Switch device and electric heating device comprising the switch device

Abstract

Switching device (10), comprising: a power transistor (50, 52) with a gate terminal (G1, G2), a collector or drain terminal (K1, K2) and an emitter or source terminal (E1, E2); a voltage source (34, 36) which is configured to supply a supply voltage to a transition between the gate terminal (G1, G2) and the emitter or source terminal (E1, E2); a device (22, 26) for measuring a voltage that is established between the gate terminal (G1, G2) and the emitter or source terminal (E1, E2) depending on a state of the power transistor (50, 52), or for measuring a gate current through the gate terminal (G1, G2) that depends on the state of the power transistor (50, 52); wherein the device (22, 26) for measuring a voltage or for measuring a gate current outputs a corresponding measurement signal (70, 71) to a control unit (12); the control unit (12) which is configured to compare the measurement signal (70, 71) with a reference (72) and, depending on the comparison result, to output at least one status signal (75); characterized by the fact that the status signal (75) indicates that there is a short circuit on a path between the collector or drain terminal (K1, K2) and the emitter or source terminal (E1, E2); and the device (22, 26) is configured to perform the measurement of the voltage or gate current and / or to generate the measurement signal (70, 71) corresponding to the measured voltage or gate current without applying a high-voltage voltage between the collector or drain terminal (K1, K2) and the emitter or source terminal (E1, E2).

Description

Technical field

[0001] Several aspects concern a switching device that includes a power transistor which is switched on and off during normal operation, as well as an electric heating device for a vehicle that incorporates such a switching device to switch one or more heating resistors. These aspects particularly include fault diagnosis with regard to the power transistor(s). Technical background

[0002] It is known that electrical devices, such as electric heaters (so-called high-voltage heaters), etc., have a (power) semiconductor switch that controls the operation of a load, for example, a heating element or an electric motor. Without limiting generality, the voltage applied to the respective load can be a clocked control or pulse-width modulation. Such semiconductor switches are typically implemented as IGBTs (insulated-gate bipolar transistors) or as power MOSFETs (metal-oxide-semiconductor field-effect transistors).

[0003] However, if a short circuit occurs on the side of the consumer in question in the semiconductor switch, this switch or such switching elements arranged in the current path may themselves be damaged.

[0004] One solution is therefore to check the semiconductor switch for a fault, such as a short circuit. In the case of the IGBT, the critical condition is a short circuit between the collector and emitter. For this purpose, current or voltage measurements are taken at the semiconductor switch or at the overall system in which the switch is integrated. In particular, a voltage is typically applied between the collector and emitter, and it is checked whether a current flows or whether the applied voltage collapses depending on the impedance.

[0005] The fault condition can therefore only be verified if the required collector-emitter voltage is applied externally or generated within the device in question, which is comparatively complex. However, there is a risk that the applied or generated voltage will be fed back into a power supply network, such as a vehicle's electrical system, which must be strictly avoided. This could potentially lead to further faults in other devices, for example, within the vehicle's electrical system.

[0006] German patent application DE 10 2015 204 343 A1 describes a device for determining a switch state. As damage to a gate oxide increases, the voltage waveform between a gate terminal and an emitter terminal of a semiconductor-based switch also changes increasingly during a switching operation. It was specifically recognized there that the degree of deviation between a measured voltage waveform and a reference signal can be interpreted as a measure of damage to the switch assembly. A voltmeter is therefore configured to measure a voltage waveform between the gate and the emitter of an IGBT and convert it into a measurement signal that can be compared with a stored reference signal. A voltage is applied between the collector and the emitter of the IGBT during this process.A characteristic feature here is a so-called Miller plateau in the voltage waveform during the switching process, the duration and / or amplitude of which can change with increasing operating time (due to aging or damage). A processing unit can determine and compare this information from the signals. Overall, this allows predictions to be made that a switch failure due to a bond wire detaching or the component detaching from a base plate is imminent after the remaining operational readiness has elapsed.

