TECHNICAL FIELD

The present invention generally relates to the field of power systems, such as, for example, power transmission systems. Specifically, the present invention relates to a circuit arrangement that is electrically connectable in a current path between an input node and an output node for conduction of a current from the input node to the output node, which circuit arrangement has a capability to reduce the voltage at the output node as compared to the voltage at the input node if the voltage at the input node exceeds a selected voltage level.

BACKGROUND

A power semiconductor device generally requires some controlling device in order to carry out a desired or required switching operation of the power semiconductor device. The controlling device generally requires a power supply. In some applications power semiconductor devices which are on a relatively high potential in relation to ground are employed. An example of an application wherein power semiconductor devices are on a relatively high potential in relation to ground, is High Voltage Direct Current (HVDC) power transmission systems.

HVDC power transmission has become increasingly important due to increasing need for power supply or delivery and interconnected power transmission and distribution systems. In a HVDC power transmission system there is generally included an interface arrangement including or constituting a HVDC converter, or converter station, which is a type of converter or converter station configured to convert high voltage DC to AC, or vice versa, which interface arrangement configured to couple an AC power system with a DC power system, or vice versa. A HVDC converter station may comprise a plurality of elements such as the converter itself (or a plurality of converters connected in series or in parallel), one or more transformers, capacitors, filters, and/or other auxiliary elements.

Converters may comprise a plurality of solid-state based devices such as semiconductor devices. HVDC technology may be classified as Current Source Converter (CSC) based HVDC and Voltage Source Converter (VSC) based HVDC. While CSC based HVDC converters employ thyristors as switches or switching elements (and/or other switches or switching elements that are not self-commutated), VSC based HVDC converters employ for example insulated gate bipolar transistors (IGBTs) as switches or switching elements (and/or other switches or switching elements that are self-commutated). A plurality of solid-state semiconductor devices such as thyristors or IGBTs may be connected together, for instance in series, to form a building block, or cell, of an HVDC converter. The converter cell may in alternative be referred to as a (HVDC) converter valve.

In some HVDC power transmission systems a power supply of linear regulator type, with about 300 V voltage output, is used, which power supply is electrically connected to the converter valve across the collector-emitter of the IGBTs in the converter valve. In other HVDC power transmission systems a power supply of a switch-mode type is used, which power supply is electrically connected to a converter valve across one or more capacitors of the converter valve. In both of these types of power supplies a series connection of metal-oxide field-effect transistors (MOSFETs) may be used to cope with the relatively large input voltage.

The above-mentioned power supply of linear regulator type may have a relatively low efficiency. With a 300 V voltage output, the gate unit for an IGBT may consume a few W. An input voltage of for example 3 kV will provide about 20-30 W of power dissipation. A power dissipation is of 20-30 W is small compared to the power dissipation of an IGBT. However, considering that a converter station may include several thousands of IGBTs, the total dissipated power for the power supplies may be up to 100 MW or even more. This problem may get worse as the blocking voltage of IGBTs increase. Some HVDC power transmission systems employ IGBTs having a blocking voltage of 6.5 kV. In such cases, the power dissipation of power supplies employing a linear regulator type as described above is not feasible, and instead power supplies employing a switch-mode type of DC/DC converter may be used, and may employ a series connection of MOSFETs to cope with the relatively large input voltage. Because of the inherent risks with simultaneously switching devices electrically connected in series, a resistor with a relatively high resistance may be connected in series at the input of the power supply. Such an arrangement may limit the current to safe levels in case of an internal fault. However, the input voltage may need to be relatively high, about 800 V, for delivering a 300 V output voltage to the gate units of the IGBTs. However, the DC/DC converter may not be able to operate at voltage levels corresponding to an input voltage of, e.g., about 800 V. For example, the DC/DC converter may stop operating if the voltage input to the DC/DC converter exceeds about 600 V. Also, if the voltage input to the DC/DC converter exceeds about 600 V, it may cause a short-circuit, which in turn may damage or even destroy the DC/DC by overheating.

SUMMARY

In view of the above, a concern of the present invention is to provide a circuit arrangement which may be used for example in a current path for supplying power to some component(s) at the output node of the current path, wherein the circuit arrangement may facilitate or even enable to reduce or even eliminate the risk of a too high voltage being input to the component(s) at the output node of the current path, which high voltage for example may cause malfunction or outage of the component(s).

