JP2000184701A - Power supply equipment with current limiting function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a safe power supply having current limiting function with no restriction on a difference in the magnitude between the input voltage and the output voltage for application conditions. SOLUTION: A first bias circuit 4 is connected between the base of a switching transistor Q1 and a control circuit 3 and a second bias circuit 7 is connected to the base of the transistor Q1. The second bias circuit 7 consists of a driving circuit 5 for supplying bias to the transistor Q1 according to a driving signal supplied from the control circuit 3 and a current limiter circuit 6a which changes the magnitude of the bias to be supplied to the transistor Q1 through the driving circuit 5 according to the output of the transistor Q1. In this configuration, the emitter of a control transistor Q4 of the current limiter circuit 6a is connected to earth.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for suppressing an inrush current generated when a power supply device is started.

[0002]

2. Description of the Related Art Usually, a capacitor (output capacitor) is connected in parallel to an output side of a power supply device for storing electric power or suppressing voltage fluctuation. At times, it causes a large transient current, that is, an inrush current. The inrush current is highly harmful, such as inducing noise and stressing circuits or devices connected to the system, and it is desirable to minimize the inrush current. Means for suppressing the inrush current of the power supply include means for connecting an impedance circuit, which is short-circuited during normal operation, to the input side of the power supply, and means for reducing the on-duty of the switching element at startup. One is well known. In addition, there are various means for suppressing inrush current. For example, there is a power supply device for suppressing inrush current having a configuration as shown in FIG.

FIG. 3 shows a circuit of a conventional power supply device capable of suppressing an inrush current by providing a current limiter circuit, and has the following configuration. FIG. 3
1, 1 and 2 indicate an input terminal and an output terminal on the high potential side, and the input terminal and the output terminal on the low potential side are connected to the ground, and are not shown. Switching transistor Q1 between input terminal 1 and output terminal 2
And the choke coil L1 are connected in series, an output capacitor C2 is connected between one end of the output terminal side 2 of the choke coil L1 and the ground, and a diode D1 is connected between the other end of the choke coil L1 and the ground. You. The switching transistor Q1, the choke coil L1, the output capacitor C2, and the diode D1 form a step-down chopper type converter circuit.

A control circuit 3 is provided, a pulse output terminal PO of the control circuit 3 is connected to the base of a switching transistor Q1 via a resistor R8, and a voltage detection terminal FB is connected in series between the output terminal 2 and ground. Resistance R1 and resistance R2
To the connection point. A resistor R9 is connected in parallel with the resistor R8.
And a series circuit of a control transistor Q5, and the base of the control transistor Q5 is connected to an output terminal 2 via a resistor R10.
Connected to Here, a current limiter circuit 8 is formed by the resistors R8, R9, the control transistor Q5, and the resistor R10. Note that C1 connected between the input terminal 1 and the ground is a filter capacitor.
In the circuit of FIG. 3 configured as described above, the general operation at the time of startup is as follows.

When a voltage is externally supplied to the input terminal 1, the control circuit 3 starts operating, and a drive signal having a predetermined on-duty appears at its pulse output terminal PO. Then, the switching transistor Q1 is turned on or off in accordance with the drive signal, and allows the current to pass through the main current path between the emitter and collector terminals in the on state. This current flows into the output capacitor C2 via the choke coil L1, and increases the voltage between the terminals. Immediately after startup, when the voltage between the terminals of the output capacitor C2 is substantially zero, the control transistor Q5 is off, and the base current of the switching transistor Q1 is substantially determined by the resistor R8. Where the resistance R
8, a high-resistance element is used, so that the base current of the switching transistor Q1 has a small value.
The peak value of the current passing between the emitter and the collector is limited to a small value. As a result, the rush current flowing into the circuit from the input terminal 1 is suppressed.

The output capacitor C2 is charged by the current passing through the switching transistor Q1, and when the voltage between its terminals increases, the control transistor Q5
Becomes conductive, and a current also flows through the series circuit of the resistor R9 and the control transistor Q5. The current flowing in the series circuit of the resistor R9 and the control transistor Q5 increases as the voltage between the terminals of the output capacitor C2 increases, and the base current of the switching transistor Q1 gradually increases. Then, the peak value of the current passing between the emitter and the collector of the switching transistor Q1 also gradually increases, and more current is supplied to the external load connected to the output capacitor C2 and the output terminal 2.

