JP2015042043A - Overvoltage protection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overvoltage protection circuit that can detect and interrupt an input of overvoltage without using any overvoltage-detection-function-enabled leakage breaker integrally having a leakage detection/interruption function and an overvoltage detection/interruption function.SOLUTION: The overvoltage protection circuit has a leakage detection section, a leakage interruption section, an input voltage detection section and a leakage generation section. The leakage detection section detects a leakage condition in which a leakage current equal to or higher than a threshold current flows between a power input line for inputting a supply voltage and a ground potential. If the leakage detection section detects the leakage condition, the leakage interruption section interrupts the input of supply voltage. The input voltage detection section determines whether the supply voltage is equal to or higher than a threshold voltage. If the input voltage detection section determines that a supply voltage equal to or higher than the threshold voltage is input, the leakage generation section connects the power input line to the ground potential to cause a flow of pseudo leakage current equal to or higher than the threshold current between the power input line and the ground potential. The input voltage detection section and the leakage generation section are arranged independently of the leakage detection section and the leakage interruption section.

Description

  The present invention relates to an overvoltage protection circuit, and more particularly to an overvoltage protection circuit having a function of detecting and protecting an overvoltage input.

  When a power supply having a voltage exceeding the rated voltage is input due to an error in construction or the like in a power supply circuit that drives various electric and electronic devices upon receiving a commercial power supply, the power supply circuit and the power supply circuit drive the power supply circuit. Several mechanisms have been proposed to protect the device from the application of overvoltage. One form of such overvoltage protection is that the power supply circuit has a wide range design that can withstand input of voltages exceeding the rated voltage. Or the structure which provides the earth leakage breaker with an overvoltage detection function in a power input part is mentioned.

  As an earth leakage breaker with an overvoltage detection function, the thing of patent document 1 is mentioned, for example. The leakage protection device described in Patent Document 1 (leakage breaker with overvoltage detection function) is obtained by adding an overvoltage detection / cutoff function to a general leakage breaker having a leakage detection / cutoff circuit. A member functioning as an earth leakage breaker and a member for exerting an overvoltage detection / shut-off function are integrally formed and provided outside a target device (hot water washing toilet seat in Patent Document 1) that supplies power. Specifically, as shown in FIG. 5 of Patent Document 1, it is formed at a portion where the power plug is inserted into the outlet.

JP 2003-51238 A

  Although an earth leakage breaker with an overvoltage detection function is commercially available, it has an overvoltage detection / cutoff function, but is more expensive than a general earth leakage breaker and is expensive. Therefore, when an electric leakage breaker with an overvoltage detection function is provided in an electric / electronic device, the cost is higher than when a simple leakage breaker is provided. Moreover, since the earth leakage breaker with an overvoltage detection function is more specific than a general earth leakage breaker, it is assumed that the earth leakage breaker cannot be stably obtained in the market.

  The problem to be solved by the present invention is an overvoltage that can detect and shut off the input of an overvoltage without using an earth leakage breaker with an overvoltage detection function that is integrally provided with an earth leakage detection / breaking function and an overvoltage detection / breaking function. It is to provide a protection circuit.

  In order to solve the above-described problem, the overvoltage protection circuit according to the present invention detects a leakage current in which a leakage current greater than a threshold current flows between a power supply input line for inputting a power supply voltage from an external power supply and a ground potential. And when the leakage detection unit detects the leakage state, the leakage blocking unit that blocks the input of the power supply voltage, and the leakage detection unit and the leakage blocking unit are arranged independently, and the power supply voltage is equal to or higher than a threshold voltage. When it is determined that the input voltage detection unit for determining whether or not, the leakage detection unit and the leakage blocking unit are independently arranged, and the input voltage detection unit receives a power supply voltage equal to or higher than the threshold voltage, The power supply input line is connected to a ground potential, and a leakage generation unit that causes a pseudo leakage current greater than the threshold current to flow between the power supply input line and the ground potential is provided.

  Here, the leakage generation unit is a switch provided between the power input line and the ground potential, the leakage detection unit and the leakage blocking unit are leakage breakers, and the input voltage detection unit is the An element or device provided on a circuit board spatially separated from the earth leakage breaker is preferable.

