Circuit for electrical safety
By designing a circuit that includes current delay circuits and switching equipment, the existing circuits are solved with the problem of slow response and high cost, and electrical safety without current isolation is achieved, providing an efficient and economical alternative.
Patent Information
- Application Number
- CN202380048554.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-06-20
- Filing Date
- 2023-04-18
- Publication Date
- 2025-02-07
AI Technical Summary
Existing circuits are slow and costly when preventing electric shock damage, and rely on current isolation, which has problems of difficulty and cost.
A circuit including a current delay circuit and a switching device is designed, and the switching state of the first switching device is controlled by a series connection between the input terminal and the output terminal, and the switching state of the first switching device is controlled by a current delay circuit, and connected to the ground through a second switching device, so as to realize Various operating modes to ensure electrical safety.
This circuit ensures personal electrical safety without current isolation, reduces reaction time and cost, and provides a safe and reliable alternative solution.
Smart Images
Figure CN119404401A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a circuit for electrical safety. The present invention also relates to a system and a corresponding method. Background Art
[0002] Residual current circuit breakers (RCCB) or residual current devices (RCD) are well known in the art. Other terms for devices with corresponding functions are ground fault circuit interrupters, ground fault interrupters, appliance leakage current interrupters and leakage current detection interrupters.
[0003] The purpose of such devices (such as RCCB and RCD) is to quickly interrupt or disconnect the circuit to prevent electric shock to people when the current is unbalanced between the supply conductor and the return conductor. In this regard, such devices generally use galvanic isolation.
[0004] Typically, RCCBs and RCDs are testable and resettable devices. A mechanical input component, such as a test button, creates a small leakage condition, and a reset button reconnects the conductors after the fault condition has cleared. Summary of the invention
[0005] It is an object of embodiments of the present invention to provide a solution that alleviates or solves the disadvantages and problems of conventional solutions.
[0006] It is another object of embodiments of the present invention to provide an alternative solution for galvanic isolation for electrical safety.
[0007] These and other objects are solved by the subject-matter of the independent claims. Further advantageous embodiments of the invention can be found in the dependent claims.
[0008] According to a first aspect of the present invention, the above and other objects are achieved by a circuit for electrical safety, the circuit comprising:
[0009] An input terminal configured to be connected to a power source;
[0010] an output terminal configured to be connected to a load;
[0011] a current delay circuit and a first switching device connected in series between the input terminal and the output terminal; and
[0012] a second switching device connected between the first switching device and ground;
[0013] Wherein the circuit is configured to operate in the following modes:
[0014] a first mode in which the first switching device is in its conducting state, thereby feeding a first current to the load, and the second switching device is in its non-conducting state;
[0015] a second mode, subsequent to the first mode, wherein the first switching device is in its conducting state, thereby feeding a first current to the load, and the second switching device is in its conducting state, thereby feeding a second current to ground; and
[0016] A third mode, subsequent to the second mode, wherein the first switching device is in its non-conducting state and the second switching device is in its conducting state.
[0017] In the present disclosure, the switch device is in its conductive state, which should be understood as current can pass through the switch device when the switch device is in its conductive state. The conductive state can also be expressed as an activated state, an ON state, an ON mode, etc. Therefore, when the switch device is in a non-conductive state, no current can pass through the switch device. The non-conductive state can also be expressed as a non-activated state, an OFF state, an OFF mode, etc.
[0018] The circuit according to the first aspect provides an alternative solution to galvanic isolation for electrical safety. Thus, the circuit solves the problem of ensuring electrical safety of persons without galvanic isolation.
[0019] In an implementation form of the circuit according to the first aspect, the current delay circuit is configured to control switching of the first switching device.
[0020] This embodiment has the advantage that the circuit can be set in a so-called safety mode when the first switching device is controlled by or via the current delay circuit.
[0021] In an implementation form of the circuit according to the first aspect, the current delay circuit is configured to control switching of the first switching device via a control line.
[0022] In an implementation form of the circuit according to the first aspect, the control line comprises an AND logic connected to the current delay circuit and the control device.
