Short-circuit detection device in a transistor and corresponding method

Abstract

The invention relates to a device for detecting a short circuit in a transistor, comprising a transistor (1) having a source (S), a drain (D), and a gate (G), and a driver integrated circuit (2) configured to detect a short circuit by comparing a voltage applied to a terminal called the DESAT terminal with a first predefined voltage threshold. The device is configured so that the voltage applied to the DESAT terminal reflects the voltage between the drain (D) and the source (S). The device further comprises an external circuit (7) to the driver integrated circuit (2), the external circuit (7) being configured such that, when the voltage at the DESAT terminal (Vcdesat) exceeds a second voltage threshold, lower than the first voltage threshold, said external circuit (7) causes a drop in the voltage between the gate and the source of the transistor. The invention also relates to the corresponding method. (See Figure 3 for the abstract.)

Description

Title of the invention: Device for detecting short circuits in a transistor and corresponding method TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the field of power electronics and in particular to inverters and their control.

[0002] She is interested in the detection of the short-circuit phenomenon in transistors in certain power electronics systems, for example inverters, and in the protection of these systems in the event of a short circuit. STATE OF THE ART

[0003] In an inverter, transistors are used to switch the current between a DC power source and a load (for example, a motor or a power conversion system).

[0004] The inverters are based on a three-arm bridge structure, and each bridge arm consists of two transistors (one top and one bottom) connected in series. Their switching state controls the direction and magnitude of the current flowing through the load.

[0005] When the transistor is short-circuited, it can no longer switch efficiently between the blocked (open) and conducting (closed) states; this results in a short-circuit situation in the bridge arm. Thus, in a situation where a transistor (for example, an IGBT or MOSFET) used in an inverter can no longer properly control the current flowing through it, the transistor may short-circuit.

[0006] Short-circuit detection in a bridge arm is crucial to ensuring the safety and reliability of the inverter. A short circuit can cause a significant overload current through the transistors, which can damage them irreversibly.

[0007] This can lead to significant malfunctions in the inverter system and, by extension, in the wider electrical or electronic system to which it is connected.

[0008] Short-circuit detection, control and protection strategies are known.

[0009] These strategies use what is commonly called a "DESAT" function (for "desaturation") which detects if a short circuit occurs in a bridge arm of the inverter and commands an appropriate interruption of the short circuit by opening the undamaged transistor in the bridge arm. This function is based on a continuous measurement of the currents and / or voltages across the transistors.

[0010] Thus, generally, the DESAT function compares the voltage across the transistor (or more precisely a voltage that reflects the voltage across the transistor) to a A predefined threshold is used. Specifically, the voltage between the drain and source (or collector and emitter) terminals of the transistor is measured or evaluated. When a short circuit occurs, a significant voltage appears across the transistor (between the drain and source or the collector and emitter of the transistor).

[0011] When a short circuit is detected, protective measures are taken. These measures may include opening the affected transistor, as well as implementing current limiting mechanisms. Thus, the interruption of the short-circuit current must be carried out more slowly than an interruption carried out during normal operation (in the absence of a short circuit), in order to limit the overvoltage generated during the interruption. This overvoltage is caused by a sudden increase in current, which can suddenly reach ten to fifteen times the nominal current. This results in a risk of avalanche (see below), a risk of thermal runaway, and therefore a risk of transistor degradation.

[0012] Two approaches are commonly used to implement this function.

[0013] According to a first approach, an external detection and desaturation circuit can be In this case, a dedicated circuit, including current meters and voltage comparators, is added to the system. This circuit actively monitors electrical signals and reacts when a short circuit is detected. Specifically, when a significant voltage appears across a power transistor, this voltage is detected by the external analog circuit, which activates a cutoff circuit to interrupt the short-circuit current. This interruption is advantageously achieved gradually, as explained in more detail below.

[0014] According to a second approach, the function can be integrated into the inverter, for example, at the level of the integrated circuit that drives the gate (or base) terminal of the transistor. This integrated circuit is sometimes called a "gate driver" or simply a "driver" according to commonly used English terminology. Thus, some drivers directly integrate the DESAT function. This approach simplifies the process, since the necessary signals are accessible via the driver.

[0015] According to this approach, the driver generally includes a terminal dedicated to the desaturation function. A voltage representative of the drain-source (or collector-emitter) voltage is read from this terminal. This voltage is, in practice, the voltage across a filter capacitor 5, and is reduced relative to the drain-source voltage by a resistor and a blocking diode with predetermined characteristics. The voltage at this terminal makes it possible to determine whether a short-circuit situation occurs and whether the switching should be controlled according to a controlled desaturation strategy.