  In addition, a capacitor may be connected between the leakage generator and the ground potential.

  In this case, a first end of the capacitor is connected to the ground potential, a first switch is connected between a hot-side line of the power input line and a second end of the capacitor, and the power input line A second switch is connected between the common side line of the capacitor and the second end of the capacitor, and the pseudo-leakage current is generated by alternately switching the first switch and the second switch. It is good to be.

In this case, further, the time interval dt for alternately switching the first switch and the second switch is set such that the capacitance of the capacitor is C, the threshold voltage is V _th , and the threshold current is I _th . It is preferable that dt ≦ C · V _th / I _th .

  The capacitor preferably functions as a capacitor for absorbing power supply noise when the power supply voltage lower than the threshold voltage is input.

  And the said electric leakage generation | occurrence | production part is good to be connected to the hot side line of the said voltage input line.

  The threshold voltage is preferably between 100V and 200V.

  In the overvoltage protection circuit according to the above invention, when the input voltage detection unit determines that the power supply voltage equal to or higher than the threshold voltage is input, the leakage generation unit generates a pseudo-leakage higher than the threshold current between the power supply input line and the ground potential. Apply current. Then, the leakage detection unit detects a pseudo leakage current that is equal to or greater than the threshold current, recognizes that a leakage state has occurred, and the leakage blocking unit blocks the power input. In this way, using the input voltage detection unit and the leakage generation unit arranged independently from the leakage detection unit and the leakage breaker unit, let the leakage detection unit recognize that a leakage state has occurred when an overvoltage exceeding the threshold voltage is input. By operating the earth leakage breaker, even if you do not use an earth leakage breaker with an overvoltage detection function that integrates an earth leakage detection / breaking function and an overvoltage detection / breaking function like a commercially available earth leakage breaker with an overvoltage detection function, And overvoltage input can be protected.

  Here, the leakage generation unit is a switch provided between the power input line and the ground potential, the leakage detection unit and the leakage cutoff unit are leakage breakers, and the input voltage detection unit is spatially separated from the leakage breaker. In the case of an element or device provided on a separated circuit board, the leakage generating portion can be configured to be simple and inexpensive. In addition, the leakage detector and the leakage breaker can be simply configured as members independent of the input voltage detector while using a leakage breaker that is highly versatile and available on the market at a low cost.

  In addition, when a capacitor is connected between the leakage generator and the ground potential, when an appropriate voltage that is not overvoltage is input, insulation is maintained between the ground potential and the power input line, When an overvoltage is input, a pseudo-leakage current can be passed between the power input line and the ground potential to activate the leakage breaker.

  In this case, the first end of the capacitor is connected to the ground potential, the first switch is connected between the hot side line of the power input line and the second end of the capacitor, and the common side line of the power input line and the capacitor According to the configuration in which the second switch is connected between the second ends and the pseudo-leakage current is generated by alternately switching the first switch and the second switch, it is instantaneously large via the capacitor. Current can flow between the power input line and ground potential. Thereby, even when the capacitance of the capacitor to be used is not large, a pseudo leakage current greater than or equal to the threshold current can be passed, and the leakage breaker can be operated.

In this case, further, the time interval dt at which the first switch and the second switch are alternately switched is dt ≦ C · V, where C is the capacitance of the capacitor, V _{th is} the threshold voltage, and I _th is the threshold current. _{If th 1} / I _th , the switching speed of the switch necessary for flowing a pseudo leakage current equal to or greater than I _th can be quantitatively estimated.

  In addition, when the above capacitor works as a power supply noise absorption capacitor when a power supply voltage lower than the threshold voltage is input, it is necessary to separately provide a capacitor specialized for overvoltage protection and power supply noise absorption. The cost required for manufacturing the overvoltage protection circuit can be further reduced.

  When the leakage generating unit is connected to the hot side line of the voltage input line, it is possible to protect against overvoltage input with higher safety compared to the case where it is connected to the common side line. it can.

