Inrush current prevention circuit

Abstract

To obtain a rush current prevention circuit which can be provided without being connected to an output side of a target voltage-applied device.SOLUTION: A rush current prevention circuit according to the present invention has a N channel type FET 2 connected to a positive terminal 111, a limit resistor 3 connected to the N channel type FET 2 in parallel, a smoothing capacitor 4 connected to the positive terminal 111 through the N channel type FET 2 and the limit resistor 3, a voltage detecting unit 5 for detecting that a voltage value of the smoothing capacitor 4 is a preset value V1 or higher, a light emitting unit 6 for emitting light, a light emission switching unit 7 for causing the light emitting unit 6 to emit light when the voltage detection unit 5 detects that the voltage value of the smoothing capacitor 4 is the preset value V1 or higher, and a photo diode 8 for receiving light emitted from the light emitting unit 6. If the photo diode 8 receives the light emitted from the light emitting unit 6, the photo diode 8 brings the N channel type FET 2 in its on-state.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This invention relates to an inrush current prevention circuit.

Background Art

[0002] Conventionally, an inrush current prevention circuit including an input switch section, a smoothing capacitor, a limiting resistor, and a relay switch has been known. The limiting resistor and the relay switch are connected in parallel with each other. The smoothing capacitor is connected to an input power supply device via the input switch section, the limiting resistor, and the relay switch. Immediately after the input switch section is turned on, current flows from the input power supply device through the limiting resistor to the smoothing capacitor, and the smoothing capacitor is charged. Thereby, an inrush current flowing from the input power supply device to the smoothing capacitor is prevented. A switching power supply device is connected to the smoothing capacitor, and the voltage of the smoothing capacitor is applied to the switching power supply device. After the value of the voltage applied to the switching power supply device reaches a preset value, the switching power supply device is driven. When the switching power supply device is driven, current flows through the relay coil and the relay switch is turned on. When the relay switch is turned on, current flows from the input power supply device through the relay switch to the smoothing capacitor. Thereby, the flow of current from the input power supply device through the limiting resistor to the smoothing capacitor is suppressed. As a result, the power consumption of the inrush current prevention circuit is reduced (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the configuration described in Patent Document 1, the relay coil is connected to the output side of the switching power supply. Therefore, a part of the inrush current prevention circuit must be connected to the output side of the device to which the voltage of the smoothing capacitor is applied. If it is not possible to connect the inrush current prevention circuit to the output side of the device to which the voltage is applied, there is a problem in that the inrush current prevention circuit cannot be installed.

[0005] This invention was made to solve the above-mentioned problems, and its purpose is to provide an inrush current prevention circuit that can be installed without being connected to the output side of a device to which voltage is applied. [Means for solving the problem]

[0006] The inrush current prevention circuit according to this invention comprises an N-channel FET connected to the positive terminal of an input power supply, a limiting resistor connected in parallel to the N-channel FET, a smoothing capacitor connected to the positive terminal via the N-channel FET and the limiting resistor, a voltage detection unit connected in parallel to the smoothing capacitor and detecting whether the voltage of the smoothing capacitor is greater than or equal to a preset value, a light-emitting unit that emits light, a light-emitting switching unit that causes the light-emitting unit to emit light when the voltage detection unit detects whether the voltage of the smoothing capacitor is greater than or equal to a preset value, and a photodiode that receives the light emitted from the light-emitting unit, thereby turning on the N-channel FET. Furthermore, the inrush current prevention circuit according to this invention further includes a detection delay unit that delays the detection by the voltage detection unit that the voltage value of the smoothing capacitor is greater than or equal to a preset value. Furthermore, in the inrush current prevention circuit according to this invention, the photodiode has its negative electrode connected to the positive terminal via an N-channel FET and a limiting resistor, and its positive electrode connected to the gate of the N-channel FET. [Effects of the Invention]

[0007] According to the inrush current prevention circuit of this invention, an inrush current prevention circuit can be installed without connecting the inrush current prevention circuit to the output side of the device to which the voltage is applied. [Brief explanation of the drawing]

[0008] [Figure 1] This is a circuit diagram showing an inrush current prevention circuit according to Embodiment 1. [Figure 2] Figure 1 is a timing chart showing the switching of the current path to the smoothing capacitor in the inrush current prevention circuit. [Modes for carrying out the invention]

[0009] Embodiment 1. Figure 1 is a circuit diagram showing an inrush current prevention circuit according to Embodiment 1. The inrush current prevention circuit according to Embodiment 1 comprises an input switch unit 1, an N-channel FET 2, a limiting resistor 3, a smoothing capacitor 4, a voltage detection unit 5, a light-emitting unit 6, a light-emitting switching unit 7, a photodiode 8, a detection delay unit 9, and a protection circuit unit 10.

