Switching unit

Abstract

The invention relates to a switching unit (14) with a load terminal (12) and a ground terminal (16), between which a switching element (20) is connected, and with a semiconductor switch (24) having two terminals (26) and a control input (38). One terminal (26) is connected to the ground terminal (16) and the other to a signal contact (28), and the control input (38) is connected to the load terminal (12). The invention further relates to a circuit (2).

Description

The invention relates to a switching unit having a load terminal and a ground terminal, between which a switching element is connected. The invention further relates to a circuit.Installations, such as industrial installations, usually have one or more actuators by means of which an activity is carried out. In an industrial installation, for example, a workpiece is created and / or machined by means of the actuator. In order for the actuator to be operated in accordance with the desired function, a control is provided by means of which an energization of the actuator is adjusted. In the simplest case, a switching element is present here, which is actuated by means of the controller. By means of the switching element, the actuator is switched on and off. For this purpose, the switching element is introduced into an electrical supply line of the actuator.If functions are carried out by means of the actuator which could lead to a risk to further machines and / or operating personnel, it is necessary for functional safety to be provided. Thus, in an emergency, the intended function of the actuator is to be ended and a safe state is to be assumed. For this purpose, it is usually necessary for the energization of the actuator to be ended and therefore for the switching element to be open. It is also necessary, for example, during maintenance of the actuator that the actuator is not operated, i.e., that the switching element is open. In both applications, it must thus be ensured that the actuator is not energized in order to exclude a further risk.For this purpose, it is possible in principle to measure the electric current currently being carried by means of the supply line. However, these usually carry comparatively high electric currents and / or electric voltages, so that such a measuring device is comparatively cost-intensive. In addition, in the event of damage to the actuator and a reaction into the supply line, the measuring device could be damaged. It would therefore not be possible to reliably judge whether the actuator is actually no longer energized.In order to check whether the actuator is currently energized, the switching state of the switching element can also be checked. A mechanical switch is usually used as the switching element, which has two contacts that are movable relative to one another, one of which is usually connected to a movably mounted contact bridge. If the switching element is electrically conductive, the contacts bear mechanically against one another, and the electrical current used for energizing the actuator is conducted via said contacts. To open the switching element, the contacts are spaced apart from one another, for which purpose the contact bridge is moved.An auxiliary contact is usually connected to the contact bridge. When the contact bridge is moved, the auxiliary contact is released from another auxiliary contact and a current flow via an auxiliary circuit into which the auxiliary contacts are introduced is interrupted. Thus, by checking whether there is a current flow in the auxiliary circuit, it is possible to judge whether the switching element is opened or closed. In this case, a reduced electric current can be carried and / or a reduced electric voltage can be applied with the auxiliary circuit, which is why the checking of the auxiliary circuit is simplified. The auxiliary circuit can also be galvanically isolated from the supply line, which further increases safety.In this type of checking the switching state of the switching element, it is necessary to use a comparatively complex mechanical switch which at least additionally has the two auxiliary contacts. The use of a semiconductor switch is not possible, however, since two circuits separate from one another cannot be opened simultaneously by means of this switch. Due to the use of the mechanical switch, an arc can be formed when it is opened, which arc is led, for example, to weld the contact, so that it can no longer be opened. Manufacturing costs are also comparatively high.The object of the invention is to specify a particularly suitable switching unit and a particularly suitable circuit, wherein manufacturing costs are advantageously reduced, and wherein safety is increased in particular.With regard to the switching unit, this object is achieved according to the invention by the features of claim 1 and with regard to the circuit by the features of claim 10. Advantageous refinements and refinements are the subject matter of the dependent claims.The switching unit is, for example, a component of a system by means of which a specific function is carried out. In particular, the installation is an industrial installation and serves, for example, for the production and / or machining of a specific workpiece. The system has an actuator for this purpose, in particular. The actuator is, for example, an electric motor, which is, for example, a rotating electric motor or a linear motor. Alternatively, the actuator is, for example, a valve that is electrically actuated. In a further alternative, the installation is, for example, a communication installation or a data center.The switching unit is suitable, in particular designed to interrupt or generate an electrical current flow. In this case, the electric current which is normally conducted and corresponds in particular to the rated current is preferably between 0.5 A and 200 A, between 1 A and 