Semiconductor switch having failure protection

Abstract

Proposed is a semiconductor switch that is formed with a multiplicity of series-connected circuit modules. The circuit modules each comprise: a first transistor (M3) having a source terminal (source3), a control terminal (Gate3) and a drain terminal; and a second transistor (Q2) having a source terminal, a control terminal and a drain terminal. The source terminal of the second transistor (Q2) is connected to the control terminal (Gate3) of the first transistor (M3), and the drain terminal of the second transistor (Q2) is connected to the source terminal (source3) of the first transistor (M3). Also provided is a driver (V2) that is connected via connections to the control terminals of the second transistors (Q1, Q2, Q3, Q4, Q5, Q6) of the individual circuit modules. The semiconductor switch is designed such that, in the event of a malfunction of one of the circuit modules, it interrupts or deactivates the connection between the control terminal of the second transistor (Q2) of the malfunctioning circuit module and the driver (V2).

Description

[0001] Description

[0002] Semiconductor switch with fail-safe protection

[0003] The invention relates to a semiconductor switch.

[0004] Advances in the development of semiconductor components have led to new switch concepts that can replace conventional, typically electromechanical switches used in low-voltage technology. These new concepts relate to, for example, circuit breakers or motor starters, but can in principle also be used for switching higher currents, e.g. using power switches. Of key importance here are the fast response times of the semiconductor components, which prevent damage caused by overload. This means that the switch switches off the current before the semiconductor components can be destroyed. Nevertheless, given the greater sensitivity of semiconductor components compared to conventional switching elements, it can still happen that the semiconductor-based switching mechanism becomes damaged and the switch no longer functions properly.It is desirable that in such situations there is a safeguard that protects the user against the consequences of such damage or limits them.

[0005] The object of the invention is to provide a semiconductor switch with failure protection.

[0006] This object is achieved by a semiconductor switch according to claim 1. Advantageous further developments are specified in the subclaims.

[0007] The term "semiconductor switch" refers to a device for switching current in which a current path is guided via at least one semiconductor component (typically a transistor) and can be interrupted by means of the semiconductor component. Such semiconductor switches are often also formed with galvanic isolation, which is usually prescribed by a standard; however, the interruption of the current path is always also carried out by at least one semiconductor component. Designs for such semiconductor switches include, for example, circuit breakers, power switches and motor starters in low-voltage technology.

[0008] The semiconductor switch according to the invention is formed with a plurality of circuit modules connected in series. These each comprise a first transistor with a source terminal, a control terminal and a drain terminal, wherein the source terminal is a source terminal or an emitter terminal, the control terminal is a gate terminal or a base terminal and the drain terminal is a drain terminal or a collector terminal. In addition, the circuit modules are formed with a second transistor which has a source terminal, a control terminal and a drain terminal, wherein the source terminal is connected to the control terminal of the first transistor and the drain terminal is connected to the source terminal of the first transistor. In addition, the semiconductor switch comprises a driver or a driver circuit (preferably only a single driver or a single driver circuit).This driver is connected via connections to the control terminals of the second transistors of the individual circuit modules.

[0009] The semiconductor switch is designed to interrupt the connection between the control terminal of the second transistor of the malfunctioning circuit module and the driver or to switch itself off autonomously in the event of the failure of one of the circuit modules. Here and in the following, "or" is not to be understood as an exclusive "or" unless explicitly stated. Specifically, this means that in one embodiment it would be possible for the semiconductor switch to both interrupt the connection between the control terminal of the second transistor of the malfunctioning circuit module and the driver and to switch itself off in order to guarantee an increased level of safety.

[0010] In the case of a malfunction of a power electronic semiconductor, one of two error states can typically be assumed. The semiconductor is either high-resistance and no longer controllable, or - and this is the most common case - it is low-resistance and no longer controllable: the switch has broken down. In the second case, there is usually a short circuit between all three terminals of the semiconductor or transistor, i.e. the gate has a low-resistance connection to drain and source (in the case of an FET) or collector and emitter (in the case of an IGBT). In this case, the entire parallel circuit is short-circuited and the semiconductor switch can no longer be controlled in the on state (low resistance between drain and source). This condition is a serious error, especially if the semiconductor switch is to be used as a protective element. The term "malfunction" refers in the narrower sense to this condition.The semiconductor switch can also be further developed to react to other malfunctions, e.g., high-impedance conditions. Although this rarely occurs, it also represents a problem with parallel circuits that is difficult to detect. The total resistance—referred to as RDSon—then increases, which can lead to thermal overload of the semiconductor switch.

