DC switch

Abstract

To provide a DC switch which autonomously operates in a simple configuration and is physically and electrically unconnected with a power source side after a line is cut.SOLUTION: A DC switch comprises: a first semiconductor switch element including a current path, which is inserted into and connected to a line, and a control end; a load voltage monitor section which includes a capacitor and a constant voltage element connected in series between lines and in which the capacitor is maintained in a charged state and both end voltages of the constant voltage element are maintained at a predetermined constant voltage when a mechanical contact is in a closed state; and a second semiconductor switch element of which the control end is driven by the predetermined constant voltage of the constant voltage element and the current path is maintained in a conducted state. The first semiconductor switch element is maintained in the conducted state by driving the control end by maintaining the second semiconductor switch element in the conducted state. When the mechanical contact is opened and both the end voltages of the constant voltage element are reduced, the second semiconductor switch element is non-conducted, such that the first semiconductor switch element is non-conducted.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a DC switch for opening and closing a line between a DC power supply and a load.

Background Art

[0002] Opening and closing of a DC line by a switch having mechanical contacts is accompanied by an arc, which leads to damage to the switch. Therefore, in order to prevent arcs, methods such as using a magnet, increasing the contact interval, and accelerating the contact opening time are used (Patent Documents 1 to 3, etc.).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the prior art, there has been a problem that a mechanical switch incorporating an arc prevention function has a complicated mechanism. Further, even when a semiconductor switch element interlocked with a mechanical switch is used, those that require an electronic control unit have a complicated circuit and high cost. Further, when a circuit including a semiconductor switch element is physically and electrically connected to the power supply side, there has been a problem of lack of safety.

[0005] In view of the above, an object of the present invention is to provide a DC switch that interlocks with a general-purpose mechanical contact, operates autonomously with a simple configuration, and becomes physically and electrically disconnected from the power supply side after the line is cut.

Means for Solving the Problems

[0006] To achieve the above object, the present invention provides the following configuration. 1) A DC switch that interlocks with a mechanical contact that opens and closes a line connecting a DC power supply and a load, a first semiconductor switch element including a first current path inserted and connected to the line and a first control terminal driven to control conduction and non-conduction of the first current path; a load voltage monitoring unit including a capacitor and a constant voltage element connected in series between a pair of the lines on the load side of the mechanical contact, the capacitor being maintained in a charged state by the DC power supply and the voltage across the constant voltage element being maintained at a predetermined constant voltage when the mechanical contact is in a closed state; a second semiconductor switch element including a second current path and a second control terminal driven to control conduction and non-conduction of the second current path, the second control terminal being driven by the predetermined constant voltage of the constant voltage element to maintain the second current path in a conductive state; the first semiconductor switch element has its first control terminal driven to maintain the first current path in a conductive state by the second current path of the second semiconductor switch element being maintained in a conductive state, when the mechanical contact is opened and the voltage across the constant voltage element drops, the second current path of the second semiconductor switch element becomes non-conductive, whereby the first current path of the first semiconductor switch element becomes non-conductive. 2) In the above aspect, the predetermined constant voltage of the constant voltage element is set to a magnitude that does not generate an arc between the mechanical contacts. 3) In the above aspect, the first semiconductor switch element and the first control terminal are a MOS type FET and its gate, and further includes a third semiconductor switch element including a third current path and a third control terminal driven to control conduction and non-conduction of the third current path to quickly turn off the MOS type FET when the mechanical contact is opened. The third control terminal is driven when the second current path of the second semiconductor switching element becomes non-conductive, and a current for discharging the gate flows through the third current path. 4) In the above aspect, further provided is an element for preventing reverse flow of current from the load side, which is inserted and connected to the line on the load side of the load voltage monitoring unit. 5) A further aspect of the present invention is a DC switchgear including a switch having mechanical contacts and the above-described DC switch interlocked with the mechanical contacts.

Effects of the Invention

[0007] According to the present invention, there is provided a DC switch interlocked with a general-purpose mechanical contact, which has a simple configuration, operates autonomously, and becomes physically and electrically disconnected from the power supply side after the line is cut off.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0009] Hereinafter, an embodiment of the DC switch according to the present invention will be described with reference to the drawings as examples.

