Dual-gate field-effect transistor and switching member comprising such a field-effect transistor

Abstract

The present invention relates to a field-effect transistor (100) with a junction and a lateral structure, comprising: - a support layer (10) of a first conductivity type; - a semiconductor layer (14) of a second conductivity type forming a channel; - a first electrode (e1) able to form a source or a drain; - a second electrode (e2) able to form a source or a drain; - a doped region (18) in contact with a gate connection terminal (g1) located between the first and second electrodes (e1, e2), the field-effect transistor (100) further comprising an additional doped region (20) in contact with another gate connection terminal (g2) located between the gate connection terminal (g1) and the second electrode (e2).

Description

[0001] Title of the invention: Double-gate field-effect transistor and cut-off device comprising such a field-effect transistor

[0002] The present invention relates to the field of power electronics, and more specifically concerns a power transistor finding a particularly advantageous application in the automotive field.

[0003] As shown in Figure 1, electric or hybrid electric vehicles include a high-voltage battery 30 to power a generally three-phase electric motor, via an inverter. This high-voltage battery 30 has a maximum no-load voltage of several hundred volts, for example 400V (volts) or 800V, hence its name "high voltage" as opposed to the maximum no-load voltage of a service battery of a conventional vehicle, this voltage being of the order of 14V.

[0004] The high-voltage battery 30 is usually connected to a high-voltage network 300 of the vehicle, to which the inverter is connected, via a first contactor 32 and a second contactor 34. However, the high-voltage network 300 comprises at least one capacitor 28 which must be pre-charged before closing the first and second contactors 32, 34 together, to avoid a current draw which would damage the high-voltage components of the vehicle.

[0005] The precharging of the capacitor 28 is carried out by a precharging circuit 50 comprising a current-limiting resistor 54 connected in series with a precharging contactor 52, this precharging circuit 50 being connected in parallel with the first contactor 32 connecting the high-voltage battery 30 to the high-voltage network 300. Thus, before closing the first contactor 32, the second contactor 34 and the precharging contactor 52 are first closed, then the precharging contactor 52 is opened and the first contactor 32 is closed.

[0006] In the event of a fault on the high-voltage network 300, the first and second contactors 32, 34 must be capable of opening while carrying a high current. In addition, a fuse 36 ensures a definitive disconnection between the high-voltage battery 30 and the high-voltage network 300 in the event of a short circuit. This system for connecting the high-voltage battery 30 to the high-voltage network 300 using contactors is sometimes replaced by electronic disconnection components (or SSR for "Solid State Relay"). These electronic disconnection components make it possible to dispense with a pre-charging circuit, by themselves ensuring a limitation of the inrush current by a linear control of these disconnection components.

[0007] In addition, the electronic cut-off components are theoretically capable of performing an unlimited number of power cuts between the high-voltage battery 30 and the high-voltage network 300, even when they are carrying a high current. This is not the case for contactors, whose contacts deteriorate during power cuts and end up sticking. They must therefore be systematically changed when such an event occurs, for example during a crash causing a short circuit of the high-voltage battery 30. However, since the contactors are often integrated with the high-voltage battery 30 in a casing called a "battery pack", this change requires removal of the casing and therefore a significant maintenance cost.

[0008] Finally, the electronic cut-off components provide a fault current limitation function, typically during a short circuit, this function allowing all the high-voltage components of the vehicle not to have to temporarily experience a very high fault current supplied by the high-voltage battery 30. This function is implemented by linear control of these components, and makes it possible to eliminate fuse 36 in the vehicle.

[0009] However, these electronic cut-off components have a higher cost than the connection system of Figure 1, based on contactors, in particular because several MOSFET transistors (from the English "metal-oxide-semiconductor field-effect transistor") are required per cut-off component to ensure all these functions, these transistors not being bidirectional in voltage. The main failure mechanism of these components, especially when they are made of silicon carbide, is the degradation of their gate oxides. Although the failure rate linked to this mode is acceptable for applications such as an inverter or a charger, its elimination by a technology without gate oxide would make it possible to cover safety applications without having to add dedicated elements such as fuses or pyrotechnic systems.

[0010] The present invention aims to remedy at least in part the aforementioned drawbacks by providing in particular a field effect transistor, a cut-off member comprising such a field effect transistor and a method for managing the supply of energy in a high voltage network of a vehicle, which make it possible to replace the mechanical cut-off of the battery contactors in a vehicle, by a reliable electronic cut-off using the cut-off member, the latter not needing to be replaced each time the circuit connecting the high voltage battery of the vehicle to the high voltage network of the vehicle is opened under current.

[0011] To this end, the invention proposes a junction field effect transistor with lateral structure, comprising:

[0012] - at least one support layer of a first type of conductivity,

[0013] - at least one semiconductor layer of a second type of conductivity superimposed on the support layer and capable of forming a channel between a source and a drain,

[0014] - a first electrode implanted on the semiconductor layer and capable of forming the source or the drain,

[0015] - a second electrode implanted on the semiconductor layer and capable of forming the drain or the source,

[0016] - a zone doped according to the first type of conductivity in contact on the one hand with the semiconductor layer and on the other hand with a gate connection terminal located between the first and second electrodes and electrically insulated from the first and second electrodes, the field effect transistor being characterized in that it further comprises an additional zone doped according to the first type of conductivity, in contact with on the one hand the semiconductor layer and on the other hand with another gate connection terminal located between the gate connection terminal and the second electrode, and electrically insulated from the gate connection terminal and the second electrode.