[0011] According to one embodiment of the semiconductor switch according to the invention, said switch comprises a number n of circuit modules connected in series and is designed by the configuration of the individual circuit modules for a maximum permissible value of a load current to be carried through the semiconductor switch in such a way that the cumulative blocking voltage of the transistors of each subset of n-1 circuit modules of the n circuit modules of the semiconductor switch, via which the load current is carried, is greater than or equal to the maximum possible value of the load voltage (i.e. the peak voltage occurring for this maximum permissible load current). This means that the semiconductor switch is dimensioned in such a way that the malfunction of one circuit module can be intercepted and the blocking voltage is then still sufficient. According to a further development, this is also met in the event of a malfunction of a plurality m>1 (where m is a natural number) of circuit modules, e.g.in the event of a malfunction of two circuit modules. In this case, for example, each subset of nm circuit modules still has sufficient blocking voltage.

[0012] According to one embodiment of the semiconductor switch according to the invention, (preferably all) circuit modules are formed with a fuse which is arranged in the connection between the control terminal of the second transistor of the circuit module and the driver. In the event of a malfunction of a circuit module, the semiconductor switch is then designed with a fuse for interrupting the connection between the control terminal of the second transistor of this circuit module and the driver by means of the fuse arranged there. If the semiconductor switch is suitably over-dimensioned for correct operation with fewer than the total number of circuit modules, it can then continue to be operated. In this case, however, it is advisable to send a fault report so that the operator is informed of the damage to the semiconductor switch and can plan for a replacement.

[0013] The interruption of the connection to a malfunctioning circuit module can be achieved, for example, by designing the semiconductor switch in such a way that, when a current threshold value on the connection between the control terminal of the second transistor of the circuit module and the driver is exceeded due to a malfunction of a circuit module, the fuse arranged there is triggered. The term "current threshold value" should also include the checking of a value derived from the current for the exceedance of a threshold, e.g., the voltage drop across a known resistor (e.g., a shunt resistor). The fuse can be designed or dimensioned to trigger when the current threshold value is exceeded. For example, it can be a fuse or a PTC resistor (i.e., a thermistor with a positive temperature coefficient). However, an electronic fuse is preferred, which, for example,with a switching transistor such as a MOSFET. In the case of an electronic fuse, the corresponding connection between the control terminal of the second transistor (of the failed circuit module) and the driver is formed with a circuit for detecting when a current threshold has been exceeded. The semiconductor switch can then comprise a control unit (e.g. MCU), and the circuit for detecting when a current threshold has been exceeded is then designed to output a signal (e.g. via an optocoupler) to the control unit, which signalizes that the current threshold has been exceeded. This signal can be used both to notify the user regardingthe malfunction can be used (whereby identification information about the malfunctioning circuit module can also be output), as well as the control unit for generating and transmitting a control signal for the (electronic) fuse to trigger it when the current threshold value is exceeded (e.g. via an optocoupler). However, it can also be provided that the circuit for detecting the exceeding of a current threshold value is itself designed to generate and transmit a control signal for the fuse to trigger it when the current threshold value is exceeded, ie the triggering does not take place via a control unit (with a view to a possibly even more reliable triggering or if there is no need for a dedicated control unit for the semiconductor switch).

[0014] According to a development of the semiconductor switch according to the invention, it is provided with an evaluation circuit (e.g. part of a control unit or MCU of the switch) which is designed to compare a voltage difference with a threshold value, the threshold value being set in accordance with the blocking voltage of a first transistor of a circuit module, and voltage measuring circuits are arranged at the input and output of the semiconductor switch and are designed to transmit measured voltage values ​​to the evaluation circuit. In addition, a circuit is then provided for switching off the semiconductor switch when the threshold value is exceeded. This then switches off the driver voltage, for example. This development can also be used to detect errors or malfunctions.be intercepted, at which a circuit module can no longer be switched through; the on-resistance when the semiconductor switch is switched on is then always greater than the blocking voltage of the circuit module.