100 A or between 10 A and 50 A. Preferably, a rated voltage of the switching unit which is present in particular at the switching unit when the switching unit is not electrically non-conductive is greater than 10 V, 20 V or 100 V and, for example, less than 10 kV, 5 kV or 1 kV. In particular, the electrical voltage is a DC voltage or an AC voltage.The switching unit has a load terminal and a ground terminal, between which a switching element is connected. If the switching element is electrically conductive, i.e. closed, the load connection and the one are contacted with one another with a low impedance. When the switching element is open and is thus in the electrically non-conductive state, on the other hand, the load terminal and the ground terminal are only connected to one another with a high impedance, so that an electrical current flow between them is not possible. The ground connection is suitable, in particular provided and configured, in this case, for a ground potential to be applied to said ground connection. The load connection, on the other hand, is suitable, in particular provided and configured, for a load to be connected to said load connection. In the mounted state, the load connection is electrically connected to a voltage source via the load. When the switching element is electrically conductive, i.e. closed, the load is energized. If, on the other hand, the switching element is open, energization of the load is interrupted.For example, the switching element is a mechanical switch such as a relay. Preferably, however, the switching element is designed as a semiconductor switch and in particular has a comparatively high current-carrying capacity. Expediently, the switching element is a field effect transistor, preferably a MOSFET, IGBT or GTO.The switching unit further includes a semiconductor switch that is separate from the switching element. In other words, the semiconductor switch is a separate component from the switching element, and the semiconductor switch is provided by a semiconductor component. The semiconductor switch has two terminals which are connected to one another with a low impedance if the semiconductor switch is electrically conductive. If, on the other hand, the semiconductor switch is open, the two connections are connected to one another with a high impedance. Furthermore, the semiconductor switch has a control input. By applying a specific electrical potential to the control input, it is possible to put the semiconductor switch into the electrically conductive or into the electrically non-conductive state. The semiconductor switch is expediently a transistor. At least, the semiconductor switch preferably has a lower current-carrying capacity than the switching element, so that production costs are reduced.One terminal of the semiconductor switch is led to the ground terminal. The other terminal is led against a signal contact of the switching unit. Preferably, the terminal is in direct electrical contact with the signal contact without there being arranged between them one or more electrical / electronic components which are, for example, at least partially electrically connected to one another in series and / or in parallel. If the semiconductor switch is electrically conductive, the signal contact is thus at the same electrical potential as the ground terminal, i.e. in particular electrically connected to ground, or at least at an electrical potential determined by means of ground. When the semiconductor switch is open, on the other hand, the electrical potential at which the signal contact is situated is different from ground and / or in particular independent thereof.The control input of the semiconductor switch is led to the load connection. For example, the control input is electrically connected directly to the load connection, or further electrical / electronic components are arranged between these. At least the electrical potential present at the control input is dependent on the electrical potential present at the load connection.Thus, if the switching element is electrically closed, the load terminal is at the same electrical potential as the ground terminal. As a result, an electrical potential corresponding to the ground terminal is present at the control input, and the semiconductor switch is in particular designed such that it is then open. Thus, the electrical potential of the signal contact is different from ground. If, on the other hand, the switching element is not electrically conductive, the electrical potential present at the load terminal is different from the electrical potential present at the ground terminal. The electrical potential present at the control input is thus also varied. In this case, the semiconductor switch is in particular configured such that it is then electrically conductive. Consequently, ground is then in particular present at the signal contact as the electrical potential, or at least they correspond to one another.In summary, it is thus possible on the basis of the interconnection to assess, on the basis of the electrical potential present at the signal contact, whether the switching element is in the electrically conductive or in the electrically non-conductive state. Safety is thus increased. The requirements for the switching element are comparatively low, so that manufacturing costs are reduced. In addition, it is possible to use a semiconductor as the switching element, and therefore manufacturing cost is reduced again.Suitably, the switching unit comprises a housing into which one or more terminals are inserted. One of the terminals is expediently electrically connected to the ground connection and the other to the load connection. This is thus made possible by the corresponding electrical potentials from outside the housing, which facilitates assembly. Alternatively or in combination therewith, for example, the signal contact