[0017] By "superimposed on the support layer" is meant that the semiconductor layer is supported by the support layer, possibly by means of other more or less doped semiconductor layers of the first or second type of conductivity.

[0018] In particular, preferably, the support layer is heavily doped, and a semiconductor layer of the first conductivity type, less doped than the support layer and produced for example by epitaxy, is intercalated between the support layer and the semiconductor layer of the second conductivity type.

[0019] In addition, the first and second electrodes are implanted on the semiconductor layer of the second conductivity type via heavily doped areas according to the second conductivity type, these heavily doped areas forming part of the source or drain formed by one or other of the first or second electrodes. The doped areas according to the first conductivity type in contact with the gate connection terminals are also preferably heavily doped and each make it possible to form, with one of the gate connection terminals, a gate of the field effect transistor according to the invention.

[0020] In addition, a first type of P-type conductivity is preferably used, i.e. the type using a deficit of electrons in the material to conduct them, and a second type of N-type conductivity, i.e. the type using a surplus of electrons in the material to conduct them. This material is preferably silicon carbide (SiC), for example with a hexagonal Wurtzite 4H crystal structure, which makes the transistor more efficient due to the high energy of its band gap. These choices make it possible to obtain a field effect transistor according to the invention that is inexpensive and efficient, i.e. supporting up to 250V7pm (volts per micrometer). Alternatively, the material used is gallium nitride, or diamond, which is much more expensive but very efficient (supporting up to 1000V / pm).By virtue of the invention, the field effect transistor according to the invention forms a single component with two gates, which makes it bipolar in the sense that it is bidirectional in current and voltage and can in particular cut off the current that it passes through the field effect transistor in one direction or the other. When the current passes through the field effect transistor according to the invention in one direction, a control voltage is applied between one of the gate connection terminals and that of the first or second electrodes used as a source, and when the current passes through the field effect transistor according to the invention in the other direction, a control voltage is applied between the other of the gate connection terminals and the other of the first or second electrodes which will then in turn be used as a source.A control voltage is applied between the first or second electrode used as a source and the one of the gate connection terminals closest to this electrode. Compared to a structure with two MOSFET transistors in series to achieve bidirectional cutoff, the current in the field effect transistor according to the invention therefore only flows through the resistance of a single channel instead of flowing through both channels of the two MOSFET transistors. Thus, the dissipation during operation of the field effect transistor according to the invention is almost half that of the structure with two MOSFET transistors.

[0021] Furthermore, thanks to the invention, a transistor is formed that is not very prone to failures because it does not have a gate oxide. Indeed, the field effect transistor according to the invention comprises an insulating layer, for example made of silicon dioxide, making it possible to electrically isolate the electrodes and the gate connection terminals from each other, but this insulating layer does not function as a gate oxide and is therefore not subject to the same constraints. Thanks to this, the field effect transistor according to the invention has a failure rate (or "Failure In Time Rate" of 10 9 / MTBF where MTBF is the average time between two failures (also called “Mean Time Between Failure”) between 10' 9 and 10 11 which complies with the safety requirements for the high-voltage network of an electric or hybrid vehicle. This failure rate is also much lower than that of an electromechanical structure with a fuse.

[0022] It should be noted that, given its lateral structure, the field effect transistor according to the invention has a lower current density than an equivalent vertical MOSFET transistor. However, given the energy dissipation peaks that the field effect transistor according to the invention must withstand during precharging phases of a high-voltage battery in a vehicle, or during opening under current, this lateral structure offers, compared to a field effect transistor with a vertical structure, a larger contact surface between the support layer and a cooler and therefore improves the heat exchange of the transistor according to the invention with this cooler.

[0023] In addition, this lateral structure facilitates the manufacturing process of the field effect transistor according to the invention, which can use etching, deposition or epitaxy steps on its upper face only. Finally, due to its lateral structure and its absence of gate oxide, the field effect transistor according to the invention allows greater tolerance to crystal defects, and therefore a more favorable manufacturing waste rate which does not penalize the cost of this type of component compared to a smaller vertical MOSFET transistor with a higher current density. The invention also relates to a cut-off device comprising a field effect transistor according to the invention, characterized in that it further comprises at least one enhancement MOSFET transistor, connected in series with the field effect transistor according to a cascode assembly.

[0024] Thanks to the cascode assembly between the enhancement MOSFET transistor and the field effect transistor according to the invention, the cut-off member is open, i.e. does not allow current to pass, when no control voltage is applied, whether on one of the gate connection terminals of the field effect transistor according to the invention or on the gate of the enhancement MOSFET transistor. Thus, the cut-off member according to the invention can be used instead of battery contactors in a vehicle, since it will leave open the circuit connecting the high-voltage battery of the vehicle to the high-voltage network of the vehicle when the latter is in standby mode, i.e. “asleep” or switched off. The enhancement MOSFET transistor is preferably a low-voltage transistor, for example supporting 16 or 25V.Thus the cost of the cut-off device according to the invention should ultimately have a lower cost price than that of an electronic cut-off component of the prior art.

[0025] The invention also relates to a method for managing the supply of energy in a high-voltage network connected to a high-voltage battery via at least one cut-off device according to the invention, the management method being characterized in that it comprises a step of activating the cut-off device comprising sub-steps of: - blocking the field-effect transistor by applying a blocking voltage between one of the gate connection terminals and that of the first or second electrode used as a source of the field-effect transistor,

[0026] - turning on the MOSFET transistor, and

[0027] - waiting for a request to close the cut-off device.

