Inrush current prevention circuit and control method thereof

Abstract

To perform control to prevent a rush current equal to or more than a predetermined value from flowing even when using a plurality of load devices, and control to prevent a current equal to or more than a constant value from flowing in the load devices.SOLUTION: A rush current prevention circuit for preventing a rush current flowing from a power supply to a load device via a connection line, comprises: a rush prevention resistor inserted into the connection line that reduces a current at start of the load device and applies the reduced current; a switch element connected in parallel with the rush prevention resistor; a current detector inserted into the connection line; and a control circuit that on / off-controls the switch element on the basis of a current value detected by the current detector. The control circuit performs control to turn on the switch element when the current value is less than a predetermined reference current, and performs control to turn off the switch element when the current value is equal to or more than the reference current.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an inrush current prevention circuit used in, for example, a power supply device, and a control method thereof. [Background technology]

[0002] 2. Description of the Related Art There are cases where power is transmitted from an AC power source via a breaker to a circuit in which a plurality of load devices, N units of which are electrical appliances, are connected in parallel.

[0003] In this case, the inrush current when current is supplied from the AC power source to multiple load devices is multiplied by N. As a result, a large current flows when each load device starts up, which may cause an instantaneous voltage drop in other facility devices.

[0004] In this case, it is necessary to select a breaker taking into consideration the large inrush current, and it is necessary to increase the breaker capacity, but if the breaker capacity is increased, the breaker may not operate if the product breaks down, and the internal equipment may burn. Also, the initial inrush current may cause a voltage rise due to the L value component of the input line, which may damage the equipment.

[0005] For example, Patent Document 1 discloses a general inrush current prevention circuit. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 3-218217 Summary of the Invention [Problem to be solved by the invention]

[0007] However, even when multiple load devices are used, there was a problem in that it was not possible to control the inrush current so that it did not exceed a predetermined value, and it was not possible to control the current so that it did not exceed a certain value.

[0008] The object of the present invention is to solve the above problems and to provide an inrush current prevention circuit and a control method thereof that can control an inrush current so that it does not exceed a predetermined value even when multiple load devices are used, and that can also control the load device so that a current exceeding a certain value does not flow. [Means for solving the problem]

[0009] An inrush current prevention circuit according to one aspect of the present invention comprises: An inrush current prevention circuit for preventing an inrush current from flowing from a power supply through a connection line to a load device, an inrush current prevention resistor that is inserted in the connection line and reduces the current that flows when the load device is started; A switch element connected in parallel with the inrush prevention resistor; a current detector inserted in the connection line; a control circuit that controls the switching element to be turned on and off based on the current value detected by the current detector, The control circuit controls the switch element to be turned on when the current value is less than a predetermined reference current, and controls the switch element to be turned off when the current value is equal to or greater than the reference current. Effect of the Invention

[0010] Therefore, with the inrush current prevention circuit of the present invention, even when multiple load devices are used, it is possible to control the inrush current so that it does not exceed a predetermined value, and it is also possible to control the current so that it does not exceed a certain value in the load device. [Brief description of the drawings]

[0011] [Figure 1] 1 is a circuit diagram showing a configuration example of an inrush current prevention circuit according to an embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the same or similar components are denoted by the same reference numerals.

[0013] (Inventor's knowledge) In order to solve the above problems, for example, by mounting an inrush current prevention circuit (unit) described in detail below immediately adjacent to the output of a breaker in a distribution panel of an AC power supply, it is possible to always suppress the inrush current at the time of power-on to a certain level. In addition, the input current can be monitored, and if a large current flows, it can be suppressed by a resistor or the like. This embodiment will be described below.

[0014] (Embodiment) 1 is a circuit diagram showing an example of the configuration of an inrush current prevention circuit according to an embodiment of the present invention. In FIG. 1, the inrush current prevention circuit according to the embodiment of the present invention is configured to include an inrush current prevention main circuit 2 and an inrush current control circuit 3.

[0015] Here, the inrush current prevention main circuit 2 is a main circuit that passes AC current from, for example, a breaker output terminal of the AC power source 1 to a load device 4, (1) A series circuit 6 including a protection circuit 5 and an inrush current prevention resistor Rp (for example, 10 Ω), (2) an electromagnetic relay RE1 connected to both ends of the series circuit 6 and turned on and off based on a control signal from the inrush current control circuit 3; (3) The voltage supply circuit 7 includes a bipolar transistor Q1 that rectifies the AC current by a rectifier circuit 21, converts it into a voltage value, and supplies the voltage to the electromagnetic relay RE1.

