Isolated circuit breakers with reduced common-source inductance

Abstract

Device comprising; a separate power switching device (35) having a gate signal path (44) via a gate pin (40) and a power signal path (43) via first (41) and second power pins (42), wherein the gate signal path (44) and the power signal path (43) have a first mutual inductance; and a printed circuit board device (51) providing a gate circuit (50) disposed adjacent to the power signal path (43), wherein the gate circuit (50) and the power switching path have a second mutual inductance that substantially cancels the first mutual inductance, wherein the first mutual inductance has a positive coupling and wherein the second mutual inductance has a negative coupling.

Description

GENERAL STATE OF THE ART

[0001] The present invention relates generally to reducing the effects of common-source inductance in separate solid-state power switching devices, and more particularly to inverter drive systems for electrified vehicles that utilize separate power switching devices with fast switching times and low losses.

[0002] Various types of semiconductor power switching devices have been introduced for high-voltage, high-power electronic switching applications, such as power MOSFETs and insulated-gate bipolar transistors (IGBTs). Due to semiconductor die sizes and heat dissipation requirements, these devices are typically contained in separate packages for mounting one or more switching devices, such as a "transistor package" (TO package). The packages of the separate power switching devices are typically mounted on a printed circuit board (PCB), which also includes additional electronics related to the switching application.

[0003] Electric vehicles such as hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs) use these power switching devices to construct inverters for electric machines to provide traction torque and regenerative braking torque. A typical electric drive system includes a DC power source (such as a battery pack or fuel cell) coupled through power contactors to a variable voltage converter (VVC) to regulate a main bus voltage via a main tie capacitor. A first inverter is connected between the main bus and a traction motor to propel the vehicle. A second inverter can be connected between the main bus and a generator to regenerate energy during braking to recharge the battery via the VVC.

[0004] The inverters contain power switching devices (typically IGBTs) connected in a bridge configuration. An electronic controller switches the switches on and off via gate drive circuits to convert a DC voltage from the bus to an AC voltage applied to the motor, or to convert an AC voltage from the generator to a DC voltage on the bus. In each case, the inverters are controlled in response to various perceived conditions by varying the frequency and duty cycle at which the power switching devices are switched on and off.

[0005] The motor pulse width inverter modulates the DC terminal voltage to provide an approximate sinusoidal current output to drive the motor at a desired speed and torque. PWM control signals applied to the IGBT gates turn them on and off as required, so that the resulting current corresponds to a desired current. The IGBTs and their reverse recovery diodes have associated switching losses that must be minimized to limit efficiency loss and waste heat generation.

[0006] Common-source inductance refers to an inductance shared by the main power circuit (i.e., the device's drain-source or collector-emitter power output) and the gate drive circuit (i.e., gate-source or gate-emitter) in a power switching device. The common-source inductance carries both the device output current (e.g., drain-source current) and the gate charge / discharge current. The voltage induced across the common-source inductance modifies the gate voltage in a way that limits turn-on / off times and increases switching losses. In a typical switching module, several factors contribute to the common-source inductance, which appears as a parasitic inductance associated with device packaging and printed circuit board (PCB) traces.The relative placement of current paths and the use of various structures to isolate and / or block inductive coupling have been used to reduce the amount of parasitic inductance generated.

[0007] US 8 519 561 B2 describes a power module having an upper branch circuit unit and a lower branch circuit unit, both having a power semiconductor element, an insulating substrate on one surface of which the units are mounted, a metal base bonded to the other surface of the substrate opposite the surface on which the units are mounted, a first connecting conductor for supplying a high potential to the upper unit from the outside, a second connecting conductor for supplying a low potential to the lower unit from the outside, an insulating film interposed between the conductors, and a resin casing arranged on the metal base to support the conductors, the conductors being flat conductors laminated with the film therebetween.The foil extends from one end of the laminated structure to ensure the creepage distance between the conductors. The housing is provided with a recess for accommodating the laminated structure. Further relevant prior art relating to the background of the invention is provided by US Pat. No. 7,589,400 B2.