[0007] US patent 10,700,678 B2 discloses a gate driver circuit for a power semiconductor element. To detect a hard-switching fault or a short circuit in the power semiconductor element, a voltage signal applied to the gate of the power semiconductor element is detected, and a reference signal, obtained by delaying the voltage signal (e.g., using an RC circuit), is subtracted from it. If the resulting difference exceeds a threshold, a short circuit is inferred. The voltage potential applied to the gate is detected when a voltage is applied between the collector and emitter.

[0008] In US 2021 / 099167A1, a gate driver system is disclosed in which a current reconstruction circuit is set up to receive a voltage across an inductance associated with an IGBT (e.g., in particular due to the bond wires connected to the IGBT) as well as a PWM signal controlling the gate of the IGBT and outputs a value for the collector current I determined by integration. CE to be provided. This is supplied with a maximum permissible collector current I CE,max The results of the comparison indicate a short-circuit state of the IGBT, and the gate terminal is controlled to a low potential.

[0009] CN 117 783 934 A describes a test procedure and apparatus for evaluating the short-circuit withstand capability of a MOSFET. The apparatus comprises a DC voltage source, a drive current supply, a capacitor, a resistor, an inductor, and a MOSFET. The test procedure includes the steps of measuring parameters such as the short-circuit current, drain-source voltage, and gate-source voltage of the MOSFET; controlling the MOSFET to switch off at different currents to obtain corresponding waveforms; recording and analyzing the short-circuit waveforms; and assessing the fault condition of the MOSFET.

[0010] In JP 2003 - 218 358 A a test method is described for checking for short circuits between a gate and a source of a TFT liquid crystal display while simultaneously checking the corrosion of the gate wiring.

[0011] Consequently, there is a need for a switching device that includes a circuit breaker, as well as a corresponding method for controlling the circuit breaker, which avoids the aforementioned disadvantages and, in particular, prevents the unintentional backfeed of a voltage applied to determine a short circuit into a supply network, e.g., the vehicle's electrical system. Presentation of various aspects

[0012] Aspects of the invention that can address such needs relate to a switching device comprising a power transistor, a voltage source, a measuring device for measuring a voltage that is established at a gate terminal depending on a state of the power transistor, or for measuring a gate current through the gate terminal that depends on the state of the power transistor, and a control unit. The power transistor has a gate terminal, a collector or drain terminal, and an emitter or source terminal, depending on whether it is, for example, an IGBT (insulated gate bipolar transistor) or a power MOSFET. Simple bipolar transistors or MOSFETs are also included.

[0013] The voltage source is configured to supply a voltage to a junction between the gate terminal and the emitter or source terminal. The voltage source can be formed arbitrarily, for example, by the terminals of a transformer in a DC / DC converter. Other voltage sources—such as those formed by an AC / DC converter—are equally possible, and the invention is not limited to the precise configuration.

[0014] The voltage measured by the measuring device according to an alternative method may differ from the supply voltage of the voltage source, particularly if the power transistor is damaged and / or degraded due to aging. However, other components such as series resistors or diodes, etc., may also be present in the current path, which can cause the measured voltage to differ from the supply voltage even under normal operating conditions.

[0015] If a short circuit occurs on a path between the collector or drain terminal and the emitter or source terminal, this also has a direct or indirect effect on the path between the gate terminal and the emitter or source terminal in an analogous manner; that is, this path also becomes low-impedance, so that the voltage potential applied to the gate terminal approaches or drops to the reference potential. Typically, such short circuits are a very rapid process that can be completed within a few clock cycles (for example, less than 10 ms at 1 kHz). Such a situation can be detected by measuring the voltage. The same applies if the measuring device is configured to measure the gate current.Due to the power supply provided by the voltage source, in the event of a short circuit the input impedance of the power transistor changes and the gate current increases dramatically, which is detected by the measuring device.