[0016] The AC power supply 1 and the load device 4 are connected via a pair of connection lines 9a and 9b, with the series circuit 6 inserted in the connection line 9a and a current detection resistor Rd (described later) inserted in the connection line 9b. The inrush prevention resistor Rp is provided to reduce and suppress the current when the load device 4 starts up.

[0017] In the inrush current prevention main circuit 2, the current from the AC power source 1 flows to the load device 4 through a protection circuit 5 and a series circuit 6 of an inrush prevention resistor Rp provided on a connection line 9a, and a return current from the load device 4 returns to the AC power source 1 through a connection line 9b. Here, the protection circuit 5 is, for example, a thermal fuse, and is disconnected when a predetermined current flows and a predetermined temperature is reached. This protection circuit 5 may be omitted depending on the circuit configuration. One end of the series circuit 6 is connected to a movable contact c of the electromagnetic relay RE1, and the other end of the series circuit 6 is connected to a fixed contact a of the electromagnetic relay RE1. After the voltage from the AC power source 1 is rectified by a rectifier circuit 21 formed by connecting diodes D1 to D4 in a bridge form, the rectified voltage is applied to the coil REc of the electromagnetic relay RE1 through a smoothing capacitor C1, a collector and emitter of a bipolar transistor Q1, a time constant circuit 8 of a capacitor C2 and a resistor R1, a diode D11, and a smoothing capacitor C3.

[0018] In the inrush current prevention main circuit 2 configured as described above, the current from the AC power supply 1 at the start-up of the load device 4 is suppressed by the inrush prevention resistor Rp and flows, and then, under the control of the inrush current control circuit 3 described later, the current falls below a predetermined threshold value. After a certain delay time by the time constant circuit 8, the bipolar transistor Q1 is turned on and a predetermined voltage is applied to the coil REc of the electromagnetic relay RE1, turning on the electromagnetic relay RE1, and the main current flows through the electromagnetic relay RE1 without passing through the inrush prevention resistor Rp.

[0019] The inrush current control circuit 3 includes: (1) A current detection resistor Rd inserted in the connection line 9b; (2) a voltage detection circuit 31 including voltage dividing resistors R11, R12 and voltage dividing resistors R13, R14; (3) A source-grounded MOS field-effect transistor (hereinafter referred to as MOS transistor) Q2, the base of which is connected to the drain of the bipolar transistor Q1, and which controls the on / off state of the bipolar transistor Q1; (4) R10, which supplies a bias voltage to the MOS transistor Q2 based on the voltage of the capacitor C1; (5) a differential amplifier circuit 32 that detects a difference voltage corresponding to a current flowing through a current detection resistor Rd; (6) a differential amplifier circuit 33 that detects a difference voltage between a reference voltage at one end (AC power supply 1 side) of a current detection resistor Rd and an output voltage from a differential amplifier circuit 32 that is output based on a voltage at the other end (ground side) of the current detection resistor Rd; (7) a comparator CM1 which compares the output voltage from the differential amplifier circuit 33 with a reference voltage Vref, and outputs a high-level output voltage signal when the current flowing through the current detection resistor Rd is equal to or greater than a reference current (hereinafter, referred to as Iref) corresponding to the reference voltage Vref, and outputs a low-level output voltage signal when the current flowing through the current detection resistor Rd is less than the reference current; (8) A resistor R41 is provided to apply the output voltage signal from the comparator CM1 to the gate of the MOS transistor Q2.

[0020] In the inrush current control circuit 3, the differential amplifier circuit 32 includes an operational amplifier OP1, input resistors R21 and R22, a feedback resistor R23, and reverse current prevention diodes D11 and D12. The differential amplifier circuit 33 includes an operational amplifier OP2, an input resistor R32, and a bias resistor R31.

[0021] Here, a reference voltage at one end of the current detection resistor Rd, based on the ground potential of the capacitor C1, is detected by voltage-dividing resistors R11 and R12 and input to the non-inverting input terminal of the operational amplifier OP1 via input resistor R22. Also, a voltage at the other end of the current detection resistor Rd, based on the ground potential of the capacitor C1, is detected by voltage-dividing resistors R13 and R14 and input to the inverting input terminal of the operational amplifier OP1 via input resistor R21. This allows the differential amplifier circuit 32 to detect a differential voltage corresponding to the current flowing through the current detection resistor Rd.

[0022] The output voltage from the differential amplifier circuit 32 is input to the inverting input terminal of the operational amplifier OP2 via the resistor R32. Also, the voltage at the non-inverting input terminal of the operational amplifier OP1 is input to the non-inverting input terminal of the operational amplifier OP2. As a result, the differential amplifier circuit 33 detects the difference voltage between the reference voltage at one end (AC power supply 1 side) of the current detection resistor Rd and the output voltage from the differential amplifier circuit 32, which is output based on the voltage at the other end (ground side) of the current detection resistor Rd.