[0028] In this patent application, the cut-off member is open when it prevents current from passing, and is closed when it conducts current. The closure application therefore aims to close the circuit connecting the high-voltage battery to the high-voltage network. The management method according to the invention is for example implemented in a vehicle computer, for example in the main computer of the vehicle, or in a specific computer. This computer is for example connected to a control circuit for the gates of the transistors constituting the cut-off member according to the invention. Of course, the value of the blocking voltage of the gate depends on the N or P type of the field-effect transistor according to the invention. Similarly, the conduction of the MOSFET transistor uses a control voltage whose value depends on the N or P type of the MOSFET transistor of the cut-off member according to the invention.

[0029] Furthermore, during the blocking step, at least one blocking voltage is actually applied, since it is possibly applied to both gate connection terminals, i.e. between each of the gate connection terminals and their nearest electrode. This option makes it possible to prevent the flow of current in both directions.

[0030] A control voltage, whether in transistor blocking or in transistor closing, is always applied between a gate connection terminal of the transistor and the electrode of the transistor proximal to this gate connection terminal. In the blocking step, at least one blocking voltage is therefore applied between that of the first or second electrode used as a source of the field effect transistor, and the gate connection terminal proximal to this electrode.

[0031] In one embodiment of the invention, the management method according to the invention comprises a step of precharging at least one capacitor connected to the high voltage network, the precharging step comprising a limitation of the current passing through the cut-off member by a progressive variation of the voltage between said one of the gate connection terminals and that of the first or second electrode used as a source of the field effect transistor.

[0032] In this embodiment, the high-voltage network comprises one or more capacitors requiring pre-charging before allowing the battery current to flow completely to the high-voltage network. This or these capacitors are connected downstream of the cut-off device or devices, for example by being connected in parallel to the terminals of the high-voltage network.

[0033] It should be noted that in this application, the terms "upstream" or "downstream" refer to the relative position of electrical components or assemblies with respect to the direction of the current leaving the high-voltage battery and heading towards consumers of the high-voltage battery, i.e. when the latter is discharging. Thus, a first component is upstream of a second component if the current leaving the high-voltage battery first passes through the first component and then the second component before entering the high-voltage battery.

[0034] Furthermore, the progressive variation of the voltage between said one of the gate connection terminals and that of the first or second electrode used as a source of the field effect transistor corresponds to a progressive change from a value close to - 15V to a value close to 0V if the field effect transistor according to the invention is of the N type, or a progressive change from a value close to + 15V to a value close to 0V if the field effect transistor according to the invention is of the P type. This voltage variation is progressive in the sense that the control voltage does not change from - 15V or 15V to 0V but takes intermediate values, the change from - 15V or 15V to 0V taking several milliseconds, the field effect transistor being crossed by a very high current. Of course, a conventional opening or closing without current passing through the field effect transistor can be done in less than a microsecond.Alternatively, the precharging step involves sending current pulses to the high-voltage network, achieved by successive closings and openings of the cut-off device. The openings of the cut-off device are preferably conditioned upon reaching a high threshold of current flowing through the cut-off device. This alternative makes it possible to dissipate less energy during precharging than the sole use of current limitation by progressive control of the control voltage of the field-effect transistor according to the invention.

[0035] In yet another alternative, the precharge step involves:

[0036] - a sub-step of sending current pulses to the high voltage network, carried out by successive closings and openings of the cut-off device, followed

[0037] - a sub-step of limiting the current passing through the cut-off member by a progressive variation of the voltage between said one of the gate connection terminals and that of the first or second electrode used as a source of the field effect transistor.

[0038] This other alternative combines the two previous precharging techniques and therefore offers the advantage of low energy dissipation while limiting current surges in the capacitors to be precharged. Preferably, the limiting sub-step is triggered when the voltage across the high-voltage network reaches a high voltage threshold. The high voltage threshold is chosen to optimize the precharging step in terms of performance, for example, is set at a value between 70% and 90% of the battery voltage.

[0039] As with the blocking step, current limiting and / or sending current pulses are optionally performed by modifying the two control voltages of the two gate connection terminals.

[0040] In an example of use of the invention, the management method according to the invention comprises a step of opening the cut-off member while a non-zero current flows through it, the opening step comprising a control of the voltage between said one of the gate connection terminals and that of the first or second electrode used as a source of the field effect transistor as a function of the voltage at the terminals of the cut-off member and / or as a function of a variation of the current passing through the cut-off member as a function of time.

[0041] This control is preferably carried out on the two control voltages of the two gate connection terminals, since the non-zero current being due to a fault, it can come from the battery or the high voltage network. This step of opening the under-current cut-off device occurs exceptionally when it is necessary to isolate the high voltage battery while high voltage equipment is still in operation, for example following a crash of a vehicle implementing the management method according to the invention. Since the impedance of the high voltage network is inductive, it is necessary to dissipate the energy stored in the wiring and filters of the connected equipment, which the cut-off device according to the invention allows. The control of the control voltage in this step makes it possible to dissipate this energy without damaging the cut-off device, in particular without causing too high an overvoltage at the terminals of the cut-off device.Alternatively, this control of the control voltage is carried out as a function of the voltage across the terminals of the field effect transistor and / or as a function of a variation in the current flowing through the cut-off device as a function of time.

