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Title:
POWER MODULE COMPRISING AN ACTIVE MILLER CLAMP
Document Type and Number:
WIPO Patent Application WO/2020/152036
Kind Code:
A1
Abstract:
A power module (2) comprising a first power switching member (4, 4') arranged on a power electronic substrate (18) is disclosed. The power module (2) comprises a plurality of control connectors (20, 21, 23, 24) and the first power switching member (4, 4') comprises a gate terminal (G, G')· The power module (2) comprises an additional switching member (10, 10', 30) being configured to reduce the gate terminal (G, G') impedance during the turn-off event.

Inventors:
RETTMANN TIM (DK)
AGGEN CHRISTIAN (DK)
Application Number:
PCT/EP2020/051087
Publication Date:
July 30, 2020
Filing Date:
January 17, 2020
Export Citation:
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Assignee:
DANFOSS SILICON POWER GMBH (DE)
International Classes:
H03K17/16; H01L25/07; H03K17/06
Domestic Patent References:
WO2007138509A22007-12-06
Foreign References:
US20160308523A12016-10-20
US20080238520A12008-10-02
US9998109B12018-06-12
Attorney, Agent or Firm:
STEVENS, Brian (DK)
Download PDF:
Claims:
Claims

1. A power module (2) comprising a first power switching member (4, 4', 8) arranged on a substrate (18), wherein the power module (2) comprises a plurality of control connectors (20, 20', 21, 21', 22, 22', 23, 24), wherein the first power switching member (4, 4') comprises a gate terminal (G, G'), characterised in that the power module (2) comprises an additional switching member (10, 10', 30) being configured to reduce the gate terminal (G, G') impedance during the turn-off event.

2. A power module (2) according to claim 1, characterised in that a first terminal (drain terminal) (D) of the additional switching member (10, 10', 30) is electrically connected to the gate terminal (G, G') of the first power switching member (4, 4') and that a second terminal (the source terminal) (S, S') of the additional switching member (10, 10', 30) is electrically connected to a terminal (the source terminal) (S, S') of the first power switching member (4, 4').

3. A power module (2) according to claim 1 or 2, characterised in that the first power switching member (4, 4') is a silicon carbide (SiC) high current metal Oxide Semiconductor Field Effect Transistor (MOSFET) switch (6) or a high current silicon (Si) MOSFET switch (6).

4. A power module (2) according to one of the preceding claims, characterised in that the additional switching member (10, 10', 30) comprises a gate terminal (G') that is electrically connected to a control connector (23).

5. A power module (2) according to one of the preceding claims, characterised in that the additional switching member (10, 10', 30) comprises a source terminal (S') that is electrically connected to a control connector (24).

6. A power module (2) according to claim 5, characterised in that the first power switching member (4, 4') comprises a source terminal (S), wherein a capacitor (Ci) is arranged between the source terminal (S') of the additional switching member (10, 10', 30) and the source terminal (S) of the first power switching member (4, 4').

7. A power module (2) according to one of the preceding claims, characterised in that the first power switching member (4, 4') comprises a MOSFET (6, 6').

8. A power module (2) according to one of the preceding claims, characterised in that the first power switching member (4, 4') comprises an insulated-gate bipolar transistor (IGBT) (8).

9. A power module (2) according to one of the preceding claims, characterised in that the substrate (18) is a direct bonded copper (DBC) substrate.

10. A power module (2) according to one of the preceding claims, characterised in that the additional switching member (10, 10', 30) comprises a signal-type MOSFET (8).

10. A power module (2) according to one of the preceding claims, characterised in that the additional switching member (10, 10', 30) comprises a 40V or 60V signal-type MOSFET (8).

11. A power module (2) according to one of the preceding claims 2-10, characterised in that a diode (12, 14) is placed across the channel of the first switching member (4, 4'). 12. A power module (2) according to one of the preceding claims 2-11, characterised in that a diode (12, 14) is placed across the signal-type MOSFET (8) of the additional switching member (10,

10', 30).