[0023] In an implementation form of the circuit according to the first aspect, the current delay circuit is configured to switch the first switching device to its non-conducting state when a current at the current delay circuit is greater than a threshold current.
[0024] The advantage of this implementation is that the circuit can be set in its safe mode according to or depending on the threshold current or the corresponding threshold voltage. Therefore, when designing the circuit, the threshold current can be regarded as a design parameter.
[0025] In an implementation form of the circuit according to the first aspect, the current delay circuit comprises an inductor.
[0026] In an implementation form of the circuit according to the first aspect, the current delay circuit is configured to control the first switching device based on a threshold voltage at a node between the first switching device and the inductor, wherein the threshold voltage corresponds to a threshold current.
[0027] This form of implementation has the advantage that by switching the first switching device to its non-conducting state it is possible to detect a threshold voltage corresponding to a threshold current before the current in the circuit increases to a dangerous level.
[0028] In an implementation form of the circuit according to the first aspect, the current delay circuit includes a first resistor connected in parallel with the inductor, and a second resistor connected in series with the first resistor and the inductor.
[0029] The advantage of this implementation form is that the threshold current can be designed according to the values of the first and second resistors respectively.
[0030] In an implementation form of the circuit according to the first aspect, the first resistance is greater than the second resistance.
[0031] In an implementation form of the circuit according to the first aspect, the current delay circuit is connected between the input terminal and the first switching device or between the first switching device and the output terminal.
[0032] In an implementation form of the circuit according to the first aspect, the second switching device is configured to switch between its conductive state and its non-conductive state based on the control signal.
[0033] In an implementation form of the circuit according to the first aspect, the second switching device comprises at least one controllable electronic switch.
[0034] The electronic / electrical switch may be a transistor, such as a field effect transistor, which means that the switching times are much faster than those of a mechanical switch.
[0035] In an implementation form of the circuit according to the first aspect, the second switching device comprises a mechanical switch connected in parallel with the controllable electronic switch.
[0036] The advantage of this implementation is that additional personal safety is provided by connecting a mechanical switch in parallel with the electronic switch. In addition, the electronic switch can be switched quickly so that no one is injured by electric shock. However, mechanical switches can meet regulatory requirements, such as those set by national laws and government agencies.
[0037] In an implementation form of the circuit according to the first aspect, the mechanical switch is configured to be in its conducting state when no voltage is applied to the mechanical switch.
[0038] The advantage of this embodiment is additional personal safety, since the second switching device is always connected to ground via the mechanical switch as long as no voltage is applied.
[0039] In an implementation form of the circuit according to the first aspect, the first switching device comprises at least one controllable electronic switch.
[0040] In an implementation form of the circuit according to the first aspect, the first switching device, the output terminal and the second switching device are connected to a common node.
[0041] In an implementation form of the circuit according to the first aspect, the ground is an earth ground or a reference ground.
[0042] According to a second aspect of the present invention, the above and other objects are achieved by using a system including a first circuit according to any of the aforementioned implementation forms and at least one second circuit, wherein the first circuit is connected to a neutral output terminal of a power supply and the second circuit is connected to a phase output terminal of the power supply, and wherein the system is configured to operate the first circuit and the second circuit synchronously.
[0043] The neutral output and the phase output can be regarded as floating voltages of the circuit. Therefore, the system according to the second aspect has the advantage that personal safety can be guaranteed even if the circuit is connected to the neutral output terminal and the phase output terminal respectively having floating voltages.
[0044] According to a third aspect of the present invention, the above-mentioned and other objects are achieved by a method for controlling a circuit for electrical safety, the circuit comprising: an input terminal configured to be connected to a power supply; an output terminal configured to be connected to a load; a current delay circuit and a first switching device connected in series between the input terminal and the output terminal; and a second switching device connected between the first switching device and ground; the method comprising:
[0045] operating the circuit in a first mode, wherein the first switching device is in its conducting state, thereby feeding a first current to the load, and the second switching device is in its non-conducting state;
[0046] After the first mode, operating the circuit in a second mode wherein the first switching device is in its conductive state feeding a first current to the load and the second switching device is in its conductive state feeding a second current to ground; and
[0047] After the second mode, the circuit is operated in a third mode in which the first switching device is in its non-conducting state and the second switching device is in its conducting state.
