JP2007189873A - Inrush current protection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inrush current protection circuit that is capable of fully limiting the inrush current during starting, and is capable of maximally eliminating the wasteful elements from a power source and supply line, after start up. <P>SOLUTION: An inrush current limiting circuit 100 has a main power source VV for supplying power source to a load circuit via a current limitation resistor RS; a large-capacity capacitor C60 connected to the load circuit 70, in parallel with respect to the power source; a switching circuit SW1 connected to the current limitation resistor in parallel; and a charging state monitoring circuit 20 which switches the switching circuit to an on-state by driving a switching control circuit PH1, when voltages at both ends of the current limitation resistor become smaller than the threshold, after the detecting of the voltages. Accordingly, efficient supplying of the power source to the load circuit can be made without limitations by the current limitation resistor after starting, even if a considerably large current limitation resistor is used, in order to suppress the peak value of the inrush current during starting. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inrush current protection circuit, and more particularly, an inrush current having a main power source that supplies power to a load circuit via a current limiting resistor, and a large-capacitance capacitor connected in parallel to the load circuit with respect to the power supply. The present invention relates to a protection circuit.

FIG. 3 is a circuit diagram showing a conventional example of this type of inrush current protection circuit. In this circuit, the resistor R1 and the diode D1 generate a reference voltage for comparison, and the error amplifier IC1 compares the voltage at the connection point between the resistor R2 and the current limiting resistor RS with the reference voltage, and based on the comparison result. Thus, the transistor Q1 is controlled so that the voltage across the current limiting resistor RS is kept constant (Patent Document 1).
JP-A-5-146143

  The conventional inrush current protection circuit as described above is skillfully controlled with a simple circuit so that a constant voltage power supply is supplied to the load circuit. However, although the inrush current at start-up is made as small as possible, the above circuit is inconvenient because it cannot remove the current-limit resistor RS in order to meet the demand for not using the current-limit resistor except at the start-up. .

  The present invention has been made in order to solve the above-described conventional problems. The inrush current is sufficiently limited at start-up, and unnecessary elements can be eliminated from the power supply line as much as possible after start-up. An object of the present invention is to provide an inrush current protection circuit capable of supplying power to the load circuit side as directly as possible.

  In order to solve the above-described problem, the present invention provides an inrush current protection having a main power supply that supplies power to a load circuit via a current limiting resistor, and a large-capacitance capacitor connected in parallel to the load circuit for power supply. In the circuit, the switching circuit connected in parallel to the current limiting resistor and the voltage across the current limiting resistor after the start of power supply are detected, and the switching circuit is turned on when the voltage falls below the threshold value The charging state monitoring circuit is provided.

  According to such a configuration, at the time of start-up, the current limiting resistor limits the peak value of the inrush current and supplies power to the load circuit side. When the charge on the large-capacity capacitor increases to some extent, the charge state monitoring circuit turns on the switching circuit and shorts out the current limiting resistor. After that, the power supply is subject to current limitation by the current limiting resistor. Therefore, it is possible to efficiently supply power to the load circuit.

  Further, the present invention includes a control switching circuit that keeps the load circuit and its peripheral circuits inactive until the charging state monitoring circuit switches the switching circuit to the ON state. Abnormality may occur if current is consumed by the load circuit and its surroundings before the voltage across the current limiting resistor falls below the threshold and power can be reliably supplied to the load circuit Therefore, the control switching circuit makes them inactive so that the load circuit and its peripheral circuits do not consume current before power can be reliably supplied to the load circuit.

  Since the inrush current protection circuit of the present invention is configured as described above, it is intended to supply power to the load circuit by limiting the peak value of the inrush current with a current limiting resistor at the time of startup. When the charge of the large-capacity capacitor increases to some extent, the charge state monitoring circuit detects this from the voltage applied to both ends of the current limiting resistor, and turns on the switching circuit to short-circuit the current limiting resistor. As a result, after the short circuit of the current limiting resistor, the power supply is efficiently supplied to the load circuit without being limited by the current limiting resistor. Therefore, even if the current limiting resistance is considerably increased for the purpose of suppressing the peak value of the inrush current, the current limiting resistance is not limited at all during normal operation. In addition, since switching of the switching circuit is determined based on the voltage across the current limiting resistor, it is less affected by fluctuations in the main power supply.