[0016] The measuring device for measuring voltage or gate current now outputs a corresponding measurement signal to the control unit, which evaluates the signal. This evaluation involves comparing the measurement signal with a reference. The measurement signal and the reference can be, for example, a simple voltage value or a current value, in analog or digital form. A time-varying measurement signal (voltage curve) or reference signal is also possible. Furthermore, the measurement signal and the reference can also contain values ​​derived (calculated) from a voltage value. The reference can be read from memory, supplied to the control unit in another way, or already stored within the control unit.

[0017] The control unit, in turn, outputs at least one status signal, depending on the comparison result. A key characteristic of this aspect is that the status signal indicates a short circuit on a path between the collector or drain terminal and the emitter or source terminal. The "display" of the status signal means that receivers of the signal are configured to interpret the short circuit on the gate-emitter path as corresponding to a short circuit on the collector-emitter path. In other words, the status signal describes the state of the power transistor (e.g., damaged or functioning).A special feature here is that the device is set up to perform the measurement of the voltage or gate current and / or to generate the measurement signal corresponding to the measured voltage or gate current when no voltage, or in particular before a voltage is applied, is present between the collector or drain terminal and the emitter or source terminal.

[0018] According to this aspect, a fault condition or the absence of a short circuit between collector and emitter (or source) is therefore not directly checked by applying a voltage between collector and emitter, but by a further fault (short circuit gate - emitter) that occurs or accompanies the fault (short circuit collector - emitter).

[0019] When a collector-emitter short circuit occurs, a short circuit or low-resistance behavior of the gate-emitter junction also occurs in over 99% of all cases with IGBTs. The cause can be found, for example, in the internal structure of the IGBT. A defect between the collector and the emitter of the device propagates rapidly, so that even if the defect is not directly at the gate, the gate structure, which is typically arranged in a grid or line pattern across a silicon chip, is affected very quickly.

[0020] Aspects of the invention utilize this effect by transferring the measurement to the gate side of the power transistor. Therefore, an additional voltage no longer needs to be applied to the collector-emitter junction (or drain-source junction). This eliminates the possibility of unintentional and potentially damaging backfeed of the additional voltage to components or switching elements of a high-voltage power supply – for example, in a vehicle.

[0021] The invention therefore has a particularly positive effect on purely electric or hybrid vehicles. Purely electric or hybrid vehicles are currently gaining increasing importance in road traffic. Unlike conventional vehicles with fuel-powered engines, where the electrical system is supplied exclusively by 12-volt lead-acid batteries, electric vehicles use vehicle batteries as energy storage devices. These allow operation at higher voltages and, consequently, the higher power consumption of electrical components makes propulsion possible in the first place.

[0022] For larger electrical consumers with power consumption of, for example, 3 kW and more, such as start-stop functions (including recuperation), electrically operated air conditioning compressors and heaters, etc., the 48-volt level has been used for some time. In contrast, the high-voltage level is used in the electrical system architecture of purely or hybrid electric vehicles, which have significantly larger components (e.g., greater than 12 kW). In the automotive sector, electrical system voltages of 250–800 V are common. A value of 60 V, for example, is considered the lower limit for the high-voltage range (see "Voltage Classes in Electromobility," published by the German Electrical and Electronic Manufacturers' Association (ZVEI), Frankfurt, December 2013).

[0023] However, problems can arise, particularly in this high-voltage operation, if the vehicle battery in an electric vehicle is connected to the drive system without further measures. This is because, due to the lack of relevant resistance in this situation, a sudden and very high current flow would occur. The switching elements within the vehicle battery are directly exposed to such a strong current and can be damaged as a result, especially since they are not designed for this type of stress over extended periods.

[0024] One measure to prevent this has so far involved installing a pre-charge resistor in the vehicle battery system. This resistor charges, for example, a filter capacitor in an intermediate circuit to 90 to 95% of its nominal voltage. Then, via appropriately configured switching elements or a relay, the pre-charge resistor is bypassed, and the battery voltage is supplied directly to the consumers or loads in the vehicle's electrical system. This process can take several hundred milliseconds. Overall, the pre-charge resistor raises the applied voltage to the nominal voltage over a predetermined period.