[0015] In the embodiments of the semiconductor switch according to the invention, it is not necessary for all circuit modules to be of the same dimensions or even of the same construction (although at least the latter is desirable for the first transistors). Any differences can be taken into account, for example, by software of a control unit of the semiconductor switch, so that the failure protection intended by the invention is also provided in such cases.

[0016] There are a wide variety of design variants for the circuit modules. For example, the first transistor can be a unipolar transistor, such as a MOSFET. However, implementation using a bipolar transistor, such as an IGBT (insulated-gate bipolar transistor) with an antiparallel protection diode (integrated or as an external freewheeling diode) is also possible.

[0017] According to one embodiment of the circuit module, the connection to the driver is formed by a conductor section into which a diode is introduced which blocks in the direction of the driver.

[0018] According to one embodiment of the circuit module, the control terminal and the source terminal of the second transistor are connected to one another, and a diode is arranged between the control terminal and the source terminal of the second transistor, which diode blocks in the direction of the control terminal.

[0019] According to one embodiment of the circuit module, the control terminal and the drain terminal of the second transistor are connected to one another, and a resistor (preferably an ohmic resistor) is arranged between the control terminal and the drain terminal of the second transistor.

[0020] According to one embodiment of the circuit module, a voltage limiter is provided in parallel with the first transistor. A capacitive resistor can also be provided in parallel with the first transistor.

[0021] According to a first alternative embodiment of the circuit module, the control terminal and the source terminal of the first transistor are connected to one another, and a diode is arranged between the control terminal and the source terminal of the first transistor, which blocks current in the direction of the control terminal. This diode is an optional feature, implemented, for example, by a Zener diode, which limits the maximum gate voltage or control terminal voltage.

[0022] For example, protective diodes and voltage limiters can also be provided selectively only for the circuit modules where the specific design of the semiconductor switch requires it. For example, the circuit module with the shortest distance to the driver, or for a symmetrically constructed semiconductor switch, the two circuit modules with the shortest distance to the driver, can be formed without a second transistor.

[0023] According to a second alternative embodiment of the circuit module, the circuit module is formed with a third transistor, wherein the third transistor is of the same type as the first transistor and the first and third transistors are each directly connected to one another via the source terminal (i.e., arranged practically in opposite directions). In this embodiment, the source terminal of the second transistor is connected to the control terminals of the first and third transistors, and the drain terminal of the second transistor is connected to the junction of the source terminals of the first and third transistors.

[0024] The invention is described in more detail below within the framework of an exemplary embodiment with reference to figures.

[0025] Fig. 1a and 1b: a circuit module for forming a semiconductor switch according to the invention,

[0026] Fig. 2: the structure of a semiconductor switch according to the invention with fuses for the circuit modules,

[0027] Fig. 3: a section of the semiconductor switch according to the invention from Fig. 2 with implementation details of the fuse, here as an electronic fuse and a threshold value adjustable via a reference,

[0028] Fig. 4: a section of the semiconductor switch according to the invention from Fig. 2 with implementation details of the fuse and a higher-level control system that is notified in the event of a malfunction and

[0029] Fig. 5: a section of the semiconductor switch according to the invention from Fig. 2 with implementation details of the fuse and a higher-level control which is notified in the event of a malfunction and triggers the fuse.