[0042] This control can be conditioned by the current flowing through the cut-off device reaching a high current threshold, significant of a fault current. For example, the opening of the cut-off device only uses such control when the current is greater than 500A (amperes).

[0043] In another example of use of the invention, the management method according to the invention comprises a step of opening the cut-off device, the latter being crossed by a zero current, the opening step comprising the sub-steps of:

[0044] - blocking the field effect transistor by applying a blocking voltage between said one of the gate connection terminals and that of the first or second electrode used as a source of the field effect transistor,

[0045] - blocking of the MOSFET transistor,

[0046] - cutting off a power supply to a control circuit of the cut-off member. During the blocking step, at least one blocking voltage is in fact applied, since it is possibly applied to the two gate connection terminals, i.e. between each of the gate connection terminals and their closest electrode. In this other example of opening the cut-off member, no control of the control voltage is used since the current is zero or almost zero, i.e. less than 100 mA. Finally, in yet another example of use of the invention, the precharging step is followed by a step of recharging the high-voltage battery via a charging terminal.In this case, the recharging step is preceded by a step in which a quasi-zero voltage is applied between the other of the gate connection terminals and that of the first or second electrode used as the source of the field effect transistor, this electrode being different between these two steps, when such a voltage was not already applied during the previous precharging step. Indeed, when only a control voltage is used, the direction of current flow must be taken into account.

[0047] In this other example of use of the invention, the capacity precharged during the precharge step is an input capacity of the charging terminal, the high voltage network then being made up of high voltage electrical connections making it possible to connect the charging terminal to the high voltage battery.

[0048] When the pre-charging step is followed by a step of energy consumption by the high voltage network, the two control voltages of the gate connection terminals of the field effect transistor of the cut-off device are almost zero, to allow the battery to be recharged during the regenerative phases of vehicle driving.

[0049] Finally, the invention relates to a vehicle comprising a high-voltage battery and a high-voltage network, each of the terminals of the high-voltage battery being connected to the high-voltage network via a cut-off device according to the invention. In this vehicle, preferably, two cut-off devices connect the high-voltage battery to the high-voltage network, this connection between the high-voltage battery and the high-voltage network being made without contactors or fuses.

[0050] Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several examples of embodiment given for informational and non-limiting purposes with reference to the attached schematic drawings on the other hand, in which:

[0051] [fig 1] already described in relation to the prior art, represents a high voltage battery of a vehicle connected to a high voltage network of the vehicle via contactors, [fig 2] represents a field effect transistor according to the invention, in one embodiment of the invention,

[0052] [fig 3] represents a cut-off member according to the invention, in one embodiment of the invention, as well as a control circuit for this cut-off member,

[0053] [fig 4] represents a high voltage battery of a vehicle, connected to a high voltage network of the vehicle by means of cut-off devices according to the invention, in one embodiment of the invention,

[0054] [fig 5] represents steps of a method for managing the supply of energy in the high voltage network of figure 4, in one embodiment of the invention, [fig 6] represents the evolution of a control voltage of a field effect transistor of a cut-off device represented in figure 4, as well as the evolution of the current in the high voltage battery represented in figure 4, and the evolution of the voltage at the terminals of the high voltage network represented in figure 4, during a precharging step of the management method of figure 5, and

[0055] [fig 7] represents an opening step under current when a fault current appears, implemented by the management method of figure 5.

[0056] According to an embodiment of the invention shown in Figure 2, a field effect transistor 100 with junction and lateral structure according to the invention comprises:

[0057] - a first support layer 10 formed of P-type silicon carbide (SiC), heavily doped with boron (which is reflected by the notation “P+” in Figure 2), for example by ion implantation,

[0058] - a second P-type semiconductor layer 12 made of silicon carbide but less heavily doped with boron (which is reflected by the notation “P-” in Figure 2), formed by epitaxy above the first support layer 10,

[0059] - a third N-type semiconductor layer 14 made of silicon carbide, also formed by epitaxy above the second support layer 12,

[0060] - a first zone 16 and a second zone 18 of N type in silicon carbide, heavily doped for example with phosphorus (which is reflected by the notation “N+” in figure 2) and produced for example by photolithography then implantation and diffusion on the third semiconductor layer 14, these first and second zones each being produced at a separate end of the semiconductor layer 14, or close to these ends,

[0061] - a third zone 20 and a fourth zone 22 of P type in silicon carbide, heavily doped for example with boron and produced for example by photolithography then implantation and diffusion on the third semiconductor layer 14, the third zone 20 being proximal to the first zone 16 relative to the second zone 18, and the fourth zone 22 being proximal to the second zone 18 relative to the first zone 16,

[0062] - a first metallic el electrode in contact with the first zone 16,

[0063] - a second metal electrode e2 in contact with the second zone 18,

[0064] - a first metal grid connection terminal gl in contact with the third zone 20,

[0065] - a second metal grid connection terminal g2 in contact with the fourth zone 22, and

[0066] - an insulating layer 15, for example made of silicon dioxide (SiO2) covering the free surface of the third conductive layer 14 and insulating between them the electrodes el, e2 and the grid connection terminals gl, g2.

[0067] The first, second, third and fourth areas 16, 18, 20, 22 each possibly extend to the surface of the third conductive layer 14 beyond the limits of the electrode or the gate connection terminal partially covering it, in which case these areas are covered, on this surface, with the insulating layer 15 where they are not covered with an electrode or a gate connection terminal. Of course the first, second, third and fourth areas 16, 18, 20, 22 do not touch each other.

