JP4214122B2 - Inrush current prevention circuit - Google Patents

Description

  The present invention relates to an inrush current prevention circuit that prevents an inrush current from flowing in a power supply line when a power supply voltage is applied from a DC power supply to a load.

  In a device (load) driven by a power supply voltage (DC voltage) supplied from a DC power supply, a smoothing capacitor for stabilizing the power supply voltage against load fluctuation is connected in parallel to the power supply line. On the other hand, when a power supply voltage is applied from a DC power supply, such a smoothing capacitor is transient between the DC power supply and the smoothing capacitor (this is referred to as a “power supply line”) until the charge charging is completed. Current (this is called “inrush current”).

  Such an inrush current is a current larger than a steady current and is not preferable because it impedes the operation of the DC power supply. Therefore, conventionally, in an apparatus driven by a DC power supply, an inrush current prevention circuit that prevents the inrush current as described above from flowing is used. Hereinafter, a conventional inrush current preventing circuit will be described with reference to FIG.

  The inrush current prevention circuit shown in FIG. 3 is connected by a conduction FET, which is a conduction element, between a DC power supply and a load (power supply line), and is determined by a resistance component and a capacitance component between the gate source and the gate drain of the conduction FET. And first and second charging circuits that charge in accordance with time constants τ1 and τ2.

  The conduction FET is, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), a source (DC power supply terminal) connected to a DC power supply, a drain (load terminal) connected to a load, a gate (control terminal), The source and drain are electrically connected with a resistance value corresponding to the gate-source voltage.

  The first charging circuit is connected between the gate and source of the conducting FET, has a capacitor C1 as a charging element, and is determined by a resistance component including a resistor R1 described later and a capacitance component including the capacitor C1. Charge is charged according to a time constant τ1 of 1. The second charging circuit includes a capacitor C2 connected between the gate and drain of the conduction FET and serving as a charging element. The second charging circuit includes a resistance component including an internal resistance (and resistance R3) of the conduction FET described later, and the capacitor C2. The charge is charged in accordance with the second time constant τ2 determined from the capacitance component included.

  Resistor R1 and resistor R2 divide the power supply voltage according to each resistance value when the power supply voltage is applied from the DC power supply between the source of the conduction FET and GND, and the divided voltage is the gate source of the conduction FET. Apply between. The resistor R3 is a resistor for adjusting the time constant τ2 of the second charging circuit. The smoothing capacitor C3 is connected in parallel to the power supply line and smoothes the voltage of the power supply line. Next, the operation of the conventional inrush current prevention circuit will be described in detail.

  When a power supply voltage (negative DC voltage) is applied between the source of the conduction FET and GND, the power supply voltage is applied to the resistors R1 and R2 connected in series between the source of the conduction FET and GND. Applied. Since the capacitor C1 is connected in parallel to the resistor R1, a voltage (a voltage between both ends) corresponding to the charging of the capacitor C1 is applied to both ends of the resistor R1. Capacitor C1 gradually charges up according to a time constant τ1 determined by a resistance component including resistor R1 and a capacitance component including capacitor C1. Thereby, the both-ends voltage (potential difference) applied to resistance R1 rises gradually until it becomes the voltage which divided the power supply voltage according to the voltage dividing ratio with resistance R2.

  Since the resistor R1 is connected between the gate and source of the conducting FET, the voltage across the resistor R1 (potential difference) gradually increases, so that the gate-source voltage (potential difference) of the conducting FET gradually increases. When the gate-source voltage of the conducting FET gradually increases and exceeds the threshold voltage of the conducting FET, the drain-source of the conducting FET conducts. In a conducting FET in which the drain and the source are conducted, the internal resistance of the conducting FET gradually decreases as the gate-source voltage increases.