[0048] The method according to the third aspect can be extended to an implementation corresponding to the implementation of the circuit according to the first aspect. Therefore, the implementation of the method comprises the feature(s) of the corresponding implementation of the circuit.
[0049] The advantages of the method according to the third aspect are the same as the advantages of the corresponding implementation form of the circuit according to the first aspect.
[0050] Further applications and advantages of embodiments of the present invention will become apparent from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS
[0051] The accompanying drawings are intended to illustrate and explain different embodiments of the present invention, in which:
[0052] Figure 1 shows the architecture of a circuit according to an embodiment of the present invention;
[0053] Figure 2a-2c shows that the circuit according to an embodiment of the present invention operates in different modes;
[0054] Figure 3 A circuit according to a further embodiment of the present invention is shown;
[0055] Figure 4 and Figure 5 A first switching device connected to and controlled by a current limiting circuit according to a further embodiment of the present invention is shown;
[0056] Figure 6 A current limiting circuit according to a further embodiment of the present invention is shown;
[0057] Figure 7 shows a second switchgear according to a further embodiment of the invention;
[0058] Figure 8 A system according to an embodiment of the present invention is shown;
[0059] Fig. 9 A flow chart of a method according to an embodiment of the present invention is shown. DETAILED DESCRIPTION
[0060] As mentioned above, RCCBs and RCDs according to conventional solutions are based on galvanic isolation of electrical circuits. However, such solutions with galvanic isolation react slowly, which means that the current can rise to levels that are dangerous or lethal to humans. In addition, galvanic isolation can also be expensive to implement, especially for solutions that aim to shorten the reaction time of galvanic isolation. Therefore, an alternative solution to galvanic isolation for personal safety is disclosed and provided herein, which eliminates the need for galvanic isolation.
[0061] Figure 11 shows an architecture of a circuit 100 according to an embodiment of the present invention. The circuit 100 includes an input terminal 102 configured to be connected to a power source 200. The circuit 100 also includes an output terminal 104 configured to be connected to a load 300. The circuit 100 also includes a first switching device 110 connected between the input terminal 102 and the output terminal 104. The circuit 100 also includes a current delay circuit 130 connected in series with the first switching device 110. The current delay circuit 130 and the first switching device 110 are connected between the input terminal 102 and the output terminal 104. The circuit 100 also includes a second switching device 120 connected between the first switching device 110 and a ground 140. In an embodiment of the present invention, the current delay circuit 130, the first switching device 110, the output terminal 104, and the second switching device 120 are connected to a common node CN, as shown in FIG. Figure 1 It can be noted that the current delay circuit 130 can be connected between the input terminal 102 and the first switch device 110 or between the first switch device 110 and the output terminal 104, as long as the current delay circuit 130 is coupled to the first switch device 110 in series.
[0062] The power supply 200 is configured to feed or deliver alternating current (AC) or direct current (DC) to the load 300 depending on the application and the load. Figure 1 Only one load 300 is shown in the figure, but it can be appreciated that more than one load can be connected to the circuit 100 and fed with AC or DC current. The power supply 200 can be any electrical power source that delivers AC or DC power / current. The load 300 can be any power consumer that is configured to consume AC or DC power directly or consume power via a power storage device such as a battery or capacitor.
[0063] In an embodiment of the invention, the ground referred to is the earth ground. This can be understood as an electrical circuit that can be connected to the potential of the earth and therefore has the same potential as the earth. In other embodiments of the invention, the ground instead is a reference ground of an electrical system having a potential different from that of the earth. For example, such a reference ground can be found in a vehicle or in any other design and construction that is conductively isolated from the earth.
[0064] Figure 2a-2c Different operating modes of the circuit 100 according to an embodiment of the invention are shown.