  Furthermore, when the power supply route switching circuit has a control switching circuit that keeps the load circuit and its peripheral circuits inactive until the switching circuit is turned on, the voltage across the current limiting resistor is below the threshold value. Therefore, if current is consumed by the load circuit and its surrounding circuits before power can be reliably supplied to the load circuit, an abnormality may occur, so the control switching circuit supplies power to the load circuit. Before it can be ensured, the load circuit and its peripheral circuits are made inactive so as not to consume current, and malfunction can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of an inrush current protection circuit of the present invention, and FIG. 2 is a circuit diagram showing in detail the configuration of each part of FIG.

  In the inrush current protection circuit 100 shown in FIG. 1, when the switch SW0 is turned on, the power from the main power supply VV is supplied from the power supply route switching circuit 10, the charge state monitoring circuit 20, and the stabilized power supply circuit 30. Then, by the action of the control switching circuit 40 and the control power supply circuit 50, it is stored in the large-capacitance capacitor C60 and supplied to subsequent circuits such as the inverter 70. Details of each of the circuits 10, 20, 30, 40, 50 described above are shown in FIG.

  As can be seen from FIG. 2, when the switch SW0 is turned on, the current starts to charge the large-capacitance capacitor C60 via the current limiting resistor RS of the power supply route switching circuit 10. In the initial stage when the switch SW0 is turned on, the large-capacity capacitor C60 has a small amount of electric charge, so that a large current flows through the current limiting resistor RS. In this case, the peak value of the flowing current is limited by the current limiting resistor RS.

  The stabilized power supply circuit 30 that has received power supply via the current limiting resistor RS starts to supply the stabilized power supply having a voltage determined by the Zener diode ZDA to the comparator CM of the charge state monitoring circuit 20. The comparator CM that receives the supply of the stabilized power supply checks whether or not the voltage between the nodes P1 and P2 at both ends of the current limiting resistor RS is equal to or lower than the threshold value. In the initial stage when the switch SW0 is turned on, the voltage between the nodes P1 and P2 at both ends of the current limiting resistor RS is large. Therefore, the comparator CM having this voltage as an input outputs “L” (low level) level. To. Therefore, the negative circuit N that receives the output of the comparator CM sets the output terminal to “H” (high level).

  When the negative circuit N sets the output terminal to “H”, since the potential of the node P3 is not lower than that of the node P1, no current flows through the line connecting the resistor R12, the switching control circuit PH1, and the diode D21. The switching control circuit PH1 keeps the switching circuit SW1 in the “off” state, and the power supply current continues to flow through the current limiting resistor RS.

  On the other hand, for the control switching circuit 40, since the output terminal of the negative circuit N is “H”, no current flows through the line connecting the resistor R41, the Zener diode ZDB, and the diode D23. Is “OFF”, and the control power supply circuit 50 is kept inactive. Therefore, the subsequent circuit, for example, the inverter 70 (FIG. 1) receiving the control power from the control power supply circuit 50 does not start operation.

  Next, when a predetermined time elapses after the switch SW0 is turned on, charging of the large-capacitance capacitor C60 proceeds, the current flowing through the current limiting resistor RS gradually decreases, and the node P1 at both ends of the current limiting resistor RS. , P2 becomes equal to or lower than the threshold value, and the comparator CM detecting this switches the output from “L” to “H”. When the output of the comparator CM becomes “H”, the output of the negative circuit N becomes “L”, and the current flows from the node P1 to the node P3 via the resistor R12, the switching control circuit PH1, and the diode D21. The flow and switching control circuit PH1 switches the switching circuit SW1 to “ON”. When the switching circuit SW1 is turned on, the current is directly applied to the large-capacitance capacitor C60 and the subsequent circuit as its load circuit via the switching circuit SW1 having a very small resistance value without being limited by the current limiting resistor RS. To be supplied.

