Input circuit for power supply

Abstract

The specific invention relates to an input circuit (ES) for a power supply. Here, an input voltage (Ue) of the input circuit (ES) is converted into an output voltage (Ua) of the input circuit (ES) by periodically switching a switching element (SE) between an on state and an off state, wherein at least partially during the switching cycle of the switching element (SE), a current (IL) flows through an inductor (L) arranged in series with the switching element (SE). The current (IL) charges a capacitor (Ca) on the output side, from which the output voltage (Ua) is provided, and in the off state of the switching element (SE) the current (IL) is absorbed by an active switching unit (FD). In addition, if a predetermined breakdown voltage (Ud) is exceeded at the switching element (SE), a current is allowed to pass (IAVAL) through the switching element (SE) in the off state. If an overvoltage is detected at the input of the input circuit (ES), the switching element (SE) can be switched to the off state. The resulting current (IAVAL) can then be transferred to the inductance (L) of the input circuit (ES), and the active switching unit (FD) can be switched off via this. For this purpose, the switching element (SE) and the inductance (L) are dimensioned such that, when an overvoltage occurs, a so-called avalanche energy is generated at the switching element (SE), in which case the switching element (SE) withstands the current (IL) flowing through the inductance (L) for the duration of the overvoltage.

Description

Technical Field

[0001] The specific invention generally relates to the field of electrical engineering, in particular to the field of power electronics and power electronic circuits. In particular, the invention relates to an input circuit for a power supply. Here, an input voltage of the input circuit is converted into an output voltage of the input circuit by periodically switching a switching element between an on state and an off state, wherein at least partially during the switching cycle of the switching element, a current flows through an inductor arranged in series with the switching element. This current charges a capacitor on the output side, from which the output voltage is provided, and in the off state of the switching element, the current is absorbed by the active switching unit. In addition, if a predetermined breakdown voltage is exceeded at the switching element, a current is allowed to flow (Stromfluss) through the switching element in the off state. Background Art

[0002] In automation technology, power supplies are currently often used: the power supply provides a DC voltage as an output voltage for supplying consumers such as control electronics or other parts of electrical installations. As a predefined supply voltage, such a power supply supplies a predetermined output voltage (for example, a 24V DC voltage as a rated output voltage, and a 28V DC voltage as a maximum output voltage). Such power supplies are usually fed from a single-phase or multi-phase (mostly three-phase) power supply network, wherein, for example, the busbar (Verschienung) of the neutral line is increasingly cancelled in electrical installations, and it is increasingly necessary to use the following power supply: the power supply can, for example, generate a 24V DC voltage from a three-phase AC voltage of 400V to 500V. For efficiency reasons, such power supplies are not uncommonly established in multiple stages. Here, the rectifier unit is often set as an input stage or input loop, and the rectifier unit converts the AC voltage from the power supply network into a usually unstable or unregulated DC voltage as an input voltage for the power supply. Furthermore, an intermediate stage or an intermediate circuit can be provided as an input circuit for the power supply, by which an unstable or unregulated input voltage is converted into a stable or regulated intermediate voltage, so that, for example, a downstream efficient converter stage receives a defined input voltage. From the regulated intermediate circuit voltage, the converter stage then generates a predefined output voltage for supplying a consumer.

[0003] Firstly, in the field of automation technology, due to the increase in power electronics and the increasing complexity of electrical installations, various devices or consumers (such as motors, power supplies, etc.) connected to the power supply network may increasingly further react to the network. For example, these reactions to the network may lead to the superposition of disturbances that leave traces on the power supply network, and thus in turn lead to higher loads on the connected consumers. In particular, consumers with relatively low power, such as power supplies, are mostly only able to limit or divert the disturbances that occur, such as overvoltages. In particular, when switching actions are performed on the power supply network (such as triggering fuses, removing or connecting large loads, etc.), in particular, overvoltage pulses may be generated by the inductive effect of longer leads (through which the current is attempted to be maintained), which consumers with relatively low power, such as power supplies, must also withstand, and which are mostly significantly greater than the sinusoidal peak voltage of the predetermined supply voltage or network voltage (for example 400V to 500V).

[0004] In power supplies connected to a three-phase power supply network, it is common to use so-called varistors, for example, in the input stage to limit overvoltage. A varistor is an electronic component that is characterized by a voltage-dependent resistance. In normal operation (for example, in the case of a predetermined network voltage), the resistance of the varistor is very large, so that the varistor does not affect the characteristics of the circuit. Above a predetermined threshold voltage that is typical for the corresponding varistor, or in the case of an overvoltage, the differential resistance of the varistor becomes relatively small almost without delay as the attached voltage rises. As a result, the varistor is suitable for protecting sensitive circuits such as power supplies from overvoltage damage. By using a varistor on the input side in the power supply, for example, very high currents can be drawn away, and overvoltage pulses from the power supply network can be limited by establishing a large pulse power loss.

[0005] However, the disadvantages of using varistors are the large tolerances of the operating voltage due to the process and the residual internal resistance, which also causes a significant increase in the following voltage when a large current flows: the voltage is required in order to be able to draw off the current. This voltage is usually called a protection level (Schutzpegel). This means that the power supply must be designed according to a voltage peak of up to 2000V in the case of overvoltage, the power supply is dimensioned for supplying an AC voltage of 500V, and the power supply must, for example, comply with safety standards such as the so-called UL508 (UL stands for Underwriters Laboratories Inc.® - one of the world's leading testing and certification organizations in the field of product safety). By complying with safety standards (such as UL508), for example, a varistor rated voltage of at least 20% above a predetermined supply voltage (such as 500V AC voltage) is pre-specified, that is, the varistor rated voltage must, for example, be at least 600V AC voltage. For example, in the case of high limiting currents (e.g. 1000 amperes and more), commercially available varistors with such a varistor rated voltage (e.g. 625 V AC voltage) have protection levels in the range from approximately 1800 V to 2000 V peak, according to which the power supply must then be designed for overvoltage situations, in particular in order that the converter stage is not damaged.

