JP5423450B2 - Gate driver for bidirectional switch - Google Patents

Description

  The present invention relates to a driving device for a bidirectional switch having four states by controlling a gate signal.

  Conventionally, a power converter circuit such as a general inverter using a unidirectional switch connects a freewheeling diode in antiparallel with each switching element, and extinguishes the energy accumulated in the motor inductance through this flywheel diode. ing.

  In the PWM control of the inverter, an operation in which a high voltage in the reverse direction is applied immediately after the forward current is supplied to the flywheel diode. At this time, the freewheeling diode instantaneously energizes a current flowing in the reverse direction called a recovery current. The recovery current is unnecessary power for driving the motor, is consumed as heat in the inverter circuit, and contributes to a reduction in power conversion efficiency of the inverter.

  When a MOS (metal-insulating film-semiconductor) transistor is used as the switching element, a parasitic diode of a MOS transistor is used as the flywheel diode. However, the parasitic diode of the MOS transistor has a long recovery time in which a recovery current flows. For this reason, power loss due to the recovery current is large and heat is likely to be generated.

  When an insulated gate bipolar transistor (IGBT) is used as the switching element, it does not have a parasitic diode, so that a flywheel diode needs to be externally attached. Switching loss can be reduced by using a fast recovery diode with a small recovery current as an external reflux diode (see, for example, Patent Document 1).

  Further, as disclosed in Patent Document 2, there is a method of generating a synchronization control signal using an AND gate or an OR gate. By using this method, the reflux current can be conducted with low loss.

Japanese Patent Application Laid-Open No. 7-222459 JP 2002-272162 A

  However, in the example of Patent Document 1, a power converter circuit such as a general inverter using a unidirectional switch is connected to a freewheeling diode in antiparallel with the switching element, and the freewheeling current is always supplied to the diode side. The number of parts of the circuit increases, and the loss due to the forward voltage of the diode when flowing in the reverse direction increases, so the size of the device such as a cooling fin or a cooling fan becomes larger, hindering downsizing and cost reduction There's a problem.

  Further, in the example of Patent Document 2, since it is necessary to add a logic circuit for generating a synchronization signal, the cost is high and there is a problem of stability due to chattering of the logic circuit from the viewpoint of signal reliability. .

  The present invention solves the above-described problem, and drives a bidirectional switch of each arm having a long return current flow time in a low loss state to avoid constantly supplying a return current to an external diode. In a period other than when switching, a low-loss bidirectional switch is energized, and the other in which the return current flows for a short time, an inverter is configured to energize an external diode. An object of the present invention is to provide a bidirectional switch drive device that can achieve low-loss and stable synchronous control as compared with a power conversion circuit such as an inverter and can reduce the cost with a simple configuration.

  In order to achieve this object, a bidirectional switch drive device according to the present invention includes a bidirectional switch that is arranged in a bridge circuit to form a single-phase or three-phase inverter, and a drive device that drives the bidirectional switch. The bidirectional switch includes a semiconductor layer stack having a channel, a first ohmic electrode and a second ohmic electrode formed on the semiconductor layer stack at a distance from each other, and the first switch A first p-type semiconductor layer and a second p-type semiconductor layer formed in this order from the first ohmic electrode side between the ohmic electrode and the second ohmic electrode, and the first p-type semiconductor layer A substrate comprising a first gate electrode formed on the second p-type semiconductor layer and a second gate electrode formed on the second p-type semiconductor layer; a drain terminal connected to the first ohmic electrode; A source terminal connected to the second ohmic electrode, a first gate terminal connected to the first gate electrode, and a second gate terminal connected to the second gate electrode; and When a gate drive signal is input only between one gate terminal and a drain terminal, a first mode in which an on-state bidirectional device and a reverse diode operate as a semiconductor connected in series from the drain terminal to the source terminal; When a gate drive signal is input only between the second gate terminal and the source terminal, a forward diode and an on-state bidirectional device operate as a semiconductor connected in series from the drain terminal to the source terminal. In the second mode, gate drive signals are input between the first gate terminal and the drain terminal and between the second gate terminal and the source terminal. A third mode that operates in a bidirectional manner between the drain terminal and the source terminal without passing through either a forward diode or a reverse diode, and between the first gate terminal and the drain terminal and the second gate terminal. A fourth mode in which a forward / reverse bidirectional current is cut off without applying a gate drive signal between any of the source terminals, and the drive device includes a first bidirectional switch and a second bidirectional switch. A signal output unit for outputting a signal source to be driven, and driving from the signal source output from the signal output unit to the first gate terminal and the second gate terminal of one of the first bidirectional switch and the second bidirectional switch Distribution means for distributing a signal, wherein one of the first bidirectional switch and the second bidirectional switch is configured such that the first gate terminal and the second gate terminal are the distribution means. And a reverse conducting element that is capable of energizing a reflux current that flows in the reverse direction during the transition time at the time of switching, and the other one of the first bidirectional switch and the second bidirectional switch. The gate terminal is always turned on, and the second gate terminal complementarily operates with one second gate terminal of the first bidirectional switch or the second bidirectional switch when the return current is applied. It is characterized by comprising synchronous control means for controlling, thereby achieving the initial purpose.

