阅读说明：本技术 驱动电路内置型功率模块 (Power module with built-in driving circuit ) 是由 荒木龙 于 2019-05-31 设计创作，主要内容包括：提供驱动电路内置型功率模块,其抑制了开关元件因超过其额定电流值流通而发生的关断时的栅电压的寄生振荡。由电流检测电路(15)监视流通于构成半桥电路的下臂部的开关元件(12、13、14)的电流,若开关元件(12、13、14)的电流比额定电流值高,则从介由通常接地布线(25)连接于电源侧接地端子的COM1切换为介由包含阻尼电阻(27)的接地布线(26)连接于电源侧接地端子的COM2。由此,提高下臂驱动电路(11)的驱动阻抗,开关元件(12、13、14)关断时的栅电压的寄生振荡受到抑制。(Provided is a power module with a built-in drive circuit, which suppresses parasitic oscillation of a gate voltage when a switching element is turned off due to the switching element flowing at a value exceeding a rated current value. A current flowing through switching elements (12, 13, 14) constituting a lower arm part of a half-bridge circuit is monitored by a current detection circuit (15), and when the current of the switching elements (12, 13, 14) is higher than a rated current value, the current is switched from COM1 connected to a power supply side ground terminal through a normal ground wiring (25) to COM2 connected to the power supply side ground terminal through a ground wiring (26) including a damping resistor (27). Thus, the driving impedance of the lower arm driving circuit (11) is increased, and parasitic oscillation of the gate voltage when the switching elements (12, 13, 14) are turned off is suppressed.)

1. A power module with a built-in drive circuit, the power module including a half-bridge circuit, an upper arm drive circuit, and a lower arm drive circuit, the half-bridge circuit including a first switching element constituting an upper arm portion and a second switching element constituting a lower arm portion, the upper arm drive circuit driving the first switching element, the lower arm drive circuit driving the second switching element, the power module with a built-in drive circuit comprising:

a power supply side ground terminal located on a ground side of the second switching element;

a first drive circuit-side ground terminal connected to the power supply-side ground terminal via a normal ground wiring;

a second drive circuit-side ground terminal connected to the power supply-side ground terminal via a ground wiring including a damping resistor;

a current detection circuit that detects a current flowing through the second switching element; and

and a control ground terminal switching circuit that switches according to the current value detected by the current detection circuit so as to connect the ground terminal of the lower arm drive circuit to the first drive circuit-side ground terminal or the second drive circuit-side ground terminal.

2. The power module with built-in driver circuit according to claim 1,

the current detection circuit includes:

a current detection resistor that converts a current output from the current sensing element incorporated in the second switching element into a voltage signal;

a reference voltage source that outputs a reference voltage corresponding to a rated current value of the second switching element; and

and a comparator that compares the voltage signal with the reference voltage and outputs a switching control signal that controls switching of the ground terminal switching circuit.

3. The power module with built-in driver circuit according to claim 2,

the control ground terminal switching circuit connects the ground terminal of the lower arm drive circuit to the first drive circuit-side ground terminal when receiving the switching control signal indicating that the voltage signal is less than or equal to the reference voltage from the current detection circuit, and connects the ground terminal of the lower arm drive circuit to the second drive circuit-side ground terminal when receiving the switching control signal indicating that the voltage signal is higher than the reference voltage from the current detection circuit.

4. The power module with built-in driver circuit according to claim 1,

the second switching element is an IGBT and a freewheeling diode, or the second switching element is a MOSFET.

5. The power module with built-in driver circuit according to claim 1, further comprising:

an upper arm current detection circuit that detects a current flowing through the first switching element;

an upper arm control ground terminal switching circuit which has an upper arm reference potential terminal, a first terminal, and a second terminal of the upper arm drive circuit, and which switches the upper arm reference potential terminal to be connected to the first terminal or the second terminal in accordance with the current value detected by the upper arm current detection circuit;

an upper arm reference potential wiring line which connects an output connection point of the first switching element and the second switching element to the first terminal of the upper arm control ground terminal switching circuit; and

and an upper arm damping resistor connected between the output connection point and the second terminal of the upper arm control ground terminal switching circuit.