When the voltage between the terminals of the output capacitor C2 exceeds a predetermined value, the control transistor Q2 is turned on, and a parallel circuit of a resistor R8 and a resistor R9 is substantially provided between the base of the switching transistor Q1 and the pulse output terminal PO. Becomes Thereby, the switching transistor Q
The base current of 1 and the value of the current passing between its emitter and collector are increased, and a sufficient current is supplied to the external load connected to the output capacitor C2 and the output terminal 2. Thereafter, the switching transistor Q1
A normal switching operation is performed according to a signal appearing at the pulse output terminal PO of the control circuit 3, and the circuit shown in FIG. 3 enters a steady operation state.

That is, the power supply device having the circuit configuration shown in FIG.
A current limiter circuit 8 including a resistor R8, a resistor R9, a control transistor Q5, and a resistor R10 narrows down the base current of the switching transistor Q1 at startup and uses the constant current characteristic of the collector saturation current of the transistor element to start the switching transistor Q1. Keep the passing current low. The current passing through the switching transistor Q1 is gradually increased according to the voltage between the terminals of the output capacitor C2, that is, the output voltage of the power supply device, and the power supply device is started while preventing a large inrush current from flowing.

[0009]

When verifying the voltages appearing at various parts of the power supply device shown in FIG. 3, when the switching transistor Q1 is in the off state, the voltage at the position of the pulse output terminal PO of the control circuit 3 is almost equal to the input. The magnitude is equal to the voltage. On the other hand, since the circuit shown in FIG. 3 has a configuration of a step-down chopper type converter, the input voltage supplied to the input terminal 1 has a higher value than the output voltage appearing at the output terminal 2. Then, the switching transistor Q1
Is in the off state, a reverse bias voltage having a magnitude corresponding to the difference between the input voltage and the output voltage is applied between the base and the emitter of the control transistor Q5 constituting the current limiter circuit 8.

If a high input voltage is applied to the input terminal 1 and the difference between the input voltage and the output voltage exceeds the breakdown voltage between the base and the emitter of the control transistor Q5, the control transistor Q5 is damaged. Might be. Therefore, the power supply device having the circuit configuration shown in FIG.
It can be applied only to the specification where the difference between the input voltage and the output voltage is always equal to or less than the reverse breakdown voltage between the base and the emitter of the control transistor Q5. There was a problem. Therefore, an object of the present invention is to provide a power supply device with a current limiter function that is highly safe and the application conditions are not limited to the magnitude of the difference between the input voltage and the output voltage.

[0011]

A power supply device with a current limiter function according to the present invention changes a flow rate of a current passing through a current control element in response to a signal from a control circuit, thereby obtaining a desired voltage value or a current value. In a power supply that obtains output,
A first bias circuit and a second bias circuit for supplying a bias to a control terminal of the current control element in accordance with a signal from the control circuit, wherein the second bias circuit comprises:
A drive circuit connected to the control terminal of the current control element and supplying a bias to the control terminal of the current control element in accordance with a signal from the control circuit; and a drive circuit connected between the drive circuit and the reference potential point, A current limiter circuit for changing the magnitude of the bias supplied to the control terminal of the current control element in accordance with a signal corresponding to a voltage or current appearing on the output side of the current control element.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first bias circuit is connected between a control terminal of a current control element and a control circuit, and a second bias circuit is connected to a control terminal of the current control element. Here, the second bias circuit includes a drive circuit for supplying a bias to the current control element according to a drive signal supplied from the control circuit, and a magnitude of the bias supplied to the current control element via the drive circuit. It comprises a current limiter circuit that changes according to the output of the current control element. Specifically,
The drive circuit complementarily connects two transistor elements having different polarities, and connects a commonly connected emitter of the complementary connection transistor circuit to a control terminal of the current control element. Further, the commonly connected bases of the complementary connection transistor circuits are connected to the control circuit, and one collector is connected to the current input terminal of the current control element.