[0065] exist Figure 2a, the circuit 100 operates in its first mode M1, wherein the first switching device 110 is in its conducting state (ON), whereby the first current i1 is fed by the circuit 100 to the load 300, while the second switching device 120 is in a non-conducting state (OFF), which means that in this mode there is no conducting connection to the ground 140. During the first time period T1, the circuit 100 operates in the first mode M1. In the disclosed non-limiting example, the value of the first current i1 fed to the load 300 has been set to 10A for illustration purposes.
[0066] exist Figure 2b , the circuit 100 operates in its second mode M2 after the first mode M1. In the second mode M2, the first switching device 110 is still in its conducting state (ON), whereby the circuit 100 feeds the first current i1 to the load 300, while the second switching device 120 is activated and switched from its non-conducting state (OFF) to its conducting state (ON), whereby the circuit 100 also feeds / provides the second current i2 to the ground 140. The circuit 100 operates in the second mode M2 during a second time period T2 after the first time period T1. During the second time period T2, the first current i1 is still 10A, while the second current i2 rises from 0A to 50A in a short time interval, for example, due to the rise time of the conductivity of the controllable electrical switch. Therefore, when the second switching device 120 is set to be in its conducting state, during the second time period T2, the current from the power supply 200 will increase to the ground 140 in the circuit 100. However, the current delay circuit 130 will delay the increase of current in the circuit 100 so that appropriate actions can be taken in the next operation mode of the circuit 100 .
[0067] exist Figure 2c , the circuit 100 operates in its third mode M3 after the second mode M2. In the third mode M3, the first switching device 110 is completely switched from its conducting state (ON) to its non-conducting state (OFF), while the second switching device 120 is still in its conducting state (ON), and is thus conductively connected to the ground 140. The circuit 100 operates in the third mode M3 during a third time period T3 that follows the second time period T2. With the switch configuration of the third mode M3, no current can flow from the power source 120 to the load 300 because the first switching device 110 is in its non-conducting mode.
[0068] In an embodiment of the present invention, if the current at the current delay circuit 130 reaches Th C If the current threshold is greater than , the third mode M3 can be triggered. Figure 2a-2c In the example shown in , the threshold is set to Th C= 60A, that is, when the sum of i1 and 2 is equal to i1 = 10 and i2 = 50. This will be explained in more detail in the following disclosure.
[0069] Figure 3 A circuit 100 is shown according to an embodiment of the present invention, wherein a first switching device 110 is controlled by or via a current delay circuit 130. The latter case may be understood as the first switching device 110 being configured to be controlled based on a voltage / current at the current delay circuit 130. In this regard, the first switching device 110 may be connected to the current delay circuit 130 via an electrical control line 160 as known in the art. The current delay circuit 130 and / or an associated control device may be configured to control switching of the first switching device 110 according to different aspects of the present invention.
[0070] In an embodiment of the present invention, the current delay circuit 130 is configured to delay the current when the current at the current delay circuit 130 is greater than the threshold current Th C , the first switching device 110 is switched from its conducting state to its non-conducting state. However, the threshold current Th C Can be transformed into the corresponding threshold voltage Th V In this case, the corresponding voltage at the current delay circuit 130 is monitored, and if the monitored voltage exceeds the current threshold Th C The corresponding threshold voltage Th V , then the first switching device 110 is set or switched to its non-conducting state. The voltage in the circuit increases before the current increases, which means that appropriate action can be taken before the current reaches a dangerous level. The relationship between the voltage and the current at the current delay circuit 130 can be derived, for example, from Ohm's law.
[0071] The above configuration also means that if the circuit 100 is set to its safe mode, then each time the first switching device 110 switches back to its conducting state when the second switching device 120 is in the conducting state, the first switching device 110 will switch back to its non-conducting state because there will be current flowing through the circuit 100 to the ground 140. Therefore, the first switching device 110 can be set to a safe mode loop as long as the second switching device 120 is connected to the ground 140. Therefore, as long as the circuit 100 is in the safe mode, that is, the second switching device 120 is connected to the ground 140, the first switching device 110 can be switched on many times without the risk of electric shock and personal injury. The safe mode of the circuit 100 is a very safe alternative to galvanic isolation.