[0010] (1) Configuration of the DC switch FIG. 1 is a circuit diagram schematically showing an embodiment of the DC switch of the present invention. The DC switch 1 is provided on a pair of lines 4 and 5 connecting a DC power supply 2 and a load 3. The positive terminal of the DC power supply 2 and the positive terminal of the load 3 are connected by a first line 4, and the negative terminal of the DC power supply 2 and the negative terminal of the load 3 are connected by a second line 5.

[0011] Here, as an example, a mechanical contact S for opening and closing the line is inserted and connected on the line 4. Thereby, the line 4 is separated into a power supply side line 4a and a load side line 4b.

[0012] The DC switch 1 has power supply side terminals 6 and 7 connected to both ends of the DC power supply 2, and load side terminals 8 and 9 connected to both ends of the load 3. The line between the terminal 6 and the terminal 8 on the positive electrode side of the DC switch 1 is a line common to the first line 4 (4b). The line between the terminal 7 and the terminal 9 on the negative electrode side of the DC switch 1 is a line common to the second line 5. The DC switch 1 is installed on the load side with respect to the mechanical contact S. Thereby, since the DC switch 1 is physically and electrically separated from the DC power supply 2 particularly in the open state of the mechanical contact S, safety can be ensured.

[0013] In the example of FIG. 1, a semiconductor switch element Q1 is inserted and connected on the second line 5. The semiconductor switch element Q1 includes a current path inserted and connected to the line 5 and a control terminal driven to control conduction and non-conduction of the current path. As an example, the semiconductor switch element Q1 is an n-channel MOS type FET (field effect transistor), the source is connected to the negative terminal of the DC power supply 2, and the drain is connected to the negative terminal of the load 3. The drain-source interval serves as a current path for the load current. Conduction and non-conduction of the drain-source interval current path are controlled by the gate-source voltage.

[0014] The DC switch 1 further includes a load voltage monitoring unit 11. The load voltage monitoring unit 11 is a circuit that operates autonomously due to a decrease in the load voltage when the mechanical contact S opens. The load voltage monitoring unit 11 is provided between the first line 4 and the second line 5 on the load side of the mechanical contact S, and is provided in parallel with the load 3. The load voltage monitoring unit 11 has a capacitor C and a constant voltage element Z1 connected in series between the line 4 and the line 5.

[0015] When a voltage equal to or higher than a predetermined constant voltage is applied to the constant voltage element Z1, the constant voltage element Z1 maintains the voltage across its two ends at the predetermined constant voltage. As an example, the constant voltage element Z1 is a Zener diode, with its anode connected to one end of the resistance element R1 and its cathode connected to the line 4. The predetermined constant voltage is the Zener voltage. The resistance element R1 connected in series between the capacitor C and the constant voltage element Z1 is for current limiting.

[0016] Furthermore, a resistance element R2 is connected in parallel with the capacitor C. The resistance element R2 serves as a discharge current path for the capacitor C when no DC voltage is applied between the lines 4 and 5. Therefore, the resistance element R2 is set to a sufficiently large value so that the time constant becomes large.

[0017] The DC switch 1 further has a semiconductor switch element Q2 including a current path and a control terminal driven to control the conduction and non - conduction of the current path. Here, as an example, the semiconductor switch element Q2 is a pnp - type bipolar transistor. The base is connected to the low - potential end of the constant voltage element Z1, that is, the anode of the Zener diode. The emitter is connected to the line 4 via a resistance element R3, and the collector is connected to the control terminal (gate) of the semiconductor switch element Q1 via a diode D which is a rectifying element. The diode D has its anode connected to the collector of the semiconductor switch element Q2 and its cathode connected to the gate of the semiconductor switch element Q1.

[0018] To protect the gate-source of the semiconductor switch element Q1 from overvoltage, a constant voltage element Z2, which is a Zener diode, is connected between one end (collector) of the semiconductor switch element Q2 and the line 5.

[0019] The DC switch 1 further has a breaking acceleration unit 12. The breaking acceleration unit 12 is a circuit that quickly shifts the semiconductor switch element Q1, which is a MOS type FET, from the conducting state to the non-conducting state. The gate of the MOS type FET has a predetermined capacitance component, and the gate is charged by the gate current flowing when changing from the non-conducting state to the conducting state. When changing from the conducting state to the non-conducting state, the gate current flows in the reverse direction and the gate is discharged. The faster the current for discharging the gate flows, the earlier the current path between the drain and source is cut off.

