Switching device for the monitored supply of a DC voltage to an active electrical load

Abstract

The invention relates to a switching device (10) for supplying a DC voltage to an electrical load (12). The switching device (10) has the following features: - a DC voltage source (16) connected to a first terminal node (20) and a second terminal node (22); - a capacitor (24) arranged between the first terminal node (20) and the second terminal node (22); - a switching unit (26) arranged between the first terminal node (20) and a first consumer node or between the second terminal node (22) and a second consumer node; - a control unit (28) for controlling the switching unit (26); - wherein the DC voltage source (16) is designed to charge the capacitor (24) when the switching unit (26) is in the open state; and - the control unit (28) is designed to - to detect and monitor a monitoring voltage that is proportional to the capacitor voltage; - to close the switching unit (26) if an increase in the monitoring voltage above a first limit voltage is detected; - to open the switching unit (26) if a drop in the monitoring voltage below a second limit voltage is detected after the switching unit (26) has previously been closed, - to keep the switching unit (26) open if a renewed increase in the monitoring voltage above the first limit voltage is detected after a drop in the monitoring voltage below a second limit voltage has previously been detected.

Description

[0001] The present invention relates to a switching device for the monitored provision of a DC voltage to an active electrical consumer and to a corresponding method for providing a DC voltage to an electrical consumer.

[0002] Various embodiments of the aforementioned switching devices and corresponding methods are already known from the prior art.

[0003] US Patent 2023 / 0370061A1 describes a switching device comprising a voltage source and a first switch located between a buffer capacitor and a driven switch. The buffer capacitor is connected to and charged by the voltage source when the first switch is off. The described switching device further comprises a comparator configured to monitor the charging of the buffer capacitor and to turn on the first switch when the buffer capacitor reaches a threshold charge, thereby initiating a redistribution of charge from the buffer capacitor to the driven switch. The described switching device also includes a delay circuit that implements a delay for the comparator to turn off a second switch, which functionally connects and disconnects the buffer capacitor from the power source.

[0004] When designing a DC power supply, for example using an AC / DC or DC / DC switching converter, it is sensible and common practice not to dimension the switching converter's power limit several times larger than the rated current required by the electrical load. The switching converter typically only operates at its highest possible efficiency above a certain power output.

[0005] Below this power output, it operates inefficiently, i.e., (possibly significantly) below its best possible efficiency.

[0006] Certain active electrical devices require a significantly higher inrush current (also known as "inrush current") than their rated current for a limited period after being switched on. Depending on the load profile of the device, this inrush current can be several times the rated current. If an electrical device requires several times its rated current to start up for a short period after being switched on, a switching current converter that can only deliver its rated current would not be able to supply the briefly required inrush current. The converter would therefore be undersized, and the device would not be able to switch on (or not reliably).

[0007] If, instead, the converter were designed according to the high inrush current required by the load, it would indeed be able to reliably supply the briefly required inrush current, but after the start-up process (i.e., during normal operation) it would operate significantly below its optimal efficiency when delivering the rated current. This would not only lead to unnecessarily high power losses in the voltage converter, but would also be associated with increased costs, because more powerful converters (along with the required external components) generally incur higher costs.

[0008] One possible solution to the problem described above can be achieved by connecting a sufficiently large starting capacitor in parallel between the switching converter and the load. However, the voltage source and the starting capacitor must only be connected to the load via a switch after the starting capacitor has been charged to a specific charge level. In the equivalent circuit diagram, the starting capacitor is represented by C. start from the voltage source V s via the source resistance R s first charged to a specific charge level within a specific time (see Fig. 1) The charging curve of the starting capacitor follows the known exponential function. VCstart=VS*(1−e−tR*C).

[0009] Since the consumer loads the voltage source after closing switch S, the voltage V CstartDepending on the load from the consumer and the capacity of the starting capacitor, the voltage can drop to a certain value (during the period t1 to t2), as shown in the... Fig. Figure 2 shows that with correct design and matching of the voltage source and the starting capacitor to the load from the consumer, the voltage V remains constant. Cstart after switching on, at time t1 above the switch-off threshold V off However, in the event that the voltage V Cstart after time t1 the shutdown threshold V off If the voltage falls below the set threshold, switch S should be opened again (the switch becomes high-resistance). In this case, the load should remain permanently disconnected from the voltage source; therefore, switch S should remain open. This means that after the voltage falls below the cut-off threshold V even once, the switch should be closed. off The circuit should keep switch S open even if the voltage V Cstart again above the switch-on threshold V onshould increase.