6. The power module with built-in driver circuit according to claim 5,

the first switching element is an IGBT and a freewheeling diode, or the first switching element is a MOSFET;

the second switching element is an IGBT and a freewheeling diode, or the second switching element is a MOSFET.

Technical Field

The present invention relates to a power module with a built-in drive circuit, and more particularly to a power module with a built-in drive circuit, which incorporates a power conversion semiconductor switching element for a motor drive inverter, a DC-DC converter, or the like, and a drive circuit for driving the switching element.

Background

As the inverter for driving the motor, a power module including a plurality of sets of half-bridge circuits in which 2 switching elements are connected in series and a drive circuit for driving the switching elements to be turned on and off is used.

Fig. 5 is a circuit diagram showing a configuration example of a power module used in a three-phase motor driving inverter, fig. 6 is a diagram showing a switching waveform when a switching element of a lower arm is turned off, fig. 6 (a) shows a case in a normal operation, and fig. 6 (B) shows a case in an abnormal operation.

The power module 100 shown in fig. 5 is a power conversion device that supplies ac power to a three-phase motor 200. Therefore, the power module 100 has 3 half-bridge circuits for U-phase, V-phase, and W-phase. The U-phase half-bridge circuit is composed of switching elements 101 and 102, the V-phase half-bridge circuit is composed of switching elements 103 and 104, and the W-phase half-bridge circuit is composed of switching elements 105 and 106. Here, as the switching elements 101 and 106, an IGBT (Insulated Gate Bipolar Transistor) and a freewheeling diode connected in reverse parallel to a collector terminal and an emitter terminal of the IGBT are used. It should be noted that, as the switching elements 101 through 106, a MOSFET (Metal-Oxide-Semiconductor Field-effect transistor) may be used.

In the U-phase half-bridge circuit, the collector terminal of the switching element 101 constituting the upper arm portion of the U-phase half-bridge circuit is connected to the P terminal of the power module 100, and the P terminal is connected to the positive terminal VDC (+) of the dc power supply. The emitter terminal of the switching element 101 is connected to the collector terminal of the switching element 102 and the U terminal of the power module 100, the switching element 102 constituting the lower arm of the U-phase half-bridge circuit in the U-phase half-bridge circuit, and the U terminal being connected to the U-phase terminal of the three-phase motor 200.

The collector terminal of the switching element 103 constituting the upper arm portion of the V-phase half-bridge circuit is connected to the P terminal of the power module 100. The emitter terminal of the switching element 103 is connected to the collector terminal of the switching element 104 and the V terminal of the power module 100, the switching element 104 constituting the lower arm of the U-phase half-bridge circuit, and the V terminal is connected to the V-phase terminal of the three-phase motor 200.

The collector terminal of the switching element 105 constituting the upper arm portion of the W-phase half-bridge circuit is connected to the P terminal of the power module 100. The emitter terminal of the switching element 105 is connected to the collector terminal of the switching element 106 and the W terminal of the power module 100, the switching element 106 constituting the lower arm of the W-phase half-bridge circuit, and the W terminal is connected to the W-phase terminal of the three-phase motor 200.

The gate terminal of the switching element 101 constituting the upper arm portion of the U-phase is connected to the OUT terminal of the upper arm drive circuit 111, and the emitter terminal of the switching element 101 is connected to the VS terminal of the upper arm drive circuit 111.

The gate terminal of the switching element 103 constituting the upper arm portion of the V-phase is connected to the OUT terminal of the upper arm drive circuit 112, and the emitter terminal of the switching element 103 is connected to the VS terminal of the upper arm drive circuit 112.

The gate terminal of the switching element 105 constituting the upper arm portion of the W phase is connected to the OUT terminal of the upper arm drive circuit 113, and the emitter terminal of the switching element 105 is connected to the VS terminal of the upper arm drive circuit 113.