[0006] For example, from the document DE 200 10 283 U1, a power supply with low-loss switch-on current limitation is known, in which a current limiting element (such as, for example, a field effect transistor or a bipolar transistor with an insulated gate electrode (IGBT)) is arranged in the DC voltage line downstream of the rectifier. With the help of a current sensor, the current through the transistor switched to conduction is measured, and with the help of a voltage sensor (Spannungsfuehler), the voltage at the transistor is measured. The signals of the two measuring devices are correlated with each other and converted into a control signal (Ansteuersignal) for the transistor. If a voltage jump occurs at the input of the power supply, for example (for example, a voltage peak during the switch-on process, operation), the voltage jump may cause a relatively high current through the transistor, which is detected with the help of a current sensor. Then, the transistor is controlled to linear operation and the current flowing in the circuit is thus limited. However, this method is only possible for relatively low input voltages (eg up to approximately 200 V) and currents to be limited of small values, since transistors (eg MOS FETs, IGBTs) have only limited performance in linear operation.

[0007] In the case of a power supply via a three-phase network, for example, with an AC voltage of up to 500 V or more, a transistor, in particular a transistor implemented as an IGBT, is blocked, for example, from a predeterminable differential voltage (for example 50 V) in order to protect the transistor from excessive power loss during linear operation. In order to charge the intermediate circuit capacitor, a resistor can be arranged, for example, in parallel with the transistor. However, the variant of the power supply known from document DE 200 10 283 U1 has the following disadvantages: for example, in the case of an overvoltage, it is only switched off when a relatively high current flows through the transistor; and the relatively high energy in the power supply may generate internal overvoltages when switched off. In addition, the power supply has a relatively high harmonic component and, as a result, requires, for example, a laminated core choke, which usually has a relatively large size and leads to additional power loss in the power supply.

[0008] Since devices such as power supplies have nonlinear load characteristic curves, even in the case of a purely sinusoidal supply voltage, distorted current and voltage variation curves may occur at the input, or current harmonic oscillations or current harmonics may occur. The grid voltage is affected by this, and harmonics may cause interference in the corresponding power supply grid and in other devices connected to the power supply grid. Therefore, in power supplies, filters are usually used in most cases after the input stage or the rectifier unit to limit harmonics. As a passive filter for limiting harmonics, for example, a choke with a large inductance can be used. Although these passive filters for limiting harmonics can be simply manufactured, only moderately good results are achieved. That is to say, with the help of chokes, harmonics can only be reduced with a reserved effect. In addition, because the frequency of the supply voltage is relatively low, a choke with a relatively large outer size is required in most cases.

[0009] Another possibility for limiting harmonics is to limit them using active filters, which try to ensure that the received current corresponds as closely as possible to the sinusoidal grid voltage. As such a filter, for example, a switching converter can be used, which can be arranged, for example, at the input stage of the power supply or downstream of the rectifier unit, or in an intermediate stage of the power supply. The switching converter can be implemented, for example, as a boost converter, in the case of which the magnitude of the output voltage is always greater than the magnitude of the input voltage. In the case of relatively large input voltages, such as, for example, in the case of grid voltages of 400 V to 500 V AC voltage, this has the disadvantage that the input voltage is further increased for the stages of the power supply that follow the boost converter.

[0010] Boost converters are usually designed for use in single-phase power grids, where the boost converter causes the current consumption to directly track the power grid voltage and obtain a very strong sine-like current shape. In the case of a three-phase power grid voltage, a bridge circuit is usually used, for example because of the different potentials between the phases, so as to obtain a sinusoidal current in all three phases. Such a bridge circuit mostly includes six individually controllable switching elements (such as MOS-FET, IGBT, etc.) and an inductor connected upstream for each phase. By appropriately controlling these six switching elements at a switching frequency that is significantly higher than the frequency of the power grid AC voltage being supplied, the desired current shape can be achieved. However, such a circuit is very component-intensive and also requires a costly control circuit, which is currently mostly implemented as a microprocessor circuit. Due to the high cost, such a circuit is mainly used in large converters, for example, because small deviations of the sinusoidal current may have a significant effect on the quality of the power grid.

[0011] Other possibilities with less overhead provide for extracting the supply current of the power supply after the passive three-phase rectifier bridge. However, a large capacitance at the output of the rectifier bridge should be avoided here. The rectifier bridge provides a fluctuating DC voltage, through which the current consumption characteristics of the connected circuit also have a significant impact on the total harmonics. That is to say, for example, the more the received current follows the pulsating output voltage of the rectifier bridge, the smaller the harmonics. Since the rectifier bridge usually only switches the highest section of the network phase in any case (the section may also cause the highest current to pass in the case of a true sinusoidal load), the input current that follows the voltage (although the current passing time of each phase is short, still) has a significant effect of reducing harmonics.

[0012] Document DE 10 2005 002 360 A1 discloses, for example, the use of a buck converter for reducing harmonic oscillations of the mains current consumption of a clocked power supply. However, the switching transistors commonly used to date are not designed for a high cut-off voltage in the event of an overvoltage. On the other hand, switching transistors with a high cut-off voltage (e.g. 1500 V) have a very high on-resistance or are, for example, only suitable for relatively low switching frequencies (e.g. up to 20 kHz), which can result in high switching losses and / or can only meet the requirements for compact dimensions of the power supply with difficulty.

[0013] From document DE 10 2004 059 455 A1, a circuit arrangement for overvoltage detection is known, in which a transient shielding device (transientenausblendung) with a switch (for example an IGBT) is arranged downstream of the rectifier unit and the filter in order to prevent overvoltage from approaching the output stage of the circuit arrangement by cutting off the switch. When the voltage limit value is exceeded, a switch-off command for the switch is sent to the switch, wherein the voltage is measured at the input and at the output of the filter. The output stage is designed, for example, as a buck converter, which includes, for example, MOS-FETs as switches and may also be used, for example, to reduce harmonics. In addition, a series circuit consisting of a further switch and a varistor can be provided in parallel with the output of the transient shielding device, wherein the switch is activated or closed only in the case of an overvoltage, and the overvoltage is eliminated by the varistor. However, the circuit arrangement known from DE 10 2004 059 455 A1 has relatively high switching losses due to the two switches (IGBT, MOS-FET), which reduce the efficiency of the circuit arrangement and therefore require further non-ground-related, potential-free or so-called floating actuation of the switches. Summary of the invention

[0014] The object of the present invention is therefore to specify an input circuit for a power supply which has a high efficiency and a high voltage resistance in the event of overvoltages and which is an improvement over the prior art.

[0015] This object is achieved by an input circuit of the type mentioned at the outset having the features according to the independent claim. Advantageous embodiments of the invention are described in the dependent claims.