  When the threshold voltage is between 100V and 200V, it is determined that 100V is an appropriate input voltage, while 200V is determined to be an overvoltage, and the input is blocked. Therefore, it is possible to protect an electric / electronic device that is assumed to be used by inputting a 100V commercial power source from an input of a 200V commercial power source. As a result, it is possible to effectively prevent an overvoltage input caused by a difference between 100 V and 200 V, which is likely to occur when using or installing an electric / electronic device.

It is the schematic which shows the structure of the overvoltage protection circuit concerning 1st embodiment of this invention. It is the schematic which shows the structure of the overvoltage protection circuit concerning 2nd embodiment of this invention. It is the schematic which shows the structure of the overvoltage protection circuit concerning 3rd embodiment of this invention.

  Hereinafter, an overvoltage protection circuit according to an embodiment of the present invention will be described in detail with reference to the drawings.

<First embodiment>
FIG. 1 shows a configuration of an overvoltage protection circuit 1 according to the first embodiment of the present invention. The overvoltage protection circuit 1 includes a leakage detection unit 11, a leakage blocking unit 12, an input voltage detection unit 13, and a leakage generation unit 14. The overvoltage protection circuit 1 is provided on the upstream side of a power input unit of an electric / electronic device (not shown) that receives power input from an external power source such as a commercial power source, and an overvoltage is input to the power input line Lin via the power plug PL. If it is detected, it plays a role of blocking the power input.

  Here, the case where the power source input from the commercial power source, which is an external power source, via the power plug PL is AC, and the AC power source that is assumed to be input as an appropriate voltage has hot and common (cold) polarities is handled. . In this case, the power input line Lin includes a hot side line Lh and a common side line Lc.

Leakage detection unit 11 is a predetermined threshold current I _th or more leakage current when leakage flow conditions between the power input line Lin and the ground potential is generated, for detecting it. In addition, the leakage breaker 12 serves to block the input of the power supply voltage to the power input line Lin when the leakage detector 11 detects a leakage state.

  The earth leakage detector 11 and the earth leakage breaker 12 may have any configuration, but a general earth leakage breaker 15 may be used as an integral unit of the earth leakage detector 11 and the earth leakage breaker 12. From the viewpoint of simplicity, it is preferable. In the common earth leakage breaker marketed, the earth leakage detection unit 11 has a configuration in which a conducting wire connected to the hot side line Lh and a conducting wire connected to the common side line Lc are passed through a ring-shaped magnetic body. When there is a difference in current flowing through the hot side line Lh and the common side line Lc due to the occurrence of electric leakage, a magnetic field is generated around the two conductors. A winding is wound around the ring-shaped magnetic body, and when such a magnetic field is generated, a voltage is generated in the winding. When this voltage is detected by an electric circuit and a predetermined threshold value is exceeded, the leakage breaker 12 comprising an appropriate switch means such as an electromagnetic switch is turned off, and the power input from the external power source to the power input line Lin Is cut off. This type of earth leakage breaker 15 is usually formed integrally with the power plug PL and arranged at the outlet to the outlet. In addition, in this specification, when only calling it "earth leakage breaker", it shall refer to the earth leakage breaker which does not have an overvoltage detection function and performs only detection and interruption for the earth leakage state.

The input voltage detector 13 determines whether the power supply voltage input from the external power supply to the power supply input line Lin via the power plug PL is an overvoltage equal to or higher than the threshold voltage _Vth or an appropriate voltage _lower than the threshold voltage _Vth . Determine. The input voltage detection unit 13 may be any element or device as long as it can read the input voltage value and compare the magnitude with the threshold voltage _Vth . For example, the input voltage detection unit 13 includes two resistors in series. The input voltage detector 13 can be configured using the voltage dividing resistor Rv and the voltage measuring means 16 connected to each other. That is, the voltage dividing resistor Rv is connected between the hot side line Lh and the common side line Lc on the downstream side of the leakage detecting unit 11 and the leakage blocking unit 12, and the divided voltage obtained at the connection point of the two resistors is What is necessary is just to make the voltage measurement means 16 read. The voltage measuring means 16 is embodied by, for example, a microcomputer 18 and can be the same as a microcomputer that controls electric and electronic equipment that operates by receiving power input from the power input line Lin. In this case, in the voltage dividing resistor Rv, the voltage dividing ratio determined by the ratio of the resistance values of the two resistors can be input to the microcomputer input port when the assumed overvoltage is input to the power input line Lin. What is necessary is just to select so that it may become a range.