The gate terminal of the switching element 102 constituting the lower arm portion of the U-phase is connected to the UOUT terminal of the lower arm drive circuit 114, and the emitter terminal of the switching element 102 is connected to the NU terminal of the power module 100.

The gate terminal of the switching element 104 constituting the lower arm portion of the V-phase is connected to the VOUT terminal of the lower arm drive circuit 114, and the emitter terminal of the switching element 104 is connected to the NV terminal of the power module 100.

The gate terminal of the switching element 106 constituting the lower arm portion of the W phase is connected to the WOUT terminal of the lower arm drive circuit 114, and the emitter terminal of the switching element 106 is connected to the NW terminal of the power module 100.

The NU terminal, NV terminal, and NW terminal of the power module 100 are externally integrated into one, and are connected to one terminal of the shunt resistor 121 for current detection, and the other terminal of the shunt resistor 121 is connected to the negative terminal VDC (-) of the dc power supply. One terminal of the shunt resistor 121 IS also connected to one terminal of the resistor 122, and the other terminal of the resistor 122 IS connected to one terminal of the capacitor 123, the cathode terminal of the diode 124, and the IS terminal of the power module 100. The other terminal of the capacitor 123 is connected to the ground terminal of the printed circuit board on which the power module 100 is mounted, and the anode terminal of the diode 124 is connected to the ground terminal of the printed circuit board. The IS terminal of the power module 100 IS connected to the IS terminal of the lower arm drive circuit 114.

The other terminal of the shunt resistor 121 is also connected to a COM terminal of the power module 100 via a ground wiring 125 of the printed circuit board, and the COM terminal is connected to a ground terminal of the printed circuit board. In the power module 100, the COM terminal is connected to the GND terminal of the upper arm drive circuits 111, 112, and 113 and the GND terminal of the lower arm drive circuit 114.

The power module 100 further includes an in (hu) terminal, an in (hv) terminal, an in (hw) terminal, an in (lu) terminal, an in (lv) terminal, and an in (lw) terminal that receive control signals from the host control device. The IN (hu) terminal is connected to the IN terminal of the upper arm drive circuit 111, the IN (hv) terminal is connected to the IN terminal of the upper arm drive circuit 112, and the IN (hw) terminal is connected to the IN terminal of the upper arm drive circuit 113. The in (lu) terminal, the in (lv) terminal, and the in (lw) terminal are connected to the UIN terminal, the VIN terminal, and the WIN terminal of the lower arm drive circuit 114, respectively.

According to the power module 100, the upper arm drive circuits 111, 112, and 113 perform on-drive and off-drive of the switching elements 101, 103, and 105 in accordance with a control signal input to the in (hu) terminal, the in (hv) terminal, or the in (hw) terminal. Similarly, when a control signal is input to the in (lu) terminal, the in (lv) terminal, or the in (lw) terminal, the lower arm drive circuit 114 drives the switching elements 102, 104, and 106 to be turned on and off.

Here, when one of the switching elements 102, 104, and 106 is turned on by the lower arm drive circuit 114, the current flowing through the switching element 102, 104, and 106 flows to the negative terminal VDC (-) of the dc power supply via the shunt resistor 121. At this time, the currents flowing through the switching elements 102, 104, and 106 are converted into voltage signals by the shunt resistors 121, and are fed back to the lower arm drive circuit 114. The lower arm drive circuit 114 monitors a voltage signal fed back to the IS terminal to detect an overcurrent and a short circuit of the switching elements 102, 104, and 106.

In this way, in the power module 100, the shunt resistor 121 is used to detect the overcurrent and the short circuit of the switching elements 102, 104, and 106 of the lower arm. Therefore, the NU terminal, NV terminal, and NW terminal, which are ground side terminals of the switching elements 102, 104, and 106 of the lower arm, and the COM terminal, which is a ground side terminal of the upper arm drive circuits 111, 112, and 113 and the lower arm drive circuit 114, are not internally connected but externally connected. The connection is made by a ground wiring 125 formed by winding the power module 100 around the printed circuit board. Therefore, the driving impedance of the lower arm driving circuit 114 includes the gate-emitter impedance of the switching elements 102, 104, and 106, the shunt resistance 121, the ground wiring 125, and the impedance of the internal wiring between the COM terminal and the GND terminal of the lower arm driving circuit 114.