[0020] The breaking acceleration unit 12 has a semiconductor switch element Q3 including a current path and a control terminal driven to control the conduction and non-conduction of the current path. Here, as an example, the semiconductor switch element Q3 is a pnp bipolar transistor. The emitter is connected to the control terminal (gate) of the semiconductor switch element Q3, the collector is connected to the line 5, and the base is connected to one end (collector) of the semiconductor switch element Q2. A resistance element R4 is connected between the base and the line 5.

[0021] The mechanical contact S is, for example, a contact such as a toggle switch, rocker switch, push button switch, rotary switch, slide switch, key lock switch, tactile switch, or a relay contact.

[0022] (2) Operation of the DC switch With reference to FIGS. 2 to 4, the operation of the DC switch 1 shown in FIG. 1 will be described. FIG. 2 schematically shows the state of the DC switch 1 when the mechanical contact S is in the closed state. FIG. 3 schematically shows the state of the DC switch 1 immediately after the mechanical contact S is opened. FIG. 4 shows the waveforms of the voltage or current of the main part of the DC switch 1 measured from the closed state (on) of FIG. 2 through the state of starting to open in FIG. 3 until the mechanical contact S is completely in the open state (off).

[0023] As shown in Fig. 2, when the mechanical contact S is in the closed state, the DC power supply 2 and the load 3 are connected. The contact voltage Vs between the contacts of the mechanical contact S is zero (see the first half of Fig. 4(c)). The voltage Vo across both ends of the load 3 is the same as the power supply voltage Vi of the DC power supply 2 (see the first half of Fig. 4(a)). Also, due to the power supply voltage Vi applied between line 4 and line 5, a current I1 flows through the circuit including the constant voltage element Z1, the resistance element R1, and the resistance element R2. The capacitor C is fully charged by the initial current (indicated by the dotted line) flowing when the mechanical contact S closes from the open state, and is maintained in the charged state when the mechanical contact S is in the closed state, and its voltage Vc across both ends is maintained constant.

[0024] A predetermined constant voltage Vz of the constant voltage element Z1 (the Zener voltage in the case of a Zener diode) is set to a voltage at which no arc occurs between the contacts of the mechanical contact S. Without limitation, the predetermined constant voltage Vz is less than 20V, preferably less than 10V. Also, if the constant voltage Vz is too small, there is a possibility of malfunction when the power supply voltage Vi fluctuates, so the constant voltage Vz is preferably at least about 5V. The power supply voltage Vi is a value sufficiently larger than this predetermined constant voltage Vz. As an example, when the power supply voltage Vi is 360V, the predetermined constant voltage Vz of the constant voltage element Z1 is set to 5V. When the mechanical contact S is in the closed state, the voltage across both ends of the constant voltage element Z1 is maintained at the predetermined constant voltage Vz.

[0025] In this way, in the load voltage monitoring unit, when the mechanical contact S is in the closed state, the capacitor C is maintained in the charged state and the voltage across both ends of the constant voltage element Z1 is maintained at the predetermined constant voltage Vz by the DC voltage Vi applied between lines 4 and 5.

[0026] Furthermore, when the voltage across the constant-voltage element Z1 is maintained at the constant voltage Vz, the base potential of the pnp transistor, which is the semiconductor switch element Q2, drops below the emitter potential, causing a base current I2 to flow through the resistor element R3. As a result, the transistor conducts and a collector current I3 flows. This means that the control terminal of the semiconductor switch element Q2 is driven by the constant voltage Vz of the constant-voltage element Z1, maintaining the current path of the semiconductor switch element Q2 in a conductive state.

[0027] Furthermore, the current I3 flows through the diode D to the control terminal of the semiconductor switch element Q1. When the gate of the n-channel MOSFET, which is the semiconductor switch element Q1, is charged by the current I3, the gate-source voltage Vg rises, causing the drain-source current path to become conductive and a load current I4 to flow (see the first half of Fig. 4(b)). This means that when the current path of the semiconductor switch element Q2 is maintained in a conductive state, the control terminal of the semiconductor switch element Q1 is driven to maintain the current path of the semiconductor switch element Q1 in a conductive state as well.

[0028] As shown in Fig. 3, when the mechanical contact S starts to open, the voltage Vo across the load 3 immediately begins to drop. When the voltage Vo across the load 3 drops by an amount equal to the magnitude of the constant voltage Vz of the constant-voltage element Z1 from the power supply voltage Vi, the voltage across the constant-voltage element Z1 becomes zero. Furthermore, the voltage Vo across the load 3 continues to drop until it reaches zero (see the middle part of Fig. 4(a)).