  According to the present invention, a bidirectional switch disposed in a bridge circuit and constituting a single-phase or three-phase inverter, and a driving device for driving the bidirectional switch, the bidirectional switch includes a semiconductor layer having a channel. A stacked body, a first ohmic electrode and a second ohmic electrode formed on the semiconductor layer stacked body at intervals, and the first ohmic electrode and the second ohmic electrode between the first ohmic electrode and the second ohmic electrode; A first p-type semiconductor layer and a second p-type semiconductor layer formed in order from the first ohmic electrode side; a first gate electrode formed on the first p-type semiconductor layer; A substrate provided with a second gate electrode formed on the p-type semiconductor layer, a drain terminal connected to the first ohmic electrode, a source terminal connected to the second ohmic electrode, A first gate terminal connected to the gate electrode and a second gate terminal connected to the second gate electrode, and when a gate drive signal is input only between the first gate terminal and the drain terminal, A first mode that operates as a semiconductor in which a bidirectional device and a reverse diode connected in series from the drain terminal to the source terminal are connected in series, and a gate drive signal only between the second gate terminal and the source terminal , A second mode in which a forward diode and an on-state bidirectional device operate as a semiconductor connected in series from the drain terminal to the source terminal, between the first gate terminal and the drain terminal, and the A gate drive signal is input between the second gate terminal and the source terminal, and a forward diode is connected between the drain terminal and the source terminal. A gate drive signal between the first gate terminal and the drain terminal and between the second gate terminal and the source terminal. A fourth mode that cuts off the forward and reverse bidirectional current without adding, and the drive device outputs a signal source that drives the first bidirectional switch and the second bidirectional switch; Distributing means for distributing a drive signal from the signal source output from the signal output unit to one of the first bidirectional terminal and the second bidirectional terminal of the second bidirectional switch, The first gate terminal and the second gate terminal of the bidirectional switch or the second bidirectional switch are controlled by the output signal from the distributing means, and flow in the reverse direction during the transition time at the time of switching. And a signal output unit that outputs a signal source that drives the first bidirectional switch and the second bidirectional switch. Distribution means for distributing a drive signal from the signal source output from the signal output unit to the first gate terminal and the second gate terminal of one of the first bidirectional switch and the second bidirectional switch, One of the one bidirectional switch and the second bidirectional switch, one of the first gate terminal and the second gate terminal is controlled by an output signal from the distributing means, and the return current flows in the reverse direction during the transition time at the time of switching. Of the first bidirectional switch or the second bidirectional switch, the other first gate terminal is always on, and the second gate terminal is a return current. When energized, it is provided with synchronous control means for controlling so as to complement the second gate terminal of one of the first bidirectional switch or the second bidirectional switch. A bidirectional switch drive device that can drive any bidirectional switch of the arm in a low loss state, reduce the loss due to Vf of the freewheeling diode, and realize a low loss power conversion circuit. Can be provided. In addition, no logic circuit is required to generate the synchronization signal, and it is possible to prevent instability due to low cost and logic circuit chattering, etc., and loss is achieved by using this bidirectional switch drive device. It is also possible to provide the single-phase or three-phase inverter with low efficiency and high efficiency. Furthermore, since the other bidirectional switch in which the flow time of the return current is short is energized to the external diode, the configuration can be simplified and the cost can be reduced.

Configuration diagram of bidirectional switch according to Embodiment 1 of the present invention Equivalent circuit diagram of the bidirectional switch ((a) Equivalent circuit diagram composed of first and second transistors, (b) Equivalent circuit diagram of the second transistor, (c) The second transistor is regarded as a diode. Equivalent circuit diagram) Correlation diagram of voltage and current of the bidirectional switch Diagram showing the operation mode of the bidirectional switch Configuration diagram of the inverter device The figure which shows the detailed structure of the synchronous control means The figure which shows the output pattern of the same signal output section Enlarged view of drive pattern of the bidirectional switch 1a, 1b The figure which shows the detailed structure of the synchronous control means of Embodiment 2 of this invention. The figure which shows the output pattern of the same signal output section Enlarged view of the drive pattern The block diagram of the ventilation fan in Embodiment 3 of this invention

  The bidirectional switch drive device according to claim 1 of the present invention includes a bidirectional switch arranged in a bridge circuit to constitute a single-phase or three-phase inverter, and a drive device for driving the bidirectional switch, The bidirectional switch includes: a semiconductor layer stack having a channel; a first ohmic electrode and a second ohmic electrode formed on the semiconductor layer stack at an interval; the first ohmic electrode; Formed on the first p-type semiconductor layer, the first p-type semiconductor layer and the second p-type semiconductor layer formed in order from the first ohmic electrode side between the second ohmic electrode and A substrate including a first gate electrode and a second gate electrode formed on the second p-type semiconductor layer; a drain terminal connected to the first ohmic electrode; and the second ohmic electrode. A source terminal connected to the pole; a first gate terminal connected to the first gate electrode; and a second gate terminal connected to the second gate electrode; and the first gate terminal and drain When a gate drive signal is input only between the terminals, the first mode operates as a semiconductor in which a bidirectional device and a reverse diode are connected in series from the drain terminal to the source terminal, and the second gate When a gate drive signal is input only between a terminal and the source terminal, a second mode in which a forward diode and an on-state bidirectional device operate as a semiconductor connected in series from the drain terminal to the source terminal; A gate drive signal is input between the first gate terminal and the drain terminal and between the second gate terminal and the source terminal to input the drain terminal. A third mode that operates in a bidirectional manner without any of a forward diode and a reverse diode between the source terminals, between the first gate terminal and the drain terminal, and between the second gate terminal and the source terminal. And a fourth mode for blocking forward and reverse bidirectional current without applying a gate drive signal to any of the above, and the drive device is a signal source for driving the first bidirectional switch and the second bidirectional switch. A signal output unit that outputs a signal and a drive signal from the signal source output from the signal output unit to the first gate terminal and the second gate terminal of the first bidirectional switch or the second bidirectional switch Distribution means, wherein one of the first bidirectional switch and the second bidirectional switch has a first gate terminal and a second gate terminal depending on an output signal from the distribution means. A reverse conducting element that controls and allows the return current flowing in the reverse direction to flow during the transition time at the time of switching, and the other first gate terminal of the first bidirectional switch or the second bidirectional switch is always on And synchronous control means for controlling the second gate terminal to perform a complementary operation with one of the first bidirectional switch and the second bidirectional switch when the return current is applied to the second gate terminal. It is characterized by providing. Thereby, in the single-phase or three-phase inverter, the driving device has the first gate terminal to energize in the third mode when a return current flows from the connected inductive load to the second bidirectional switch, Since the control signal is sent to the second gate terminal and the second bidirectional switch is driven, the bidirectional switch of each arm having a long flow time of the return current is driven in a low loss state. The other, which has a short flow time, can reduce the loss due to Vf of the freewheeling diode by energizing the external diode, and realize a low-loss power conversion circuit and reduce the cost with a simple configuration. It is possible to provide a drive device for a bidirectional switch that enables the above. In addition, no logic circuit is required to generate the synchronization signal, and it is possible to prevent instability due to low cost and logic circuit chattering, etc., and loss is achieved by using this bidirectional switch drive device. The present invention provides a bidirectional switch drive device that can provide the single-phase or three-phase inverter with low efficiency and high efficiency.