13. A power module (2) according to one of the preceding claims 2-12, characterised in that the power module (2) comprises two or more power switching members (4, 4') arranged in parallel.

14. A power module (2) according to one of the preceding claims, characterised in that the additional switching member (10, 10',

30) comprises:

- a switch (36) electrically connected to a control connection (23);

- a rectifier (32) arranged to rectify current towards a connector (21) that is electrically connected to the gate terminal (G) of the first power switching member (4, 4') and

- a capacitor (C2) and arranged between the rectifier (32) and the source terminal (S) of the first power switching member (4, 4'), wherein the switch (36) is arranged and configured to electrically connect and disconnect the connection between a first node (38) between the capacitor (C2) and the rectifier (32) and a second node (40) between the switch (36) and the gate terminal (G) of the first power switching member (4, 4').

15. A system comprising a power module (2) according to one of the preceding claims and a control system (16), wherein the control system (16) comprises a plurality of terminals each being electrically connected to a control connector (20, 20', 21, 21', 22,

22', 23, 24) of the power module (2).

Description:
Power Module Comprising an Active Miller Clamp

Field of invention

The present invention relates to a power module having a first power switching member arranged on a substrate, wherein the switching member comprises a gate terminal. More particularly, the present invention relates to a power module that is configured to reduce the gate terminal impedance during the turn-off event.

Prior art

There is an increasing use of high-speed switching devices for power modules applied in automotive, solar, wind and industrial applications. Active Miller clamping is a well-known technique used in the prior art to avoid parasitic dVos/dt (the rate of drain-source voltage change over time) triggered turn-on. The Miller clamping function of the gate driver is, however, mostly implemented in the gate driver integrated circuit (IC). In the prior art is known that a long trace between the gate driver IC and the internal switch inside a power module equipped with an active Miller clamp can be a challenge. This trace has an impedance that limits the function of the Miller clamp significantly. Therefore, it would be desirable to be able to provide a power module that reduces or even eliminates these disadvantages of the prior art.

Summary of the invention

The object of the present invention can be achieved by a power module as defined in claim 1 and by a system as defined in claim 15. Preferred embodiments are defined in the dependent subclaims, explained in the following description and illustrated in the accompanying drawings. The power module according to the invention is a power module comprising a first power switching member arranged on a substrate, wherein the power module comprises a plurality of control connectors, wherein the first power switching member comprises a gate terminal, wherein the power module comprises an additional switching member being configured to reduce the gate terminal impedance during the turn-off event.

Hereby, it is possible to provide a power module, in which the gate terminal impedance during the turn-off event can be reduced. This is an advantage when the stray inductance is too high. It has to be noted that the impedance also depends on other parameters such as the permittivity and geometry of the substrate.

The invention makes it possible to provide a power module, in which only a single positive gate voltage (e.g. +15V/0V) is used instead of the prior art solutions, in which the gate driver applies a bipolar gate voltage (e.g. +15V/-8V). Therefore, the power module enables use of faster switching devices and thus the power module is capable of providing faster switching. Moreover, the power module makes it possible to reduce or even avoid parasitic triggered turn-on hereby protecting the switch members or the whole system.

The first power switching member is arranged on a substrate. In one embodiment, the substrate is a DCB (Direct Copper Bonded) substrate. The DCB substrate may comprise a ceramic material such as aluminium oxide (AI2O3), aluminium nitride (AI N), silicon nitride (S13N4) or beryllium oxide (BeO).

In one embodiment, the substrate is a flexible printed circuit board. In one embodiment, the substrate is a FR-4 PCB comprising a thin layer of copper foil that is laminated to one or both sides of an FR-4 glass epoxy panel.

The control connectors can be made of any suitable conducting material such as copper or aluminum.

The first power switching member comprises a gate terminal, wherein the power module comprises an additional switching member being configured to reduce the gate terminal impedance during the turn-off event.

The first power switching member may comprise any suitable combination of various electronic discrete components including one or more resistors, capacitors, inductors, diodes, transistors.

