Overvoltage protector for an electronic switch element

Abstract

Proposed is an electrical switch device (5 to 7) which, for the purposes of connecting an electrical potential (U0, U1, U2) to a load (8), has a switch element (9) comprising a first power connection (10), a second power connection (11) and a first control connection (12). The switch element (9) has a breakdown voltage up to which it can be operated at a maximum. The first control connection (12) is connected to a first driver circuit (13) by means of which a first control signal (S1) can be fed to the first control connection (12) such that, depending on the value of the first control signal (S1), the switch element (9) is rendered conductive or non-conductive for a flow of current from the first to the second power connection (10, 11). The first control connection (12) is connected via a first diode circuit (16) to the first power connection (10). The first diode circuit (16) comprises a first and a second diode (17, 18) connected in series. As viewed from the first power connection (10) to the first control connection (12), the first diode (17) is forward biased and the second diode (18) is reverse biased. The second diode (18) is designed as a Zener diode and has a breakdown voltage between an operating voltage (U) of the electrical switch device (5 to 7) and the breakdown voltage of the switch element (9). The first diode (17) has a breakdown voltage higher than the breakdown voltage of the switch element (9).

Description

[0001] Description

[0002] Overvoltage protection for an electronic switching element

[0003] The present invention is based on an electrical switching device for connecting an electrical potential to a load,

[0004] - wherein the switching device comprises a switching element with a first power terminal, a second power terminal and a first control terminal,

[0005] - wherein the switching element has a breakdown voltage up to which it can be operated,

[0006] - wherein the first control terminal is connected to a first driver circuit via which a first control signal can be supplied to the first control terminal, so that the switching element is switched on or off for a current flow from the first to the second power terminal depending on the value of the first control signal,

[0007] - wherein the first control terminal is connected to the first power terminal via a first diode circuit,

[0008] - wherein the first diode circuit comprises a series connection of a first and a second diode,

[0009] - wherein, viewed from the first power terminal to the first control terminal, the first diode is forward-biased and the second diode is reverse-biased,

[0010] - wherein the second diode is designed as a Zener diode and has a breakdown voltage between an operating voltage of the electrical switching device and the breakdown voltage of the switching element.

[0011] Such a switching device is generally known. It is used particularly in converters.

[0012] When the switching element—for example, an IGBT—is turned off, a brief overvoltage occurs due to parasitic and stray inductances. The magnitude of this overvoltage can reach the breakdown voltage of the switching element, particularly in the event of a short circuit, and even exceed it if it is not limited. In this case, the overvoltage could destroy the switching element.

[0013] The first diode circuit serves to limit such an overvoltage.

[0014] The first diode of the diode circuit has the function of preventing a current flow from the first driver circuit to the first power terminal when the switching element is on (i.e. when the two power terminals are connected to each other with low resistance). The blocking voltage or breakdown voltage of the first diode therefore only needs to be greater than the maximum possible output voltage of the first driver circuit. In practice, the maximum possible output voltage of the first driver circuit for power switches is usually in the range between 25 V and 50 V, and often even in the range between 30 V and 40 V. The first diode is designed accordingly in the state of the art.

[0015] The actual overvoltage protection is provided by the second diode, which is in the form of a Zener diode. If the overvoltage exceeds the Zener voltage of the Zener diode, the Zener diode becomes conductive. This causes current to flow from the first power terminal to the first control terminal. This current slows down the switching element's switching-off process. This reduces the speed at which the switched current drops. The overvoltage is reduced due to the reduced speed. The Zener voltage of the Zener diode is usually chosen so that it is approximately halfway between the operating voltage of the electrical switching device and the breakdown voltage of the switching element.

[0016] Such protection against overvoltages can be easily implemented with a two-level converter. With a three-level converter, such protection for the switching elements that connect the high and low DC potential of the three-level converter to the AC voltage terminal of the three-level converter is also easily implemented. However, with a three-level converter, it may be the case that such protection for the switching elements that connect the medium DC potential of the three-level converter to the AC voltage terminal cannot be implemented, or can only be implemented with considerable difficulty. In particular, in the prior art it may be necessary for this purpose to contact a terminal of such a switching element that is not easily accessible.

