DE102020206253B3 - Overvoltage protection - Google Patents

Abstract

The invention relates to an overvoltage protection device (16) having a first connection (18) and a second connection (20), between which a strand (28) with a resistor (30) is electrically connected. The resistor (30) is connected between the first connection (18) and a switching element (32) having a control input (34), the control input (34) of the switching element (32) having a further switching element (44) having a further control input (44). 42) is electrically connected to the second connection (20). The further switching element (42) is actuated as a function of the electrical voltage occurring across the switching element (32). The invention also relates to the use of an overvoltage protection device (16).

Description

The invention relates to overvoltage protection.

Electrical devices usually have a nominal electrical voltage at which they are operated. If this nominal voltage is significantly exceeded, damage to the electrical device is possible. Exceeding the nominal voltage occurs, for example, due to a technical defect in the electrical device or some other component of the circuit of which the electrical device is a component. To protect the electrical device against such electrical voltages, fuses or circuit breakers are usually used.

It is also necessary that electrical devices are secured against overvoltage, which may arise, for example, due to a lightning strike in a line of the circuit or the electrical device itself. It is also possible that such an overvoltage arises within the circuit due to an inductive coupling of a component of the circuit with a lightning bolt. In addition, due to electromagnetic pulses (EMP) or due to electrostatic discharges (ESD) as well as switching processes in the circuit, such overvoltages can occur, which can lead to damage to the device. Such overvoltages exceed the nominal voltage to a comparatively large extent. The overvoltages also arise due to external events and can therefore not be influenced by the electrical device and therefore cannot be avoided.

To protect the electrical device against overvoltages, overvoltage protection is used, which is connected in parallel to the device to be protected. The overvoltage protection itself has, for example, a spark gap or a varistor. In this case, the overvoltage is diverted around the device to be protected, with an electric arc being generated, for example. The spark gap and the varistor are subject to aging effects, so that after a certain period of time the electrical voltage at which the overvoltage protection responds varies. Occurring overvoltages also lead to wear of the overvoltage protection. As a result, there is no guarantee that all overvoltages that could lead to damage to the device will always be intercepted by means of the overvoltage protection. The overvoltage protection must therefore be replaced after certain periods of time in order to ensure that it functions as intended.

the DE 10 2008 025 986 A1 shows an overvoltage protection device with a capacitance discharge device in which a resistor and a switching element are connected in series, the switching element being controlled by a monitoring circuit via a Schmitt trigger.

the EP 0 308 642 A1 shows a method for limiting the starting current of a DC / DC converter by charging a buffer capacitor.

the US 2010/0296210 A1 shows an overvoltage protection device in which a cascade of switching elements releases parallel arrester paths.

the US 2018/0183433 A1 shows a semiconductor component for current control, which has three parallel paths, each path having a switching element, and wherein the switching elements are controlled via a common voltage divider.

The invention is based on the object of specifying a particularly suitable overvoltage protection device and also a particularly suitable use of an overvoltage protection device, in particular increasing safety and preferably reducing production and / or operating costs.

With regard to overvoltage protection, this object is achieved according to the invention by the features of claim 1 and with regard to the use by the features of claim 7. Advantageous further developments and refinements are the subject of the subclaims.

The overvoltage protection has a first connection and a second connection. The overvoltage protection serves to avoid an (electrical) overvoltage between the first connection and the second connection. The overvoltage protection is expediently suitable, provided and / or set up for this. The overvoltage is, for example, an alternating voltage or a direct voltage. For example, the overvoltage protection is suitable, in particular provided and set up, to protect (other) components with an (electrical) rated voltage from an overvoltage. The nominal voltage is preferably greater than or equal to 12 V, 24 V, 48 V, 100 V or 200 V. For example, the maximum nominal voltage is 6kV, 5kV, 4.5kV, 4kV, 3kV, 2kV, 1,500 V, 1,200V, 1,100 V, 1,000 V, 900 V or 800 V.

The overvoltage protection has a branch which is connected between the two connections and, for example, is electrically connected directly to them. Alternatively, at least one of the connections, for example both, is via a additional component electrically connected to the string. In particular, one or more diodes are used as such a component.

Such a component is expediently a B4 bridge. As a result, it is possible to operate the overvoltage protection bidirectionally. In particular, the overvoltage protection is thus designed to be bidirectional, this being done, for example, by means of the B4 bridge. Alternatively, the bidirectionality is provided by means of further components. In an alternative to this, the overvoltage protection is designed to be unidirectional.

