q305 and the switching FET Q306 have the same gate potential and source potential, the ON / OFF behavior is also common.

The switching FET Q307 has its drain terminal connected to the source terminal of the main FET Q102, its gate terminal connected to the output terminal (Out) of the drive circuit Drive302 via the resistor R302, and its source terminal connected to the switching FET Q308. Connected to the source terminal.

The switching FET Q308 has a drain terminal commonly connected to the second input terminal of the DC / AC inverter and the anode of the diode D302, and a gate terminal connected to the output terminal (Out) of the drive circuit Drive302 via the resistor R302. The source terminal is connected to the source terminal of the switching FET Q307.

The drive circuit Drive 302 generates a control signal for controlling ON / OFF of the switching FET Q307 and the switching FET Q308 using the voltage source E102 as a power source, and outputs the control signal via the output terminal. Since the switching FET Q307 and the switching FET Q308 have the same gate potential and source potential, the ON / OFF behavior is also common.

The switching FET Q309 has its drain terminal connected to the source terminal of the main FET Q103, its gate terminal connected to the output terminal (Out) of the drive circuit Drive303 via the resistor R303, and its source terminal connected to the switching FET Q310. Connected to the source terminal.

The switching FET Q310 has its drain terminal connected to the second output terminal of the DC / AC inverter via the inductor L2, further connected to the anode of the diode D303, and its gate terminal connected to the drive circuit Drive303 via the resistor R303. The output terminal (Out) of the switching FET Q309 is connected to the source terminal of the switching FET Q309.

The drive circuit Drive 303 generates a control signal for controlling ON / OFF of the switching FET Q309 and the switching FET Q310 using the voltage source E103 as a power source, and outputs the control signal via the output terminal. Since the switching FET Q309 and the switching FET Q310 have the same gate potential and source potential, the ON / OFF behavior is also common.

The switching FET Q311 has its drain terminal connected to the source terminal of the main FET Q104, its gate terminal connected to the output terminal (Out) of the drive circuit Drive304 via the resistor R304, and its source terminal connected to the switching FET Q312. Connected to the source terminal.

The switching FET Q312 has its drain terminal connected in common to the second input terminal of the DC / AC inverter and the anode of the diode D304, and its gate terminal connected to the output terminal (Out) of the drive circuit Drive304 via the resistor R304. The source terminal is connected to the source terminal of the switching FET Q311.

The drive circuit Drive 304 generates a control signal for controlling ON / OFF of the switching FET Q311 and the switching FET Q312 using the voltage source E304 as a power source, and outputs the control signal via the output terminal. Since the switching FET Q311 and the switching FET Q312 have the same gate potential and source potential, the ON / OFF behavior is also common.

The anode of the diode D301 is connected to the first output terminal of the DC / AC inverter via the inductor L1, and further connected to the drain terminal of the switching FET Q306, and the cathode thereof is connected to the drain terminal of the main FET Q101 and the DC / AC. Commonly connected to the first input terminal of the inverter. As the diode D301, a type of diode whose recovery current is small (compared to the body diode of each main FET) or does not cause a problem is adopted. Specifically, the diode D301 may be a Schottky barrier diode.

The anode of the diode D302 is commonly connected to the drain terminal of the switching FET Q308 and the second input terminal of the DC / AC inverter, and the cathode is connected to the first output terminal of the DC / AC inverter via the inductor L1. Further, it is connected to the drain terminal of the main FET Q102. As the diode D302, a diode whose recovery current is small (compared to the body diode of each main FET) or does not cause a problem is employed. Specifically, the diode D302 may be a Schottky barrier diode.

The anode of the diode D303 is connected to the second output terminal of the DC / AC inverter via the inductor L2, and further connected to the drain terminal of the switching FET Q310, and its cathode is connected to the drain terminal of the main FET Q103 and the DC / AC. Commonly connected to the first input terminal of the inverter. As the diode D303, a diode whose recovery current is small (compared to the body diode of each main FET) or does not cause a problem is employed. Specifically, the diode D303 may be a Schottky barrier diode.

The anode of the diode D304 is commonly connected to the drain terminal of the switching FET Q312 and the second input terminal of the DC / AC inverter, and the cathode is connected to the second output terminal of the DC / AC inverter via the inductor L2. Further, it is connected to the drain terminal of the main FET Q104. As the diode D304, a diode whose recovery current is small (compared to the body diode of each main FET) or does not cause a problem is employed. Specifically, the diode D304 may be a Schottky barrier diode.