In the current limiter circuit, a main current path of a control transistor is connected between the other collector of the drive circuit and a reference potential point, and a base of the control transistor is connected to a current control element via a resistance element. The capacitor is connected to the output side terminal, and a capacitor element is connected between the base of the control transistor and the reference potential point. Note that the circuit configuration may be such that the base of the control transistor is connected to one end of the output capacitor of the power supply device and the capacitor element is omitted.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a circuit diagram of a power supply device with a current limiter function according to a first embodiment of the present invention, in which application conditions are not limited to the magnitude of a difference between an input voltage and an output voltage. In the circuit shown in FIG. 1, the switching transistor Q1, the choke coil L1, the diode D1, and the output capacitor C2 are connected so as to have a circuit configuration of a step-down chopper type converter similarly to the circuit of FIG. A circuit portion provided between the base of the switching transistor Q1 and the control circuit 3 for supplying a bias to the switching transistor Q1 has the following configuration. A resistor R4 is connected between the base of the switching transistor Q1 and the pulse output terminal PO of the control circuit 3. This resistor R4 becomes the first bias circuit 4.

First and second driving transistors Q2 and Q3 having different polarities are provided in a circuit in the form of a complementary operation circuit in which bases and emitters are commonly connected to each other. The common connection point of the emitters of the driving transistors Q2 and Q3 is connected to the base of the switching transistor Q1 via a parallel circuit of a base current limiting resistor R3 and a capacitor C3. The common connection point between the bases of the driving transistors Q2 and Q3 is connected to the pulse output terminal PO of the control circuit 3,
The common connection point is connected to the input terminal 1 via the resistor R5. The collector of the first driving transistor Q2 is connected to the input terminal 1.

The collector of the control transistor Q4 is connected to the collector of the second driving transistor Q3, and the emitter of the control transistor Q4 is connected to the ground. The base of the control transistor Q4 is connected to the current output terminal of the switching transistor Q1 via the resistor R6, that is, the collector, and the resistor R7 and the capacitor C4 are connected between the base of the control transistor Q4 and the ground. The driving circuit 5 is formed by the first and second driving transistors Q2 and Q3 and the resistor R5, and a current limiter circuit 6a is formed by the control transistor Q4, the resistors R6 and R7, and the capacitor C4. And the current limiter circuit 6a constitute a second bias circuit 7.

In such a circuit configuration, when a voltage is externally supplied to the input terminal 1, the control circuit 3 starts operating, and a predetermined on-duty drive signal appears at the pulse output terminal PO. . In the circuit of FIG. 1, when the voltage at the position of the pulse output terminal PO is low, the first path from the base of the switching transistor Q1 to the pulse output terminal PO via the resistor R4 and the resistor R3 from the base of the switching transistor Q1 The base current of the switching transistor Q1 flows in a second path from the parallel circuit of the capacitor C3, the driving transistor Q3 which has been turned on, and the ground via the control transistor Q4. Therefore, the switching transistor Q1 is biased by the base current flowing through each path according to the drive signal appearing at the pulse output terminal PO,
On and off operations are performed.

By the way, immediately after the start of the power supply, the voltage between the terminals of the capacitor C4 is almost zero, and the control transistor Q4 is in the off state. For this reason, no current can flow through the second path, and the switching transistor Q1 operates by receiving a bias only from the base current flowing through the first path. Here, if an element having a high electric resistance is applied to the resistor R4, the base current of the switching transistor Q1 becomes small due to the high resistance of the resistor R4. Then, the peak value of the current passing between the emitter and the collector of the switching transistor Q1 is limited to a small value. As a result, the rush current flowing from the input terminal 1 into the circuit is suppressed.

The current passing through the switching transistor Q1 flows into the output capacitors C2 and C4 via the choke coil L1 or the resistor R6, and charges each capacitor. When the voltage between the terminals of the capacitor C4 rises due to the charging, the control transistor Q4 is eventually turned on, and the base current of the switching transistor Q1 also flows through the second path. As the voltage between the terminals of the capacitor C4 increases, the current passing through the control transistor Q4, that is, the current flowing through the second path increases, and the total base current of the switching transistor Q1 gradually increases. Then, the switching transistor Q
The peak value of the current passing between the emitter and the collector of the first capacitor also gradually increases, and more current is supplied to an external load connected to the output capacitor C2 and the output terminal 2.