The strand has a resistor, which is expediently an ohmic resistor. The resistor is connected between the first connection and a switching element, the switching element being part of the strand. In other words, the switching element and the resistor are electrically connected in series. By means of the switching element, it is possible to interrupt a current flow via the strand. In other words, when the switching element is switched on or off, the strand is electrically closed or disconnected.

The switching element has a control input by means of which the switching element is actuated. The switching state of the switching element is thus changed in particular as a function of an electrical potential applied to the control input. By actuating the switching element, it is thus possible to electrically close the strand so that a current flows between the two connections via the strand. As a result, an electrical voltage is limited or an electrical current flow is set on the basis of the associated resistance. It is therefore possible to limit the electrical voltage occurring between the two connections and thus prevent the overvoltage between the two connections.

If an overvoltage is present between the connections, the switching element is preferably actuated so that the strand is initially live. As a result, an electrical voltage between the two connections drops. If this is less than a certain value, the string is switched off, i.e. the switching element is opened, so that a current flow through it is prevented, which is why an electrical voltage between the two connections rises again, but to a lower value than the original overvoltage.

For example, the switching element is implemented by means of a relay. However, the switching element is particularly preferably a semiconductor switch, so that maintenance is simplified. The formation of an arc during actuation is also avoided. Since the switching element is current-carrying only in the event of an overvoltage, that is to say when an overvoltage or at least a certain electrical voltage is present between the two connections, electrical losses that occur are only temporary and thus limited. For example, the switching element is an IGBT, IGTC or GTO. However, the switching element is particularly preferably a field effect transistor and particularly preferably a MOSFET. This is comparatively inexpensive and available in different performance classes, so that the area of application of the overvoltage protection is increased. This also has a freewheeling diode, so that operation of the overvoltage protection is simplified.

The overvoltage protection also has a further switching element which comprises a further control input. Here, the further switching element is actuated as a function of an electrical potential applied to the further control input and is thus in the electrically conductive or electrically non-conductive state. The further switching element is connected between the control input of the switching element and the second connection. In other words, the control input of the switching element is electrically connected to the second connection via the further switching element.

The further switching element is actuated as a function of the electrical voltage occurring across the switching element. For this purpose, the overvoltage protection preferably has a corresponding interconnection and / or suitable electrical / electronic components. The further switching element is preferably actuated when the electrical voltage occurring across the switching element exceeds a certain value. Then, when the further switching element is actuated, the control input of the switching element is switched to the electrical potential of the second connection, or at least to an electrical potential that is dependent on the electrical potential at the second connection. As a result, the switching element is converted, in particular, into the electrically non-conductive state, so that a current flow via the strand is interrupted.

Because of the further switching element, when a certain electrical voltage occurs across the switching element, it is switched off. In particular, a corresponding electrical voltage, which leads to disconnection, occurs when a resistance of the switching element increases. The resistance increases, for example, due to an overload of the switching element. As a result of the shutdown by means of the further switching element, the current flow is thus reduced Interrupted via the switching element so that destruction is prevented. Furthermore, due to the switching as a function of the electrical voltage, excessive heating due to an increased internal resistance is avoided, which can also lead to overloading and therefore destruction of the switching element. For example, if the electrical potential applied to the control input of the switching element changes and in particular approaches the electrical potential at which the switching element is switched off, the internal resistance of the switching element is gradually increased. Because of the further switching element, the switching element is not switched off gradually, but essentially suddenly, which is why overloading of the switching element is avoided. As a result, safety is increased and there is no need to replace components of the surge protector, which is why operating costs are reduced. It is also possible to use a comparatively inexpensive component for the switching element, which is why manufacturing costs are reduced.

For example, a further component is also present between the control input and the second connection, which is thus connected in parallel to the further switching element. By means of the further component, in particular further functions are taken over, so that functionality is increased.

In particular, the further switching element is a field effect transistor. For example, the switching element and also the further switching element are designed as MOSFETs. The further switching element is, for example, identical in construction to the switching element. However, the further switching element is particularly preferably suitable for lower (electrical) voltages than the switching element, so that a more cost-effective component can be used. The activation of the further switching element takes place, for example, by means of suitable components.

The overvoltage protection has an additional switching element which comprises an additional control input. Here, the additional switching element is actuated as a function of the electrical potential applied to the additional control input. The additional control input is routed to the second connection via the additional switching element. It is thus possible to actuate the further switching element and therefore the switching element by actuating the additional switching element. Here, an electrical voltage required to control the additional switching element is lower than for the further switching element, which is why comparatively inexpensive components can be used. In particular, the additional switching element is a transistor, which further reduces manufacturing costs.

