AU2014295534B2

AU2014295534B2 - Electronic switch and control method for electronic switch

Info

Publication number: AU2014295534B2
Application number: AU2014295534A
Authority: AU
Inventors: Kwok Hung Lau; Chunbo Ouyang; Yu Tian
Original assignee: Schneider Electric Australia Pty Ltd
Current assignee: Schneider Electric Australia Pty Ltd
Priority date: 2013-07-26
Filing date: 2014-07-24
Publication date: 2017-09-07
Anticipated expiration: 2034-07-24
Also published as: WO2015010637A1; CN104348456A; AU2014295534A1; CN104348456B; MY174719A; NZ716670A

Abstract

An electronic switch and a control method for an electronic switch, which are applied to the technical field of electronic devices. In an electronic switch, in the time period of controlling a main switch from power-off to power-on by a control unit, the change in a current on a load is mainly caused by the change in the voltages at the two ends of the main switch in this time period, while an electricity taking circuit continues to be charged in this time period, so that the voltages at the two ends of the main switch will not become zero. Thus, in this time period, the voltages at the two ends of the main switch will not suddenly change from zero but will suddenly change from a charging voltage of the electricity taking circuit, so that the rate of change is smaller, and the change in the current on the load is also smaller, thereby reducing the electromagnetic interference due to larger rate of change in the current of the load, that is, reducing the electromagnetic interference of the electronic switch.

Description

ELECTRONIC SWITCH AND CONTROL METHOD FOR 2014295534 17 Aug 2017

ELECTRONIC SWITCH

TECHNICAL FIELD

[0001] The present invention relates to the technical field of electronic devices, and in particular to an electronic switch and a method for controlling an electronic switch.

BACKGROUND OF THE INVENTION

[0002] A two-wire electronic switch includes a main switch and a power-taking circuit; the main switch is connected between a live wire and a load, and the power-taking circuit provides power for the operations of the main switch and the like. The power-taking circuit takes power mainly in two manners: series, and parallel.

[0003] Under parallel power-taking, the power-taking circuit and the main switch are connected in parallel, between a live wire and a load; the main switch is periodically turned on and off, which results in a discontinuous load current, and causes electromagnetic interference.

SUMMARY OF THE INVENTION

[0004] The embodiments of the present invention provide an electronic switch and a method for controlling an electronic switch, which can reduce electromagnetic interference in the electronic switch.

[0005] An embodiment of the present invention provides an electronic switch, comprising a power-taking circuit, a control unit and a main switch, wherein [0006] the main switch and the power-taking circuit are connected in parallel between a live wire and a load; [0007] the control unit comprises a first control terminal, a second control terminal and a feedback terminal; the first control terminal is connected to an on/off control terminal of the main switch; the second control terminal is connected to a control terminal for connecting/disconnecting the power-taking circuit to/from a main loop; the feedback terminal is connected to an output terminal of the power-taking circuit; 1 [0008] the control unit is configured to, when an input voltage is at zero-crossing, control the main switch to be turned off through the first control terminal and control the power-taking circuit to be connected to the main loop through the second control terminal such that the power-taking circuit is charged; and when the feedback terminal receives a signal outputted from the power-taking circuit indicating that a charged voltage of the power-taking circuit reaches a predetermined value, control the main switch to be turned on through the first control terminal. 2014295534 17 Aug 2017 [0008a] wherein when the control unit controls the main switch to be switched from off to on, a voltage across the main switch increases from the charged voltage of the power-taking circuit.

[0009] An embodiment of the present invention provides a method for controlling an electronic switch , the electronic switch to which the method is applicable comprises a power-taking circuit, a control unit and a main switch, wherein the main switch and the power-taking circuit are connected in parallel between a live wire and a load; the control unit comprises a first control terminal, a second control terminal and a feedback terminal; the first control terminal is connected to an on/off control terminal of the main switch; the second control terminal is connected to a control terminal for connecting/disconnecting the power-taking circuit to/from a main loop; the feedback terminal is connected to an output terminal of the power-taking circuit; [0010] the method comprises: [0011] controlling, by the control unit in the electronic switch, the main switch in the electronic switch to be turned off, and the power-taking circuit in the electronic switch to be charged, when the input voltage of the electronic switch is at zero-crossing; [0012] controlling, by the control unit, the main switch to be turned on, when a charged voltage of the power-taking circuit reaches a predetermined value.