[0016] Other approaches are known, for example, indirect detection of a short-circuit situation by measuring current. Such an approach is developed by example in document US20140307495.

[0017] In the inverters of electric vehicle powertrains, IGBT or MOSFET transistors are commonly used. IGBT transistors are frequently used in electric vehicles operating with a high-voltage architecture. MOSFET transistors are more commonly used in the electrical systems of hybrid vehicles or in lower-power, often lower-voltage architectures.

[0018] While the use of a DESAT function is widespread, even virtually universal, in systems using IGBT transistors, it is generally absent from systems using MOSFETs. In the case of inverters using MOSFETs, the increased risk of short-circuiting is frequently addressed by confining the inverter so that the risk of fire remains limited to the inverter alone. This approach is, however, imperfect, in that it requires the creation of reliable fire containment and potentially leads to complete destruction of the inverter in the event of a short circuit.

[0019] It is nevertheless quite possible to implement a DESAT function regardless of the type of transistor used, including MOSFETs. However, the characteristics of transistors depend on their technology. For example, MOSFETs and IGBTs have different switching characteristics and different static characteristics; in particular, the forward characteristic (drain current Id as a function of drain-source voltage Vds) differs between MOSFETs and IGBTs, which justifies a lower protection threshold for a MOSFET. The DESAT function must therefore be adapted to the transistor technology used.

[0020] For example, in the case of an IGBT, in the event of a short circuit, the voltage rises extremely rapidly, but, in certain normal and transient operating conditions, the current through the IGBT can be two to three times greater than the system's nominal current, resulting in a rise in the voltage across the IGBT. Therefore, a relatively high voltage threshold must be adopted for the DESAT function associated with IGBTs. This allows for reliable short-circuit detection, while avoiding false positives.

[0021] MOSFETs, on the other hand, require a much lower voltage threshold. Using a DESAT function adapted for IGBTs on a system containing MOSFETs would lead to very high currents in the event of a short circuit followed by desaturation, and therefore to the inefficiency of the DESAT function.

[0022] Thus, for the protection of inverters using MOSFETs, it is possible to use an external protection circuit configured to have a lower detection threshold than for IGBTs. However, if one wishes to benefit from the advantages of a DESAT function integrated into the driver in an inverter using MOSFETs, it is not It is not possible to use simple drivers, which are generally designed to provide DESAT functionality for IGBT transistors. Therefore, in this case, it is necessary either to create a specialized driver, which is expensive and impractical for a range of inverters, some of which use IGBTs and others MOSFETs, or to use a configurable or programmable driver, particularly with regard to the voltage threshold used. Such a configurable driver is expensive and complex (which increases the development and debugging time of the driver software in particular).

[0023] In general, there is no solution allowing the use of the same driver reference in inverters of different technologies, adapted to operate at various voltages such as 48 V, 400 V and 800 V. Description of the invention

[0024] The present invention aims to remedy all or part of the disadvantages of the prior art mentioned above.

[0025] To this end, the invention relates to a device for detecting a short circuit in a transistor, comprising a transistor having a source, a drain, and a gate, and a driver integrated circuit connected to the transistor and configured to detect a short circuit by comparing a voltage applied to a terminal called the DESAT terminal of the driver integrated circuit with a first predefined voltage threshold. The device is configured so that the voltage applied to the DESAT terminal reflects the voltage between the drain (D) and the source (S). The device further comprises a circuit external to the driver integrated circuit, the external circuit being configured such that, when the voltage at the DESAT terminal exceeds a second voltage threshold, lower than the first voltage threshold, said external circuit causes a drop in the voltage between the gate and the source of the transistor.

[0026] By adding an external circuit to the driver integrated circuit, the device according to the present invention enables the transistor to be desaturated and turned on in two phases. The transistor is turned on first by discharging the gate through a low resistance in an external circuit, which lowers the gate current of the transistor and quickly triggers the short-circuit breaking, even before the voltage at the DESAT terminal of the driver integrated circuit has reached a first voltage threshold for detecting a short circuit. Secondly, when the drain-source voltage has increased sufficiently for the voltage measured at the DESAT terminal of the driver integrated circuit to reach said first threshold, the driver integrated circuit signals to a microcontroller of the system that it has detected a short circuit.Control is then carried out conventionally by the integrated control circuit, for example by a controlled command of the opening of the transistor of . power (for example by piloting according to a "two level turn-off" or a "soft turn-off", as explained below).