[0017] The object of the present invention is to further develop a switching device of the type mentioned above in such a way that it can provide overvoltage protection for the switching element regardless of the location of a larger circuit where the switching device is used. In particular, the overvoltage protection should also be possible when the switching device is used to connect the average DC voltage potential of a three-level converter to the AC voltage terminal of the three-level converter.

[0018] The object is achieved by a switching device having the features of claim 1. Advantageous embodiments of the switching device are the subject of dependent claims 2 to 15.

[0019] According to the invention, a switching device of the type mentioned at the outset is designed in that the first diode has a breakdown voltage above the breakdown voltage of the switching element.

[0020] In many cases the switching element is designed as a voltage-controlled switching element, for example based on an IGBT or an FET. This design is widespread, works reliably and has low switching losses. Preferably the second diode is arranged in front of the first diode as viewed from the first power connection to the first control connection. This design has the advantage that only (exactly) two diodes are required to implement the overvoltage protection and on the one hand a connection point is still accessible which is located behind the second diode as viewed from the first power connection to the first control connection, but on the other hand there is a further diode between the connection point and the first control connection, namely the aforementioned first diode. This design has advantages for certain functions of controlling the first control connection.

[0021] Alternatively, it is possible for the first diode to be arranged upstream of the second diode, as seen from the first power terminal to the first control terminal, but for the first diode circuit to additionally comprise a third diode which, as seen from the first power terminal to the first control terminal, is arranged downstream of the second diode and is forward-biased, as seen from the first power terminal to the first control terminal. In this case, the position of the connection point is realized between the second and third diodes.

[0022] It is also possible for the first diode to have a breakdown voltage above the breakdown voltage of the switching element. In this case, the breakdown voltage of the third diode can be chosen almost arbitrarily. However, the first and third diodes are equivalent as far as overvoltage protection is concerned. In a modification of the basic principle of the present invention, it is therefore possible for the first diode to have a breakdown voltage below the breakdown voltage of the switching element, but for the sum of the breakdown voltages of the first and third diodes to be above the breakdown voltage of the switching element. In this case, the required resulting breakdown voltage is, so to speak, divided between the first and third diodes.In some cases, as far as the switching device is concerned, it may be permissible for a current flow from the second to the first power connection to be possible regardless of whether the switching element is switched on or blocked due to the first control signal for the current flow from the first to the second power connection. In this case, the current flow from the second to the first power connection is generally controlled by a further switching device, which is generally also designed according to the invention. Such a case occurs, for example, with a two-level converter. In this case, a respective switching device can connect the high and low DC voltage potential to the AC voltage connection of the two-level converter, and each of the switching devices can be designed according to the invention.In a three-level converter, this applies to those switching elements that connect the high and low DC voltage potentials to the AC voltage terminal of the three-level converter.

[0023] However, the switching device according to the invention is often used to connect the average DC voltage potential of a three-level converter to the AC voltage terminal of the three-level converter. In this case, the switching element has a second control terminal connected to a second driver circuit, via which a second control signal can be fed to the second control terminal, so that the switching element is switched on or off for a current flow from the second to the first power terminal, depending on the value of the second control signal. Thus, the current flow can be switched on or off in both directions as required.

[0024] In most cases, the two control terminals are controlled in a similar way. In this case, the first and second driver circuits can be combined into a common driver circuit. In order to ensure complete overvoltage protection in the event that the current flow from the second to the first power terminal can be switched through or blocked by means of the second control signal, the switching device is preferably designed such that

[0025] - that the second control terminal is connected to the second power terminal via a second diode circuit,

[0026] - that the second diode circuit comprises a series connection of a fourth and a fifth diode,

[0027] - that, viewed from the second power terminal to the second control terminal, the fourth diode is forward-biased and the fifth diode is reverse-biased,

[0028] - that the fourth diode has a breakdown voltage above the breakdown voltage of the switching element and

[0029] - that the fifth diode is designed as a Zener diode and has a breakdown voltage between the operating voltage and the breakdown voltage of the switching element.