The additional switching member may be any suitable type of switching member. In one embodiment, the additional switching member is a field-effect transistor (FET). In another embodiment, the additional switching member is a bipolar transistor.

In one embodiment, a first terminal of the additional switching member is electrically connected to the gate terminal of the first power switching member and a second terminal (e.g. a source terminal) of the additional switching member is electrically connected to a terminal first power switching member. The electrical connection may be achieved by means of any conductor and/or electronic discrete component.

In one embodiment, the first terminal may be a drain terminal. In one embodiment, the second terminal may be a source terminal.

In one embodiment, the first power switching member comprises a source terminal and the additional switching member comprises a drain terminal and a source terminal, wherein the drain terminal is electrically connected to the gate terminal of the first power switching member, wherein the source terminal of the additional switching member is electrically connected to the source terminal of the first power switching member. The electrical connection may be achieved by means of any conductor and/or electronic discrete component.

In a preferred embodiment, the first power switching member is a silicon carbide (SiC) high current metal-oxide-semiconductor field- effect transistor (MOSFET) switch or a high current silicon (Si) MOSFET switch. Hereby, only a very low input current is needed to control the load current. By using a MOSFET which is a high frequency, high efficiency switching member, it is possible to provide a fast switching power module.

In one embodiment, the MOSFET is a N-channel MOSFET.

In one embodiment, the MOSFET is a P-FET (P-channel MOSFET).

In one embodiment, the additional switching member comprises a gate terminal that is electrically connected to a control connector. Hereby, it is possible to control the additional switching member through the gate terminal by means of a control system such as a gate driver.

It may be an advantage that the additional switching member comprises a source terminal that is electrically connected to a control connector.

In one embodiment, the first power switching member comprises a source terminal, wherein a capacitor is arranged between the source terminal of the additional switching member and the source terminal of the first power switching member. The use of this capacitor makes it possible to reduce the stray inductance. In one embodiment, the capacitance of the capacitor is in the range 0.1- 10 nF such as InF. In another embodiment, the capacitance of the capacitor is in the range 100 nF-10 mR such as ImR.

In a preferred embodiment, the first power switching member comprises a MOSFET. This MOSFET may be a N-channel MOSFET.

In one embodiment, the first power switching member may comprise a resistor electrically connected to the gate terminal of the MOSFET.

In one embodiment, the drain terminal of the MOSFET is electrically connected to a first control connector, wherein the source terminal of the MOSFET is electrically connected to a second control connector.

In one embodiment, the additional switching member is a MOSFET, wherein the gate terminal for the MOSFET is electrically connected to a control connector, wherein the drain terminal of the MOSFET is electrically connected to another control connector.

In one embodiment a resistor is arranged between the drain terminal of the MOSFET and the distal end of the control connector that is electrically connected to the drain terminal.

In one embodiment, the first power switching member comprises an insulated-gate bipolar transistor (IGBT). Hereby, it is possible to provide a high efficiency and fast switching power module.

In a preferred embodiment, the substrate is a DBC substrate. Hereby, it is possible to provide a substrate having a good thermal conductivity.

In one embodiment, the additional switching member comprises a MOSFET. In a preferred embodiment, the additional switching member comprises a signal-type MOSFET.

In one embodiment, the additional switching member comprises a 40V signal-type MOSFET.

In one embodiment, the additional switching member comprises a 60V signal-type MOSFET.

In one embodiment, the power module comprises two or more power switching members arranged in parallel. This may be an advantage when the power module comprises several circuit sections each comprising both a first switching member and an additional switching member (as shown in and explained with reference to Fig. 1A).

In one embodiment, the additional switching member comprises:

- a switch electrically connected to a control connection;

- a rectifier (e.g. a diode) arranged to rectify current towards a connector that is electrically connected to the gate terminal of the first power switching member and

- a capacitor and arranged between the rectifier and the source terminal of the first power switching member,

wherein the switch is arranged and configured to electrically connect and disconnect the connection between a first node between the capacitor and the rectifier and a second node between the switch and the gate terminal of the first power switching member.