can be perceived at least indirectly from outside the housing.For example, the switching element is designed as a mechanical switch, which can be actuated, for example, only manually. Alternatively, the switching element has, for example, a control input via which the switching unit is actuated. Expediently, the electrical potential of the switching element is changed in this case as a function of an electrical potential present at the control input. It is thus possible to set the electrical current flow between the load terminal and the ground terminal remote from the switching unit, in particular within the scope of a process control. Preferably, the switching element is a semiconductor. In one development, the switching unit is, for example, a component of a circuit breaker, wherein the switching element is actuated in particular as a function of a fault, such as, for example, an overcurrent, a short-circuit current, an overvoltage or another malfunction, for example of the possible load.The signal contact is preferably led to a first resistor. In this case, a further electrical component is arranged in particular between the signal contact and the first resistor, or the signal contact is electrically connected directly to the first resistor. By means of the first resistor, it is ensured in particular that the electrical current carried by means of the semiconductor switch is comparatively low if said electrical current is electrically conductive. Thus, safety is increased and electrical losses are reduced. In addition, in this way, loading of the switching element is further reduced, so that it can be configured comparatively cost-effectively.For example, the first resistor is led to a supply connection. In the mounted state / when using the switching unit, an electrical potential is preferably present at the supply terminal, which is suitably constant over time. Here, the voltage applied between the ground terminal and the power terminal is lower than 50 V, 20 V, 10 V, or 5 V. Thus, the requirements of the first resistor, the signal contact, and the semiconductor switch are further reduced, and therefore, manufacturing costs can be reduced. Expediently, the switching unit comprises a terminal which is electrically connected to the supply connection and is in particular introduced into the possible housing. It is thus possible to apply the corresponding electrical potential to the supply terminal from outside the housing.Preferably, a control unit is present which is electrically connected to the supply connection. This is thus also operated on the basis of the electrical potential present there. Thus, susceptibility to errors is reduced and operation of the control unit is possible independently of the electrical voltage present between the ground terminal and the load terminal. Preferably, the switching element is actuated by means of the control unit.In an alternative to this, the first resistor is connected to the load connection via a second resistor. Thus, the separate supply connection is not required, which facilitates assembly. Manufacturing costs are also reduced in this way. When the semiconductor switch is open, the electrical potential present at the signal contact corresponds to the electrical potential present at the load terminal. The two resistors ensure that an electric current flowing from the load terminal via the semiconductor switch to the ground terminal is comparatively low, so that a load on the semiconductor switch is reduced. This also ensures that no undesired energization of any load connected to the load terminal takes place when the switching element is open. Due to the series connection of the two resistors, the requirement for the individual resistors is reduced, so that they can be designed to be comparatively small and cost-effective.The second resistor is preferably connected to the ground connection via a Zener diode. In this case, the reverse direction of the zener diode is expediently directed away from the ground connection. Thus, the zener diode is connected in parallel with the series circuit including the first resistor and the semiconductor switch. In particular, the Zener diode is also electrically connected in parallel with the series circuit having the second resistor and the switching element. By means of the Zener diode, formation of an overvoltage is in particular avoided, which could lead to destruction of the switching element or semiconductor switch. The second resistor ensures that the maximum electric current flowing via the Zener diode is comparatively low, so that a comparatively cost-effective component can also be used here.Preferably, the first resistor is connected to a third resistor. In this case, the first resistor is expediently electrically connected directly to the third resistor. The third resistor is in turn connected via a first diode to the load connection. Furthermore, the third resistor is connected to the control input via a fourth resistor and a second diode.Expediently, the two diodes and the fourth resistor are connected electrically in series. The reverse direction of the two diodes is in particular opposite to one another, and the reverse direction of the second diode is directed from the control input to the fourth resistor. In particular, the two diodes are structurally identical to one another, which is why production costs are reduced. In this way, the mode of operation of the switching unit is also improved. Preferably, the two diodes are thermally connected to each other and are expediently arranged next to each other. Thus, the two diodes always have substantially the same behavior. In this case, the first resistor, for example, is led to the supply connection, with the result that the third resistor is also led to the supply connection. Alternatively, the second resistor is present and the third resistor is also led in particular to