[0068] The distance separating the first gate connection terminal gl from the second gate connection terminal g2 is for example between 15 and 20 pm (micrometers) for a field effect transistor 100 supporting up to 1200V. In addition, for such a field effect transistor 100, the distance separating the first gate connection terminal gl from the first electrode el, as well as the distance separating the second gate connection terminal g2 from the second electrode e2, are of the order of 1 pm. Finally, the thickness of the epitaxial layers is for example 4 to 6 pm for such a field effect transistor 100.

[0069] The field effect transistor 100 therefore has an N channel formed by the third conductive layer 14. The first electrode el can be used as a drain or source. When it is used as a drain, then the second electrode e2 is used as a source and the second gate connection terminal g2 makes it possible to open the field effect transistor 100 by applying a control voltage Vg2 (referenced in FIG. 3) of approximately -15V between the second gate connection terminal g2 and this second electrode e2, that is to say by putting the second electrode e2 at a potential 15V higher than the second gate connection terminal g2.

[0070] When, on the contrary, the first electrode el is used as a source, then the second electrode e2 is used as a drain and the first gate connection terminal gl makes it possible to open the field effect transistor 100 by applying a control voltage Vgl (referenced in figure 3) of approximately -15V between the first gate connection terminal glet the first electrode el, that is to say by putting the first electrode el at a potential 15V higher than the first gate connection terminal gl.

[0071] Of course, many embodiment variants are possible, for example, as a variant, the field effect transistor according to the invention is a P-type channel, in which case the types of the different layers must be reversed. Also, other types of dopant than boron or phosphorus are of course usable, and manufacturing variants are usable, for example, the formation of the second semiconductor layer 12 uses a diffusion furnace or ion implantation.

[0072] Figure 3 now illustrates how the field effect transistor 100 is connected in a cut-off device 200 according to the invention. In order to make the cut-off device 200 open in the absence of a control voltage, an enhancement MOSFET 110 transistor, of type N in this embodiment of the invention, is connected in series to the field effect transistor 100, in cascode assembly.

[0073] A first terminal of the cut-off member 200 is the first electrode el of the field effect transistor 100. The drain of the MOSFET transistor 110 is connected to the second electrode e2 of the field effect transistor 100, and the source of the MOSFET transistor 110 comprises an electrode e3 forming a second terminal of the cut-off member 200.

[0074] The source of the MOSFET transistor 110 is connected to the second gate connection terminal g2 through a resistor or resistive connection Rg.

[0075] A control circuit 4 makes it possible to apply:

[0076] - a first control voltage Vgl between the first grid connection gl and the first electrode el,

[0077] - a second control voltage Vg2 between the second gate connection g2 and the second electrode e2, and

[0078] - a third control voltage Vg3 between the gate of the MOSFET transistor 110 and the source of the MOSFET transistor 110.

[0079] The control circuit 4 is capable of receiving a voltage measurement Vc carried out by a voltmeter 2 at the terminals of the cut-off member 200, that is to say between the electrodes e1 and e3. It is also capable of receiving a measurement of the current passing through the cut-off member 200.

[0080] When the MOSFET transistor 110 turns off, the second control voltage Vg2 becomes negative due to the resistive connection between the second gate connection terminal g2 and the source of the MOSFET transistor 110, turning off the field effect transistor 100 as soon as this second control voltage Vg2 becomes lower than the turning-off voltage of the field effect transistor 100.

[0081] Of course, other connection variants are possible to form the cut-off member 200, in particular the MOSFET transistor can be connected by its drain or its source to the first electrode el depending on the role of the latter. In addition, when the MOSFET transistor is of a different type from the field effect transistor (for example respectively P and N), the connections are modified accordingly.

[0082] As shown in Figure 4, in an example of use of the invention, two cut-off members 200 and 202 according to the invention are used instead of battery contactors in the high voltage circuit of Figure 1. The resistive connections Rg of these cut-off members are not shown to simplify Figure 4. In particular, the cut-off member 200 is connected by the first electrode el corresponding to its first terminal to a positive terminal of the battery 30, and is connected by the electrode e3 corresponding to its second terminal, to a first terminal of the high voltage network 300.

[0083] The cut-off member 202 is identical to the cut-off member 200, in particular it comprises a field effect transistor 102 identical to the field effect transistor 100 and connected in series with an enrichment MOSFET transistor 112 identical to the MOSFET transistor 110. The electrodes and connection terminals of the field effect transistor 102 and of the MOSFET transistor 112 are therefore referenced in the same way as the electrodes and connection terminals of the field effect transistor 100 and of the MOSFET transistor 110.

[0084] The source electrode e3 of the MOSFET transistor 112 is connected to a negative terminal of the battery 30, and the first electrode el of the field effect transistor 102 is connected to a second terminal of the high voltage network, distinct from the first terminal of the high voltage network.

[0085] Thus the potential at the first electrode el of the field effect transistor 100, 102 is always higher than the potential at the source of the MOSFET transistor 110, 112 when the battery is connected to energy consumers, which ensures natural blocking of the MOSFETs 110, 112 when they are not powered. The high voltage network 300 comprises a capacitor 28 connected between its first terminal and its second terminal, as well as an inverter connected in parallel with the capacitor 28, and a three-phase electric motor connected to the output of the inverter. The voltage across the terminals of the high voltage network 300 is denoted VHT, and the voltage across the terminals of the high voltage battery 30 is denoted VBATT.