  When the conducting FET conducts, the resistor R1 is connected to the capacitor C2 and the internal resistance of the conducting FET (and the resistor R3). Further, when the conducting FET is conducted, the DC power supply terminal and the load terminal are connected via an internal resistor. Thereby, the voltage charged in the capacitor C1 is applied to the internal resistance (and the resistance R3) of the capacitor C2 and the conduction FET. That is, when the capacitor C1 is regarded as a power source (generating a charged voltage), an integrating circuit composed of the capacitor C2 and the internal resistance of the conduction FET (and the resistor R3) is connected to the power source (capacitor C1). (That is, the second charging circuit is an integrating circuit including the capacitor C2 and the internal resistance of the conducting FET).

  Therefore, the drain voltage of the conducting FET, which is the connection point between the capacitor C2 and the internal resistance of the conducting FET, gradually converges to the source voltage of the conducting FET according to the time constant τ2 of the second charging circuit that is this integration circuit. Go. At this time, the capacitor C2 is determined by the resistance component including the internal resistance (and the resistance R3) of the conduction FET and the capacitance component including the capacitor C2 until the voltage across the same voltage as the voltage across the resistor R1 is applied. The electric charge is gradually charged according to the second time constant τ2.

  As a result, the gate-drain voltage (potential difference) of the conducting FET to which the capacitor C2 is connected gradually increases. When the capacitor C2 charges the electric charge, one terminal of the capacitor C2 (terminal to which the resistor R3 is connected) gradually converges so as to be the same voltage as the gate voltage of the conducting FET, and the other terminal (of the conducting FET). The terminal) connected to the source gradually converges so as to be the same voltage as the source voltage (ie, power supply voltage) of the conducting FET. Thereby, a voltage is applied so that the voltage applied to the smoothing capacitor C3 gradually converges to the power supply voltage.

  Then, the internal resistance of the conducting FET decreases as the gate-source voltage (potential difference) of the conducting FET increases (with this, the internal resistance of the conducting FET also decreases, so the time constant τ2 also decreases), and the capacitor C3 It becomes the smallest (approximately zero ohms) when charging is completed and the power supply voltage is supplied to the load. As described above, in the conventional inrush current prevention circuit, when the power supply voltage is applied from the DC power supply to the load, the voltage applied to the smoothing capacitor C3 is gradually converged to the power supply voltage, whereby the charge to the smoothing capacitor C3 is Charging is performed gradually to prevent inrush current from flowing through the power line.

  However, the conventional inrush current prevention circuit has a problem that it becomes difficult to prevent an inrush current from flowing through the power supply line when the power supply voltage applied to the source of the conducting FET repeatedly fluctuates in a short time. . This will be described in detail below.

  In the conventional inrush current prevention circuit, when the power supply voltage is no longer applied to the source of the conducting FET, the capacitor of each charging circuit starts discharging. After each capacitor is completely discharged (initialized), when a power supply voltage is applied to the source of the conducting FET again, the inrush current prevention circuit conducts the power supply voltage applied to the source of the conducting FET. By gradually applying to the drain of the FET, it is possible to prevent inrush current from flowing through the smoothing capacitor.

  However, since the time constants τ1 and τ2 as described above are set so that the capacitors of the respective charging circuits are gradually charged, each capacitor can only be gradually discharged as in the case of charging. If each capacitor is not fully discharged (while the conducting FET is still conducting) and the power supply voltage is applied again to the source of the conducting FET, the internal resistance of the conducting FET is reduced, so the time constant Capacitor C3, where τ2 is small and the voltage drops due to discharge, suddenly charges to fill the potential difference with the power supply voltage applied to the source of the conducting FET, and inrush current (re-inrush current) enters the power supply line. Shed.

  An object of the present invention is to solve the above-described problems. Specifically, it prevents the re-entry current from flowing when the power supply voltage applied to the source of the conducting FET repeatedly fluctuates in a short time. The purpose is to realize an inrush current prevention circuit.