To address at least one of this concern and other concerns, a circuit arrangement in accordance with the independent claim is provided. Preferred embodiments are defined by the dependent claims.

According to a first aspect, a circuit arrangement is provided. The circuit arrangement is electrically connectable in or to a current path between at least one input node and at least one output node for conduction of a current from the input node to the output node. Thus, current may be conveyed from the input node to the output node via the circuit arrangement.

The circuit arrangement comprises at least one switching element. The at least one switching element comprises at least a first terminal, a second terminal and a third terminal. The at least one switching element is arranged such that current may flow in a current path between the first terminal and the second terminal. The at least one switching element is arranged such that the third terminal governs the electrical conductivity of the current path between the first terminal and the second terminal based on voltage at the third terminal relatively to the voltage at the second terminal. The switching element is arranged such that current flows unimpeded (or substantially unimpeded) from the first terminal to the second terminal in the current path between the first terminal and the second terminal unless the voltage at the third terminal relatively to the voltage at the second terminal is within a predefined switching element threshold voltage range. The third terminal is electrically connected to the second terminal via a resistor and additionally to at least one electrical conductor via voltage regulating circuitry (VRC). The VRC is configured such that it conducts current therethrough in a direction towards the at least one electrical conductor when the voltage over the VRC is within a predefined VRC threshold voltage range, wherein, when the voltage at the input node is within the predefined VRC threshold voltage range (e.g., when the voltage at the input node is above the predefined VRC threshold voltage range), the VRC conducts current therethrough towards the at least one electrical conductor, whereby at least a portion of the current from the input node is diverted via the electrical connection between the second terminal and the third terminal from the current path between the input node and the output node so as to flow towards the at least one electrical conductor via the third terminal and the VRC. The resistor is arranged with a resistance based on the predefined switching element threshold voltage range and current corresponding to the predefined VRC threshold voltage range such that the diverted current (which is flowing towards the at least one electrical conductor via the third terminal and the VRC) causes the voltage at the third terminal relatively to the voltage at the second terminal to be within the predefined switching element threshold voltage range. By means of such a configuration of the VRC and the resistor, if the voltage at the input node is within the predefined VRC threshold voltage range, the voltage at the output node may be reduced relatively to the voltage at the input node by at least a voltage within the predefined VRC threshold voltage range corresponding to a voltage over the VRC when it begins to conduct current therethrough in a direction towards the at least one electrical conductor. The reduction in the voltage at the output node is due to the at least a portion of the current from the input node that is being diverted from the current path between the input node and the output node so as to flow towards the at least one electrical conductor.

The VRC may for example be configured such that it conducts current therethrough in a direction towards the at least one electrical conductor when the voltage over the VRC exceeds a limit (e.g., a lower limit) of the predefined VRC threshold voltage range. The predefined VRC threshold voltage range may for example be VVRC > Vth, such that when the voltage over the VRC, VVRC, exceeds the voltage Vth, the VRC conducts current therethrough in a direction towards the at least one electrical conductor, whereas the VRC does not conduct current therethrough in a direction towards the at least one electrical conduct when VVRC≤ Vth. In this case, by means of such a configuration of the VRC and the resistor, the voltage at the output node may be reduced relatively to the voltage at the input node by at least Vth.

The circuit arrangement may for example be used in a current path for supplying power to a DC/DC converter as mentioned in the foregoing, for delivering an output voltage to the gate units of the IGBTs of a converter valve. In the light of the foregoing discussion, by means of the configuration of the VRC(s) and the resistor(s) in the circuit arrangement, and in particularly by arranging the VRC(s) with selected VRC threshold voltage range(s), it may be facilitated or even enabled to reduce or even eliminate the risk of a too high voltage being input to DC/DC converter. As indicated in the foregoing, a DC/DC converter used for delivering an output voltage to the gate units of the IGBTs of a converter valve may stop operating if the voltage input to the DC/DC converter exceeds a threshold voltage, e.g., about 600 V. Also, if the voltage input to the DC/DC converter exceeds a threshold voltage, e.g., about 600 V, it may cause a short-circuit, which in turn may damage or even destroy the DC/DC by overheating.