the second resistor.By means of the fourth resistor and the third resistor, it is possible to set the voltage level which leads to an actuation, preferably the switching on, of the semiconductor switch. In other words, the third, fourth and first resistors act in particular in the manner of a voltage divider. In summary, it is thus possible to realize that the semiconductor is actuated even if an electrical voltage different from 0 V is produced via the switching element. Thus, a comparatively high internal resistance can also be present in the switching element, or it can be operated in a current-limited mode. However, it is securely signaled at the signal contact that the electrical current flow is present. Only from a further increase in the electrical voltage arising via the switching element is the electrical potential present at the signal contact changed.For example, only a single switching element is present, which is preferably configured bidirectionally. Alternatively, the switching element is only unidirectional, and thus it is possible to use only the switching unit for unidirectional operation. In a development, a second switching element is present, which is expediently identical in construction to the switching element. The second switching element is connected between the ground terminal and a second load terminal. In this case, the third resistor is led via a third diode to the second load connection. The reverse direction of the third diode is directed away from the second load terminal. Thus, the signal contact also carries out signaling of the switching state of the second switching element.For example, the two load connections are separate from one another. Alternatively, for example, the two load connections are electrically contacted with one another with a low impedance. These are preferably formed by means of a common (mechanical) clamp or the like, which are introduced, for example, into the possible housing of the switching unit. In this case, the two switching elements are preferably each of unidirectional design and arranged opposite one another between the ground connection and the respective load connection. Consequently, the switching unit is viable for bidirectional operation even if the two switching elements are configured only unidirectionally. In this case, due to the third diode, it is possible to use only the single semiconductor switch, and therefore, manufacturing costs are comparatively low.In an alternative embodiment, for example, the third diode is not present, but the second switching element. In this case, the switching unit is in particular configured at least partially mirrored. Thus, a further semiconductor switch is expediently present, which is associated with the second switching element. The further semiconductor switch, which is suitably structurally identical to the semiconductor switch, is guided by means of its control input in particular to the further load terminal, and the two terminals of the further semiconductor switch are guided to the ground terminal and a further signal contact. Preferably, this is led against a further first resistor, which is led, for example, against the possible supply connection. Alternatively, for example, the further first resistor is connected to the second load connection via a further second resistor. Expediently, a further zener diode is present, via which the further second resistor is led to the ground connection. Alternatively or in combination therewith, the further first resistor is led to a further third resistor which is led via a further first diode to the second load connection and via a further fourth resistor and a further second diode to the control input of the further semiconductor switch.For example, the load terminal is electrically connected to the ground terminal only by means of the switching element. Alternatively, the switching element is bridged by means of a fourth resistor, so that the ground terminal is also electrically contacted to the load terminal by means of the fourth resistor. In this case, the resistance value of the fourth resistor is comparatively high, and therefore an electric current flowing via the fourth resistor is comparatively low or negligible. The individual components of the switching unit, in particular the possible first, second and / or third resistor, are expediently designed in such a way that the switching of the switching element takes place already at a comparatively low electrical voltages present at the switching element. If the switching unit and any electrical circuit in which the switching unit is used or at least the possible load are functioning properly, an electrical potential is thus always present at the control input, for which reason the electrical potential present at the signal contact corresponds to ground.However, if ground is present at the load terminal as the electrical potential, for example due to a broken line, the semiconductor switch is open, so that the electrical potential present at the signal contact does not correspond to ground. If, for example, a changed electrical voltage is present at the load terminal on account of a shunt / conductor connection, this can likewise be read out at the signal contact by means of a corresponding selection of the resistors. In other words, the switching unit thus carries out a signaling / checking operation to determine whether the conductor connection / shunt connection is present.The signal contact is connected to an LED, for example. The LED (light-emitting diode) is expediently introduced into a housing of the switching unit, so that the LED is also visible from outside the switching unit.If the first resistor is present, the LED is expediently connected between the first resistor and the semiconductor switch, wherein contact of the LED with the signal contact is expediently electrically contacted. The other