[0023] The comparator CM1 compares the output voltage from the differential amplifier circuit 33 with a reference voltage Vref, and outputs a high-level output voltage signal when the current flowing through the current detection resistor Rd is equal to or greater than the reference current Iref corresponding to the reference voltage Vref, and outputs a low-level output voltage signal when the current flowing through the current detection resistor Rd is less than the reference current Iref. The output voltage signal is applied to the gate of the MOS transistor Q2 via a resistor R41. The MOS transistor Q2 is controlled to be turned on and off based on the output voltage signal. Here, when the current flowing through the current detection resistor Rd is equal to or greater than the reference current, the MOS transistor Q2 is turned on, and at this time, the bipolar transistor Q1 is turned off, and the voltage supply to the coil REc of the electromagnetic relay RE1 is stopped. On the other hand, when the current flowing through the current detection resistor Rd is less than the reference current, the MOS transistor Q2 is turned off, and at this time, the bipolar transistor Q1 is turned on, and the voltage supply to the coil REc of the electromagnetic relay RE1 is performed.

[0024] The load device 4 and the other end of the current detection resistor Rd are grounded to a different ground from the ground of the internal circuits of the inrush current prevention main circuit 2 and the inrush current control circuit 3.

[0025] The operation of the inrush current prevention circuit configured as above will now be described.

[0026] (1) When the load device 4 is started, the electromagnetic relay RE1 is turned off, so a predetermined current flows through the inrush prevention resistor Rp. After that, a predetermined voltage is applied to the coil REc of the electromagnetic relay RE1 from the voltage supply circuit 7, but when an inrush current flows from the AC power source 1 to the load device 4, the voltage corresponding to the current flowing through the current detection resistor Rd is detected by the voltage detection circuit 31 and the differential amplifier circuits 32 and 33 of the inrush current control circuit 3 so as not to turn on the electromagnetic relay RE1. At this time, the output voltage signal of the comparator CM1 becomes high level, turning on the MOS transistor Q2, and turning off the bipolar transistor Q1, and stopping the voltage supply from the voltage supply circuit 7 to the coil REc of the electromagnetic relay RE1. (2) When the current flowing through the current detection resistor Rd is less than a predetermined reference current Iref, the output voltage signal of the comparator CM1 goes low, turning off the MOS transistor Q2 and turning on the bipolar transistor Q1. Voltage is supplied from the voltage supply circuit 7 to the coil REc of the electromagnetic relay RE1, turning on the electromagnetic relay RE1. This state is the steady state of the inrush current prevention circuit. (3) For example, if a component such as a semiconductor element in the load device 4 is damaged and a large current greater than the reference current Iref flows through the current detection resistor Rd, the voltage corresponding to the current flowing through the current detection resistor Rd is detected by the voltage detection circuit 31 and the differential amplifier circuits 32, 33 of the inrush current control circuit 3, and the voltage supply from the voltage supply circuit 7 to the coil REc of the electromagnetic relay RE1 is stopped again, as in the case of (1) above.

[0027] In addition, since a protection circuit 5 such as a thermal fuse is connected in series to the inrush prevention resistor Rp, it is possible to prevent a large current from flowing to the load device 4.

[0028] As described above, according to this embodiment, the user can select a breaker on the output side of the AC power supply 1 by only considering the current that always flows, without worrying about inrush current. In addition, when multiple load devices 4 are connected, momentary voltage drops are unlikely to occur in the load devices 4 of other facilities, so the influence of the input voltage on the surrounding circuits can be reduced. Furthermore, when damage occurs in the load device 4, as described above, the current flowing through the load device 4 is suppressed, so that a current equal to or greater than the reference current Iref does not flow, and it is possible to prevent components in the load device 4 from burning.

[0029] Furthermore, when a large current equal to or greater than the reference current Iref flows through the load device 4, the electromagnetic relay RE1 is turned off and a current flows through the inrush prevention resistor Rp. This prevents a current equal to or greater than the reference current Iref from flowing through the load device 4 on the output side, and also prevents damage or fire due to an overcurrent on the primary side.

[0030] Furthermore, by incorporating a protection circuit 5 such as a thermal fuse in series with the inrush prevention resistor Rp, the inrush prevention resistor Rp can also be prevented from catching fire.

[0031] (Modification) In the above embodiment, the electromagnetic relay RE1 is used, but the present invention is not limited to this, and a switching element such as a semiconductor switching element, for example, a MOS transistor, may be used.