[0010] In common circuit devices without a holding function, such as the standard window comparator (without a latch function), the entry of the input voltage into a defined switching window leads to a change in the output voltage. Previous state changes are not taken into account.

[0011] In previously known devices, start capacitors are used to provide increased power for the start-up process. In particular, some devices employ window comparators (without a latching or holding function) where the switching on of an electrical load depends on an upper and a lower voltage threshold of the input voltage. However, such devices cannot implement switching the electrical load on and off while taking previous events into account. This has the disadvantage, for example, that in some fault situations, uncontrolled, oscillating switching of the electrical load can occur. This problem, which is addressed in the Fig. The phenomenon shown in Figure 3 can occur, for example, when the starting capacitor is undersized relative to the current draw of the electrical load and is therefore overloaded. In this case, the switch-off threshold is exceeded or fallen below several times within a short period. The oscillating switching on and off of the electrical load described above can lead to additional stress on the load and thus a shorter lifespan for the load.

[0012] Based on the problem described above, the object of the present invention is to provide a switching device that ensures a monitored voltage supply to an electrical load by guaranteeing sequential switching on and off with clearly defined switching conditions. This ensures both that the defined switching on occurs only when the capacitor reaches a high charge level and prevents an undefined, oscillating switching state below a low charge level. To solve this problem, the present invention proposes a switching device for supplying a DC voltage to an electrical load, wherein the switching device comprises the following: - a DC voltage source connected to a first terminal node and a second terminal node; - a capacitor located between the first terminal node and the second terminal node; - a switching unit arranged between the first connection node and a first consumer node or between the second connection node and a second consumer node, wherein the first consumer node and the second consumer node are designed to be connected to the electrical consumer, and wherein the switching unit is designed to provide a consumer current flowing through the consumer when the switching unit is closed and to prevent a consumer current (i.e., a current flowing through the electrical consumer) when the switching unit is open; - a control unit for controlling the switching unit; - wherein the DC voltage source is designed to charge the capacitor when the switching unit is in the open state; and - the control unit is designed to - to detect and monitor a monitoring voltage that is proportional to the voltage applied to the capacitor (also known as the capacitor voltage); - to close the switching unit if an increase in the monitoring voltage above a first limit voltage (i.e., an exceedance of the first limit voltage) is detected; - to open the switching unit if a drop in the monitoring voltage below a second limit voltage (i.e., a fall below the second limit voltage) is detected after the switching unit was previously closed; - to keep the switching unit open if a renewed increase in the monitoring voltage above the first limit voltage (i.e., a renewed exceedance of the first limit voltage) is detected after a previous drop in the monitoring voltage below a second limit voltage has been detected.

[0013] The control unit according to the invention enables optimized switching behavior for the electrical load, taking into account past events. This means that not only the current voltage values ​​applied to a monitoring node are considered, but also the behavior of the switching device in the past. This prevents, for example, oscillating switching behavior in the event of a fault, which is caused by repeatedly exceeding and falling below a threshold voltage. Overall, the control unit according to the invention ensures increased operational reliability and prevents unnecessary stress on the electrical load caused by frequent, uncontrolled switching on and off.

