Inrush current protection device

Abstract

A current detection element (R1) detects a current flowing through a target circuit. A switch (SW1) controls the magnitude of the current flowing through the target circuit. When the current detected by the current detection element (R1) exceeds a first threshold, a control circuit (21) controls the switch (SW1) so as to reduce the current flowing through the target circuit. When the current detected by the current detection element (R1) exceeds a second threshold higher than the first threshold, a control circuit (22) controls the switch (SW1) so as to reduce the current flowing through the target circuit. The control circuit (22) has an operating speed higher than the operating speed of the control circuit (21).

Description

Inrush Current Protection Device

[0001] The present disclosure relates to an inrush current protection device.

[0002] When a failure such as a short circuit occurs in a load device or the like, an inrush current may be generated or a large current may continue to flow, which may damage the power supply or other circuits as a result. Therefore, it is required to protect electric circuits from inrush current or overcurrent.

[0003] For example, Patent Document 1 discloses a DC-DC converter having an overcurrent protection function.

[0004] Japanese Unexamined Patent Publication No. Hei 9-308239

[0005] It is desirable for an inrush current protection device to stop the current flowing through a target circuit as quickly as possible when an inrush current occurs. However, if the protection device is configured to stop the current early by, for example, setting a lower threshold, the protection device may operate even in a steady state where no inrush current occurs, and there is a risk that the protection device will oscillate by repeating between an operating state and a non-operating state. Therefore, it is required to protect a target circuit faster than conventional techniques when an inrush current occurs while preventing oscillation.

[0006] An object of the present disclosure is to provide an inrush current protection device capable of protecting a target circuit faster than conventional techniques when an inrush current occurs while preventing oscillation.

[0007] An inrush current protection device according to one aspect of the present disclosure includes: a current detection element that detects a current flowing through a target circuit; a first switch that controls the magnitude of the current flowing through the target circuit; a first control circuit that controls the first switch to reduce the current flowing through the target circuit when the current detected by the current detection element exceeds a first threshold; and a second control circuit that controls the first switch to reduce the current flowing through the target circuit when the current detected by the current detection element exceeds a second threshold that is higher than the first threshold, wherein the second control circuit has an operating speed higher than that of the first control circuit.

[0008] This allows for faster protection of the target circuit when an inrush current occurs, while simultaneously preventing oscillation.

[0009] According to an inrush current protection device relating to one aspect of the present disclosure, the first control circuit comprises a first operational amplifier, the second control circuit comprises a second operational amplifier, and the second operational amplifier has a higher operating speed than the operating speed of the first operational amplifier.

[0010] This makes it possible to provide a second control circuit having a higher operating speed than the first control circuit.

[0011] According to an inrush current protection device relating to one aspect of the present disclosure, the first control circuit comprises an operational amplifier, and the second control circuit comprises a second switch and a Zener diode, wherein the second switch and the Zener diode have an operating speed higher than the operating speed of the operational amplifier.

[0012] This makes it possible to provide a second control circuit having a higher operating speed than the first control circuit.

[0013] According to an inrush current protection device relating to one aspect of the present disclosure, the first control circuit comprises an operational amplifier, the second control circuit comprises a shunt regulator, and the shunt regulator has an operating speed higher than the operating speed of the operational amplifier.

[0014] This makes it possible to provide a second control circuit having a higher operating speed than the first control circuit.

[0015] An inrush current protection device relating to one aspect of this disclosure can protect the target circuit at a faster speed than conventional devices when an inrush current occurs, while preventing oscillation.

[0016] This is a schematic circuit diagram showing an example configuration of the inrush current protection device 2 according to the embodiment. This is a schematic circuit diagram showing an example configuration of the inrush current protection device 2A according to a comparative example. This is a timing chart showing the operation of the inrush current protection device 2A in Figure 2. This is a timing chart showing the operation of the inrush current protection device 2 in Figure 1. This is a graph showing the operation of the inrush current protection device 2A in Figure 2. This is a graph showing the operation of the inrush current protection device 2 in Figure 1. This is a schematic circuit diagram showing an example configuration of the inrush current protection device 2B according to the first modified example of the embodiment. This is a timing chart showing the operation of the inrush current protection device 2B in Figure 7. This is a schematic circuit diagram showing an example configuration of the inrush current protection device 2C according to the second modified example of the embodiment. This is a timing chart showing the operation of the inrush current protection device 2C in Figure 9.

[0017] Hereinafter, embodiments relating to one aspect of this disclosure will be described with reference to the drawings. In each drawing, the same reference numerals indicate the same components.