[0016] According to the invention, this task is solved by an input circuit for a power supply, wherein the input circuit has at least one switching element arranged on the input side, an inductor arranged in series with the switching element, and an active switching unit. By periodically switching the switching element between an on state and an off state, the input voltage of the input circuit is converted to an output voltage of the input circuit, wherein the output voltage is provided at a capacitor arranged on the output side. During the switching cycle of the switching element, a current at least partially flows through the inductor, which charges the capacitor arranged on the output side. In the case of the off state of the switching element, the current is absorbed by the active switching unit. In addition, in the off state of the switching element, and when a predetermined breakdown voltage is exceeded at the switching element, a current is allowed to pass through the switching element, wherein the predetermined breakdown voltage is higher or greater than the continuous operating voltage of the switching element. When an overvoltage is detected on the input side of the input circuit, the switching element can be switched to the off state. The current passing through the switching element can be transmitted to the inductor, and the current passing will turn off the active switching unit. The switching element and the inductance are dimensioned in such a way that, when an overvoltage occurs, a so-called avalanche energy is generated at the switching element, in which case the switching element withstands the current flowing through the inductance for the duration of the overvoltage.

[0017] The essential aspect of the solution proposed according to the invention is that it is utilized that a current can flow through the switching element in the cut-off state when the voltage applied to the switching element in the cut-off state exceeds a predetermined breakdown voltage. In this case, the predetermined breakdown voltage is above the continuous operating voltage or rated voltage of the switching element. In this case, the predetermined breakdown voltage is the voltage value from which a current is allowed to flow through the switching element, wherein energy loss (for example in the form of heat) is generated in the switching element by the current flow. This energy loss can also be referred to as so-called avalanche energy or breakdown energy. In data sheets, this energy is usually referred to by the abbreviation E. AR The term “single pulse energy” is indicated and provided, for example, with the explanation that it is mostly given at a barrier temperature of 25° C. Typical values ​​for the permissible avalanche energy are usually in the range from 0.2 joule to 0.5 joule.

[0018] The switching element and the inductance (through which the current allowed to flow in the blocked state is transmitted via the switching element) are dimensioned in such a way that, when an overvoltage or an overvoltage pulse occurs at the input of the input circuit, avalanche energy is generated, in which case the switching element withstands the current flowing through the inductance for the duration of the overvoltage. In normal switching operation of the switching element, no predetermined breakdown voltage occurs, since otherwise extreme and undesirable losses could occur in the switching element or the switching element could possibly overheat.

[0019] The input circuit according to the invention has the following advantages: it has a circuit topology that is easy to implement and, by correspondingly dimensioning the switching elements and the inductance, has a high voltage resistance in the case of overvoltage, so that, in the case of overvoltage, it can be used without problems, for example, in power supply networks with an AC voltage of 400 V to 500 V. In addition, the input circuit according to the invention has a high efficiency or a very good and high efficiency due to the simplification of the circuit or the components used, since, for example, no additional switches such as IGBTs with forward power losses and control losses are used for overvoltage protection. In addition, the input circuit has an external size that can be installed, for example, in a switch cabinet, simply and without additional space requirements.

[0020] It is also advantageous to additionally dimension the switching element and the inductor in such a way that the predetermined breakdown voltage at the switching element and the output voltage yield at least one sum value, at which the current flowing through the inductor remains below a predetermined maximum value when the maximum overvoltage to be expected occurs. This makes it possible to additionally increase the voltage resistance of the input circuit in a simple manner. By correspondingly dimensioning the switching element and the inductor, it is ensured that a current with a predetermined maximum value flows through the inductor, thereby limiting the current flow through the switching element even in the case of an overvoltage. That is, the switching element can also withstand the current flowing through the inductor more easily and better during the duration of the overvoltage.

[0021] According to an advantageous embodiment of the input circuit of the invention, an actuation unit is provided for actuating the switching element. The actuation unit can, for example, in normal operation, place the switching element from an on state into a off state or from an off state into an on state. For this purpose, the actuation unit can take into account the output voltage of the input circuit, for example, via feedback, in order to regulate the output voltage to a predetermined value. Furthermore, the actuation unit can be used, for example, to place the switching element into the off state when an overvoltage is detected at the input side of the input circuit.

[0022] In order to identify an overvoltage at the input side of the input circuit, a comparator unit is provided, which can be implemented as an autonomous unit, for example, or can be integrated into the control unit. For example, by means of voltage monitoring, the overvoltage on the input side can be identified by the comparator unit. For this purpose, a voltage value measured indirectly or directly at the input side of the input circuit can be supplied to the comparator unit, wherein the voltage measurement value is compared with a predeterminable reference value. As a predeterminable reference value for comparison with the measured voltage measurement value, for example, a value of a predetermined breakdown voltage at the switching element or a slightly lower value can be used. Then, when the measured voltage measurement value measured and supplied to the comparator unit exceeds the predeterminable reference value, the switching element is placed in a cut-off state, for example, by means of the control unit. In this way, in an ideal case, a shutdown command is sent to the switching element before a large current can be formed.

[0023] Alternatively, the comparator unit can also be constructed so that an overvoltage on the input side can be identified based on a current that is established later or due to an overvoltage. For this purpose, a current measurement value determined by means of a current sensor can be supplied to the comparator unit. Then, the determined current measurement value is compared with a predeterminable reference value, and when the current measurement value determined and supplied to the comparator unit exceeds the predeterminable reference value, the switching element is placed in a cut-off state, for example, by means of a control unit. For this purpose, the current sensor for determining the current measurement value is, for example, arranged in a current path as follows: the current path includes a current passing through the switching element, and in the cut-off state, when a predetermined breakdown voltage is exceeded, the current is allowed to pass at the switching element. When the current measurement value is used to switch the switching element to the cut-off state, in the case of an overvoltage, the established current can be reacted to very quickly in an advantageous manner, because (as long as the current exceeds the predeterminable reference value, then) the current currently flowing is turned off with a small delay or even without delay.

[0024] Advantageously, the switching element is implemented as a semiconductor switch based on silicon carbide, in particular a metal oxide field effect transistor or MOS-FET. Transistors based on silicon carbide (SiC), such as SiC-MOS-FET, are suitable for applications in which they must withstand high temperatures due to their good thermal conductivity. That is to say, semiconductor switches based on SiC are suitable for withstanding higher cut-off voltages, for example. Ideally, semiconductor switches based on silicon carbide have a minimum acceptance capacity for so-called avalanche energy, such as so-called avalanche rating, which is pre-specified as a component characteristic value. In this way, the input circuit and in particular the switching element can be designed very simply for the expected overvoltage event or the expected maximum overvoltage value.