[0014] In the switching device according to the invention, the capacitor (also referred to as the start capacitor within the scope of the present invention) is charged in the open state of the switching unit (i.e., the high-resistance state of the switching unit), and the switching unit is closed (i.e., switched to a low-resistance state) when the monitoring voltage exceeds a first limit voltage (also referred to as the reference voltage or threshold voltage). The switching unit can, for example, be designed as a power transistor. In particular, the switching unit can be designed as a FET or a MOSFET. The monitoring voltage can either be measured directly at the capacitor or, alternatively, at a monitoring node where a voltage proportional to the capacitor voltage is established. For example, the monitoring voltage can be measured at the first terminal node, while the second terminal node is grounded.The first threshold voltage is set such that the electrical load is supplied with a sufficiently high voltage as soon as the switching unit closes. After the switching unit closes, the monitoring voltage drops due to the load. If the monitoring voltage falls below a second threshold voltage, the switching unit opens, as this is interpreted as an undersupply to the electrical load. Since the switching unit has already opened previously (due to the voltage falling below the second threshold voltage), it remains open even if the monitoring voltage again exceeds the first threshold voltage. This prevents unwanted, oscillating switching on and off of the switching unit, thereby increasing the service life of the electrical load.

[0015] According to the present invention, different implementation variants can be used, as will be explained in detail below. In particular, the control unit can be implemented as a microcontroller or using logic switching elements. Implementation using a microcontroller allows for high flexibility and easy reprogramming, which enables the specific characteristics of the electrical load to be taken into account. Implementation using logic switching elements allows for a cost-effective embodiment of the switching device according to the invention.

[0016] Preferably, the switching device according to the invention may be provided with a reset function so that the control unit can be reset when a manual reset input is made by the user. If a fault (for example, caused by a short circuit or other temporary overcurrent condition at the load) has been rectified, a reset input can be made so that the control unit is reset and the switching unit can subsequently be closed again when the monitoring voltage exceeds the first limit voltage.

[0017] In the switching device according to the invention, the control unit may include a first comparator designed to detect the monitoring voltage at a monitoring node, compare it with a first threshold voltage (also referred to as the first reference voltage), and output a first signal that depends on the difference between the monitoring voltage and the first reference voltage. In this embodiment of the invention, a first input of the comparator may be connected to the monitoring node, while a second input of the comparator may be connected to a first reference voltage node. The first reference voltage, which can be used as a first threshold for triggering a switching event, is provided at the first reference voltage node.

[0018] The switching device according to the invention can also be provided with a control unit comprising a second comparator designed to detect the monitoring voltage at a monitoring node, compare it with a second threshold voltage, and output a second signal that depends on the difference between the monitoring voltage and the second threshold voltage. A first input of the second comparator can be connected to the monitoring node, while a second input of the comparator is connected to a second reference voltage node. The second reference voltage is provided at the second reference voltage node and can serve as a second threshold for triggering a switching event.

[0019] Preferably, the switching device according to the invention may also include a control unit comprising a first flip-flop designed to receive the first output signal of the first comparator as an input signal and to generate a third output signal (also referred to as the output signal of the first flip-flop) that is dependent on the first output signal of the first comparator. In particular, the first flip-flop may be configured as a D flip-flop, preferably a D flip-flop with set and reset functionality (also referred to as an SRD flip-flop).In particular, it may be provided that the first flip-flop is configured as a first SRD flip-flop with a D(Data) input, a CLK(Clock) input, a CLR(Clear) input and a PRE(Preset) input, wherein the first flip-flop is preferably configured to receive the first output signal of the first comparator at its CLR input, to receive a set / reset signal at its PRE input, and to receive a supply signal at its D input and the CLK input.

[0020] In some preferred embodiments of the switching device according to the invention, the control unit may include a second flip-flop configured to receive the second output signal provided by the second comparator as an input signal and to generate a fourth output signal (also referred to as the output signal of the second flip-flop) that depends on the second output signal provided by the second comparator and the third output signal provided by the first flip-flop. In particular, the second flip-flop may be configured as a D flip-flop, preferably as a set-and-reset D flip-flop (SRD flip-flop).In particular, the second flip-flop may also be configured as a second SRD flip-flop with a D(Data) input, a CLK(Clock) input, a CLR(Clear) input and a PRE(Preset) input, wherein the second flip-flop is preferably configured to receive the output signal of the second comparator (also referred to as the second output signal) at its CLK input, to receive a set / reset signal at its PRE input and at its CLR input, and to receive the third output signal provided by the first flip-flop at its D input.