[0029] When the voltage across the constant-voltage element Z1 becomes zero, the base current of the semiconductor switch element Q2 stops flowing and the semiconductor switch element Q2 becomes non-conductive. As a result, the current to the gate of the semiconductor switch element Q1 via the diode D also disappears, the gate-source voltage drops, and the semiconductor switch element Q1 becomes non-conductive. As a result, the line 5 is cut off and the load current stops flowing (see the middle part of Fig. 4(b)). The changes up to this point occur almost instantaneously when the mechanical contact S starts to open.

[0030] While the above-mentioned instantaneous change occurs, the voltage Vc across the capacitor C is maintained at almost the same value as in the state of FIG. 2. This is because the value of the resistance element R2 is sufficiently large, so the capacitor C discharges extremely slowly. Therefore, the potential of the load-side terminal of the mechanical contact S is maintained almost the same as the potential of the positive electrode side of the capacitor C. On the other hand, the potential of the power supply-side terminal of the mechanical contact S is the same as the positive electrode side potential of the DC power supply 2. Therefore, the voltage across the contacts of the mechanical contact S is maintained at a value almost equal to the magnitude of the constant voltage Vz of the constant voltage element Z1 (see the latter half from the center of FIG. 4(c)).

[0031] In this way, since only a voltage of about the constant voltage Vz (for example, about 5V) is generated between the contacts of the mechanical contact S, the generation of an arc can be prevented. As shown in each waveform of FIG. 4, no chattering or continuous flow of an arc is observed when the mechanical contact S is opened. As a result, burning of the mechanical contact S and the like can be prevented.

[0032] In a preferred embodiment, a cut-off promoting section for promoting the cut-off of the current path of the semiconductor switch element Q1 is provided. The semiconductor switch element Q3 is in a non-conductive state when the semiconductor switch element Q2 is in a conductive state. When the semiconductor switch element Q2 is cut off and the current disappears, the base potential of the pnp-type transistor, which is the semiconductor switch element Q3, drops below the emitter potential, so that the base current I5 flows and it becomes a conductive state. Thereby, the collector current I6 amplified by the current amplification factor h FE of the transistor flows from the gate of the MOS-type FET, which is the semiconductor switch element Q1. As a result, the charge accumulated in the gate is rapidly discharged. As a result, the semiconductor switch element Q1 can be quickly turned off and the line 5 can be cut off.

[0033] Fig. 5(a) shows the waveform of the measured load voltage Vo when the mechanical contact S transitions from the open state (off) to the closed state (on), and (b) shows the waveform of the measured load current I4. Also in this case, chattering is not observed and there is no response delay during turning on. When the mechanical contact S is closed, the capacitor C is immediately fully charged and the voltage across the constant voltage element Z1 becomes the constant voltage Vz. That is, it becomes the state shown in Fig. 2.

[0034] Although not shown in the figure, even when the mechanical contact S of Fig. 1 is provided on line 5 instead of on line 4, the above operations are exactly the same. Also when the mechanical contact S is provided on line 5, the DC switch 1 is attached on the load side of the mechanical contact S.

[0035] Fig. 6 is a comparative example, and (a) shows the voltage between contacts when the contacts are opened in a conventional magnetic switch, and (b) shows the waveform of the measured load current. The time axis of Fig. 6 is the same scale as Fig. 4. Comparing with Fig. 4(c), in the present invention, only a voltage of about the constant voltage Vz is applied between the contacts, but in Fig. 6(a), a voltage of the same magnitude as the power supply voltage is applied between the contacts. Also comparing with Fig. 4(b), in the present invention, the load current immediately becomes zero, whereas in Fig. 6(b), an arc current flows for about 3 mS.

[0036] (3) Other embodiments Fig. 7 is a circuit diagram schematically showing another embodiment of the DC switch. In the DC switch 1A of Fig. 7, a diode D1 which is a rectifying element is inserted and connected on line 4. The diode D1 is inserted into the line on the load side of the load voltage monitoring unit 11, the anode is connected to the cathode of the constant voltage element Z1, and the cathode is connected to the terminal 8 on the positive electrode side of the load 3. The diode D1 is provided when the load 3 is a capacitive load, that is, a capacitor.