contact of the LED, on the other hand, is electrically contacted with the first resistor. The signal contact is thus led via LED to the first resistor.Alternatively or in combination, the switching unit preferably comprises the possible control unit which is guided against the signal contact. In particular, the control unit is electrically connected directly to the signal contact. During operation, a check is made by means of the control unit as to whether the switching element is electrically conductive or electrically non-conductive. For this purpose, the control unit is in particular suitable, preferably provided and configured. Suitably, the control unit is connected by signal technology to a communication input of the switching unit, which is suitable, in particular provided and configured, to be connected to a superordinate controller. In this case, communication with the controller is carried out via the communication input, in particular by means of the control unit, and in particular it is communicated whether the switching element is closed or open. Alternatively or in combination therewith, the switching element is also operated by means of the control unit. It is thus possible to directly check by means of the control unit whether the activation of the switching element has been correctly implemented or whether, for example, a malfunction of the switching element is present. For example, the control unit is discretely constructed or has, for example, an integrated circuit.The circuit has a voltage source which comprises two current connections. In this case, for example, an electrical alternating voltage or preferably an electrical direct voltage is provided by means of the voltage source, which is thus present between the two current connections. In particular, the electrical DC voltage provided is greater than 100 V. In addition, the circuit has a load which is formed, for example, by means of an actuator. The circuit also comprises a switching unit having a load terminal and a ground terminal, between which a switching element is connected. The switching unit further comprises a semiconductor switch having two terminals and a control input. One terminal is connected to the ground terminal and the other to a signal contact, and the control input is connected to the load terminal.One of the current connections of the voltage source is electrically connected to ground, in particular directly. The other current connection of the voltage source, on the other hand, is conducted to the load. The load in turn is guided against the load connection. Thus, the one of the power terminals is electrically connected to the load terminal of the switching unit via the load. For example, only the load is present here, or, for example, further loads are also present, which are connected, for example, electrically in parallel and / or in series with the load. The ground terminal of the switching unit is electrically connected to ground. Thus, when the switching element is closed, an electric current flow occurs and the load is operated. If, on the other hand, the switching element is open, the electric current flow via the switching unit is prevented and the load is not operated. The circuit is, for example, a component of a system, such as an industrial system or a telecommunication system. In particular, the switching unit serves at least partially to provide functional safety in the circuit.The developments and advantages explained in connection with the switching unit are also to be transferred analogously to the circuit and vice versa.Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. Shown therein are: FIG. 1 schematically shows a circuit with a load and a switching unit, and FIGS. 2-4 show a simplified circuit diagram of a variant of the switching unit.Corresponding parts are provided with the same reference numerals in all figures.FIG. 1 schematically shows, in simplified form, a circuit 2 which is part of an industrial plant. The circuit 2 comprises a load 4, which is a component of an actuator, not shown in detail. During operation, a workpiece is machined / produced by means of the actuator, and the load 4 is an electric motor in the example shown. For operating the load 4, the circuit 2 comprises a voltage source 6 which has two current connections 8. The voltage source 6 is provided by means of a rectifier, and an electrical direct voltage which is several 100 V is present between the power terminals 8.One of the power connections 8 is electrically connected to ground 10, namely electrically directly to ground 10. The other power connection 8 is led against the load 4. The load 4 is furthermore led against a load terminal 12 of a switching unit 14, with the result that the load 4 is electrically connected between the load terminal 12 and one of the power terminals 8. The switching unit 14 further comprises a ground terminal 16 electrically connected directly to ground 10. Thus, the ground terminal 16 has the same electrical potential as one of the current terminals 8. The load terminal 12 and the ground terminal 16 comprise terminals, not shown in detail, which are introduced into a housing 18 of the switching unit 14.A switching element 20 arranged in the housing 18 is connected between the load terminal 12 and the ground terminal 16, said switching element being configured as a MOSFET. If the switching element 20 is controlled in such a way that it is electrically conductive, the load terminal 12 and the ground terminal 16 are connected with a low impedance. As a result, an electric current flow from the one of the current connections 8 via the load 4 and the switching unit 14 to ground 10 is possible. As a result, the load 4 is operated. If, on the other hand, the switching element 20 is controlled in such a way that it is electrically non-conductive, the current flow is interrupted and the load 4 is not