[0021] Furthermore, the switching device according to the invention may be provided that the control unit has an AND gate (also called an AND gate) which is designed to receive the third output signal and the fourth output signal at its inputs and to generate a fifth output signal (also called the output signal of the AND gate) that depends on the third output signal and the fourth output signal.

[0022] Furthermore, the switching device according to the invention can be configured to have a control unit that opens and closes the switching unit depending on the fifth output signal. For example, the control unit can be configured to close the switching unit when the fifth output signal is "1" and to open the switching unit when the fifth output signal is "0".

[0023] Furthermore, in the switching direction according to the invention, an additional voltage divider can be provided, arranged in parallel with the capacitor, and comprising a first resistor and a second resistor connected in series with the first resistor, wherein the control unit is designed to detect the monitoring voltage at a monitoring node arranged between the first resistor and the second resistor. By using the voltage divider, the voltage value provided at the capacitor can be reduced to a voltage value that can be evaluated by the first comparator and the second comparator.

[0024] In some embodiments of the present invention, an additional microcontroller may be provided which is designed to evaluate the monitoring voltage and generate a control signal for controlling the switching unit, wherein the control signal is designed to - to close the switching unit if an increase in the monitoring voltage above a first limit voltage is detected; - to open the switching unit if a drop in the monitoring voltage below a second limit voltage is detected after the switching unit has previously been closed, - to keep the switching unit open if a renewed increase in the monitoring voltage above the first limit voltage is detected after a previous drop in the monitoring voltage below a second limit voltage has been detected.

[0025] The microcontroller can be easily programmed and thus flexibly adapted to the specific application. Switching events can be taken into account during microcontroller programming, and the threshold values ​​to be considered when controlling the switching unit can be adapted quickly and easily. In some embodiments of the invention, the microcontroller may be part of the control unit or may constitute the control unit itself.

[0026] In some embodiments of the switching device according to the invention, the electrical load may be configured as a sensor. For example, the electrical load may be configured as a vehicle sensor or as a sensor for an aircraft. In some embodiments of the invention, the electrical load may be configured as an angle sensor.

[0027] Furthermore, to solve the problem described above, the present invention proposes a method for providing a DC voltage to an electrical consumer, wherein the method comprises the following steps: - Providing a voltage at a first and a second terminal node, between which a capacitor is placed, using a DC voltage source; - Monitoring a monitoring voltage proportional to the capacitor voltage using a control unit; - Closing a switching unit arranged between the first connection node and a first consumer node or between the second connection node and a second consumer node, if an increase in the monitoring voltage above a first limit voltage is detected; - After the switching unit has been closed: Open the switching unit if a drop in the monitoring voltage below a second limit voltage is detected; - After a drop in the monitoring voltage below the second limit voltage has been detected: Keep the switching unit open if a renewed increase in the monitoring voltage above the first limit voltage is detected.

[0028] The method according to the invention allows a clearly defined and temporally sequential control of the switching unit, which makes it possible to prevent an oscillating switching on and off of the electrical load, whereby fault cases in the system after the consumer has been switched on lead to a permanent disconnection of the consumer from the voltage source.

[0029] The present invention is explained in more detail below with reference to the figures. These figures show... Fig. 1 a switching device with a control unit; Fig. 2. the voltage curve across a starting capacitor and the current curve through the electrical load; Fig. 3 different voltage waveforms for a switching device according to the state of the art in a fault case that leads to an oscillating control voltage; Fig. 4 an embodiment of the switching device according to the invention; Fig. 5 different voltage profiles of the switching device according to the invention for normal operation; Fig. 6. Various voltage waveforms of the switching device according to the invention in the event of an incorrect matching of the voltage source and the electrical load; and Fig. 7 Various voltage waveforms of the switching device according to the invention in the case of correct matching of the voltage source and the electrical load and a subsequent fault case which leads to the separation of source and load by the switching device.