[0018] [Configuration of the Embodiment] Figure 1 is a schematic circuit diagram showing an example configuration of the inrush current protection device 2 according to the embodiment. The inrush current protection device 2 is inserted between the power supply device 1 and the load device 3. The power supply device 1 is, for example, a DC power supply, and the load device 3 operates by receiving DC power from the power supply device 1. If an inrush current or overcurrent occurs due to a failure in the load device 3, for example a short circuit, the inrush current protection device 2 reduces or stops the power supply from the power supply device 1 to the load device 3.

[0019] The inrush current protection device comprises a current detection element R1, a resistor R2, a switch SW1, a first control circuit 21, and a second control circuit 22.

[0020] The current detection element R1 detects the current I1 flowing through the target circuit. Here, the "target circuit" is any circuit that is protected by the inrush current protection device 2, and includes the power supply unit 1, the load unit 3, and the inrush current protection device 2 itself. The current detection element R1 is, for example, a current detection resistor inserted in series with the power bus between the power supply unit 1 and the load unit 3.

[0021] Switch SW1 is inserted in series with the power bus between the power supply unit 1 and the load device 3 to control the magnitude of the current I1 flowing through the target circuit. Switch SW1 can be, for example, a MOSFET, a transistor, or an IGBT. The following describes the case where switch SW1 is an n-channel MOSFET. Switch SW1 has a gate threshold voltage Vth1.

[0022] The control circuit 21 controls switch SW1 to reduce the current I1 flowing through the target circuit when the current I1 detected by the current detection element R1 exceeds a first threshold. The control circuit 21 includes operational amplifiers CMP11 and CMP12, a reference voltage source E11, resistors R11 to R16, and a capacitor C11. The resistors R11 to R14 and the operational amplifier CMP11 constitute a differential amplifier circuit and convert the current I1 flowing through the current detection element R1 into a voltage V1. The reference voltage source E11 supplies a reference voltage Vref1 that indicates a first threshold. When the voltage V1 exceeds the reference voltage Vref1, the operational amplifier CMP12 outputs a voltage V2 that gradually decreases according to the magnitude of the voltage V1. The operational amplifier CMP12, together with resistors R15 to R16 and the capacitor C11, constitutes an integrating circuit and operates with a predetermined time constant.

[0023] The control circuit 22 controls switch SW1 to reduce the current I1 flowing through the target circuit when the current I1 detected by the current detection element R1 exceeds a second threshold that is higher than the first threshold. The control circuit 22 includes a reference voltage source E12, an operational amplifier CMP13, and a diode D11. The reference voltage source E12 supplies a reference voltage Vref2 that indicates the second threshold. The operational amplifier CMP13 outputs a voltage V3 that gradually decreases in proportion to the magnitude of voltage V1 when the voltage V1 exceeds the reference voltage Vref2. Diode D11 is connected so that current flows from the gate of switch SW1 to the output terminal of operational amplifier CMP13. As a result, when the voltage V3 becomes small, the charge at the gate of switch SW1 is drawn out through diode D11, and switch SW1 is turned off.

[0024] In the example shown in Figure 1, the operational amplifier CMP12 of control circuit 21 operates with a predetermined time constant by being connected to resistors R15 to R16 and capacitor C11. On the other hand, the operational amplifier CMP13 of control circuit 22 operates faster than the operational amplifier CMP12 because it is not directly connected to the resistors and capacitor. Therefore, control circuit 22 has a higher operating speed than control circuit 21.

[0025] Both control circuits 21 and 22 are connected to the gate of switch SW1 via resistor R2.

[0026] The following parameters will be used for explanation purposes.

[0027] Power supply voltage of power supply unit 1: 24V; R1: 0.5mΩ; R11: 10kΩ; R12: 1MΩ; R13: 10kΩ; R14: 1MΩ; Vref1: 0.6V; Vref2: 2.5V

[0028] [Operation of the Embodiment] Figure 2 is a schematic circuit diagram showing an example configuration of an inrush current protection device 2A according to a comparative example. The inrush current protection device 2A is configured in the same way as the inrush current protection device 2 in Figure 1, except that the control circuit 22 has been removed.

[0029] Figure 3 is a timing chart showing the operation of the inrush current protection device 2A in Figure 2.