[0086] A management method 400 according to the invention, of the supply of energy in the high voltage network 300 by the battery 30, is now described in relation to FIG. 5. The management method 400 is for example implemented in software in a main computer of the vehicle equipped with the battery 30, the cut-off devices 200, 202 and the high voltage network 300. This computer is connected via a CAN bus (from the English "Controller Area Network") to the analog control circuit 4. Prior to the implementation of the management method 400, the vehicle is in a standby state 402, that is to say asleep, a user of the vehicle having parked the vehicle and having locked the doors.In this state 402, the control circuit 4 is not powered and the cut-off members 200, 202 are open, in particular because a zero voltage is naturally established between the gate and the source of each of the MOSFET transistors 110, 112 in the absence of a control voltage between this gate and this source. As a result, a negative voltage appears between the gate connection terminal g2 and the second electrode e2 of each of the field effect transistors 100 and 102, which has the effect of blocking them. This is the cascode effect.

[0087] When the vehicle comes out of standby mode, the control circuit 4 is powered and the main computer of the vehicle activates 404 the cut-off members 200, 202 so as to allow rapid closing of these. This activation step 404 comprises the sub-steps of:

[0088] - blocking 4040 of each field effect transistor 100, 102 by applying a blocking voltage of - 15 V between the second gate connection g2 of the field effect transistor 100, 102 and its second electrode e2 which functions as a source of the field effect transistor 100, 102, and by applying a blocking voltage of - 15 V between the first gate connection gl of the field effect transistor 100, 102 and its first electrode el which functions as a drain of the field effect transistor 100, 102,

[0089] - turning on 4042 the MOSFET transistors 110, 112 by applying a positive voltage of approximately 15V between the gate of each of them and the source of each of them, and

[0090] - waiting 4044 for a request to close the cut-off devices 200, 202.

[0091] Once the cut-off members 200, 202 are activated, their closing or opening is triggered solely by the control of the gate connection terminals gl and g2 of their field effect transistor 100, 102. The control voltages Vg2 and Vgl applied to close the field effect transistors 100, 102 are each approximately 0V, for example between 0V and -IV, and the control voltages Vg2 and Vgl applied to open the field effect transistors 100, 102 are each approximately -15V, for example between -10V and -20V. The MOSFET transistors 110, 112 only serve to keep the high voltage circuit of the vehicle open in the absence of power supply to the control circuit 4.

[0092] To summarize, each field effect transistor 100, 102 is:

[0093] - equivalent to an open circuit when its control voltages Vgl and Vg2 are equal to the blocking voltage of the field effect transistor 100, 102,

[0094] - equivalent to a closed circuit when its control voltages Vgl and Vg2 are almost zero,

[0095] - equivalent to a diode passing in the direction from the second electrode e2 to the first electrode el when the control voltage Vgl is almost zero while the control voltage Vg2 is equal to the blocking voltage of the field effect transistor 100, 102, and

[0096] - equivalent to a passing diode in the direction from the first electrode el to the second electrode e2 when the control voltage Vg2 is almost zero while the control voltage Vgl is equal to the blocking voltage of the field effect transistor 100, 102.

[0097] Although in this embodiment of the management method 400 according to the invention, the operating mode of the field effect transistors 100, 102 corresponding to diodes is not used, such use is conceivable in an alternative embodiment.

[0098] When the main computer of the vehicle receives a request to close the cut-off devices 202, 204, for example following a request to start the vehicle's electric motor, it implements a precharging step 406 of the capacitor 28.

[0099] The precharging step 406 comprises a first sub-step of sending current pulses 4060 to the high-voltage network 300, carried out by successive closings 24 and openings of the cut-off members 200, 202, as shown in FIG. 6. Of course, as a variant, one of the cut-off members 200, 202 can be kept closed while the other cut-off member 202, 200 carries out the successive closings 24 and openings. In this case, the cut-off member carrying out the current pulses alternates with the other cut-off member, for example at each different precharging step 406 or on the same precharging step 406 to symmetrize their wear and / or limit their heating.

[0100] Each opening following a closing 24 is triggered as soon as a high threshold iMax of the current Ibatt passing through the battery is reached, this high threshold IMax being for example set at 200 A, and preferably being between 50 and 500 A.

[0101] The duration of the successive closures 24 is a few hundred microseconds each and increases as the voltage VHT at the terminals of the high voltage network 300 increases, because the time t that the current Ibatt takes to reach the high threshold IMax also increases gradually, the voltage Vc at the terminals of the cut-off device 200 being (VBATT - VHT). Each closure 24 is made by a steep voltage front Vg2, Vgl from -15V to 0V, while each opening following a closure 24 is controlled so as to limit the overvoltage on the cut-off device 200, 202.

[0102] These successive closures 24 and openings make it possible to gradually charge the capacity 28 and therefore gradually increase the voltage VH at the terminals of the high voltage network 300.

[0103] When the voltage VHT at the terminals of the high voltage network 300 reaches a high voltage threshold, set for example at 70% of the voltage VBATT of the battery 30, the main computer of the vehicle implements, in this precharging step 406, a second sub-step of limiting the current 4062 passing through the cut-off members 200, 202. In this sub-step of limiting the current 4062, a progressive (continuous) increase 26 of the control voltages Vg2, Vgl causes them to go from approximately -15V to approximately 0V.