[0030] In the Fig. Figure 1 is a switching device 10 for providing a DC voltage to an electrical load 12, described schematically according to the prior art. The switching device 10 has a DC voltage source 16, the power rating of which is dimensioned according to the rated power of the electrical load 12. The DC voltage source 16 has a source resistance 18. The DC voltage source 16 is connected to a first terminal 20 and a second terminal 22. A capacitor 24, also referred to as a starting capacitor, is provided between the two terminals 20 and 22. The switching device is connected to and disconnected from the electrical load 12 via a switching unit 26. In the case described in the Fig. In the embodiment shown in Figure 1, the switching unit 26 is arranged between the first connection node 20 and a first load node 23a. Alternatively, the switching unit 26 could also be arranged between the second connection node 22 and a second load node 23b. In particular, the switching unit can be designed as a MOSFET. The electrical load 12 is arranged between the first load node 23a and the second load node 23b. The switching unit 26 can be set to an open (= high resistance) and a closed (= low resistance) state. The switching device 10 also has a control unit 28, which is provided for controlling the switching unit 26. For example, in the embodiment shown in the Fig. In the switching device 10 shown, the voltage at the capacitor 24 is monitored, wherein the switching unit 26 is closed by the control unit 28 if the capacitor voltage is higher than a predetermined voltage value, while the switching unit 26 is opened if the capacitor voltage is lower than a predetermined voltage value.

[0031] In the Fig. Figure 2 shows a voltage curve across a starting capacitor and a current curve for an electrical load located in the Fig. The switching device shown in Figure 1 is schematically represented. As can be seen in this figure, the switching unit is initially open during the time interval t0 to t1, allowing the capacitor to charge. At time t1, the capacitor voltage reaches a predetermined voltage value (V). on), which triggers the closing of the switching unit. From time t1, a current thus flows through the electrical load. During the time interval t1 to t2, the starting capacitor discharges due to the power consumed by the electrical load, which can be significantly higher during the start-up phase of the electrical load (t1 to t2) compared to normal operation. After the end of the start-up phase, the electrical load only consumes a nominal current I. L,nom and the current through the electrical consumer adjusts to this nominal current.

[0032] In the Fig. Figure 3 shows various voltage waveforms for a switching device according to the prior art in a fault condition that leads to an oscillating control voltage. As can be seen in this figure, the capacitor voltage fluctuates around a predetermined reference value due to the charging and discharging of the capacitor. This can occur, for example, if the starting capacitor is undersized for the load. The successive exceeding and falling below the reference voltage causes the switch to be alternately turned on and off, thus reducing the safety when operating the load. The voltage shown in the figure is a reference to the voltage waveform of the switching device. Fig. The behavior shown in section 2 is undesirable and it is an object of the present invention to prevent such behavior.

[0033] In the Fig. Figure 4 schematically illustrates an embodiment of the control unit 28 according to the invention. The switching device 10 shown in this figure also has a DC voltage source 16 and a capacitor 24, which is arranged between two connection nodes 20 and 22. A voltage divider 30 is provided in parallel with the capacitor 24, which has a first resistor 32 and a second resistor 34 connected in series with the first resistor 32. A node located between the first resistor 32 and the second resistor 34 is referred to here as the monitoring node 36. A voltage proportional to the capacitor voltage can be tapped and evaluated at the monitoring node 36.In this way, the voltage values, which would otherwise be tapped directly at capacitor 24, can be mapped to a value range that can be evaluated by the logic switching elements (comparators) used in the switching device 10, which are explained below. A monitoring voltage is tapped at monitoring node 36 and fed into an input of a first comparator 38 and into an input of a second comparator 40. The first comparator 38 compares the monitoring voltage tapped at monitoring node 36 with a first limit voltage (= V). ref_onFor example, the first threshold voltage can be 5 V. The first comparator 38 generates a first output signal that depends on the result of the comparison operation. If the monitoring voltage rises to the first threshold voltage, a logic "0" is output at the first comparator. This signal is active-low and is transmitted to a first flip-flop 42. More precisely, the output terminal of the first comparator 38 is connected to the CLR terminal of the first flip-flop 42. If a logic "0" is present at the CLR input of the first flip-flop 42, a logic "1" is output at the first flip-flop 42. The output signal generated by the first flip-flop 42 is transmitted, on the one hand, to an input of an AND gate 46 and, on the other hand, to an input of a second flip-flop 44, namely the D input of the second flip-flop 44.