[0030] In the second diode circuit, the above-explained embodiments of the first diode circuit can be implemented in an analogous manner. The fourth diode can therefore be arranged before or after the fifth diode, as seen from the second power connection to the second control connection. If arranged before the fifth diode, a sixth diode is preferably additionally present, which is arranged after the fifth diode, as seen from the second power connection to the second control connection, and is forward-biased as seen from the second power connection to the second control connection. If necessary - analogous to the first and third diodes - the total required breakdown voltage can again be divided between the fourth and sixth diodes.

[0031] In many cases, the switching element has a first and a second transistor element, wherein the first and the second transistor element are connected in series. In this case, the first control terminal is a component of the first transistor element, and the second control terminal is a component of the second transistor element. A freewheeling diode is connected in parallel with each of the two transistor elements. The first freewheeling diode connected in parallel with the first transistor element is reverse-biased as seen from the first to the second power terminal, and the second freewheeling diode connected in parallel with the second transistor element is forward-biased.

[0032] Preferably, in the case of a series connection of the two transistor elements, the second transistor element is arranged in front of the first transistor element, as seen from the first to the second power terminal. This configuration is generally common.

[0033] As an alternative to a series connection of the two transistor elements, it is possible for the switching element to have two transistor elements, but the two transistor elements to be connected in parallel. In this case too, the first control terminal is a component of the first transistor element and the second control terminal is a component of the second transistor element. However, diodes connected in parallel or in series, similar to the freewheeling diodes in a series connection of two transistor elements, are not present. One such switching element is marketed, for example, by the company Fuji.

[0034] As an alternative to using two transistor elements, it is also possible for the switching element to be designed as an intrinsically bidirectionally switchable switching element. Such a switching element is, for example, a so-called bidirectional switch, particularly one based on GaN. Such a switch is marketed, for example, by Panasonic.

[0035] As already mentioned, the first power terminal is preferably connected to a middle of three DC voltage potentials of a three-level converter, and the second power terminal is connected to an AC voltage terminal of the three-level converter. In this embodiment, the present invention demonstrates its full advantages.

[0036] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of the embodiments, which are explained in more detail in conjunction with the drawings. Herein, in schematic representation:

[0037] FIG 1 an electrical circuit,

[0038] FIG 2 a converter unit,

[0039] FIG 3 a modification of the converter unit of FIG 2,

[0040] FIG 4 a converter unit,

[0041] FIG 5 shows a modification of the converter unit of FIG 4,

[0042] FIG 6 a switching element,

[0043] FIG 7 another switching element and

[0044] FIG 8 another switching element.

[0045] According to FIG. 1, a DC voltage circuit 1 has a low potential U1 and a high potential U2. The two potentials U1 and U2 are connected to each other by a capacitor device 2. In this case, the capacitor device has two capacitor units 3 connected in series. As a result, the DC voltage circuit 1 is capable of providing a medium potential U0 in addition to the low potential U1 and the high potential U2.

[0046] The three potentials UO, Ul, U2 are connected to several (usually three) converter units 4. The converter units 4 - this is shown in FIG 1 for only one of the converter units 4 - each have a first, a second and a third electrical switching device 5 to 7. Via the respective switching device 5 to 7 (more precisely: via a respective AC voltage connection of the respective converter unit 4) one of the three potentials UO, Ul, U2 can be supplied to a load 8. In the circuit of FIG 1, the converter units 4 are each designed as three-level converters. The respective third switching device 7 could, however, also be omitted. In this case, the converter units 4 are each designed as two-level converters. In this case, the capacitor device 2 could also be designed as a uniform capacitor device.The division into two capacitor units 3 connected in series could therefore be omitted, so that the average potential UO is not made available at all.