[0025] In such electrically powered vehicles, voltage adjustment via a pre-charge resistor takes place in a phase shortly after battery start-up. The test measurement according to the invention can be carried out to a great advantage during or before this phase, without the risk of damage to the vehicle battery or pre-charge circuit in the event of a short circuit, thus avoiding the costly replacement of these components.

[0026] It should be noted that aspects of the invention can also be advantageously applied to electric heaters, such as those used in fuel-powered vehicles at lower load voltages, etc. In principle, the invention can also be used in many other applications where power transistors are implemented, and the invention is not limited to the applications described above and below.

[0027] In a specific embodiment, the measuring device is configured to measure a voltage potential, with a series resistor assigned to the gate terminal. In this case, the voltage potential is measured at a junction between the series resistor and the gate terminal. The control unit is configured to use the reference potential or a reference voltage as a benchmark, providing a meaningful limit for comparison. If a short circuit or a very low-resistance connection exists between the gate and emitter terminals, the measured voltage potential drops to the value of the reference potential or at least approaches it very closely.

[0028] According to an alternative embodiment, the measuring device is configured to measure a gate current, with the control unit configured to use a short-circuit current as a reference for comparison. If the gate current is determined via a potential, voltage, or current measurement across a shunt resistor (where the branch point is located between the shunt resistor and the voltage source), the reference depends on the shunt resistor. Other implementations of the current measurement are also possible.

[0029] According to a further development of the switching device in accordance with the above aspects, it also includes a first switching unit configured to switch the voltage supply potential of the voltage source to the gate terminal depending on an enable signal from the control unit. This enables the start of the test measurement. Similarly, after evaluating the measurement signal, the control unit can also terminate the activation or the test measurement.

[0030] Based on this, the control unit can be configured to receive a battery start signal, particularly from an external vehicle electrical system module or a battery management system of a vehicle battery, especially via digital communication over a vehicle bus (communication bus, e.g., LIN or CAN, etc.). Such a signal can indicate to the control unit that a high-voltage voltage is about to be applied to the path between the collector or drain terminal and the emitter or source terminal.

[0031] According to this design, the control unit is configured to output the enable signal to the first switch unit depending on the received battery start signal. In other words, the test measurement for damage to the power transistor can be started before the collector-emitter junction is energized. This prevents a sudden surge of large current in the event of a short circuit, which could damage components in the vehicle battery or the pre-charging circuit.

[0032] According to further training, the control unit is configured to output the status signal via the communication bus to the vehicle electrical system and / or the battery management system. This allows, for example, measures to be initiated on the vehicle battery side to protect the relevant components.

[0033] According to another embodiment, a second switching unit can be provided, which is configured to receive a control signal from the control unit during normal operation and, depending on the control signal, to supply the gate terminal with the voltage supply potential of the voltage source, preferably by pulsed or periodic actuation of an internal switch. This corresponds to the normal operation of the power transistor. Some embodiments provide that the first and second switching units are combined.

[0034] Another aspect of the invention provides for an electric heating device comprising the switching device according to the aspects, embodiments, or further developments mentioned above. The switching device has two power transistors, namely a first low-side power transistor and a second high-side power transistor, which are connected in series with one or more intermediate heating resistors with respect to their paths between the collector or drain terminal and the emitter or source terminal. During operation, the power transistors are switched by pulse-width modulation (PWM) to achieve the desired heating effect.

[0035] Each of the two power transistors is assigned a voltage source, a measuring device for measuring a voltage potential or for measuring a gate current to generate a measurement signal which is received by the control unit, and a second switching unit, each of which is set up to be controllable by a control signal.

[0036] The status signal generated by the control unit additionally indicates whether the short circuit is present on a path between the collector or drain terminal and the emitter or source terminal of the low-side transistor, or on a path between the collector or drain terminal and the emitter or source terminal of the high-side power transistor. In other words, the status signal identifies which of the two power transistors is defective or damaged.