The present invention includes a DC power supply terminal connected to a DC power supply, a load terminal connected to a load, and a control terminal, and the DC power supply terminal has a resistance value corresponding to a voltage applied to the control terminal. A conductive element that conducts between the load terminal and the DC power supply terminal and the control terminal; when a DC voltage is applied to the DC power supply terminal, a voltage corresponding to the DC voltage is used as a resistance component. is connected between the first charging circuit to be applied to the control terminal while charging the first capacitor having a capacitance component as a first time constant determined by the capacity component, the control terminal and the load terminal, After the conducting element is turned on, a voltage corresponding to the voltage charged in the first charging circuit is charged into a second capacitor having a capacitance component that becomes a second time constant determined by a resistance component and a capacitance component. While applying the second to the load terminal A smoothing circuit connected in parallel to the load terminal by gradually applying a DC voltage supplied from a DC power source to the load terminal when a DC voltage is applied to the DC power terminal. An inrush current preventing circuit for preventing an inrush current from flowing through the capacitor, the first discharge circuit having a first discharge resistor connected in parallel to the first capacitor via a switch, and the second A second discharge circuit for discharging the electric charge of the capacitor, wherein the first discharge circuit turns on the switch when a DC voltage is not applied to the DC power supply terminal. Reducing the time constant of the first charging circuit to promote the discharge of the voltage charged in the capacitive component of the first charging circuit, and to accelerate the initialization of the voltage applied to the control terminal, thereby preventing the re-inrush current. Features and That.

Further, the second discharge circuit reduces the second time constant and reduces the voltage charged in the capacitance component of the second charging circuit when no DC voltage is applied to the DC power supply terminal. It is desirable to promote discharge and accelerate the initialization of the voltage applied to the load terminal .

The second discharge circuit has a second discharge resistor connected in parallel to the second capacitor via a switch, and the switch is turned on when a DC voltage is not applied to the DC power supply terminal. It is desirable to turn it on .

  According to the present invention, it is possible to realize an inrush current prevention circuit that prevents a re-inrush current from flowing when the power supply voltage applied to the source of the conducting FET repeatedly fluctuates in a short time.

  Hereinafter, the inrush current prevention circuit according to the present embodiment will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of an inrush current preventing circuit according to the first embodiment of the present invention. FIG. 2 is a circuit diagram showing a configuration of an inrush current preventing circuit according to the second embodiment of the present invention.

  Note that the inrush current prevention circuit described in this embodiment shares a power supply line via a connector with a plurality of communication units for each communication line, and inserts and removes the communication unit while the communication device main body is operating. Thus, it is assumed that it is mounted on a communication device such as a telephone exchange or the communication unit accommodated therein, which can add or maintain a communication line. First, the inrush current preventing circuit according to the first embodiment of the present invention will be described in detail with reference to FIG. In addition, the same code | symbol is attached | subjected to the structure similar to the conventional circuit shown in FIG. 3, and description is abbreviate | omitted.

“First Embodiment”
The inrush current prevention circuit shown in FIG. 1 includes a first discharge circuit for reducing the first time constant τ1 and promoting the discharge of the capacitor C1 when the power supply voltage is not applied to the source of the conducting FET. And a voltage detection circuit for detecting a power supply voltage applied to the source of the conduction FET.

  The first discharge circuit is connected in parallel with the capacitor C1 and is turned on when the power supply voltage is detected by the voltage detection circuit; the discharge resistor R4 for discharging the charge charged in the capacitor C1; Are connected in series. Note that the resistance value of the resistor R4 is smaller than the resistor R1 so as to reduce the time constant τ1 of the first charging circuit when the switch SW1 is turned on and promote the discharge of the charge charged in the capacitor C1 ( R1 >> R4).

  The voltage detection circuit is connected to the source side of the conduction FET and detects a power supply voltage applied to the source of the conduction FET. This power supply detection circuit is composed of a resistor R6 and a relay K1 connected in series. The resistor R6 is a resistor for allowing a current to flow when a power supply voltage is applied. The relay K1 is a relay that turns off the switch SW1, which is a contact of the relay K1, when a current flows through the resistor R6, and turns on the switch SW1 when no current flows.

  Thus, the inrush current prevention circuit according to the first embodiment of the present invention immediately discharges the charge charged in the capacitor C1 when the power supply voltage is not applied to the source of the conduction FET, The gate-source voltage can be quickly initialized (to zero volts). Next, the operation of the inrush current prevention circuit according to the first embodiment will be described in detail.