[0025] Alternatively, the switching element may include a semiconductor switch and a unit arranged in parallel with the semiconductor switch for limiting and absorbing avalanche energy in the event of an overvoltage. The unit arranged in parallel for limiting and absorbing avalanche energy relieves the semiconductor switch from receiving avalanche energy, because in the event of an overvoltage, the semiconductor switch is placed in a cut-off state and current is allowed to pass into the inductor primarily via the unit arranged in parallel for limiting and absorbing avalanche energy. In this case, the entire avalanche energy converted in the switching element is first defined by the magnitude and duration of the overvoltage, by determining the size of the inductor and the current flowing into the inductor before this. As the semiconductor switch, for example, a switching transistor with an avalanche rating (such as, for example, a silicon-based MOS-FET, etc.) or a switching transistor without an avalanche rating (such as, for example, a transistor based on gallium nitride) can be used, wherein the switching transistor without an avalanche rating must be protected, in particular from overvoltage damage, by the unit for limiting and absorbing avalanche energy.

[0026] Here, the unit for limiting and receiving the so-called avalanche energy can be advantageously implemented as a so-called suppressor diode, wherein, for example, a silicon-based power Zener diode can be used as a suppressor diode. The semiconductor switch of the switching element is protected from overvoltage damage by the suppressor diode. In particular, the silicon-based power Zener diode is designed, for example, according to a high rated voltage (for example, up to 440V) and a high current pulse or pulse energy. Here, the suppressor diode is designed so that when a predetermined breakdown voltage is exceeded at the switching element, a current is allowed to pass, which can be transferred to the inductance of the input circuit, and the switching element withstands the current flowing through the inductance during the duration of the overvoltage. This means that the suppressor diode is designed so that the breakdown voltage or avalanche voltage of the suppressor diode is ideally below the destruction limit of the switching element, or the size of the suppressor diode is determined so that the distribution of the avalanche energy between the switching element and the suppressor diode occurs according to the characteristic curve, and thus neither of the two parts is overloaded.

[0027] Alternatively, the unit for limiting and receiving avalanche energy can be constructed as a voltage-limiting protection wiring, which includes at least one capacitor and at least one diode. Here, the voltage-limiting protection wiring is constructed so that it can be connected through a diode and imitates the function of the breakdown voltage by means of a capacitor. In order to discharge the capacitor, for example, a resistor and / or a Zener diode can be arranged in parallel with the capacitor.

[0028] Ideally, the input circuit has at least a buck converter topology. On the one hand, by using a buck converter topology, an unstable and unregulated input voltage can be converted into a stable and regulated output voltage of smaller magnitude. In addition, a reduction in harmonics can be achieved by the buck converter topology.

[0029] It is also convenient if the active switching unit of the input circuit is implemented as a diode or as a so-called Schottky diode. A Schottky diode is a special diode that does not have a semiconductor-semiconductor junction but a cut-off metal-semiconductor junction (so-called Schottky contact) and has a small saturation capacity. As a result, Schottky diodes are particularly suitable for high-frequency applications as "fast" diodes and are particularly suitable for voltage reduction of inductors (freewheeling diodes). Ideally, so-called Schottky diodes are implemented as semiconductor components based on silicon carbide, because they are available up to relatively high cut-off voltages and are very close to ideal diodes, because they have almost no forward recovery characteristics and at least no reverse recovery characteristics, and therefore cut off very quickly.

[0030] In an advantageous embodiment of the input circuit according to the invention, the capacitor arranged on the output side is designed as a ceramic capacitor or an electrolytic capacitor or as a plastic film capacitor.

[0031] Furthermore, the switching element is ideally arranged in the positive voltage branch of the input circuit. Alternatively, it is conceivable to arrange the switching element in the negative voltage branch of the input circuit.

[0032] In order to use the input circuit according to the invention in a multi-stage power supply or for supplying in an AC voltage supply network, a rectifier unit is connected upstream of the input circuit on the input side. Ideally, the rectifier unit is designed so that the input circuit can be connected to at least a two-phase voltage supply, but primarily to a three-phase voltage supply. In this case, the usually unstable or rectified output voltage supplied by the rectifier unit forms the input voltage of the input circuit according to the invention.

[0033] In order to protect and limit overvoltages from the power supply grid, at least one varistor can also be provided on the input side. A varistor is an electronic component that is characterized by a voltage-dependent resistance. By using at least one varistor, overvoltage pulses can be limited to a predeterminable or estimable overvoltage value by creating a large pulse power loss.

[0034] Furthermore, when the input circuit according to the invention is used in a multi-stage power supply, a converter stage, in particular a potential-isolated converter stage, can be arranged downstream. The input voltage of this converter stage is formed by the output voltage of the input circuit, which is provided at the capacitor. In this case, the converter stage arranged downstream is protected from overvoltage in an advantageous manner by the input circuit according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The invention is then explained in an exemplary manner with reference to the attached figures.

[0036] Figure 1 Schematically shows an exemplary implementation form of an input circuit for a power supply according to the present invention,

[0037] Figure 2 Schematically shows other exemplary implementation forms of the input circuit for the power supply according to the present invention,

[0038] Figure 3 exemplarily shows the time profile of the voltage and the current in the input circuit according to the invention during an overvoltage on the input side,

[0039] Figure 4 The application of the input circuit according to the present invention in a three-phase power supply is schematically and exemplarily shown. DETAILED DESCRIPTION

[0040] Figure 1 The embodiment of the input circuit ES for the power supply according to the present invention is schematically and exemplarily shown, which can be connected to a single-phase or multi-phase (especially at least two-phase or three-phase) power supply network, for example. The input circuit ES has, for example, at least a circuit topology of a buck converter. However, alternatively, the input circuit can also be constructed as a combination of a buck converter and a boost converter. On the input side of the input circuit ES, an input capacitor Ce is arranged, to which a mostly unstable or unregulated input voltage Ue is attached. The input voltage Ue can be provided, for example, by an input stage of the power supply, through which the connection to the power supply network is made.

[0041] Here, the input capacitor Ce has, for example, the function of an input circuit ES, which operates at a frequency significantly higher than the mains frequency of the input voltage Ue (for example, a multiple of 1000) to provide a high-frequency pulse current. Here, the size C of the input capacitor is, for example, dimensioned such that the entire input circuit ES does not exceed a predeterminable limit value for the mains current harmonics.