[0008] Despite known practices, the common-source inductance for separate power switching devices introduced through packaging (e.g., TO-247 and TO-220) can still be as high as 10 nH. As new generations of power switching devices (e.g., CoolMOS, SiC, and GaN devices) become increasingly faster, the common-source inductance dramatically limits switching speed and increases switching losses.

[0009] The object is to counteract a voltage induced across the common-source inductance. This object is achieved by a device according to claim 1 and an inverter according to claim 11. SUMMARY OF THE INVENTION

[0010] In one aspect of the invention, an apparatus enables switching of a separate power switching device. The power switching device has a gate signal path via a gate pin and a power signal path via first and second power pins, wherein the gate signal path and the power signal path have a first mutual inductance. A printed circuit board device provides a gate circuit disposed adjacent to the power signal path, wherein the gate circuit and the power switching path have a second mutual inductance that substantially cancels the first mutual inductance. The resulting reduction in common-source inductance prevents the reductions in switching speed and the increased switching losses otherwise introduced by the common-source inductance. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic diagram showing a phase branch of an inverter using a pair of IGBTs. Fig. Figure 2 is a perspective view of a power switching device in a TO package, attached to a printed circuit board by means of a conventional socket. Fig. 3 is a plan view showing a magnetic flux generated by a drain-source current in a conventional power switching device. Fig. 4 is a plan view showing a magnetic flux generated by a gate-source current in a conventional power switching device. Fig. Figure 5 is a schematic diagram showing an additional mutual inductance with a negative coupling that cancels the inherent common-source inductance of the switching device. Fig. 6 is a diagram illustrating rerouting a gate signal outside the power switching device to provide negative coupling according to the present invention. Fig. Figure 7 is a diagram showing overlapping magnetic flux patterns corresponding to Fig. 6 shows. Fig. Figure 8 shows an auxiliary base according to the invention which attaches a power switching device to a printed circuit board. Fig. 9 is a plan view of the auxiliary base of Fig. 8. Fig. 10 is a front view of the auxiliary base of Fig. 8. Fig. 11 is a perspective view showing a layout of embedded conductors in the auxiliary base of Fig. 8 shows. Fig. 12 is a plan view showing circuit board traces for an embodiment of a gate circuit according to the invention. Fig. 13 is a plan view showing circuit board traces for another embodiment of a gate circuit according to the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0011] Devices 11 and 12 have gate drivers 20 and 22 with corresponding gate coupling resistors 21 and 23 for driving corresponding gate terminals 24 and 25. The power output terminals 26 and 27 of device 11 and the power output terminals 28 and 29 of device 12 are collector-emitter terminals when using IGBTs, and drain-source terminals when using, for example, a power MOSFET. The inherent parasitic common-source inductance (i.e., the mutual inductance coupling the gate current to the main device output current) is represented by inductors 30 and 31. Many factors can contribute to the common-source inductance, both internal and external to devices 11 and 12. In particular, the mutual inductance occurring within devices 11 and 12 has become an increasingly significant disadvantage in the prior art.

[0012] The power switching devices of the present invention can often be mounted on a printed circuit board (PCB) using a socket, such as in Fig. 2. A PCB 32 with traces 33 has a socket 34 soldered to the corresponding traces and configured to receive a separate power switching device 35. Device 35 is shown with a transistor package (TO) type of packaging, with output pins extending in a row from one edge of the device. This type of packaging, after placement within socket 34, allows for device attachment to a heat sink, as is known in the art. Traces 33 may include enlarged traces 36 for carrying an output power signal and a trace 37 for carrying a gate signal.

[0013] Fig. Figure 3 shows the device 35 with a typical arrangement of terminal pins, including a gate pin 40 at one end, a drain (or collector) pin 41, and a source (or emitter) pin 42. When the device 35 is turned on, an output current flows between the power output pins 41 and 42, providing a power signal path 43 across pins 41 and 42 and across a main body of the device 35 between pins 41 and 42. The resulting magnetic flux generated by the power signal is represented by X inside the power circuit of the power signal path 43 representing flux directed into the side and O outside the power circuit representing magnetic flux directed out of the side.