Here, since the ground wiring 125 includes a resistance component, a capacitance component, and an inductance component, which are long and much longer than the internal wiring of the lower arm driving circuit 114, the driving impedance of the lower arm driving circuit 114 increases accordingly. The higher the switching frequency of the switching elements 102, 104, 106, the greater the influence of the ground wiring 125. Further, there is a tendency that: as the current flowing through the switching elements 102, 104, and 106 increases, parasitic oscillation of the gate voltage (gate-emitter voltage) is more likely to occur due to the influence of the ground wiring 125. Next, a case of a normal operation in which no parasitic oscillation occurs and a case of an abnormal operation in which parasitic oscillation occurs will be described using the switching waveforms shown in fig. 6 (a) and 6 (B).

In fig. 6 (a) and 6 (B), the gate-emitter voltage Vge, the collector current Ic, and the collector-emitter voltage Vce of the switching elements 102, 104, and 106 are indicated by broken lines, thin lines, and thick lines, respectively.

When the switching elements 102, 104, and 106 are turned on and a current equal to or less than the rated current value having a small influence on the ground wiring 125 flows, the gate-emitter voltage Vge, the collector current Ic, and the collector-emitter voltage Vce do not change greatly, respectively, as shown in fig. 6 (a). When the gate-emitter voltage Vge decreases to turn off the switching elements 102, 104, and 106, the collector current Ic decreases and the collector-emitter voltage Vce increases and stabilizes at that time.

On the other hand, there are cases where: when the switching elements 102, 104, and 106 are repeatedly turned on, a current exceeding the rated current value flows, and at some point of turning off, parasitic oscillation of the gate-emitter voltage Vge as shown in fig. 6 (B) occurs suddenly. When such parasitic oscillation occurs, the switching elements 102, 104, and 106 may be turned on by mistake during the period to be turned off, and breakdown may be caused in a short time. When a current exceeding the rated current value flows at the time of turning on, the switching waveform shown in fig. 6 (a) appears in the switch in the previous cycle in which the parasitic oscillation shown in fig. 6 (B) occurs.

For the generation of such parasitic oscillation of the gate voltage, a technique of suppressing the parasitic oscillation is known (for example, see patent document 1). In patent document 1, resistance value frequency dependent elements are provided between a source output terminal and a drain (sink) output terminal of a drive circuit and a gate terminal of a switching element, and parasitic oscillation is suppressed by optimizing the rising operation and the falling operation of the switching element individually.

Disclosure of Invention

Technical problem

However, in the suppression of the parasitic oscillation by patent document 1, each switching element requires 2 resistance value frequency-dependent elements, and the resistance value frequency-dependent elements themselves are large in size, so that there is a problem that the power module itself is large in size.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a power module with a built-in drive circuit, which suppresses parasitic oscillation of a gate voltage at the time of turn-off of a switching element caused by the flow of current exceeding a rated current value thereof without increasing the size of the power module.

Technical scheme

In order to solve the above-described problems, the present invention provides a power module with a built-in drive circuit, including a half-bridge circuit having a first switching element constituting an upper arm portion and a second switching element constituting a lower arm portion, an upper arm drive circuit driving the first switching element, and a lower arm drive circuit driving the second switching element. The power module with a built-in drive circuit includes: a power supply side ground terminal located on a ground side of the second switching element; a first drive circuit-side ground terminal connected to a power supply-side ground terminal via a normal ground wiring; a second drive circuit-side ground terminal connected to the power supply-side ground terminal via a ground wiring including a damping resistor; a current detection circuit that detects a current flowing through the second switching element; and a control ground terminal switching circuit that switches according to the current value detected by the current detection circuit so as to connect the ground terminal of the lower arm drive circuit to the first drive circuit side ground terminal or the second drive circuit side ground terminal.