The additional control input is routed to a first additional resistor and a second additional resistor, which in particular are electrically connected in series with one another. In other words, the first additional resistor and the second additional resistor are electrically contacted with one another and with the additional control input. The two additional resistors are expediently ohmic resistors, which is why manufacturing costs are reduced. Dimensioning and design of the overvoltage protection are also simplified in this way.

By means of the two additional resistors, in particular an additional voltage divider is provided, by means of which the switching element is bridged. The second additional resistor is led to the second connection. The first additional resistor is in electrical contact with the first connection via the resistor. In summary, the additional control input is thus routed via the first additional resistor and the resistor to the first connection and via the second additional resistor to the second connection. In this case, a diode is suitably arranged between the first additional resistor and the resistor, so that an electrical current flow is only possible in a single direction, expediently from the first additional resistor to the resistor. As a result, feedback and unwanted effects are avoided. In addition, there is also no overloading of the additional switching element due to the electrical contact with the strand.

In particular, the second additional resistor is bridged with an additional capacitor. Thus, the additional switching element is switched on and switched off with a delay, which is why only brief excessive voltages on the switching element do not lead to an actuation of the additional switching element and therefore the further switching element and thus the switching element. As a result, a reliability of the surge protector is increased.

In one development, the additional control input is routed to the first connection via the first additional resistor and a resistor element. For example, no further components are arranged between the resistance element and the first additional resistance element. Particularly preferably, however, at least one additional diode is arranged between these, by means of which an electrical current flow from the first additional resistor to the resistance element is prevented. Alternatively or in In combination with this, an ohmic resistor is arranged between the first additional resistor and the resistor element, so that different resistors are connected in series. Thus, protection is improved.

For example, the resistance element is an ohmic resistor. However, the resistance element is particularly preferably a Zener diode, by means of which a current flow from the first connection to the first additional resistor is prevented if an electrical voltage is lower than the breakdown voltage of the Zener diode, also referred to as a Zener diode. In particular, the resistance element is led against the control input of the switching element, so that when an overvoltage is present between the two connections, the switching element is switched on due to the resistance element. Consequently, no additional electrical / electronic components are required to actuate the switching element, which is why manufacturing costs are reduced.

In a further development, the further control input is routed to the second connection via a further Zener diode. The additional switching element is thus bridged by means of the further Zener diode, so that the electrical voltage is always diverted if this is greater than the breakdown voltage of the further Zener diode. Consequently, the additional switching element is protected by means of the further Zener diode. This also ensures that the further switching element is switched on accordingly, so that it is actuated accordingly. Thus, security is increased.

Alternatively or particularly preferably in combination with this, the further control input is routed to the first connection via a further diode. The electrical potential present at the further control input is therefore dependent on the electrical potential of the first connection, so that, if necessary, a corresponding control of the further switching element can take place. In this case, the further control input is preferably also routed to the second connection via the further Zener diode, so that the electrical voltage present between the connections is taken into account when the further switching element is activated. The reverse direction of the further diode is preferably opposite to the reverse direction of the Zener diode.

An additional component, for example the resistance element, is preferably connected between the further diode and the first connection, so that the full electrical potential applied to the first connection is not applied to the further control input, which is why, in particular, the further switching element and the switching element are not actuated at the same time he follows.

The further control input is particularly preferably routed to the first connection via a further resistor. The further resistor is expediently an ohmic resistor, which reduces manufacturing costs. The value of the further resistor is preferably greater than the value of the resistance of the strand. The further switching element is thus protected by means of the further resistor. The further Zener diode is suitably present so that a voltage divider is at least partially formed.

For example, the overvoltage protection is designed without varistors and thus varistor-free. Manufacturing costs are thus reduced, and aging of the overvoltage protection is also essentially prevented. As an alternative to this, a varistor is connected in parallel with the switching element. Due to the varistor, any electrical voltage that remains due to the actuation of the switching element is reduced, so that the overvoltage protection is transferred to an essentially currentless state after operation. Alternatively or in combination with this, a further capacitor is connected in parallel to the switching element, and thus also to the varistor, if any, so that a voltage spike in the electrical voltage applied to the switching element due to the switching off of the switching element is avoided. A diode is preferably connected in parallel with the further capacitor / varistor / switching element, so that the formation of an oscillating circuit by means of the possible further capacitor and the varistor is avoided. The diode is, for example, a TVS diode (suppressor diode) or a Zener diode.