When the voltage between the terminals of the capacitor C4 becomes equal to or more than a predetermined value, the control transistor Q4 enters a full ON state, and the base current of the switching transistor Q1 becomes the maximum after the start. It is assumed that the control circuit 3 used in the circuit of FIG. 1 has a configuration in which a drive signal is displayed by connecting or disconnecting the pulse output terminal PO and the ground by an internal transistor element. In such a case, the maximum value of the base current of the switching transistor Q1 is substantially equal to the resistance R3 and the capacitor C3.
And the impedance value of the parallel circuit of the resistor R4 and the magnitude of the input voltage. This eliminates the effect of suppressing the current (rush current) flowing into the power supply device at the time of startup, and thereafter the power supply circuit shown in FIG. 1 enters a steady operation state.

In the power supply device with a current limiter function shown in FIG. 1, the base of the control transistor Q4 has a resistance R
6, the collector of the switching transistor Q1 is connected, and the emitter of the control transistor Q4 is connected to the reference potential point, that is, the ground. With this configuration, even when an input voltage having a high voltage value is applied, a large reverse bias voltage is not applied between the base and the emitter of the control transistor Q4 as in the related art (FIG. 3). As a result, the effect that the control transistor Q4 is not damaged and the application condition of the power supply device is not limited by the difference between the input voltage and the output voltage can be obtained.

In the current limiter circuit 6a of FIG. 1, the capacitor C4 is connected between the base of the control transistor Q4 and the ground, and the base of the control transistor Q4 is connected to the collector of the switching transistor Q1 via the resistor R6. ing. With this configuration, the amount of change in the amount of conduction of the control transistor Q4 with time at the time of startup is determined by the resistance R
6 and the capacitance value of the capacitor C4, it is possible to obtain an additional effect such that it becomes easy to set the starting conditions to those according to the load specifications and the input specifications.

FIG. 2 is a circuit diagram of a power supply device with a current limiter function according to a second embodiment of the present invention. In the circuit shown in FIG. 2, one end of the resistor R6 connected to the collector of the switching transistor Q1 in the circuit of FIG. 1 is connected to one end of the output capacitor C2.
This is a circuit in which the capacitor C4 in the circuit of FIG. 1 is omitted. The circuit in FIG. 1 changes the conduction state of the control transistor Q4 according to the voltage between the terminals of the capacitor C4. On the other hand, the circuit shown in FIG. 2 uses the voltage between the terminals of the output capacitor C2 instead of the voltage between the terminals of the capacitor C4 in the circuit of FIG. 1, and controls the control transistor Q4 according to the voltage between the terminals of the output capacitor C2. It changes the conduction state.

The circuit of FIG. 2 having such a configuration is the same as that of FIG.
There is an advantage that the number of components related to the capacitor C4 in the circuit described above can be reduced. However, when it is necessary to set the amount of change with time of the conduction state of the control transistor Q4, a capacitor is further connected between the base and the emitter of the control transistor Q4 in the circuit of FIG. 2 as in the circuit of FIG. It does not matter. The operation of the current limiter circuit 6b and the entire power supply device shown in FIG. 2 is basically the same as that of the circuit of FIG. 1 except that the function of the capacitor C4 is basically replaced by the output capacitor C2.

In the circuits shown in FIGS. 1 and 2 described above, the driving circuit 5 includes the first driving transistor Q2 and the second driving transistor Q2.
Is constituted by a circuit in which the driving transistor Q3 is complementarily connected. However, it is not always necessary to adopt this circuit configuration in practicing the present invention. For example, one of the two driving transistors may be omitted, and a position where the main current path of the omitted driving transistor is connected may be used. A circuit configuration for connecting a resistance element having a relatively high electric resistance may be used. Further, as a power supply device to which the present invention is applied,
In the circuits of the respective embodiments, a step-down chopper type converter circuit is illustrated. However, the power supply circuit to which the present invention can be applied is not limited to this, and is also applicable to a boost chopper type converter circuit and an insulation type switching power supply circuit using a transformer.