If the voltage at the input node is not within the predefined VRC threshold voltage range (e.g., if the voltage at the input node is below the predefined VRC threshold voltage range), the circuit arrangement may permit the current from the input node to flow unimpeded (or substantially unimpeded) towards the output node. Put in another way, when the voltage at the input node is not within the predefined VRC threshold voltage range, the VRC may not conduct current therethrough towards the at least one electrical conductor, wherein no portion of the current from the input node may be diverted via the electrical connection between the second terminal and the third terminal from the current path between the input node and the output node.

The resistor may for example be arranged with a resistance based on the predefined switching element threshold voltage range and current corresponding to the predefined VRC threshold voltage range such that the diverted current (which is flowing towards the at least one electrical conductor via the third terminal and the VRC) causes the voltage at the third terminal relatively to the voltage at the second terminal to be within the predefined switching element threshold voltage range (e.g., so as to generate a negative voltage, or bias, on the third terminal relatively to the second terminal) such that the switching element still conducts current therethrough, at least to some extent.

For example, in accordance with one or more embodiments of the present invention, the resistor may be arranged with a resistance based on the predefined switching element threshold voltage range and current corresponding to the predefined VRC threshold voltage range such that the diverted current (which is flowing towards the at least one electrical conductor via the third terminal and the VRC) causes the voltage at the third terminal relatively to the voltage at the second terminal to be within the predefined switching element threshold voltage range so as to cause the switching element to operate in an ohmic mode.

In the context of the present application, by a switching element it is meant an electrical device or element which is capable of switching (parts or portions of) electrical signals or electrical power, and which may also be capable of attenuating or blocking and/or amplifying electrical signals or electrical power. The switching element could in alternative - in accordance with one or more embodiments of the present invention - be referred to as a switching transistor element.

As will be further described in the following, the switching element may for example comprise at least one transistor. The ohmic mode may in alternative be referred to as a linear region operational mode of the switching element. In the context of the present application, by ohmic mode or linear region operational mode of the switching element, it is meant a part of the active region of the switching element (e.g., a transistor) wherein the output voltage of the switching element or transistor is linearly (or substantially linearly) dependent on the input voltage of the switching element or transistor. Thus, when the switching element is operating in ohmic mode, or linear region operational mode, the switching element is not shut off, but may still conduct current therethrough at least to some extent.

The resistor of the at least one switching element, via which resistor the third terminal of the at least one switching element is electrically connected to the second terminal of the at least one switching element, may be arranged such that its resistance is defined by a ratio between a threshold voltage of the switching element and a current corresponding to a lower limit of the predefined VRC threshold voltage range. The threshold voltage of the switching element may be defined by a lower limit of the predefined switching element threshold voltage range. The switching element may for example comprise a transistor, such as, for example, a filed-effect transistor (FET). The FET may for example comprise or be constituted by a MOSFET and/or a junction gate FET (JFET). The lower limit of the predefined switching element threshold voltage range may for example correspond to the threshold gate-source threshold voltage, which for a MOSFET may be 3 V, or about 3 V. The VRC may for example comprise a Zener diode. The so called 'knee current' of the Zener diode, i.e. the current above which the Zener diode permits significant conduction of current in the reverse direction (i.e. from its cathode to its anode), may for example be 50 μΑ, or about 50 μΑ. Assuming a threshold gate-source threshold voltage of the MOSFET of 3 V and a knee current of the Zener diode of 50 μΑ, the resistance of the resistor may be 60 kΩ, or about 60 kQ.

According to a second aspect, a system is provided. The system comprises a current path between at least one input node and at least one output node for conduction of a current from the at least one input node to the at least one output node. The system comprises a circuit arrangement according to the first aspect, which circuit arrangement is electrically connected in or to the current path. The system may comprise an overcurrent protecting device electrically connected to the at least one output node.

Further objects and advantages of the present invention are described in the following by means of exemplifying embodiments. It is noted that the present invention relates to all possible combinations of features recited in the claims. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the description herein. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplifying embodiments of the present invention will be described below with reference to the accompanying drawings.

Figures 1 and 2 are schematic views of systems according to embodiments of the present invention.

Figure 3 is a schematic view of a DC/DC converter in accordance with an embodiment of the present invention.

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate embodiments of the present invention, wherein other parts may be omitted or merely suggested. DETAILED DESCRIPTION

The present invention will now be described hereinafter with reference to the accompanying drawings, in which exemplifying embodiments of the present invention are shown. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments of the present invention set forth herein; rather, these embodiments are provided by way of example so that this disclosure will convey the scope of the present invention to those skilled in the art.