[0030] The invention is based on a semiconductor switch which is formed with circuit modules connected in series. Fig. 1a and Fig. 1b show an embodiment of such a circuit module. The module comprises a MOSFET M3 with a source connection source!, a gate connection Gate3 and a drain connection and a PNP bipolar transistor Q2 with an emitter connection, a base connection and a collector connection, the emitter connection being connected to the gate connection Gate3 of the MOSFET M3 and the collector connection being connected to the source connection sourceS of the MOSFET M3. The gate connection Gate3 and the source connection source! of the MOSFET M3 are connected to one another, and between these connections a diode D5 (preferably a Zener diode) is arranged which blocks in the direction of the gate connection Gate3.The base terminal and emitter terminal of the PNP bipolar transistor Q2 are connected together, and a diode D4 is arranged in the junction, which blocks the base terminal. The base terminal of the PNP bipolar transistor Q2 is also connected to its collector terminal, with a resistor R5 looped into the junction.

[0031] In addition, a connection is provided from the base terminal of the PNP bipolar transistor Q2 to a driver V2. This can be seen from Fig. 2, which shows a semiconductor switch formed from modules connected in series with a driver V2. The driver V2 is connected to the PNP bipolar transistors Q1 - Q6 of six circuit modules connected in series. A diode D1, D6, D7, D12, D14 and D16 is also inserted between the driver V2 and the base terminals of the PNP bipolar transistors Q1 - Q6, which diodes block the direction of the driver V2. A fuse SI - S6 is also provided between the driver V2 and the diodes D1, D6, D7, D12, D14 and D16.In this switch geometry, the semiconductor switch is formed from an even number of modules, the first half of the circuit modules being connected in series with the same conduction direction and the second half of the circuit modules being connected in series with the opposite conduction direction. In Fig. 1a and Fig. 1b, the semiconductor circuit module is shown twice, with the conduction direction being different. The semiconductor switch in Fig. 2 is therefore made up of half modules according to Fig. 1a and half modules according to Fig. 1b. The Zener diodes D5 and D18 in Fig. 1a and Fig. 1b are optional. In the middle of the circuit in Fig. 2, two modules with opposite conduction directions are connected in series.Driver V2 is connected to the junction of the two circuit modules connected in opposite conduction directions (source) and is connected to ground via this connection and the resistor R11. A resistor R2 and R6, respectively, are provided between this connection and the base terminals of the PNP bipolar transistors of the two circuit modules. Furthermore, a resistor R1 is inserted between the positive terminal of driver V2 and the connections of the circuit modules in a conduction direction. A capacitor C1 - C6 and a voltage limiter U1 - U6 (e.g., in the form of a suppressor diode or a varistor) are also connected in parallel to each of the circuit modules. This voltage limiter is an optional component of the circuit modules. A supply voltage V1 and a load R3 fed from this voltage are also shown.

[0032] Regarding the semiconductor switch structure shown in Fig. 2, the following two points are relevant:

[0033] Firstly, it is a circuit for alternating current flow (AC or DC with both current flow directions). For unipolar current flow, only half of the circuit shown would be required (i.e., only the modules with transistors of a forward direction).

[0034] On the other hand, the driver-related modules can, in principle, be designed without the transistors Q5 and Q6 for switching on. The elements D13, D14, D17, and R17, or D15, D16, D18, and R10, can then also be omitted, so that the modules then consist only of the MOSFETs M1 and M4. However, to ensure the simultaneous switching off of all series-connected components, or to symmetrically balance the switching-off behavior, it is advantageous to design these two modules similarly to the others.

[0035] According to one embodiment of the semiconductor switch, it is designed to assume a safe "off" state (high resistance between drain and source) even in the event of a fault. The semiconductor switch can also be designed to maintain its functionality in the event of failure of a circuit module or of the MOSFET of this circuit module (or in the event of failure of a specified number of circuit modules). In this case, transition to the safe "off" state is not absolutely mandatory; however, continued operation despite a failed circuit module would generally only occur as a bridge until the damage is repaired.

[0036] The simpler case is the transition to the safe "off" state. The safety of this state is ensured by the number of circuit modules and the design of the MOSFETs. Both are adjusted so that if one power semiconductor fails, the remaining sum of the blocking voltages of all still functional power semiconductors is greater than the peak value of the load voltage.

[0037] As soon as a MOSFET in a circuit module in the series circuit fails, its gate signal is short-circuited, or the MOSFET's control circuit, formed by a PNP bipolar transistor, is overloaded, and the gate signal (output driver) collapses. Therefore, one can monitor either the current of the driver output or the gate voltage or supply voltage of the driver stage to detect an overload.

