JP5251553B2 - Semiconductor device - Google Patents

Description

  The present invention relates to a semiconductor device in which a high-side switching element and a low-side switching element are connected in series between a power supply potential and a GND potential.

  A bridge circuit, a three-phase AC inverter circuit, or the like is used for power control of a load such as a motor. Both the bridge circuit and the three-phase AC inverter circuit have a high-side switching element and a low-side switching element connected in series between the power supply potential and the GND potential as a basic unit. The midpoint of these two switching elements is connected to a load, and the load is controlled by controlling on / off of the high side and low side switching elements.

  The load of a motor or the like is often controlled with a large current, and the high-side switching element is generally an IGBT (Insulated Gate Bipolar Transistor) having a gate, an emitter, and a collector, or a power MOSFET. The on / off operation of the high side switching element is controlled by a gate drive signal transmitted from a circuit called a high voltage side drive circuit.

  The reference potential of the high voltage side drive circuit is supplied from a Vs terminal provided in the high voltage side drive circuit. The potential of the Vs terminal (referred to as Vs potential) is given by connecting the Vs terminal to the emitter of the high side switching element. In order to avoid an erroneous output of the gate drive signal by the high-voltage side drive circuit, the Vs potential is required to be stable and not to suddenly shift to the minus side without being affected by parasitic elements. Patent Documents 1 to 3 describe a configuration that can stabilize the potential of the Vs terminal.

JP 2005-160268 A JP 2005-160177 A Japanese Patent Laid-Open No. 11-285266

  The potential at the Vs terminal is negative with respect to the GND potential due to the forward voltage VF of the freewheeling diode connected in antiparallel with the low-side switching element or the induced electromotive force given by the product of the wiring inductance and di / dt. May shift to. There is a problem that the high voltage side drive circuit erroneously outputs the gate drive signal due to the Vs potential shifting to the minus side.

  As a cause of the erroneous output described above, for example, when the Vs potential returns from the negative side, a current flows through the level shift circuit included in the high-voltage side drive circuit, and the current is erroneously recognized as a high-side input signal. It may be possible to operate (erroneous output). Therefore, the negative Vs potential itself can cause a problem of erroneous output.

  Here, Patent Document 1 discloses a configuration in which a resistor is disposed between the Vs terminal and the emitter of the high-side switching element. This resistance can suppress the Vs potential from shifting to the negative side. However, in such a configuration, even when the Vs potential does not shift to the negative side, the output voltage as the gate drive signal is always divided (divided) between the gate and the emitter of the high-side switching element and the aforementioned resistance. The Rukoto. As a result, there is a problem that the gate-emitter voltage of the high-side switching element is lowered and the switching speed is lowered.

  The present invention has been made in order to solve the above-described problems, and is a semiconductor that suppresses erroneous output of a gate drive signal to a high-side switching element and does not reduce the switching speed of the high-side switching element. An object is to provide an apparatus.

  A semiconductor device according to the present invention is a high-voltage side switching element connected in series between a power supply potential and a GND potential, which is a high-side switching element having a gate, an emitter, and a collector, and a low-voltage side switching element. A low-side switching element, a high-voltage side drive circuit connected to the gate of the high-side switching element and transmitting a gate drive signal to the gate, and a reference potential for the high-voltage side drive circuit provided in the high-voltage side drive circuit Vs terminal. Further, a resistor having one end connected to the emitter of the high-side switching element and the other end connected to the Vs terminal, and a diode having an anode connected to one end of the resistor and a cathode connected to the other end of the resistor. It is characterized by having.

  Another semiconductor device according to the invention of the present application is a high-voltage side switching element having a gate, an emitter, and a collector, and a low-voltage side switching element, which are connected in series between a power supply potential and a GND potential. A low-side switching element, a high-voltage side drive circuit connected to the gate of the high-side switching element and transmitting a gate drive signal to the gate, and a reference potential of the high-voltage side drive circuit provided in the high-voltage side drive circuit Vs terminal for providing Further, a resistor having one end connected to the emitter of the high-side switching element and the other end connected to the Vs terminal, and a switching element having one end connected to one end of the resistor and the other end connected to the other end of the resistor. And a control device for controlling on / off of the switching element. The control device is characterized in that the switching element is turned off so as to prevent the voltage at the Vs terminal from dropping to the extent that the high-voltage side drive circuit erroneously outputs the gate drive signal.