When the input voltage detection unit 13 detects that an overvoltage equal to or higher than the threshold voltage _Vth is input to the power supply input line Lin, the leakage generation unit 14 connects the power supply input line Lin to the ground potential. The leakage generation unit 14 includes, for example, a switch SW, a capacitor C1 (for leakage), and a switch control unit 17. When receiving an input of a signal indicating that an overvoltage input has been detected from the voltage measuring means 16, the switch control means 17 outputs an electrical signal to the switch SW and turns on the switch SW. The switch control means 17 can be embodied by a microcomputer, and is preferably the same as the microcomputer that functions as the voltage measurement means 16. The switch SW is connected between the hot side line Lh and the ground potential, insulates between the hot side line Lh and the ground potential in the off state, and conducts between the hot side line Lh and the ground potential in the on state. Form. The switch SW can be constituted by a relay switch, for example, and one end of the input side terminal may be connected to the hot side line Lh and the other end connected to the switch control means 17 (microcomputer output port). Then, one end of the output side terminal may be connected to the hot side line Lh, and the other end may be connected to the leakage capacitor C1. The leakage capacitor C1 is connected between the output-side terminal of the switch SW and the ground potential.

  Here, the voltage dividing resistor Rv that constitutes the input voltage detector 13, the switch SW that constitutes the leakage generator 14 and the leakage capacitor C 1, and the microcomputer that functions as the input voltage detector 13 and the switch control means 17 It is mounted on a circuit board that is independent (spatially separated) from the part 11 and the leakage breaker 12. For example, as will be described later, when the overvoltage protection circuit 1 is provided in the warm water flush toilet seat, the circuit board on which these circuits are mounted is accommodated in a device accommodating portion provided in a casing behind the toilet seat, and the power plug The earth leakage detector 11 and the earth leakage interrupter 12 provided as the earth leakage breaker 15 integrally with the PL are spatially completely separated.

  In addition to the above members, the overvoltage protection circuit 1 is provided with a noise absorbing capacitor C2 in parallel with the output side of the switch SW and the leakage capacitor C1 between the hot side line Lh and the ground potential. The noise absorbing capacitor C2 serves to remove noise components contained in the input voltage from the external power source.

When an appropriate voltage lower than the threshold voltage _Vth is input to the power input line Lin and no leakage has occurred, it is not determined that the input voltage detection unit 13 is in an overvoltage state, and the leakage generation unit 14 The switch control means 17 does not output a signal to the switch SW. As a result, the switch SW is maintained in the OFF state, and the hot side line Lh of the power input line Lin and the ground potential are maintained in an insulated state. Then, the leakage current does not flow between the power input line Lin and the ground potential, and the state where the leakage breaker 12 does not block the voltage input to the power input line Lin is maintained. Therefore, the state in which the power supply voltage is supplied to the downstream electrical / electronic device via the overvoltage protection circuit 1 is continued.

On the other hand, when an overvoltage equal to or higher than the threshold voltage _Vth is input to the power input line Lin, the input voltage detection unit 13 detects the input of the overvoltage and indicates the occurrence of an overvoltage state in the switch control means 17 of the leakage generation unit 14. Communicate the signal. Then, the switch control means 17 outputs a signal to the switch SW. As a result, the switch SW is turned on, and conduction is formed between the hot-side line Lh of the power input line Lin and the ground potential. Then, a current (pseudo-leakage current I _ps ) flows from the hot side line Lh to the ground potential via the leakage capacitor C1, and leakage occurs. The pseudo leakage current I _ps is, if the threshold current I _th or more values is recognized as the electric leakage detection unit 11 is in leak state, determines leakage detection unit 11 is electric leakage occurs, fault interrupter 12 power The input of the power supply voltage to the input line Lin is cut off. In this manner, overvoltage input is detected in the overvoltage protection circuit 1 and eliminated.