  When the power supply voltage is applied from the DC power source to the source of the conduction FET, the voltage detection circuit detects that the power supply voltage is applied to the source of the conduction FET and turns off the switch SW1. At this time, in the inrush current prevention circuit according to the first embodiment, the first and second charging circuits are charged in accordance with the first and second time constants τ1 and τ2, similarly to the conventional inrush current prevention circuit. By gradually charging the battery, inrush current can be prevented from flowing through the power supply line.

  Next, when the power supply voltage is no longer applied from the DC power source to the source of the conducting FET, the voltage detection circuit detects that the power source voltage is not applied to the source of the conducting FET and turns on the switch SW1. As described above, the discharge resistance R4 is set to such a value that the first time constant τ1 decreases when the switch SW1 is turned on. For this reason, the capacitor C1 can discharge electric charges earlier than when it was charged.

  As the electric charge charged in the capacitor C1 is quickly discharged, the voltage between the gate and the source of the conducting FET is quickly reduced. In the conducting FET, the internal resistance between the drain and the source rises quickly due to the early drop of the gate-source voltage, and the conduction FET becomes non-conductive when the gate-source voltage falls below the threshold value.

  Thus, even if the power supply voltage is applied to the source of the conducting FET again in a state where the drain and source of the conducting FET are not conducting, the internal resistance of the conducting FET is sufficiently large. As described above, the smoothing capacitor C3 is not rapidly charged so as to fill the potential difference from the power supply voltage applied to the source of the conducting FET. Therefore, the inrush current prevention circuit according to the first embodiment of the present invention can prevent re-inrush current from flowing when the power supply voltage applied to the source of the conducting FET repeats fluctuation in a short time. .

“Second Embodiment”
The inrush current prevention circuit shown in FIG. 2 is further improved from the inrush current prevention circuit described in the first embodiment. In the inrush current prevention circuit described in the first embodiment, the capacitor C2 has the same time constant at the time of charging and discharging as in the conventional case, so that the charge charged in the capacitor C2 is discharged only gradually. Therefore, the inrush current prevention circuit shown in the second embodiment reduces the second time constant τ2 when the power supply voltage is not applied to the source of the conduction FET, and discharges the charge charged in the capacitor C2. By promoting the configuration, the inrush current prevention circuit can be initialized more quickly. The inrush current preventing circuit according to the second embodiment of the present invention will be described in detail below with reference to FIG.

  The inrush current prevention circuit shown in FIG. 2 newly includes a second discharge circuit for reducing the second time constant τ2 when the power supply voltage is not applied to the source of the conducting FET. The second discharge circuit is connected in parallel with the capacitor C2 and is turned on when the power supply voltage is detected by the voltage detection circuit, a discharge resistor R5 for discharging the charge charged in the capacitor C2, Are connected in series. Note that the resistance value of the resistor R5 is an arbitrary design matter, and is a value that reduces the time constant τ2 of the second charging circuit when the switch SW2 is turned on and promotes the discharge of the charge charged in the capacitor C2. Is set.

  As a result, the inrush current prevention circuit according to the second embodiment of the present invention quickly discharges the charge charged in the capacitor C2 when the power supply voltage is not applied to the source of the conducting FET. Can be initialized more quickly. Next, the operation of the inrush current prevention circuit according to the second embodiment will be described.

  When the power supply voltage is applied from the DC power source to the source of the conducting FET, the voltage detection circuit detects that the power source voltage is applied to the source of the conducting FET, and the switch SW2 (and the switch SW1) is turned off. At this time, in the inrush current preventing circuit according to the second embodiment, the first and second charging circuits are charged in accordance with the first and second time constants τ1 and τ2, similarly to the conventional inrush current preventing circuit. By gradually charging the battery, inrush current is prevented from flowing through the power supply line.

  When the power supply voltage is no longer applied from the DC power source to the source of the conducting FET, the voltage detection circuit detects that the power source voltage is not applied to the source of the conducting FET, and the switch SW2 (and the switch SW1) is turned on. As described above, the discharge resistance R5 is set to such a value that the second time constant τ2 decreases when the switch SW2 is turned on. For this reason, the capacitor C2 can discharge electric charges earlier than when it was charged.