Technical effects

The power module with a built-in drive circuit having the above-described configuration has an advantage that parasitic oscillation at the time of turn-off can be suppressed because the drive impedance of the switching element is increased to suppress the current value flowing when the switching element flows beyond its rated current value.

The above and other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings which illustrate preferred embodiments which are examples of the present invention.

Drawings

Fig. 1 is a circuit diagram showing a part of the smart power module of the first embodiment.

Fig. 2 is a diagram showing a change in switching loss with respect to a collector current when the switching element is turned off.

Fig. 3 is a diagram showing a switching waveform when the switching element is turned off, where fig. 3 (a) shows a case where there is no damping resistance, and fig. 3 (B) shows a case where there is a damping resistance.

Fig. 4 is a circuit diagram showing a part of the smart power module of the second embodiment.

Fig. 5 is a circuit diagram showing a configuration example of a power module used in an inverter for driving a three-phase motor.

Fig. 6 is a diagram showing a switching waveform when the switching element of the lower arm is turned off, fig. 6 (a) shows a case during normal operation, and fig. 6 (B) shows a case during abnormal operation.

Description of the symbols

10. 10a intelligent power module

11 lower arm drive circuit

12. 13, 14 switching element

Freewheel diodes 12a, 13a, 14a

15 current detection circuit

16 control grounding terminal switching circuit

17. 18, 19 current detecting resistor

20. 21, 22 comparator

23 logic AND circuit

24 reference voltage source

25 general ground wiring

26 ground wiring

27 damping resistor

41 upper arm drive circuit

42 switching element

42a freewheel diode

43 Current detection Circuit

44 control ground terminal switching circuit

45 damping resistor

46 upper arm reference potential wiring

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, taking as an example a case where the present invention is applied to an intelligent power module for driving a three-phase motor. In the drawings, the same components are denoted by the same reference numerals. In addition, each embodiment can be implemented by partially combining a plurality of embodiments within a range where there is no contradiction.

Fig. 1 is a circuit diagram showing a part of an intelligent power module according to a first embodiment, fig. 2 is a diagram showing a change in switching loss with respect to a collector current when a switching element is turned off, fig. 3 is a diagram showing a switching waveform when the switching element is turned off, fig. 3 (a) shows a case where there is no damping resistance, and fig. 3 (B) shows a case where there is a damping resistance.

The smart power module 10 shown in fig. 1 includes a lower arm drive circuit 11, a switching element 12 constituting a U-phase lower arm portion, a switching element 13 constituting a V-phase lower arm portion, and a switching element 14 constituting a W-phase lower arm portion. The smart power module 10 also has a current detection circuit 15 and a control ground terminal switching circuit 16. The switching elements 12, 13, and 14 are IGBTs, and flywheel diodes 12a, 13a, and 14a are connected in reverse parallel to the collector-emitter terminals of the switching elements 12, 13, and 14, respectively. Each of the switching elements 12, 13, and 14 further includes a current sensing element that indirectly detects a current proportional to the collector current. In fig. 1, the main IGBT elements and the current sensing elements of the switching elements 12, 13, 14 are denoted by one IGBT symbol, and only the emitter terminals of the switching elements 12, 13, 14 are separately denoted as the emitter terminal of the main IGBT element and the sense emitter terminal of the current sensing element.

The lower arm drive circuit 11 has a UIN terminal, VIN terminal, WIN terminal, UOUT terminal, VOUT terminal, WOUT terminal, and GND terminal. The UIN terminal, VIN terminal, and WIN terminal are input terminals for controlling signals of the switching elements 12, 13, and 14 of the lower arm portion, and the UOUT terminal, VOUT terminal, and WOUT terminal are output terminals connected to gate terminals of the switching elements 12, 13, and 14.