[0014] Fig. 4 represents a gate current flowing along a gate signal path 44 across pins 40 and 42 and within the body of device 35 between pins 40 and 42. The magnetic flux of the gate path is primarily coincident with the magnetic flux from the power signal path (i.e., positively coupled). Thus, a mutual inductance exists with a net positive coupling.

[0015] Due to the arrangement of the structures (including, but not limited to, the pin arrangement) associated with the power switching device, the internally generated common-source inductance of the separate power switching devices is unavoidable in all currently available separately packaged power switching devices. To avoid the reduced performance associated with this internal common-source inductance, the present invention cancels the positive coupling inherent in the device by adding an external mutual inductance with an opposite coupling. As in Fig. 5, inductors 45 and 46 represent the inherent common-source inductances associated with the device packaging. The present invention adds mutual inductors 47 and 48 external to, but proximate to, devices 11 and 12, respectively, with the added inductors being negatively coupled (i.e., having opposite polarity) with respect to the inherent mutual inductance. Since the power switching device typically has positive coupling of the gate signal path to the power signal path (i.e., the mutual voltage has the same polarity as the mutual current), the added mutual inductance typically provides negative coupling, such that the internal mutual inductance is substantially or completely canceled.Specifically, a spatial wiring pattern of the gate signal leading into the separated device is designed as a circuit that interacts with the power signal path in a manner that results in substantially no net coupling between the gate signal path and the power signal path. As used herein, substantially canceled means that the effects of mutual inductance inherent in the separated device are reduced by more than about 50%.

[0016] Fig. 6 shows a gate circuit 50 provided by a printed circuit board device 51 disposed adjacent to the separate power switching device 35 in proximity to its power signal path (e.g., power pins 41 and 42). The printed circuit board device 51 may include an auxiliary socket for attaching the device 35 to a printed circuit board (PCB) or may, for example, include a special arrangement of conductive traces on a PCB. To substantially cancel a first mutual inductance of the power signal path (e.g., positive coupling), the gate circuit 50 is configured to provide one or more winding turns 52 with a winding direction opposite to a circuit formed by the gate signal path within the device 35 (between the gate and source pins) that overlaps the power signal path.A magnetic flux in the winding turns 52 is shown as being opposite to the magnetic flux generated internally in the device 35 and opposite to the magnetic flux generated by the power signal path.

[0017] To provide the desired winding direction opposite to the winding direction of the inherent, non-variable portion of the gate signal path within device 35, gate circuit 50 may include a gate terminal leg 53 spanning device pins 40-42 and a source terminal leg 55 defining a winding turn spanning device power pins 41 and 42. In a preferred embodiment, when printed circuit board device 51 consists of an auxiliary header, a separate gate connection 54, separate from and laterally offset from gate pin 40, and a Kelvin-source connection 56, separate from and laterally offset from source pin 42, may extend from the auxiliary header to enable the desired placement of winding loop 50.The use of a Kelvin source is a well-known technique whereby the contributing gate current appearing in the device output is separated from the main power output current flowing between the drain and source terminals of the device.

[0018] Fig. Figure 7 shows magnetic flux associated with the isolated power switching device in the present invention. Thus, a first magnetic flux region 57 is created by the device's output current along the power signal path. A magnetic flux region 58, created by the internal, inherent gate signal path within the device, has a positive coupling with region 57. The gate circuit creates a negatively coupled magnetic flux region 59. By configuring the gate circuit to create magnetic flux with equal and opposite coupling, the invention achieves no net mutual inductance between the gate current and the power output current, thereby speeding up device switching and reducing switching losses.

[0019] Fig. Figure 8 shows a preferred embodiment wherein the printed circuit board apparatus includes an auxiliary socket 60 capable of receiving device 35 and adapted to be attached to a printed circuit board 65 via a plurality of socket pins 61-64. The auxiliary socket 60 has an outer profile adapted to contain any desired three-dimensional gate circuitry. In particular, the profile may, for example, be offset from one side of the device 35. Pin 61 may be a gate pin, pin 62 may be a Kelvin source pin, pin 63 may be an output source pin, and pin 64 may be an output drain pin. The auxiliary socket 60 may have an orientation that places the device 35 either vertically or horizontally with respect to the plane of the PCB 65.