Figure 1 is a schematic view of a system according to an embodiment of the present invention. The system comprises a circuit arrangement 100 that is electrically connected in a current path 1 between an input node 10 and two output nodes 11, 12 for conduction of a current from the input node 10 to the output nodes 11, 12. The system comprises a circuit arrangement 100 that is electrically connected in the current path 1 between the input node 10 and the output nodes 11, 12. There may possibly be more than one input node, or less or more than two output nodes.

In accordance with the embodiment of the present invention illustrated in

Figure 1, a DC/DC converter 80 is electrically connected to the output nodes 11, 12. The circuit arrangement 100 may for example be used for supplying power to the DC/DC converter 80 from a power supply (not shown) electrically connected to the input node 10. The circuit arrangement 100 may for example be used for supplying power to the DC/DC converter 80 for delivering an output voltage to the gate units of the IGBTs of a converter valve (not shown in Figure 1). The DC/DC converter 80 may for example comprise a step- down switch-mode converter.

In accordance with the embodiment of the present invention illustrated in Figure 1, the circuit arrangement 100 comprises a plurality of switching elements 20, 30, 40, which may, as illustrated in Figure 1, be electrically connected in series, so as to form a series connection of switching elements 20, 30, 40. It is however to be understood that in accordance with one or more other embodiments of the present invention, the circuit arrangement 100 may comprise less or more than three switching elements, for example one switching element, or two switching elements or four or more switching elements (which may be connected in series).

Each of the switching elements 20, 30, 40 comprises a first terminal 21, 31 and 41, respectively, a second terminal 22, 32 and 42, respectively, and a third terminal 23, 33 and 43, respectively. Each of the switching elements 20, 30, 40 is arranged such that current may flow in a current path between the first terminal 21, 31, 41 and the second terminal 22, 32, 42 of the respective one of the switching elements 20, 30, 40, and further such that the third terminal 23, 33, 43 of the respective one of the switching elements 20, 30, 40 governs the electrical conductivity of the current path between the first terminal 21, 31, 41 and the second terminal 22, 32, 42 of the respective one of the switching elements 20, 30, 40 based on voltage V_gl, V_g2, V_g3 at the third terminal 23, 33, 43 of the respective one of the switching elements 20, 30, 40 relatively to the voltage V_sl, V_s2, V_s3 at the second terminal 22, 32, 42 of the respective one of the switching elements 20, 30, 40.

Each of the switching elements 20, 30, 40 is arranged such that current flows unimpeded from the first terminal 21, 31, 41 to the second terminal 22, 32, 42 of the respective one of the switching elements 20, 30, 40 in the current path between the first terminal 21, 31, 41 and the second terminal 22, 32, 42 of the respective one of the switching elements 20, 30, 40 unless the voltage at the third terminal 23, 33, 43 relatively to the voltage at the second terminal 22, 32, 42 of the respective one of the switching elements 20, 30, 40 is within a predefined switching element threshold voltage range for the respective switching element 20, 30, 40. Thus, in accordance with the embodiment of the present invention illustrated in Figure 1, each of the switching elements 20, 30, 40 is a switching element that is "normally on" in the sense that it may conduct current unless a particular voltage at the third terminal 23, 33, 43 relatively to the voltage at the second terminal 22, 32, 42 of the respective one of the switching elements 20, 30, 40 is applied.

In accordance with the embodiment of the present invention illustrated in Figure 1, each of the switching elements 20, 30, 40 comprises a depletion mode metal-oxide semiconductor field-effect transistor (MOSFET). It is however to be understood that that in accordance with one or more other embodiments of the present invention, each or any one of the switching element(s) comprised in the circuit arrangement may comprise another type or other types of switching elements.

For example, each or any one of the switching element(s) comprised in the circuit arrangement may comprise or be constituted by at least one transistor, which for example may comprise or be constituted by at least one field-effect transistor (FET). The first terminal, the second terminal and the third terminal of the switching element may for example comprise a drain terminal, a source terminal and a gate terminal, respectively, of at least one FET. The at least one FET may for example comprise or be constituted by a MOSFET, such as a depletion mode MOSFET as indicated in the foregoing, and/or a junction gate FET (JFET). In alternative or in addition, each or any one of the switching element(s) comprised in the circuit arrangement may comprise or be constituted by another type or other types of switching elements which are "normally-on" type(s) of switching element(s), similarly to a depletion mode MOSFET or a JFET, which may conduct current unless a predefined voltage is applied to the switching element, e.g., a predefined voltage at the gate terminal relatively to the voltage at the source terminal, in case of a FET.