[0034] Furthermore, in the Fig. In the embodiment of the invention shown in Figure 4, the monitoring voltage detected at the monitoring node 36 is transmitted to an input of a second comparator 40, which is designed to compare the monitoring voltage with a second limiting voltage (= V). ref_offThe second limit voltage is compared. The second limit voltage is lower than the first limit voltage. Depending on the comparison result, the second comparator 40 generates a second output signal, which is fed into the CLK input of the second flip-flop 44. When the switching unit is switched on, the monitoring voltage assumes a value that is higher than the second limit voltage. For example, at a certain time the monitoring voltage may be 4 V, while the second limit voltage is 2 V. In this case, a logic "0" is generated at the output of the second comparator 40. If the second limit voltage is undershot, however, the second comparator 40 generates a logic "1" at its output. This change at the CLK input of the second flip-flop 44 triggers the second flip-flop 44. In this case, the second flip-flop 44 generates an output signal that is transmitted to the second input of the AND gate 46.Depending on the signals applied to the AND gate 46, the AND gate 46 generates an output signal that is used to control the switching unit. The [signals] in the... Fig. The circuit shown in Figure 4 is an example of how a control system for the switching unit can be implemented with just a few logic components, preventing oscillating behavior of the switching unit.

[0035] In the Fig. Figure 5 shows various voltage waveforms for the switching device according to the invention for normal operation, which were determined using simulation software (LTspice). In the case shown here, the voltage source and the starting capacitor are matched to the electrical load such that after switching on (at time t1 at approximately 1 ms), the voltage across the starting capacitor (= V) Cstart ) although it drops slightly due to the load, it never falls below the second limit voltage (= V) after switching on.ref_off ) drops out. The electrical appliance therefore remains switched on.

[0036] In the Fig. Figure 6 shows various voltage waveforms for the switching device according to the invention in the case of an incorrect matching of the voltage source and the electrical load. In the case shown here, the voltage source and the starting capacitor are undersized compared to the electrical load. Consequently, the voltage V Cstart The voltage above the starting capacitor is so heavily loaded by the electrical load at time t1 after switching on that it falls below the second limit voltage V. ref_off drops. The control voltage V ctr_on-off The switching unit, which controls the circuit, is therefore switched from the "ON" state (5 V) to the "OFF" state (0 V) when the second limit voltage is reached. After the electrical load is disconnected from the voltage source by opening the switching unit, the voltage V rises. CstartAlthough the voltage exceeds the first limit again, the switching unit remains open, so the electrical consumer is not switched on again.

[0037] In the Fig. Figure 7 shows various voltage waveforms for the switching device according to the invention in the case of correct matching of the voltage source and the electrical load. However, at a certain point after switching on, an unexpected fault occurs in the electrical load. This fault could, for example, be a short circuit. In this case, the switching unit opens because V Cstart below the second limit voltage V ref_off The voltage drops. Disconnecting the faulty electrical device from the voltage source increases the supply voltage V. Cstart again above the first limit voltage V ref_onThe switch is on, but the switching unit remains open. The electrical device is therefore not switched back on. This prevents the electrical device from being reconnected to the power source in the event of a fault. This increases safety when operating the electrical device. REFERENCE MARK LIST 10 Switching device 12 electrical consumers 16 DC voltage source 18 Source resistance 20 first connection node 22 second connection node 23a first consumer node 23b second consumer node 24 Capacitor 26 switching unit 28 Control unit 30 voltage dividers 32 first resistance 34 second resistor 36 monitoring nodes 38 first comparator 40 second comparator 42 first flip-flop 44 second flip-flop 46 AND gates