[0020] Fig. Figure 9 shows a top view of auxiliary socket 60, including a gate receptacle 70, a drain receptacle 71, and a source receptacle 72 for receiving a gate pin, drain pin, and source pin, respectively, of the isolated power switching device. Auxiliary socket 60 has embedded conductors for forming the gate circuit. The conductors include a first embedded conductor 73 connected at one end to gate receptacle 70 and at the other end to a gate pin connection 61a. A second embedded conductor 74 is connected between source socket 72 and a Kelvin-source pin connection 62a.

[0021] The layout of the embedded conductors is further shown in the front view of Fig. 10. Conductor 73 extends from pin 61 for approximately 1 1 / 2 turns to a gate-to-socket connection 70a, and conductor 74 extends from pin 62 for approximately 1 / 2 turns to a Kelvin-to-source connection 72a, such that the winding direction of the co-formed winding turns creates a negative coupling with the power signal path. Fig. Figure 11 is a perspective view showing the three-dimensional arrangement of the embedded conductors 73 and 74 in greater detail. Preferably, the auxiliary header 60 has a main plastic body that may be molded over the embedded conductors, or may include internal passages into which the conductors are inserted. Preferably, the auxiliary gate pin 61 is laterally offset from the gate pin of the power switching device to allow the gate circuit to traverse the power signal path as shown. With the auxiliary header 60 attached to the PCB 65, pins 61 and 62 are connected together with a gate driver (not shown), while pins 63 and 64 are connected to the input and output rails of the inverter.

[0022] In an alternative embodiment, the printed circuit board device consists of a printed circuit board carrying conductive traces adapted to configure a portion of the power signal path and the gate circuit with a layout that generates the negatively coupled mutual inductance for canceling the first mutual inductance at the board itself, regardless of whether a socket is used for the power switching device.

[0023] As in Fig. As shown in Figure 12, a PCB substrate 80 (preferably a multilayer substrate) supports the power switching device such that the device pins are connected to a gate pad 81, drain pad 82, and source pad 83. Power traces 84 and 85 are arranged on the substrate 80 in series with the drain and source pads 82 and 83, forming a portion of the power signal path. A gate trace 86 extends from the gate pad 81 to a gate driver circuit 88, which consists of an integrated circuit that is also attached to the PCB substrate 80. A Kelvin source trace 87 is attached to substrate 80 and connects source pad 83 to a corresponding terminal on gate driver circuit 88. Gate trace 86 and Kelvin source trace 87 intersect (and are isolated from) power sources 84 and 85 to form gate circuit 90 to provide the negatively coupled mutual inductance to cancel the common source inductance inherent in the switching device.The loop size and number of turns for traces 86 and 87 are adjusted to provide a desired negative coupling with a magnitude selected to substantially cancel the first mutual inductance seen at the device pins connected to pads 81-83. Further, the circuit board is comprised of multiple layers, including conductive and insulating layers, with traces 86 and 87 defining a desired plurality of winding loops using the plurality of multiple layers.

[0024] In another example, which is Fig. As shown in Figure 13, a substrate 91 supports a gate circuit 93 with additional turns. A gate trace 92 defines multiple turns, with a via 94 interconnecting different layers to connect different portions of the multiple turns.