[0027] This allows the use of a simple driver integrated circuit with a transistor for which it is not normally suited. Typically, a driver integrated circuit whose saturation detection threshold is suitable for IGBTs can thus be used with MOSFETs, while ensuring adequate system protection in the event of a transistor short circuit.

[0028] The DESAT terminal of the driver integrated circuit can be connected to the transistor drain via a resistor and a diode.

[0029] The external circuit may include a comparator and a logic level transistor, arranged so that the comparator compares the voltage at the DESAT terminal (Vcdesat) to the second voltage threshold, and drives the closing of the logic level transistor when the voltage at the DESAT terminal (Vcdesat) exceeds said second voltage threshold.

[0030] The external circuit may include a resistor and when the logic level transistor is conducting, the gate G of the transistor discharges through the resistor and through the logic level transistor, which triggers the opening of the transistor.

[0031] The external circuit may include a voltage divider that determines the second voltage threshold.

[0032] The transistor in question may be a MOSFET.

[0033] The first voltage threshold may, in particular, be between 6V and 9V, and the second voltage threshold is lower than the first voltage threshold. The second voltage threshold may, in particular, be between 2V and 3V.

[0034] When a short circuit is detected by said driver integrated circuit (2), the driver integrated circuit can control an opening of the transistor according to a two-level switching or soft switching method.

[0035] The device may include a microprocessor for controlling the inverter, and when a short circuit is detected by the control integrated circuit, said control integrated circuit sends a signal to the microprocessor. The microprocessor then commands (possibly after a time delay) the application of a fallback mode for the inverter.

[0036] The invention also relates to an inverter comprising a device as described above.

[0037] The invention also relates to a method for protecting a power electronics device comprising a transistor having a source, a drain, and a gate; an integrated circuit for driving the transistor having a terminal called the DESAT terminal connected to the transistor such that the voltage applied to said DESAT terminal reflects the drain voltage between the drain and the source, the method comprising the steps of: - when the voltage at the DESAT terminal exceeds a voltage threshold, called At the second voltage threshold, the transistor's gate is discharged through a resistor to lower the voltage between the gate and the source, which triggers the transistor to open; then - when the voltage at the terminal of the AT exceeds a voltage threshold, called the first voltage threshold, which is greater than the second voltage threshold, the integrated control circuit commands the opening of the transistor according to a two-level switching or progressive switching process.

[0038] In such a method, when the voltage at the DESAT terminal exceeds a voltage threshold, a signal is sent by the control integrated circuit to a microcontroller which then commands the application of a refuge mode of the inverter. BRIEF DESCRIPTION OF THE FIGURES

[0039] Other advantages, purposes and particular features of the present invention will become apparent from the following non-limiting description of at least one particular embodiment of the devices and methods of the present invention, with reference to the accompanying drawings, in which: - Figure 1 represents part of an electrical circuit illustrating a method of detecting a short circuit in a transistor in accordance with the prior art, thanks to a driver integrating a DESAT function, - [Fig. 2] is a graph representing the evolution of various tensions and currents in the transistor when a MOSFET type transistor is associated with integrated protection in a driver incorporating a DESAT function designed for an IGBT; - [Fig.3] represents a part of an electrical circuit, corresponding to the part shown in [Fig.1], according to an embodiment of the invention; - Figure 4 represents, on a graph similar to that of Figure 2, the effect of the application of the circuit of [Fig.3]. DETAILED DESCRIPTION OF THE INVENTION

[0040] The present description is given as a non-limiting example of an embodiment.

[0041] Fig. 1 illustrates how the problem of desaturation can be dealt with in an inverter according to the prior art using an integrated control circuit or driver integrating a DESAT function for the detection and treatment of the short-circuit situation of a transistor.

[0042] The circuit includes a transistor 1. Since this transistor is used in an inverter, the inverter generally comprises six transistors for a three-phase inverter. The transistors are then divided into two groups: three transistors on the "bottom" side, i.e., placed between ground and the electrical load, for example, the motor controlled by the inverter, and three on the "top" side, i.e., placed between the electrical source and the charge. In this case, the measures taken with regard to desaturation are illustrated for one transistor, here on the low side, but they apply in the same way to each transistor of the inverter considered.