[0032] In the above embodiment, the AC power supply 1 is used, but the present invention is not limited to this, and a power supply such as a DC power supply may be used. When a DC power supply is used, circuits such as the rectifier circuit 21 are not required.

[0033] In the above embodiment, the inrush prevention resistor Rp and the current detection resistor Rd are inserted into different connection lines 9a and 9b, but the present invention is not limited to this, and they may be inserted into the same connection line 9a or 9b.

[0034] In the above embodiment, the current flowing through the connection line 9b is detected using the current detection resistor Rd and the voltage detection circuit 31, but the present invention is not limited to this and other current detection means such as a current detector may be used. [Industrial Applicability]

[0035] As described above in detail, the inrush current prevention circuit of the present invention can control the inrush current so that it does not exceed a predetermined value, even when multiple load devices are used, and can also control the load devices so that currents exceeding a certain value do not flow. [Explanation of symbols]

[0036] 1 AC power supply 2. Inrush current prevention main circuit 3. Inrush current control circuit 4 Load device 5 Protection circuit 6 Series Circuits 7 Voltage supply circuit 8 Time constant circuit 9a,9b connecting wire 21 Rectifier circuit 31 Voltage detection circuit 32,33 Differential amplifier circuit C1~C3 capacitors CM1 Comparator D1~D12 Diodes OP1, OP2 operational amplifiers Q1 Bipolar transistor Q2 MOS transistor R1~R41 Resistors Rd Current detection resistor RE1 Electromagnetic relay Rec coil Rp Inrush protection resistor

Claims

1. 1. An inrush current prevention circuit for preventing an inrush current from flowing from a power supply to a load device through a pair of connection lines including a first connection line and a second connection line, a first resistor that is an inrush prevention resistor that is inserted into the first connection line and reduces and flows a current at the start of the load device; A switch element connected in parallel with the first resistor; a current detector that detects a current value of a current flowing through the second connection line by using a second resistor inserted in the second connection line; a control circuit that controls the switching element to be turned on and off based on the current value detected by the current detector, the control circuit controls the switch element to be turned on when the current value is less than a predetermined reference current, and controls the switch element to be turned off when the current value is equal to or greater than the reference current; the control circuit controls the switch element to be turned on after a predetermined delay time using a time constant circuit including a capacitor and a resistor when the current value is less than a predetermined reference current; The control circuit includes: a first differential amplifier circuit that detects a differential voltage corresponding to a current flowing through the second resistor and outputs a first output voltage; a second differential amplifier circuit that detects a difference voltage between a first reference voltage at one end of the second resistor and a first output voltage from the first differential amplifier circuit based on a voltage at the other end of the second resistor, and outputs a second output voltage; a comparator that compares a second output voltage from the second differential amplifier circuit with a predetermined second reference voltage to output a control signal for controlling the on / off of the switch element. Inrush current prevention circuit.

2. The switch element is an electromagnetic relay.

2. The inrush current prevention circuit according to claim 1.

3. 3. The inrush current prevention circuit according to claim 1, further comprising a protection circuit connected in series with the first resistor and cut off when a current equal to or greater than a predetermined value flows.

4. 4. The inrush current prevention circuit according to claim 3, wherein the protection circuit is a thermal fuse.

5. 1. A method for controlling an inrush current prevention circuit that prevents an inrush current from flowing from a power supply to a load device through a pair of connection lines including a first connection line and a second connection line, comprising: The inrush current prevention circuit includes: a first resistor that is an inrush prevention resistor that is inserted into the first connection line and reduces and flows a current at the start of the load device; A switch element connected in parallel with the first resistor; a current detector that detects a current value of a current flowing through the second connection line by using a second resistor inserted in the second connection line; a control circuit that controls the switching element to be turned on and off based on the current value detected by the current detector, The control method includes a step of controlling the control circuit to turn on the switch element when the current value is less than a predetermined reference current, and to turn off the switch element when the current value is equal to or greater than the reference current, The step of controlling includes performing control such that, when the current value is less than a predetermined reference current, the control circuit turns on the switch element after a predetermined delay time using a time constant circuit including a capacitor and a resistor; The controlling step includes: a first differential amplifier circuit detecting a difference voltage corresponding to a current flowing through the second resistor and outputting a first output voltage; a second differential amplifier circuit detecting a difference voltage between a first reference voltage at one end of the second resistor and a first output voltage from the first differential amplifier circuit based on a voltage at the other end of the second resistor, and outputting a second output voltage; a comparator comparing a second output voltage from the second differential amplifier circuit with a predetermined second reference voltage to output a control signal for controlling the on / off of the switch element.

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