Each of the switching elements 20, 30, 40 is arranged such that the third terminal 23, 33, 43 of the respective one of the switching elements 20, 30, 40 is electrically connected to the second terminal 22, 32, 42 of the respective one of the switching elements 20, 30, 40 via a resistor 24, 34, 44 corresponding to the respective one of the switching elements 20, 30, 40, and additionally to an electrical conductor 50 via voltage regulating circuitry (VRC) 25, 35, 45 corresponding to the respective one of the switching elements 20, 30, 40. Each of the VRCs 25, 35, 45 is configured such that it conducts current therethrough in a direction towards the at least one electrical conductor 50 when the voltage over the VRC 25, 35, 45 is within a predefined VRC threshold voltage range for the respective VRC 25, 35, 45.

In accordance with the embodiment of the present invention illustrated in Figure 1, the VRCs 25, 35, 45 of the respective ones of the switching elements 20, 30, 40 are electrically connected in series, so as to form a series connection of VRCs 25, 35, 45. As illustrated in Figure 1, the series connection of the VRCs 25, 35, 45 is electrically connected to the electrical conductor 50.

In accordance with the embodiment of the present invention illustrated in Figure 1, each of the VRCs 25, 35, 45 comprises a Zener diode. Each or any one of the VRCs 25, 35, 45 may in accordance with one or more other embodiments of the present invention comprise more than one Zener diode, e.g., two or more Zener diodes which may be connected in series. It is to be understood that that in accordance with one or more other embodiments of the present invention, each or any one of the VRCs 25, 35, 45 may comprise another type or other types of voltage regulating circuitry. For example, each or any one of the VRCs 25, 35, 45 may for example comprise one or more transistors, which for example may be connected in series. According to another example, each or any one of the VRCs 25, 35, 45 may comprise one or more avalanche diodes.

In accordance with the embodiment of the present invention illustrated in Figure 1, wherein each of the VRCs 25, 35, 45 comprises a Zener diode, the predefined VRC threshold voltage range of the respective VRCs 25, 35, 45 may be defined by V > V_zl, V > V_z2, and V > V_z3, respectively, where V is voltage and V_zl, V_z2 and V_z3 is the Zener breakdown voltage of the VRCs (Zener diodes) 25, 35 and 45, respectively.

For illustrating principles of one or more embodiments of the present invention, one of the switching elements 20, 30, 40 comprised in the circuit arrangement 100 may be considered, for example the switching element 20.

With respect to the switching element 20, if the voltage V_in at the input node is within the predefined VRC threshold voltage range (e.g., if the voltage V_in at the input node is above the predefined VRC threshold voltage range - for example if V_in >V_zl), the VRC 25 conducts current therethrough towards the electrical conductor 50, whereby a portion of the current from the input node 10 is diverted via the electrical connection between the second terminal 22 and the third terminal 23 from the current path between the input node 10 and the output nodes 11, 12 so as to flow towards the electrical conductor 50 via the third terminal 23 and the VRC 25. The electrical conductor 50 may for example be configured to convey the diverted current to a grounding point 60, or ground, as illustrated in Figure 1. The grounding point 60 may for example comprise an electrical connection to ground. The resistor 24 is arranged with a resistance R_gsl based on the predefined switching element threshold voltage range of the switching element 20 and current corresponding to the predefined VRC threshold voltage range of the VRC 25 such that the diverted current causes the voltage V_gl at the third terminal 23 relatively to the voltage V_sl at the second terminal 22 to be within the predefined switching element threshold voltage range of the switching element 20 (e.g., so as to generate a negative voltage, or bias, on the third terminal 23 relatively to the second terminal 22). The switching element 20 may thereby be caused to begin operating in an ohmic mode.