  According to the present invention, erroneous output to the high-side switching element can be suppressed without any harmful effects.

1 is a circuit diagram illustrating a semiconductor device of Embodiment 1. FIG. 2 is a timing chart for explaining the operation of the circuit of FIG. 1. FIG. 6 is a circuit diagram illustrating a semiconductor device of Embodiment 2. It is a graph explaining the relationship between the return current which flows into the low-side return diode, and Vs potential. It is a figure explaining the modification of Embodiment 2. FIG. 6 is a timing chart illustrating the operation of the circuit illustrated in FIG. 5. It is a circuit diagram explaining a comparative example.

Embodiment 1
This embodiment will be described with reference to FIGS. First, FIG. 1 which is a circuit diagram illustrating the semiconductor device of the present embodiment will be described. The semiconductor device of this embodiment includes a high side switching element 12 and a low side switching element 18 connected in series between a power supply 24 and a GND 25.

  In the present embodiment, both the high-side switching element 12 and the low-side switching element 18 are IGBTs and have a gate, an emitter, and a collector. The collector of the high side switching element 12 is connected to the high voltage side of the power supply 24. The emitter of the high side switching element 12 is connected to the collector of the low side switching element 18. The emitter of the low-side switching element 18 is connected to the GND 25 via the shunt resistor 36. Thus, the high side switching element 12 and the low side switching element 18 are connected in series between the power supply potential and the GND potential.

  Further, the first diode 12 is connected in antiparallel with the high side switching element 12. That is, the cathode of the first diode 12 is connected to the collector of the high side switching element 12, and the anode is connected to the emitter of the high side switching element 12. Similarly, the second diode 20 is connected in antiparallel with the low side switching element 18. The first diode 12 and the second diode 20 are free-wheeling diodes.

  One end of a load 22 is connected to the midpoint between the high-side switching element 12 and the low-side switching element 18. The other end of the load 22 is connected to the emitter of the low-side switching element 18. In the present embodiment, the load 22 is an L load motor, but is not particularly limited thereto.

  On / off control of the high-side switching element 12 and the low-side switching element 18 that control the power of the load 22 is performed by the high-voltage side drive circuit 10 and the low-voltage side drive circuit 16, respectively. The high-voltage side drive circuit 10 controls on / off of the high-side switching element 12 by transmitting a gate drive signal to the gate of the high-side switching element 12. The same applies to the low-voltage side drive circuit 16.

  Further, the high voltage side drive circuit 10 includes a Vs terminal 27, and the low voltage side drive circuit 16 includes a Vs terminal 29. The Vs terminal is a terminal for acquiring the reference potential of the high-voltage side drive circuit 10 or the low-voltage side drive circuit 16. The Vs terminal 27 of the high-voltage side drive circuit 10 is connected to the emitter of the high-side switching element 12 via the resistor 26. Further, a diode 28 is connected in parallel with the resistor 26 described above. That is, the anode of the diode 28 is connected to the end connected to the emitter of the resistor 26, and the cathode is connected to the end connected to the Vs terminal 27 of the resistor 26.

  On the other hand, the Vs terminal 29 of the low-voltage side drive circuit 16 is connected to the emitter of the low-side switching element 18. That is, the Vs terminal 29 is connected to the GND 25 through the shunt resistor 36. Therefore, the potential of the Vs terminal 29 does not shift to the minus side and can stably supply the reference potential of the low-voltage side drive circuit 16.

  In this embodiment, a bootstrap system is adopted as a driving method of the high side switching element 12 and the low side switching element 18. That is, as understood from FIG. 1, one end of the bootstrap unit capacitor 30 is connected between the resistor 26 and the Vs terminal 27. The other end of the bootstrap unit capacitor 30 is connected to the cathode of the bootstrap unit diode 32. Further, a bootstrap unit current limiting resistor 34 is connected to the anode of the bootstrap unit diode 32. The bootstrap driving method is a known technique and will not be described in detail. The semiconductor device of this embodiment has the above-described configuration. Although the semiconductor device shown in FIG. 1 of the present embodiment describes only the circuit configuration for one phase, it is general to control the load by a plurality of phases. FIG. 1 shows only the portions necessary for explaining the present embodiment.