In the circuit of the embodiment shown in each figure, a resistor R7 is connected between the base of the control transistor Q4 and the ground.
Is connected, for example, a constant voltage diode element may be connected instead of the resistance element, or may be omitted in some cases. Further, in the circuit of the embodiment shown in each figure, when the control transistor Q2 is turned on, the resistor R3 limits the base current of the switching transistor Q1, and the capacitor C3 is a speed-up capacitor. . Therefore, this resistance R
The parallel circuit of the capacitor 3 and the capacitor C3 only needs to be connected on the second path connecting the base of the switching transistor Q1 and the emitter of the control transistor Q4, and the operation of the circuit does not change depending on the connection position.

In the circuit of the embodiment shown in each figure,
The other end of the first bias circuit 4 is connected to the pulse output terminal PO of the control circuit 3 to supply a drive signal directly to the base of the switching transistor Q1. However, a circuit in which a drive circuit including a transistor whose base is connected to the pulse output terminal PO is connected in series to the first bias circuit 4, and a drive signal is indirectly supplied to the base of the switching transistor Q1. It may be configured. As described above, the power supply device with the current limiter function according to the present invention is not limited to the circuit configurations shown in FIGS.
Various modifications are possible without changing the gist of the present invention.

[0028]

As described above, the power supply device with a current limiter function according to the present invention has two bias circuits, one of which drives a current limiting element in accordance with a signal from a control circuit. And a current limiter circuit connected between the drive circuit and the reference potential point. With such a configuration, the emitter of the control transistor in the current limiter circuit is connected to the ground, and the control transistor is not likely to be damaged even if the difference between the input voltage and the output voltage increases. As a result, the application condition of the power supply device is not limited by the difference between the input voltage and the output voltage.

The amount of change in the conduction state of the control transistor at the time of startup can be arbitrarily determined by the capacitor and the first resistor connected between the control terminal of the control transistor in the current limiter circuit and one end of the main current path. Can be set.
For this reason, it is possible to obtain an additional effect that the starting condition can be easily set according to the load specification and the input specification. Therefore, according to the present invention, it is possible to provide a highly safe power supply device with a current limiter function without being limited by the difference between the input voltage and the output voltage.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply device with a current limiter function according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a power supply device with a current limiter function according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a conventional power supply device capable of suppressing an inrush current by providing a current limiter circuit.

[Description of Signs] 1: Input terminal 2: Output terminal 3: Control circuit
4: First bias circuit 5: Drive circuit
6a, 6b: current limiter circuit 7: second bias circuit C2: output capacitor C4: capacitor (capacitive element) PO: pulse output terminal
Q1: Switching transistor (current control element)
Q1: second driving transistor (driving transistor) Q3: second driving transistor (driving transistor) Q4: control transistor R4: resistance (third resistance) R6: resistance (first resistance or second resistance) Resistance)

Claims (5)

[Claims] 1. A power supply device for changing a flow rate of a current passing through a current control element in accordance with a signal from a control circuit to obtain a desired voltage value or a current value. A first bias circuit and a second bias circuit for supplying a bias to the control terminal of the current control element, wherein the second bias circuit is connected to the control terminal of the current control element. A drive circuit for supplying a bias to a control terminal of the current control element in response to a signal from the control circuit; a drive circuit connected between the drive circuit and a reference potential point; A current limiter circuit for changing the magnitude of the bias supplied to the control terminal in accordance with a signal corresponding to a voltage or current appearing on the output side of the current control element. Power supply with miter function. 2. The current limiter circuit comprises: a control transistor having a main current path connected between the drive circuit and a reference potential point; a control terminal of the control transistor and a current output terminal of the current control element. 2. The current limiter according to claim 1, further comprising a first resistor connected between the first and second terminals, and a capacitor connected between a control terminal of the control transistor and one end of the main current path. Power supply with function. 3. The current limiter circuit further comprises: a control transistor having a main current path connected between the drive circuit and a reference potential point; a control terminal of the control transistor; and one end of an output capacitor forming a power supply circuit. 2. The power supply device with a current limiter function according to claim 1, further comprising a second resistor connected between the first and second resistors. 4. The drive circuit according to claim 1, further comprising a drive transistor having a control terminal connected to the control circuit and one end of a main current path connected to a control terminal of the current control element. The power supply device with a current limiter function according to any one of claims 1 to 3. 5. The control circuit according to claim 1, wherein said first bias circuit comprises a third resistor connected between a control terminal of said current control element and said control circuit. The power supply device with a current limiter function described in 1.