[0010] The inrush current prevention circuit according to Embodiment 1 is positioned between the input power supply unit 11 and the voltage-to-apply device 12. Current is supplied from the input power supply unit 11 to the voltage-to-apply device 12 via the inrush current prevention circuit according to Embodiment 1. The inrush current prevention circuit according to Embodiment 1 prevents a momentary rising voltage from being applied to the voltage-to-apply device 12 when current is supplied from the input power supply unit 11 to the voltage-to-apply device 12.

[0011] The input power supply unit 11 has a positive terminal 111 and a negative terminal 112. The current output from the input power supply unit 11 is a direct current.

[0012] The voltage-applied device 12 has a positive terminal 121 and a negative terminal 122. The current input to the voltage-applied device 12 is a DC current. An example of the voltage-applied device 12 is a DC power supply. When the voltage-applied device 12 is a DC power supply, a DC current is supplied from the voltage-applied device 12 to a current-supplying device (not shown).

[0013] The input switch unit 1 is connected to the positive terminal 111 of the input power supply unit 11.

[0014] The N-channel FET 2 has a gate G, a drain D, and a source S. The N-channel FET 2 is connected to the positive terminal 111 of the input power supply unit 11. Specifically, the drain D of the N-channel FET 2 is connected to the positive terminal 111 of the input power supply unit 11 via the input switch unit 1.

[0015] The limiting resistor 3 is connected in parallel to the N-channel FET 2. Specifically, the limiting resistor 3 is connected to the drain D and source S of the N-channel FET 2.

[0016] The smoothing capacitor 4 has a first electrode 401 and a second electrode 402. The smoothing capacitor 4 is connected to the positive terminal 111 of the input power supply unit 11 via the input switch unit 1, the N-channel FET 2, and the limiting resistor 3. Specifically, the first electrode 401 of the smoothing capacitor 4 is connected to the positive terminal 111 of the input power supply unit 11 via the input switch unit 1, the N-channel FET 2, and the limiting resistor 3. The second electrode 402 of the smoothing capacitor 4 is connected to the negative terminal 112 of the input power supply unit 11. Therefore, current is supplied from the input power supply unit 11 to the smoothing capacitor 4 via the input switch unit 1, the N-channel FET 2, and the limiting resistor 3.

[0017] The first electrode 401 of the smoothing capacitor 4 is connected to the positive terminal 121 of the voltage application target device 12. The second electrode 402 of the smoothing capacitor 4 is connected to the negative terminal 122 of the voltage application target device 12. Therefore, the voltage of the smoothing capacitor 4 is applied to the voltage application target device 12.

[0018] The voltage detection unit 5 is connected in parallel to the smoothing capacitor 4. The voltage detection unit 5 detects that the value of the voltage of the smoothing capacitor 4 is equal to or greater than a preset value V1.

[0019] The voltage detection unit 5 includes a first resistor 501, a first Zener diode 502, a second Zener diode 503, a second resistor 504, and a third resistor 505.

[0020] The first resistor 501 is connected to the first electrode 401 of the smoothing capacitor 4. The third resistor 505 is connected to the second electrode 402 of the smoothing capacitor 4. The first resistor 501, the first Zener diode 502, the second Zener diode 503, the second resistor 504, and the third resistor 505 are connected in series in the order of the first resistor 501, the first Zener diode 502, the second Zener diode 503, the second resistor 504, and the third resistor 505.

[0021] When the value of the voltage of the smoothing capacitor 4 is equal to or greater than the value obtained by adding the Zener voltage value V2 of the first Zener diode 502 and the Zener voltage value V3 of the second Zener diode 503, a current flows through the first Zener diode 502 and the second Zener diode 503. Therefore, the value obtained by adding the Zener voltage value V2 of the first Zener diode 502 and the Zener voltage value V3 of the second Zener diode 503 becomes the preset value V1 detected by the voltage detection unit 5.