For example, the overvoltage protection only has the single strand, which is why any overvoltage between the two connections can only be intercepted by means of the one strand. Particularly preferably, however, the overvoltage protection has a plurality of strings which are connected in parallel to one another. The strand here is one of the strands. The strings are structurally identical to one another or at least have the same circuit and thus each have a resistor and a switching element with a control input, the respective resistor being connected between the first connection and the switching element of the respective strand. Due to the large number of strands, it is possible to set the ohmic resistance between the two connections by actuating the switching elements differently.

In particular, the overvoltage protection has between 2, 3 or 4 corresponding strings. The number of strands is expediently between 5 strands and 20 strands and, for example, between 6 strands and 15 strands. The space requirement is thus not excessively increased, with a lower electrical voltage being applied to each of the strands due to the plurality of strands, which is why comparatively inexpensive components can be used.

Furthermore, the overvoltage protection preferably has a voltage divider which is connected between the control input of one of the switching elements and the first connection. The voltage divider has a number of resistance elements electrically connected in series that corresponds to the number of strings. Thus, the number of resistance elements is, for example, the same as the number of strings or in a fixed relationship thereto. In particular, the number of resistance elements is less than or greater by 1 than the number of strings. A tap is formed between adjacent resistor elements, and each tap is led to the control input of one of the remaining switching elements. Thus, each tap is assigned a different switching element, and each of the switching elements is electrically contacted with the voltage divider, that is to say with the end or one of the taps.

Due to the voltage divider, the switching elements were then actuated successively as a function of the electrical (over) voltage applied between the two connections. If this has fallen by more than a value predetermined by means of the voltage divider, at least one of the strings is switched off, namely the strand whose switching element is in contact with one end of the voltage divider. If the (over) voltage drops further, the switching element is actuated, which is electrically contacted with the tap closest to this end, etc. Thus, the switching elements are not actuated at the same time, even if the resistance elements should have comparatively large manufacturing tolerances.

For example, the individual switching elements are different from one another or implemented by means of different types of switches. In particular, all switching elements and / or resistors are structurally identical to one another. In particular, the control input of each of the switching elements is routed to the second connection via a respectively assigned further switching element, which is actuated as a function of the electrical voltage occurring across the respectively assigned switching element. This means that there are just as many other switching elements as there are strands. In particular, an additional switching element is assigned to each of the further switching elements. In particular, a first and a second additional resistor are assigned to each additional switching element. The additional control input of each additional switching element is routed to the first connection via the respectively assigned first additional resistor and preferably via the resistor element, the resistor element expediently being part of the voltage divider. Alternatively or in combination with this, the further control input of all further switching elements is routed to the first connection via an associated further diode and / or a further resistor and also the common resistance element, the resistance element in particular also being the same as that for the additional control input is used, and / or that is part of the voltage divider. Alternatively, the voltage divider is led via this resistance element to the first connection, which is therefore not part of the voltage divider.

For example, the resistance elements are components that are different from one another or, particularly preferably, components that are similar to one another, the values of the components differing, for example. For example, the resistance elements or at least one of them is an ohmic resistor or a capacitor. However, one of the resistance elements, preferably all of the resistance elements, is particularly preferably a Zener diode. In other words, the resistance elements are Zener diodes. Here, the resistance elements are, for example, identical to one another or differ on the basis of the respective breakdown voltage. Since the resistance elements are Zener diodes, also referred to as Z diodes, the electrical voltage that leads to the switching of the respectively assigned switching element is constant, even if the electrical current flowing between the connections via the respective strand assumes different values. This simplifies the dimensioning and design of the overvoltage protection. It is also ensured in this way that the switching elements are always actuated at the same electrical voltage assigned in each case, which is thus set by means of the voltage divider. The reverse direction of the Zener diodes is expediently directed in the direction of the first connection, so that the switching elements are actuated only when a certain electrical voltage is applied between the two connections. In other words, the flow of current from the first connection via the voltage divider is prevented if the electrical voltage is less than a specific value that is specified on the basis of the resistance elements.

For example, each tap is in direct electrical contact with the respectively assigned control input. Particularly preferably, however, a further component is arranged between each tap and the respectively assigned control input, for example a second diode. Here, the second diode is expediently arranged in such a way that an electrical current flow from the control input to the tap is prevented. This prevents the individual switching elements from having any effect on other switching elements. Alternatively or particularly preferably in combination with this, a second resistor is connected between each tap and the respective control input. The second resistor is in particular an ohmic resistor. The respectively assigned switching element is protected on the basis of the second resistor. A second diode and / or a second resistor is preferably also connected between one of the ends of the voltage divider and the control input assigned to this end, so that this switching element is also protected or any reaction from it is prevented.