[0037] However, it is not absolutely necessary to test both the high-side and low-side power transistors by measuring voltage or current. It is also possible, for example, to diagnose only the low-side transistor. This already ensures that no undesirably high current is flowing. The high-side power transistor could then be tested with the applied high voltage. This approach has the advantage that testing the high side might be more technically complex, thus reducing the overall effort.

[0038] In this case, depending on the status signal, the control unit generates a control signal for the power transistor not affected by that status signal, such that its internal switch is permanently open to switch off the corresponding power transistor. This applies to a normally off power transistor. In the special case where normally conducting power transistors are used, the corresponding internal switch is closed.

[0039] This aspect has the particular advantage that, for the continued operation of the vehicle under high voltage, the short circuit of one power transistor can remain without consequences, since no current can flow through the collector-emitter paths.

[0040] Overall, the aspects of the invention offer a simple and cost-effective way to test IGBTs or power MOSFETs without applying a corresponding high-voltage voltage. Accordingly, this also results in no feedback to the vehicle.

[0041] Further advantages, features, and details of the various aspects will become apparent from the claims, the following description of preferred embodiments, and the drawings. In the figures, identical reference numerals denote identical features and functions. Brief description of the drawings

[0042] They show: Fig. 1 a simple circuit diagram of a switching device according to a first embodiment of the present invention; Fig. 2 a simple circuit diagram of a switching device according to a second embodiment of the present invention; Fig. 3: an overview of an embodiment of an electric heating device in an electrically powered vehicle comprising a switch device similar to that in Fig. 1; Fig. 4 A system diagram of the electronics in an electrically powered vehicle. Preferred embodiment(s) of the invention

[0043] In the following description of a preferred embodiment, it should be noted that the present disclosure of the various aspects is not limited to the details of the construction and arrangement of the components as illustrated in the following description and in the figures. All embodiments, including those not shown in the figures, can be implemented or carried out in practice in various ways. Furthermore, it should be noted that the language and terminology used here are employed solely for the purpose of concrete description and should not be interpreted restrictively by those skilled in the art.Furthermore, in the following description, identical reference symbols in the figures denote identical or similar features or objects, so that in some cases a repeated detailed description of the same is omitted in order to preserve the compactness and clarity of the presentation.

[0044] In the Fig. Figure 1 shows a simple, highly schematic circuit diagram of a switching device 10 according to a first embodiment of the present invention. A voltage source 34, for example a DC / DC converter, supplies a DC voltage of, for example, 15 V (supply voltage potential versus reference potential). A measuring device 22 is configured to measure a voltage potential applied to a gate terminal G1. For this purpose, the measuring device is connected to a branch through which a gate terminal G1 of a power transistor 50—in this example a normally-off n-channel IGBT—is connected to the terminal of the voltage source 34 that provides the supply voltage potential. An ohmic series resistor 28 is connected in the branch, and the tap point to the measuring device is located between the series resistor and the gate terminal G1.

[0045] The power transistor 50 also has a collector terminal K1 and an emitter terminal E1. During operation of the in Fig. In the switch device shown in Figure 1 for measuring the voltage potential applied to the gate terminal G1, there is no voltage between the collector terminal K1 and the emitter terminal E1 (in particular, no high-voltage voltage is applied).

[0046] If the power transistor 50 is undamaged, a corresponding voltage drop occurs across the gate-emitter junction between the gate and emitter terminals. If, however, the power transistor 50 is damaged, a short circuit may occur across this junction. In this case, the voltage drop is essentially across the series resistor 28, and the measuring device 22 will detect a voltage potential close to the reference potential. The series resistor 28 has a low resistance value, so that, in the case of an undamaged power transistor 50, a voltage potential very close to the supply voltage potential (here 15 V) is obtained.