The collector terminals of the switching elements 12, 13, and 14 are connected to the U terminal, the V terminal, and the W terminal of the smart power module 10. Emitter terminals of the switching elements 12, 13, and 14 are connected to a NU terminal, an NV terminal, and an NW terminal, which are power supply side ground terminals of the smart power module 10. The sense emitter terminals of the switching elements 12, 13, 14 are connected to a current detection circuit 15.

The current detection circuit 15 has current detection resistors 17, 18, and 19, comparators 20, 21, and 22, and a logical and circuit 23. One terminal of the current detection resistors 17, 18, 19 is connected to the sense emitter terminal of the switching elements 12, 13, 14 and the non-inverting input terminal of the comparators 20, 21, 22, and the other terminal of the current detection resistors 17, 18, 19 is connected to the ground terminal of the smart power module 10. The inverting input terminals of the comparators 20, 21, and 22 are connected to the positive terminal of a reference voltage source 24 that outputs a reference voltage, and the negative terminal of the reference voltage source 24 is connected to the ground terminal of the smart power module 10. Output terminals of the comparators 20, 21, and 22 are connected to an input terminal of the and logic circuit 23, and an output terminal of the and logic circuit 23 is connected to a control terminal of the control ground terminal switching circuit 16.

The control ground terminal switching circuit 16 has a movable contact connected to the GND terminal of the lower arm drive circuit 11, 2 fixed contacts, and a control terminal. The movable contact of the control ground terminal switching circuit 16 is connected to the GND terminal of the lower arm drive circuit 11. One of the 2 fixed contacts is connected to the COM1 terminal (first driver-side ground terminal) of the smart power module 10, and the other of the 2 fixed contacts is connected to the COM2 terminal (second driver-side ground terminal) of the smart power module 10. The control ground terminal switching circuit 16 is preferably constituted by a semiconductor switching element.

The NU terminal, NV terminal, and NW terminal of the smart power module 10, which are power supply side ground terminals, are connected to the negative terminal VDC (-) of the dc power supply. The power supply side ground terminal of the smart power module 10 is also connected to the COM1 terminal via a normal ground wiring 25, and the normal ground wiring 25 is formed on a printed circuit board on which the smart power module 10 is mounted. The NU terminal, NV terminal, and NW terminal are also connected to the COM2 terminal through a ground wiring 26 including a damping resistor 27. The damping resistor 27 is used to suppress parasitic oscillation, and can be a resistance value frequency-dependent element such as a chip ferrite bead or a bead core.

Note that, although only the components related to the lower arm portion of the half-bridge circuit are shown in the smart power module 10 of fig. 1, actually, as shown in fig. 5, an upper arm drive circuit and switching elements related to the upper arm portion of the half-bridge circuit are also included.

In the current detection circuit 15, the collector current is detected in the form of a voltage by supplying the current output from the sense emitter terminals of the switching elements 12, 13, and 14 to the current detection resistors 17, 18, and 19. The reference voltage of the reference voltage source 24 has a value corresponding to the rated current value of the switching elements 12, 13, 14. Therefore, the comparators 20, 21, and 22 compare the voltages detected by the current detection resistors 17, 18, and 19 with the reference voltage, and output a signal of the ground level (L level) when the value of the collector current of the switching elements 12, 13, and 14 is equal to or less than the rated current value. When the collector current values of the switching elements 12, 13, and 14 exceed the rated current value, the comparators 20, 21, and 22 output signals of the level (H level) of the power supply voltage. When the comparators 20, 21, and 22 output the L-level signal, the and logic circuit 23 outputs the L-level signal, and when one of the comparators 20, 21, and 22 outputs the H-level signal, the and logic circuit 23 outputs the H-level signal.

Upon receiving the L-level signal as the control signal from the current detection circuit 15, the control ground terminal switching circuit 16 functions to connect the GND terminal (ground terminal) of the lower arm drive circuit 11 to the COM1 terminal of the smart power module 10. Thus, the COM1 terminal of the smart power module 10, which is the lower arm drive circuit side ground terminal, is connected to the power supply side ground terminal (the NU terminal, the NV terminal, and the NW terminal) via the normal ground wiring 25. In this case, since the ground wiring 25 is normally low in impedance, the driving impedance of the lower arm driving circuit 11 is also low, and the switching loss (turn-off loss) can be suppressed to be low.