Particularly preferably, each control input or at least one of the control inputs is routed to the second connection via a further resistance element. On the basis of the further resistance element, a reference potential is established so that the electrical voltage applied to each control input is relatively precisely defined, which leads to the switching of the respective switching element. Operational reliability is thus increased.

For example, the further resistance elements are ohmic resistors. However, these are particularly preferably designed as Zener diodes, also referred to as Zener diodes. In this case, the blocking direction is in particular such that a current flow from the respective control input to the second connection is prevented if a specific electrical voltage is not exceeded. In this way, the respective switching element is also protected against an excessively applied electrical voltage. Operational reliability is thus further increased. This also ensures that the switching elements are always actuated when the overvoltage is present between the connections.

The overvoltage protection is used to secure a device to be protected against an overvoltage and / or an impulse current. In other words, the overvoltage protection is used to protect the device to be protected, in particular for electrical protection. An overvoltage on the device to be protected or a pulse current flowing through the device to be protected is preferably avoided by means of the overvoltage protection. The overvoltage / impulse current occurs independently of the overvoltage protection and the device to be protected, in particular due to an external event such as a lightning strike. The overvoltage / impulse current is such that it would damage the device to be protected, and the overvoltage protection device expediently limits the electrical voltage applied to the device to be protected. The overvoltage protection preferably functions as an arrester and is, for example, an overvoltage and / or lightning current arrester.

The device to be protected is, for example, a switch or has at least one switch. For example, the switch is a semiconductor switch, a relay, or has both, which are connected in parallel to one another, for example. Thus, by means of the overvoltage protection, an overvoltage that is present when the switch is switched on or when the switch is switched off is avoided or at least reduced. In a further alternative, the device to be protected is, for example, a cell phone mast or some other electrical device.

The overvoltage protection has a first connection and a second connection, between which a strand with a resistor is electrically connected, which is connected between the first connection and a switching element having a control input. Furthermore, the overvoltage protection comprises a further switching element with a further control input, via which the control input of the switching element is electrically connected to the second connection. The further switching element is actuated as a function of the electrical voltage occurring across the switching element.

The device to be protected is connected between the first connection and the second connection and is thus bridged by means of the overvoltage protection or at least by means of the string. In other words, the line is connected in parallel to the device to be protected. The invention also relates to such an interconnection of a device to be protected with overvoltage protection.

The surge protector is used to pre-charge a main capacitor. The overvoltage protection has a first connection and a second connection, between which a strand with a resistor is electrically connected, which is connected between the first connection and a switching element having a control input. Furthermore, the overvoltage protection comprises a further switching element with a further control input, via which the control input of the switching element is electrically connected to the second connection. The other switching element is in Actuated as a function of the electrical voltage occurring across the switching element.

The main capacitor is electrically connected in series with the string, preferably for complete overvoltage protection. In other words, one of the connections of the main capacitor is in electrical contact with the first or the second connection. Due to the overvoltage protection, when a circuit having the main capacitor is switched on, the overvoltage protection is used to precharge the main capacitor, so that an electric current flow and an electric voltage that are caused by the main capacitor are initially limited in the electric circuit. An unlimited voltage / current flow would, for example, damage other components of the circuit or trigger a circuit breaker or a fuse by means of which the circuit is protected. The overvoltage protection prevents tripping and protects the other components of the circuit from overload. The main capacitor is, for example, an intermediate circuit capacitor of a converter, and the precharging is carried out, for example, before commissioning or for commissioning the converter.

An embodiment not claimed also relates to such an interconnection of a main capacitor with overvoltage protection.

If individual components are referred to as further, additional, first, second, third ... component, this is only used to denote the respective component. In particular, this does not imply the presence of a specific number of components.

The advantages and developments mentioned in connection with the overvoltage protection and / or the circuit are also to be applied analogously to the use and the interconnections as well as to one another and vice versa.

• 1 schematisch vereinfacht eine Verschaltung mit einem Überspannungsschutz, einem zu schützenden Gerät und einem Hauptkondensator,
• 2 einen Schaltplan des Überspannungsschutzes,
• 3 ein Teil des Schaltplans, und
• 4 einen weiteren Teil des Schaltplans.

An exemplary embodiment of the invention is explained in more detail below with reference to a drawing. Show in it:

• 1 schematically simplified an interconnection with an overvoltage protection, a device to be protected and a main capacitor,
• 2 a circuit diagram of the surge protection,
• 3 part of the schematic, and
• 4th another part of the schematic.

Corresponding parts are provided with the same reference symbols in all figures.