The VRC 25 may for example be configured such that it conducts current therethrough in a direction towards the electrical conductor 50 when the voltage over the VRC 25 exceeds a limit (e.g., a lower limit) of the predefined VRC threshold voltage range of the VRC 25. As indicated in the foregoing, in accordance with the embodiment of the present invention illustrated in Figure 1, wherein each of the VRCs 25, 35, 45 comprises a Zener diode, the predefined VRC threshold voltage range of the VRC 25 may be V > V_zl, where V is voltage and V_zl is the Zener breakdown voltage of the VRC (Zener diode) 25.

In this case, by means of the above-described configuration of the VRC 25 and the resistor 24, the voltage V_out at the output nodes 11, 12 may be reduced relatively to the voltage V_in at the input node 10 by at least V_zl.

In alternative or in addition to the electrical conductor 50 being configured to convey the diverted current to a grounding point 60, such as illustrated in Figure 1, the electrical conductor 50 may be configured to convey the diverted current to the input node 10. By such an arrangement, the current that may be diverted from the current path between the input node 10 and the output nodes 11, 12 may be fed back to the input node 10, and possibly to a power supply (not shown) that may be providing the input voltage V_in at the input node 10.

For further illustrating principles of one or more embodiments of the present invention, two of the series-connected switching elements 20, 30, 40 comprised in the circuit arrangement 100 may be considered, for example the switching elements 20 and 30, which have corresponding VRCs 25 and 35, respectively, and corresponding resistors 24 and 34, respectively.

An aggregated VRC threshold voltage may be defined by a sum of the lower limits of the predefined VRC threshold voltage ranges of the respective ones of the series- connected VRCs 25 and 35 such that the series-connected VRCs 25 and 35 conduct current therethrough in a direction towards the electrical conductor 50 when the voltage over the series-connected VRCs 25 and 35 exceeds the aggregated VRC threshold voltage.

As indicated in the foregoing, in accordance with the embodiment of the present invention illustrated in Figure 1, wherein each of the VRCs 25, 35, 45 comprises a Zener diode, the predefined VRC threshold voltage range of the VRC 25 may be V > V_zl, where V is voltage and V_zl is the Zener breakdown voltage of the VRC (Zener diode) 25, and the predefined VRC threshold voltage range of the VRC 35 may be V > V_z2, where V is voltage and V_z2 is the Zener breakdown voltage of the VRC (Zener diode) 35. The aggregated VRC threshold voltage may then be V_zl + V_z2.

If the voltage V_in at the input node 10 exceeds the aggregated VRC threshold voltage (e.g., V_zl + V_z2), then, for each of the switching elements 20 and 30,

corresponding to the series-connected VRCs 25 and 35, respectively, a portion of the current from the input node 10 is diverted via a respective electrical connection between the second terminal 22, 32 and the third terminal 23, 33 of the respective switching element 20, 30 from the current path between the input node 10 and the output nodes 11, 12 so as to flow towards the electrical conductor 50 via the third terminal 23, 33 and the corresponding VRC 25, 35 of the respective switching element 20, 30. Each of the resistors 24, 34 is arranged with a resistance R_gsl, R_gs2 based on the predefined switching element threshold voltage range of the respective switching element 20, 30 and current corresponding to the predefined VRC threshold voltage range of the corresponding VRC 25, 35 such that the diverted current causes the voltage at the third terminal 23, 33 relatively to the voltage at the second terminal 22, 32 to be within the predefined switching element threshold voltage range of the respective switching element 20, 30 (e.g., so as to generate a negative voltage, or bias, on the third terminal 23, 33 relatively to the second terminal 22, 32). The respective switching elements 20, 30 may thereby be caused to begin operating in an ohmic mode.

Thus, if the voltage V_in at the input node 10 exceeds the aggregated VRC threshold voltage (e.g., V_zl + V_z2), portions of the current from the input node 10 are diverted from the current path between the input node 10 and the output nodes 11, 12 at the electrical connection between the second terminal 22 and the third terminal 23 of the switching element 20, and at the electrical connection between the second terminal 32 and the third terminal 33 of the switching element 30.

Thereby, the voltage V_out at the output nodes 11, 12 may be reduced relatively to the voltage V_in at the input node 10 by at least a voltage corresponding to the aggregated VRC threshold voltage (e.g., V_zl + V_z2).

Similar principles apply for any additional switching elements connected in series with the switching elements 20 and 30. For further illustrating principles of one or more embodiments of the present invention, all of the switching elements 20, 30, 40 comprised in the circuit arrangement 100 may be considered.