  According to another aspect of the present invention, the signal output unit outputs a single gate drive signal to the first bidirectional switch and the second bidirectional switch. . As a result, it is not necessary for the driving device to output signals to each of the total four gate terminals of the first bidirectional switch and the second bidirectional switch, and the gate drive unit can be simplified and at the same time low loss is achieved. A simple power conversion circuit can be realized.

  According to another aspect of the present invention, the signal output unit of the drive device outputs a rectangular wave drive signal. As a result, in the generation of the gate drive signal when energizing the return current of the rectangular wave drive to the bidirectional switch, the modulation of either the upper or lower arm that switches the phase is often in the on state, so it is always There is no big difference in gate power consumption when the gate is turned off and when the logic circuit generates a gate-off state, and there is no complicated circuit or gate drive timing generation software. A circuit can be realized.

  According to a fourth aspect of the present invention, there is provided a motor driving apparatus using the bidirectional switch driving apparatus according to any one of the first to fourth aspects. Accordingly, since the loss is reduced by energizing the bidirectional switch when energizing the return current, a power conversion device having good conversion efficiency and energy saving effect can be obtained.

  An air conditioner according to a fifth aspect uses the bidirectional switch drive device according to any one of the first to fourth aspects. Thereby, since loss is reduced by the synchronization control means, an air conditioner with good conversion efficiency and energy saving effect can be obtained.

(Embodiment 1)
The configuration of the bidirectional switch 1 will be described with reference to FIG. As shown in FIG. 1, the bidirectional switch 1 includes a first gate terminal 2, a second gate terminal 3, a drain terminal 4, and a source terminal 5. The bidirectional switch 1 has a thickness of 1 μm formed by alternately laminating 10 nm thick aluminum nitride (AlN) and 10 nm thick gallium nitride (GaN) on a substrate 6 made of silicon (Si). A buffer layer 7 is formed, and a semiconductor layer stack 8 is formed thereon. In the semiconductor layer stacked body 8, a first semiconductor layer and a second semiconductor layer having a band gap larger than that of the first semiconductor layer are sequentially stacked from the substrate side. The first semiconductor layer is a GaN (undoped gallium nitride) layer 9 having a thickness of 2 μm, and the second semiconductor layer is an n-type AlGaN (aluminum gallium nitride) layer 10 having a thickness of 20 nm. In the vicinity of the hetero interface between the GaN layer 9 and the AlGaN layer 10, charges are generated due to spontaneous polarization and piezoelectric polarization. Accordingly, and mobility 1 × 1013cm- ² or sheet carrier concentration channel region is generated a 1000 cm ² V / sec or more two-dimensional electron gas (2DEG) layer. That is, the semiconductor layer stack 8 has a channel region that is a two-dimensional electron gas (2DEG) layer and is formed on the substrate. On the semiconductor layer stacked body 8, a first ohmic electrode 11A and a second ohmic electrode 11B are formed at a distance from each other. The first ohmic electrode 11A and the second ohmic electrode 11B are formed by stacking titanium (Ti) and aluminum (Al), and form an ohmic junction with the channel region. Further, in order to reduce the contact resistance, a part of the AlGaN layer 10 is removed and the GaN layer 9 is dug down by about 40 nm. The example formed so that it may contact | connect an interface with is shown. Note that the first ohmic electrode 11 </ b> A and the second ohmic electrode 11 </ b> B may be formed on the AlGaN layer 10. In the region between the first ohmic electrode 11A and the second ohmic electrode 11B on the n-type AlGaN layer 10, the first p-type semiconductor layer 12A and the second p-type semiconductor layer 12B are spaced from each other. And selectively formed. A first gate electrode 13A is formed on the first p-type semiconductor layer 12A, and a second gate electrode 13B is formed on the second p-type semiconductor layer 12B. The first gate electrode 13A and the second gate electrode 13B are each formed by stacking palladium (Pd) and gold (Au), and the first p-type semiconductor layer 12A and the second p-type semiconductor layer 12B. Ohmic contact. A protective film 14 made of silicon nitride (SiN) is formed so as to cover the AlGaN layer 10, the first p-type semiconductor layer 12A, and the second p-type semiconductor layer 12B. By forming the protective film 14, it is possible to ensure a defect that causes so-called current collapse and to improve current collapse. The first p-type semiconductor layer 12A and the second p-type semiconductor layer 12B each have a thickness of 300 nm and are made of p-type GaN doped with magnesium (Mg). The first p-type semiconductor layer 12A, the second p-type semiconductor layer 12B, and the AlGaN layer 10 form PN junctions. As a result, when the voltage between the first ohmic electrode 11A and the first gate electrode 13A is 0 V, for example, the depletion layer spreads from the first p-type GaN layer into the channel region, so that the current flowing through the channel is cut off. Similarly, when the voltage between the second ohmic electrode 11B and the second gate electrode 13B is, for example, 0 V or less, a depletion layer spreads from the second p-type GaN layer into the channel region. Thus, a semiconductor element capable of interrupting a current flowing through the channel and performing a so-called normally-off operation is realized. The potential of the first ohmic electrode 11A is V1, the potential of the first gate electrode 13A is V2, the potential of the second gate electrode 13B is V3, and the potential of the second ohmic electrode 11B is V4. In this case, if V2 is higher than V1 by 1.5V or more, the depletion layer extending from the first p-type semiconductor layer 12A into the channel region is reduced, so that a current can flow in the channel region. Similarly, if V3 is higher than V4 by 1.5V or more, the depletion layer extending from the second p-type semiconductor layer 12B into the channel region is reduced, and current can flow through the channel region. That is, the so-called threshold voltage of the first gate electrode 13A and the so-called threshold voltage of the second gate electrode 13B are both 1.5V. In the following, the threshold voltage of the first gate electrode 13A at which the depletion layer extending in the channel region below the first gate electrode 13A is reduced and current can flow through the channel region is set to the first threshold voltage. The threshold voltage is set to the second gate electrode 13B so that the depletion layer extending in the channel region on the lower side of the second gate electrode 13B is reduced and current can flow in the channel region. The threshold voltage is used. The distance between the first p-type semiconductor layer 12A and the second p-type semiconductor layer 12B can withstand the maximum voltage applied to the first ohmic electrode 11A and the second ohmic electrode 11B. Configure.