Hereby, it is possible to provide a power module that can be controlled by a control system (e.g. a gate driver) that comprises four terminals.

In one embodiment, the power module is configured to be controlled by a control system (e.g. a gate driver) comprising five terminals.

In a preferred embodiment, the additional switching member is arranged between the distal end of the control connection configured to be electrically connected to the control system (e.g. a gate driver) and the gate-pad of the MOSFET switching member of the first switching member. Hereby, it is possible to reduce the stray inductance between additional switching member (e.g. a signal-type MOSFET) and the first switching member (e.g. a SiC MOSFET). It is an advantage to provide a short distance between additional switching member (e.g. a signal-type MOSFET) and the first switching member (e.g. a SiC MOSFET).

In a preferred embodiment, the additional switching member is arranged between the gate pad of the first power switching member being a MOSFET and an external gate-pin of the power module.

The electrical connections between electronic components may be achieved by means of any suitable conductor e.g. a metal track or metal circuit trace.

The power module according to the invention significantly reduces the impedance (in situation, in which the stray inductance is too high) between the gate driver and gate-pad of the first switching member. The invention further makes it possible to apply only a single positive gate voltage (e.g. +15V/0V) instead of a bipolar gate voltage (e.g. + 15V/-8V) of the gate driver. Additionally, the invention makes it possible to provide a power module that enables faster switching. Since future gate driver ICs offers the possibility to drive external N- MOFETs to reduce the impedance in the gate path, the invention can be implemented

The prior art Miller clamping function of the gate driver is typically implemented in the gate driver IC. However, future gate driver ICs offers the possibility to drive external MOFETs (e.g. N-channel MOSFETs) to reduce the impedance in the gate

path. This may be advantageous and required when applying for fast switching devices such as SiC MOSFETs. This invention offers an effective solution by moving the external MOSFETs inside the power module. This is particularly, advantageous when various switches are arranged in parallel inside the power module.

The MOSFET pulls down the gate during off-state. The off-state condition is monitored by the gate driver and sensing the gate voltage over the clamping terminal. The clamp function is activated as soon as the gate voltage drops below a configurated threshold voltage. This level is configurated on the gate driver.

The system according to the invention comprises a power module according the invention and a control system, wherein the control system comprises a plurality of terminals each being electrically connected to a control connector of the power module.

Description of the Drawings

The invention will become more fully understood from the detailed description given herein below. The accompanying drawings are given by way of illustration only, and thus, they are not limitative of the present invention. In the accompanying drawings:

Fig. 1A shows a circuit diagram of a power module according to the invention; Fig. IB shows a circuit diagram of another power module according to the invention;

Fig. 2A shows a circuit diagram of a power module according to the invention;

Fig. 2B shows a circuit diagram of another power module according to the invention;

Fig. 3A shows a circuit diagram of a first switching member according to the invention;

Fig. 3B shows a first layout of a power module according to the invention.

Fig. 4A shows a second layout of a power module according to the invention.

Fig. 4B shows a third layout of a power module according to the invention and

Fig. 5 shows a graph showing the voltage as function of time for components of a power module according to the invention.

Detailed description of the invention

Referring now in detail to the drawings for the purpose of illustrating preferred embodiments of the present invention, a power module 2 of the present invention is illustrated in Fig. 1A.

Fig. 1A is a circuit diagram of a power module 2 according to the invention. The power module 2 comprises a first circuit section and a second circuit section. The first circuit section comprises a first power switching member 4. The first power switching member 4 comprises a MOSFET 6 and a Zener diode 12 placed across the channel of the MOSFET 6. The drain terminal D of the MOSFET 6 is electrically connected to a terminal 34. In applications in which the power module 2 is used in half-bridge topologies, the terminal 34 would be an alternating current AC terminal. The source terminal S of the MOSFET 6 is electrically connected to a terminal 38 and to a control connector 22 that is electrically connected to a first gate driver 16 of a control system assembly. The gate terminal G of the MOSFET 6 is electrically connected to a control connector 20 that is electrically connected to the first gate driver 16.