  Hereinafter, the operation of the semiconductor device of this embodiment will be described. First, the high-side switching element 12 is turned on, and power is supplied to the load 22. Next, when the high-side switching element 12 is turned off, the energy accumulated in the load 22 is released as a return current via the second diode 20. At this time, a forward voltage (VF) is generated in the second diode 20 due to the reflux current flowing through the second diode 20.

  Here, in order to explain the technical significance of the present embodiment, the configuration shown in FIG. 7 will be described as a comparative example of the present embodiment. The semiconductor device shown in FIG. 7 has the same configuration as that of FIG. 1 except that the resistor 26 and the diode 28 in FIG. 1 are not provided. In such a configuration, when a forward voltage (VF) is generated in the second diode 20, the voltage of the Vs terminal 27 connected to the cathode of the second diode 20 may shift below the GND potential to the minus side.

  In addition, wiring inductance that occurs parasitically in the internal wiring that connects the high-side switching element 12, the low-side switching element 18, the first diode 14, and the second diode 20, and the inductance of the external wiring such as the shunt resistor 36 and di / Due to the induced electromotive force obtained by the product of dt, the voltage at the Vs terminal 27 may fall below the GND potential and shift to the negative side. Due to these factors, there has been a problem that an erroneous output of the gate drive signal may occur when the voltage of the Vs terminal 27 becomes a negative value equal to or lower than the GND potential.

  However, according to the configuration of the present embodiment, the above problem can be solved. That is, even when a forward voltage (VF) is generated in the second diode 20 or an induced electromotive force is generated due to the switching of the high-side switching element 12, these voltages are transmitted through the resistor 26 to Vs. Applied to terminal 27. Therefore, since the potential at the Vs terminal 27 can be prevented from suddenly decreasing, the above-described problem of erroneous output can be avoided.

  Further, the output voltage as the gate drive signal is always divided between the gate and the emitter of the high-side switching element 12 and the resistor 26 even if the potential of the Vs terminal 27 does not shift to minus by simply providing the resistor 26. It will be. Therefore, in the configuration as it is, there can be a problem that the gate-emitter voltage of the high-side switching element 12 is lowered and the switching speed is lowered.

  However, since the semiconductor device of this embodiment includes the diode 28 in parallel with the resistor 26 as described above, this problem can be solved. That is, when the high-side switching element 12 is transitioned from the off state to the on state, the current for gate charge flows also to the diode 28, so that the time required for gate charge can be shortened compared with the case where the diode 28 is not provided. . Therefore, a decrease in switching speed can be suppressed. The current for gate charging refers to a current that flows from the high-voltage side drive circuit 10 to the Vs terminal 27 via the gate of the high-side switching element 12 and the emitter of the high-side switching element 12.

  FIG. 2 is a timing chart for explaining the difference in rising of the high-side switching element 12 depending on the presence or absence of the diode 28. Va in FIG. 2 is the gate voltage of the high-side switching element 12. That is, Va is the potential difference between the gate and the Vs terminal as shown by the double-sided arrow in FIG. Vb is an output voltage, that is, a voltage across the load 22. Vb is also indicated by a double-sided arrow in FIG.

  From FIG. 2, it can be seen that the configuration having the diode 28 can quickly raise the gate voltage of the high-side switching element 12. FIG. 2 also shows a drop in the output voltage Vb, which is a factor that lowers the Vs potential.

  As described above, in a semiconductor device that constitutes a so-called arm, there is a problem that the reference potential of the high-voltage side drive circuit that controls on / off of the high-side switching element is likely to shift to the negative side with respect to the GND potential. The feature of this embodiment is that it can be solved without any harmful effects. Accordingly, various modifications can be made without departing from the characteristics of the present invention.

  In the present embodiment, the materials of the high-side switching element 12, the low-side switching element 18, the first diode 14, and the second diode 20 are not particularly mentioned, but these may be manufactured using a material such as SiC. Manufacturing a semiconductor element such as a switching element or a diode with SiC capable of increasing the withstand voltage is useful for increasing the withstand voltage and increasing the current of the semiconductor device, and will be described in this embodiment and the following embodiments. It may be applied to a semiconductor element.