  Further, when the output of the comparator CM becomes “H” and the output of the negative circuit N becomes “L”, a current is also applied to the line connecting the resistor R41 of the control switching circuit 40, the Zener diode ZDB, and the diode D23. As a result, the control switching circuit 40 is turned on, and the control power supply circuit 50 is switched to active. When the control power supply circuit 50 becomes active, the subsequent inverter 70 receives control power from the control power supply circuit 50 and receives drive power from the switching circuit SW1, and starts normal operation. At this time, the drive power supply line does not have an element that lowers the voltage or wastes power like the current limiting resistor RS, and only passes through the switching circuit SW1 with low power consumption.

  Therefore, in the inrush current protection circuit 100, in the initial stage when the switch SW0 is turned “on”, the peak of the inrush current can be reduced as desired by increasing the current limiting resistance RS, and a predetermined time is reached. At the time when the large-capacitance capacitor C60 has been charged, the current limiting resistor RS can be disconnected to eliminate unnecessary voltage drop or power consumption. In this example, by providing the stabilized power supply circuit 30, the charging state monitoring circuit 20 can operate stably, and the charging state monitoring circuit 20 determines the degree of charging by the potential difference between both ends of the current limiting resistor RS. Therefore, there is an advantage that it is hardly influenced by the voltage fluctuation of the main power supply VV.

  That is, the charging state monitoring circuit 20 determines the degree of charging by the potential difference between the first end and the second end of the current limiting resistor RS. For this reason, the charge state monitoring circuit 20 is not affected by the voltage drop even if the voltage of the main power supply VV decreases, particularly when the main power supply VV is a rechargeable battery such as a secondary battery. The state of charge can be reliably monitored.

  As a preferable example, a FET (field effect transistor) is used for the switching circuit SW1 of the power supply route switching circuit 10. For this reason, when a voltage is supplied from the main power supply VV to the inverter 70 side via the switching circuit SW1, there is almost no voltage drop, and an inrush current protection circuit compared to the case where a normal NPN transistor is used as a switch. 100 power consumption can be reduced.

  Further, as shown in FIGS. 1 and 2, a switch SW0 is directly provided on the positive side of the main power supply VV, a first unit composed of the main power supply VV and the switch SW0, an inrush power supply protection circuit 100, The second unit composed of the inverter 70 and the large-capacitance capacitor C60 can be set separately. Accordingly, there is an advantage that the first unit can be placed on the user's hand side and the second unit can be arranged on the actual device side including the motor, which is practically effective.

  In this type of circuit, the current consumed by the control power supply circuit 50 and the current limiting resistor RS (for example, when the current limiting resistor RS is increased to reduce the inrush current peak value) are used. It can be estimated that the current flowing in is equal, and the voltage across the current limiting resistor RS does not drop below a certain value. However, in this example, since the control switching circuit 40 and the control power supply circuit 50 are provided, the control switching circuit 40 causes the control power supply circuit 50 to be switched until the charging of the large-capacitance capacitor C60 reaches a desired level. Since the “off” state is maintained, there is an advantage that such a phenomenon can be surely prevented.

It is a block diagram which shows embodiment of the inrush current protection circuit of this invention. It is a circuit diagram which shows the structure of each part of FIG. 1 in detail. It is a circuit diagram which shows the prior art example of an inrush current protection circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Power supply route switching circuit 20 Charge state monitoring circuit 30 Stabilized power supply 40 Control switching circuit 50 Control switching circuit 60 Large capacity capacitor 70 Inverter 100 Inrush current protection circuit RS Current limiting resistance SW0 switch SW1 switching circuit

Claims (2)

In an inrush current protection circuit having a main power supply that supplies power to a load circuit via a current limiting resistor, and a large-capacitance capacitor connected in parallel to the load circuit for power supply,
A switching circuit connected in parallel with the current limiting resistor;
Inrush current protection circuit comprising a charge state monitoring circuit that detects the voltage across the current limiting resistor after the start of power supply and switches the switching circuit to an on state when the voltage falls below a threshold value .   2. The inrush current protection circuit according to claim 1, further comprising a control switching circuit that keeps the load circuit and its peripheral circuits inactive until the charging state monitoring circuit switches the switching circuit to the on state.

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