[0072] The above-described safe mode configuration also means that the circuit 100, or more precisely the first switching device 110 and the second switching device 120, can be controlled by a single external control signal applied at the second switching device 120, because the voltage / current at the current delay circuit 130 will always reach the threshold value when the second switching device 120 is in the conductive state connecting the circuit 100 to the ground 140. In other words, the second switching device 120 can be configured to switch between its conductive state and non-conductive state based on the control signal 162 from, for example, the control device 170.
[0073] Figure 4 and Figure 5 A first switching device 110 controlled by or via a current limiting circuit 130 according to an embodiment of the present invention is shown. Figure 4 An example is disclosed in which the first switching device 110 is directly controlled by the current limiting circuit 130, and Figure 5 An example is disclosed when the first switching device 110 is controlled by the current limiting circuit 130 and the control device 170 providing the external control signal 160′. In both non-limiting examples, the current delay circuit 130 includes an inductor L, and the first switching device 110 is illustrated as a transistor having a gate G, a drain D, and a source S. The drain D of the transistor is connected to the input terminal 102, the source S of the transistor is connected to the first node 150 at the current delay circuit 130, and the gate G of the transistor for controlling the transistor is connected to the control line 160 that connects the gate G of the transistor to the current delay circuit 130. The inductor L has a first connection point connected to the first node 150 and a second connection point connected to the common node CN of the circuit 100. In addition, the first switching device 110 (illustrated as a transistor in this case) is controlled based on a threshold voltage at the first node 150 between the first switching device 110 and the inductor L of the current delay circuit 130.
[0074] exist Figure 4 In the embodiment, when the voltage at the first node 150 exceeds the threshold voltage, the first switching device 110 will be set in its OFF mode by applying the voltage at the first node 150 to the gate G pin of the transistor via the inverter 174 and the driver 172. For an N-MOS transistor, when a negative voltage is applied at the gate G pin, the transistor is turned off, so Figure 4 174 in the circuit shown in FIG. 17. However, the transistor may be of P-MOS type and the opposite is also true, i.e. the transistor is turned off when a positive voltage is applied. The driver 172 amplifies the received signal with current amplification, causing the transistor to switch to its OFF mode.
[0075] on the other hand, Figure 5An example is shown when the first switching device 110 is further controlled based on an external control signal 160′ from a control device 170. The control device 170 and the first node 150 are connected to respective inputs of an AND block / logic 180. However, if the transistor is of N-MOS type, then the first node 150 is connected to the AND block 180 via an inverter 174, as explained previously. The output of the AND block 180 is further connected to the gate G pin via a driver 172 that amplifies the current. When the voltage at the first node 150 exceeds the threshold voltage and at the same time an activation control signal is applied by the control device 170, a common control signal will be applied at the gate G of the transistor, which will switch the transistor to its non-conducting state.
[0076] The control device 170 can be a software solution, a hardware solution or a combination of software and hardware. For example, as a software solution, the control component can be implemented in a microcontroller, while as a hardware solution, the control component can be implemented in a physical logic circuit.
[0077] Figure 6 A current limiting circuit 130 according to a further embodiment of the present invention is shown, wherein the current delay circuit 130 includes a first resistor R1 connected in parallel with an inductor L. The current delay circuit 130 also includes a second resistor R2 connected in series with the first resistor R1 and the inductor L. As a result, the voltage will be divided across the first resistor R1 and the second resistor R2 in the current delay circuit 130. By selecting appropriate values of R1 and R2, the threshold voltage and therefore the corresponding threshold current can be designed to be a suitable value, for example, L=3 microhenries, R1=99 milliohms, R2=1 milliohm. In general, the first resistor R1 is larger or much larger than the second resistor R2, because the inductor should be able to delay the rise of the current in the circuit 100, so the current should pass through the inductor rather than through the first resistor R1.
[0078] In addition, Figure 6 Two different voltages may be considered in the design of. The first voltage V1 defines a potential difference between a first node 150 of the current delay circuit 130 and a common node CN. The first voltage V1 may be used to control the first switching device 110 without any voltage amplification, because if the first resistor R1 has a large value, the voltage at the first node 150 will increase to a high value. However, current amplification may be required to switch the transistor to its OFF state, for example, by using a driver 172. On the other hand, the second voltage V2 defines a potential difference between a second node 152 of the current delay circuit 130 located between the inductor L and the second resistor R2 and a common node CN. The second voltage V2 may be used to control the first switching device 110, but with an intermediate voltage amplification.