  That is, the bidirectional switch 1 includes a semiconductor layer stack 8 having a channel region, a first ohmic electrode 11A and a second ohmic electrode 11B formed on the semiconductor layer stack 8 with a space therebetween, A first p-type semiconductor layer 12A and a second p-type semiconductor layer 12B formed in order from the first ohmic electrode 11A side between the first ohmic electrode 11A and the second ohmic electrode 11B; A substrate comprising a first gate electrode 13A formed on one p-type semiconductor layer 12A and a second gate electrode 13B formed on a second p-type semiconductor layer 12B; A drain terminal 4 connected to the ohmic electrode 11A; a source terminal 5 connected to the second ohmic electrode 11B; a first gate terminal 2 connected to the first gate electrode 13A; Composed of the second gate terminal 3 connected to the gate electrode 13B of 2.

  Next, the operation of the bidirectional switch 1 will be described. For explanation, the potential of the first ohmic electrode 11A is set to 0V, the voltage applied to the first gate terminal 2 is Vg1, the voltage applied to the second gate terminal 3 is Vg2, and the second ohmic electrode 11B and the first The voltage between the ohmic electrode 11A is Vs2s1, and the current flowing between the second ohmic electrode 11B and the first ohmic electrode 11A is Is2s1.

  When V4 is higher than V1, for example, when V4 is + 100V and V1 is 0V, the input voltages Vg1 and Vg2 of the first gate terminal 2 and the second gate terminal 3 are set to the first threshold voltage and the first threshold voltage, respectively. The voltage is equal to or lower than the threshold voltage of 2, for example, 0V. As a result, the depletion layer extending from the first p-type semiconductor layer 12A extends in the channel region toward the second p-type GaN layer, so that the current flowing through the channel can be blocked. Therefore, even when V4 is a positive high voltage, it is possible to realize a cut-off state in which a current flowing from the second ohmic electrode 11B to the first ohmic electrode 11A is cut off. On the other hand, when V4 is lower than V1, for example, even when V4 is −100 V and V1 is 0 V, the depletion layer extending from the second p-type semiconductor layer 12B is in the channel region in the first p-type semiconductor layer. The current spreads in the direction of 12A and can flow through the channel. For this reason, even when a negative high voltage is applied to the second ohmic electrode 11B, the current flowing from the first ohmic electrode 11A to the second ohmic electrode 11B can be blocked. That is, the bidirectional current of the bidirectional switch 1 can be cut off.

  In the structure and operation as described above, the first gate electrode 13A and the second gate electrode 13B share a channel region for ensuring a withstand voltage. In this device, the bidirectional switch 1 can be realized with the area of the channel region for one device. Considering the entire bidirectional switch 1, two diodes and two normally-off type AlGaN / GaN-HFETs are provided. The chip area can be reduced as compared with the case where it is used, and the bidirectional switch 1 can be reduced in cost and size.

  Next, when the input voltages Vg1 and Vg2 of the first gate terminal 2 and the second gate terminal 3 are higher than the first threshold voltage and the second threshold voltage, respectively, for example, 5V, the first voltage Both of the voltages applied to the gate electrode 13A and the second gate electrode 13B are higher than the threshold voltage. Accordingly, since the depletion layer does not extend from the first p-type semiconductor layer 12A and the second p-type semiconductor layer 12B to the channel region, the channel region is also formed below the first gate electrode 13A. It is not pinched off on the lower side of 13B. As a result, it is possible to realize a conductive state in which current flows bidirectionally between the first ohmic electrode 11A and the second ohmic electrode 11B.

  Next, the operation when Vg1 is higher than the first threshold voltage and Vg2 is equal to or lower than the second threshold voltage will be described. When the bidirectional switch 1 having the first gate terminal 2 and the second gate terminal 3 is represented by an equivalent circuit, a first transistor 15 and a second transistor 16 are connected in series as shown in FIG. It can be regarded as a circuit. In this case, the source (S) of the first transistor 15 corresponds to the first ohmic electrode 11A, the gate (G) of the first transistor 15 corresponds to the first gate electrode 13A, and the source ( S) corresponds to the second ohmic electrode 11B, and the gate (G) of the second transistor 16 corresponds to the second gate electrode 13B. In such a circuit, for example, when Vg1 is 5V and Vg2 is 0V, the fact that Vg2 is 0V is equivalent to the state where the gate and the source of the second transistor 16 are short-circuited. Can be regarded as a circuit as shown in FIG.

  Further, description will be made assuming that the source (S) of the second transistor 16 shown in FIG. 2B is the A terminal, the drain (D) is the B terminal, and the gate (G) is the C terminal. When the potential of the B terminal shown in the figure is higher than the potential of the A terminal, it can be regarded as a transistor in which the A terminal is a source and the B terminal is a drain. In such a case, the C terminal (gate) and the A terminal Since the voltage between the source and the source is 0 V and is equal to or lower than the threshold voltage, no current flows from the B terminal (drain) to the A terminal (source). On the other hand, when the potential of the A terminal is higher than the potential of the B terminal, the transistor can be regarded as a transistor in which the B terminal is a source and the A terminal is a drain. In such a case, since the potentials of the C terminal (gate) and the A terminal (drain) are the same, when the potential of the A terminal is equal to or lower than the threshold voltage with respect to the B terminal, the A terminal (drain) to the B terminal Do not supply current to the (source). When the potential of the A terminal becomes equal to or higher than the threshold voltage with reference to the B terminal, a voltage higher than the threshold voltage is applied to the gate with reference to the B terminal (source), and current flows from the A terminal (drain) to the B terminal (source). be able to. That is, when the gate and the source of the transistor are short-circuited, the transistor functions as a diode having a drain as a cathode and a source as an anode, and the forward rising voltage becomes the threshold voltage of the transistor. Therefore, the portion of the second transistor 16 shown in FIG. 2A can be regarded as a diode, and an equivalent circuit as shown in FIG. In the equivalent circuit shown in FIG. 2C, when the potential of the drain terminal 4 of the bidirectional switch 1 is higher than the potential of the source terminal 5, 5 V is applied to the first gate terminal 2 of the first transistor 15. In this case, the first transistor 15 is in an on state, and a current can flow from S2 to S1. However, an on-voltage is generated due to the forward rising voltage of the diode. Further, when the potential of S1 of the bidirectional switch 1 is higher than the potential of S2, the voltage is carried by the diode composed of the second transistor 16, and the current flowing from S1 to S2 of the bidirectional switch 1 is blocked. That is, by applying a voltage equal to or higher than the threshold voltage to the first gate terminal 2 and applying a voltage equal to or lower than the threshold voltage to the second gate terminal 3, a so-called bidirectional device is turned on and the cathode side of the diode is connected in series to the drain side. A switch capable of connected operation can be realized.