[0047] Furthermore, it is assumed here that the energy flow occurs from the DC circuit 1 to the load 8. In principle, however, the reverse energy flow is also possible.

[0048] The structure of the first electrical switching device 5 is explained in more detail below in conjunction with FIG. 2, using one of the converter units 4. Analogous explanations apply to the second electrical switching device 6. The structure of the third electrical switching device 7 will be explained separately later.

[0049] According to FIG. 2, the first switching device 5 has a switching element 9 with a first power terminal 10 and a second power terminal 11. Typically, the switching element 9 is designed as a voltage-controlled switching element, for example as an IGBT or as an FET.

[0050] The first power terminal 10 is connected to the potential U2. The second power terminal 11 is connected to the load 8. The switching element 9 also has a first control terminal 12 and a first driver circuit 13. The first driver circuit 13 is connected to the first control terminal 12 (usually via a resistor 14) so ​​that a first control signal S1 is supplied to the first control terminal 12 from the first driver circuit 13. The first control signal S1 is generally binary, i.e. it has either a high or a low value. At one of the values, the switching element 9 is switched on for a current flow from the first to the second power terminal 10, 11. At the other of the values, the switching element 9 is blocked for a current flow from the first to the second power terminal 10, 11.

[0051] The direction of the current flow is relevant in this case. This is because a freewheeling diode 15 is clearly connected in parallel with the switching element 9. The freewheeling diode 15 can be an intrinsic component of the switching element 9. Alternatively, it can be an independent diode (i.e. a discrete component). A current flow in the opposite direction (i.e. from the second to the first power connection 11, 10) is possible via the freewheeling diode 15, regardless of whether the switching element 9 is switched on or off due to the first control signal S1 for the current flow from the first to the second power connection 10, 11. Whether or not a current actually flows from the second to the first power connection 11, 10 is generally controlled by one of the switching devices 5 to 7 of one of the other converter units 4.

[0052] The first control terminal 12 is connected to the first power terminal 10 via a first diode circuit 16. The first diode circuit 16 comprises a series connection of a first and a second diode 17, 18. Viewed from the first power terminal 10 to the first control terminal 12, the first diode 17 is forward-biased. The second diode 18 is reverse-biased.

[0053] The first diode 17 is designed as a "normal" diode. The second diode 18, however, is designed as a Zener diode.

[0054] The decisive factor for the present invention is the design of the first and second diodes 17, 18, specifically the determination of the breakdown voltage of the first diode 17 and the determination of the breakdown voltage of the second diode 18. The starting point is the remaining design of the electrical switching device 5. Firstly, the switching element 9 has a breakdown voltage up to which it can be operated. Furthermore, the electrical switching device 5 is operated with an operating voltage U. The operating voltage U is the difference between the high potential U2 and the low potential Ul. The second diode 18 has a breakdown voltage between the operating voltage U and the breakdown voltage of the switching element 9. The first diode 17, on the other hand, has a breakdown voltage above the breakdown voltage of the switching element 9.

[0055] If, for example, the operating voltage U is approximately 400 V, the breakdown voltage of the switching element 9 must first be sufficiently above 400 V. Otherwise, proper functioning of the switching element 9 would not be possible. In particular, the current flow from the first to the second power terminal 10, 11 could not otherwise be blocked by the switching element 9. Typically, with an operating voltage U of approximately 400 V, the breakdown voltage of the switching element 9 is approximately 650 V. The breakdown voltage of the second diode 18 (i.e. the Zener voltage) is usually approximately halfway between the operating voltage U and the breakdown voltage of the switching element 9, in this case approximately 525 V. In contrast, the breakdown voltage of the first diode 17 must in this case be above 650 V, for example between 700 V and 1000 V.