[0047] The measuring device generates a measurement signal 70 based on the detected voltage potential, which it feeds to an evaluation unit 12a of a control unit 12. The evaluation unit 12a compares the measurement signal 70 with a reference stored within it. For example, the reference corresponds to a value of the reference potential (0 V) plus a tolerance. If the voltage potential corresponding to the measurement signal 70 falls below this value, a short circuit or damage to the gate-emitter junction is inferred, and consequently, damage or a short circuit to the collector-emitter junction is also inferred. Accordingly, the evaluation unit 12a generates a status signal 75 and feeds it to an interface unit 12b of the control unit 12. This unit can then perform further actions, in particular send warning or control signals to protect the components associated with the switching unit.

[0048] In Fig. Figure 2 shows a similar simple circuit diagram of a switching device according to a second embodiment of the present invention. To avoid repetition, we will only point out the differences compared to the first embodiment. Fig. 1. In the branch between the voltage source 34 and the gate terminal G1 of the power transistor 50, a measuring device 22 for measuring a gate current is connected. In the event of a short circuit on the gate-emitter junction, the gate current increases considerably and is limited only by the output resistance of the voltage source, a low-resistance residual (input resistance of the low-resistance path) on the gate-emitter junction, and / or, if a shunt resistor is used for current measurement, by the shunt resistor itself. As described above, the measuring device 22 generates a measurement signal 70 from this, which is compared in the evaluation unit 12a with a reference that is calculated and stored beforehand from the information above.If the gate current associated with the measurement signal 70 exceeds this reference value, or comes close to it within a specified tolerance, the status signal 75 is generated, indicating that there is a short circuit on a path between the collector or drain terminal (K1, K2) and the emitter or source terminal (E1, E2), and is output to the interface unit 12b, which can initiate or take protective measures as described.

[0049] It should be emphasized that even in this embodiment, the detection of a short circuit on the gate-emitter path indicates damage to the collector-emitter path.

[0050] In Fig. Figure 3 is an overview of an embodiment of an electric heating device in an electrically powered vehicle comprising a switch device 10 similar to that in Fig. 1 shown. Fig. Figure 4 shows a system diagram illustrating the basic structure of the relevant electronics in the vehicle. The following explanations build upon the above description of the Fig. Turn off 1 to avoid repetitions.

[0051] The electric heating device is a high-voltage heater. The switching device 10 comprises two power transistors 50, 52, namely a low-side power transistor 50 and a high-side power transistor 52, whose collector-emitter paths (collector terminals K1, K2, emitter terminals E1, E2) are connected in series with one or more intermediate heating resistors 40.

[0052] The gate terminals G1 and G2 of both power transistors 50 and 52 are supplied with power by their respective voltage sources 34 and 36, which are pulsed during normal operation by second switching units 30 and 32 (pulse width modulation, PWM). This allows the heating resistors 40 to be switched with the desired power when a high-voltage voltage is applied. The second switching units 30 and 32 are controlled by a control unit 12. The control unit 12 can be configured as described in the Fig. 1 and Fig. 2 shown, set up as shown. Fig. 3 indicates the status signal 75 that is internally output to the interface unit 12b.

[0053] The switch unit 10 further has separate measuring devices 22, 26 for each power transistor 50, 52, which detect the voltage potential applied to the corresponding gate terminal G1, G2 (the series resistors 28 are as if with bend to the Fig. (as described in 1) and generate separate measurement signals 70 and 71 from each of these and transmit them to the control unit 12. This can be done in an analog or digital manner.

[0054] The control unit 12 reads a reference 72 from a memory 14 and compares it with the two measurement signals 70, 71. If one of the two measurement signals 70, 71, whose content can be the measured value of the voltage potential, lies within a predefined range of the value according to the reference, the control unit generates a status signal depending on this comparison. Fig. Figure 3 shows some possibilities for status signal 75, one of which was described above (internal status signal to the interface). Furthermore, it is also possible to send the status signal 75 externally for diagnostic purposes, for example during maintenance ( Fig. 3 below).

[0055] Furthermore, it is possible for the status signal 75 to be sent from the control unit via a communication or vehicle bus to an on-board power supply module 80 to indicate the short circuit and to initiate protective measures in the area of ​​the vehicle battery unit 90. For this purpose, the on-board power supply module can send information to a battery management system 91, which can, for example, actuate main contactors 95, 97 and / or a pre-charge contactor 96 to prevent or disconnect a high-voltage supply from the vehicle battery 92 in order to protect individual components and switching elements.