[0104] Alternatively, the precharging step 406 is performed solely by a command to gradually increase the voltages Vg2, Vgl up to a value close to 0V, or else solely by sending current pulses of increasingly longer durations. Once the voltage VHT at the terminals of the high-voltage network 300 almost reaches the voltage VBATT at the terminals of the high-voltage battery 30, the control voltages Vgl, Vg2 are maintained at the value close to zero and the high-voltage battery 30 operates in discharge during a step 410 of supplying the high-voltage equipment of the vehicle.

[0105] Alternatively, when the high voltage battery 30 is connected via the cut-off members 200, 202 to a charging terminal, the precharging step 406 having served to charge an input capacity of the charging terminal, then the management method 400 implements a charging step 408 of the high voltage battery 30.

[0106] Once the charging step 408 or the supply step 410 of the high voltage network is completed, the main computer of the vehicle commands the opening of the cut-off devices 200, 202. As an example, we consider the case where a discharge 410 has just ended.

[0107] During a step 414 immediately following this opening command, if the current passing through the cut-off members 200, 202 is zero or almost zero (branch Y of test 412 in Figure 5), the vehicle being for example stopped and no high-voltage equipment of the vehicle running, then the step 414 of opening the cut-off members 200, 202 comprises the sub-steps of:

[0108] - blocking 4140 of the field effect transistors 100, 102 by applying control voltages Vg2, Vgl of -15V between the second gate connection terminal g2 and the second electrode e2 of each field effect transistor 100, 102 and respectively between the first gate connection terminal gl and the first electrode el of each field effect transistor 100, 102, then

[0109] - blocking 4142 of the MOSFET transistors 110, 112 by applying a zero voltage between their gates and their respective sources, then

[0110] - 4144 cut-off of the power supply to control circuit 4.

[0111] The vehicle can thus return to standby mode, with minimal energy consumption by the vehicle's 14V on-board network, in particular to allow the main computer to be woken up later.

[0112] In a case of use of the invention where a fault appears in the high voltage network 300 or in the high voltage battery 30 (branch N of the test 412 in FIG. 5), generating an abnormally high current, the main computer of the vehicle implements a step 416 of opening the cut-off members 200, 202 under current. The opening step 416 comprises a first sub-step 4160 of limiting the fault current, shown in FIG. 7. When the fault current reaches a high ISM threshold, for example 500A, the current passing through the cut-off members 200, 202 (equal to the current Ibatt passing through the high voltage battery 30) is limited so as to limit the energy to be dissipated during the opening which will follow, as well as the thermal stress of the cables and connectors which undergo the fault current.

[0113] To achieve this current limitation 4160, the gate control voltage Vg2 of each field effect transistor 100, 102 and the gate control voltage Vgl of each field effect transistor 100, 102 are reduced until a low current threshold Isc is reached from which the field effect transistors 100, 102 are blocked 4612 during a second sub-step. The low threshold Isc is for example 100 mA. Indeed, it is the variation in current die / dt which creates the overvoltage on the field effect transistor 100, 102 to be limited by the gate controls. This limitation can be done until the current le is completely cancelled.

[0114] The reduction in the gate control voltages Vg2, Vgl of the field effect transistors 100, 102 allowing the current Ibatt to reach a low current threshold Isc, results from a control of these gate control voltages Vg2, Vgl as a function of the voltage Vc measured at the terminals of the cut-off member 200, that is to say that the gate control voltages Vg2, Vgl are adjusted so that the voltage Vc measured at the terminals of the cut-off member does not exceed a critical voltage withstand threshold of the field effect transistors 100, 102, reduced by a safety margin of, for example, around twenty volts.

[0115] Alternatively, the gate control voltages Vg2, Vgl are controlled as a function of the measurement of the current passing through the cut-off member 200 and more precisely as a function of the variation die / dt of this current as a function of time. Thus the gate control voltages Vg2, Vgl are adjusted so that this variation does not exceed a predetermined threshold of maximum variation of the current.

[0116] In another variant, the gate control voltages Vg2, Vgl are controlled both as a function of the measurement of the current passing through the cut-off member 200 and as a function of the voltage Vc measured at the terminals of the cut-off member 200, so that neither the critical voltage withstand threshold of the field effect transistors 100, 102, less the safety margin, nor the predetermined threshold of maximum current variation, are reached.

[0117] Once the low current threshold Isc is reached, the cutting devices are opened by:

[0118] - the second sub-step 4162 of blocking the field effect transistors 100, 102, by applying control voltages Vg2, Vgl of -15V between the second gate connection terminal g2 and the second electrode e2 of each field effect transistor 100, 102 and respectively between the first gate connection terminal gl and the first electrode el of each field effect transistor 100, 102, followed

[0119] - by a third sub-step of blocking 4164 of the MOSFET transistors 110, 112 by applying a zero voltage between their gates and their respective sources, followed

[0120] - by a fourth sub-step 4166 of cutting off the power supply to the control circuit 4.

[0121] The current-operated opening step 416 is performed so as not to damage the cut-off members 200, 202, and can therefore be repeated many times without needing to replace these cut-off members 200, 202, preferably integrated into the battery pack to guarantee an absence of voltage on the connectors of the battery pack. The invention therefore makes it possible to achieve savings compared to a conventional contactor system, which requires a dedicated precharging system, and makes it possible to preserve the cables and connectors of the high-voltage network 300 of the vehicle thanks to the current-limiting function performed by the cut-off members 200, 202.