When any one of the comparators 20, 21, and 22 of the current detection circuit 15 detects that the current value is higher than the rated current value of the switching elements 12, 13, and 14, a signal at the H level is input from the current detection circuit 15 to the control ground terminal switching circuit 16 as a control signal. At this time, the control ground terminal switching circuit 16 functions to connect the GND terminal (ground terminal) of the lower arm drive circuit 11 to the COM2 terminal of the smart power module 10. Thus, the COM2 terminal of the smart power module 10 is connected to the power supply side ground terminal (the NU terminal, the NV terminal, and the NW terminal) via the ground wiring 26 including the damping resistor 27. Since the damping resistor 27 is interposed between the NU terminal, the NV terminal, and the NW terminal and the COM2 terminal, the driving impedance of the lower arm driving circuit 11 increases accordingly. Thereby, although the switching loss (turn-off loss) of the switching elements 12, 13, 14 increases, the parasitic oscillation of the gate voltage when the switching elements 12, 13, 14 are turned off is reduced.

Fig. 2 shows a change in switching loss when the control ground terminal switching circuit 16 switches the ground wiring. In fig. 2, the horizontal axis represents collector currents of the switching elements 12, 13, and 14, and the vertical axis represents switching loss at the time of off. In fig. 2, a curve 30 shows a change in switching loss with respect to collector current Ic when the NU terminal, NV terminal, and NW terminal are connected to the COM1 terminal only by the normal ground wiring 25, and the loss becomes smaller in the entire current range. On the other hand, a curve 31 shows a change in switching loss with respect to the collector current Ic when the NU terminal, NV terminal, and NW terminal are connected to the COM2 terminal by the ground wiring 26 including the damping resistor 27, and the loss becomes large in the entire current range. In the present invention, the switching to the normal ground wiring 25 or the ground wiring 26 including the damping resistor 27 is performed by detecting the rated current value, and the switching loss can be changed as shown by the curve 32. That is, when the collector current Ic is equal to or less than the rated current value at which parasitic oscillation of the gate voltage does not occur, the damping resistor 27 is not present, so that the switching loss can be reduced. When the value of collector current Ic is higher than the rated current value, the occurrence of parasitic oscillation can be suppressed by increasing the switching loss by damping resistor 27.

By switching the impedance of the ground wiring in accordance with the current value of the switching elements 12, 13, and 14 in this way, the switching loss can be optimized while suppressing parasitic oscillation of the gate voltage.

Fig. 3 (a) and 3 (B) show switching waveforms of the switching elements 12, 13, and 14 when the ground terminal switching circuit 16 is controlled to switch the ground wiring. Fig. 3 (a) shows a case where the power supply side ground terminal and the lower arm drive circuit side ground terminal are connected only by the normal ground wiring 25 without the damping resistor 27. Fig. 3 (B) shows a case where the power supply side ground terminal and the lower arm drive circuit side ground terminal are connected by a ground wiring 26 including a damping resistor 27. In fig. 3 (a) and 3 (B), the gate-emitter voltage Vge as the gate voltage of the switching elements 12, 13, and 14 is indicated by a broken line, the collector current Ic is indicated by a thin line, and the collector-emitter voltage Vce is indicated by a thick line.

When collector current Ic is less than or equal to the rated current value, no parasitic oscillation occurs as shown in fig. 3 (a). When the value of collector current Ic is higher than the rated current value, the drive impedance of lower arm drive circuit 11 is increased by damping resistor 27, so that the value of the gate voltage at the time of turn-off is suppressed as shown in fig. 3 (B), and the occurrence of parasitic oscillation is suppressed.

In the present embodiment, the current detection circuit 15 and the control ground terminal switching circuit 16 are provided outside the lower arm drive circuit 11, but the functions of either or both of the current detection circuit 15 and the control ground terminal switching circuit 16 may be combined with the lower arm drive circuit 11.