[0042] In addition, the input circuit ES has a switching element SE arranged on the input side, which can be arranged, for example, in the positive voltage branch of the input circuit or in the negative voltage branch of the input circuit. The inductor L is arranged directly or indirectly downstream of the switching element SE. In addition, the input circuit ES also includes an active switching unit FD, which can be considered to be arranged in series with the switching element SE or in parallel with the inductor L in terms of circuit technology. The active switching unit FD is implemented, for example, as a diode or as a so-called Schottky diode, which can be switched to the cut-off state very quickly in an ideal case or has a very small cut-off delay time. The Schottky diode FD can be implemented, for example, as a semiconductor device based on silicon carbide.

[0043] On the output side, an output or intermediate circuit capacitor Ca is arranged at which a generally stable or regulated output voltage Ua of the input circuit ES is provided, for example, for a connected consumer or, in the case of a multi-stage power supply, for a converter stage arranged downstream. In terms of circuit technology, the output capacitor Ca can be arranged in series with the inductor L and therewith in parallel with the active switching unit FD. Furthermore, the capacitor Ca can be designed, for example, as a ceramic capacitor, an electrolytic capacitor or as a plastic film capacitor.

[0044] Furthermore, the input circuit ES has an actuation unit AS, which generates actuation pulses GS for the switching element SE based on the control variables R1, R2. In normal operation of the input circuit ES, the input voltage Ue attached to the input side is converted into a stable or regulated output voltage Ua, which is usually smaller in magnitude than the input voltage Ue, for example, by periodically switching the switching element SE. For this purpose, the actuation pulses GS are generated by the actuation unit AS based on the first control variable R1 measured on the output side (for example, the measured output voltage value, etc.). With the aid of the actuation pulses GS, the switching element SE is alternately placed in the on state and the off state. That is, the switching element SE is alternately switched on and off during the switching cycle. Here, at least partially during the switching cycle or when the switching element SE is switched on, the current I L Flowing through the inductor L, the current I L The capacitor Ca arranged on the output side is charged. The active switching unit FD is blocked. In the blocked state of the switching element SE, the current I LBy demagnetizing the inductance L, commutation to the active switching unit FD occurs, wherein the energy stored in the inductance L is released to the capacitor Ca arranged on the output side until the inductance L is demagnetized. Then, the switching element SE is switched to the conductive state again by means of the actuation unit AS. The switching process of the switching element SE is repeated cyclically in normal operation of the input circuit ES in order to provide a regulated output voltage Ua at the output.

[0045] In the case of an overvoltage, interference in the form of an overvoltage and / or a voltage peak from the power supply network appears as an input voltage Ue on the input side of the input circuit ES, wherein such an overvoltage can be limited (for example to 2000 V) by means of at least one varistor arranged on the input side, for example. When an overvoltage Ue on the input side occurs and is detected, the switching element SE can be placed in a blocked state via a control pulse GS of the control unit AS. In this case, a cut-off voltage Usp drops at the switching element SE, wherein when the cut-off voltage Usp at the switching element exceeds a predetermined breakdown voltage, a current is allowed to flow through I via the switching element SE. AVAL , which is above the continuous operating voltage or rated voltage of the switching element SE. The circuit point between the switching element SE, the inductor L and the active switching unit FD has a voltage potential Us. The current through the switching element SE is I AVAL Can be transferred to the inductor L, voltage U L The voltage drops to the inductor L, and the inductor L turns off the active switching unit FD, or the active switching unit FD is cut off.

[0046] In order for the input circuit ES to have the required withstand voltage for overvoltage situations, the switching element SE and the inductor L are dimensioned such that, in the event of an overvoltage, a so-called avalanche energy is generated at the switching element SE, in which case the switching element withstands the current I flowing through the inductor L for the duration of the overvoltage. L Typically, such an overvoltage pulse or surge voltage is only a few microseconds long (for example, with a rise time of 1 to 2 μs and a half-value time of less than 10 μs). The avalanche energy at the switching element SE is reduced by the current through the blocked switching element through I AVAL For example, in the form of heat, the switching element SE must withstand the current flow in the event of an overvoltage. Given a predetermined breakdown voltage at the switching element SE, the current flow I can be influenced by correspondingly dimensioning the inductance L. AVAL and thus the avalanche energy at the switching element SE.

[0047] For this purpose, the switching element SE and the inductance L can additionally be dimensioned such that the predetermined breakdown voltage at the switching element SE and the output voltage Ua result in at least one sum value at which, in the event of a maximum expected overvoltage, the current I L That is, if an overvoltage Ue occurs at the input of the input circuit ES, for example, and the overvoltage Ue is limited to 2000 V by means of at least one varistor, then the voltage U L Dropped on the inductor L, the voltage U L The difference between the input voltage Ue, the predetermined breakdown voltage or cutoff voltage Usp at the switching element SE and the output voltage Ua is also considered to be approximately constant (eg 400 V). L The maximum value of the inductance L and the measurable voltage U L In the case of , the inductance L can be dimensioned very simply. The breakdown voltage Usp at the switching element SE can be predetermined, for example, by the selection or design of the switching element SE.

[0048] In the case of an input-side overvoltage Ue of, for example, 2000 V, which persists for, for example, 20 μs, and in the case of an output voltage Ua of, for example, 400 V and a predetermined breakdown voltage Usp of, for example, 1200 V at the switching element SE, for example as a voltage drop U at the inductance L L Maintain, for example, 400 V, which magnetizes the inductor L. According to the formula U L =L*di / dt, when deformed to I L = (U / L) * t, the current I in the inductor can be measured L At a known voltage U L and for current I L In the case of a predeterminable maximum value, a specific dimensioning of the inductance L can be determined therefrom.

[0049] In order to detect an overvoltage on the input side, a comparator unit is provided in the input circuit ES. The comparator unit can be designed as an independent unit or can be integrated into the control unit AS. The comparator unit takes into account the second control variable R2, based on which the control unit AS generates a control pulse GS, by which the switching element SE is placed in the blocking state. For example, a voltage measurement value or a current measurement value can be used as the second control variable R2.

[0050] In the case of a voltage measurement value as the second controlled variable R2, the voltage measurement value is determined, for example, indirectly or directly, on the input side of the input circuit. For example, the input voltage Ue can be measured directly at the input of the input circuit, or the voltage can be measured, for example, at the output of a stage that may be connected upstream. The determined voltage measurement value can then be supplied to a comparator unit so that the supplied voltage measurement value is compared with a predeterminable reference value, which can be above the input voltage Ue common for normal operation and at most a predeterminable breakdown voltage of the switching element SE. When the predeterminable reference value is exceeded, the switching element SE is placed in the blocked state.