[0043] In the system shown, the transistor is an IGBT (insulated-gate bipolar transistor), and therefore has three terminals, namely an emitter E, a collector C, and a base B.

[0044] Transistor 1 is driven by a driver integrated circuit 2. The driver integrated circuit 2 has a number of terminals, in this case twenty-two terminals labeled PI to P22 in the example shown. The connections and functions of these different terminals are not detailed here. However, in the example shown, one of the terminals (here terminal P13) allows the transistor to be controlled via a gate driver circuit 6, and one of the terminals (here terminal P15), called the DESAT terminal, is dedicated to short-circuit detection and desaturation, as explained below.

[0045] This integrated control circuit 2 is suitable for operation under high voltage, i.e. for example with an electrical power source having a nominal voltage of 400 V or 800 V.

[0046] In case of a short circuit, the voltage between the collector and the emitter VCe increases sharply.

[0047] To detect such a situation, terminal P15 is connected to the collector C of transistor 1 by a very simple electrical circuit consisting of a resistor 3 and a diode 4. The voltage Vcdesat, which is the voltage across a capacitor 5 placed between resistor 3 and ground (or the emitter or source potential), reflects the measured voltage between the drain and the source (in the case of a MOSFET) or between the collector and the emitter (in the case of an IGBT). It is measured at terminal P15 of the driver. By "reflects," we mean that there is generally a function, in particular a bijective function, between the drain-source voltage and the voltage at the DESAT terminal. Generally, the voltage at the DESAT terminal corresponds to the drain-source voltage up to a constant (or "offset").

[0048] The Vcdesat voltage measured at terminal P15 is compared to a first voltage threshold, called the DESAT threshold, generally located between 6V and 9V depending on the driver considered. When the measured Vcdesat voltage exceeds the first threshold or DESAT threshold, which indicates that the voltage between the collector and the emitter exceeds a certain threshold, the driver integrated circuit 2 considers the relevant bridge arm to be in a short-circuited state.

[0049] One measure that can be taken by the integrated control circuit is to interrupt the short-circuit current using a two-level switching method, generally referred to by the English expression "two-level turn-off" (TLTO). The purpose of the TLTO is to ensure efficient opening of transistors in two stages to ensure smooth and controlled switching of switching devices.

[0050] Another solution is to achieve a gradual switch-off, or “soft turn-off”.

[0051] Another pin of the driver integrated circuit 2, here pin P8, sends the short-circuit signal to the microcontroller. Then, the microcontroller manages the inverter's protection mode.

[0052] Thus, during transistor desaturation, in a first step, the voltage across the transistor (gate-source voltage Vgs) is rapidly reduced to an intermediate level. This limits the short-circuit current and brings it back to reasonable values ​​to allow the switching to continue. In a second step, after the voltage reduction, the transistor is completely switched off by cutting off the control current or by applying a zero or negative voltage.

[0053] These strategies make it possible to avoid a too rapid cutoff which would result in an extremely high voltage peak and potentially destructive to the transistor.

[0054] If we consider the device in [Fig. 1] and wish to use it to protect an inverter using MOSFET-type transistors (for "Metal-Oxide-Semiconductor Field-Effect Transistor", which means in French "Metal-oxide-semiconductor field-effect transistors" (MOSFETs), which are typically used at a lower rated voltage than IGBTs, for example 48V, this device generally proves ineffective because it is unsuitable. Figure 2 illustrates this. Figure 2 shows an example of the time evolution of various voltages and currents in a transistor, obtained experimentally on a MOSFET located on the low side of one of the phases of the power module, in this case phase U (i.e., the first phase in a three-phase U, V, W system), with the DC power supply voltage of the system set to 52V.

[0056] Curve Cl represents the voltage Vcdesat, which is applied to terminal P15 of the driver integrated circuit 2 as explained above. The scale is 2 V per division.

[0057] Curve C2 represents the voltage between the gate and the source of the transistor. The scale is 2V per division.

[0058] Curve C3 represents the voltage between the drain and source of the transistor. The scale is 20V per division.

[0059] Curve C4 represents the current intensity through the transistor. The scale is 2kA per division.

[0060] T=0 is defined as the instant at which the voltage between the gate and the source reaches the conduction threshold of the transistor, i.e. 2V in the example shown.

[0061] The DES AT threshold of the driver (or first threshold) is 6 V. At the moment when Cl reaches At the first threshold, the protection function is activated. Here, the short-circuit current is detected at T = 3.4ps.