operated.The switching element 10 is controlled by means of a control unit 22, which is likewise arranged in the housing 18. The control unit 22 is connected by signal technology to a communication input, not shown, which is likewise introduced into the housing 18. Via the communication input, the control unit 22 is connected to a higher-order control of the circuit 2, not shown in detail, so that the actuator is operated by means of the higher-order control. In this case, the controller specifies whether or not the load 4 is to be operated, and the control unit 22 actuates the switching element 20 accordingly, that is to say opens or closes it. For this purpose, a corresponding electrical potential is applied to a control input of the switching element 20 by means of the control unit 22. However, it is possible that due to a malfunction, for example, material fatigue or aging, the switching state of the switching element 20 does not match the specification.In order to check the actual switching state of the switching element 20, the switching unit 14 therefore comprises a semiconductor switch 24, which is designed as a transistor. The semiconductor switch 24 has two terminals 26, one of which is led to the ground terminal 16. In this case, this terminal 26 is electrically contacted directly with ground terminal 16 and thus always has ground 10 as the electrical potential. The other terminal 26 is led against a signal contact 28 and electrically connected directly thereto. The signal contact 28 is in turn electrically connected directly to the control unit 22, which has an integrated circuit, not shown in detail.The signal contact 28 is furthermore led against a first resistor 30 and for this purpose electrically connected directly to the latter. The first resistor 30 in turn is led against a supply connection 32 and electrically connected directly thereto. Thus, the supply terminal 32 is connected to one of the terminals 26 of the semiconductor switch 24 via the first resistor 30 and the signal contact 28. The supply connection 32 comprises a terminal, not shown in detail, which is introduced into the housing 18 and which is electrically connected by means of a line to a second current connection 34 of a second voltage source 36. The second voltage source 36 has a total of two second current connections 34, wherein the remaining current connection 34 is electrically connected directly to ground 10. In this case, an electrical DC voltage of 12 V is provided by means of the second voltage source 34, which is present between the two second current connections 34.The control unit 22 is in this case likewise electrically contacted with the supply connection 32 and the ground connection 16, so that an electrical supply of the control unit 22 takes place by means of the second voltage source 36.The semiconductor switch 24 furthermore has a control input 38, wherein the two connections 26 are connected either electrically with low impedance or with high impedance depending on the electrical potential present at the control input 38. In other words, the semiconductor switch 24 is opened or closed depending on the applied electric potential. The control input 38 is led via a second diode 40, a fourth resistor 42 and a first diode 44 to the load connection 12 and is electrically connected directly thereto.The two diodes 40, 44 are structurally identical to one another and are arranged directly next to one another mechanically, with the result that they are thermally coupled to one another. Thus, the two diodes 40, 44 have the same temperature and therefore essentially always the same behavior. In this case, the reverse direction of the two diodes 40, 44 is different from one another, wherein the reverse direction of the second diode 40 is directed away from the control input 38. In contrast, the reverse direction of the first diode 44 is directed away from the load terminal 12. The switching unit 14 further comprises a third resistor 46, by means of which the first resistor 30 is connected to the first diode 44 and the fourth resistor 42.If the switching element 20 is placed in the electrically conductive state by means of the control unit 22, ground 10 is essentially present as an electrical potential at the load terminal 12. A correction follows only on the basis of an internal resistance of the switching element 20 which is comparatively low. As a result, an electric current flows from the one second current terminal 34 predominantly via the third resistor 46, the first diode 44, the switching element 20 to ground 10. At least, substantially no current flow takes place via the fourth resistor 42 and the second diode 40, and substantially ground 10 is present at the control input 38 as an electrical potential, wherein a correction is due to the fourth resistor 44. As a result, the semiconductor switch 24 is opened. Therefore, the signal contact 28 has the electrical potential of the associated second current connection 34 as the electrical potential, wherein a correction is possible on the basis of the first resistor 30. At least, the electrical potential is different from ground 10.If the switching element 20 is open, the electrical current flow from the associated second current connection 34 to ground 10 is not possible via the switching element 20, which is why the electrical potential at the control input 38 is increased. This corresponds substantially to that of the associated second current connection 34, wherein a correction takes place on the basis of the second diode 40, the fourth resistor 42 and the third resistor 46. The first diode 44 ensures that the voltage source 6 has no influence on the switching state of the semiconductor switch 40. Due to the increased electrical potential present at the control input 38, the semiconductor switch 24 is closed, so that the two terminals 26 are connected to one another with a low