Driver circuit and semiconductor module having same

An output of a gate driver that drives a main switch is connected to the gate of the main switch, and a low-voltage side power supply terminal of the gate driver is connected to a source of the main switch via a current limiting resistor. Moreover, a suppression capacitor for suppressing rapid changes in current, having a prescribed capacitance, is connected between the drain of the main switch of a main circuit and the low-voltage side power supply terminal of the gate driver. This makes it possible to suppress the rapid change in current that occurs when the main switch switches OFF as well as to prevent extremely large currents from occurring in a low-voltage side power supply line of the driver circuit.

BACKGROUND OF THE INVENTION

Technical Field

The present invention relates to a driver circuit for use in a power converter such as a DC-DC converter or an inverter for driving a motor, and to a semiconductor module including the driver circuit.

Background Art

In discrete power semiconductors such as metal-oxide-semiconductor field-effect transistors (MOSFETs) and insulated-gate bipolar transistors (IGBTs), as well as in intelligent power modules (IPMs) and modules that include such devices in a single product, driver circuits are used to drive the power semiconductor devices (hereinafter, main switches). In the driver circuit illustrated inFIG. 5, for example, an output terminal (Vout)73of a gate driver72in a driver circuit70is connected to the gate of a main switch (M11)81of a main circuit80, another terminal (a low-side power supply terminal (VL)74of the driver circuit70) is connected to a source (VS)82of a power semiconductor device (the main switch M11)81, and thus the gate-source (GS) voltage of the main switch (M11)81is controlled to switch the main switch (M11)81ON and OFF. In a module-type product, this driver circuit would be embedded with the power semiconductor device in a module. Moreover, here the symbol VSis intended to indicate both the source terminal itself as well as the source voltage (and the same applies below).

A corresponding configuration can be achieved when using an IGBT for the main switch of the main circuit80by replacing the source of the MOSFET with the emitter, replacing the drain of the MOSFET with the collector, and replacing the gate-source (GS) with a gate-emitter (GE). Furthermore, in the case described below where the main switch is a MOSFET, the drain-source (DS) would be replaced with collector-emitter (CE) to achieve the corresponding configuration.

FIG. 5illustrates an example of a typical configuration of a conventional driver circuit. InFIG. 5, the output terminal (Vout)73of the gate driver72in the driver circuit70and the gate of the main switch (M11)81of the main circuit80are connected together via a gate resistor (Rg)75in order to suppress rapid changes in current (di/dt) during turning ON and turning OFF of the main switch (M11)81.

FIG. 6is a diagram for explaining the operation (first example) of a conventional driver circuit.FIG. 6shows the driver circuit illustrated inFIG. 5, and when the main switch (M11)81switches OFF, a parasitic inductance component caused by wiring or the like present between the source side of the main switch (M11)81and a reference voltage, as well as a rapid change in current (−di/dt) when the main switch (M11)81switches OFF, cause the source voltage (VS)82of the main switch (M11)81to decrease rapidly below the reference voltage. When the source voltage (VS)82of the main switch (M11)81becomes a low voltage, the source of the main switch in the circuit and the low-voltage side power supply terminal (VL)74of the driver circuit70are connected together by low impedance. This can potentially allow an excessively large current to flow from the reference voltage to the source (VS)82via the low-voltage side power supply line of the driver circuit, which could cause the low-voltage side power supply line of the driver circuit to burn out or cause the driver circuit to malfunction.

FIG. 7is a diagram for explaining the operation (second example) of a conventional driver circuit. As illustrated inFIG. 7and described in Patent Document 1, in order to address the potential issues described above with reference toFIG. 6, the output terminal (Vout)73of the gate driver72in the driver circuit70is connected directly to the gate terminal of the main switch (M11)81, and a current limiting resistor (RR)76is inserted between the other terminal (the low-voltage side power supply terminal (VL)74of the driver circuit70) and the source82of the main switch (M11)81. This reduces the possibility of burnout or malfunctions due to excessively large currents in the low-voltage side power supply line of the driver circuit.

FIG. 8is a diagram for explaining the operation (third example) of a conventional driver circuit. InFIG. 8, the driver circuit illustrated inFIG. 7is arranged on the high side, and the high-side driving power supply utilizes a bootstrap configuration to drive the driver circuit. In other words, inFIG. 8, when a low-side main switch2(M12)84(illustrated in the lower right) switches ON, current from a driving power supply110(illustrated in the upper left) flows to a bootstrap diode (D1)111to a bootstrap capacitor (C1)112and thereby stores power therein.