[0062] However, a DES AT threshold of the order of 2V to 3V is more suitable for a MOSFET transistor under the aforementioned conditions of use, the use of a driver with such a detection threshold for its DES AT function leads to a loss of approximately 1.5 ps for this detection.

[0063] Thus the opening of the power MOSFET begins to be controlled (see the evolution of C2) at T=3.6ps.

[0064] On the other hand, at the moment of switching off, the drain-source voltage, Vds, (curve C3) reaches approximately 110V, and the current through the transistor reaches 11.5kA (curve C4). These values ​​may be beyond the permissible characteristics for the transistor.

[0065] Under these conditions, the MOSFET is likely to operate in an avalanche region. As a reminder, avalanche breakdown occurs when the voltage applied across the transistor reaches a critical level called the "avalanche breakdown voltage." When this voltage is exceeded, electrical charges are accelerated to high energies in the transistor's semiconductor material, causing the release of additional electrons.

[0066] This can lead to a rapid increase in current through the transistor, which can damage the device if the current is not controlled. Avalanche phenomena are generally undesirable because they can cause irreversible damage to the component and lead to malfunctions or failures.

[0067] [Fig.3] represents, according to a view similar to that of [Fig.1], an example of a circuit according to an embodiment of the present invention.

[0068] The basic circuit is identical to that of [Fig.1], and thus comprises a transistor 1, a driver integrated circuit 2, a resistor 3, a diode 4, a filter capacitor 5 and a gate drive circuit 6 arranged as explained with reference to [Fig.1].

[0069] In the circuit shown in [Fig.3], transistor 1 is of the MOSFET type. It therefore comprises a source S, a drain D, and a gate G.

[0070] The driver integrated circuit 2 is of the same type as that of [Fig.1], with a DESAT threshold (or first threshold) of the driver of 6V.

[0071] The circuit shown in [Fig.3] differs from that of [Fig.1], by the presence of an external circuit 7, vis-à-vis the integrated control circuit 2.

[0072] The external circuit 7 is designed to trigger a transistor switching command as soon as a voltage threshold (second voltage threshold) is reached at the DESAT terminal of the driver integrated circuit 2. The second voltage threshold is lower than the first voltage threshold, since the aim is to detect a short-circuit situation as early as possible in order to protect the transistor. The second voltage threshold can therefore be set at approximately 2V, or approximately 3V (while the first voltage threshold is generated (a groan between 6V and 9V, for example here 6V as indicated above).

[0073] In the external circuit example 7 shown here, this circuit is based on a voltage comparator 8, namely an open-collector comparator. It also includes a logic-level transistor 9 (in this case, a MOSFET). Finally, it includes a set of resistors (RH, RL, Rsink, Rsc). Resistors RH and RL form a voltage divider to set the second voltage threshold Vref.

[0074] When a short circuit occurs in the relevant bridge arm, the drain-source voltage Vds increases. This drain-source voltage is observed—as in the circuit of [Fig. 1]—via the circuit comprising resistor 3 and diode 4, by observing the voltage Vcdesat measured at terminal P15 of the driver integrated circuit 2. Furthermore, thanks to the external circuit 7, as soon as the voltage at terminal P15 exceeds the second voltage threshold Vref, for example by 2V (i.e., even before the first voltage threshold is reached), the comparator output goes high, which triggers the logic-level transistor 9.

[0075] The logic level transistor 9 then allows the passage of a current and begins to discharge the capacitance Cgs (interposed between the gate and the source) and to discharge the gate of transistor 1 to the low state with a low resistance Rsc.

[0076] The drop in current and voltage of the gate thus triggers the opening phase of transistor 1, even before the voltage Vcdesat measured at the terminal of DES AT of the integrated circuit reaches the first threshold.

[0077] The drain-source voltage continues to increase, and consequently the Vcdesat voltage measured at the DES AT terminal, until it reaches the first voltage threshold, for example, 6V. The driver integrated circuit 2 then recognizes a short-circuit situation and sends a corresponding signal. The driver integrated circuit then commands a controlled opening of the transistor using a TLTO or soft turn-off method. As in the prior art according to [Fig. 1], an alert is therefore sent to the inverter's microcontroller via a pin of the driver integrated circuit 2, here pin P8.

[0078] The microcontroller then commands the inverter's operating mode to switch to a "refuge" mode, aimed at protecting the system, for example an "ASC" mode (according to the English acronym for "Active Short Circuit") or "freewheeling" mode.