Claims

[1] Switching device (10) for providing a DC voltage to an electrical load (12), wherein the switching device (10) comprises: - a DC voltage source (16) connected to a first terminal node (20) and a second terminal node (22); - a capacitor (24) arranged between the first terminal node (20) and the second terminal node (22); - a switching unit (26) arranged between the first connection node (20) and a first consumer node (23a) or between the second connection node (22) and a second consumer node (23b), wherein the first consumer node (23a) and the second consumer node (23b) are designed to be connected to the electrical consumer (12), and wherein the switching unit (26) is designed to provide a consumer current flowing through the consumer (12) when the switching unit (26) is closed and to prevent the consumer current when the switching unit (26) is open; - a control unit (28) for controlling the switching unit (26); - wherein the DC voltage source (16) is designed to charge the capacitor (24) when the switching unit (26) is in the open state; and - the control unit (28) is designed to - to detect and monitor a monitoring voltage that is proportional to the voltage applied to the capacitor; - to close the switching unit (26) if an increase in the monitoring voltage above a first limit voltage is detected; - to open the switching unit (26) if a drop in the monitoring voltage below a second limit voltage is detected after the switching unit (26) has previously been closed; and - to keep the switching unit (26) open if a renewed increase in the monitoring voltage above the first limit voltage is detected after a drop in the monitoring voltage below a second limit voltage has previously been detected. [2] Switching device (10) according to claim 1, characterized by, that the control unit (28) has a first comparator (38) designed to detect the monitoring voltage at a monitoring node (36), compare it with a first limit voltage, and output a first output signal which depends on the difference between the monitoring voltage and the first limit voltage. [3] Switching device (10) according to claim 1 or 2, characterized by , that the control unit (28) has a second comparator (40) designed to detect the monitoring voltage at a monitoring node (36), compare it with a second limit voltage and output a second output signal which depends on the difference between the monitoring voltage and the second limit voltage. [4] Switching device (10) according to one of claims 1 to 3, characterized by, that the control unit (28) has a first flip-flop (42) designed to receive the first output signal of the first comparator (38) as an input signal and to generate a third output signal which depends on the first output signal of the first comparator (38). [5] Switching device (10) according to claim 4, characterized by , that the control unit (28) has a second flip-flop (44) designed to receive the second output signal of the second comparator (40) as an input signal and to generate a fourth output signal which depends on the second output signal provided by the second comparator (40) and on the third output signal provided by the first flip-flop (42). [6] Switching device (10) according to claim 5, characterized by, that the control unit (28) has an AND gate (46) designed to receive the third output signal and the fourth output signal at its inputs and to generate a fifth output signal dependent on the third output signal and the fourth output signal. [7] Switching device (10) according to claim 6, characterized by , that the control unit (28) is designed to open and close the switching unit (26) depending on the fifth output signal. [8] Switching device (10) according to any one of claims 1 to 7, characterized by an additional voltage divider (30) arranged in parallel to the capacitor (24) and comprising a first resistor (32) and a second resistor (34), wherein the control unit (28) is designed to detect the monitoring voltage at a monitoring node (36) arranged between the first resistor (32) and the second resistor (34). [9] Switching device (10) according to any one of claims 1 to 8, characterized by a microcontroller designed to evaluate the monitoring voltage and generate a control signal for controlling the switching unit (26), wherein the control signal is designed to - to close the switching unit (26) if an increase in the monitoring voltage above a first limit voltage is detected; - to open the switching unit (26) if a drop in the monitoring voltage below a second limit voltage is detected after the switching unit (26) has previously been closed, - to keep the switching unit (26) open if a renewed increase in the monitoring voltage above the first limit voltage is detected after a drop in the monitoring voltage below a second limit voltage has previously been detected. [10] Switching device (10) according to any one of claims 1 to 9, characterized by, that the electrical consumer (12) is designed as a sensor. [11] Method for supplying a DC voltage to an electrical load (12) wherein the method comprises the following steps: - Providing a voltage at a first and a second terminal node (20, 22), between which a capacitor (24) is arranged, using a DC voltage source (16); - Monitoring a monitoring voltage proportional to the voltage applied to the capacitor using a control unit (28); - Closing a switching unit (26) arranged between the first connection node (20) and a first consumer node (23a) or between the second connection node (22) and a second consumer node (23b), if an increase in the monitoring voltage above a first limit voltage is detected; - After the switching unit (26) has been closed: Opening the switching unit (26) if a drop in the monitoring voltage below a second limit voltage is detected; - After a drop in the monitoring voltage below the second limit voltage has been detected: Keep the switching unit (26) open if a renewed increase in the monitoring voltage above the first limit voltage is detected.