Then, when the low-side main switch2(M12)84switches OFF and a high-side main switch (M11)81switches ON, the power stored in the bootstrap capacitor (C1)112becomes the high-side driving power supply, and a gate driver92in a high-side driver95is operated via control of a controller91in a driver circuit90.

When the output of the gate driver92switches ON the high-side main switch1(M11)81, power from the main circuit80is supplied to a load (not illustrated in the figure) that is connected to the source side of the high-side main switch1(M11)81.

Moreover, a current limiting resistor (RR)113illustrated inFIG. 8is similar to the current limiting resistor (RR)76illustrated inFIG. 7and prevents excessive currents resulting from the switching of the main switches from flowing to the low-voltage side power supply line of the driver circuit. Note that parasitic inductance83caused by power supply lines or the like is also present between the source of the low-side main switch2(M12)84and a main circuit reference voltage. Furthermore, similar to the high-side driver, a low-side driver96has the same configuration illustrated inFIG. 7and therefore will not be described here.

RELATED ART DOCUMENT

Patent Document

SUMMARY OF THE INVENTION

Adding the current limiting resistor (RR) connects together the source of the main switch and the low-voltage side power supply terminal of the driver circuit via the current limiting resistor (RR). Therefore, even if the source voltage becomes a lower voltage than the reference voltage of the driver circuit due to parasitic inductance on the source side of the main switch and due to a rapid change in current (−di/dt) when the main switch switches OFF, the current limiting resistor (RR) makes it possible to reduce the current flowing from the reference voltage of the driver circuit to the source of the main switch via the low-voltage side power supply line of the driver circuit.

This, in turn, makes it possible to suppress the flow of current from the low-side power supply of the driver circuit to the source of the main switch when the source takes a negative voltage.

Here, in order to suppress the rapid change in current (di/dt) that occurs when the main switch switches OFF, the resistance of the current limiting resistor (RR) must be set to a large value. However, setting the resistance of the current limiting resistor (RR) to a large value conversely causes the following problems.

(1) When the resistance of the current limiting resistor (RR) is set to a large value, the impedance between the source of the main switch and the low-voltage side power supply terminal of the driver circuit becomes high regardless of whether the main switch is ON or OFF. As a result, the main switch is more prone to erroneously switching ON or OFF due to other switches (not illustrated in the figure) in the driver circuit switching ON and OFF or due to external noise.

(2) When a plurality of power semiconductor devices (main switches) are used to form an upper/lower arm configuration and a gate driver in the driver circuit drives the high-side main switch, it is common to use a bootstrap configuration for the high-side driving power supply (seeFIG. 8). However, when the low-side main switch is switched ON to charge a bootstrap capacitor (C1) that then becomes the high-side driving power supply, because the current limiting resistor (RR) is present on the charging path of the bootstrap capacitor (C1), the current limiting resistor (RR) impedes the charging of the bootstrap capacitor (C1).

Accordingly, the present invention is directed to a scheme that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. In particular, in some embodiments, the present invention aims to provide a driver circuit that, without having to excessively increase the resistance of a current limiting resistor (RR), suppresses the rapid changes in current (di/dt) accompanying switching of a power semiconductor device and also prevents excessively large currents resulting from such rapid changes (di/dt) from occurring in a low-voltage side power supply line of the driver circuit. Moreover, the present invention aims to provide a semiconductor module including such a driver circuit.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, in one aspect, the present disclosure provides a driver circuit, including: a main circuit part that includes a power semiconductor device, the main circuit supplying power to a load to be connected thereto by power conversion through switching ON and OFF the power semiconductor device; a driver circuit part that includes a gate driver that drives the power semiconductor device of the main circuit part and a controller that controls the gate driver, an output of the gate driver being connected to a gate of the power semiconductor device to switch ON and OFF the power semiconductor device; a current limiting resistor provided in series in a path connecting a low-voltage side power supply terminal of the gate driver to a source of the power semiconductor device; and a suppression capacitor connected between a drain of the power semiconductor device and the low-voltage side power supply terminal of the gate driver.

In the driver circuit, the gate driver may be provided in a high-side driver circuit part for driving the load.

Moreover, in the driver circuit, the gate driver may be provided in a low-side driver circuit part for driving the load.

Furthermore, the current limiting resistor may be packaged together with the power semiconductor device.

