Device for detecting a short circuit 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) comprising a source (S), a drain (D) and a gate (G) and a driving integrated circuit (2) configured to detect a short circuit by comparison between a voltage applied to a terminal called the DESAT terminal and 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 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. The invention also relates to the corresponding method. figure for the abstract: figure 3

Description

Title of the invention: Device for detecting a short circuit 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] It is concerned with the detection of the short-circuit phenomenon in transistors in certain power electronic systems, for example inverters, and 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 current between a DC power source and a load (e.g., a motor or power conversion system).

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

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

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

[0007] This can lead to significant malfunctions in the inverter system and, by extension, in the larger 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" (for "desaturation") function which makes it possible to detect whether a short circuit occurs in a bridge arm of the inverter, and to command an appropriate cut-off of the short circuit by appropriately opening the undamaged transistor of the bridge arm. This function is based on a continuous measurement of the currents and / or voltages at the transistor terminals.

[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 predefined threshold. In particular, 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 collector and emitter of the transistor).

[0011] When a short circuit is detected, protective measures are taken. These measures may include opening the relevant transistor, as well as implementing current limiting mechanisms. Thus, the short-circuit current cut-off must be performed more slowly than a cut-off performed during normal operation (in the absence of a short circuit), in order to limit the overvoltage generated during the cut-off. 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 damage to the transistor.

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

[0013] According to a first approach, an external detection and desaturation circuit can be used. In this case, a dedicated circuit, including current measurements and voltage comparators, is added to the system. This circuit actively monitors the electrical signals and reacts when a short circuit is detected. In particular, when a significant voltage appears across a power transistor, this voltage is detected by the external analog circuit, which activates a cut-off circuit to cut the short-circuit current. This cut-off is advantageously carried out 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 for driving the gate (or base) terminal of the transistor. This integrated circuit is sometimes called a “gate driver” or “gate driver” or simply “driver” according to the commonly used English terminology. Thus, some drivers directly integrate the DESAT function. This approach simplifies the process, because the necessary signals are accessible via the driver.

[0015] According to this approach, the driver generally comprises a terminal dedicated to the desaturation function. On this terminal, a voltage representative of the voltage between the drain and the source (or collector and emitter) is read. This voltage is in practice the voltage across a filter capacitor 5, and is reduced compared to the voltage between the drain and the source by a resistor and a blocking diode whose characteristics are predetermined. The voltage at this terminal makes it possible to determine whether a short-circuit situation occurs and whether the cut-off must be controlled according to a controlled desaturation strategy.

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

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

[0018] While the use of a DESAT function is widespread, if not nearly widespread, in systems using IGBT transistors, it is generally absent from systems using MOSFETs. In the case of inverters using MOSFETs, the risk of aggravated short circuit 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 results in complete destruction of the inverter in the event of a short circuit.

[0019] It is nevertheless entirely possible to implement a DESAT function regardless of the type of transistor used, in particular MOSFETs. However, the characteristics of the transistors depend on their technology. For example, MOSFETs and IGBTs have different switching characteristics and different static characteristics, in particular, the direct characteristic (drain current Id as a function of the drain-source voltage Vds) is different in MOSFETs and IGBTs, which justifies a lower protection threshold on 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 increases extremely quickly, but, in certain normal and transient use cases, the current through the IGBT can be two to three times higher than the nominal current of the system, which results in a rise in the voltage across the IGBT. A relatively high voltage threshold must therefore be adopted for the DESAT function associated with IGBTs. This allows reliable detection of a short circuit, while avoiding false detections (false positives).

[0021] MOSFETs, on the other hand, require the use of a much lower voltage threshold. Using a DESAT function adapted to IGBTs on a system comprising MOSFETs would lead to very high currents in the event of a short circuit followed by desaturation, and therefore to 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. If one nevertheless 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 that are generally designed to provide a DESAT function for IGBT type transistors. Thus, in this case, it is necessary either to create a specialized driver, which is expensive and does not make sense in the context of a range of inverters, some of which include 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 fine-tuning time of the driver software in particular).

[0023] Generally speaking, there is no solution allowing the same driver reference to be used in inverters of different technologies, adapted to operate at various voltages such as 48 V, 400 V and 800 V. Statement of the invention

[0024] The present invention aims to remedy all or part of the drawbacks of the state of the art cited above.