  3 shows the relationship between Vs2s1 and Is2s1 of the bidirectional switch 1. FIG. 3 (a) shows a case where Vg1 and Vg2 are changed simultaneously, and FIG. 3 (b) shows Vg2 as a second threshold value. FIG. 3C shows a case where Vg1 is changed by setting Vg1 to 0 V which is lower than the first threshold voltage. In FIG. 3, the voltage between S2 and S1 (Vs2s1), which is the horizontal axis, is a voltage based on the first ohmic electrode 11A, and the current between S2 and S1 (Is2s1), which is the vertical axis, is the second ohmic. The current flowing from the electrode 11B to the first ohmic electrode 11A is positive. As shown in FIG. 3A, when Vg1 and Vg2 are 0 V and 1 V, Is2s1 does not flow regardless of whether Vs2s1 is positive or negative, and the bidirectional switch 1 is cut off. . Further, when both Vg1 and Vg2 become higher than the threshold voltage, a conductive state in which Is2s1 flows bidirectionally according to Vs2s1 is established. On the other hand, as shown in FIG. 3B, when Vg2 is set to 0 V that is equal to or lower than the second threshold voltage and Vg1 is set to 0 V that is equal to or lower than the first threshold voltage, Is2s1 is blocked in both directions. However, when Vg1 is 2V to 5V that is equal to or higher than the first threshold voltage, Is2s1 does not flow when Vs2s1 is less than 1.5V, but Is2s1 flows when Vs2s1 becomes 1.5V or higher. That is, a reverse blocking state is reached in which current flows only from the second ohmic electrode 11B to the first ohmic electrode 11A, and no current flows from the first ohmic electrode 11A to the second ohmic electrode 11B. Further, when Vg1 is set to 0V and Vg2 is changed, as shown in FIG. 3C, a current flows only from the first ohmic electrode 11A to the second ohmic electrode 11B, and the second ohmic electrode A reverse blocking state in which no current flows from 11B to the first ohmic electrode 11A is obtained.

  As described above, the bidirectional switch 1 has a function of interrupting and energizing the bidirectional current according to the gate bias condition, and can also operate as a diode, and can also switch the direction in which the current of the diode is energized.

  As described above, the operation can be performed in the four operation modes shown in FIG. 4 according to the ON or OFF condition of the first gate terminal 2 and the second gate terminal 3 of the bidirectional switch 1. That is, when the bidirectional switch 1 inputs a gate drive signal only between the first gate terminal 2 and the drain terminal 4 (in short, only the first gate terminal 2 is turned on), the drain terminal 4 A first mode that operates as a semiconductor in which a bidirectional device and a reverse diode connected in series from the source terminal 5 to the source terminal 5 are connected in series, and a gate drive signal only between the second gate terminal 3 and the source terminal 5 Is input (in short, only the second gate terminal 3 is turned on), a forward diode and an on-state bidirectional device are connected in series from the drain terminal 4 to the source terminal 5. A second mode that operates as a semiconductor, and a gate drive signal is input between the first gate terminal 2 and the drain terminal 4 and between the second gate terminal 3 and the source terminal 5 ( In short, a signal for turning on the first gate terminal 2 and the second gate terminal 3 is input), and neither a forward diode nor a reverse diode is interposed between the drain terminal 4 and the source terminal 5. A gate drive signal is not applied to the third mode that operates in both directions, between the first gate terminal 2 and the drain terminal 4 and between the second gate terminal 3 and the source terminal 5 (simplification). In other words, the first mode has a fourth mode in which the first and second gate terminals 2 and 3 are turned off to block forward and reverse currents.

  This structure is similar to a JFET, but operates on a completely different operating principle from a JFET that performs carrier modulation in a channel region by a gate electric field in that carrier injection is intentionally performed. Specifically, it operates as a JFET up to a gate voltage of 3V. However, when a gate voltage of 3V or more exceeding the built-in potential of the pn junction is applied, holes are injected into the gate, and the current flows through the mechanism described above. Increases, and a large current and low on-resistance operation becomes possible.

  In the bidirectional switch 1, the first gate electrode 13A is formed on the first p-type semiconductor layer 12A having p-type conductivity, and the second gate electrode 13B has p-type conductivity. It is formed on the second p-type semiconductor layer 12B. For this reason, a forward bias is applied from the first gate electrode 13A and the second gate electrode 13B to the channel region generated in the interface region between the first semiconductor layer and the second semiconductor layer. Thus, holes can be injected into the channel region. In a nitride semiconductor, the mobility of holes is much lower than the mobility of electrons, so that holes injected into the channel region hardly contribute as carriers for passing current. For this reason, holes injected from the first gate electrode 13A and the second gate electrode 13B generate the same amount of electrons in the channel region, so that the effect of generating electrons in the channel region is increased, and the donor is increased. It functions like an ion. That is, since the carrier concentration can be modulated in the channel region, it is possible to realize a normally-off type nitride semiconductor layer bidirectional switch having a large operating current.

  Next, a three-phase inverter 17 that is a motor drive device as a power conversion device using the bidirectional switch 1 will be described with reference to FIG. As shown in FIG. 5, the three-phase inverter 17 includes half-bridge circuits 18 a, 18 b and 18 c in which two bidirectional switches 1 are connected in series, and includes first gate terminals 2 a to 2 f and a second gate terminal 3 a. A driving device 19 for driving 12 gates of 3 to 3f is provided. The bidirectional switches 1a, 1c, and 1e are connected in parallel with diodes 20a, 20b, and 20c as reverse conducting elements. Here, the two bidirectional switches 1 connected in series form upper and lower arms of the half bridge circuits 18a, 18b, 18c, and the bidirectional switches 1a, 1c, 1e are upper arms, bidirectional. The switches 1b, 1d, and 1f are the lower arms. As an output of the three-phase inverter 17, for example, a brushless DC motor is connected as an inductive load 21 to an intermediate connection point of the half bridge circuits 18a, 18b, and 18c. Although a three-phase inverter is used here, a single-phase load may be connected as a configuration having two pairs of half-bridge circuits.