An aggregated VRC threshold voltage may be defined by a sum of the lower limits of the predefined VRC threshold voltage ranges of the respective ones of the series- connected VRCs 25, 35 and 45 such that the series-connected VRCs 25, 35 and 45 conduct current therethrough in a direction towards the electrical conductor 50 when the voltage over the series-connected VRCs 25, 35 and 45 exceeds the aggregated VRC threshold voltage.

As indicated in the foregoing, in accordance with the embodiment of the present invention illustrated in Figure 1, wherein each of the VRCs 25, 35, 45 comprises a Zener diode, the predefined VRC threshold voltage range of the VRC 25 may be V > V_zl, where V is voltage and V_zl is the Zener breakdown voltage of the VRC (Zener diode) 25, the predefined VRC threshold voltage range of the VRC 35 may be V > V_z2, where V is voltage and V_z2 is the Zener breakdown voltage of the VRC (Zener diode) 35, and the predefined VRC threshold voltage range of the VRC 45 may be V > V_z3, where V is voltage and V_z3 is the Zener breakdown voltage of the VRC (Zener diode) 45. The aggregated VRC threshold voltage may then be V_zl + V_z2 + V_z3.

If the voltage V_in at the input node 10 exceeds the aggregated VRC threshold voltage (e.g., V_zl + V_z2 + V_z3), then, for each of the switching elements 20, 30 and 40, corresponding to the series-connected VRCs 25, 35 and 45, respectively, a portion of the current from the input node 10 is diverted via a respective electrical connection between the second terminal 22, 32, 42 and the third terminal 23, 33, 43 of the respective switching element 20, 30, 40 from the current path between the input node 10 and the output nodes 11, 12 so as to flow towards the electrical conductor 50 via the third terminal 23, 33, 43 and the corresponding VRC 25, 35, 45 of the respective switching element 20, 30, 40. Each of the resistors 24, 34, 44 is arranged with a resistance R_gsl, R_gs2, R_gs 3based on the predefined switching element threshold voltage range of the respective switching element 20, 30, 40 and current corresponding to the predefined VRC threshold voltage range of the corresponding VRC 25, 35, 45 such that the diverted current causes the voltage at the third terminal 23, 33, 43 relatively to the voltage at the second terminal 22, 32, 42 of the respective switching element 20, 30, 40 to be within the predefined switching element threshold voltage range of the respective switching element 20, 30, 40 (e.g., so as to generate a negative voltage, or bias, on the third terminal 23, 33, 43 relatively to the second terminal 22, 32, 42). The respective switching elements 20, 30, 40 may thereby be caused to begin operating in an ohmic mode.

Thus, if the voltage V_in at the input node 10 exceeds the aggregated VRC threshold voltage (e.g., V_zl + V_z2 + V_z3), portions of the current from the input node 10 are diverted from the current path between the input node 10 and the output nodes 11, 12 at the electrical connection between the second terminal 22 and the third terminal 23 of the switching element 20, at the electrical connection between the second terminal 32 and the third terminal 33 of the switching element 30, and at the electrical connection between the second terminal 42 and the third terminal 43 of the switching element 40. Thereby, the voltage V_out at the output nodes 11, 12 may be reduced relatively to the voltage V_in at the input node 10 by at least a voltage corresponding to the aggregated VRC threshold voltage (e.g., V_zl + V_z2 + V_z3).

Similar principles may apply for any additional switching elements connected in series with the switching elements 20, 30 and 40.

However, if the voltage V_in at the input node 10 is not exceeding the aggregated VRC threshold voltage (e.g., V_zl + V_z2 + V_z3), the circuit arrangement 100 may permit the current from the input node 10 to flow unimpeded (or substantially

unimpeded) towards the output nodes 11, 12 (via the switching elements 20, 30, 40). Put in another way, when the voltage V_in at the input node 10 is not exceeding the aggregated VRC threshold voltage, the VRCs 25, 35, 45 may not conduct current therethrough towards the electrical conductor 50, wherein no portions of the current from the input node 10 may be diverted via the electrical connections between the second terminal 22, 32, 42 and the third terminal 23, 33, 43 of the respective switching elements 20, 30, 40 from the current path between the input node 10 and the output nodes 11, 12.