[0056] 2, the second diode 18 is arranged upstream of the first diode 17, as seen from the first power terminal 10 to the first control terminal 12. However, as shown in FIG. 3, it is alternatively also possible to provide the reverse order. In this case, the first diode 17 is arranged upstream of the second diode 18, as seen from the first power terminal 10 to the first control terminal 12. In this case, the first diode circuit 16 preferably additionally comprises a third diode 19, as shown in FIG. 3. The third diode 19 is arranged downstream of the second diode 18, as seen from the first power terminal 10 to the first control terminal 12, and is forward-biased as seen from the first power terminal 10 to the first control terminal 12.

[0057] The third diode 19 also has a breakdown voltage. In principle, the breakdown voltages of the first and third diodes 17, 19 can be added together. In the embodiment according to FIG. 3, it is therefore possible for the first diode 17 to have a breakdown voltage below the breakdown voltage of the switching element 9. This is because it is sufficient for the sum of the breakdown voltages of the first and third diodes 17, 19 together to be above the breakdown voltage of the switching element 9.

[0058] FIG. 4 shows a further converter unit 4. The structure of the third electrical switching device 7 is explained in more detail in conjunction with FIG. 4. As far as the first and second switching devices 5, 6 are concerned, these can be designed as explained above in conjunction with FIGS. 2 and 3. However, they can also be designed differently. As far as the third electrical switching device 7 has the same components as the first electrical switching device 5, the same reference numerals are used below.

[0059] According to FIG 4, the third switching device 7 has a switching element 9 with a first power connection 10 and a second power connection 11. The first power connection 10 in the third switching device 7 is connected to the average potential U0. The second power connection 11 is connected to the load 8. The switching element 9 also has a first control connection 12 and a first driver circuit 13. The first driver circuit 13 is connected to the first control connection 12 (usually via a resistor 14) so ​​that a first control signal S1 is supplied to the first control connection 12 from the first driver circuit 13. The first control signal S1 is generally binary, i.e. has either a high or a low value. At one of the values, the switching element 9 is switched through for a current flow from the first to the second power connection 10, 11.At the other of the values, the switching element 9 is blocked for a current flow from the first to the second power terminal 10, 11.

[0060] The direction of the current flow is still relevant in the present case. This is because, in addition to the first control terminal 12, the switching element 9 has a second control terminal 20 and a second driver circuit 21. The second driver circuit 21 is connected to the second control terminal 20 (usually via a resistor 22), so that a second control signal S2 is supplied to the second control terminal 20 from the second driver circuit 21. The second control signal S2 is generally also binary, i.e. has either a high or a low value. At one of the values, the switching element 9 is switched on for a current flow from the second to the first power terminal 11, 10. At the other of the values, the switching element 9 is blocked for a current flow from the second to the first power terminal 11, 10.

[0061] By means of the switching element 9 of the third switching device 7, it is possible to independently set whether the switching element 9 is switched on or off for the respective current flow in both directions. Possible configurations of the switching element 9 of the third switching device 7 will be explained in more detail later.

[0062] The first control terminal 12 is connected to the first power terminal 10 via a first diode circuit 16. The first diode circuit 16 comprises a series connection of a first and a second diode 17, 18. Viewed from the first power terminal 10 to the first control terminal 12, the first diode 17 is forward-biased. The second diode 18 is reverse-biased. The first diode 17 is designed as a "normal" diode. The second diode 18, in contrast, is designed as a Zener diode.

[0063] In an analogous manner, the second control terminal 20 is connected to the second power terminal 11 via a second diode circuit 23. The second diode circuit 23 comprises a series circuit of a fourth and a fifth diode 24, 25.

[0064] Viewed from the second power terminal 11 to the second control terminal 20, the fourth diode 24 is forward-biased. The fifth diode 25 is reverse-biased. The fourth diode 24 is designed as a "normal" diode. The fifth diode 25, on the other hand, is designed as a Zener diode.