In 1 is a schematically simplified circuit 2 with a DC voltage source 4th shown having a first pole 6th and a second pole 8th having. The first pole 6th is through a switch 10 that is a device to be protected 12th represents, with a main capacitor 14th tied together. The main capacitor 14th is part of a converter not shown in detail and with the second pole 8th the DC voltage source 4th tied together. Hence is the main capacitor 14th electrically in series with the device to be protected 12th switched.

The device to be protected 12th is by means of a surge protector 16 bridged that a first connection 18th and a second port 20th having. Here is the device to be protected 12th between the first connection 18th and the second port 20th switched. Also is the surge protection 16 electrically in series with the main capacitor 14th switched.

The surge protection 16 serves to secure the device to be protected 12th from an overvoltage. If on the device to be protected 12th If an electrical voltage is present that is greater than a certain value, the overvoltage protection is activated 16 activated so that it is at least partially live. As a result, the one between the two ports 18th , 20th applied electrical voltage is limited, and damage to the device to be protected 12th will be prevented. The overvoltage occurs, for example, when the switch is operated 10 on, so if there is an electrical current flow between the first pole 6th and the second pole 8th is to be interrupted, the current flow due to an inductance of the interconnection, not shown in detail 2 is at least partially maintained.

Also is the surge protector 16 to secure the device to be protected 12th used against a pulse current, i.e. if in the interconnection 2 Excessive electrical current occurs due to lightning strike or other external influences, which is not coming from the DC power source 4th is caused, and otherwise to the destruction of the device to be protected 12th , so the switch 10 , would lead.

Another application is overvoltage protection 16 to precharge the main capacitor 14th used. If for commissioning, i.e. if the main capacitor 14th is not charged, the switch 10 is closed, a comparatively large electric current is carried over it, and a comparatively large one falls electrical voltage. In this case, too, the overvoltage protection 16 activated so that the device to be protected 12th , so the switch 10 , applied electrical voltage is not the same as that between the two poles 6th , 8th applied electrical voltage. Only when the main capacitor 14th due to the means of the overvoltage protection 16 reduced electrical current flow is at least partially charged, the overvoltage protection 16 deactivated, so that then the rest of the charging of the main capacitor 14th over the switch 10 he follows. For pre-charging the main capacitor 14th in particular the switch 10 not closed, but the electrical current is essentially only by means of the overvoltage protection 16 guided.

In 2 is a circuit diagram of the surge protection 16 shown, of the first connection 18th and the second port 20th having. Between these is the switch 10 switched, the one line semiconductor switch 22nd includes. A main varistor is provided for additional protection 24 to the power semiconductor switch 22nd connected in parallel by means of a controller 26th is operated depending on current requirements. The main varistor 24 serves to provide additional security in the event of overvoltage protection 16 should be faulty.

The surge protection 16 exhibits a number of strands 28 on that are parallel to each other and between the first port 18th and the second port 20th are switched. Thus are the strands 28 also electrically in series with the main capacitor 14th switched. Each of the strands 28 exhibits a resistance 30th on, which is designed as an ohmic resistor. Furthermore, each strand has 28 a switching element 32 with a control input 34 on. The switching elements 32 are designed as MOSFET throughout, and the resistors 30th are ohmic resistances. In an alternative, IGBTs are used as switching elements 32 used. Any control input 34 is via a further resistance element 36 in the form of a Zener diode against the second connection 20th guided. In parallel with the further resistance element 36 is a second further resistance 40 switched, which is an ohmic resistor.

The second further resistance 40 is in each case by means of a further switching element 42 bridged, each a further control input 44 having. Each additional control input 44 is via another zener diode 46 against the second connection 20th guided. It is by means of both the further resistance elements 36 as well as the other Zener diodes 46 in each case a current flow to the second connection 20th only possible if the applied electrical voltage is applied to the respective further resistance element 36 or at the respective further Zener diode 46 is greater than the respective breakdown voltage.

Each additional Zener diode 46 is also by means of an additional switching element 48 bridged in the form of a transistor, each with an additional control input 50 having. The additional control input 50 is about a second additional resistor 52 against the second connection 20th led, with the second additional resistance 52 by means of an additional capacitor 54 is bridged.

Furthermore, each additional control input is 50 via a first additional resistance 56 as well as the resistance 30th of the switching element 32 assigned strand 28 , the one with the associated further switching element 42 as well as the additional switching element 48 is connected to the first connection 18th guided. By means of an additional resistor between the first 46 and the respective resistance 30th arranged diode 58 there is a current flow from the strand 28 to the additional control input 50 and thus an overload of the respective additional switching element 48 prevented.