[0051] If, as an alternative, a current measurement value is used as the second controlled variable R2 for detecting an overvoltage Ue on the input side, the current that is established due to the overvoltage Ue can be taken into account for this purpose. For this purpose, the current measurement value can be determined using a current sensor, wherein the current sensor is arranged, for example, in a current path that includes the current through the switching element SE via I AVAL . The current measurement value can then be supplied to the comparator unit so that it is compared with a predefined reference value. When the current measurement value determined and supplied to the comparator unit exceeds a predefined reference value, the switching element SE is placed in a blocked state by means of the control unit AS. Furthermore, it is also possible that, in order to detect an overvoltage Ue on the input side, a voltage measurement value is taken into account and compared with a predefined reference value, and that a current measurement is additionally performed. In this way, for example, depending on the voltage shape and the increase in the overvoltage Ue over time, the switching element SE can be turned off either based on the voltage measurement value or based on the current measurement.

[0052] The switching element SE of the input circuit ES according to the invention can be implemented, for example, as a semiconductor switch or switching transistor S based on silicon carbide (SiC). In particular, the semiconductor switch S based on silicon carbide can be a metal oxide field effect transistor or MOS-FET or SiC-MOS-FET. Ideally, the SiC-MOS-FET has a predetermined minimum absorption capacity or so-called avalanche rating for avalanche energy as a component characteristic value, whereby the switching element SE can be dimensioned very simply for overvoltage situations.

[0053] Alternatively, the switching element SE (as in Figure 1 ) may include a semiconductor switch S (eg, a MOS-FET based on silicon or gallium nitride) and a unit D arranged in parallel for limiting and absorbing avalanche energy in the event of an overvoltage. The unit D may, for example, (as shown in FIG. Figure 1As shown in FIG. 1 , the MOSFET 200 is implemented as a suppressor diode D. As the suppressor diode D, for example, a silicon-based power Zener diode can be used.

[0054] exist Figure 2 , schematically shows another exemplary embodiment of the input circuit ES1 according to the present invention. Except for the construction of the switching element SE1, the embodiment ES1 corresponds to the input circuit ES according to the present invention. Figure 1 In this alternative embodiment variant ES1, the switching element SE1 comprises a semiconductor switch S (for example a MOS-FET) and a voltage-limiting protective wiring arranged in parallel therewith, via which, in the event of an overvoltage, a current is allowed to flow through I when the semiconductor switch S is blocked. AVAL , or simulate the function of the breakdown voltage and protect the semiconductor switch S. Such a protection wiring can, for example, include at least one capacitor Cb and at least one diode Db, wherein the capacitor Cb has, for example, a precharge, by which a predetermined breakdown voltage can be defined. In the event of an overvoltage, the capacitor Cb can be connected via the diode Db. In addition, a discharge resistor can be arranged in parallel with the capacitor Cb, which can be implemented, for example, as a suppressor diode Dz or as an ohmic resistor R.

[0055] During input side overvoltage, Figure 3 The time profile of the voltage and current in the input circuit according to the invention is shown by way of example and schematically. For this purpose, the time t is plotted on the x-axis. On the y-axis are schematically plotted the input voltage Ue of the input circuit ES, the voltage potential Us at the circuit point between the switching element SE, the inductor L and the active switching unit FD, the output voltage Ua, the current through the switching element SE through I AVAL , voltage U at inductor L L And the current I in the inductor L L .

[0056] Before the first time t0, the input circuit ES is in normal operation. That is, the continuous operating voltage (e.g. 800V) common for normal operation is applied as the input voltage Ue at the circuit. The switching element SE is switched, for example, to the blocking state, wherein the entire input voltage Ue plus, for example, a very small diode flux voltage (e.g. 1V) of the active switching unit FD is applied as the current blocking voltage Usp at the switching element SE. Figure 3 For example, the distance between the two curves of the input voltage Ue and the voltage Us shows the respective current cut-off voltage Usp at the switching element SE. The inductor L is demagnetized and the current I in the inductor L L The current I LAlso flows via the active switching unit FD. The voltage at the potential point Us is lower than 0 Volt by the flux voltage of the active switching unit FD. At the capacitor arranged on the output side, a constant output voltage Ua (eg 400 V) is provided.

[0057] At a first time t0, an overvoltage occurs on the input side, which can be limited to a predefined value (e.g. 2000 V) by means of one or more varistors arranged on the input side, for example. Due to the overvoltage that is established, the input voltage Ue increases. In addition, the inductance L is demagnetized. However, the cut-off voltage Usp at the switching element SE increases with the increase in the input voltage Ue, until at a second time t1, the cut-off voltage Usp currently applied to the switching element reaches or exceeds the predefined breakdown voltage Ud. From the second time t1, a current flows through I at the switching element SE. AVAL From the second time point t1, the current I flowing through the active switch unit FD is L The current I through the inductor L is switched to the switching element SE, or the current through the active switching unit FD is turned off. L From the second time point t1 onwards AVAL (As in Figure 3 At the second time t1, a predetermined breakdown voltage Ud (eg, 1700 V) is applied to the switching element SE, and a power loss is generated in the switching element SE, which is the result of the cutoff voltage Usp multiplied by the current I L or I AVAL The product of .

[0058] At the third time t2, the input voltage Ue reaches, for example, an overvoltage value (for example, 2000 V) which can be predefined by means of a varistor. Furthermore, until the third time t2, the voltage Us and the voltage U at the inductor L L The voltage Ud at the inductor L is also increased (for example, to the difference between the input voltage Ue and the sum of the breakdown voltage Ud at the switching element SE and the output voltage Ua). When the input voltage Ue is, for example, 2000 V, the output voltage Ua is, for example, 400 V, and the predetermined breakdown voltage Ud is, for example, 1700 V, a voltage Ud at the inductor L of -100 V is obtained, for example. L That is, the current through the switch element SE passes through I AVAL (the current is passed to the inductor L), the voltage U L The current I through the inductor L increases, which inductor L receives a lower demagnetization voltage and can only be demagnetized slowly. L Also only slowly decreases, or the current through the switching element SE passes through I AVAL Also slowly decreasing.