An additional switching member 10 comprising a signal-type MOSFET 6" is arranged between the distal end of the control connection 21 and the gate-pad of the MOSFET 6, wherein the control connection 21 is electrically connected to the gate driver 16. Hereby, it is possible to reduce the stray inductance between the signal-type MOSFET 6" and the first switching member 4. The MOSFET 6" of the additional switching member 10 comprises a drain terminal D" that is electrically connected to the control connector 20.

The MOSFET 6" comprises a source terminal S" that is electrically connected to the terminal 38. The MOSFET 6" comprises a gate terminal G" is electrically connected to a control connector 21 being electrically connected to the first gate driver 16. A diode 12 is placed across the channel of the MOSFET 6". The diode 12 may be a silicon diode.

The second circuit section comprises a first power switching member 4' comprising a MOSFET 6"' and a diode 12 placed across the channel of the MOSFET 6"'. The diode 12 may be a silicon diode.

The MOSFET 6"' comprises a drain terminal D'" that is electrically connected to a terminal 40. The MOSFET 6"' has a source terminal S that is electrically connected to the terminal 34 and to a control connector 22" that is electrically connected to a second gate driver 16' of a control system assembly. The MOSFET 6"' comprises a gate terminal G being electrically connected to a control connector 20' that is electrically connected to the second gate driver 16'. The second circuit section comprises an additional switching member 10' having a signal-type MOSFET 6' that is arranged between the distal end of the control connection 21' and the gate-pad of the MOSFET 6'". Accordingly, the MOSFET 6' is arranged between the control connector 20' and the source terminal S'" of the first power switching member 4' of the second circuit section. The control connection 21' is electrically connected to the gate driver 16'. The signal-type MOSFET 6' makes it possible to reduce the stray inductance between the signal-type MOSFET 6' and the first switching member 4'.

The MOSFET 6' of the additional switching member 10' comprises a drain terminal D' being electrically connected to the control connector 20'. The MOSFET 6' also comprises a source terminal S' being electrically connected to the output 34 and the source terminal S'" of the first power switching member 4'. The MOSFET 6' comprises a gate terminal G' that is electrically connected to a control connector 21' being electrically connected to the second gate driver 16'. A diode 12 is placed across the channel of the MOSFET 6'. The diode 12 may be arranged in parallel. The body diode 12 of the MOSFET is a part of the silicon. It can be seen that the power module 2 is arranged on a substrate 18.

Fig. IB illustrates a circuit diagram of another power module 2 according to the invention. The power module 2 comprises a first power switching member 4 arranged on a substrate 18 and comprising a MOSFET 6. A silicon diode 14 is placed across the channel of the MOSFET 6. An internal gate resistor R.2 of the silicon is symbolised in front of the gate terminal G. The internal gate resistor R2 is sketched as being electrically connected to a control connector 20 that is electrically connected to a gate driver 16.

The drain terminal D of the MOSFET 6 is electrically connected to a (negative or zero voltage direct current) terminal 26 and to a control connector 20 being electrically connected to the gate driver 16. The source terminal S of the MOSFET 6 is electrically connected to a (positive or zero voltage direct current) terminal 25 and to a control connector 22 that is electrically connected to the gate driver 16. The gate terminal G is electrically connected to the control connector 20.

The power module 2 comprises an additional switching member 10 arranged on the substrate 18. The additional switching member 10 comprises a MOSFET, wherein a diode 12 placed across the channel of the MOSFET. The gate terminal G' of the MOSFET is electrically connected to the gate driver 16 by means of a control connector 23. The source terminal S' of the MOSFET is electrically connected to source terminal S of the MOSFET of the first power switching member 4 by means of a connector 28. The drain terminal D' of the MOSFET is electrically connected to the gate driver 16 by means of the control connector 21. A resistor Ri is arranged between the distal end of the control connector 21 and the drain terminal D'.

The MOSFET 6 in the first switching member 4 may be replaced with an IGBT as shown in Fig. 3.