[0079] In this ASC mode, the electronic switches of the power stage located on the same side of the H-bridges formed in the inverter are closed, thus allowing current to flow. The poles of the electric machine (typically three for a three-phase motor) are then short-circuited. The ASC mode can be coupled with an active discharge method, allowing current dissipation and a voltage drop in the system. The application of the mode ASC specifically prevents current from passing through the inverter capacitors, and causes a voltage drop in the system, which protects the electronic components of the system, and in particular the inverter capacitors.

[0080] In the so-called "freewheeling" mode, the electronic switches are all in the open state and are not controlled.

[0081] Furthermore, the driver integrated circuit 2 discharges capacitor 5 to reset its voltage to zero. At comparator 8, the voltage at the DESAT terminal of the driver falls below the second voltage threshold Vref. The comparator output goes low, which causes logic-level transistor 9 to switch off.

[0082] Thus, the gate of transistor 1 (power transistor) no longer discharges via the resistance Rsc and it is the control integrated circuit 2 which then controls the gate of transistor 1 to continue the process of opening said transistor 1.

[0083] Regarding the electronic components used in the external circuit 7, the following general design rules can be noted.

[0084] For comparator 8, it is advantageous to use a fast comparator, with fast propagation delays, compatible with the short-circuit withstand of the transistor, preferably less than 500 ns, and more preferably less than 300 ns.

[0085] For the logic level 9 transistor, a MOSFET is preferably used having a low threshold voltage, a peak drain current sufficient to support the gate discharge current through the Rsc resistor, a drain-source voltage greater than the maximum gate voltage and a low gate load.

[0086] For the resistor network, it should be noted that the combination of RL and RH must limit the current injected into the driver. The resistance RL is set according to the desired second voltage threshold, depending on the transistor technology used and the inverter's nominal voltage. The resistance Rsink must limit the current in the comparator and ensure sufficient load for driving the logic-level transistor. The resistance Rsc is chosen such that a compromise is reached allowing the drain-source voltage to remain below a maximum permissible voltage both in the first phase of transistor turn-on, controlled by the external circuit, and during the second phase, in which the driver and microcontroller take over control of the transistor. The resistors used are precisely calibrated, with tight tolerances.

[0087] The device in [Fig. 3] thus proves perfectly effective in providing protection in the event of a short circuit of a MOSFET-type power transistor with a driver integrated circuit 2 that incorporates a DESAT function adapted to IGBTs. Of course, those skilled in the art could consider certain modifications to the external circuit 7 shown in [Fig.3] as an example, in order to achieve the same objective, without going out of the scope of the present invention.

[0088] The effectiveness of this system is illustrated in [Fig.4].

[0089] The Cl to C4 curves represent the same parameters, with the same scales as the Cl to C4 curves of [Fig.2].

[0090] Comparing the results presented with those presented in [Fig.2] (in the absence of the external circuit 7), we note that the behavior of the power transistor has improved in short circuit.

[0091] Thus, as can be seen on the curve C2 from the instant T=3.0 ps, ​​the external circuit causes the voltage between the gate and the source of the transistor Vgs to drop, which corresponds to a control to open the transistor.

[0092] The voltage at the DES AT terminal, corresponding to the curve Cl, continues to increase until it exceeds the first voltage threshold at which the control integrated circuit determines that a short-circuit situation occurs, and takes over to control the opening of the transistor, for example according to a TLTO principle.

[0093] It can be seen that in the example shown in [Fig.4], which is identical to that of [Fig.2] except for the presence of the external circuit 7, the peak current has been limited to 9kA (see curve C4) and the drain-source voltage is reduced by about 15V and does not exceed 95V, which is compatible for example with a transistor that can admit a maximum voltage peak of 100V.

[0094] Consequently, the power semiconductor operates in a safe area.

[0095] The present invention thus enables the use of a driver integrated circuit (or driver) having an integrated short-circuit detection and desaturation function using a first voltage threshold with a transistor requiring a lower detection threshold, while ensuring adequate circuit protection. The typical application is the use of a driver suitable for IGBTs in a high-voltage circuit (e.g., 400V or 800V) with a MOSFET-type transistor in a low-voltage circuit (e.g., 48V).