[0022] The light emitting unit 6 has a resistor 601 and a light emitting diode 602. The resistor 601 is connected to the positive terminal 111 of the input power supply device 11 via the input switch unit 1, the N-channel type FET 2, and the limiting resistor 3. The light emitting diode 602 is connected to the light emitting switching unit 7. The resistor 601 and the light emitting diode 602 are connected in series with each other. The value of the current supplied to the light emitting diode 602 is determined by the resistor 601.

[0023] The light emitting switching unit 7 is composed of a transistor. The light emitting switching unit 7 has a base B, an emitter E, and a collector C.

[0024] The base B of the light emitting switching unit 7 is connected to a portion between the second resistor 504 and the third resistor 505 in the voltage detection unit 5. The emitter E of the light emitting switching unit 7 is connected to the second electrode 402 of the smoothing capacitor 4.

[0025] When the value of the voltage of the smoothing capacitor 4 is greater than or equal to the value obtained by adding the zener voltage value V2 of the first zener diode 502 and the zener voltage value V3 of the second zener diode 503, a voltage is applied to the third resistor 505. By applying a voltage to the third resistor 505, the same voltage as the voltage applied to the third resistor 505 is applied between the base B and the emitter E in the light emitting switching unit 7.

[0026] The value of the voltage applied to the third resistor 505 is a voltage value sufficient to turn on the light emitting switching unit 7. Therefore, by applying the same voltage as the voltage applied to the third resistor 505 between the base B and the emitter E in the light emitting switching unit 7, the light emitting switching unit 7 is turned on. When the light emitting switching unit 7 is turned on, the collector C and the emitter E in the light emitting switching unit 7 are electrically connected to each other.

[0027] The collector C of the light-emitting switching unit 7 is connected to the light-emitting diode 602 of the light-emitting unit 6. Therefore, when the light-emitting switching unit 7 is turned on, current is supplied from the input power supply unit 11 to the light-emitting diode 602, and the light-emitting diode 602 emits light.

[0028] In other words, when the voltage detection unit 5 detects that the voltage value of the smoothing capacitor 4 is equal to or greater than a preset value V1, the light-emitting switching unit 7 causes the light-emitting unit 6 to emit light.

[0029] The photodiode 8 is positioned to receive light emitted from the light-emitting unit 6. The photodiode 8 has a positive electrode and a negative electrode. The positive electrode of the photodiode 8 is connected to the gate G of the N-channel FET 2. The negative electrode of the photodiode 8 is connected to the positive terminal 111 of the input power supply unit 11 via the input switch unit 1, the N-channel FET 2, and the limiting resistor 3.

[0030] When the photodiode 8 receives light emitted from the light-emitting unit 6, the voltage at the positive electrode of the photodiode 8 becomes higher than the voltage at the negative electrode of the photodiode 8. The voltage value generated between the positive and negative electrodes of the photodiode 8 when the photodiode 8 receives light emitted from the light-emitting unit 6 is a voltage value sufficient to turn on the N-channel FET 2. Therefore, when the photodiode 8 receives light emitted from the light-emitting unit 6, the photodiode 8 turns on the N-channel FET 2.

[0031] The detection delay unit 9 includes a capacitor 901 and a resistor 902. The capacitor 901 and the resistor 902 are connected in parallel with each other. The capacitor 901 is connected to the portion between the first Zener diode 502 and the second Zener diode 503. The capacitor 901 is also connected to the second electrode 402 of the smoothing capacitor 4.

[0032] When the voltage of the smoothing capacitor 4 becomes equal to or greater than a preset value V1, current flows through the first Zener diode 502 and the second Zener diode 503. The current flowing through the first Zener diode 502 and the second Zener diode 503 causes current to flow through the first resistor 501, the second resistor 504, and the third resistor 505. Capacitor 901 delays the flow of current through the second resistor 504 and the third resistor 505. The delay in the flow of current through the third resistor 505 causes the detection delay unit 9 to delay the detection by the voltage detection unit 5 that the voltage of the smoothing capacitor 4 is equal to or greater than a preset value V1.