  When the leakage detector 11 and the leakage breaker 12 are constituted by the leakage breaker 15, if the input of the power supply voltage is blocked by the overvoltage input and then the input of the overvoltage is stopped by pulling out the power plug PL from the outlet, etc. The earth leakage breaker 15 is reset. Therefore, the input of the appropriate voltage can be continued as long as control is performed using the switch control means 17 so that the switch SW is turned off when the appropriate voltage is input thereafter.

  Thus, without using the leakage breaker with an overvoltage detection function integrally provided with the leakage detection / cutoff function and the overvoltage detection / cutoff function as shown in Patent Document 1, the leakage detection unit 11 and the leakage breaker 12 With the configuration in which the independent input voltage detection unit 13 and the leakage generation unit 14 are provided, the overvoltage state can be detected and eliminated. As described above, as the leakage detection unit 11 and the leakage breaker 12, a general-purpose and inexpensive leakage breaker 15 can be used as it is, and the input voltage detection unit 13 and the leakage generation unit 14 are also general-purpose elements and microcomputers. Therefore, the leakage protection circuit can be manufactured at a low cost and with a simple configuration. In addition, since highly specialized parts such as an earth leakage breaker with an overvoltage detection function are not used, stable production is hardly affected by unstable factors in parts supply due to circumstances of the market or parts manufacturers. be able to.

Moreover, since the overvoltage protection circuit 1 uses the leakage detection unit 11 and the leakage breaker 12 to cut off the power supply input, it simultaneously performs both protection against overvoltage input and leakage due to various factors. Can do. In other words, even if a leakage occurs in any part of the power input line Lin or the downstream electrical / electronic device due to a factor other than the generation of the pseudo leakage current I _ps due to the detection of the overvoltage, the leakage detection unit 11 detects the leakage. Then, the leakage breaker 12 cuts off the power input.

Here, the threshold voltage _Vth may be arbitrarily set depending on the input voltage assumed in the region where the overvoltage protection circuit 1 is used and the specifications of the electric and electronic equipment receiving power supply, etc., but between 100V and 200V It is preferable to set to. In Japan, AC of 100V is widely used as a commercial power supply, while AC of 200V is also used. Therefore, when using or constructing electrical / electronic equipment with a rated voltage of 100V, the equipment is mistakenly connected to the 200V power supply. This is because it is easy to happen.

In the overvoltage protection circuit 1, the switch SW of the leakage generator 14 is connected between the hot side line Lh of the power input line Lin and the ground potential, but it is not necessarily connected to the hot side line Lh. You may connect between the common side line Lc and earth | ground potential. A single-phase three-wire system is widely used for supplying commercial power that can use both 100V and 200V AC. In this case, 100V AC is supplied with hot and common polarities. Has no common polarity. Therefore, even when the switch SW is connected to either the hot side line Lh or the common side line Lc in the overvoltage protection circuit 1 in a situation where 100V AC is assumed as the rated input voltage, When alternating current is input, a pseudo leakage current I _ps can flow between the power input line Lin and the ground potential. However, not only when the overvoltage is input due to the difference between 100V and 200V in the single-phase three-wire system, but also when the overvoltage is instantaneously applied during 100V input, or the 200V AC in the single-phase two-wire system Considering that the overvoltage protection function is activated and the safety is improved even when the switch SW is input, it is preferable to connect the switch SW between the hot side line Lh and the ground potential.

  When using a 2-pin power plug PL that is widely used in Japan, the user or the installer does not necessarily connect the power supply by making the overvoltage protection circuit 1 side correspond to the hot side and the common side of the power supply side. However, when a 3-pin power plug PL having a ground terminal in addition to the hot side terminal and the common side terminal is used, the correspondence between the hot side and the common side is required between the overvoltage protection circuit 1 side and the power source side. The relationship is defined in one way. Therefore, when the 3-pin power plug PL is used, the switch SW is connected between the hot-side line Lh and the ground potential instead of the common-side line Lc, compared to the case where the 2-pin power plug PL is used. The effect of improving the safety of the storage is greatly enjoyed.