Fig. 2A illustrates a circuit diagram of a power module 2 according to the invention. The power module 2 basically corresponds to the one shown in Fig. IB. However, the power module 2 comprises an additional (negative voltage) control connector 24 electrically connected to the gate driver 16. Moreover, a capacitor Ci is arranged between the source S of the first power switching member 4 and the source S' of the additional switching member 10. Accordingly, the power module 2 shown in Fig. 2A can turn off the MOSFET 6 off with a negative voltage by means of the additional control connector 24. This may be required, when the power module 2 is used in very high switching devices or normal high-power SiC power modules. If the MOSFET 6 is a P-FET, only a positive voltage is needed.

The capacitor Ci may have a capacity within the range 0.1nF-l^F.

In one embodiment, the capacity of the capacitor Ci is 1 nF. In another embodiment, the capacitance of the capacitor is in the range 100 nF-10 mR such as ImR.

The MOSFET 6 of the first power switching member 4 may be exchanged by an IGBT like the one shown in Fig. 3A.

The first resistor Ri may have a resistance in the range 0.1-15 W, preferably in the range 0.1-10 W such as 2.5-3.5 W. The preferred value of the first resistor Ri would typically depend on the additional switching member 10. In one embodiment, it is possible to provide an external resistor in front of the first resistor Ri.

The second resistor R2 may have a resistance in the range 0.01-10 W, preferably in the range 0.02-8 W such as 1.-6 W. The resistance of the second resistor R2 will typically be defined by the manufacture of the MOSFET 6.

Fig. 2B illustrates a circuit diagram of another power module 2 according to the invention. The power module 2 comprises a first power switching member 4 corresponding to the one shown in Fig. IB and Fig. 2A. The power module 2, however, comprises an additional switching member 30 that does not comprise a MOSFET. The switching member 30 comprises a rectifier (diode) 32 electrically connected to the control connector 21 and to a first node 37 arranged between the rectifier 32 and a capacitor C2 that is electrically connected to the source terminal S of the first switching member 4 by means of a connector 28.

The switching member 30 comprises a switch 36 electrically connected to a control connector 23, through which the switch 36 can be controlled. The switch 36 is configured to connect and disconnect the connection between the first node 37 and a second node 38 arranged between the two resistors Ri and R.2.

Accordingly, the power module 2 requires four control connectors 20, 21, 22, 23 to be electrically connected to the gate driver 16, wherein the power module shown in Fig. 2A, requires five control connections.

During the start-up phase of the gate driver 16, the capacitor C2 is charged with a negative voltage level (e.g. -4V). Hereafter the gate driver 16 starts to drive the MOSFET 6 of the first power switching member 4 with a positive and negative voltage (e.g. +15V / -4V). This may be done with any desired frequency at any required number of times.

The capacitor C2 will be charged again if the gate driver 16 turns from delivering a positive voltage to delivering a negative voltage. The Miller clamping is edge rate controlled and thus is changed from positive to negative potential by means of a voltage. For an IGBT the voltage may decrease from +15V to -8V, whereas for a SiC the voltage may decrease from +18V to -4V. After a predefined level of the gate voltage (e.g. within a range between 3V and lowest negative voltage level such as -8V for an IGBT and 0V to -4 V for a SiC: range of 0V to -4V) the switch 36 establishes an electric connection between the first node 37 and the second node 39. For a short time period this will reduce the resulting resistance of the first resistor Ri and the second resistor R2 (e.g. 3.3 W + 20 GTIW) to the lower value of the second resistor R2 (e.g. 10-15 W for a SiC).

In additional, the gate voltage between the first resistor Ri and the second resistor R2 will be discharged faster to the negative voltage level. Accordingly, this embodiment can reduce the stray inductance and protect again parasitic turn-on in the power module 2.