[0065] The design of the first and second diodes 17, 18 and of the fourth and fifth diodes 24, 25 is crucial for the present invention, specifically the determination of the breakdown voltages of said diodes 17, 18, 24 and 25.

[0066] The above statements made in connection with FIG. 2 continue to apply to the first and second diodes 17, 18. The second diode 18 thus has a breakdown voltage between the operating voltage U and the breakdown voltage of the switching element 9, while the first diode 17 has a breakdown voltage above the breakdown voltage of the switching element 9.

[0067] Analogous designs apply to the fourth and fifth diodes 24, 25. Thus, the fifth diode 25 has a breakdown voltage between the operating voltage U and the breakdown voltage of the switching element 9, while the fourth diode 24 has a breakdown voltage above the breakdown voltage of the switching element 9.

[0068] In the embodiment of the third switching device 7 explained above in connection with FIG. 4, the second diode 18 is arranged upstream of the first diode 17, as seen from the first power terminal 10 to the first control terminal 12. Likewise, the fifth diode 25 is arranged upstream of the fourth diode 24, as seen from the second power terminal 11 to the second control terminal 20. However, as shown in FIG. 5, it is alternatively also possible to provide the reverse sequence.

[0069] As in the embodiment of FIG. 3, the first diode circuit 16 in this case preferably additionally comprises the third diode 19, as shown in FIG. 5. For further embodiments, in particular the design of the third diode 19 and, if appropriate, the distribution of the required breakdown voltage between the first and third diodes 17, 19, the statements relating to FIG. 3 continue to apply.

[0070] In an analogous manner, in the embodiment of FIG. 5, the second diode circuit 23 preferably additionally comprises a sixth diode 26. The sixth diode 26 is arranged after the fifth diode 25, as seen from the second power terminal 11 to the second control terminal 20, and is forward-biased, as seen from the second power terminal 11 to the second control terminal 20.

[0071] Just as with the interaction of the first and third diodes 17, 19, the breakdown voltages of the fourth and sixth diodes 24, 26 can also be added together. Analogous to the first and third diodes 17, 19, in the embodiment according to FIG. 5, it is therefore possible for the fourth diode 24 to have a breakdown voltage below the breakdown voltage of the switching element 9. This is because it is sufficient for the sum of the breakdown voltages of the fourth and sixth diodes 24, 26 together to be above the breakdown voltage of the switching element 9.

[0072] Just as in the embodiments of FIGS. 2 and 3, the switching element 9 in the embodiments of FIGS. 4 and 5 is also preferably designed as a voltage-controlled switching element. Possible embodiments of the switching element 9 of the third switching device 7 are explained below in conjunction with FIGS. 6 to 8. The diode circuits 16, 23 are shown only as units in FIGS. 6 to 8. The internal structure of the diode circuits 16, 23 is as explained above in conjunction with FIGS. 4 and 5.

[0073] In the embodiment according to FIG. 6, the switching element 9 has a first and a second transistor element 27, 28. The two transistor elements 27, 28 are connected in series.

[0074] In this embodiment, the first control terminal 12 is a component of the first transistor element 27, and the second control terminal 20 is a component of the second transistor element 28. Furthermore, a first freewheeling diode 29 is connected in parallel with the first transistor element 27. The first freewheeling diode 29 is reverse-biased, as seen from the first to the second power terminal 10, 11. Likewise, a second freewheeling diode 30 is connected in parallel with the second transistor element 28, but is forward-biased, as seen from the first to the second power terminal 10, 11.

[0075] In the embodiment according to FIG. 6, the second transistor element 28 is arranged in front of the first transistor element 27, as seen from the first to the second power terminal 10, 11. This arrangement is preferred. In principle, however, the reverse arrangement would also be possible. Furthermore, the transistor elements 27, 28 are usually designed as voltage-controlled transistors, for example as IGBTs or as FETs. As a result, the switching element 9 as a whole is also designed as a voltage-controlled switching element.