As described above, when the input voltage detection unit 13 detects an input of an overvoltage and the switch SW of the leakage generation unit 14 is turned on, the pseudo leakage current I _ps is connected to the hot side line Lh via the leakage capacitor C1. Although the current flows between the ground potentials, the leakage capacitor C1 is not always necessary when focusing only on the point of forming a continuity between the hot side line Lh and the ground potential and allowing the pseudo-leakage current _Ips to flow. However, at least in Japan, the law stipulates that the power input line Lin and the ground potential should not be directly connected, and a capacitor is provided as a leakage capacitor C1 at this position. In view of the role of the capacitor for accumulating electric charge, a capacitor is optimal as an element provided at this position, but a resistor or the like can be substituted. However, when the power input to the power input line Lin is DC instead of AC, a leakage current cannot flow between the power input line Lin and the ground potential via a capacitor. It is necessary to use an element that can pass through at this position. About the structure of those other than this, the said overvoltage protection circuit 1 used with respect to AC power supply can be used as it is also with respect to DC power supply.

  The overvoltage protection circuit 1 as described above can be widely used in electric and electronic devices that are driven by receiving an input from an external power source. For example, it can be suitably used for a warm water washing toilet seat that ejects warm water for local body washing. Since the warm water flush toilet seat is used in direct contact with the human body and is installed around the water, even if an overvoltage input or electric leakage occurs, it will be promptly removed. It is required to detect and resolve. If the overvoltage protection circuit 1 according to this embodiment is used, early detection and cancellation of both overvoltage input and electric leakage are possible.

Here, assuming that 100V alternating current is regarded as an appropriate voltage and 200V alternating current is regarded as an overvoltage, for example, the pseudo-leakage current _Ips flowing between the power input line Lin and the ground potential, and the leakage detection unit 11 is in a leakage state. It determines that it estimates the relationship between the threshold current I _th to operate the fault interrupter 12. First, assuming that the capacitance of the leakage capacitor C1 is C and the voltage applied to both ends of the leakage capacitor C1, that is, the input voltage is V,
I _ps = C · dV / dt Equation (1)
The relationship becomes true.
Here, since the commercial power source is a sine wave, V ₀ is the maximum value.
V = V ₀ · sin (2πft) Equation (2)
It can be expressed as.
Substituting equation (2) into equation (1),
I _ps = 2πV ₀ fC · cos (2πft) = I ₀ · cos (2πft) Equation (3)
It becomes.
That is, the maximum value I ₀ of the pseudo leakage current I _ps is
I ₀ = 2πfV ₀ C Formula (4)
It becomes.

Next, V ₀ = 100 V, f = 50 Hz, and C = 4700 pF are substituted into Equation (4). The capacitance of 4700 pF is the practically maximum value of a capacitor that is commonly available as a capacitor connected between the power input line Lin and the ground potential. The result of the substitution is I ₀ = 0.148 mA. That is, the maximum value of the pseudo leakage current I _ps is 0.148 mA, and if the threshold current I _th for detecting that the leakage detection unit 11 is in the leakage state is 0.148 mA or less, the pseudo leakage current having the maximum value I ₀ is obtained. When the current I _ps flows, the leakage detection unit 11 recognizes that a leakage state has occurred, and can cause the leakage blocking unit 12 to block the power input to the power input line Lin.

However, as described above, when the leakage detection unit 11 and the leakage breaker 12 are configured by a commercially available leakage breaker 15, obtaining the leakage breaker 15 having a rated sensitivity current of 0.148 mA or less is not possible. Have difficulty. Therefore, it is desirable to adopt a method in which the pseudo leakage current I _ps is set to a larger value. The overvoltage protection circuit 2 according to the second embodiment corresponds to this.