[0079] Figure 7A second switching device 120 according to an embodiment of the present invention is shown, wherein the second switching device 120 comprises an electronic switch 122, such as a transistor, which is controlled by a control signal 162. In addition, the second switching device 120 may also comprise a mechanical switch 124 connected in parallel with the electronic switch 122. Therefore, if either the electronic switch 122 or the mechanical switch 124 is in its on-state, the circuit 100 will be connected to the ground 140. The electronic switch 122 has a very short response time, while on the other hand, the mechanical switch 124 has a longer response time. This means that if they are activated by the same activation signal or by two different activation signals that are activated at the same time, the mechanical switch 124 will be set to its on-state after the electronic switch 122. Therefore, in an embodiment, the mechanical switch 124 and the electronic switch 122 are activated at the same time, which may also be the case during deactivation.
[0080] To improve personal safety, in an embodiment, the mechanical switch 124 can be configured to not apply voltage to the mechanical switch 124 (ie, Figure 7 This means that if no power / voltage is applied, the second switching device 120 will always be connected to ground 140 via the mechanical switch 124. Therefore, if the first switching device 110 is controlled by the threshold current / voltage at the current delay circuit 130, the circuit 100 in the unpowered state will be set to its safe mode.
[0081] Figure 8 A system according to an embodiment of the present invention is shown. Figure 8 As shown in FIG. 5 , the system 500 includes a first circuit 100 and at least one second circuit 100′ according to an embodiment of the present invention. The first circuit 100 is connected to the first phase P1 output terminal 210 of the power supply 200, and the second circuit 100′ is connected to the second phase P2 output terminal 220 of the power supply 200. Note that the first circuit 100 and the second circuit 100′ are connected to a common ground 140.
[0082] Figure 8 The system 500 in the embodiment can be configured to synchronously operate the first circuit 100 and the second circuit 100′, which means that the switching devices of the first circuit 100 and the second circuit 100′ are coordinated and synchronously controlled. Thus, with its advantages, the present solution can also be implemented in a system using a floating ground, where the first phase P1 and the second phase P2 are floating and can vary.
[0083] Fig. 9A flow chart of a method according to an embodiment of the present invention is shown. The method disclosed herein is for controlling a circuit 100 as previously described. The method 400 comprises operating 410 the circuit 100 in a first mode M1, wherein the first switching device 110 is in its conducting state, whereby the circuit 100 feeds a first current i1 to the load 300, and the second switching device 120 is in its non-conducting state. The method 400 further comprises operating 420 the circuit 100 in a second mode M2 after the first mode M1, wherein the first switching device 110 is in its conducting state, whereby the circuit 100 feeds the first current i1 to the load 300, and the second switching device 120 is in its conducting state, whereby the circuit 100 feeds a second current i2 to the ground 140. The method 400 further comprises operating 430 the circuit 100 in a third mode M3 after the second mode M2, wherein the first switching device 110 is in its non-conducting state, and the second switching device 120 is in its conducting state.
[0084] Finally, it should be understood that the present invention is not limited to the embodiments described above, but also relates to and combines all embodiments within the scope of the attached independent claims.
Claims
1. A circuit (100) for electrical safety, the circuit (100) comprising: An input terminal (102) configured to be connected to a power source (200); An output terminal (104) configured to be connected to a load (300); a current delay circuit (130) and a first switching device (110) connected in series between the input terminal (102) and the output terminal (104); and a second switching device (120) connected between the first switching device (110) and ground (140); The circuit (100) is configured to operate in the following modes: a first mode (M1) in which the first switching device (110) is in its conducting state, thereby feeding a first current (i1) to the load (300), and the second switching device (120) is in its non-conducting state; a second mode (M2), subsequent to the first mode (M1), wherein the first switching device (110) is in its conducting state, thereby feeding a first current (i1) to the load (300), and the second switching device (120) is in its conducting state, thereby feeding a second current (i2) to the ground (140); and A third mode (M3), subsequent to the second mode (M2), wherein the first switching device (110) is in its non-conducting state and the second switching device (120) is in its conducting state.