As can be seen, in the electronic switch according to the embodiment of the present invention, in the time period during which the control unit controls the main switch from being off to being on, the change in the current on the load is mainly due to the change in the voltage across the main switch in the same time period. The power-taking circuit continues to be charged in the time period, so that the voltage across the main switch will not become zero. Therefore, in this time period, the voltage across the main switch will not change suddenly from zero, but from the charged voltage of 2 the power-taking circuit, hence involving a smaller rate of change and thus a smaller change in the current on the load. Consequently, electromagnetic interference caused by the large rate of change in the current of the load is reduced, that is, electromagnetic interference of the electronic switch is reduced. 2014295534 17 Aug 2017

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For a clear description of the technical solutions of the embodiments of the present invention as well as the prior art, accompanying drawings used in the illustration of the embodiments or the prior art will be briefly introduced below. Clearly, the accompanying drawings below are only some of the embodiments of the invention; those skilled in the art can obtain other drawings based on these drawings without inventive effort.

[0014] FIG. 1 is a schematic structural diagram illustrating an electronic switch according to an embodiment of the present invention; [0015] FIG. 2 is a schematic diagram illustrating the correspondence between the electronic parameters for various elements in the electronic switch and time according to an embodiment of the present invention; [0016] FIG. 3 is a schematic structural diagram illustrating an electronic switch according to another embodiment of the present invention; [0017] FIG. 4 is a flow chart illustrating a method for controlling an electronic switch according to an embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

[001S] The technical solutions in the embodiments of the present invention will be described hereinafter in detail in conjunction with the accompanying drawings of the embodiments of the invention. Clearly, the embodiments described herein are only some, not all of the embodiments of the present invention. Any other embodiment obtained by those skilled in the art based on the embodiments of the present invention without inventive effort shall fall within the scope of protection of the present invention.

[0019] An embodiment of the present invention provides an electronic switch, mostly a two-wire electronic switch, a schematic structural diagram of which is shown as Figure 1. The 3 electronic switch includes: a power-taking circuit 12, a control unit 11 and a main switch 10. The power-taking circuit 12 is a circuit that can store energy, for example, a capacitor; the power-taking circuit 12 may be charged by a main loop. Specifically: 2014295534 17 Aug 2017 [0020] The main switch 10 and the power-taking circuit 12 are connected in parallel between a live wire and a load.

[0021] The control unit 11 comprises a first control terminal a, a second control terminal b and a feedback terminal c; the first control terminal a is connected to an on/off control terminal of the main switch 10; the second control terminal b is connected to a control terminal for connecting/disconnecting the power-taking circuit 12 to/from the main loop; the feedback terminal c is connected to an output terminal of the power-taking circuit 12. The main loop refers to the circuit between the live wire and the load; connecting/disconnecting ... to/from the main loop refers to the power-taking circuit being connected or not connected between the live wire and the load.

[0022] The control unit 11 is configured to, when an input voltage is at zero-crossing, control the main switch 10 to be turned off through the first control terminal and the power-taking circuit 12 to be connected to the main loop through the second control terminal, so that the power-taking circuit 12 can be charged by the input voltage. When the feedback terminal receives a signal outputted from the power-taking circuit 12 indicating that a voltage of the power-taking circuit 12 reaches a predetermined value, which indicates that the voltage charged for the power-taking circuit 12 reaches a certain value enough for providing energy for the normal operations of such devices as the main switch 10, the main switch 10 is controlled to be turned on through the first control terminal. Input voltage being at zero-crossing refers to that as time varies, the value of the input voltage will become greater or smaller than zero in a period of time after it is equal to zero. The predetermined value does not need to be large, as long as it is enough for the normal operations of the devices such as the main switch 10 and the control unit 11.

[0023] As shown in Figure 2, in the electronic switch according to the embodiment, the live wire input terminal provides an input voltage; and Figure 2-a shows the correspondence between the input voltage and time, wherein in a period of time A; after the input voltage crosses zero, the control unit 11 controls the main switch 10 to be turned off through the first control terminal.

[0024] When the input voltage crosses zero, the control unit 11 controls the main switch 10 to be turned off, and controls the power-taking circuit 12 to be connected to the main loop so that 4 the power-taking circuit 12 is charged. When the power-taking circuit 12 is charged to a certain extent, the power-taking circuit 12 outputs a signal to the feedback terminal of the control unit 11, indicating that the voltage of the power-taking circuit 12 reaches a predetermined value. Therefore, the control unit 11 at time T1 controls the main switch 10 to be turned on and maintains the power-taking circuit 12 at a charging state, hence the load current continues. However, when the main switch 10 is turned on, the voltage across the main switch 10 drops to nearly zero, and the power-taking circuit 12 connected in parallel to the main switch 10 stops taking power, hence the current which formerly flows through the power-taking circuit 12 now shifts to the main loop. Figure 2-b shows the correspondence between the voltage across the power-taking circuit 12 and the main switch 10 and time; Figure 2-d shows the correspondence between the current flowing through the main switch 10 and time; Figure 2-e shows the correspondence between the current of the power-taking circuit 12 and time. Hence, in a period of time A after time Tl, i.e., during the time when the main switch 10 is on, the power-taking circuit 12 continues to be charged until V’, at which time the main switch 10 is turned on, and the voltage across and the current of the power-taking circuit 12 decrease to zero, and then the current of the main switch 10 increases to Γ. 2014295534 17 Aug 2017 [0025] In the above process, a correspondence relation between the load current and time is shown in Figure 2-c. During the time in which the main switch 10 is switched from off to on, the change in the current on the load, i.e. AT, is mainly caused by the change in the voltage across the main switch 10 in this time period. The power-taking circuit 12 continues to be charged in the time period, so that the voltage across the main switch 10 will not become zero. Therefore, in this time period, the voltage across the main switch 10 will not change suddenly from zero, but from the charged voltage of the power-taking circuit 12, hence involving a smaller rate of change and thus a smaller change in the current on the load. Thereby, electromagnetic interference caused by the large rate of change in the current of the load is reduced, that is, electromagnetic interference of the electronic switch is reduced.