<Second Embodiment>
Focusing on the above formula (1), it can be seen that the leakage current _Ips increases when the time dt during which the voltage change (dV) occurs is shortened. FIG. 2 shows the configuration of the overvoltage protection circuit 2 according to the second embodiment of the present invention, which is configured to change the voltage applied to the leakage capacitor C1 in a short time.

  Unlike the overvoltage protection circuit 1 according to the first embodiment in which a single switch SW is connected to the leakage capacitor C1, the overvoltage protection circuit 2 includes a first switch SW1 connected to the leakage capacitor C1. And the second switch SW2 are connected. As in the case of the first embodiment, the leakage capacitor C1 has one terminal (first end) connected to the ground potential. The first switch SW1 is connected between the hot side line Lh of the power input line Lin and the other terminal (second end) of the leakage capacitor C1, and the second switch SW2 is connected to the power input line Lin. The common line Lc is connected between the second end of the leakage capacitor C1. Both the first switch SW1 and the second switch SW2 are on / off controlled by the switch control means 17. The other configuration is the same as that of the overvoltage protection circuit 1 according to the first embodiment.

  In the overvoltage protection circuit 2, when the input voltage detector 13 detects an input of an overvoltage, the switch control means 17 alternately switches the first switch SW1 and the second switch SW2 alternately at high speed. That is, a switching cycle of “first switch SW1 turned on → first switch SW1 turned off → second switch SW2 turned on → second switch SW2 turned off” is repeated at intervals of time dt. Then, during the time interval dt, a voltage change dV equal to the input voltage at the maximum is created at both ends of the leakage capacitor C1. Here, the time interval dt is the time from when the first switch SW1 is turned on until the second switch SW2 is turned on, and after the second switch SW2 is turned on, the first switch SW1 is turned on. It indicates the time to make a state.

Next, in Formula (1), in order to obtain the pseudo leakage current I _ps of 15 mA, which is the most common rated sensitivity current of the leakage breaker 15, or larger than that, the first switch SW1 and the second switch SW2 It is estimated how much the switching interval dt should be set. From equation (1),
dt = C · dV / I _ps equation (5)
It is.
Assuming that the voltage change amount dV is 200 V and the capacitance of the leakage capacitor C1 is 4700 pF as in the first embodiment, in order to satisfy I _ps ≧ 15 mA in the equation (5), dt ≦ It is necessary to satisfy 0.0627 msec. In other words, if the switching of the first switch SW1 and the second switch SW2 is repeated at a time interval of 0.0627 milliseconds or less, the input of the power supply voltage of 200 V is cut off using the leakage breaker with the rated sensitivity current of 15 mA. Can do.

The above is an estimate when 200 V is regarded as an overvoltage. However, when the formula (5) is generalized and displayed, the second overvoltage protection circuit 2 is used to block an input of an overvoltage exceeding the threshold voltage _Vth. Therefore, the switching time interval dt between the first switch SW1 and the second switch SW2 may be determined as shown in the following equation (6).
dt ≦ C · V _th / I _th formula (6)

  In FIG. 2, the first switch SW1 and the second switch SW2 are displayed as relay switches for the sake of convenience so as to be easily understood in comparison with FIG. It is difficult to switch relay switches in time. If, for example, digital transistors are used as the first switch SW1 and the second switch SW2, such high-speed switching can be handled.

  Further, in the overvoltage protection circuit 2 according to the present embodiment, the switch SW1 and the switch SW2 are used to generate alternating current having a period different from that of the input power supply voltage and flow it through the capacitor. In addition, the overvoltage protection function can be used by using the same configuration.

<Third embodiment>
FIG. 3 shows the configuration of the overvoltage protection circuit 3 according to the third embodiment of the present invention. The overvoltage protection circuit 3 according to the third embodiment is different from the overvoltage protection circuit 2 according to the second embodiment of FIG. 2 in that the noise absorbing capacitor C2 is not provided. In the overvoltage protection circuit 3, a shared capacitor Cc is provided at a position where the leakage capacitor C1 is in contact with the overvoltage protection circuit 2, and the shared capacitor Cc serves as the leakage capacitor C1 and the noise absorbing capacitor C2. Have both.