[0076] In the embodiment according to FIG 7, the switching element 9 also has a first and a second transistor element 27, 28.

[0077] However, the two transistor elements 27, 28 are not connected in series, but in parallel. In this embodiment, too, the first control terminal 12 is a component of the first transistor element 27, and the second control terminal 20 is a component of the second transistor element 28. Freewheeling diodes are not present. Analogous to FIG. 6, the transistor elements 27, 28 are usually designed as voltage-controlled transistors, for example as IGBTs or FETs. As a result, the switching element 9 as a whole is also designed as a voltage-controlled switching element.

[0078] In the embodiment according to FIG. 8, the switching element 9 is designed as an intrinsically bidirectionally switchable switching element 9. Here, too, the switching element 9 is designed as a voltage-controlled switching element.

[0079] In summary, the present invention relates to the following:

[0080] An electrical switching device 5 to 7 has a switching element 9 with a first power connection 10, a second power connection 11 and a first control connection 12 for connecting an electrical potential UO, Ul, U2 to a load 8. The switching element 9 has a breakdown voltage up to which it can be operated. The first control connection 12 is connected to a first driver circuit 13, via which a first control signal S1 can be fed to the first control connection 12, so that the switching element 9 is switched on or blocked depending on the value of the first control signal S1 for a current flow from the first to the second power connection 10, 11. The first control connection 12 is connected to the first power connection 10 via a first diode circuit 16. The first diode circuit 16 comprises a series connection of a first and a second diode 17, 18.Viewed from the first power terminal 10 to the first control terminal 12, the first diode 17 is forward-biased, and the second diode 18 is reverse-biased. The second diode 18 is designed as a Zener diode and has a breakdown voltage between an operating voltage U of the electrical switching device 5 to 7 and the breakdown voltage of the switching element 9. The first diode 17 has a breakdown voltage above the breakdown voltage of the switching element 9.

[0081] The present invention has many advantages. It is simple and reliable and can be used with many switching devices 5 to 7. Above all, however, it can also be used when the switching device 5 to 7—as in the present case with the third switching device 7—is to be operated bidirectionally. This applies in this case regardless of the specific design of the corresponding switching element 9.

[0082] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited to the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims

Patent claims 1. Electrical switching device for connecting an electrical potential (UO, Ul, U2) to a load (8), - wherein the switching device comprises a switching element (9) with a first power terminal (10), a second power terminal (11) and a first control terminal (12), - wherein the switching element (9) has a breakdown voltage up to which it can be operated, - wherein the first control terminal (12) is connected to a first driver circuit (13), via which a first control signal (S1) can be supplied to the first control terminal (12), so that the switching element (9) is switched through or blocked for a current flow from the first to the second power terminal (10, 11) depending on the value of the first control signal (S1), - wherein the first control terminal (12) is connected to the first power terminal (10) via a first diode circuit (16), - wherein the first diode circuit (16) comprises a series connection of a first and a second diode (17, 18), - wherein, viewed from the first power terminal (10) to the first control terminal (12), the first diode (17) is forward-biased and the second diode (18) is reverse-biased, - wherein the second diode (18) is designed as a Zener diode and has a breakdown voltage between an operating voltage (U) of the electrical switching device and the breakdown voltage of the switching element (9), characterized in that the first diode (17) has a breakdown voltage above the breakdown voltage of the switching element (9).

2. Switching device according to claim 1, characterized in that the switching element (9) is designed as a voltage-controlled switching element.

3. Switching device according to claim 1 or 2, characterized in that, viewed from the first power terminal (10) to the first control terminal (12), the second diode (18) is arranged in front of the first diode (17).

4. Switching device according to claim 1, 2 or 3, characterized in that the first diode (17) is arranged in front of the second diode (18) as seen from the first power connection (10) to the first control connection (12), that the first diode circuit (16) additionally comprises a third diode (19), that the third diode (19) is arranged after the second diode (18) as seen from the first power connection (10) to the first control connection (12), and that the third diode (19) is polarized in the forward direction as seen from the first power connection (10) to the first control connection (12).