[0056] Conversely, the on-board power supply module 80 can send a battery start signal 76 to the control unit 12 to indicate that the high-voltage voltage, pre-adjusted via the pre-charge resistor 93, is about to be applied. Based on the battery start signal 76, the control unit 12 generates a test or enable signal 77, which is transmitted to the first switching units 20 and 24, each corresponding to the power transistors 50 and 52. These then switch the voltage supply potential provided by the voltage sources 34 and 36 to the measuring devices 22 and 24 at the gate terminals G1 and G2, respectively, so that the voltage potential measurement, as described above, is enabled and can be carried out. At this point, the high-voltage voltage is not yet applied. There is still no voltage across the collector-emitter junctions.

[0057] If the control unit 12 determines during the comparison that there is no damage to the power transistors, it can, for example, transmit a corresponding positive status signal to the on-board power supply module so that the battery start procedure can continue.

[0058] If the control unit 12 detects that one of the power transistors 50, 52 is damaged (inference from short circuit on gate-emitter path to short circuit on collector-emitter path as described above), it can generate the internal status signal, whereupon a control signal 73 or 74 is transmitted to the second switching unit 30 or 32 of the respective other, undamaged power transistor, with which this power transistor is switched off.

[0059] The Fig. Figure 4 shows a further abstracted system block diagram, in which the present embodiment and in particular also the one in Fig. 3. Overview given. A higher-level control unit 100 is embedded via a vehicle bus 200 with several high-voltage electrical components of the vehicle, in particular a battery control unit 130, a traction inverter 150, a high-voltage heater 160, which includes the electric heating device, a DC / DC converter 170, and an on-board charger 180. Via the vehicle bus 200, the higher-level control unit, which is connected to the on-board power supply module 80, signals Fig.3 corresponds, for example, to the battery control unit 130, that all the aforementioned high-voltage components are operational, so that the battery control unit can initiate a pre-charge of the high-voltage circuit. The battery control unit 130 is part of the high-voltage battery box 110, which also includes electronics 120 comprising high-voltage contactors, pre-charge electronics, and a main battery fuse. These electronics 120 are connected via high-voltage lines 300 to a power distribution box 140, a distribution box with fuses, from which the individual high-voltage components, including the HV heater with the electric heating device described here, are supplied with HV power. REFERENCE MARK LIST: 10 Switch device 12 Control unit 14 storage 20 first switch unit 22 Measuring device 24 first switch unit 26 Measuring device 28 Series resistor 30 second switch unit 32 second switch unit 34 Voltage source 36 Voltage source 40 heating resistor 50 low-side power transistor 52 high-sided power transistor 70 Measurement signal 71 Measurement signal 72 Reference 73 Control signal 74 Control signal 75 Status signal 76 Battery start signal 77 Release signal 80 On-board power supply module 90 Vehicle battery unit 91 Battery Management System 92 Vehicle battery 93 Pre-charge resistor 95 Main Gunner 1 97 Main Gunner 2 96 Loading guard 100 higher-level control unit 110 High-voltage battery box 110 120 Electronics 130 Battery control unit 140 Power Distribution Box, Distributor 150 traction inverters 160 HV heater 160, comprising the electric heating device 170 DC / DC converter 180 On-board chargers 200 vehicle buses (LIN, CAN) 300 high-voltage lines