The surge protection 16 also has a voltage divider 60 on, the one to the number of strands 28 Corresponding number of resistance elements 62 which are electrically connected in series. Here is the number of resistance elements 62 equal to the number of strands 28 and thus three. Between neighboring resistance elements 62 are each taps 64 formed so that a total of two taps 64 available.

The voltage divider 60 is via a (common) resistance element 66 against the first connection 18th guided. The remaining end of the voltage divider 60 is via a second diode 68 and a second resistor 70 against the control input 34 one of the switching elements 32 guided. The taps 64 are also each via a second diode 68 as well as a second resistor 70 against one of the control inputs 34 guided. The resistance elements 62 as well as the common resistance element 66 are each designed as Zener diodes. By means of the resistance elements 62 as well as the common resistance element 66 is a current flow from the first connection 18th to the control inputs 34 prevented, provided that the applied electrical voltage is not greater than the respective breakdown voltage. Because of the second diode 68 there is a current flow from the respective control input 34 to the first connection 18th prevented.

Any control input 34 is via an additional diode 72 and a respective further resistance 74 as well as the common resistance element 66 against the first connection 18th guided. Using the other diodes 72 there is a current flow from the other control inputs 44 to the first connection 18th prevented.

Any additional control input 50 is also via a first additional diode 76 as well as a common second additional diode 78 , a common third additional resistor 80 and via the common resistance element 66 with the first connection 18th contacted. So there are a total of three first additional diodes 76 , but only a single second additional diode 78 as well as a single third additional resistor 80 available. In parallel with the three series connections each consisting of one of the second additional resistors 52 , one of the first additional resistors 56 as well as one of the first additional diodes 76 is an additional Zener diode 82 switched, with a current flow from the second connection due to their reverse direction 20th to the first connection 18th is always possible.

To one of the switching elements 32 , namely the one whose control input 34 via the smallest number of resistance elements 62 with the first connection 18th connected is a varistor in parallel 84 connected, to which in turn another capacitor in parallel 86 is switched. There is also a second resistance element 88 parallel to the other capacitor 86 and thus also to the varistor 84 switched. The second resistance element 88 is a Zener diode in this version.

In 3 is the surge protection 16 shown in simplified form in part to explain part of the functionality. Here are essentially just the strands 28 as well as the voltage divider 60 with the resistance elements 62 and the taps 64 shown. If between the two connections 18th , 20th an overvoltage or some other excessive electrical voltage occurs, a successively reduced electrical voltage drops at all taps 64 as well as at the end of the voltage divider 60 away. As a result, the control inputs 34 of the switching elements provided with an electrical potential, so that the switching elements 32 be placed in the electrically conductive state. As a result, all of the strands are 28 electrically conductive, which is why an electrical current flow between the connections 18th , 20th over the strands 28 is possible so that the electrical voltage between the terminals 18th , 20th is reduced. This is done by means of the resistors 30th electrical energy converted, which is why the electrical voltage is further reduced.

If the at the connections 18th , 20th applied electrical voltage has fallen below a certain value, it is that of the first connection 18th most distant resistive element 62 of the voltage divider 60 falling electrical voltage is less than its breakdown voltage. As a result, that will be towards the end of the voltage divider 60 guided switching element 32 put into the electrically non-conductive state, which is why this strand 28 is no longer conductive. In the event of a further decrease in the between the connections 18th , 20th applied electrical voltage is the voltage between the two taps 64 arranged resistance element 62 the dropping electrical voltage is less than its breakdown voltage, which is why another strand 28 is no longer conductive. Thus, successively due to the resistances 30th those between the ports 18th , 20th applied electrical voltage is reduced, whereby the electrical current flow is also reduced.

The voltage divider 60 and each of the further resistance elements 36 acts on each of the switching elements 32 as the respective voltage divider. As the resistance elements 62 if there are Zener diodes, the switching elements are actuated 32 with essentially always the same occurring electrical voltage, regardless of the respective electrical current. By means of the second diodes 68 this ensures that there is a reaction between the individual strands 28 is prevented. By means of the second resistors 70 the switching elements are protected 32 .

In 4th is another part of surge protection 16 shown in simplified form in order to explain a further part of the functionality. For moving each of the switching elements 32 in the electrically non-conductive state, there is a change in the at the respective control input 34 applied electrical potential, this via the associated further resistance element 36 as well as the second further resistance 40 is successively brought to the electrical potential of the second connection. As a result, the internal resistance of the switching element increases 32 to, so that over the switching element 32 an increased electrical voltage occurs, with an electrical current flow still being present. Thus, the increases by means of the switching element 32 converted energy, and there is a heating that can lead to damage.