Embodiment 2
This embodiment will be described with reference to FIGS. In addition, the same code | symbol may be attached | subjected to the component which is the same as that of the component demonstrated in Embodiment 1, or respond | corresponds, and description of multiple times may be abbreviate | omitted.

  FIG. 3 is a circuit diagram illustrating the semiconductor device of this embodiment. As can be understood from FIG. 3, the load 22 includes the U phase composed of the high side switching element 12 and the low side switching element 18, the V phase composed of the high side switching element 50 and the low side switching element 58, and the high side switching element 54 and the low side switching element. Controlled by a three-phase AC inverter circuit consisting of 62 and consisting of a W phase.

  A switching element 72 is connected in parallel with the resistor 26 that connects the emitter of the high-side switching element 12 and the Vs terminal 27. The switching element 72 is, for example, an FET, and it is desirable that the resistance can be ignored in actual operation. A control device 65 for performing on / off control of the switching element 72 is connected to the switching element 72.

  The control device 65 includes a current detection circuit 66 that detects a current by the shunt resistor 36. The control device 65 further includes an MCU (microcontroller) 68 that calculates whether the switching element 72 is turned on or off from the current value detected by the current detection circuit 66. The control device 65 further includes a drive circuit 70 that applies a voltage to be actually turned on or off to the switching element 72 based on a command to turn on or off the switching element 72 obtained from the MCU 68.

  The operation of the semiconductor device of this embodiment is as follows, for example. First, the high side switching element 12 and the low side switching element 58 are turned on, and the load 22 is energized. Next, the high-side switching element 12 is turned off to enter the reflux mode. At this time, the current flows back through the path of the load 22, the low-side switching element 58, and the second diode 20. Here, the current value of the return current is detected by the current detection circuit 66. The detected current value is compared with a predetermined value in the MCU 68. The MCU 68 calculates whether or not the voltage at the Vs terminal 27 suddenly decreases to the extent that the high-voltage side drive circuit 10 erroneously outputs when the switching element 72 is kept on.

  When the aforementioned erroneous output is predicted from the calculation result of the MCU 68, a command to turn off the switching element 72 is transmitted to the drive circuit 70. On the other hand, if no erroneous output is foreseen, a command to keep the switching element 72 on is transmitted to the drive circuit 70.

  Next, the drive circuit 70 turns on or off the switching element 72 in accordance with the above-described command.

  The semiconductor device of the present embodiment is characterized in that when the control device 65 detects the return current and an erroneous output of the high-voltage side drive circuit 10 is expected, the control is performed to turn off the switching element 72. When the switching element 72 is in the off state, the VF and the induced electromotive force described above are applied to the Vs terminal 27 via the resistor 26, so that the Vs potential can be prevented from rapidly decreasing. On the other hand, when the switching element 72 is in the ON state, a low-resistance path via the switching element 72 is supplied between the emitter of the high-side switching element 12 and the high-voltage side drive circuit 10. Here, if the switching element 72 is in the ON state, the gate of the high-side switching element 12 can be quickly raised as described above.

  Generally, the larger the current flowing through the high-side switching element, the greater the return current flowing through the diode connected in antiparallel with the low-side switching element. As already described, if the reflux current increases, VF increases, and the Vs potential further decreases.

  FIG. 4 is a graph for explaining the dependence of the Vs potential on the reflux current. As described above, when the reflux current increases, the decrease in Vs becomes significant. Therefore, as in this embodiment, the erroneous output described above can be effectively prevented by detecting the return current and determining whether the switching element 72 is on or off.

  As described above, when a sudden decrease in the Vs potential is predicted by the control device, it is a feature of this embodiment that the switching element 72 in the on state is turned off and the sudden decrease in the Vs potential is suppressed by the resistor 26. Accordingly, various modifications can be made without departing from the characteristics of the present invention.

