Input protection circuit

Abstract

To provide an input protection circuit capable of suppressing inrush current as well as reducing the path resistance during a measurement.SOLUTION: An input protection circuit 2 is provided between a protected circuit 13 and a measurement target 11. An overcurrent protection circuit 9 is connected in parallel to a current limiting resistor 5 constituting the input protection circuit 2. The overcurrent protection circuit 9 becomes a normal state in which a first resistance value RNORMAL remains the same in a case where a value of current flowing through an internal resistor 10 having a first resistance value RNORMAL lower than a resistance value Rs of the current limiting resistor 5 is less than a predetermined threshold value, and becomes a high resistance state in which a resistance value of the internal resistor 10 transitions to a second resistance value higher than the first resistance value RNORMAL in a case where a value of current flowing through the internal resistor 10 is equal to or greater than the predetermined threshold value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an input protection circuit.

Background Art

[0002] Conventionally, a measuring device (for example, a battery tester) for measuring the internal impedance of a measurement target has a generation circuit and a detection circuit for impedance measurement, and each is individually connected to the measurement target (for example, a battery). In such a measuring device, it is necessary to protect the generation circuit and the detection circuit from the inrush current generated when, for example, a battery is connected to the device as the measurement target. Therefore, a technique of providing an input protection circuit (a circuit including a resistor and an overvoltage protection diode) between the generation circuit or the detection circuit and the measurement target is known (see Patent Document 1 below).

[0003] Hereinafter, taking a battery tester as an example of the measuring device, the configuration of the measuring device will be described with reference to FIGS. 3 and 4. The battery tester 100 has a generation circuit 110 for supplying an alternating current required for four-terminal alternating current resistance measurement and a detection circuit 120 for detecting an alternating voltage. A battery 111 as a measurement target is connected to the generation circuit 110 via a coupling capacitor 112, and a battery 111 as a measurement target is connected to the detection circuit 120 via a coupling capacitor 113.

[0004] The coupling capacitor 112 has a function of protecting the generation circuit 110 from the battery voltage of the battery 111 as the measurement target, and the coupling capacitor 113 has a function of protecting the detection circuit 120 from the battery voltage of the battery 111 as the measurement target. Although details will be described later, a resistor and an overvoltage protection diode are connected in series to these coupling capacitors 112 and 113, and the coupling capacitors, resistors, and overvoltage protection diodes constitute an input protection circuit. Note that the battery voltage is a direct current voltage and is set to a level that is not allowed to be directly applied to the generation circuit 110 and the detection circuit 120.

[0005] Here, when the battery 111 is connected to the generation circuit 110, an inrush current i flows into the input protection circuit 115 as shown in FIG. 4. t Let the peak current value of the inrush current i be Ipeak. Then, Ipeak = (V t - Vz) / Rs (see FIG. 4). Here, V BAT is the battery voltage of the battery 111, and R BAT is the internal impedance of the battery 111. In the detection circuit, an AC voltage V (= internal impedance R BAT × measured current I) is detected, and based on the amplitude and phase of the detected AC voltage V and the amplitude and phase (known) of the measured current I, the internal impedance R BAT of the battery 111 is calculated. Rs is the resistance value of the resistor 140, and Vz is the voltage limited to that level or lower across both ends due to the action of the overvoltage protection diode 150. Note that Vz is at a level acceptable to the subsequent protected circuit (generation circuit 110 or detection circuit 120), and the protected circuit 110 (120) is protected by this voltage limitation. BAT

[0006] The inrush current i t charges the coupling capacitor 130. The charge stored in the coupling capacitor 130 generates a voltage in a direction to cancel the battery voltage V BAT . After a certain period of time, the battery voltage V BAT and the voltage of the coupling capacitor 130 balance out, and the inrush current i t ceases to flow. Since the signals applied to and detected by the battery tester 100 for the battery 111 are AC signals, the AC signals are transmitted even with the coupling capacitor 130 in between.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] Incidentally, the resistor 140 in FIG. 4 is a resistor existing on the measurement path. For the detection circuit 120, the resistor on the path generates thermal noise, which is not desirable in high-precision measurements. For the generation circuit 110, the resistor on the path causes a voltage drop when a signal is applied, deteriorating the application performance (such as the allowable value of contact resistance) by that much, so it is also not desirable. On the other hand, if the resistor 140 is made small to suppress thermal noise, the peak value of the inrush current when the battery is connected increases. The adverse effects of this excessive inrush current, namely the possibility of exceeding the ratings of the components used, the possibility of damaging the measurement cable and the wiring inside the measuring instrument, the generation of large spark discharges during probing, increasing the psychological burden on the measuring instrument user and the electromagnetic noise generated, etc., are undesirable.