[0059] At the fourth time t3 (for example, after 20 to 30 μs), the overvoltage on the input side decays and the input voltage Ue decreases again until, at the fifth time t4, the predetermined breakdown voltage Ud at the switching element SE is not exceeded. Between the fourth time t3 and the fifth time t4, (under the condition of the breakdown voltage or cut-off voltage Ud to be assumed to be constant at the switching element SE), the voltage Us at the circuit point between the switching element SE, the inductor L and the active switching unit FD also decreases in parallel with the input voltage Ue. Similarly, the voltage Us at the inductor L L Also decreases again, that is, the inductor L obtains a larger demagnetization voltage from the fourth time point t3, thereby the current I L Can descend more quickly.

[0060] If the breakdown voltage Ud of the switching element SE is reached or not exceeded at the fifth time t4, the entire demagnetization voltage Ud is again applied to the inductor L. L , and the current I L can be discharged without interference to the capacitor Ca arranged on the output side. Now, the current I L As before the overvoltage, the current increases, and then decreases, and the current through the switching element SE passes through I AVAL The switching element SE no longer allows current to flow, that is, from the fifth time point t4 onwards.

[0061] At the sixth time point t5, the overvoltage on the input side has completely decayed. The input voltage Ue drops again to the common continuous operation voltage (e.g. 800V). The inductor L is also demagnetized until the seventh time point t6, when the entire energy of the inductor L is released to the capacitor Ca. Then, the current I in the inductor L L The input circuit ES can then be operated again in normal operation or the switching element SE can be switched into the conductive state by means of actuation pulses GS.

[0062] For example, in order to determine the dimensions of the input circuit ES, the maximum permissible avalanche energy for the switching element SE or for the switching element assembly SE1 (that is, for the components forming the switching element SE or SE1) is first determined from the corresponding data sheet. In this case, the maximum operating temperature to be expected during operation of the switching element SE, SE1 or of all components receiving avalanche energy is additionally taken into account. This can lead to a reduction in the permissible avalanche energy.

[0063] Then, determine the maximum current through I AVAL, which allows that in the event of an overvoltage, a predetermined limit value for the switching element SE, SE1 or the individual components forming the switching element SE, SE1 is not exceeded. For this purpose, the maximum current is determined at the end of the overvoltage (that is, at Figure 3 At the fifth time point t4, at which the overvoltage is greatly attenuated, so that no current flows through I through the switching elements SE and SE1. AVAL )The current I passing through the inductor L L For the purpose of measurement, it is assumed that the current through the switching elements SE and SE1 is caused by the overvoltage through I AVAL at the time point (that is, at Figure 3 At the second time t1 at which the input voltage / overvoltage Ue exceeds the breakdown voltage Ud of the switching element SE, SE1), the inductor L conducts the current I L According to the magnitude of the overvoltage and the limiting voltage of the switching elements SE and SE1, during the occurrence of the overvoltage, the current I L Will slowly drop in the inductance L, or will still rise further. In order to cover all cases, the current I is taken into account for dimensioning the input circuit ES under the most unfavorable load conditions and input and output voltage conditions. L The current value at the second time point t1 is used as the output condition I0.

[0064] Due to the overvoltage and the subsequent current flowing through I AVAL , the voltage at which the inductance L can be demagnetized is reduced. Depending on the overvoltage, the breakdown voltage Ud of the switching elements SE, SE1 and the output voltage Ua of the input circuit ES, for example, not only a slowdown of the demagnetization may occur, but even a magnetization of the inductance L may occur (if, for example, during the overvoltage, the voltage Us at the circuit point between the switching element SE, the inductance L and the active switching unit FD rises to a value above the output voltage Ua). When determining the dimension, this is taken into account in the formulas 1 and 2 given below, where, as a simplification, the time interval between the time points t1 and t2 or t3 and t4 is assumed to be extremely short. In addition to simplifying the calculation, this assumption also represents a conservative approach for determining the dimension. The network overvoltage pulse is usually difficult to estimate, but rather can be defined via the energy content. That is, the voltage rise time is usually not predeterminable, so it is meaningful to design the input circuit ES for the worst case - as described by formulas 1 and 2.

[0065] The current I through the inductor L at the end of the overvoltage can thus be determined as follows: LThe maximum value of the overvoltage is reached at the end of the overvoltage, that is, at the fifth time t4, at which the overvoltage has been greatly reduced, so that no current flows through the switching elements SE, SE1. AVAL :

[0066] Formula 1: .

[0067] Here:

[0068] - I0 is the current I passing through the inductor L at the second time point t1 L At this second time point, due to the overvoltage Ue, the current through the switching elements SE and SE1 begins to flow through I AVAL ;

[0069] - Ue is the input voltage or overvoltage;

[0070] - Usp is the cut-off voltage applied to the switching element SE or to the main switching element SE1 by means of additional wiring during overvoltage operation. During overvoltage operation, the current flows through I AVAL flow;

[0071] - Ua is the output voltage of the input circuit ES and L is the inductance L of the input circuit ES.

[0072] In order to determine the avalanche energy E occurring at the switching element SE, SE1 between the times t1 and t4 AS , then it can be determined according to the following formula:

[0073] Formula 2: .

[0074] Here, the time profile of the cutoff voltage Usp at the switching element SE, SE1 and the current through I via the switching element SE, SE1 are plotted between the time points t1 and t4. AVAL Integrate the product of the time variation curves. Figure 3 As can be seen in the figure, the current through I AVAL The variation curve of the current I through the inductor L corresponds to L The change curve.

[0075] Finally, the measured avalanche energy E occurring at the switching element SE, SE1 AS A comparison is also made with the following avalanche energy: the avalanche energy is the maximum permissible avalanche energy specified by the respective manufacturer of the switching element SE, SE1 or the switching element component. AS Below the maximum permissible avalanche energy, switching elements SE, SE1 can then be used for the input circuit ES.

[0076] Figure 4 An exemplary application of the input circuit ES according to the present invention in an exemplary three-phase and multi-stage constructed power supply is shown. In order to supply power, the exemplary power supply is connected to a three-phase power supply network with three phases L1, L2, and L3. Alternatively, a single-phase or two-phase AC voltage can also be provided as the power supply. A varistor is arranged directly at the time of grid connection or upstream of the input stage GL, through which the overvoltage can be limited to a pre-given overvoltage value (for example, 2000V). In this way, the parts of the power supply arranged downstream thereof are protected from damage by high overvoltage pulses or voltage peaks of overvoltage on the grid side. An input stage GL of the power supply is arranged after the varistor, and the input stage is constructed as a rectifier unit GL (for example, in the case of a three-phase voltage supply device, it is constructed as a 6-phase rectifier). Through the rectifier unit GL, an unstable or unregulated input voltage Ue is generated for the downstream stage of the power supply from the AC voltage of the power supply grid.