[0096] To achieve this, the power transistor is first opened in the event of a short circuit by discharging its gate through a low resistance in an external circuit. This allows for rapid short-circuit interruption and limits the current peak. Subsequently, the driver integrated circuit and the system's microcontroller take over and command a controlled opening of the power transistor (for example, by a "two-level tum-off" or "soft tum-off" control).

[0097] Overall, short-circuit detection is improved and overvoltage is attenuated. The drain-source voltage can thus be kept below its maximum nominal value to prevent avalanche breakdown and therefore failure of the power MOSFET.

[0098] In conclusion, the present invention makes it possible to use the same driver reference simple, non-programmable, on several inverter variants, whether the circuit power supply has a nominal voltage of 48V, 400V, or 800V, etc.

[0099] This is particularly advantageous in an industrial context where a range of different inverters is used, for example for an automotive manufacturer, as it allows more components to be common across a range, limits development, makes architectures operating at low voltage more reliable, while limiting the risks of software failures.

Claims

Claims

1. Device for detecting a short circuit in a transistor comprising: a transistor (1) comprising a source (S), a drain (D) and a gate (G), a driving integrated circuit (2) connected to the transistor and configured to detect a short circuit by comparison between a voltage applied to a terminal called the DESAT terminal of the driving integrated circuit (2) and a first predefined voltage threshold, the device being configured so that the voltage applied to the DESAT terminal reflects the voltage between the drain (D) and the source (S), characterized in that the device further comprises an external circuit (7) to the driving integrated circuit (2), the external circuit (7) being configured so that, when the voltage at the DESAT terminal (Vcdesat) exceeds a second voltage threshold, lower than the first voltage threshold, said external circuit (7) causes a drop in the voltage between the gate and the source of the transistor.

2. Device according to claim 1, wherein the DESAT terminal of the integrated driver circuit is connected to the drain of the transistor via a resistor (3) and a diode (4).

3. Device according to claim 1 or claim 2, in which the external circuit comprises a comparator (8) and a logic level transistor (9), arranged so that the comparator compares the voltage at the DESAT terminal (Vcdesat) with the second voltage threshold, and controls the closing of the logic level transistor (9) when the voltage at the DESAT terminal (Vcdesat) exceeds said second voltage threshold.

4. Device according to claim 3, in which the external circuit (7) comprises a resistor (Rsc) and in which when the logic level transistor (9) is on, the gate G of the transistor (1) discharges via said resistor (Rsc) and via the logic level transistor (9), which triggers the opening of the transistor (1).

5. Device according to one of the preceding claims, in which the external circuit (7) comprises a divider bridge which determines the second voltage threshold.

6. Device according to one of the preceding claims, in which the transistor 1 is a MOSFET.

7. Device according to one of the preceding claims, in which the first voltage threshold is between 6V and 9V and in which the second voltage threshold is lower than the first voltage threshold.

8. Device according to claim 7, in which the second voltage threshold is between 2V and 3V.

9. Device according to one of the preceding claims, wherein when a short circuit is detected by said integrated driving circuit (2), the integrated driving circuit controls an opening of the transistor according to a two-level cut-off or progressive cut-off method.

10. Device according to claim 9, comprising a microprocessor for controlling an inverter, in which when a short circuit is detected by the integrated control circuit (2), said integrated control circuit emits a signal to the microprocessor and in which the microprocessor controls the application of a refuge mode of the inverter, namely an active short circuit mode or a freewheel mode.

11. Inverter comprising a device according to one of the preceding claims.

12. Method for protecting a power electronics device comprising a transistor comprising a source (S), a drain (D) and a gate (G), an integrated circuit (2) for driving the transistor comprising a terminal called the DESAT terminal linked to the transistor so that the voltage applied to said DESAT terminal reflects the drain voltage between the drain (D) and the source (S); the method comprising the steps of: - when the voltage at the DESAT terminal exceeds a voltage threshold, called the second voltage threshold, the gate of the transistor is discharged through a resistor in order to lower the voltage between the gate and the source, which triggers an opening of the transistor;then - when the voltage at the DESAT terminal exceeds a voltage threshold, called the first voltage threshold, which is higher than said second voltage threshold, the integrated control circuit commands opening of the transistor according to a two-level cut-off or progressive cut-off method.;

13. Method according to claim 12, in which when the voltage at the DESAT terminal exceeds a voltage threshold a signal is sent by the integrated control circuit to a microcontroller controlling an inverter which then controls the application of a refuge mode of the inverter, namely an active short-circuit mode or a freewheel mode.

Images