[0009] Therefore, an object of the present invention is to provide an input protection circuit that can reduce the path resistance during measurement and suppress the inrush current.

Means for Solving the Problem

[0010] In order to solve the above problems, one aspect of the input protection circuit according to the present invention is an input protection circuit provided between a protected circuit for at least one of current supply and voltage detection having a pair of input / output terminals connected to a measurement object and the measurement object, wherein a coupling capacitor, a current limiting resistor, and an overvoltage protection diode are provided in a path from one terminal of the measurement object to the pair of input / output terminals of the protected circuit and the other terminal of the measurement object, an overcurrent protection circuit is connected in parallel to the current limiting resistor, and the overcurrent protection circuit is in a normal state where the first resistance value remains the same when the current value of the current flowing through the internal resistance having a first resistance value lower than the resistance value of the current limiting resistor is less than a predetermined threshold value determined in advance, and when the current value of the current flowing through the internal resistance becomes equal to or greater than the predetermined threshold value, it becomes a high-resistance state where the resistance value of the internal resistance transitions to a second resistance value higher than the first resistance value.

[0011] On one aspect of the input protection circuit according to the present invention, in an overcurrent protection circuit in a high-resistance state, when the current flowing through the internal resistance of the overcurrent protection circuit or the voltage applied to the overcurrent protection circuit becomes less than a predetermined threshold value, it returns to the normal state, and according to the magnitude of the current value of the current flowing through the internal resistance, the overcurrent protection circuit repeats the transition from the normal state to the high-resistance state and the transition from the high-resistance state to the normal state.

Advantages of the Invention

[0012] According to the present invention, it is possible to provide an input protection circuit that can reduce the path resistance during measurement and suppress the inrush current.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0014] <One Embodiment> Hereinafter, with reference to FIGS. 1 and 2, an input protection circuit according to an embodiment of the present invention will be described.

[0015] FIG. 1 is a diagram for explaining the path through which an inrush current flows immediately after connecting a measurement target in the input protection circuit 2 according to an embodiment of the present invention. FIG. 2 is a diagram for explaining the main path of signal transmission during internal impedance measurement of a measurement target in the input protection circuit 2 according to an embodiment of the present invention. The arrow in FIG. 2 indicates the path of signal transmission necessary for measurement. When the protected circuit 13 is a generation circuit, the signal is transmitted in the direction from the generation circuit to the measurement target (battery 11) (leftward arrow in FIG. 2), and when the protected circuit 13 is a detection circuit, the signal is transmitted in the direction from the measurement target (battery 11) to the detection circuit (rightward arrow in FIG. 2).

[0016] [Configuration of Input Protection Circuit 2] Hereinafter, taking the battery tester 1 as an example of a measuring device, the battery tester 1 has a protected circuit 13 which is a generation circuit for supplying an alternating current necessary for four-terminal resistance measurement and a detection circuit for detecting an alternating voltage. Hereinafter, either the generation circuit or the detection circuit will be described as the protected circuit 13. The battery voltage of the battery 11 is a direct current voltage and is set to a level that is not allowed to be directly applied to the protected circuit 13.

[0017] The input protection circuit 2 is provided between the battery 11 which is the measurement target and the protected circuit 13, and includes a coupling capacitor 3, a resistor 5 connected in series to the coupling capacitor 3, an overvoltage protection diode 7, and an overcurrent protection circuit 9 connected in parallel to the resistor 5.

[0018] Here, the terminal N1 is a Hi-side current supply terminal connected to the Hi-side output terminal (one of the output terminals of the generation circuit) of the generation circuit when the protected circuit 13 is a generation circuit, and is a Hi-side detection terminal connected to the Hi-side input terminal (one of the input terminals of the detection circuit) of the detection circuit when the protected circuit 13 is a detection circuit. The terminal N2 is a Lo-side current supply terminal connected to the Lo-side output terminal (the other output terminal of the generation circuit) of the generation circuit when the protected circuit 13 is a generation circuit, and is a Lo-side detection terminal connected to the Lo-side input terminal (the other input terminal of the detection circuit) of the detection circuit when the protected circuit 13 is a detection circuit.