Furthermore, in the driver circuit, the driver circuit part, the main circuit part, and the current limiting resistor are installed together in a single module.

In another aspect, the present disclosure provides a semiconductor module including the driver circuit of the aforementioned aspect, wherein the driver circuit part, the main circuit part, the current limiting resistor, and the suppression capacitor are installed together in a single module.

The driver circuit according to the present invention makes it possible to, without having to excessively increase the resistance of a current limiting resistor, suppress the rapid changes in current (di/dt) accompanying switching of a power semiconductor device such as an IGBT or a MOSFET and also prevent extremely large currents resulting from such rapid changes (di/dt) from occurring in a low-voltage side power supply line of the driver circuit. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory, and are intended to provide further explanation of the invention as claimed.

DETAILED DESCRIPTION OF EMBODIMENTS

Next, an embodiment of the present invention will be described in detail.

FIG. 1illustrates a configuration of a driver circuit according to the embodiment of the present invention. The driver circuit according to the embodiment of the present invention can be generally divided into a driver circuit10and a main circuit20. In this case, the driver circuit10and the main circuit20can be embedded in a single product to form a semiconductor module100.

The driver circuit10illustrated inFIG. 1includes a controller1that controls and drives a gate driver2; the gate driver2, in which a first transistor T1and a second transistor T2are directly connected in series between a driving power supply and a reference voltage, and in which an output (Vout)3is obtained from a node between the transistors T1and T2; a current limiting resistor (RS)5connected between a low-voltage side power supply terminal (VL)4of the gate driver2(the source of the second transistor T2) and the source of a power semiconductor device (a main switch M1)21; and a suppression capacitor (CS)6connected between the low-voltage side power supply terminal (VL)4of the gate driver2and the drain of the power semiconductor device (main switch M1)21.

Note that although the controller1and the gate driver2are depicted as being separate components in the example illustrated inFIG. 1, these components may be embedded into a single product to form a module or may be integrated into the same semiconductor integrated circuit.

Similarly, although in the example illustrated here the current limiting resistor (RS)5and the suppression capacitor (CS)6are depicted as being separate components from the controller1and the gate driver2, these components may be packaged together along with the controller1and the gate driver2into the same module.

The output (Vout)3of the gate driver2that drives the power semiconductor device (main switch M1)21is connected to the gate of the main switch (M1), and the low-voltage side power supply terminal (VL)4of the gate driver2is connected to a source (VS)22of the main switch (M1) via the current limiting resistor (RS)5.

Moreover, the suppression capacitor (CS)6(for suppressing rapid changes in current) has a prescribed capacitance and is connected between the drain of the main switch (M1) of the main circuit20and the source of the second transistor T2of the gate driver2; i.e., the low-voltage side power supply terminal4of the gate driver2.

With this configuration, increasing the capacitance of the suppression capacitor (CS)6makes it possible to, without having to set the resistance of the current limiting resistor (RS)5to a large value, suppress the rapid change in current (di/dt) that occurs when the power semiconductor device (main switch M1)21switches OFF. This will be described in more detail later.

Furthermore, the current limiting resistor (RS)5makes it possible to suppress current flowing through the reference voltage (such as ground) of the driver circuit10and the low-voltage side power supply terminal (VL)4to the source22of the power semiconductor device (main switch M1)21, which takes a negative voltage when the main switch (M1) switches OFF. The suppression capacitor (CS)6makes it possible to suppress the rapid change in current (di/dt) that occurs when the main switch (M1) switches OFF. This will also be described in more detail later.

FIG. 2is a diagram for explaining the operation of the driver circuit according to the embodiment of the present invention. Next, the following items will be described with reference toFIG. 2.

<1> Suppressing Rapid Changes in Current (di/dt)

InFIG. 2, the controller1controls the gates of the transistors T1and T2of the gate driver2in order to apply a prescribed output (Vout)3from the gate driver2to the gate of the main switch (M1)21. The output (Vout)3of the gate driver2causes the gate voltage of the switch (M1)21of the main circuit20to increase and also causes the gate-source voltage (VGS) of the switch (M1)21to increase.

When the VGS of the switch (M1)21exceeds the operating threshold of the switch (M1)21, the switch (M1)21transitions from the OFF state to the ON state (switches ON), and when the VGS of the switch (M1)21becomes less than the operating threshold, the switch (M1)21transitions from the ON state to the OFF state (switches OFF).