[0030] For example, when a current I1 of 1A flows through the power bus, a voltage of 0.5mV is generated across the resistor R1. This voltage is amplified 100 times (1 × 10⁻¹⁰) by a differential amplifier circuit including the operational amplifier CMP11. ６ / 10 x 10 ３ It is amplified to ). Therefore, voltage V1 becomes 50mV. As long as voltage V1 does not exceed the reference voltage Vref1 of 0.6V, voltage V2 is higher than the gate threshold voltage Vth1 of switch SW1, and therefore switch SW1 is ON.

[0031] At time t0, a short circuit occurs in the load device 3, and the current I1 begins to increase. In accordance with the increase in current I1, the voltage V1 also begins to increase.

[0032] At time t1, when a current I1 of 12A flows, the voltage V1 reaches 0.6V and the voltage V2 begins to decrease.

[0033] Subsequently, at time t2, the voltage V2 becomes lower than the gate threshold voltage Vth1 of switch SW1, and switch SW1 is turned off. Once switch SW1 is turned off, the current I1 gradually decreases, and from time t3 onward, the current I1 is maintained at 12A.

[0034] The control circuit 21 is equipped with resistors R15 to R16 and a capacitor C11 for stable operation. However, due to the influence of resistors R15 to R16 and capacitor C11, a relatively long time (e.g., several hundred microseconds) is taken from the time the control circuit 21 starts the operation to turn off switch SW1 (time t1) until switch SW1 is actually turned off (time t2). During the time t1 to t2, the current I1 continues to increase, reaching 100A in the example shown in Figure 3. In this case, the continued flow of a large current may damage the power supply 1 or other circuits. Therefore, it is necessary to protect the target circuit faster than the inrush current protection device 2A in Figure 2 when an inrush current occurs.

[0035] Figure 4 is a timing chart showing the operation of the inrush current protection device 2 in Figure 1.

[0036] In the initial state, both voltages V2 and V3 are higher than the gate threshold voltage Vth1 of switch SW1, and therefore switch SW1 is ON.

[0037] At time t10, a short circuit occurs in the load device 3, and the current I1 begins to increase. In accordance with the increase in current I1, the voltage V1 also begins to increase.

[0038] At time t11, when a current I1 of 12A flows, the voltage V1 reaches 0.6V and the voltage V2 begins to decrease.

[0039] At time t12, when a current I1 of 50A flows, the voltage V1 reaches 2.5V, and the voltage V3 begins to decrease.

[0040] Thereafter, at time t13, voltage V3 becomes lower than the gate threshold voltage Vt1h1 of switch SW1, and switch SW1 is turned off. When switch SW1 is turned off, current I1 gradually decreases, and after time t14, current I1 is maintained at 12A.

[0041] FIG. 5 is a graph showing the operation of the inrush current protection device 2A of FIG. 2. FIG. 6 is a graph showing the operation of the inrush current protection device 2 of FIG. 1. FIGS. 5 and 6 show temporal changes of the gate-source voltage Vgs1 of the switching element SW5 and the current I1. Referring to FIG. 5, it takes 200 microseconds from when the current I1 starts increasing to when it decreases and returns to a steady state. On the other hand, referring to FIG. 6, it takes 40 microseconds from when the current I1 starts increasing to when it decreases and returns to a steady state. According to the inrush current protection device 2 according to the embodiment, by providing the additional control circuit 22, the switch SW1 operates at a higher speed, and the duration for which a large current flows can be shortened.

[0042] [Effects of the Embodiment] According to the inrush current protection device 2 according to the embodiment, by providing the additional control circuit 22 having an operation speed higher than that of the control circuit 21, when an inrush current occurs, the switch SW1 can be turned off faster than in the case of a comparative example.

[0043] According to the inrush current protection device 2 according to the embodiment, the additional control circuit 22 uses a reference voltage Vref2 higher than the reference voltage Vref1 of the control circuit 21. On the other hand, in order to stop the current I1 at an early stage, it is not necessary to reduce the reference voltage Vref1 of the control circuit 21. Therefore, a reduction in the threshold does not induce oscillation in which the protection device repeatedly switches between an operating state and a non-operating state in a steady state where no inrush current occurs.

[0044] According to the inrush current protection device 2 according to the embodiment, both overcurrent protection in a steady state and high-speed inrush current protection can be achieved at the same time.

[0045] As described above, according to the inrush current protection device 2 according to the embodiment, while preventing oscillation, when an inrush current occurs, the target circuit can be protected faster than in the conventional art.

[0046] [Modification of Embodiment] The inrush current protection device according to the embodiment may include another control circuit instead of the control circuit 22 including the operational amplifier CMP133.