[0038] When this overload is detected, the driver sets the gate signal of the MOSFETs to 0V, thus preventing current from flowing into the defective MOSFET (no driving voltage is available anymore). This also initiates the switch-off process for all other, still functioning MOSFETs or circuit modules. The semiconductor switch goes into the "off" state. The occurrence of this error or this error state can now either be passed on to a higher-level controller to block the semiconductor switch from being switched on again, or it can be switched off again during each subsequent switch-on process after the overload of the control circuit of the defective MOSFET is detected. Current control circuits already provide this functionality. For example, a UCC5390EC from TI (gate driver from Texas Instruments) has a UVLO, which means that if the supply voltage is too low, the output is held at "low".This means that if the driver supply voltage cannot provide the required driver power, the driver switches off and the semiconductor switch goes into the "off" state. This error state is then locked against unauthorized re-activation, e.g. via a message to a higher-level controller (e.g. MCU) of the semiconductor switch, which is programmed not to allow re-activation if an error occurs. For example, when the semiconductor switch is switched on again, the driver circuit is checked by the higher-level controller and if necessary (e.g. if the driver output remains at "low") the semiconductor switch is switched off again.

[0039] According to one embodiment of the invention, the faulty path is selectively isolated, or the faulty circuit module is disconnected. This is possible with the semiconductor switch shown in Fig. 2, since the potential isolation to the driver is provided by diodes D1 and D6 in the off state. As shown in Fig. 2, a fuse S1-S6 is connected in series with each of the diodes D1-D6. In the event of a fault, the fuse in whose path the fault current flows can blow, thereby separating the faulty part or circuit module from the circuit module assembly. This fuse does not necessarily have to be a fuse; electronic solutions are also conceivable, e.g., a so-called "electronic fuse" (see https: / / www.elektronik-kompendium.de / news / thema / elektronische-sicherung / ).

[0040] Fig. 3 shows the use of an electronic fuse in the semiconductor switch of Fig. 2. For the sake of simplicity, only one circuit module is shown that can be disconnected by such a fuse. On the left is the driver V3, and on the right is a circuit module formed by the MOSFET M7, the PNP bipolar transistor Q7, the Zener diode D21, the diodes D19 and D20, and the resistor R14.

[0041] The electronic fuse is implemented with a shunt resistor R12, with the help of which the gate current is detected and checked to see whether a limit value is exceeded. The operational amplifier U8 detects the voltage drop caused by the gate current across the resistor R12 and amplifies the voltage signal, which is then compared with a predetermined reference voltage by the comparator circuit formed by the operational amplifier U9 and the resistors R13 and R15. If a reference value for this voltage signal is exceeded (which corresponds to a limit value for the maximum gate voltage), a signal is output at the comparator output which triggers the transistor U7 to switch off the gate path. In order to filter out the current pulse when the MOSFET M7 is switched on during current measurement, it may be advisable to attach a capacitor C7 in parallel with the resistor R12.

[0042] In a further development (see Fig. 4), when the gate current is measured and a predefined setpoint is detected to be exceeded, a message is sent to a higher-level microcontroller or MCU as a warning or parameter for control measures to be carried out by the MCU. Preferably, there is potential isolation for the MCU. The message can then be sent, for example, via an optocoupler U10.

[0043] According to one embodiment, the gate path is switched off by a higher-level microcontroller or MCU (Fig. 5). As in the embodiment of Fig. 4, a message is transmitted to the MCU via the optocoupler U10. The MCU then outputs control information to another optocoupler U11, which interrupts the path by means of a MOSFET M8.

[0044] The semiconductor switch shown in Figures 2 to 5 allows continued operation of the switch using simple means in the majority of fault cases which are based on stochastic failure mechanisms, if the series connection contains redundant circuit modules. The FIT rate (failure in time) which is reduced by connecting a large number of power semiconductors can thus be significantly increased and it can also be ensured that the safe "switched off" state is reached. The FIT rate is described, for example, in https: / / de.wikipedia.org / wiki / FailureInTime and, in short, is the value FIT= 109h / MTBF. With an MTBF (Mean Time Between Failure) of one billion hours, the value for the FIT parameter is 1.