5. Switching device according to claim 4, characterized in that although the first diode (17) has a breakdown voltage below the breakdown voltage of the switching element (9), the sum of the breakdown voltages of the first and the third diode (17, 19) together is above the breakdown voltage of the switching element.

6. Switching device according to one of claims 1 to 5, characterized in that a current flow from the second to the first power connection (11, 10) is possible regardless of whether the switching element (9) is switched on or blocked due to the first control signal (S1) for the current flow from the first to the second power connection (10, 11).

7. Switching device according to one of claims 1 to 5, characterized in that - that the switching element (9) has a second control terminal (20) which is connected to a second driver circuit (21) via which a second control signal (S2) can be supplied to the second control terminal (20), so that the switching element (9) is switched through or blocked for a current flow from the second to the first power terminal (11, 10) depending on the value of the second control signal (S2), - that the second control terminal (20) is connected to the second power terminal (11) via a second diode circuit (23), - that the second diode circuit (23) comprises a series connection of a fourth and a fifth diode (24, 25), - that, viewed from the second power terminal (11) to the second control terminal (20), the fourth diode (24) is forward-biased and the fifth diode (25) is reverse-biased, - that the fourth diode (24) has a breakdown voltage above the breakdown voltage of the switching element (9) and - that the fifth diode (25) is designed as a Zener diode and has a breakdown voltage between the operating voltage (U) and the breakdown voltage of the switching element (9).

8. Switching device according to claim 7, characterized in that, viewed from the second power terminal (11) to the second control terminal (20), the fifth diode (25) is arranged in front of the fourth diode (24).

9. Switching device according to claim 7 or 8, characterized in that, viewed from the second power terminal (11) to the second control terminal (20), the fourth diode (24) is arranged in front of the fifth diode (25), that the second diode circuit (23) additionally comprises a sixth diode (26), that the sixth diode (26) is arranged after the fifth diode (25) viewed from the second power terminal (11) to the second control terminal (20), and that the sixth Diode (26) is forward-polarized as seen from the second power terminal (11) to the second control terminal (20).

10. Switching device according to claim 9, characterized in that although the fourth diode (24) has a breakdown voltage below the breakdown voltage of the switching element (9), the sum of the breakdown voltages of the fourth and the sixth diode (24, 26) together is above the breakdown voltage of the switching element (9).

11. Switching device according to one of claims 7 to 10, characterized in that - that the switching element (9) has a first and a second transistor element (27, 28), - that the first and second transistor elements (27, 28) are connected in series, - that the first control terminal (11) is a component of the first transistor element (27) and the second control terminal (20) is a component of the second transistor element (28), - that a first freewheeling diode (29) is connected in parallel with the first transistor element (27), which is reverse-biased as seen from the first to the second power terminal (10, 11), and - that a second freewheeling diode (30) is connected in parallel with the second transistor element (28), which is polarized in the forward direction as seen from the first to the second power terminal (10, 11).

12. Switching device according to claim 11, characterized in that, viewed from the first to the second power terminal (10, 11), the second transistor element (28) is arranged in front of the first transistor element (27).

13. Switching device according to one of claims 7 to 10, characterized in that that the switching element (9) has a first and a second transistor element (27, 28), that the first and the second transistor element (27, 28) are connected in parallel and that the first control terminal (11) is a component of the first transistor element (27) and the second control terminal (20) is a component of the second transistor element (28).

14. Switching device according to one of claims 7 to 10, characterized in that the switching element (9) is designed as an intrinsically bidirectionally switchable switching element.

15. Switching device according to one of claims 7 to 14, characterized in that the first power terminal (10) is connected to a middle (U0) of three direct voltage potentials (U0, Ul, U2) of a three-level converter (4) and the second power terminal (11) is connected to an alternating voltage terminal of the three-level converter (4).

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