Because of both this switching element 32 associated additional resistances 52 , 56 lies when over the switching element 32 a comparatively large electrical voltage occurs at the associated additional control input 50 an electrical voltage, which is why the associated additional switching element 48 is actuated and transferred to the electrically conductive state. Because this additional switching element 48 is electrically conductive, this is applied to the assigned further control input 44 applied electrical potential to the electrical potential of the second connection 40 switched, so this further switching element 42 is electrically conductive. As a result, at the control input 34 of the switching element 32 essentially suddenly the electrical potential of the second connection 20th applied, and this is thus suddenly put into the electrically non-conductive state. As a result, there is no further heating of the switching element 32 , and, if there are other strands 28 are present, by means of this a current flow between the two connections 18th , 20th accepted.

Because of the further Zener diode 46 it is ensured that the further switching element 42 is only placed in the electrically conductive state when an actuation of the additional switching element 48 he follows. This takes place by means of the further resistor 74 a protection of the further switching element 42 , by means of the further diode 72 an unwanted reaction is avoided. By means of the resistance element 66 it is ensured that the additional switching element 48 is in the electrically non-conductive state, if via the switching element 32 there is insufficient electrical voltage.

In summary, the additional switching element is thus actuated 48 and therefore also of the further switching element 42 depending on the over the respectively assigned switching element 32 occurring electrical voltage. Because of the additional capacitor 54 the additional switching element is switched on with a delay 48 so that short-term voltage peaks do not cause the switching element to switch off prematurely 32 to lead.

Provided all strands 28 are in the electrically non-conductive state, a remaining electrical potential difference between the two terminals 18th , 20th by means of the varistor 84 implemented, by means of the further capacitor 86 and the second resistance element 88 it is ensured that the electrical energy is completely removed.

The invention is not restricted to the exemplary embodiment described above. Rather, other variants of the invention can also be derived therefrom by the person skilled in the art without departing from the subject matter of the invention.

List of reference symbols

2

Interconnection

4th

DC voltage source

6th

first pole

8th

second pole

10

counter

12th

device to be protected

14th

Main capacitor

16

Overvoltage protection

18th

first connection

20th

second connection

22nd

Power semiconductor switch

24

Main varistor

26th

steering

28

strand

30th

resistance

32

Switching element

34

Control input

36

another resistance element

40

second further resistance

42

further switching element

44

further control input

46

another Zener diode

48

additional switching element

50

additional control input

52

second additional resistance

54

additional capacitor

56

first additional resistance

58

diode

60

Voltage divider

62

Resistance element

64

Tap

66

common resistance element

68

second diode

70

second resistance

72

another diode

74

further resistance

76

first additional diode

78

second additional diode

80

third additional resistance

82

additional zener diode

84

Varistor

86

another capacitor

88

second resistance element

Claims (7)

Overvoltage protection (16), with a first connection (18), and with a second connection (20), between which a strand (28) with a resistor (30) is electrically connected, which is connected between the first connection (18) and a Control input (34) having switching element (32) is switched, wherein the control input (34) of the switching element (32) is electrically connected to the second connection (20) via a further control input (44) having further switching element (42), which in Depending on the electrical voltage occurring across the switching element (32), the further control input (44) is led via an additional switching element (48) having an additional control input (50) to the second connection (20), and the additional control input (50) via a first additional resistor (56) and the resistor (30) to the first connection (18) and via a second additional resistor (52) to the second connection (20) is led. Overvoltage protection (16) Claim 1 , characterized in that the additional control input (50) is routed to the first connection (18) via the first additional resistor (56) and a resistor element (66). Overvoltage protection (16) according to one of the Claims 1 until 2 , characterized in that the further control input (44) is led to the second connection (20) via a further Zener diode (46). Overvoltage protection (16) according to one of the Claims 1 until 3 , characterized in that the further control input (44) is led to the first connection (18) via a further diode (72) and / or a further resistor (74). Overvoltage protection (16) according to one of the Claims 1 until 4th , characterized in that a varistor (84) is connected in parallel with the switching element (32). Overvoltage protection (16) according to one of the Claims 1 until 5 , characterized by a plurality of strands (28) which are each connected in parallel to one another, and by a voltage divider (60) which is connected between the control input (34) of one of the switching elements (32) and the first connection (18), and which has a number of electrically series-connected resistance elements (62) corresponding to the number of strands (28), a tap (64) being formed between adjacent resistance elements (62), and each tap (64) against the control input one of the remaining switching elements (32) is guided. Use of an overvoltage protection (16) according to one of the Claims 1 until 6th for protecting a device (12) to be protected against overvoltage and / or a pulse current, which is connected between the first connection (18) and the second connection (20).

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