[0047] FIG. 7 is a circuit diagram schematically showing a configuration example of an inrush current protection device 2B according to a first modification of the embodiment. The inrush current protection device 2B includes a control circuit 22B instead of the control circuit 22 in FIG. 1.

[0048] The control circuit 22B controls the switch SW1 to reduce the current I1 flowing through the target circuit when the current I1 detected by the current detection element R1 exceeds a second threshold. The control circuit 22B includes a Zener diode ZD11, a resistor R17, and a switch SW2. The cathode of the Zener diode ZD11 is connected to the output terminal of the operational amplifier CMP11 (that is, the node of the voltage V1), and the anode of the Zener diode ZD11 is connected to the control terminal of the switch SW2 via the resistor R17. The breakdown voltage of the Zener diode ZD11 corresponds to the second threshold. The switch SW2 is, for example, an n-channel MOSFET. The switch SW2 has a gate threshold voltage Vth2. When the voltage V1 exceeds the breakdown voltage of the Zener diode ZD11, the gate-source voltage Vgs2 of the switch SW2 starts to increase, and when the gate-source voltage Vgs2 exceeds the gate threshold voltage Vth2, the switch SW2 is turned on. Accordingly, the electric charge at the gate of the switch SW1 is drawn out through the switch SW2, and the switch SW1 is turned off.

[0049] The switch SW2 and the Zener diode ZD11 operate faster than the operational amplifier CMP12. Therefore, the control circuit 22B has an operation speed higher than that of the control circuit 21.

[0050] Hereinafter, for description, the breakdown voltage of the Zener diode ZD11 is set to 2.5 V.

[0051] FIG. 8 is a timing chart showing the operation of the inrush current protection device 2B in FIG. 7.

[0052] In the initial state, voltage V1 is lower than the breakdown voltage of the Zener diode ZD11, and voltage V2 is higher than the gate threshold voltage Vth1 of switch SW1; therefore, switch SW1 is ON.

[0053] At time t20, a short circuit occurs in the load device 3, and the current I1 begins to increase. In accordance with the increase in current I1, the voltage V1 also begins to increase.

[0054] At time t21, when a current I1 of 12A flows, the voltage V1 reaches 0.6V and the voltage V2 begins to decrease.

[0055] At time t22, when a current I1 of 50A flows, the voltage V1 reaches 2.5V, and the gate-source voltage Vgs2 of switch SW2 begins to increase. Furthermore, when the gate-source voltage Vgs2 exceeds the gate threshold voltage Vth2, switch SW2 is turned on, and the voltage V2 decreases further.

[0056] Subsequently, at time t23, the voltage V2 becomes lower than the gate threshold voltage Vt2h1 of switch SW1, and switch SW1 is turned off. Once switch SW1 is turned off, the current I1 gradually decreases, and from time t24 onward, the current I1 is maintained at 12A.

[0057] According to the inrush current protection device 2B in Figure 7, similar to the inrush current protection device 2 in Figure 1, it is possible to protect the target circuit at a faster speed than conventional devices when an inrush current occurs, while preventing oscillation.

[0058] Figure 9 is a schematic circuit diagram showing an example of the configuration of an inrush current protection device 2C according to a second modified embodiment. The inrush current protection device 2C includes a control circuit 22C instead of the control circuit 22 in Figure 1.

[0059] The control circuit 22C controls switch SW1 to reduce the current I1 flowing through the target circuit when the current I1 detected by the current sensing element R1 exceeds a second threshold. The control circuit 22C is a shunt regulator. The anode of the control circuit 22C is grounded, the cathode of the control circuit 22C is connected to the gate of switch SW1 via resistor R2, and a voltage V1 is applied to the reference terminal of the control circuit 22C. The voltage applied to the reference terminal when the control circuit 22C is turned on corresponds to the second threshold. When the voltage V1 exceeds the threshold of the control circuit 22C, the control circuit 22C is turned on. As a result, the charge on the gate of switch SW1 is drawn out via switch SW2, and switch SW1 is turned off.

[0060] The shunt regulator operates faster than the operational amplifier CMP12. Therefore, the control circuit 22C has a higher operating speed than the control circuit 21.

[0061] For the purposes of this explanation, the voltage at the reference terminal of the control circuit 22C will be denoted as "V4". However, voltage V4 is the same as voltage V1.

[0062] Figure 10 is a timing chart showing the operation of the inrush current protection device 2C shown in Figure 9.

[0063] In the initial state, voltage V2 is higher than the gate threshold voltage Vth1 of switch SW1, and voltage V4 is lower than the threshold voltage of control circuit 22C; therefore, switch SW1 is ON.