  As a result, the second discharge circuit can quickly discharge the electric charge charged in the capacitor C2 and accelerate the initialization of the inrush current prevention circuit. Therefore, the inrush current prevention circuit according to the second embodiment of the present invention can prevent the reinrush current from flowing when the power supply voltage applied to the source of the conducting FET repeats fluctuations in a short time. .

  As described above, the inrush current prevention circuit according to the present embodiment reduces the first time constant τ1 when the power supply voltage is not applied to the source of the conducting FET, and discharges the charge charged in the capacitor C1. And a second discharge circuit that accelerates the discharge of the electric charge charged in the capacitor C2 by reducing the second time constant τ2, thereby providing an initial inrush current prevention circuit. It is possible to prevent the re-entry current from flowing when the power supply voltage applied to the source of the conducting FET repeatedly fluctuates in a short time.

  In addition, although this embodiment demonstrated the inrush current prevention circuit mounted in communication apparatuses, such as a telephone switchboard, or the communication unit accommodated in it, it says that the meaning of this invention is not limited to it. Not too long. In this embodiment, a relay is used for switching the time constant. However, the switching means is not limited to the relay, and may be a semiconductor switch. By providing an external switch SW in series with K1, it is possible to add a function for remote ON / OFF from the external switch SW. By preventing the inrush current, the stress applied to the conduction FET is reduced, and the reliability of the inrush current prevention circuit is improved. Further, the reliability of the entire system is improved in terms of voltage stabilization and current capacity reduction.

1 is a circuit diagram illustrating an inrush current preventing circuit according to a first embodiment of the present invention. It is a circuit diagram which shows the inrush current prevention circuit which concerns on the 2nd Embodiment of this invention. It is a circuit diagram which shows the conventional inrush current prevention circuit.

Explanation of symbols

  R1, R2, R3, R4, R5, R6 resistor, C1, C2, C3 capacitor, FET conduction FET, K1 relay.

Claims (3)

A DC power supply terminal connected to the DC power supply, a load terminal connected to the load, and a control terminal; and a resistance value corresponding to a voltage applied to the control terminal between the DC power supply terminal and the load terminal. A conducting element that conducts between;
A first time constant that is connected between the DC power supply terminal and the control terminal and that determines a voltage corresponding to the DC voltage by a resistance component and a capacitance component when a DC voltage is applied to the DC power supply terminal ; A first charging circuit that applies to a control terminal while charging a first capacitor having a capacitance component of:
A second time is connected between the control terminal and the load terminal, and after the conducting element is turned on, a voltage corresponding to the voltage charged in the first charging circuit is determined by a resistance component and a capacitance component. a second charging circuit for applying to the load terminal while charging the second capacitor having a capacitance component is a constant,
With
When a DC voltage is applied to the DC power supply terminal, an inrush current flows through a smoothing capacitor connected in parallel to the load terminal by gradually applying a DC voltage supplied from the DC power supply to the load terminal. Inrush current prevention circuit for preventing
A first discharge circuit having a first discharge resistor connected in parallel to the first capacitor via a switch; and a second discharge circuit for discharging the charge of the second capacitor;
The first discharge circuit includes:
When a DC voltage is not applied to the DC power supply terminal, the switch is turned on to lower the first time constant and promote the discharge of the voltage charged in the capacitive component of the first charging circuit. And an inrush current prevention circuit that prevents re-inrush current by speeding up initialization of the voltage applied to the control terminal. The inrush current prevention circuit according to claim 1,
The second discharge circuit includes:
When a DC voltage is not applied to the DC power supply terminal, the second time constant is reduced to promote the discharge of the voltage charged in the capacitive component of the second charging circuit and applied to the load terminal. Inrush current prevention circuit characterized by speeding up initialization of voltage . The inrush current prevention circuit according to claim 2 ,
The second discharge circuit includes a second discharge resistor connected in parallel to the second capacitor via a switch, and turns on the switch when a DC voltage is not applied to the DC power supply terminal. An inrush current prevention circuit.

Images