[0033] Resistor 902 discharges capacitor 901 when the voltage across smoothing capacitor 4 falls below a preset value V1.

[0034] The protection circuit section 10 includes a diode 101 and a resistor 102. The diode 101 and the resistor 102 are connected in parallel with each other.

[0035] The positive electrode of diode 101 is connected to the gate G of N-channel FET 2. The negative electrode of diode 101 is connected to the positive terminal 111 of input power supply 11 via input switch unit 1, N-channel FET 2, and limiting resistor 3. This prevents the voltage applied to the source S of the N-channel FET 2 from exceeding the voltage applied to the gate G.

[0036] Resistor 102 makes the gate voltage G of the N-channel FET2 match the source voltage S when the photodiode 8 is not turned on the N-channel FET2.

[0037] Next, the operation of the inrush current prevention circuit according to Embodiment 1 will be described. Figure 2 is a timing chart showing the switching of the current path to the smoothing capacitor in the inrush current prevention circuit of Figure 1. Figure 2 shows the relationship between the time t1 when the input switch unit 1 is switched from off to on, the voltage of the smoothing capacitor 4, the time t2 when the N-channel type FET 2 is switched from off to on, and the current path from the input power supply unit 11 to the smoothing capacitor 4.

[0038] When the input switch unit 1 is turned on at time t1, current is supplied from the input power supply unit 11 to the smoothing capacitor 4 via the limiting resistor 3. This increases the voltage across the smoothing capacitor 4 and prevents inrush current from flowing from the input power supply unit 11 to the smoothing capacitor 4.

[0039] As the voltage across the smoothing capacitor 4 continues to increase, at time t2, the voltage of the smoothing capacitor 4 becomes equal to or greater than a preset value V1. When the voltage of the smoothing capacitor 4 becomes equal to or greater than the preset value V1, the voltage detection unit 5 detects that the voltage of the smoothing capacitor 4 is equal to or greater than the preset value V1.

[0040] When the voltage detection unit 5 detects that the voltage value of the smoothing capacitor 4 is equal to or greater than a preset value V1, the light-emitting switching unit 7 causes the light-emitting unit 6 to emit light.

[0041] When the light-emitting part 6 emits light, the photodiode 8 receives the light emitted from the light-emitting part 6. As a result, the photodiode 8 turns on the N-channel type FET 2.

[0042] When the N-channel FET 2 is turned on, current is supplied from the input power supply 11 to the smoothing capacitor 4 via the N-channel FET 2. This suppresses the flow of current from the input power supply 11 to the smoothing capacitor 4 via the limiting resistor 3. As a result, the power consumption of the inrush current prevention circuit is reduced.

[0043] As described above, the inrush current prevention circuit according to Embodiment 1 comprises an N-channel FET 2, a limiting resistor 3, a smoothing capacitor 4, a voltage detection unit 5, a light-emitting unit 6, a light-emitting switching unit 7, and a photodiode 8. The N-channel FET 2 is connected to the positive terminal 111 of the input power supply unit 11. The limiting resistor 3 is connected in parallel to the N-channel FET 2. The smoothing capacitor 4 is connected to the positive terminal 111 of the input power supply unit 11 via the N-channel FET 2 and the limiting resistor 3. The voltage detection unit 5 is connected in parallel to the smoothing capacitor 4 and detects whether the voltage value of the smoothing capacitor 4 is equal to or greater than a preset value V1. The light-emitting unit 6 emits light. The light-emitting switching unit 7 causes the light-emitting unit 6 to emit light when the voltage detection unit 5 detects that the voltage value of the smoothing capacitor 4 is equal to or greater than a preset value V1. The photodiode 8 receives the light emitted from the light-emitting unit 6. The photodiode 8 receives light emitted from the light-emitting unit 6, which in turn turns on the N-channel FET 2. With this configuration, when the voltage value of the smoothing capacitor 4 is greater than or equal to a preset value V1, the N-channel FET 2 is turned on, and current is supplied from the input power supply unit 11 to the smoothing capacitor 4 via the N-channel FET 2. This makes it possible to install an inrush current prevention circuit without connecting an inrush current prevention circuit to the output side of the voltage-applied device 12.