[0019] The coupling capacitor 3 has a function of protecting the protected circuit 13 from the battery voltage of the battery 11 to be measured. The resistor 5 has a function of suppressing the peak current value Ipeak of the inrush current i flowing in when the battery 11 is connected to the protected circuit 13. t

[0020] The overvoltage protection diode 7 is provided at a position on the path connecting the Hi-side output terminal and the Lo-side output terminal of the protected circuit 13. The overvoltage protection diode 7 is preferably composed of a circuit composed of a plurality of elements so as to have, for example, the function of a bidirectional Zener diode. The Zener diode to which a reverse bias is applied shows a controlled breakdown, and current flows so that the voltage across the diode becomes equal to the Zener voltage. Note that the voltage Vz across both ends of the overvoltage protection diode 7 is a voltage limited to be equal to or lower than the Zener voltage at both ends thereof due to the above-described action of the overvoltage protection diode 7.

[0021] The overcurrent protection circuit 9 has the following properties. The resistance value R of the internal resistance 10 of the overcurrent protection circuit 9 in the normal state is relatively low and is defined as a value lower than the resistance value Rs of the resistor 5. When the current value of the current flowing through the internal resistance 10 of the overcurrent protection circuit 9 exceeds a predetermined threshold value, the overcurrent protection circuit 9 instantaneously transitions (trips) to a high-resistance state having a high resistance value. Note that this threshold value may be set to a value corresponding to, for example, the Peak current value (peak current value) of the inrush current i estimated from the measurement target, but is not limited thereto. NORMAL t

[0022] That is, when the current value of the current flowing through the internal resistance 10 of the overcurrent protection circuit 9 is less than the threshold value, it is in the normal state where the resistance value of the internal resistance 10 is low resistance (in the state where the inrush current (not shown) can flow from the battery 11 toward the overcurrent protection circuit 9 in FIG. 2), but when the current value of the current flowing through the internal resistance 10 becomes equal to or greater than the threshold value, it becomes a high-resistance state (trip state) where the resistance value of the internal resistance 10 transitions to high resistance.

[0023] Subsequently, in the overcurrent protection circuit 9 in the high-resistance state, when the voltage applied to the overcurrent protection circuit 9 is removed (or the current value of the current flowing internally becomes less than the threshold value), it returns to the above-described normal state. In this way, the overcurrent protection circuit 9 can repeatedly change between the normal state and the trip state any number of times.

[0024] Note that the above-described current limiting function can be realized by a circuit combining individual devices such as a FET (Field Effect Transistor), or an IC supplied in one package may be used. Examples of the IC include "electronic fuses".

[0025] [Operation of Input Protection Circuit 2] The operation flow of the input protection circuit 2 will be described by taking the case where the protected circuit 13 is a generating circuit as an example. When one terminal (Hi-side terminal) of the battery 11 is connected to the Hi-side current supply terminal N1 of the battery tester 1 and the other terminal (Lo-side terminal) of the battery 11 is connected to the Lo-side current supply terminal N2 of the battery tester 1, an inrush current i t flows into the input protection circuit 2.

[0026] When the current value of the inrush current i t flowing through the internal resistance 10 becomes equal to or greater than a predetermined threshold value, the overcurrent protection circuit 9 instantaneously enters the trip state, and almost no current flows in. Therefore, this inrush current i t is limited by the resistor 5. Here, it is assumed that an appropriate value has been selected for the resistor 5 from the viewpoints of inrush current suppression and coupling capacitor charging time. Then, charging of the coupling capacitor 3 proceeds through the resistor 5. When the charging of the coupling capacitor 3 proceeds and the voltage applied to the resistor 5 and the overcurrent protection circuit 9 falls below a predetermined threshold value, the overcurrent protection circuit 9 returns to the normal state and becomes ready to shift to the current supply step for the next measurement.

[0027] Thereafter, a measurement current (alternating current) is supplied to a path that starts from one output terminal (Hi-side output terminal) of the generation circuit, passes through the Hi-side current supply terminal N1, the battery 11 to be measured, and the Lo-side current supply terminal N2, and reaches the other output terminal (Lo-side output terminal) of the generation circuit.

[0028] Here, since the resistance value of the internal resistance 10 of the overcurrent protection circuit 9 is smaller than the resistance value of the resistor 5, measurement (signal application) can be performed on a measurement path (the path indicated by the arrow in FIG. 4) that passes through the overcurrent protection circuit 9 in a low-resistance state (normal state) without depending on the magnitude of the resistor 5. Therefore, the inrush current i in the generation circuit t operates in a trip state only immediately after it occurs, and when the voltage applied to the resistor 5 and the overcurrent protection circuit 9 falls below a predetermined threshold value, the overcurrent protection circuit 9 returns to the normal state, so that it is possible to simultaneously satisfy the requirement of suppressing the inrush current in the generation circuit and reducing the resistance of the path during measurement current supply.