  Next, the modulation patterns of the bidirectional switches 1a to 1f are such that the PWM control is performed for each terminal and the bidirectional switches 1b, 1d, and 1f, which are upper arms, are always turned on every 120 electrical degrees of output. There is a method of performing PWM control only for the bidirectional switches 1a, 1c, and 1e that are arms, or a modulation pattern in which the upper arm and the lower arm are reversed. However, since they are generally performed, detailed description is omitted here. .

  Next, the internal configuration of the drive device 19 will be described with reference to FIG. Since each of the drive devices 19 corresponding to the half bridge circuits 18a, 18b, and 18c has the same configuration, only the portion corresponding to the half bridge circuit 18a will be described as a representative. As shown in FIG. 6, the drive device 19 is connected to the signal output unit 22 that outputs a PWM control signal for each carrier cycle to the bidirectional switch 1a of the upper arm, A signal sharing means 23 as a single gate drive signal and a synchronization control means for complementary operation; a distribution means 24 for distributing a signal for the bidirectional switch 1a to the first gate terminal 2a and the second gate terminal 3a; A gate output unit 25 is provided for outputting a signal after insulation or level shifting to the first gate terminal. Here, the first gate terminal 2a and the second gate terminal 3a, which are signals to the bidirectional switch 1a, differ only in the reference potential, and do not change the timing or logic. “Same as H210038. There is no description that I heard that the upper arm is specially controlled.” Also, the lower arm side that is driven directly from the signal output unit 22 without the distribution means 24 is the high potential side. One gate terminal 2b is configured to be always on. Further, the signal output unit 22 outputs drive signals 2ag, 2cg, 2eg for performing rectangular wave driving to the first gate terminals 2a, 2c, 2e of the upper arm in a pattern as shown in FIG. Yes.

  The drive signals 3bg, 3dg, and 3fg to the second gate terminals 3a, 3c, and 3e of the upper arm and the second gate terminals 3b, 3d, and 3f of the lower arm pass through the signal sharing means 23 as described above. Is output. Therefore, while the number of output signals in the signal output unit 22 is 3, the first gate terminal 2b of the bidirectional switch 1b which is distributed to 9 after passing through the distributing means 24 and is always on. 12 gate signals are controlled by 3 signals including 3 signals of 3d, 3cg and 3eg to 2d and 2f.

  Next, FIG. 8 shows an enlarged chart of drive patterns for the correlation between the drive states of the gate terminals and the drive states of the bidirectional switches 1a and 1b. Although only one output phase is shown in FIG. 8, the other output phases are only shifted by 120 degrees in electrical angle from the one phase, and the basic operation is the same, so detailed description is omitted. From the top of the timing chart, the signal from the gate signal source (signal A), the voltage between the first gate terminal 2a and the drain terminal 4a of the upper arm (signal B), and the voltage between the second gate terminal 3a and the source terminal 5a of the upper arm (Signal C), the driving state of the upper arm (Signal D), and similarly the lower arm are also represented in the following order. In the driving state (signal D, signal G), the shaded portion indicates the third mode, the Lo portion is the fourth mode, and the Hi portion of the signal G is the first mode. Here, the case where the upper arm of the U phase flows current in the forward direction (current flows through the inductive load 21 in the forward direction) will be described. That is, the upper arm bidirectional switch 1a is turned on in the forward direction during the period in which the drive state (signal D) is in a shaded state. Further, the lower arm bidirectional switch 1b is driven in the first mode as shown in the case other than the hatched portion where the forward current of the upper arm bidirectional switch 1a is cut off, that is, in the Hi portion of the signal G. . That is, when the bidirectional switch 1a on the upper arm is switched to the shaded portion (third mode), the bidirectional switch 1b on the lower arm has already been switched to the first mode, and the source terminal 5b is switched to the drain terminal 4b. A state in which current can be supplied in the reverse direction is ensured. Therefore, when a current is supplied to the inductive load 21 in the forward direction, the driving state is appropriately switched so that current can be continuously supplied to the inductive load 21 even if switching by PWM (pulse width modulation) is performed. be able to. Next, the case where the lower arm of the U phase flows current in the forward direction (current flows from the inductive load 21) will be described. When current flows from the inductive load 21, forward current (current flowing from the drain terminal 4b to the source terminal 5b) flows through the bidirectional switch 1b of the lower arm. When the bidirectional switch 1b of the lower arm is switched by PWM to change its state and switched from the third mode to the first mode, forward current cannot be supplied to the lower arm. During this period, both the first gate terminal 2a and the second gate terminal 3a of the upper arm bidirectional switch 1a are also in the off state, so that the upper arm bidirectional switch 1a is in the first or third mode. It is not possible to energize during that time. During this period, the diode 20a as a reverse conducting element inserted in antiparallel with the bidirectional switches 1a, 1c, and 1e is energized. The current energization state of FIG. 8 shows an energization path according to the states of the first gate terminals 2a and 2b and the second gate terminals 3a and 3b of the bidirectional switches 1a and 1b. Therefore, even when a current flows from the inductive load 21, the driving state can be appropriately switched so that the current from the inductive load 21 can be continuously supplied. Here, in this embodiment, the flow time of the return current is long on the lower arm side, and the bidirectional switches 1b, 1d, and 1f of the lower arm are driven in a low loss state when the return current flows. In addition, the first gate terminals 2b, 2d, and 2f are always in an on state, and it is avoided to always supply a reflux current to an externally attached diode. Since the upper arm bidirectional switches 1a, 1c, and 1e have a short time for the return current to flow, the first gate terminals 2a, 2c, and 2e are not always turned on. As described above, the external diode is energized only during the transition time for mode switching.