Claims

[1] Device comprising; a separate power switching device (35) with a gate signal path (44) via a gate pin (40) and a power signal path (43) via first (41) and second power pins (42), wherein the gate signal path (44) and the power signal path (43) have a first mutual inductance; and a printed circuit board device (51) providing a gate circuit (50) arranged next to the power signal path (43), wherein the gate circuit (50) and the power signal path have a second mutual inductance which essentially cancels out the first mutual inductance, where the first mutual inductance has a positive coupling and where the second mutual inductance has a negative coupling. [2] Device according to claim 1, wherein the power switching device (35) comprises a bipolar transistor with an insulated gate in a power transistor housing. [3] Device according to claim 1, wherein the gate circuit (50) defines a plurality of winding turns (52). [4] Device according to claim 1, wherein the printed circuit board device (51) consists of an auxiliary base (60) which accommodates the power switching device (35) and is adapted to be attached to a printed circuit board (65). [5] Device according to claim 4, wherein the auxiliary base (60) consists of a plastic body with a plurality of embedded conductors forming a gate circuit (50). [6] Device according to claim 5, wherein the auxiliary base (60) comprises an auxiliary gate pin (61) extending from the plastic body and offset laterally from the gate pin (61) of the power switching device gate pin (40). [7] Device according to claim 6, wherein the auxiliary base (60) comprises a Kelvin source pin extending from the plastic body and connected to one of the power pins (41, 42), and wherein the Kelvin source pin and the auxiliary gate pin (61) are adapted to be further connected to a gate driver. [8] Device according to claim 7, wherein a first section of the gate circuit (50) is connected between the power switching device gate pin (40) and the auxiliary gate pin (61), and wherein a second section of the gate circuit (50) is connected between the one power pin (41, 42) and the Kelvin source pin. [9] Device according to claim 1, wherein the printed circuit board device (51) consists of a printed circuit board (65) with a power switching device (35) attached thereto, wherein the device further comprises a gate driver circuit (88) which is attached to the printed circuit board (65), and wherein the printed circuit board (65) consists of the following: a substrate (80); a pair of power pathways (84, 85) arranged in series with the power signal path (43) on the substrate (80); a gate track (86) that connects the power switching device gate pin (40) to the gate driver circuit (88); and a Kelvin source track (87) that connects one of the power pins to the gate driver circuit (88); wherein the gate track (86) and the Kelvin source track (87) cross the power tracks (85, 85) to form the gate circuit (50) which has the second mutual inductance. [10] Device according to claim 9, wherein the printed circuit board (65) consists of multiple layers, and wherein the gate track (86) and the Kelvin source track (87) in cooperation define a plurality of winding turns (52) using a plurality of multiple layers. [11] Inverter for driving a traction motor of an electric vehicle, comprising: a plurality of separate semiconductor power switching devices connected together in a bridge configuration to convert a DC voltage input into an AC voltage output for driving the traction motor, each power switching device having a corresponding gate signal path via a corresponding gate pin and a corresponding power signal path via corresponding first and second power pins, the corresponding gate signal path and the corresponding power signal path having a corresponding first mutual inductance; and a printed circuit board device providing a plurality of corresponding gate circuits, each arranged alongside a corresponding power signal path, wherein the corresponding gate circuit and the corresponding power signal path have a corresponding second mutual inductance that substantially cancels out the corresponding first mutual inductance, and wherein each corresponding first mutual inductance has a positive coupling and wherein each corresponding second mutual inductance has a negative coupling. [12] Inverter according to claim 11, wherein the printed circuit board device consists of a plurality of auxiliary sockets, each accommodating a corresponding power switching device and adapted to be attached to a printed circuit board, wherein each auxiliary socket consists of a plastic body with a plurality of embedded conductors forming the corresponding gate circuit, and wherein each auxiliary socket comprises an auxiliary gate pin extending from the plastic body and offset laterally from the gate pin of the corresponding power switching device gate pin. [13] Inverter according to claim 11, wherein the printed circuit board device consists of a printed circuit board with power switching devices mounted thereon, wherein the inverter further comprises a plurality of gate driver circuits mounted on the printed circuit board, and wherein the printed circuit board consists of the following: a substrate; a corresponding pair of power pathways arranged in series with each corresponding power signal path on the substrate; a corresponding gate track that connects each corresponding power switching device gate pin to the corresponding gate driver circuit; and a corresponding Kelvin source track that connects one of the corresponding power pins to the corresponding gate driver circuit; wherein each corresponding gate track and corresponding Kelvin gate track crosses the corresponding power tracks to form each corresponding gate circuit which has the corresponding second mutual inductance.

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