[0029] The above-described embodiment is an example when the circuit to be protected 13 is the generation circuit, but even when the circuit to be protected 13 is a detection circuit, when an inrush current i t occurs when connecting the Hi-side detection terminal N3 and the Lo-side detection terminal N4 to the battery 11, similarly to the above, the overcurrent protection circuit 9 instantaneously enters the trip state, and the inrush current i t is limited by the resistor 5. When the charging of the coupling capacitor 3 progresses and the voltage applied to the resistor 5 and the overcurrent protection circuit 9 falls below a specified value, the overcurrent protection circuit 9 returns to the normal state and becomes a state where it is possible to shift to the next detection step.

[0030] Thereafter, the detection circuit detects the amplitude and phase of the alternating voltage generated across the battery 11 by the measurement current I applied from the generation circuit. Note that V in FIG. 2 BAT is the battery voltage (open terminal voltage) of the battery 11, and R BAT is the internal impedance of the battery 11. In the detection circuit, the alternating voltage V (= internal impedance R BATThe alternating voltage V is detected, and based on the amplitude and phase of the detected alternating voltage V and the amplitude and phase (known) of the measurement current I, the internal impedance R of the battery 11 is calculated. BAT Since the battery voltage V of the battery 11 is a direct current voltage, it is blocked by the coupling capacitor 3 and not detected. BAT Since the battery voltage V of the battery 11 is a direct current voltage, it is blocked by the coupling capacitor 3 and not detected.

[0031] Here, since the resistance value of the internal resistance 10 of the overcurrent protection circuit 9 is smaller than the resistance value of the resistor 5, measurement (detection of a signal) can be performed on the measurement path (the path indicated by the arrow in FIG. 2) passing through the overcurrent protection circuit 9 in a low-resistance state without depending on the magnitude of the resistor 5. Therefore, the detection circuit operates in a trip state only immediately after the inrush current i is generated, and when the voltage applied to the resistor 5 and the overcurrent protection circuit 9 falls below a predetermined threshold value, the overcurrent protection circuit 9 returns to the normal state. Thus, it is possible to simultaneously satisfy the requirement of suppressing the inrush current in the detection circuit and reducing the resistance of the path during measurement signal detection. t Here, since the resistance value of the internal resistance 10 of the overcurrent protection circuit 9 is smaller than the resistance value of the resistor 5, measurement (detection of a signal) can be performed on the measurement path (the path indicated by the arrow in FIG. 2) passing through the overcurrent protection circuit 9 in a low-resistance state without depending on the magnitude of the resistor 5. Therefore, the detection circuit operates in a trip state only immediately after the inrush current i is generated, and when the voltage applied to the resistor 5 and the overcurrent protection circuit 9 falls below a predetermined threshold value, the overcurrent protection circuit 9 returns to the normal state. Thus, it is possible to simultaneously satisfy the requirement of suppressing the inrush current in the detection circuit and reducing the resistance of the path during measurement signal detection.

[0032] As described above, according to the invention according to the above-described embodiment, due to the operation of the overcurrent protection circuit 9 as described above, the path resistance changes between the protection time (immediately after the battery is connected) and the measurement time. Therefore, it is possible to achieve both suppression of the inrush current i and reduction of the resistance of the path during measurement. Furthermore, since the overcurrent protection circuit operates spontaneously due to the inrush current, there is no need for active control such as monitoring the state of the measuring device and performing switching by a switch or the like only immediately after the battery is connected for switching the path resistance. Thus, there is an advantage that the system design can be simplified. t As described above, according to the invention according to the above-described embodiment, due to the operation of the overcurrent protection circuit 9 as described above, the path resistance changes between the protection time (immediately after the battery is connected) and the measurement time. Therefore, it is possible to achieve both suppression of the inrush current i and reduction of the resistance of the path during measurement. Furthermore, since the overcurrent protection circuit operates spontaneously due to the inrush current, there is no need for active control such as monitoring the state of the measuring device and performing switching by a switch or the like only immediately after the battery is connected for switching the path resistance. Thus, there is an advantage that the system design can be simplified.

[0033] Note that the embodiments of the present invention are not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present invention.