[0045] The rare occurrence of high impedance can be detected by measuring the voltage at the input and output of the semiconductor switch. In this fault situation, when the series circuit is switched on, a voltage difference of the order of magnitude of the maximum blocking voltage of a power semiconductor (regardless of whether caused by an avalanche of a power semiconductor or the response of part of the overvoltage limiter) occurs between the input and output, whereupon the switch can and must be switched off again.

Claims

Patent claims 1. Semiconductor switch with - a plurality of circuit modules connected in series, each formed with - a first transistor (M3) having a source terminal (source3), a control terminal (Gate3) and a drain terminal, wherein - the source terminal (source!) is a source terminal or an emitter terminal, the control terminal (gate!) is a gate terminal or a base terminal and the sink terminal is a drain terminal or a collector terminal, and - a second transistor (Q2) having a source terminal, a control terminal and a drain terminal, wherein - the source terminal is connected to the control terminal (gate!) of the first transistor (M3), - the drain terminal is connected to the source terminal of the first transistor (M3), and - with a driver (V2) which is connected via connections to the control terminals of the second transistors (Ql, Q2, Q3, Q4, Q5, Q6) of the individual circuit modules, wherein - the semiconductor switch is designed to interrupt the connection between the control terminal of the second transistor (Q2) of the malfunctioning circuit module and the driver (V2) or to switch itself off in the event of a malfunction of one of the circuit modules.

2. Semiconductor switch according to claim 1, characterized in that the semiconductor switch is designed by the number n of circuit modules connected in series and the design of the individual circuit modules for a maximum permissible value of a load current to be carried through the semiconductor switch such that the cumulative blocking voltage of each subset of n-1 circuit modules of the n circuit modules of the semiconductor switch is greater than or equal to the maximum value of the load voltage. 3 . Semiconductor switch according to claim 1 or 2, characterized in that - circuit modules of the semiconductor switch are formed with a fuse which is arranged in the connection between the control terminal of the second transistor (Q2) of the circuit module to the driver (V2), and - the semiconductor switch is designed in the event of a malfunction of a circuit module with a fuse for interrupting the connection between the control terminal of the second transistor (Q2) of this circuit module to the driver (V2) by means of the fuse arranged there.

4. Semiconductor switch according to claim 3, characterized in that the semiconductor switch is designed so that when a current threshold value on the connection between the control terminal of the second transistor (Q2) of the circuit module and the driver (V2) is exceeded due to a malfunction of a circuit module, the fuse arranged there is triggered.

5. Semiconductor switch according to claim 4, characterized in that the fuse is designed to trigger when the current threshold value is exceeded.

6. Semiconductor switch according to one of the preceding claims, characterized in that - it is an electronic security device, and - the connection between the control terminal of the second transistor (Q2) to the driver (V2) is formed with a circuit for detecting the exceeding of a current threshold value. 7 . Semiconductor switch according to claim 6 , characterized in that - the semiconductor switch comprises a control unit, and - the circuit for detecting the exceeding of a current threshold value is designed to output a signal to the control unit which signals the exceeding of the current threshold value.

8. Semiconductor switch according to claim 7, characterized in that the control unit is designed to generate and transmit a control signal for the fuse for triggering it when the current threshold value is exceeded.

9. Semiconductor switch according to claim 6 or 7, characterized in that the circuit for detecting the exceeding of a current threshold value is designed to generate and transmit a control signal for the fuse for triggering it when the current threshold value is exceeded. 10 . Semiconductor switch according to one of the preceding claims, characterized by - an evaluation circuit which is designed to compare a voltage difference with a threshold value, wherein the threshold value is determined in accordance with the blocking voltage of a first transistor (M3) of a circuit module, - voltage measuring circuits at the input and output of the semiconductor switch, which are designed to transmit measured voltage values ​​to the evaluation circuit, and - a circuit for switching off the semiconductor switch when the threshold value is exceeded.

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