The drive circuit Drive 301, the drive circuit Drive 302, the drive circuit Drive 303, and the drive circuit Drive 304 are a switching FET Q305 and a switching FET Q306, a switching FET Q307 and a switching FET Q308, a switching FET Q309 and a switching FET Q310, and a switching FET Q311 and a switching FET Q312. Are turned ON / OFF, and the main FET Q101, the main FET Q102, the main FET Q103, and the main FET Q104 are turned ON / OFF in conjunction with them, thereby the first output terminal OUT1 and the second of the DC / AC inverter. AC power is supplied to the output terminal OUT2.

In the DC / AC inverter of FIG. 7, the recovery current is effectively reduced as compared with the DC / AC inverter of FIG. For example, when the switching FET Q311 and the switching FET Q312 are switched from the OFF state to the ON state, the gate-source voltage V _gs of the main FET Q104 substantially matches the electromotive force of the voltage source E304 (> the threshold voltage of the main FET Q104). Therefore, the main FET Q104 is turned on.

On the other hand, when the switching FET Q311 and the switching FET Q312 are switched from the ON state to the OFF state, the source potential of the main FET Q104 substantially matches the gate potential, and the main FET Q104 is also switched from the ON state to the OFF state. Since the switching FET Q311 and the switching FET Q312 are in the OFF state and the directions of these body diodes are contradictory, in the dead time, regardless of the channel resistance of the main FET Q104, Current does not flow. Specifically, even if the drain current of the main FET Q104 flows from the source terminal to the drain terminal immediately before the main FET Q104 switches from the ON state to the OFF state, the current is switched in the OFF state. It is blocked by the FET Q312 and its body diode (reverse bias) and bypasses the diode D304. Therefore, even if the switching FET Q309, the switching FET Q310, and the main FET Q103 are switched from the OFF state to the ON state after the dead time ends, the recovery current does not flow through the body diode of the main FET Q104.

As described above, the DC / AC inverter according to the second embodiment does not directly drive the main FET but drives the switching FET pair connected in series to the main FET on / off. Since the switching FET pairs have their source terminals connected in common, the directions of their body diodes are opposite. Therefore, when the switching FET pair is switched from the ON state to the OFF state, the corresponding main FET is also switched from the ON state to the OFF state, and the forward current of the body diode of the main FET is changed to the switching FET in the OFF state. And its body diode (reverse bias). Therefore, according to this DC / AC inverter, it is possible to prevent generation of a recovery current in the body diode of the main FET regardless of the channel resistance of the main FET.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

C101, C102, C103, C104, C201, C202, C203, C204, CO: capacitors D101, D102, D103, D104, D205, D206, D207, D208, D209, D210, D211, D212, D301, D302, D303 , D304... Diode D201, D202, D203, D204... Body diode Drive101, Drive102, Drive103, Drive104, Drive201, Drive202, Drive203, Drive204, Drive301, Drive302, Drive102, Drive102, Drive102E E103, E201, E202, E203, E304 ... Voltage source L1, L2 ... In Kuta OUT1, OUT2 ··· output terminal Q101, Q102, Q103, Q104, Q205, Q206, Q207, Q208 ··· main FET
Q105, Q106, Q107, Q108, Q305, Q306, Q307, Q308, Q309, Q310, Q311, Q312 ... switching FET
R101, R102, R103, R104, R105, R106, R107, R108, R109, R110, R111, R112, R202, R203, R205, R206, R208, R209, R211, R212, R301, R302, R303, R304, R305, R306, R307, R308, R309, R310, R311, R312... Resistors