[0025] For this purpose, the invention relates to a device for detecting a short circuit in a transistor comprising a transistor comprising a source, a drain and a gate, and a driving integrated circuit 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 and 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 driving integrated circuit, the external circuit being configured so 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 integrated driver circuit, the device according to the present invention allows for desaturation and opening of the transistor in two phases. The opening of the transistor is first carried out by discharging the gate through a low resistance of an external circuit, which lowers the gate current of the transistor and quickly triggers the breaking of the short circuit, even though the voltage at the DESAT terminal of the integrated driver circuit has not reached a first voltage threshold allowing the detection of a short circuit situation. In a second stage, when the drain-source voltage has increased sufficiently so that the voltage measured at the DESAT terminal of the integrated driver circuit reaches said first threshold, the integrated driver circuit indicates to a microcontroller of the system that it detects a short circuit.The control is then carried out conventionally by the integrated control circuit, for example by a controlled command of the opening of the transistor. 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 IC, with a transistor for which it is not normally suitable. Typically, a driver IC whose saturation detection threshold is suitable for IGBTs can thus be used with MOSFETs, while ensuring adequate protection of the system in the event of a transistor short circuit.

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

[0029] The external circuit may comprise a comparator and a logic level transistor, 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 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 on, the gate G of the transistor discharges via the resistor and via the logic level transistor, which triggers the opening of the transistor.

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

[0032] The transistor considered 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 integrated driving circuit (2), the integrated driving circuit can control an opening of the transistor according to a two-level cut-off or progressive cut-off method.

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

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

[0037] The invention finally relates to a method for protecting a power electronics device comprising a transistor comprising a source, a drain and a gate; an integrated circuit 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 and the source, the method comprising the steps of: - when the voltage at the DESAT terminal exceeds a voltage threshold, called second voltage threshold, the transistor gate 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 DES AT 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 using a two-level cut-off or progressive cut-off method.

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

[0039] Other advantages, aims and particular characteristics of the present invention will emerge from the following non-limiting description of at least one particular embodiment of the devices and methods which are the subject of the present invention, with reference to the appended drawings, in which: - [Fig. 1] represents a part of an electrical circuit illustrating a method of detecting a short circuit in a transistor in accordance with the state of the art, using 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 protection integrated into 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.l], according to an embodiment of the invention; - [Fig.4] represents on a graph similar to that of [Fig.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 embodiment.

[0041] [Fig.l] illustrates how the problem of desaturation can be addressed in an inverter according to the state of the art using an integrated control circuit or driver integrating a DESAT function for detecting and processing the short-circuit situation of a transistor.

[0042] The circuit comprises a transistor 1. As this is a transistor equipping an inverter, said inverter generally comprises six transistors for a three-phase inverter. The transistors are then separated into two groups, three transistors on the "low" side, i.e. placed between the ground and the electrical load, for example the motor controlled by the inverter, and three on the "high" side, i.e. placed between the electrical source and the load. 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. Driver integrated circuit 2 has a number of terminals, in this case twenty-two terminals referenced 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 DESAT terminal is dedicated to the detection of a short-circuit situation and to a desaturation function, as explained below.

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

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

[0047] In order to detect such a situation, terminal P15 is here connected to collector C of transistor 1 by a very simple electrical circuit, composed 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 potential of the emitter or source), reflects the voltage measurement 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 terminal DESAT. Generally, the voltage at terminal DESAT corresponds to the voltage between the drain and the source to within a constant (or "offset").

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

[0049] One measure that can be taken by the integrated control circuit then consists of cutting off the short-circuit current using a two-level cut-off method, generally referred to as “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 turning off of switching devices.

[0050] Another solution is to carry out a progressive cut-off, or “soft turn-off”.

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

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

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

[0054] If we consider the device of [Fig. 1] and we 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 Transistor"), which are typically used at a lower nominal voltage than IGBTs, for example 48V, this device generally proves to be inefficient because it is unsuitable. [Fig.2] illustrates this.

[0055] [Fig.2] represents an example of the time evolutions of various voltages and currents in a transistor, obtained experimentally on a MOSFET transistor 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 system U, V, W), with a voltage of the direct current electrical source of the system set to 52V.

[0056] Curve Cl represents the voltage Vcdesat, which is applied to terminal P15 of the integrated driver 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 is the voltage between the drain and source of the transistor. The scale is 20V per division.

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

[0060] We define T=0 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 the first threshold, the protection function is activated. Here, the short-circuit current is detected at T = 3.4ps.

[0062] Nevertheless, a DES AT threshold of the order of 2V to 3 V being 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 time of cut-off, the drain-source voltage, Vds, (curve C3) reaches approximately 110V, and the current flowing through the transistor reaches 11.5kA (curve C4). These values ​​may be beyond the admissible characteristics for the transistor.