During these transitions, the current IDS flowing through the drain-source voltage (VDS) of the switch (M1)21causes rapid changes in magnitude (di/dt). This will be described in more detail later with reference toFIGS. 4A and 4B.

<2> Suppressing Negative Voltage at Low-Voltage Terminal of Main Switch

When the switch (M1)21switches OFF, the current IDS flowing through the drain-source voltage (VDS) of the main switch (M1)21is blocked. When this happens, due to the rapid change in current (di/dt) and parasitic inductance (L)23such as wiring inductance present between the source of the main switch (M1)21and the reference voltage of the driver circuit, the source voltage (VS)22of the main switch (M1)21takes a negative value relative to the reference voltage, as illustrated inFIG. 7.

Here, as explained above with reference toFIG. 6, if no current limiting resistor were present between the low-voltage side power supply terminal (VL)4of the driver circuit10and the source22of the main switch (M1)21, the low-voltage side power supply terminal (VL)4of the driver circuit10would takes a voltage equal to the voltage (VS) of the source22, and a large current would flow from the reference voltage on the driver circuit10side to the source22(which has a negative voltage) via the low-voltage side power supply line.

FIG. 3illustrates a configuration (second example) of the driver circuit according to an embodiment of the present invention. The driver circuit illustrated inFIG. 3can be generally divided into a driver circuit30and a main circuit40. With respect to the driver circuit30, the configuration of the driver circuit illustrated inFIG. 1is used for both the high side and the low side, and a bootstrap configuration is used in the high-side driving power supply. In this configuration, the driver circuit30and the main circuit40can still be embedded into a single product to form a semiconductor module200.

InFIG. 3, when a low-side main switch2(M2)43switches ON, current from a driving power supply50(illustrated in the upper left) flows through a bootstrap diode (D1)51to a bootstrap capacitor (C1)52and thereby stores electrical energy therein.

Then, when the low-side main switch2(M2)43switches OFF, the electrical energy stored in the bootstrap capacitor (C1)52becomes the high-side driving power supply. Furthermore, a gate driver32in a high-side driver is operated via control performed by a controller31in the driver circuit30, which uses the bootstrap capacitor (C1)52as a power supply.

An output terminal (Vout)33of the gate driver32is connected to the gate of a high-side main switch1(M1)41, and when the output of the gate driver32is high level and causes the gate voltage of the main switch1(M1)41to exceed the operating threshold, the high-side main switch1(M1)41switches ON. When this happens, power from the main circuit40is supplied to a load (not illustrated in the figure) that is connected to the source side of the high-side main switch1(M1)41.

Moreover, a low-side driver is always driven by the driving power supply50. Furthermore, the capacitor (C2)53is a decoupling capacitor added to the driving power supply50line. The operation of the low-side driver is the same as the operation of the high-side driver and therefore will not be described here.

Moreover, a current limiting resistor (RS1)35and a current limiting resistor (RS2)65illustrated inFIG. 3are both equivalent to the current limiting resistor (RR)76illustrated inFIG. 7and are respectively connected between a source (VS1)42of the high-side main switch1(M1)41and a low-voltage side power supply terminal (VL1)34of the gate driver Hi32and between a source (VS2)44of the low-side main switch2(M2)43and a low-voltage side power supply terminal (VL2)64of a gate driver Lo62. A suppression capacitor (CS1)36and a suppression capacitor (CS2)66are both equivalent to the suppression capacitor (CS)6illustrated inFIG. 1. Moreover, the reference character45indicates a parasitic inductance connected to the source (VS2) of the low-side main switch2(M2)43.

FIGS. 4A and 4Bare diagrams for explaining, using a model, the operation of a low-side circuit that suppresses the rapid changes in current (di/dt) that occur when a main switch according to the embodiments of the present invention switches ON and OFF. This model corresponds to the configuration (second example) of the driver circuit as illustrated inFIG. 3. Moreover, the rapid change in current (di/dt) that occurs when the main switch switches ON is similar to when the main switch switches OFF, therefore will not be described here.

FIG. 4Aillustrates how current flows when a low-side main switch Tr (122) is ON.

As illustrated inFIG. 4A, the left end of a current limiting resistor RS(124) is connected to ground in order to reference the voltage to a reference voltage (such as ground) of the low-side driver circuit.

When the main switch Tr (122) illustrated inFIG. 4Aswitches ON and reaches steady-state, di/dt becomes approximately zero, and therefore the source VSof the main switch Tr (122) becomes approximately 0V relative to the reference voltage (ground) of the low-side driver circuit. As a result, there is no voltage difference across the terminals of the current limiting resistor RS(124), and no current flows to the current limiting resistor RS(124).