2. The circuit (100) of claim 1, wherein the current delay circuit (130) is configured to control switching of the first switching device (110).
3. The circuit (100) according to claim 1 or 2, wherein the current delay circuit (130) is configured to control switching of the first switching device (110) via a control line (160).
4. The circuit (100) of claim 3, wherein the control line (160) includes AND logic (180) connected to the current delay circuit (130) and a control device (170).
5. The circuit (100) of any one of claims 2 to 4, wherein the current delay circuit (130) is configured to switch the first switching device (110) to its non-conducting state when the current at the current delay circuit (130) is greater than a threshold current.
6. The circuit (100) of any one of the preceding claims, wherein the current delay circuit (130) comprises an inductor (L).
7. The circuit (100) of claim 6, wherein the current delay circuit (130) is configured to control the first switching device (110) based on a threshold voltage at a node (150) between the first switching device (110) and the inductor (L), wherein the threshold voltage corresponds to the threshold current.
8. The circuit (100) according to claim 6 or 7, wherein the current delay circuit (130) includes a first resistor (R1) connected in parallel with the inductor (L), and a second resistor (R2) connected in series with the first resistor (R1) and the inductor (L).
9. The circuit (100) of claim 8, wherein the first resistance (R1) is greater than the second resistance (R2).
10. The circuit (100) according to any of the preceding claims, wherein the current delay circuit (130) is connected between the input terminal (102) and the first switching device (110) or between the first switching device (110) and the output terminal (104).
11. The circuit (100) of any one of the preceding claims, wherein the second switching device (120) is configured to switch between its conducting state and its non-conducting state based on a control signal (162).
12. The circuit (100) according to any of the preceding claims, wherein the second switching device (120) comprises at least one controllable electronic switch (122).
13. The circuit (100) of claim 12, wherein the second switching device (120) comprises a mechanical switch (124) connected in parallel with the controllable electronic switch (122).
14. The circuit (100) of claim 13, wherein the mechanical switch (124) is configured to be in its conductive state when no voltage is applied to the mechanical switch (124).
15. The circuit (100) according to any of the preceding claims, wherein the first switching device (110) comprises at least one controllable electronic switch (112).
16. The circuit (100) according to any one of the preceding claims, wherein the first switching device (110), the output terminal (104) and the second switching device (120) are connected to a common node (CN).
17. The circuit (100) of any one of the preceding claims, wherein the ground (140) is earth ground or a reference ground.
18. A system (500) comprising a first circuit (100) and a second circuit (100′) according to any one of the preceding claims, wherein the first circuit (100) is connected to a neutral output terminal (210) of a power supply (200) and the second circuit (100′) is connected to a phase output terminal (220) of the power supply (200), and wherein the system (500) is configured to operate the first circuit (100) and the second circuit (100′) synchronously.
19. A method (400) of controlling a circuit (100) for electrical safety, the circuit (100) comprising: An input terminal (102) configured to be connected to a power source (200); An output terminal (104) configured to be connected to a load (300); a current delay circuit (130) and a first switch device (110) connected in series between the input terminal (102) and the output terminal (104); and a second switch device (120) connected between the first switch device (110) and ground (140); the method (400) comprising: operating (410) the circuit (100) in a first mode (M1) wherein the first switching device (110) is in its conducting state, thereby feeding a first current (i1) to the load (300), and the second switching device (120) is in its non-conducting state; operating (420) the circuit (100) in a second mode (M2) after the first mode (M1), wherein the first switching device (110) is in its conducting state, thereby feeding a first current (i1) to the load (300), and the second switching device (120) is in its conducting state, thereby feeding a second current (i2) to the ground (140); and After the second mode (M2), the circuit (100) is operated (430) in a third mode (M3) in which the first switching device (110) is in its non-conducting state and the second switching device (120) is in its conducting state.