That is, when the input voltage detection unit 13 detects an input of an overvoltage equal to or higher than _Vth , the switch control unit 17 sets the first switch SW1 and the second switch SW2 to a time interval as in the case of the second embodiment. Switching alternately at dt. Thereby, the shared capacitor Cc functions as a leakage capacitor.

On the other hand, when the input voltage detection unit 13 detects an input of an appropriate voltage less than _Vth , the switch control means 17 turns on the first switch SW1 and turns off the second switch SW2. By maintaining this state, the hot-side line Lh of the power input line Lin is connected to the ground potential via the shared capacitor Cc. That is, the shared capacitor Cc functions as a noise absorbing capacitor.

  In this way, the number of capacitors to be used can be reduced by providing both roles by using a single shared capacitor Cc without providing a leakage capacitor and a noise absorbing capacitor independently. it can. Thereby, the manufacturing cost of an overvoltage protection circuit can be reduced.

  As mentioned above, although embodiment of this invention was described in detail, this invention is not limited to the said Example at all, A various change is possible in the range which does not deviate from the summary of this invention. For example, in each of the above embodiments, the switch control means 17 that controls the switch is configured using a microcomputer, but the switch control means 17 can also be configured using only analog elements. For example, the divided voltage obtained by the voltage dividing resistor Rv may be input to the transistor via an appropriate resistor, and the output of the transistor may be input to the switch SW formed of a relay switch.

1, 2, 3 Overvoltage protection circuit 11 Earth leakage detector 12 Earth leakage interrupter 13 Input voltage detector 14 Earth leakage generator 15 Earth leakage breaker 16 Voltage measuring means 17 Switch control means 18 Microcomputer C1 Earth leakage capacitor C2 Noise absorbing capacitor Cc Shared capacitor Lin Power input line Lh Hot side line Lc Common side line SW Switch SW1 First switch SW2 Second switch Rv Voltage dividing resistor

Claims (8)

A leakage detection unit for detecting a leakage state in which a leakage current greater than or equal to a threshold current flows between a power supply input line for inputting a power supply voltage from an external power supply and a ground potential;
When the leakage detection unit detects the leakage state, the leakage blocking unit that blocks the input of the power supply voltage;
An input voltage detection unit that is arranged independently from the leakage detection unit and the leakage breaker, and determines whether the power supply voltage is equal to or higher than a threshold voltage;
The power supply input line is connected to a ground potential when the power supply voltage that is arranged independently of the ground leakage detection unit and the ground leakage interruption unit and the input voltage detection unit determines that a power supply voltage equal to or higher than the threshold voltage is input, and the power supply An earth leakage generating portion for causing a pseudo earth leakage current greater than the threshold current between the input line and the ground potential,
An overvoltage protection circuit comprising: The leakage generator is a switch provided between the power input line and the ground potential,
The leakage detection unit and the leakage breaker are leakage breakers,
The overvoltage protection circuit according to claim 1, wherein the input voltage detection unit is an element or a device provided on a circuit board spatially separated from the leakage breaker.   The overvoltage protection circuit according to claim 1, wherein a capacitor is connected between the leakage generation unit and the ground potential.   A first end of the capacitor is connected to the ground potential, a first switch is connected between a hot side line of the power input line and a second end of the capacitor, and a common side line of the power input line And a second switch is connected between the second end of the capacitor and the pseudo-leakage current is generated by alternately switching the first switch and the second switch. The overvoltage protection circuit according to claim 3. The time interval dt for alternately switching between the first switch and the second switch is dt ≦ C · V, where C is the capacitance of the capacitor, V _{th is} the threshold voltage, and I _th is the threshold current. overvoltage protection circuit according to claim 4, characterized in that the _{th /} I _th.   6. The overvoltage protection circuit according to claim 4, wherein the capacitor functions as a capacitor for absorbing power supply noise when the power supply voltage lower than the threshold voltage is input.   The overvoltage protection circuit according to any one of claims 1 to 6, wherein the leakage generation unit is connected to a hot-side line of the voltage input line.   The overvoltage protection circuit according to claim 1, wherein the threshold voltage is between 100V and 200V.

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