Fig. 3A illustrates a circuit diagram of a first power switching member according to the invention. The first switching member is an IGBT 8 comprising a collector terminal C, a gate terminal G and an emitter terminal E. The IGBT 8 is a three terminal, transconductance device that combines an insulated gate N-channel MOSFET 6 and a PNP bipolar transistor 50 connected in a type of Darlington configuration in such a way that the current amplified by the MOSFET 6 is amplified further by the PNP bipolar transistor 50. The use of this configuration enables a higher current gain than each transistor 6, 50 taken separately. The IGBT 8 shown in Fig. 3 may be used as an alternative of the MOSFET of the first switching member shown in Fig. 1A, Fig. IB, Fig. 2A and Fig. 2A.

Fig. 3B illustrates a view of a first layout of a power module 2 according to the invention. The power module 2 comprises a casing 44 and a first main substrate 18 arranged within the casing 44. Three terminals 38, 40, 46 protrudes from the casing 44. The power module 2 comprises a first section comprising a metallised track 42 (e.g. made of copper), in which a first power switching member 4 is arranged. The first power switching member 4 has a gate terminal G that is electrically connected to an additional switching member 10 by means of a connector. The additional switching member 10 is arranged on a substrate 18' being arranged on the top of the metallised track 42 that is arranged on the top of the main substratel8.

The distance between the gate terminal G and the additional switching member 10 is smaller than the dimension of the additional switching member 10. The power module 2 comprises a second section comprising a metallised track 42' (e.g. made of copper), in which a power switching member 4' is arranged. The power switching member 4' comprises a gate terminal G' that is electrically connected to an additional switching member 10' by means of a connector. The additional switching member 10' is arranged on a third substrate 18" arranged on the top of a metallised track 42" arranged on the top of the main substrate 18.

The distance between the gate terminal G' and the additional switching member 10' is smaller than the dimension of the additional switching member 10'.

The first power switching member 4 is electrically connected to a metallised track 42' by means of wire bonds 48. Likewise, the power switching member 4' is electrically connected to the track 42" by means of wire bonds 48. The metallised track 42' is arranged on the top of the first substrate 18.

The uppermost terminal 40 is a positive DC terminal. The lowermost terminal 38 is a negative DC terminal, whereas the lateral terminal 46 is an AC terminal. Fig. 3B illustrates a power module 2 comprising a single main substrate 18 on which there are power tracks 42, 42', 42" and two power switching members 4, 4'. The additional switching members 10, 10' are shown mounted on separate substrates 18', 18", but here the substrates 18', 18" are in turn mounted above the main substrate 18. To reduce the creepage distance between the Miller Clamping circuit and the distal end of the uppermost terminal 40, the separate substrate 18' may be placed on the lateral terminal 46.

The substrates 18', 18" are mounted on top of two of the metal conducting tracks 42, 42", respectively. However, the substrates 18', 18" could alternatively be mounted in other areas such as on top of the separation between two of the metallised conducting tracks 42, 42', 42". It is an advantage of this embodiment, that space can be saved on the original substrate 18 by having this additional switching member mounted above 10, 10'.

In one embodiment, the substrate 18', 18" on which the additional switching members 10, 10' is a standard printed circuit board (PCB) or a flexible printed circuit board (FPCB).

In particular, the use of an FPCB, which is less sensitive to heat than a standard PCB, makes the reduction of the power module 2 cheaper and simpler, because it can be mounted without fear of it becoming damaged later on in the production process which requires heat.

Fig. 4A illustrates a view of a second layout of a power module 2 according to the invention. The power module 2 comprises a casing 44 and a first substrate 18 arranged within the casing 44. Three terminals 38, 40, 46 protrudes from the casing 44.

The power module 2 comprises a first section comprising a copper track 42, in which a first power switching member 4 is arranged. The first power switching member 4 comprises a gate terminal G that is electrically connected to an additional switching member 10 by means of a connector.