[0064] At time t30, a short circuit occurs in the load device 3, and the current I1 begins to increase. In accordance with the increase in current I1, the voltage V1 also begins to increase.

[0065] At time t31, when a current I1 of 12A flows, the voltage V1 reaches 0.6V and the voltage V2 begins to decrease.

[0066] At time t32, when a current I1 of 50A flows, the voltage V4 reaches 2.5V, and the control circuit 22C is turned on. At this time, the voltage V2 drops to the gate threshold voltage Vt3h1 of switch SW1.

[0067] Subsequently, the voltage V2 becomes lower than the gate threshold voltage Vt3h1 of switch SW1, and switch SW1 is turned off. Once switch SW1 is turned off, the current I1 gradually decreases, and after time t33, the current I1 is maintained at 12A.

[0068] According to the inrush current protection device 2C in Figure 9, similar to the inrush current protection device 2 in Figure 1, it is possible to protect the target circuit at a faster speed than conventional devices when an inrush current occurs, while preventing oscillation.

[0069] [Summary] The inrush current protection devices relating to each aspect of this disclosure may be expressed as follows:

[0070] The inrush current protection device 2 according to the first aspect of this disclosure comprises a current detection element R1, a first switch SW1, a first control circuit 21, and second control circuits 22, 22B, 22C. The current detection element R1 detects the current flowing through the target circuit. The first switch SW1 controls the magnitude of the current flowing through the target circuit. The first control circuit 21 controls the first switch SW1 to reduce the current flowing through the circuit when the current detected by the current detection element R1 exceeds a first threshold. The second control circuits 22, 22B, 22C control the first switch SW1 to reduce the current flowing through the circuit when the current detected by the current detection element R1 exceeds a second threshold that is higher than the first threshold. The second control circuits 22, 22B, 22C have a higher operating speed than the first control circuit 21.

[0071] According to the inrush current protection device 2 relating to the second aspect of this disclosure, the first control circuit 21 may include a first operational amplifier CMP 12, and the second control circuit 22 may include a second operational amplifier CMP 13. In this case, the second operational amplifier CMP 13 has a higher operating speed than the first operational amplifier CMP 12.

[0072] According to the inrush current protection device 2C relating to the third aspect of this disclosure, the first control circuit 21 may include an operational amplifier CMP 12, and the second control circuit 22 may include a second switch and a Zener diode. In this case, the second switch SW2 and the Zener diode ZD 11 have a higher operating speed than the operating speed of the operational amplifier CMP 12.

[0073] According to the inrush current protection device 2D relating to the fourth aspect of this disclosure, the first control circuit 21 may include an operational amplifier CMP 12, and the second control circuit 22 may include a shunt regulator. In this case, the shunt regulator has an operating speed higher than that of the operational amplifier CMP 12.

[0074] An inrush current protection device relating to one aspect of this disclosure is applicable to protecting power supplies, load devices, and other circuits (e.g., the inrush current protection device itself) from inrush currents and overcurrents.

[0075] 1 Power supply unit 2, 2B, 2C Inrush current protection device 3 Load device 21, 22, 22B, 22C Control circuit C11 Capacitor CMP11~CMP13 Operational amplifier D11 Diode E11, E12 Reference voltage source R1 Current sensing element R2, R11~R17 Resistor SW1, SW2 Switch ZD11 Zener diode

Claims

1. An inrush current protection device comprising: a current detection element for detecting a current flowing through a target circuit; a first switch for controlling the magnitude of the current flowing through the target circuit; a first control circuit for controlling the first switch to reduce the current flowing through the target circuit when the current detected by the current detection element exceeds a first threshold; and a second control circuit for controlling the first switch to reduce the current flowing through the target circuit when the current detected by the current detection element exceeds a second threshold higher than the first threshold, wherein the second control circuit has a higher operating speed than the first control circuit.

2. The inrush current protection device according to claim 1, wherein the first control circuit comprises a first operational amplifier, the second control circuit comprises a second operational amplifier, and the second operational amplifier has an operating speed higher than the operating speed of the first operational amplifier.

3. The inrush current protection device according to claim 1, wherein the first control circuit comprises an operational amplifier, and the second control circuit comprises a second switch and a Zener diode, wherein the second switch and the Zener diode have an operating speed higher than the operating speed of the operational amplifier.

4. The inrush current protection device according to claim 1, wherein the first control circuit comprises an operational amplifier, the second control circuit comprises a shunt regulator, and the shunt regulator has an operating speed higher than the operating speed of the operational amplifier.

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