Claims

DC which inputs a DC voltage through the first input terminal and the second input terminal, and outputs an AC voltage generated by converting the DC voltage through the first output terminal and the second output terminal / AC inverter,
A first normally-off transistor inserted between the first input terminal and the first output terminal;
A second normally-off transistor inserted between the second input terminal and the first output terminal;
A third normally-off transistor inserted between the first input terminal and the second output terminal;
A fourth normally-off transistor inserted between the second input terminal and the second output terminal;
A fifth normally-off transistor that includes a first terminal, a second terminal, and a control terminal, and is connected in series to the first normally-off transistor via the first terminal;
A sixth normally-off transistor comprising a first terminal, a second terminal, and a control terminal, and being connected in series to the second normally-off transistor via the first terminal;
A seventh normally-off transistor comprising a first terminal, a second terminal, and a control terminal, and being connected in series to the third normally-off transistor via the first terminal;
An eighth normally-off transistor comprising a first terminal, a second terminal, and a control terminal, the eighth normally-off transistor connected in series to the fourth normally-off transistor via the first terminal;
A first voltage source that fixes a potential difference between a control terminal of the first normally-off transistor and a second terminal of the fifth normally-off transistor;
A second voltage source for fixing a potential difference between a control terminal of the second normally-off transistor and a second terminal of the sixth normally-off transistor;
A third voltage source for fixing a potential difference between a control terminal of the third normally-off transistor and a second terminal of the seventh normally-off transistor;
A fourth voltage source for fixing a potential difference between a control terminal of the fourth normally-off transistor and a second terminal of the eighth normally-off transistor;
A first driving circuit for ON / OFF driving the fifth normally-off transistor;
A second drive circuit for ON / OFF driving the sixth normally-off transistor;
A third drive circuit for ON / OFF driving the seventh normally-off transistor;
A fourth drive circuit for ON / OFF driving the eighth normally-off transistor,
The breakdown voltages of the fifth normally-off transistor, the sixth normally-off transistor, the seventh normally-off transistor, and the eighth normally-off transistor are the first normally-off transistor and the second normally-off transistor. The breakdown voltage of the third normally-off transistor and the fourth normally-off transistor is low.
DC / AC inverter.
A first diode connecting the first terminal and the second terminal of the fifth normally-off transistor;
A second diode connecting between a first terminal and a second terminal of the sixth normally-off transistor;
A third diode connecting between the first terminal and the second terminal of the seventh normally-off transistor;
A fourth diode connecting the first terminal and the second terminal of the eighth normally-off transistor;
The forward voltages of the first diode, the second diode, the third diode, and the fourth diode are the first normally-off transistor, the second normally-off transistor, and the third normally-off voltage, respectively. Smaller than the forward voltage of the type transistor and the fourth normally-off type transistor,
The DC / AC inverter according to claim 1.
The DC / AC inverter according to claim 1, wherein the second voltage source and the fourth voltage source are shared.
DC which inputs a DC voltage through the first input terminal and the second input terminal, and outputs an AC voltage generated by converting the DC voltage through the first output terminal and the second output terminal / AC inverter,
A first normally-off transistor inserted between the first input terminal and the first output terminal;
A second normally-off transistor inserted between the second input terminal and the first output terminal;
A third normally-off transistor inserted between the first input terminal and the second output terminal;
A fourth normally-off transistor inserted between the second input terminal and the second output terminal;
A first normally-off transistor pair connected in series to the first normally-off transistor;
A second normally-off transistor pair connected in series with the second normally-off transistor;
A third normally-off transistor pair connected in series with the third normally-off transistor;
A fourth normally-off transistor pair connected in series to the fourth normally-off transistor;
A first voltage source that fixes a potential difference between a control terminal of the first normally-off transistor and a common terminal of the first normally-off transistor pair;
A second voltage source for fixing a potential difference between a control terminal of the second normally-off transistor and a common terminal of the second normally-off transistor pair;
A third voltage source for fixing a potential difference between a control terminal of the third normally-off transistor and a common terminal of the third normally-off transistor pair;
A fourth voltage source for fixing a potential difference between a control terminal of the fourth normally-off transistor and a common terminal of the fourth normally-off transistor pair;
A first drive circuit for ON / OFF driving the first normally-off transistor pair;
A second driving circuit for ON / OFF driving the second normally-off transistor pair;
A third driving circuit for ON / OFF driving the third normally-off transistor pair;
A fourth drive circuit for ON / OFF driving the fourth normally-off transistor pair,
The breakdown voltages of the first normally-off transistor pair, the second normally-off transistor pair, the third normally-off transistor pair, and the fourth normally-off transistor pair are the first normally-off transistor and the second normally-off transistor pair. Lower than the withstand voltage of the normally-off transistor, the third normally-off transistor, and the fourth normally-off transistor.
DC / AC inverter.
A first diode connecting between the first input terminal and the first output terminal;
A second diode connecting between the second input terminal and the first output terminal;
A third diode connecting between the first input terminal and the second output terminal;
A fourth diode connecting between the second input terminal and the second output terminal; and
The forward voltages of the first diode, the second diode, the third diode, and the fourth diode are the first normally-off transistor, the second normally-off transistor, and the third normally-off voltage, respectively. Smaller than the forward voltage of the type transistor and the fourth normally-off type transistor,
The DC / AC inverter according to claim 4.