In this embodiment, the shunt resistor is not used for current detection of the switching elements 12, 13, and 14, but the current detection circuit 15 detects the current of the switching elements 12, 13, and 14, and therefore can use the detection signal. That is, the lower arm drive circuit 11 can perform overcurrent protection and load short-circuit protection by monitoring the detection signal detected by the current detection circuit 15. By eliminating the shunt resistance, the lower arm drive circuit 11 can further lower the drive impedance and further reduce the switching loss.

Fig. 4 is a circuit diagram showing a part of the smart power module of the second embodiment. In fig. 4, the same or equivalent components as those shown in fig. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. In fig. 4, only the circuit related to the U phase is shown for simplification of the illustration.

The intelligent power module 10a according to the second embodiment switches the drive impedance according to the current value not only to the ground wiring of the lower arm drive circuit 11 but also to the corresponding wiring of the upper arm drive circuit.

In the smart power module 10a, the control configuration of the lower arm portion is the same as that shown in fig. 1 except that only the circuit related to the U-phase is shown, and therefore, a detailed description of the lower arm driving circuit 11 is omitted here. The control structure of the upper arm portion is only shown for the U-phase related circuit, and the V-phase related circuit and the W-phase related circuit are the same as those of the U-phase shown in the figure and are therefore omitted.

The smart power module 10a includes an upper arm drive circuit 41 for the U-phase, a switching element 42 constituting an upper arm portion of a half-bridge circuit for the U-phase, a current detection circuit 43, a control ground terminal switching circuit 44, and a damping resistor 45. The freewheeling diode 42a is connected in anti-parallel with the collector-emitter terminal of the switching element 42. The switching element 42 includes a current sensing element, similarly to the switching element 12 constituting the lower arm portion of the U phase.

The upper arm drive circuit 41 has an OUT terminal connected to the gate terminal of the switching element 42 and a VS terminal which defines the U-phase upper arm reference potential and is connected to the control ground terminal switching circuit 44.

The collector terminal of switching element 42 is connected to the P terminal of smart power module 10a, and the emitter terminal of switching element 42 is connected to the U terminal of smart power module 10 a. The sense emitter terminal of the switching element 42 is connected to the current detection circuit 43.

An output connection point between the emitter terminal of the switching element 42 and the U terminal of the smart power module 10a is connected to the control ground terminal switching circuit 44 via an upper arm reference potential wiring 46. The connection point between the emitter terminal of the switching element 42 and the U terminal of the smart power module 10a is further connected to a control ground terminal switching circuit 44 via a damping resistor 45. The current detection circuit 43 includes a current detection resistor, a comparator, and a reference voltage source, as in the lower arm current detection circuit 15. However, since the current detection circuit 43 detects only the current value of the switching element 42, it does not have a current detection resistor, a comparator, and a logical and circuit for another phase, which are provided in the lower arm current detection circuit 15.

According to the smart power module 10a, the current detection circuit 43 monitors the current value of the switching element 42, and when the current value of the switching element 42 is smaller than or equal to the rated current value of the switching element 42, the current detection circuit 43 outputs a signal of L level. Thus, the control ground terminal switching circuit 44 connects the VS terminal of the upper arm drive circuit 41 to the upper arm reference potential wiring 46. When the current value of the switching element 42 is higher than the rated current value of the switching element 42, the current detection circuit 43 outputs an H-level signal, and the ground terminal switching circuit 44 is controlled to connect the VS terminal of the upper arm drive circuit 41 to the damping resistor 45. This increases the drive impedance of the upper arm drive circuit 41, and suppresses the occurrence of parasitic oscillation of the gate voltage when the switching element 42 is turned off.

The foregoing is considered as illustrative only of the principles of the invention. Further, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention, and the present invention is not limited to the exact construction and application examples shown and described above, and all modifications and equivalents corresponding thereto are to be regarded as being within the scope of the present invention defined by the appended claims and their equivalents.