impedance. As a result, an electrical current flow from the associated second current terminal 34 via the supply terminal 32, the first resistor 30, the semiconductor switch 24 and the ground terminal 16 to ground 10 takes place. However, due to the closed semiconductor switch 24, the electrical potential of the signal contact 28 is equal to ground 10, wherein a slight correction due to the internal resistance of the semiconductor switch 24 is optionally present.The dimensioning of the resistors 30, 46, 42 is such that, on the one hand, the flowing electric currents are always comparatively low. On the other hand, these are selected in such a way that a change in the electrical potential of the signal contact 28 takes place, depending on whether the switching element 20 is electrically conductive or electrically non-conductive.During operation, the switching state of the switching element 20 is set by means of the control unit 22. Subsequently, the electrical potential present at the signal contact 28 is detected and checked on the basis of this whether the switching state of the switching element 20 corresponds to the setting. If there is a difference, a warning message is output via the communication input and the switching element 20 is placed in the electrically non-conductive state. Thus, the load 4 is attempted to be stopped and brought into a safe state.FIG. 2 shows a modification of the switching unit 14. The switching element 20 connected between the ground terminal 16 and the load terminal 12 is not changed. Also present is the semiconductor switch 24 with the two terminals 26, one of which is electrically contacted with the ground terminal 26. The other terminal 26 is electrically contacted via the signal contact 28 with the first resistor 30, which is also further conducted by means of the third resistor 46 against the first diode 44 and the fourth resistor 42. The fourth resistor 42 is also connected between the first diode 44 and the second diode 40, which is electrically connected to the control input 38. The first diode 44 is also furthermore led against the load connection 12. Also present are the control unit 22 and the housing 18, which is not shown in detail here, however.In contrast to the preceding embodiment, the supply connection 32 is no longer present. Instead, the first resistor 30 is connected to the load terminal 12 via a second resistor 48. In this case, the third resistor 46 is connected between the second resistor 48 and the fourth resistor 42. When the switching element 20 is open, an electrical potential is thus applied to the control input 38 which corresponds to the electrical potential of the current connection 8 which is assigned to the load connection 16, wherein a correction is effected on the basis of the load 4, the second resistor 48, the third resistor 46 and the fourth resistor 42. The resistors 42, 46, 48 are selected in such a way that overloading of the semiconductor switch 24 is ruled out, and in this case the semiconductor switch 24 is closed. When the semiconductor switch 24 is closed, the electrical current flows from the load terminal 12 via the second resistor 48, the first resistor 30 to the ground terminal 16. Due to the electrically conductive semiconductor switch 24, the electrical potential of the signal contact 28 is here likewise substantially equal to ground 10.In addition, a zener diode 49 is present, by means of which the second resistor 48 is connected to the ground connection 16. The reverse direction of the zener diode 49 is directed toward the ground terminal 16. The Zener diode 49 ensures that an electrical voltage present at the semiconductor switch 24 is limited, and therefore the electrical potential present at the signal contact 28 is also limited. Destruction of the control unit 22 in the event of a malfunction of the load 4 is thus avoided.FIG. 3 shows a further modification of the switching unit 14, which has all the constituent parts of the variant shown in FIG. 1. In addition, a second switching element 50 is present, which is identical in construction to the switching element 20. The second switching element 50 is connected between a second load terminal 52 and the ground terminal 16. In this case, the forward direction of the two switching elements 20, 50 is different, so that the switching unit 14, in contrast to the variant shown in FIG. 1, is configured bidirectionally. Furthermore, a third diode 54 is present, wherein the third resistor 46 is led via the third diode 54 to the second load terminal 52. In this case, the fourth resistor 42 is led via the third diode 54 to the second load terminal 52, and the reverse direction of the third diodes 54 is directed away from the second load terminal 52.Thus, depending on the current direction or to which load terminal 12, 52 the load 4 is connected, the semiconductor switch 24 is always reliably actuated when the two switching elements 20, 50 are open, so that the electrical potential that is present at the signal contact 28 is changed.In addition, an LED 56 is connected between the signal contact 28 and the first resistor 30. In this case, the signal contact 28 is led against the LED 56. If the semiconductor switch 24 is electrically conductive, the LED 56 is energized, so that it lights up. If the semiconductor switch 24 is opened, the LED 56 does not light. The switching state of the two switching elements 20, 50 is thus likewise signaled by means of the LED 56. The LED 56 is inserted into an opening of the housing 18 so that the switching state is visible from outside the housing 18.FIG. 4 shows a further variant of the switching unit 14. This variant corresponds substantially to the embodiment shown in FIG. 2, which is however largely mirrored. This variant thus has all the constituent parts of the embodiment shown in FIG. 2, wherein the second switching element 50 is additionally present, which