  For example, it is conceivable to include a control device 89 as shown in FIG. A control device 89 shown in FIG. 5 includes an MCU 90 and a drive circuit 92. In the control device of FIG. 5, the MCU 90 acquires information on the gate drive signal of the high-voltage side drive circuit 10. The MCU 90 should turn off the switching element 72 with respect to the drive circuit 92 when the gate drive signal of the high-voltage side drive circuit 10 transitions from the drive signal to turn on the high-side switching element 12 to the drive signal to turn off. Make a command. The drive circuit 92 quickly turns off the switching element 72.

  When the off operation of the high-side switching element 12 is started, di / dt is generated and the above-described induced electromotive force is generated. The off timing of the high side switching element 12 is also the start timing of the reflux state. Therefore, as described above, when the gate drive signal becomes a signal to turn off the high-side switching element, the switching element 72 is turned off to suppress the decrease in the Vs potential due to the VF or the induced electromotive force.

  FIG. 6 is a timing chart for explaining the operation of the semiconductor device of FIG. The switching element 72 is turned off at the timing when the gate drive signal to the high side switching element transitions to a signal that should turn off the high side switching element. The off state of the switching element 72 is maintained even after the high side switching element 12 is turned off. The length of this time is such that there is no concern about the aforementioned “false output” due to the decrease in the Vs potential, and is typically about 3 μ [sec].

  Further, the “calculation as to whether or not the voltage at the Vs terminal 27 suddenly drops to the extent of erroneous output” performed by the MCU 68 may be performed simply by comparing the value of the reflux current with the rating.

  In the semiconductor device of this embodiment and Embodiment 1, the bootstrap method is adopted as a driving method of the high-side switching element and the low-side switching element, but the present invention is not limited to this. That is, the present invention is effective for all semiconductor devices in which unstable operation such as erroneous output occurs in the high-voltage side drive circuit by shifting the reference potential of the high-voltage side drive circuit to the minus side (lower than the GND potential). . Therefore, the present invention can be widely applied to those that can cause such unstable operation.

  DESCRIPTION OF SYMBOLS 10 High voltage side drive circuit, 12 High side switching element, 18 Low side switching element, 14 1st diode, 20 2nd diode, 22 Load, 24 Power supply, 25 GND, 26 Resistance, 28 Diode

Claims (7)

A high-side switching element connected in series between a power supply potential and a GND potential, a high-side switching element having a gate, an emitter, and a collector, and a low-side switching element that is a low-voltage side switching element;
A high-voltage side drive circuit connected to the gate of the high-side switching element and transmitting a gate drive signal to the gate;
A Vs terminal for providing a reference potential of the high-voltage side drive circuit provided in the high-voltage side drive circuit;
A resistor having one end connected to the emitter of the high-side switching element and the other end connected to the Vs terminal;
A semiconductor device comprising: a diode having an anode connected to one end of the resistor and a cathode connected to the other end of the resistor. A high-side switching element connected in series between a power supply potential and a GND potential, a high-side switching element having a gate, an emitter, and a collector, and a low-side switching element that is a low-voltage side switching element;
A high-voltage side drive circuit connected to the gate of the high-side switching element and transmitting a gate drive signal to the gate;
A Vs terminal for providing a reference potential of the high-voltage side drive circuit provided in the high-voltage side drive circuit;
A resistor having one end connected to the emitter of the high-side switching element and the other end connected to the Vs terminal;
A switching element having one end connected to one end of the resistor and the other end connected to the other end of the resistor;
A control device for controlling on / off of the switching element,
The control device turns off the switching element so as to prevent the voltage at the Vs terminal from dropping to the extent that the high-voltage side drive circuit erroneously outputs the gate drive signal. A shunt resistor connected between the low-side switching element and the GND potential;
3. The semiconductor device according to claim 2, wherein the control device detects a current between the shunt resistor and the low-side switching element, and turns off the switching element when a value of the current exceeds a predetermined value. .   The control device detects information of the gate drive signal of the high-voltage side drive circuit, and turns off the switching element when the gate drive signal makes a transition from what should turn on the high side switching element to what should be turned off. The semiconductor device according to claim 2.   The semiconductor device according to claim 1, further comprising a free-wheeling diode connected in antiparallel with the low-side switching element.   The semiconductor device according to claim 1, wherein the high-side switching element or the low-side switching element is made of SiC.   The semiconductor device according to claim 5, wherein the free wheel diode is made of SiC.

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