[0077] A filter unit F (for example a transformer unit as an EMC filter) can also be arranged downstream of the input stage GL. After the input stage GL or the filter unit F, an input circuit ES according to the invention is arranged, which uses the supply voltage rectified by the input stage GL as an unstable or unregulated input voltage Ue. This input voltage Ue is converted into a stable or regulated output voltage Ua of the input circuit ES via the input circuit ES. This stable or regulated output voltage Ua then forms the input voltage for the converter stage WS arranged downstream, which then supplies the supply voltage for the consumer. The converter stage WS can be implemented, for example, as a potential-separated converter, as a resonant converter, etc., and is protected from overvoltage damage on the input side by the input circuit ES according to the invention.

Claims

1. An input circuit for a power supply, comprising at least: - a switching element (SE) arranged on the input side; - an inductor (L), said inductor (L) being arranged in series with said switching element (SE); and a diode (FD); wherein an input voltage (Ue) can be converted into an output voltage (Ua) by periodically switching the switching element (SE) between an on state and an off state; wherein at least partially during a switching period of the switching element (SE), the current (I L ) flows through the inductor (L), the current (I L ) charges a capacitor (Ca) arranged on the output side, at which the output voltage (Ua) can be provided; in When the switching element (SE) is in the off state, the diode (FD) absorbs the current (I L );and In the blocked state of the switching element (SE), a current is allowed to flow (I d ) via the switching element (SE) when a predetermined breakdown voltage (Ud) is exceeded at the switching element (SE). AVAL ), characterised in that the switching element (SE) can be switched into the blocking state when an overvoltage is detected on the input side of the input circuit (ES), The current (I AVAL ), and the current through the switching element (SE) passes (I AVAL ) turns off the diode (FD), Furthermore, the switching element (SE) and the inductance (L) are dimensioned such that, when the overvoltage occurs, a so-called avalanche energy is generated at the switching element (SE), in which case the switching element (SE) withstands the current (I L ).

2. The input circuit according to claim 1, characterized in that: Furthermore, the switching element (SE) and the inductance (L) are dimensioned such that the predetermined breakdown voltage (Ud) at the switching element (SE) and the output voltage (Ua) result in at least one sum value, at which the current (I L ) is kept below a predeterminable maximum value.

3. The input circuit according to any one of the preceding claims, characterized in that An actuation unit (AS) is provided for actuating the switching element (SE) such that actuation pulses (GS) are supplied to the switching element, which actuation pulses (GS) alternately place the switching element (SE) in the conducting state and in the blocking state.

4. The input circuit according to any one of claims 1 to 2, characterized in that: In order to detect the overvoltage on the input side, a comparator unit is provided, to which a voltage measurement value (R2) determined at the input side of the input circuit (SE) can be supplied directly or indirectly, so that when the determined and supplied voltage measurement value (R2) exceeds a predeterminable reference value, the switching element (SE) is placed in the blocking state.

5. The input circuit according to any one of claims 1 to 2, characterized in that: In order to detect the overvoltage on the input side based on the continuously built-up current, a comparator unit is provided, to which a current measurement value (R2) determined by means of a current sensor can be supplied, so that the switching element (SE) is placed in the blocking state when the determined and supplied current measurement value (R2) exceeds a predeterminable reference value.

6. The input circuit according to any one of claims 1 to 2, characterized in that: The switching element (SE) is designed as a semiconductor switch (S) based on silicon carbide.

7. The input circuit according to claim 6, characterized in that: The semiconductor switch (S) based on silicon carbide has a minimum absorption capacity for the so-called avalanche energy which is predefined as a component characteristic value.

8. The input circuit according to any one of claims 1 to 2, characterized in that: The switching element (SE, SE1) comprises a semiconductor switch (S) and comprises a unit for limiting and receiving the so-called avalanche energy, which is arranged in parallel with the semiconductor switch (S).

9. The input circuit according to claim 8, characterized in that: The unit for limiting and absorbing the so-called avalanche energy is designed as a suppressor diode (D).

10. The input circuit according to claim 8, characterized in that The means for limiting and absorbing the so-called avalanche energy is implemented as a voltage-limiting protection circuit which comprises at least one capacitor (Cb) and at least one diode (Db).

11. The input circuit according to any one of claims 1 to 2, characterized in that: The input circuit (ES) has at least a buck converter topology.

12. The input circuit according to any one of claims 1 to 2, characterized in that: The diode (FD) is designed as a so-called Schottky diode.

13. The input circuit according to claim 12, characterized in that: The so-called Schottky diode is implemented as a semiconductor component based on silicon carbide.

14. The input circuit according to any one of claims 1 to 2, characterized in that: The capacitor (Ca) arranged on the output side is designed as a ceramic capacitor or an electrolytic capacitor or as a plastic film capacitor.

15. The input circuit according to any one of claims 1 to 2, characterized in that: The switching element (SE) is arranged in a positive voltage branch of the input circuit (ES).

16. The input circuit according to any one of claims 1 to 2, characterized in that: The switching element (SE) is arranged in a negative voltage branch of the input circuit (ES).

17. The input circuit according to any one of claims 1 to 2, characterized in that: A rectifier unit (GL) is arranged on the input side for connecting the input circuit (ES) to at least two-phase voltage supplies (L1, L2, L3).

18. The input circuit according to any one of claims 1 to 2, characterized in that: At least one varistor is provided on the input side to limit the overvoltage that occurs.

19. The input circuit according to any one of claims 1 to 2, characterized in that: On the output side, a converter stage (WS) is arranged downstream of the input circuit (ES), the output voltage (Ua) of the input circuit (ES) provided at the capacitor (Ca) forming the input voltage of the converter stage (WS).

20. The input circuit according to claim 6, characterized in that The switching element (SE) is designed as a metal oxide field effect transistor.

21. The input circuit according to claim 8, characterized in that The semiconductor switch (S) is a switching transistor.

22. The input circuit according to claim 9, characterized in that The unit for limiting and absorbing the so-called avalanche energy is implemented as a silicon-based power Zener diode.

23. The input circuit according to claim 19, characterized in that The converter stage (WS) is a potential-isolated converter stage.

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