is connected between the ground terminal 16 and the second load terminal 52. Furthermore, a further semiconductor switch 58 is present, which is structurally identical to the semiconductor switch 24. The latter thus also has the two connections 26, one of which is electrically connected to the ground connection 16. The other terminal 26 is electrically contacted to the second load terminal 52 via a further signal contact 60 having a further first resistor 62, which is structurally identical to the first resistor 30, and a further second resistor 64, which is structurally identical to the second resistor 48.The control input 38 of the further semiconductor switch 58 is electrically contacted to the second load terminal 52 via a further second diode 66, a further fourth resistor 68 and a further first diode 70. These are each identical in construction to the second diode 40, the fourth resistor 42 and the first diode 44. a further third resistor 72 is also present, which is identical in construction to the third resistor 46 and whose arrangement corresponds to the arrangement of the third resistor 46. A further zener diode 74 is also present, by means of which the further second resistor 46 is led to the ground connection 16. In summary, this arrangement corresponds substantially to the bidirectionally configured variant of FIG. 2. in addition, the two switching elements 20, 50 are bridged by fourth resistors 76 of identical construction. The two fourth resistors 76 are designed to have a high impedance, so that a power loss remains low.The mode of operation of the switching unit 14 corresponds substantially to the variant shown in FIG. 2, and when the two switching elements 20, 50 are open, the electrical potential present at the signal contacts 28, 60 is increased. If a shunt / conductor connection is present, the electrical potential is at least slightly changed at one of the two load connections 12, 52 compared to the other. As a result, an electric current flow is possible between the two load terminals 12, 52, namely via the fourth resistors 46. The electrical potential present at the signal contacts 28, 60 is thus increased, which is detected by means of the control unit 22. This variant of the switching unit 14 is thus enabled for detecting a shunt / line fault. The configuration of the individual electrical components of the switching unit 14 is here correspondingly adapted.The invention is not limited to the above-described embodiments. Rather, other variants of the invention can also be derived from this by the person skilled in the art without departing from the subject matter of the invention. In particular, all the individual features described in connection with the individual exemplary embodiments can also be combined with one another in another manner without departing from the subject matter of the invention.List of reference characters2 Circuit 4 Load 6 Voltage source 8 Current connection 10 Ground 12 Load connection 14 Switching unit 16 Ground connection 18 Housing 20 Switching element 22 Control unit 24 Semiconductor switch 26 Connection 28 Signal contact 30 First resistor 32 Supply connection 34 Second current connection 36 Second voltage source 38 Control input 40 Second diode 42 Fourth resistor 44 First diode 46 Third resistor 48 Second resistor 49 Zener diode 50 Second switching element 52 Second load connection 54 Third diode 56 LED 58 Further semiconductor switch 60 Further signal contact 62 Further first resistor 64 Further second resistor 66 Further second diode 68 Further fourth resistor 70 Further first diode 72 Further third resistor 74 Further Zener diode 76 Fourth resistor

Claims

Switching unit (14) having a load terminal (12) and a ground terminal (16), between which a switching element (20) is connected, and having a semiconductor switch (24), which has two terminals (26) and a control input (38), wherein one terminal (26) is led to the ground terminal (16) and the other is led to a signal contact (28), and wherein the control input (38) is led to the load terminal (12).Switching unit (14) according to Claim 1, characterized in that the signal contact (28) is led against a first resistor (30).Switching unit (14) according to Claim 2, characterized in that the first resistor (30) is led against a supply connection (32).Switching unit (14) according to Claim 2, characterized in that the first resistor (30) is led via a second resistor (48) to the load connection (12).Switching unit (14) according to Claim 4, characterized in that the second resistor (48) is led via a zener diode (49) to the ground connection (16).Switching unit (14) according to one of Claims 2 to 5, characterized in that the first resistor (30) is led to a third resistor (46), which is led via a first diode (44) to the load connection (12) and via a fourth resistor (42) and a second diode (40) to the control input (38).Switching unit (14) according to Claim 6, characterized by a second switching element (50) which is connected between the ground connection (16) and a second load connection (52), wherein the third resistor (46) is led via a third diode (54) to the second load connection (52).Switching unit (14) according to one of Claims 1 to 7, characterized in that the switching element (20) is bridged by means of a fourth resistor (76).Switching unit (14) according to one of Claims 1 to 8, characterized in that the signal contact (28) is led to an LED (56) and / or to a control unit (20).Circuit (2) having a load (4), having a voltage source (6) which has two current connections (8), and having a switching unit (14) according to one of Claims 1 to 9, wherein one of the current connections (8) is electrically connected to ground (10) and the other current connection (8) is led to the load (4) which is led to the load connection (12), wherein the ground connection (16) is electrically connected to ground (10).

Images