Therefore, a current i0that flows from a power supply VDDof the main circuit through a load121proceeds to flow to the drain (D) and the source (S) of the switched-ON main switch Tr (122) to a parasitic inductance L (125) and the ground. Due to this, electrical energy accumulates in the parasitic inductance L (125). Moreover, the load121represents the total impedance of the high-side configuration as viewed from the low side.

Meanwhile,FIG. 4Billustrates how current flows when the main switch Tr (122) transitions from ON to OFF and will be used to explain how the rapid change in current (di/dt) flowing to the parasitic inductance L (125) that occurs when the main switch Tr (122) of the low-side driver circuit switches OFF is suppressed, as well as how the large negative voltage that occurs at the source VSof the main switch Tr (122) due to this rapid change in current (di/dt) is reduced.

As illustrated inFIG. 4B, when the main switch Tr (122) switches OFF, the source VSof the main switch Tr (122) becomes negative, and current begins to flow to the current limiting resistor RS(124).

This current includes a current i1that flows from the power supply VDDof the main circuit through the load121and then flows through both ends of a suppression capacitor CS(123), as well as a current i2that circulates in from the ground on the left end of the current limiting resistor RS(124) (that is, current that is supplied from the low-voltage side power supply line of the driver circuit), which combine as a current i that flows to the current limiting resistor RS(124). This current i also flows to the parasitic inductance L (125).

Analyzing the transient response of a circuit including the current limiting resistor RS(124) and the parasitic inductance L (125) illustrated in the figure in this state yields the following.
i=i1+i2(1)
RS×i+L(di/dt)=0   (2)
(di/dt)=−(RS/L)×i(3)

The current i that occurs when the main switch switches OFF corresponds to the transient response of the current i0from when the main switch is ON, and therefore:
i=i0exp(−t/(L/RS))   (4)
(di/dt)=−(RS/L)×i0exp(−t/(L/RS))   (5)

Thus, as the resistance of the current limiting resistor RS(124) decreases, the time constant increases, (di/dt) decreases, and the fall in the source voltage VSdecreases. Conversely, as the resistance of the current limiting resistor RS(124) increases, the time constant decreases, (di/dt) increases, and the fall in the source voltage VSincreases.

Moreover, a portion of the current i0that was flowing through the load121continues to flow to the suppression capacitor CS(123) side as the current i1even when the main switch Tr (122) switches OFF, thereby making it possible to reduce the current i2supplied from the low-voltage side power supply line of the driver circuit by a corresponding amount. In other words, this makes it possible to reduce the flow of excess current to the driver circuit. Furthermore, the load121typically has a non-zero inductance component including some degree of parasitic inductance, and therefore the larger this inductance component is, the larger the portion of the current i0that continues to flow as the current i1is.

The present embodiment also exhibits another (di/dt) suppression effect in addition to the one described above. The analysis above assumes that the current flowing to the main switch Tr (122) is instantaneously blocked when transitioning from the state illustrated inFIG. 4Ato the state illustrated inFIG. 4B. In the present embodiment, however, such an abrupt shutdown of the current actually does not occur; i.e., the rate of change (di/dt) of the current flowing to the main switch Tr (122) is reduced.

As described above, when the gate voltage VG of the main switch Tr (122) is decreased to attempt to switch OFF the main switch Tr (122), the source voltage VSof the main switch Tr (122) takes a negative voltage. When this happens, because VSis negative, the gate-source voltage VGS=VG−VSof the main switch Tr (122) increases. In other words, when the gate voltage VG is decreased to switch OFF the main switch Tr (122), a feedback effect that inhibits this change is applied to the gate-source voltage VGS, thereby making it possible to make the current flowing to the main switch Tr (122) change more gradually. This, in turn, makes it possible to reduce the rate of change (di/dt) in current flowing to the parasitic inductance.

Although the circuit model illustrated inFIGS. 4A and 4Bare examples for a low-side circuit, the same approach can be applied to a high-side circuit example (not illustrated in the figure) except in that the load would be connected between the source of the main switch and the source VS, and therefore this case will not be described here.

INDUSTRIAL APPLICABILITY

The driver circuit of the present invention is not limited to use in switching power supplies (power converters) such as motor-driving inverters and DC-DC converters and can also be applied to power supplies (power converters) for computers, communication devices, and the like.