Claims

[1] Switching device (10), comprising: a power transistor (50, 52) with a gate terminal (G1, G2), a collector or drain terminal (K1, K2) and an emitter or source terminal (E1, E2); a voltage source (34, 36) which is configured to supply a supply voltage to a transition between the gate terminal (G1, G2) and the emitter or source terminal (E1, E2); a device (22, 26) for measuring a voltage that is established between the gate terminal (G1, G2) and the emitter or source terminal (E1, E2) depending on a state of the power transistor (50, 52), or for measuring a gate current through the gate terminal (G1, G2) that depends on the state of the power transistor (50, 52); wherein the device (22, 26) for measuring a voltage or for measuring a gate current outputs a corresponding measurement signal (70, 71) to a control unit (12); the control unit (12) which is configured to compare the measurement signal (70, 71) with a reference (72) and, depending on the comparison result, to output at least one status signal (75); characterized by , that the status signal (75) indicates that there is a short circuit on a path between the collector or drain terminal (K1, K2) and the emitter or source terminal (E1, E2); and the device (22, 26) is configured to perform the measurement of the voltage or gate current and / or to generate the measurement signal (70, 71) corresponding to the measured voltage or gate current without applying a high-voltage voltage between the collector or drain terminal (K1, K2) and the emitter or source terminal (E1, E2). [2] Switching device (10) according to claim 1, wherein the power transistor (50, 52) is an IGBT or a power MOSFET. [3] Switching device (10) according to claim 1 or 2, wherein the device (22) is set up to measure a voltage, wherein a series resistor (28) is associated with the gate terminal (G1, G2), wherein the voltage is measured at a branch point between the series resistor (28) and the gate terminal (G1, G2), wherein the control unit (12) is configured to use a reference potential or a reference voltage as a reference (72) to be compared. [4] Switching device (10) according to claim 1 or 2, wherein the device (22) is configured to measure a gate current, wherein the control unit (12) is configured to use a short-circuit current as a reference (72) for comparison. [5] Switching device (10) according to any one of claims 1 to 4, wherein the device (22, 26) further comprises: a first switching unit (20, 24) which is configured to switch the supply voltage of the voltage source (34, 36) to the gate terminal (G1, G2) depending on an enable signal (77) of the control unit (12). [6] Switching device (10) according to claim 5, wherein the control unit (12) is configured to receive a battery start signal (76) indicating an impending application of a high-voltage voltage to the path between the collector or drain terminal (K1, K2) and the emitter or source terminal (E1, E2); and the control unit is set up to output the enable signal (77) to the first switch unit (20) depending on the received battery start signal (76). [7] Switching device (10) according to claim 6, wherein a communication bus, preferably a LIN bus or a CAN bus, is provided which connects the control unit (12) to an on-board power supply unit (80) and / or to a battery management system (91), wherein the control unit (12) receives the battery start signal (76) via the communication bus. [8] Switching device (10) according to claim 7, wherein the control unit (12) is configured to output the status signal (75) via the communication bus to the on-board power supply unit (80) and / or the battery management system (91). [9] Switching device (10) according to one of the preceding claims, wherein a second switching unit (30, 32) is provided which is configured to receive a control signal (73, 74) from the control unit (12) during normal operation, and depending on the control signal, to supply the gate terminal (G1, G2) with the supply voltage of the voltage source (34, 36), preferably by periodically actuating an internal switch. [10] Electric heating device comprising the switching device (10) according to claim 9, wherein the switching device (10) comprises a first low-side power transistor (50) and a second high-side power transistor (52), which are connected in series with one or more intermediate heating resistors (40) with respect to their paths between the collector or drain terminal (K1, K2) and the emitter or source terminal (E1, E2), wherein each of the two power transistors (50, 52) is associated with a voltage source (34, 36), a device (22, 26) for measuring a voltage potential or for measuring a gate current to generate a measurement signal (70, 71) which is received by the control unit (12), and a second switching unit (30, 32) which is each configured to be controllable by a control signal (73, 74); wherein the status signal (75) generated by the control unit (12) additionally indicates whether the short circuit is on a path between the collector or drain terminal (K1) and the emitter or source terminal (E1) of the low-side transistor or on a path between the collector or drain terminal (K2) and the emitter or source terminal (E2) of the high-side power transistor, wherein the control unit (12) depending on the status signal (75) with regard to the corresponding power transistor (50, 52) not affected by the status signal, generates the control signal (73, 74) such that the internal switch is permanently open in order to switch off the corresponding power transistor.

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