[0122] Furthermore, although the cut-off members 200, 202 require cooling, and the control circuit 4 requires a power supply, this power supply and this cooling are possibly implemented by equipment integrated into the battery pack and not specific to the cut-off members 200, 202. For example, the power supply of the power supply circuit 4 is shared with that of the vehicle's on-board network, while the cooling of the cut-off members 200, 202 reuses, for example, a system for cooling the battery cells. It should be noted that the invention is not limited to an application in a motor vehicle, but can find other applications, in particular in any system comprising a high-voltage battery which must be disconnected from its consumers during shutdown or maintenance phases.For example, the cut-off device according to the invention can be used in an energy storage system using a photovoltaic generator, and in various systems equipped with high-voltage batteries such as construction machinery.

[0123] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention. In particular, the characteristics of the different variant embodiments of the invention envisaged in this application can be combined to achieve the invention, insofar as these variants are not incompatible with each other.

Claims

CLAIMS 1- Field effect transistor (100, 102) with junction and lateral structure, comprising: - at least one support layer (10) of a first conductivity type, - at least one semiconductor layer (14) of a second type of conductivity superimposed on the support layer (10) and capable of forming a channel between a source and a drain, - a first electrode (el) implanted on the semiconductor layer (14) and capable of forming the source or the drain, - a second electrode (e2) implanted on the semiconductor layer (14) and capable of forming the drain or the source, - a zone (18) doped according to the first type of conductivity in contact on the one hand with the semiconductor layer (14) and on the other hand with a gate connection terminal (gl) located between the first and second electrodes (el, e2) and electrically insulated from the first and second electrodes (el, e2), the field effect transistor (100, 102) being characterized in that it further comprises an additional zone (20) doped according to the first type of conductivity, in contact with on the one hand the semiconductor layer (14) and on the other hand with another gate connection terminal (g2) located between the gate connection terminal (gl) and the second electrode (e2), and electrically insulated from the gate connection terminal (gl) and the second electrode (e2). 2- Cut-off member (200, 202) comprising a field effect transistor (100, 102) according to claim 1, characterized in that it further comprises at least one MOSFET transistor (110, 112) with enhancement, connected in series with the field effect transistor (100) according to a cascode assembly. 3- Method for managing (400) the supply of energy in a high-voltage network (300) connected to a high-voltage battery (30) via at least one cut-off device (200) according to claim 2, the management method (400) being characterized in that it comprises a step of activating (404) the cut-off device (200) comprising sub-steps of: - blocking (4040) of the field effect transistor (100) by applying a blocking voltage between one of the gate connection terminals (g2) and that of the first or second electrode (e2) used as a source of the field effect transistor (100) - turning on (4042) the MOSFET transistor (110), and - waiting (4044) for a request to close the cut-off device (200). 4- Method for managing (400) the supply of energy in a high voltage network (300) according to claim 3, comprising a step of precharging at least one capacitor (28) connected to the high voltage network (300), the precharging step comprising a limitation of the current (le) passing through the cut-off member (200) by a progressive variation of the voltage (Vg2) between said one of the gate connection terminals (g2) and that of the first or second electrode (e2) used as a source of the field effect transistor (100). 5- Method for managing (400) the supply of energy in a high voltage network (300) according to claim 3, comprising a step of precharging at least one capacitor (28) connected to the high voltage network (300), the precharging step comprising sending current pulses to the high voltage network (300), carried out by successive closings and openings of the cut-off device (200). 6- Method for managing (400) the supply of energy in a high voltage network (300) according to claim 3, comprising a step of precharging (406) at least one capacity (28) connected to the high voltage network (300), the precharging step (406) comprising: - a sub-step of sending current pulses (4060) to the high voltage network, carried out by successive closings and openings of the cut-off device (200), followed - a sub-step of limiting the current (4062) passing through the cut-off member (200) by a progressive variation of the voltage (Vg2) between said one of the gate connection terminals (g2) and that of the first or second electrode (e2) used as a source of the field effect transistor (100). 7- Method for managing (400) the supply of energy in a high-voltage network (300) according to any one of claims 3 to 6, comprising a step of opening (416) the cut-off member (200) while the latter is crossed by a non-zero current (le), the opening step (416) comprising a control of the voltage between said one of the gate connection terminals (g2) and that of the first or second electrode (e2) used as a source of the field effect transistor (100) as a function of the voltage (Vc) across the terminals of the cut-off member (200) and / or as a function of a variation of the current (le) passing through the cut-off member (200) as a function of time (t). 8- Method for managing (400) the supply of energy in a high-voltage network (300) according to any one of claims 3 to 6, comprising a step of opening (414) the cut-off member (200), the latter being crossed by a zero current (Ic), the opening step (414) comprising the sub-steps of: - blocking (4140) the field effect transistor (100) by applying a blocking voltage between said one of the gate connection terminals (g2) and that of the first or second electrode (e2) used as a source of the field effect transistor (100), - blocking (4142) of the MOSFET transistor (110), - cutting (4144) of a power supply to a control circuit (4) of the cutting member (200). 9- Method for managing (400) the supply of energy in a high voltage network (300) according to any one of claims 4 to 6, in which the precharging step (406) is followed by a step of recharging (408) the high voltage battery (30) by a charging terminal. 10- Vehicle comprising a high voltage battery (30) and a high voltage network (300), each of the terminals of the high voltage battery (30) being connected to the high voltage network (300) via a cut-off member (200, 202) according to claim 2.

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