[0037] When the load 3 is a capacitor, the capacitor is charged by the power supply voltage when the mechanical contact S is in the closed state. The capacitor has the property of maintaining the voltage across its terminals. Therefore, when the mechanical contact S is opened, if a discharge current flows from the capacitor of the load 3 through the line 4 to the constant voltage element Z1, the voltage across the constant voltage element Z1 may not decrease. As a result, the semiconductor switch elements Q2 and Q1 are not cut off, and the DC switch does not operate normally. The diode D1 can prevent the reverse flow of the current from the capacitor of the load 3. Thereby, the normal operation of the DC switch 1A can be ensured.

[0038] FIG. 8 is a schematic circuit diagram of still another embodiment of the DC switch. In the DC switch 1B of FIG. 8, a p-channel MOS type FET is used as the semiconductor switch element Q1, and npn type bipolar transistors are used as the semiconductor switch elements Q2 and Q3. The current path of the semiconductor switch element Q1 is inserted and connected on the line 4 on the positive electrode side. The circuit operation of the DC switch 1B is substantially the same as that of the DC switch 1 described above.

[0039] Although not shown, in each of the embodiments described above, any of MOS type FETs, bipolar transistors, or IGBTs can be used as the semiconductor switch elements Q1, Q2, and Q3.

[0040] FIG. 9 shows a form in which the DC switch 1 of the present invention is applied to double-break type mechanical contacts S1 and S2. Also in this case, the operation of the DC switch 1 is the same as that described above.

[0041] Furthermore, a DC switch device configured by combining various switches having mechanical contacts (including relays) and the above-described DC switch interlocked with the switch is also one of the embodiments of the present invention.

[0042] The DC switch of the present invention described above does not require a complex mechanical mechanism or an electronic control unit, and can prevent the generation of an arc occurring between mechanical contacts only by autonomous operation. In addition, although the embodiments of the present invention have been described with reference to the configurations as examples, the specific configurations are not limited thereto. As long as it follows the principle of the present invention, various modified forms are also included in the scope of the present invention.

Explanation of Reference Numerals

[0043] 1, 1A, 1B DC switch 2 DC power supply 3 Load 4 First line 4a Power supply side line 4b Load side line 5 Second line 6, 7 Power supply side terminals 8, 9 Load side terminals 11 Load voltage monitoring unit 12 Interruption promotion unit Q1, Q2, Q3 Semiconductor switch elements Z1, Z2 Constant voltage elements C Capacitor D, D1 Rectifying elements R1, R2, R3, R4 Resistance elements S Mechanical contact

Claims

1. A DC switch that interlocks with a mechanical contact for opening and closing a line connecting a DC power supply and a load, a first semiconductor switch element including a first current path inserted and connected to the line and a first control terminal driven to control conduction and non-conduction of the first current path, a load voltage monitoring unit including a capacitor and a constant voltage element connected in series between a pair of the lines on the load side of the mechanical contact, the capacitor being maintained in a charged state by the DC power supply and the voltage across the constant voltage element being maintained at a predetermined constant voltage when the mechanical contact is in a closed state, a second semiconductor switch element including a second current path and a second control terminal driven to control conduction and non-conduction of the second current path, the second control terminal being driven by the predetermined constant voltage of the constant voltage element to maintain the second current path in a conductive state, the first semiconductor switch element being such that when the second current path of the second semiconductor switch element is maintained in a conductive state, the first control terminal is driven to maintain the first current path in a conductive state, a DC switch, wherein when the mechanical contact is opened and the voltage across the constant voltage element decreases, the second current path of the second semiconductor switch element becomes non-conductive, whereby the first current path of the first semiconductor switch element becomes non-conductive.

2. The DC switch according to claim 1, wherein the predetermined constant voltage of the constant voltage element is set to a magnitude that does not cause an arc between the mechanical contacts.

3. the first semiconductor switch element and the first control terminal being a MOS-type FET and its gate, further comprising a third semiconductor switch element including a third current path and a third control terminal driven to control conduction and non-conduction of the third current path in order to quickly turn off the MOS-type FET when the mechanical contact is opened, the DC switch according to claim 1 or 2, wherein the third control terminal is driven by the second current path of the second semiconductor switch element becoming non-conductive, causing a current to flow through the gate to discharge the gate in the third current path.

4. The DC switch according to claim 1 or 2, further comprising an element inserted and connected to the line on the load side of the load voltage monitoring unit to prevent reverse flow of current from the load.

5. A DC switching device comprising a switch having mechanical contacts and the DC switch according to claim 1 or 2 interlocked with the mechanical contacts.

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