  In addition, since the time of the shaded portion of the drive state of the bidirectional switch 1a of the upper arm and the time of the shaded portion of the drive state of the bidirectional switch 1b of the lower arm are not overlapped, the upper arm and the lower arm are simultaneously turned on. Switching control can be performed so that a short-circuit current does not flow from the high potential side to the low potential side. Also, the diode inserted in antiparallel is energized only during the dead time td until the upper arm shifts to the shaded portion, and after the dead time td, the bidirectional switch 1a of the upper arm is turned on. Since the forward voltage Vf, which is a low loss, that is, the multiplication result of the on-resistance and the energization current, is smaller than the forward voltage of the diode, the bidirectional switch 1a is energized.

  Although a diode is inserted in order to energize the current from the inductive load 21 continuously, an energization path may be secured by inserting a capacitor or the like between the lines of output to the inductive load 21.

  As described above, an inverter is constructed that avoids constantly supplying a reflux current to an external diode connected in reverse parallel to the bidirectional switch 1 and energizes a low-loss bidirectional switch during periods other than switching. Therefore, the loss due to Vf of the freewheeling diode can be reduced, a low-loss power conversion circuit can be realized, a logic circuit is not required for generating a synchronization signal, and the cost is low and it is not caused by chattering of the logic circuit. It is possible to prevent the stabilization, and further, by using the driving device 19 of the bidirectional switch 1, it is possible to realize the three-phase inverter 17 with low loss and high efficiency.

  Further, since the signal sharing means 23 can share and share the signal source of the first gate terminal 2 and the second gate terminal 3 of the bidirectional switch 1, it is input to the first gate terminal 2 and the second gate terminal 3. Therefore, it is possible to reduce the number of signal sources to be driven and to drive the same number of signal sources as in a normal unidirectional switch, and to further reduce the cost.

(Embodiment 2)
Hereinafter, the driving device 19 of the bidirectional switch 1 will be described with reference to FIGS. 9 to 11 for the second embodiment.

  In addition, what has the same function as Embodiment 1 attaches | subjects the same code | symbol, and abbreviate | omits detailed description.

  FIG. 9 shows the configuration of the drive device 19B when rectangular wave energization control is performed. As illustrated in FIG. 9, the driving device 19 </ b> B inputs magnetic pole position information by inputting a position sensor signal, and performs gate driving based on the position information and the output of the signal output unit 22. The position sensor signal is connected so as to be used as a signal for switching the phase for conducting the electrical angle of 120 degrees in the U, V, and W phases. As a result, a driving timing chart of the first gate terminals 2a to 2f and the second gate terminals 3a to 3f is shown in FIG. Signals for driving the first gate terminals 2a to 2f are respectively represented as drive signals 2ag to 2fg by adding g to a symbol representing the gate terminal. Similarly, signals for driving the second gate terminals 3a to 3f are drive signals 3ag to 3fg. As shown in the figure, the upper arm of each phase is switched at every carrier cycle, and the lower arm of each phase is always on for a period of 120 degrees in electrical angle so as to perform phase switching for energization switching. .

  Next, FIG. 11 shows an enlarged chart of drive patterns for rectangular wave energization control. As shown in the figure, the gate voltage (signal B, signal C) is turned on or off at the same timing along the gate signal source (signal A) by the bidirectional switch 1a of the upper arm. On the other hand, in the bidirectional switch 1b of the lower arm, the first gate terminal 2b is always on, and the forward current flowing from the drain terminal 4b to the source terminal 5b also flows from the source terminal 5b to the drain terminal 4b. It is also possible to energize the reverse current (reflux current). In addition, the current flows through the freewheeling diode in antiparallel with the bidirectional switch 1 only in the dead time which is the transitional period of the switching of the upper arm. 1 is energized. This is the same timing as in the case of sine wave energization because the lower arm needs to perform a complementary operation after the upper arm is switched. Although not shown, since the upper arm (for example, the bidirectional switch 1a) is in the off state when the lower arm (for example, the bidirectional switch 1b) is switched from the constantly on state to the off state for a period of 120 degrees, the reverse conducting element A reflux current can be passed through the diode 20a. However, the timing at which the reflux current flows through the diode 20a is only once per rotation, and the influence on the loss is small.

  As described above, an inverter is constructed that avoids constantly supplying a reflux current to the freewheeling diode in antiparallel with the bidirectional switch 1 and energizes the low-loss bidirectional switch during periods other than switching. Loss due to Vf of the diode can be reduced, a low-loss power conversion circuit can be realized, a logic circuit is not required for generating a synchronization signal, and the cost is low and unstable due to chattering of the logic circuit. Furthermore, by using the drive device 19 of the bidirectional switch 1, it is possible to realize the three-phase inverter 17 with low loss and high efficiency.

  In the present embodiment, the position sensor signal is received by the OR gate to control the second gate terminals 3b, 3d, and 3f. However, if there is a restriction on the mounting position, a logic is added. It is good also as a structure which responds | corresponds or outputs a signal separately from the signal output part 22. FIG.

(Embodiment 3)
The block diagram of the ventilation fan 26 as an air conditioner in Embodiment 3 of this invention is demonstrated, referring FIG. In addition, what has the same function as Embodiment 1 or Embodiment 2 attaches | subjects the same code | symbol, and abbreviate | omits detailed description.

  As shown in FIG. 12, the ventilation fan 26 includes a main body casing 27, a fan 28, a brushless DC motor 29, a three-phase inverter 17, and an operation unit 30. By turning on and off at the operation unit 30, it is input to the drive device 19 of the three-phase inverter 17, calculates the modulation rate so as to have a desired rotational speed, and drives the bidirectional switches 1a to 1f. As a result, the brushless DC motor 29 can be driven and the fan 28 can rotate to blow air.

  In the present embodiment, an example of the air conditioner is a ventilation fan, but it may be used as an inverter for other devices, and may be a single-phase inverter instead of a three-phase inverter.