[0044] Furthermore, the inrush current prevention circuit according to Embodiment 1 includes a detection delay unit 9. The detection delay unit 9 delays the detection by the voltage detection unit 5 that the voltage value of the smoothing capacitor 4 is equal to or greater than a preset value V1. With this configuration, the voltage detection unit 5 can more accurately detect that the voltage value of the smoothing capacitor 4 is equal to or greater than a preset value V1.

[0045] Furthermore, in the inrush current prevention circuit according to Embodiment 1, the photodiode 8 has its negative electrode connected to the positive terminal 111 of the input power supply unit 11 via the N-channel FET 2 and limiting resistor 3, and its positive electrode connected to the gate G of the N-channel FET 2. With this configuration, there is no need to install a new power supply unit to apply a voltage between the gate G and source S of the N-channel FET 2. This simplifies the configuration of the inrush current prevention circuit.

[0046] In the inrush current prevention circuit according to Embodiment 1, the configuration of the inrush current prevention circuit in which the light-emitting switching unit 7 is composed of a transistor was described. However, the light-emitting switching unit 7 is not limited to a transistor; any component that can cause the light-emitting unit 6 to emit light when the voltage detection unit 5 detects that the voltage value of the smoothing capacitor 4 is equal to or greater than a preset value V1 is acceptable.

[0047] Furthermore, in the inrush current prevention circuit according to Embodiment 1, a configuration in which the detection delay unit 9 has a resistor 902 has been described. However, the detection delay unit 9 may also be configured in which it does not have a resistor 902.

[0048] Furthermore, in the inrush current prevention circuit according to Embodiment 1, a configuration in which the light-emitting section 6 has a light-emitting diode 602 was described. However, the light-emitting section 6 is not limited to a light-emitting diode 602; it may have any component that emits light when current is supplied.

[0049] Although a preferred embodiment 1 of the inrush current prevention circuit has been described above, the invention is not limited to the inrush current prevention circuit of embodiment 1 described above. Various modifications and transformations can be made to the inrush current prevention circuit of embodiment 1 described above without departing from the scope of the claims. [Explanation of symbols]

[0050] 1 Input switch section, 2 N-channel FET, 3 Limiting resistor, 4 Smoothing capacitor, 5 Voltage detection section, 6 Light-emitting section, 7 Light-emitting switching section, 8 Photodiode, 9 Detection delay section, 10 Protection circuit section, 11 Input power supply unit, 12 Voltage application target device, 101 Diode, 102 Resistor, 111 Positive terminal, 112 Negative terminal, 121 Positive terminal, 122 Negative terminal, 401 First electrode, 402 Second electrode, 501 First resistor, 502 First Zener diode, 503 Second Zener diode, 504 Second resistor, 505 Third resistor, 601 Resistor, 602 Light-emitting diode, 901 Capacitor, 902 Resistor.

Claims

1. An N-channel FET (2) connected to the positive terminal (111) of the input power supply unit (11), A limiting resistor (3) connected in parallel to the N-channel FET (2), A smoothing capacitor (4) connected to the positive terminal (111) via the N-channel FET (2) and the limiting resistor (3), A voltage detection unit (5) is connected in parallel to the smoothing capacitor (4) and detects whether the voltage value of the smoothing capacitor (4) is equal to or greater than a preset value. A light-emitting part (6) and A light-emitting switching unit (7) causes the light-emitting unit (6) to emit light when the voltage detection unit (5) detects that the voltage value of the smoothing capacitor (4) is equal to or greater than the preset value, A photodiode (8) that receives light emitted from the light-emitting part (6), Equipped with, An inrush current prevention circuit in which the photodiode (8) receives light emitted from the light-emitting part (6), causing the photodiode (8) to turn on the N-channel type FET (2).

2. The inrush current prevention circuit according to claim 1, further comprising a detection delay unit (9) that delays the detection by the voltage detection unit (5) that the voltage value of the smoothing capacitor (4) is equal to or greater than the preset value.

3. The inrush current prevention circuit according to claim 1 or claim 2, wherein the photodiode (8) has a negative electrode connected to the positive electrode terminal (111) via the N-channel FET (2) and the limiting resistor (3), and the positive electrode is connected to the gate of the N-channel FET (2).

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