[0026] A more specific example is given below for illustrating the electronic switch of the embodiment. As shown in Figure 3, the electronic switch of the embodiment of the present invention mainly includes two parts: the first part being operating modules of the electronic switch in an ON state, including a zero-crossing detection circuit, a linear power supply, and a main loop including a main switch; the second part being operating modules of the electronic switch in an 5 OFF state. The on and off of the electronic switch may be controlled manually through a peripheral device. Specifically: 2014295534 17 Aug 2017 [0027] (1) When the electronic switch is in an ON state, it sends an ON signal to a port 1 of a control unit U3. The control unit U3 may be a digital chip such as a microcontroller unit (MCU) or the like.

[0028] In this case, the mains supply (i.e., input voltage) is converted by a bridge rectifier D1 into a unidirectional voltage V+. A comparator A1 and resistors R1 and R2 form a voltage zero-crossing detection circuit; the voltage zero-crossing detection circuit is connected to two output terminals of the bridge rectifier, mainly for sending a voltage zero-crossing signal to the control unit U3 when the rectified, unidirectional voltage is detected to be at zero-crossing.

[0029] Once a port 4 of the control unit U3 receives a voltage zero-crossing signal, a high level is outputted via a port 3 to turn on a MOSFET S2, hence connecting the power-taking circuit to the main loop; therefore, the mains supply charges the capacitor Cl in the power-taking circuit via S2, and provides power for the control unit U3 through a voltage regulating circuit U2. The control unit U3 also outputs a tum-off-main-switch signal via a port 6, for controlling the main switch SI to be turned off.

[0030] A comparator A2, a power supply Vcc and a reference voltage Vref form a voltage detection circuit. The voltage detection circuit is connected to the power-taking circuit, mainly for generating and sending a voltage protection signal to a port 2, i.e., the feedback terminal, of the control unit U3, when the charged voltage of the power-taking circuit, i.e., the voltage on the capacitor Cl, is detected to be reaching a predetermined value (for example, 6V). The control unit U3 generates a high-level signal, i.e., a tum-on-main-switch signal (turn on triac signal), and drives U1 via the port 6 to turn the main switch S1 on.

[0031] After the main switch S1 is turned on, the voltage across the linear power supply consisting of the main switch S1, the capacitor C1 and the voltage regulating circuit U2 drops to nearly zero, the bridge rectifier D1 is cut off, charging of the capacitor Cl in the power-taking circuit is stopped and the capacitor Cl enters a discharging state, and the voltage decreases. When another voltage zero-crossing point is reached after half cycle, the main switch SI is turned off, and the capacitor C1 is recharged. 6 [0032] (2) When the electronic switch is in an OFF state, it sends an OFF signal to the port 1 of the control unit U3. 2014295534 17 Aug 2017 [0033] In this case, the control unit U3 also works normally, mainly including operating modules in an OFF state, i.e., a voltage-source providing circuit whose output terminal is connected to a power-supply terminal of the control unit U3, so that a voltage source is provided for the operation of the control unit U3 when the electronic switch is in an OFF state. Specifically, when the electronic switch is in an OFF state, the main switch S1 is turned off, the mains supply (input voltage) is applied across the main switch SI, i.e., between the live wire and the load wire, and provides a stable voltage source for the control unit U3 through a bridge rectifier D2, a power transformer Tl, a voltage feedback i.e. an optocoupler feedback, a voltage biasing circuit and a voltage clamp.