[0034] [Summary of Effects] The input protection circuit 2 according to the present embodiment is an input protection circuit 2 provided between the protected circuit 13 for at least one of current supply and voltage detection having a pair of input / output terminals connected to the measurement object and the measurement object 11. A coupling capacitor 3, a current limiting resistor 5 and an overvoltage protection diode 7 are provided on a path extending from one terminal of the object to be measured 11 to a pair of input / output terminals of the protected circuit 13 and the other terminal of the object to be measured 11; An overcurrent protection circuit 9 is connected in parallel to the current limiting resistor 5. The overcurrent protection circuit 9 has a first resistance value R lower than the resistance value Rs of the current limiting resistor 5. NORMAL When the current value of the current flowing through the internal resistor 10 having the first resistance value R NORMAL remains unchanged, and when the current value of the current flowing through the internal resistor 10 becomes equal to or greater than a predetermined threshold, the resistance value of the internal resistor 10 becomes equal to the first resistance value R NORMAL The resistance value transitions to a second resistance value higher than the first resistance value, resulting in a high resistance state. Therefore, according to the above configuration, the overcurrent protection circuit transitions from the normal state to the high resistance state and from the high resistance state to the normal state depending on the magnitude of the current value of the current flowing through the internal resistance, so that the resistance on the path between the measurement target and the protected circuit can be changed immediately after the measurement target is connected and during measurement. The change in the resistance value of the resistance on this path, that is, when the inrush current is large, the resistance state is set to the high resistance state to suppress the current value of the large inrush current immediately after the measurement target is connected, and after the current value of the inrush current has decreased, the resistance state is set to the normal state to reduce the combined resistance of the current limiting resistor and the internal resistance of the overcurrent protection circuit, so that the resistance value of the path resistance from the measurement target to the protected circuit can be suppressed.

[0035] In the input protection circuit 2 of this embodiment, when the overcurrent protection circuit 9 is in a high resistance state, and the current flowing through the internal resistance 10 of the overcurrent protection circuit 9 or the voltage applied to the overcurrent protection circuit 9 falls below a predetermined threshold, the overcurrent protection circuit 9 returns to a normal state, and depending on the magnitude of the current value of the current flowing through the internal resistance, the overcurrent protection circuit 9 repeats transitions from the normal state to a high resistance state and from the high resistance state to the normal state. Therefore, according to the above configuration, it is in a high-resistance state while the inrush current is increasing, but it can return to the normal state as the inrush current decreases. Thus, the inrush current can be suppressed without changing the resistance element to reduce the resistance value of the current-limiting resistor in order to suppress the increase in the peak current of the inrush current. For this reason, while suppressing the adverse effect of reducing the resistance value of the current-limiting resistor, that is, the increase in the peak current of the inrush current when connecting the measurement target, the current application performance of the generation circuit and the detection accuracy of the detection circuit can be improved by reducing the resistance of the path resistance during measurement.

Explanation of Signs

[0036] 1 Battery Tester 2 Input Protection Circuit 3 Coupling Capacitor 5 Resistor 7 Overvoltage Protection Diode 9 Overcurrent Protection Circuit 10 Internal Resistance 11 Battery (Measurement Target) N1 Hi-side Current Supply Terminal N2 Lo-side Current Supply Terminal N3 Hi-side Detection Terminal N4 Lo-side Detection Terminal

Claims

1. An input protection circuit provided between a protected circuit for at least one of current supply and voltage detection having a pair of input / output terminals connected to a measurement target and the measurement target, a coupling capacitor, a current limiting resistor, and an overvoltage protection diode are provided in a path from one terminal of the measurement target to the pair of input / output terminals of the protected circuit and the other terminal of the measurement target, an overcurrent protection circuit is connected in parallel to the current limiting resistor, in the overcurrent protection circuit, when the current value of the current flowing through an internal resistor having a first resistance value lower than the resistance value of the current limiting resistor is less than a predetermined threshold value, the first resistance value remains as it is and it is in a normal state, and when the current value of the current flowing through the internal resistor becomes equal to or greater than the predetermined threshold value, the resistance value of the internal resistor transitions to a second resistance value higher than the first resistance value and it is in a high resistance state, An input protection circuit characterized by the above.

2. In the overcurrent protection circuit in the high resistance state, when the current flowing through the internal resistor of the overcurrent protection circuit or the voltage applied to the overcurrent protection circuit becomes less than the predetermined threshold value, it returns to the normal state, and according to the magnitude of the current value of the current flowing through the internal resistor, the overcurrent protection circuit repeats the transition from the normal state to the high resistance state and the transition from the high resistance state to the normal state, The input protection circuit according to claim 1, characterized by the above.

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