The additional switching member 10 is arranged on a second substrate 18' separated from the first substrate 18. Alternatively, the additional switching member 10 may be arranged on a second substrate 18', wherein the first substrate 18 and the second substrate 18' are arranged on the top of each other. The distance d between the gate terminal G and the additional switching member 10 is shown. This distance d is smaller than the dimension of the additional switching member 10 and smaller than the dimensions of the gate terminal G. The power module 2 comprises a second section comprising a copper track 42', in which a power switching member 4' is arranged. The power switching member 4' comprises a gate terminal G' being electrically connected to an additional switching member 10' by means of a connector. The additional switching member 10' is arranged on a third substrate 18" that is separated from the first substrate 18. The distance d between the gate terminal G' and the additional switching member 10' is illustrated. This distance d is smaller than the dimension of the additional switching member 10' and smaller than the dimensions of the gate terminal G'.

The first power switching member 4 is electrically connected to the copper track 42' by means of wire bonds 48. Likewise, the power switching member 4' is electrically connected to the track 42" of the terminal 38 by means of wire bonds 48. The uppermost terminal 40 is a positive DC terminal. The lowermost terminal 38 is a negative DC terminal, whereas the lateral terminal 46 is an AC terminal.

Fig. 4B illustrates a view of a third layout of a power module 2 according to the invention. The power module 2 basically corresponds to the one shown in Fig. 4A, however, the power module 2 only comprises a single substrate 18. Accordingly, the three substrates 18, 18', 18" shown in Fig. 4A are provides as a single large substrate 18 in the power module 2 shown in Fig. 4B.

Fig. 5 illustrates four graphs 52, 54, 56, 58 depicted against time T. The graphs 52, 54, 56, 58 relates to the additional switching member 30 shown in Fig. 2B.

Fig. 5 shows a first graph 52 (dotted line) depicting the pulse current I through the switch 36 in the additional switching member 30 shown in Fig. 2B versus time T. Fig. 5 shows a second graph 54 (solid line) depicting the gate voltage U of the MOSFET 6 of the first switching member 4 shown in Fig. 2B as it would have looked if the additional switching member 30 (Miller clamping) was removed.

Fig. 5 shows a third graph 56 (dotted line) depicting the clamp control voltage U applied to control the switch 36 of the additional switching member 30 shown in Fig. 2B.

Fig. 5 shows a fourth graph 58 (dotted line) depicting the gate voltage U of the MOSFET 6 of the first switching member 4 shown in Fig. 2B (having the additional switching member 30).

At the time between 89.5me and 94me the clamp control voltage U is 0 volt (V). At the time 94.2me the clamp control voltage U is raised to 3 V. Accordingly, at the time 94.2me the pulse current I through the switch 36 in the additional switching member 30 shown in Fig. 2B drops to approximately -90 ampere (A) and hereafter raises very fast to the initial 0A level. The graph 56 shows that, at the time 94.2me the gate voltage U of the MOSFET 6 of the first switching member 4 shown in Fig. 2B drops almost instantaneously to -8V, whereas the graph 54 depicting the gate voltage U of the MOSFET 6 without the additional switching member 30 is exponentially decreasing from the time 94.2m5.

Fig. 5 illustrates that the setup shown in Fig. 2B, is an effective active Miller clamp. Accordingly, a power module having such active Miller clamp enables a faster switching frequency. List of reference numerals

2 Power module

4, 4' Power switching member

6, 6' Metal Oxide Semiconductor Field Effect Transistor (MOSFET) 8 Insulated-gate bipolar transistor (IGBT)

10, 10' Signal-type MOSFET

12 Diode

14 Silicon diode

16 Control system (e.g. gate driver)

18, 18' Substrate

18" Substrate

20, 21 Control connector

22, 23 Control connector

24 Control connector

25, 26 Terminal

28 Connector

30 Switching member

32 Rectifier

34 Terminal

36 Switch

37, 39 Node

38, 40 Terminal

42, 42' Track (e.g. copper)

42" Track (e.g. copper)

44 Casing

46 AC terminal

48 Wire bonds

50 Transistor

52, 54 Graph

56, 58 Graph

d, d' Distance D, D' Drain terminal D", D' Drain terminal G, G' Gate terminal G", G' Gate terminal S, S' Source terminal

S", S' Source terminal Ri, 2 Resistor

Ci, C2 Capacitor

T Time

I Current

u Voltage

E Emitter terminal

C Collector terminal