Figure 2 is a schematic view of a system according to another embodiment of the present invention. The system illustrated in Figure 2 is similar to the system illustrated in Figure 1, and the same reference numerals in Figures 1 and 2 indicate the same or similar components, having the same or similar functions.

The system illustrated in Figure 2 differs from the system illustrated in Figure

1 in that in the system illustrated in Figure 2, each of the switching elements 20, 30, 40 comprises a thermistor 26, 36, 46. It is to be understood that not all of the switching elements may comprise a thermistor, but that only one or some of the switching elements possibly may comprise a thermistor. As illustrated in Figure 2, the thermistor 26 may be electrically connected in series with the second terminal 22, possibly in the current path between the first terminal 21 and the second terminal 22. The thermistor 36 may be electrically connected in series with the second terminal 32, possibly in the current path between the first terminal 31 and the second terminal 32. The thermistor 46 may be electrically connected in series with the second terminal 42, possibly in the current path between the first terminal 41 and the second terminal 42.

As known in the art, a thermistor is a type of resistor the resistance of which is dependent on temperature (to a greater degree than most, or if not all, other types of resistors). Each or any one of the thermistors 26, 36, 46 may for example comprise a Positive

Temperature Coefficient (PTC) thermistor, whose resistance R_ptcl, R_ptc2, R_ptc3 increases as temperature rises to protect against overcurrent conditions. Thus, the thermistors 26, 36, 46 may be used to protect against any overcurrent condition occurring in the switching elements 20, 30 and 40, respectively. The thermistors 26, 36 and 46 may for example be used to sense the temperature of the switching elements 20, 30 and 40, respectively. As illustrated in Figure 2, the system may in addition or in alternative comprise another type of overcurrent protecting device. The system illustrated in Figure 2 comprises an overcurrent protecting device, schematically indicated by component 70 in Figure 2, electrically connected to the output nodes 11, 12. The overcurrent protecting device 70 can hence be used in alternative or in addition to the thermistors 26, 36, 46. According to the embodiment of the present invention illustrated in Figure 2, the overcurrent protecting device 70 is electrically connected to the output nodes 11, 12 via the at least one DC/DC converter 80 (e.g., at the output of the DC/DC converter 80). The overcurrent protecting device 70 may for example comprises at least one fuse.

As noted in the foregoing, the DC/DC converter 80 may for example comprise a step-down switch-mode converter.

Figure 3 is a schematic view of a DC/DC converter 80 in accordance with an embodiment of the present invention. According to the embodiment of the present invention illustrated in Figure 3, the DC/DC converter 80 comprises a step-down switch-mode converter. In addition to the capacitors, the diode, the inductor and the transistor illustrated in Figure 3, the DC/DC converter 80 may further comprise driver circuitry 81 electrically connected at a terminal of the transistor. The driver circuitry 81 may for example comprise gate driver circuitry electrically connected at a gate terminal of the transistor. The DC/DC converter 80 may further comprise a step-down controller 82 connected to the driver circuitry 81. The step-down controller 82 may control the voltage V_out2 output from the DC/DC converter 80 to a desired or required voltage level.

In conclusion a circuit arrangement is disclosed that is electrically connectable in a current path. The circuit arrangement comprises at least one switching element, comprising at least a first terminal, a second terminal, and a third terminal and being arranged such that current may flow in a current path between the first terminal and the second terminal, and further such that the third terminal governs the electrical conductivity of the current path between the first terminal and the second terminal, based on voltage at the third terminal relatively to the voltage at the second terminal (22, 32, 42). The at least one switching element is arranged such that current flows unimpeded from the first terminal to the second terminal in the current path between the first terminal and the second terminal unless the voltage at the third terminal relatively to the voltage at the second terminal is within a predefined switching element threshold voltage range. The at least one switching element may hence be considered as a "normally on" switching element. The third terminal is electrically connected to the second terminal via a resistor and additionally to at least one electrical conductor via voltage regulating circuitry, wherein the voltage regulating circuitry is configured such that it conducts current therethrough in a direction towards the at least one electrical conductor when the voltage over the voltage regulating circuitry is within a predefined VRC threshold voltage range. While the present invention has been illustrated in the appended drawings and the foregoing description, such illustration is to be considered illustrative or exemplifying and not restrictive; the present invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the appended claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.