[0065] Under these conditions, the MOSFET risks operating in an avalanche zone. As a reminder, an avalanche 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 semiconductor material of the transistor, 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, in 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.l], and thus comprises a transistor 1, an integrated control circuit 2 or driver, a resistor 3, a diode 4, a filter capacitor 5 and a gate driver circuit 6 arranged as explained with reference to [Fig.l].

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

[0071] The circuit shown in [Fig.3] is distinguished from that of [Fig.l] by the presence of an external circuit 7, with respect to the integrated control circuit 2.

[0072] The external circuit 7 aims to trigger an opening command of the transistor as soon as a voltage threshold (second voltage threshold) is reached at the DESAT terminal of the integrated control circuit 2. The second voltage threshold is lower than the first voltage threshold, insofar as it is a question of detecting a short-circuit situation as early as possible in order to protect the transistor. The second voltage threshold can thus be set at approximately 2V, or approximately 3V (while the first voltage threshold is gener- rattling between 6V and 9V, for example here 6V as indicated above).

[0073] In the example of external circuit 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 divider bridge making it possible to set the second voltage threshold Vref.

[0074] When a short circuit occurs in the bridge arm concerned, the drain-source voltage Vds increases. This drain-source voltage is observed - as in the circuit of [Fig.l] - via the circuit comprising the resistor 3 and the diode 4, by observing the voltage Vcdesat measured at terminal P15 of the integrated driver 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 2V (therefore even before the first voltage threshold is reached), the output of the comparator goes to the high state, 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 capacitor Cgs (interposed between the gate and the source) and to discharge the gate of the transistor 1 towards the low state with a low resistance Rsc.

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

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

[0078] The microcontroller then controls the operating mode of the inverter to switch to a “refuge” mode, aimed at protecting the system, for example a mode called “ASC” (according to the English acronym for “Active Short Circuit”) or “freewheeling” (meaning “free wheel”).

[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 so that they allow the passage of a current. The poles of the electrical machine (typically three in number for a three-phase motor) are then in a short-circuit situation. The ASC mode can be coupled with a so-called active discharge means, allowing dissipation of the current and a drop in voltage in the system. The application of the mode In particular, ASC prevents current from flowing through the inverter capacitors, causing 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 integrated driver circuit 2 discharges the capacitor 5 to reset its voltage to zero. At the comparator 8, the voltage at the DESAT terminal of the driver falls below the second voltage threshold Vref. The output of the comparator goes low, which causes the logic level transistor 9 to turn off.

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

[0083] Concerning the electronic components used in the external circuit 7, the following main 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 resistance of the transistor, preferably less than 500 ns, and more preferably less than 300 ns.

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

[0086] For the resistor network, we note that the combination of RL and RH must limit the current injected into the driver. The resistor RL is set according to the second desired voltage threshold, depending on the transistor technology used and the nominal voltage of the inverter. The resistor Rsink must limit the current in the comparator and ensures sufficient charge for the control of the logic level transistor. The resistor Rsc is chosen so that a compromise is obtained allowing the drain-source voltage to remain below a maximum admissible voltage both in the first opening phase of the transistor controlled by the external circuit and during the second phase during which the driver and the microcontroller have taken back control of the transistor control. The resistors used are precisely calibrated, according to small tolerances.

[0087] The device of [Fig.3] thus proves to be perfectly effective in ensuring a protection function in the event of a short circuit of a MOSFET type power transistor with an integrated control circuit 2 which integrates a DESAT function adapted to IGBTs. Obviously, the person skilled in the art could envisage certain modifications of the external circuit 7 presented in [Fig.3] as an example, in order to achieve the same objective, without departing from the scope of the present invention.

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

[0089] Curves C1 to C4 represent the same parameters, with the same scales as curves C1 to C4 in [Fig.2].

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

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

[0092] The voltage at terminal DES AT, corresponding to curve Cl, continues to increase until it exceeds the first voltage threshold at which the integrated control 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 approximately 15V and does not exceed 95V, which is for example compatible with a transistor capable of admitting a maximum voltage peak of 100V.

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

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

[0096] To this end, the power transistor is opened in the event of a short circuit first by discharging the gate through a low resistance of an external circuit, which makes it possible to quickly trigger the breaking of the short circuit and limit the current peak. Then, the integrated control circuit and the microcontroller of the system take back control and command a controlled opening of the power transistor (for example by control according to a “two level tum-off” or a “soft tum-off”).

[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 avoid avalanche and therefore breakdown of the power MOSFET.

[0098] Ultimately, 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 advantageous in particular in an industrial context where a range of different inverters is used, for example for a car manufacturer, in that it makes it possible to make more components common across an entire range, to limit developments, to make 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.

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