[0034] Further, an embodiment of the present invention provides a method for controlling an electronic switch, mainly applicable with the electronic switches described in the embodiments above. The method of the present embodiment is a method executed by the control unit in the electronic switch. As shown in the flow chart of Figure 4, the method includes: [0035] Step 101: when the input voltage of the electronic switch is at zero-crossing, a control unit in the electronic switch controls the main switch in the electronic switch to be turned off, and controls the power-taking circuit in the electronic switch to be charged. Since the power-taking circuit is an energy storage circuit such as a capacitor, the power-taking circuit may be controlled to be connected to the main loop (a loop including the main switch) so that the input voltage in the main loop can charge the power-taking circuit.

[0036] Step 102: it is determined whether the charged voltage of the power-taking circuit reaches a predetermined value, and if so, step 103 is performed; if not, the process is ended.

[0037] Step 103: the control unit directly controls the main switch to be turned on, rather than controlling the power-taking circuit to be disconnected from the main loop; and after the main switch is turned on, the voltage across the main switch decreases to nearly zero, and the charging of the power-taking circuit is stopped. Therefore, the current of the load will not change with a large rate of change, and electromagnetic interference of the electronic switch is thereby reduced. 7 [0038] It is noted that the method including step 101 to step 103 is a control method for an electronic switch which is in an ON state; when the electronic switch is in an OFF state, a circuit other than the control unit, i.e., a voltage-source providing circuit will be needed for providing a voltage source for the operation of the control unit, so that the control unit can provide energy for the normal operations of the other devices in the electronic switch. 2014295534 17 Aug 2017 [0039] Those skilled in the art shall understand that all or some of the steps in the methods according to the embodiments above can be implemented with a program instructing relevant hardware; the program may be stored in a computer-readable storage medium, and the storage medium may include a ROM (read-only memory), a RAM (random-access memory), a magnetic disk, an optical disc, or the like.

[0040] An electronic switch and a method for controlling an electronic switch according to the embodiments of the present invention are described in detail above. Specific examples are used herein to explain the principles and embodiments of the present invention, and the description of the embodiments is only for facilitating understanding of the methods of the present invention and the core idea thereof. Those skilled in the art can make variations in specific embodiments and applications according to the ideas of the present invention. In conclusion, the content of the description shall not be construed as a limitation to the present invention.

[0041] It will be understood that the term “comprise” and any of its derivatives (eg comprises, comprising) as used in this specification is to be taken to be inclusive of features to which it refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.

[0042] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge. 8

Claims

1. An electronic switch, characterized in comprising: a power-taking circuit, a control unit and a main switch, wherein the main switch and the power-taking circuit are connected in parallel between a live wire and a load; the control unit comprises a first control terminal, a second control terminal and a feedback terminal; the first control terminal is connected to an on/off control terminal of the main switch; the second control terminal is connected to a control terminal for connecting/disconnecting the power-taking circuit to/from a main loop; the feedback terminal is connected to an output terminal of the power-taking circuit; the control unit is configured to, when an input voltage is at zero-crossing, control the main switch to be turned off through the first control terminal and control the power-taking circuit to be connected to the main loop through the second control terminal such that the power-taking circuit is charged; and when the feedback terminal receives a signal outputted from the power-taking circuit indicating that a charged voltage of the power-taking circuit reaches a predetermined value, control the main switch to be turned on through the first control terminal; wherein when the control unit controls the main switch to be switched from off to on, a voltage across the main switch increases from the charged voltage of the power-taking circuit.

2. The electronic switch according to claim 1, characterized in further comprising: a bridge rectifier, a zero-crossing detection circuit and a voltage detection circuit, wherein the bridge rectifier is connected across the main switch, for converting an input voltage into a unidirectional voltage; the zero-crossing detection circuit is connected to two output terminals of the bridge rectifier, for sending a voltage zero-crossing signal to the control unit when the unidirectional voltage is detected to be at zero-crossing; the voltage detection circuit is connected to the power-taking circuit, for sending a voltage protection signal to the feedback terminal of the control unit when a charged voltage of the power-taking circuit is detected to be a predetermined value.

3. The electronic switch according to claim 1 or 2, characterized in that: the control unit further comprises a power-supply terminal; the electronic switch further comprises a voltage-source providing circuit; the voltage-source providing circuit has an output terminal connected to the power-supply terminal, for providing a voltage source for the operation of the control unit when the electronic switch is in an off state.

4. A method for controlling an electronic switch, characterized in that it is applied to the electronic switch according to any one of claims 1 to 3, the method comprises: controlling, by the control unit in the electronic switch, the main switch in the electronic switch to be turned off and the power-taking circuit in the electronic switch to be charged, when the input voltage of the electronic switch is at zero-crossing; controlling, by the control unit, the main switch to be turned on, when a charged voltage of the power-taking circuit reaches a predetermined value.

5. The method according to claim 4, characterized in that the method further comprises: providing, by the voltage-source providing circuit in the electronic switch, a voltage source for the operation of the control unit when the electronic switch is in an off state.