  The bidirectional switch gate drive circuit according to the present invention includes a bidirectional switch arranged in a bridge circuit to constitute a single-phase or three-phase inverter, and a drive device for driving the bidirectional switch, the bidirectional switch Includes a semiconductor layer stack having a channel, a first ohmic electrode and a second ohmic electrode formed on the semiconductor layer stack at an interval, the first ohmic electrode, and the second ohmic electrode. A first p-type semiconductor layer and a second p-type semiconductor layer formed in order from the first ohmic electrode side between the ohmic electrode and a first p-type semiconductor layer formed on the first p-type semiconductor layer. A substrate comprising a gate electrode and a second gate electrode formed on the second p-type semiconductor layer; a drain terminal connected to the first ohmic electrode; and the second ohmic current. A source terminal connected to the first gate electrode, a first gate terminal connected to the first gate electrode, and a second gate terminal connected to the second gate electrode, and the first gate terminal and the drain terminal When a gate driving signal is input only between the first terminal and the second gate terminal, the first device operates as a semiconductor in which a bidirectional device and a reverse diode are connected in series from the drain terminal to the source terminal. And a second mode in which a forward diode and an on-state bidirectional device operate as a semiconductor connected in series from the drain terminal to the source terminal when the gate drive signal is input only between the source terminal and the source terminal, A gate drive signal is input between the first gate terminal and the drain terminal and between the second gate terminal and the source terminal to input the drain terminal. A third mode that operates in a bidirectional manner without passing through either a forward diode or a reverse diode between the source terminals; and between the first gate terminal and the drain terminal and between the second gate terminal and the source terminal. And a fourth mode that cuts off a forward / reverse bidirectional current without applying a gate drive signal to either of them, and the drive device sends a forward current to a first bidirectional switch of the bidirectional switches. In the case where the forward current is interrupted by switching and the load current of the single-phase or three-phase inverter is caused to flow as a return current to the second bidirectional switch, the second bidirectional switch is The state of the first gate terminal and the second gate terminal of the second bidirectional switch is synchronized with the driving state of the first bidirectional switch so as to energize in the mode. Synchronization control means for making the first and second gate terminals of the first bidirectional switch and the second bidirectional switch have different turn-on and turn-off times. The timing is synchronized with. Accordingly, the synchronous control means is configured to cause the first gate to energize in the third mode when a return current flows from the connected inductive load to the second bidirectional switch in the single-phase or three-phase inverter. Since the control signal is sent to the terminal and the second gate terminal and the second bidirectional switch is driven, it is possible to avoid constantly supplying the reflux current to the diode externally attached to the reflux diode in reverse parallel to the bidirectional switch, An inverter that energizes a low-loss bidirectional switch during a period other than the switching time can be configured to reduce the loss due to Vf of the freewheeling diode, making it possible to realize a low-loss power conversion circuit A driving device for a directional switch can be provided. In addition, no logic circuit is required to generate the synchronization signal, and it is possible to prevent instability due to low cost and logic circuit chattering, etc., and loss is achieved by using this bidirectional switch drive device. Therefore, it is possible to provide the single-phase or three-phase inverter with low efficiency and high efficiency.

DESCRIPTION OF SYMBOLS 1 Bidirectional switch 1a-1f Bidirectional switch 2 1st gate terminal 2a-2f 1st gate terminal 3 2nd gate terminal 3a-3f 2nd gate terminal 4a-4f Drain terminal 5a-5f Source terminal 6 Substrate 7 Buffer layer 8 Semiconductor layer laminate 9 GaN layer 10 AlGaN layer 11A first ohmic electrode 11B second ohmic electrode 12A first p-type semiconductor layer 12B second p-type semiconductor layer 13A first gate electrode 13B second gate electrode DESCRIPTION OF SYMBOLS 14 Protective film 15 1st transistor 16 2nd transistor 17 Three-phase inverter 18a-18c Half bridge circuit 19 Drive apparatus 20a-20c Diode 21 Inductive load 22 Signal output part 23 Signal sharing means 24 Distribution means 25 Gate output part 26 Ventilation fan 27 Body casing 28 Fan 29 Siles DC motor 30 operation unit

Claims (5)

A bidirectional switch disposed in a bridge circuit to form a single-phase or three-phase inverter; and a driving device for driving the bidirectional switch, wherein the bidirectional switch includes a semiconductor layer stack having a channel, and the semiconductor A first ohmic electrode and a second ohmic electrode formed on the layer stack at intervals, and the first ohmic electrode side between the first ohmic electrode and the second ohmic electrode; A first p-type semiconductor layer and a second p-type semiconductor layer formed in order, a first gate electrode formed on the first p-type semiconductor layer, and a second p-type semiconductor layer. A substrate having a second gate electrode formed thereon, a drain terminal connected to the first ohmic electrode, a source terminal connected to the second ohmic electrode, and a first gate electrode When the gate drive signal is input only between the first gate terminal and the drain terminal, the first gate terminal is connected to the second gate electrode and the second gate terminal is connected to the second gate electrode. When a gate drive signal is input only between the second gate terminal and the source terminal, a first mode that operates as a semiconductor in which a bidirectional device and a reverse diode connected in series toward the source terminal are connected in series, A second mode in which a forward diode and an on-state bidirectional device operate in series from the drain terminal to the source terminal, and operate between the first gate terminal and the drain terminal, and the second gate terminal. A gate drive signal is input between the source terminal and the forward terminal and the reverse direction between the drain terminal and the source terminal. A third mode that operates in both directions without passing through any of the diodes, and forward / reverse without applying a gate drive signal between the first gate terminal and the drain terminal and between the second gate terminal and the source terminal. A fourth mode that cuts off a bidirectional current, and the driving device outputs a signal source that drives a first bidirectional switch and a second bidirectional switch; and the signal output unit Distributing means for distributing a drive signal from the signal source output from the first bidirectional switch or the second bidirectional switch to one of the first gate terminal and the second gate terminal of the first bidirectional switch, Alternatively, one of the second bidirectional switches, the first gate terminal and the second gate terminal are controlled by the output signal from the distribution means, and the reflux current flows in the reverse direction during the transition time at the time of switching. A reverse conducting element capable of energizing a current, the other first gate terminal of the first bidirectional switch or the second bidirectional switch is always on, and the second gate terminal energizes the reflux current. At the same time, the bidirectional switch drive device further comprises synchronization control means for controlling the first bidirectional switch or the second bidirectional switch so as to complement the second gate terminal of one of the first bidirectional switch and the second bidirectional switch. . 2. The bidirectional switch drive device according to claim 1, wherein the signal output unit outputs a single gate drive signal to the first bidirectional switch and the second bidirectional switch. 2. The bidirectional switch drive device according to claim 1, wherein the signal output unit of the drive device outputs a rectangular wave drive signal. 4. A motor drive device using the bidirectional switch drive device according to claim 1. An air conditioner using the bidirectional switch drive device according to any one of claims 1 to 3.

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