JPH08126331A - Regulated dc power source circuit - Google Patents

Abstract

PURPOSE: To provide a power source circuit which can be manufactured at a low cost even when the capacity of the circuit is increased and is provided with a rush current preventing circuit by simplifying the constitution of magnetic parts, such as a coil, a transformer, etc., and by reducing the size of the power source circuit itself by reducing the number of parts used in the circuit. CONSTITUTION: In a power source circuit 1 provided with a power factor improving circuit 4 which is connected to a rectifier circuit 3 and equipped with at least an input capacitor 44, a resistor 80 is provided between the circuits 3 and 4 and, at the same time, a thyristor 81 is connected in parallel with the resistor 80 and a rush current preventing circuit which triggers the thyristor 81 when the voltage across the terminals of the input capacitor 44 in the circuit 4 reaches a set value is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for improving a DC stabilized power supply circuit having a power factor correction circuit.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing an example of a general DC stabilized power supply circuit. In this figure, 1 is a stabilized DC power supply circuit (hereinafter referred to as a power supply circuit), 2 is an AC power supply, 20 is an input filter circuit connected to this AC power supply 2 to cut noise, and 3 is a conversion of AC to DC. For example, a rectifier circuit 4 including a full-wave rectifier bridge is a power factor correction circuit.

The power factor correction circuit 4 is a circuit to which a boost converter is applied, for example, and includes a coil 41, a semiconductor switch 42 such as a field effect transistor, and a diode 4.
3. A power factor correction control circuit 40 for controlling the large-capacity input capacitor 44 and the semiconductor switch 42 whose capacities are determined according to the size of the load and the time of input instantaneous interruption protection.
Made of. The power factor correction circuit 4 is configured to reduce the harmonic component and the effective value of the input current and improve the power factor of the power supply circuit 1 as a whole.

Reference numeral 45 is a pulse width control circuit, 5 is an insulation transformer having the pulse width control circuit 45 connected to the primary side, and 6 is a secondary side of the insulation transformer 5 comprising diodes 60, 61, a choke coil 62 and an output capacitor 63. Is an output rectifier circuit that rectifies the pulse output to the output and smoothes and outputs it to DC.

In the power supply circuit 1 configured as described above, a charging current flows through the input capacitor 44 at the moment when an AC input is applied at the time of starting, but no charge is stored in the input capacitor 44. When a high voltage is applied to the large-capacity input capacitor 44 at the time of, a large current, which is generally called an inrush current, flows instantaneously. The inrush current increases as the capacity of the input capacitor 44 increases as the load increases, and as the input voltage increases.

The inrush current has the same AC power supply 2
In addition to having a great influence on other circuits connected to the power supply circuit 1, stress may be applied to the rectifying bridge 3 and the power supply input fuse (not shown) of the power supply circuit 1 to shorten the life and sometimes damage the fuse. Therefore, various measures have been conventionally taken to suppress the inrush current.

First, FIG. 4 is a circuit diagram showing a main part of a power supply circuit 1 using a simplest protection circuit for suppressing the inrush current. In FIG. 4, an AC power supply 2 and an input filter 20 are shown. A rush current prevention resistor 70 is inserted between the two.

FIG. 5 is a circuit diagram showing a main part of the power supply circuit 1 using the next simplest protection circuit for suppressing the inrush current. In this example, a power thermistor 7 is used instead of the inrush current prevention resistor 70 of the power supply circuit 1 shown in FIG.
0'is inserted.

The power thermistor 70 'has a property that its resistance value becomes smaller as the temperature rises. For this reason, since the resistance value is relatively high at the moment when the AC input is applied, the rush current can be prevented, and the resistance value is lowered by heat generation after several tens of milliseconds, and the loss can be reduced.

Further, in the power supply circuit 1 shown in FIG. 6, an inrush current prevention resistor 70 is inserted between the rectifying bridge 3 and the power factor correction circuit 4, and a thyristor 71 is arranged in parallel with the inrush current prevention resistor 70. It is provided. On the other hand, the coil forming the power factor correction circuit 4 is a choke coil 41a,
A secondary coil 41b is provided on this, and this secondary coil 41b
Power is taken from the diode 72 and the protection resistor 7
3 is input to the trigger terminal of the thyristor 71.

Therefore, at the moment when the AC input is applied to the power supply circuit 1 shown in FIG. 6, a current flows into the input capacitor 44 through the inrush current prevention resistor 70, so that the inrush current can be prevented. Then, after that, the thyristor 71 is powered by the power supplied by the secondary coil 41b.
Is triggered, and thereafter, the current is supplied through the thyristor 71, so that the loss due to the inrush current prevention resistor 70 can be eliminated.

Furthermore, in the power supply circuit 1 shown in FIG. 7, the electric power which gives the trigger input of the thyristor 71 is taken out from the winding 50 provided in the insulating transformer 5 connected to the output of the pulse width control circuit 45, and the power shown in FIG. Similarly, it is input to the trigger terminal of the thyristor 71.

Therefore, in the power supply circuit 1 shown in FIG. 7, like the power supply circuit 1 shown in FIG. 6, at the moment when an AC input is applied, a current flows into the input capacitor 44 through the inrush current prevention resistor 70. Inrush current can be prevented. Then, when the voltage across the terminals of the input capacitor 44 exceeds a certain level thereafter, the pulse width control circuit operates and the winding 50
The electric power is supplied to the thyristor 71, and the thyristor 71 is triggered by the electric power. Therefore, the electric current is thereafter supplied through the thyristor 71, and the loss due to the inrush current prevention resistor 70 can be eliminated.

Further, in addition to the above-mentioned inrush current prevention method, although not shown, there is also a method of using a commercially available hybrid IC having a built-in inrush current prevention circuit in the power supply circuit 1.

[0015]

However, the conventional power supply circuit described above has the following drawbacks. First, in the power supply circuit shown in FIG. 4, since a current always flows through the inrush current prevention resistor 70, a large power loss always occurs. Further, since a large current flows through the inrush current prevention resistor 70, the inrush current prevention resistor 70 itself becomes large, and the power supply circuit 1 in which the inrush current prevention resistor 70 is inserted also has an extremely large size in consideration of this heat dissipation. is there.

The power supply circuit shown in FIG. 5 can reduce the power loss as compared with the power supply circuit of FIG. 4, but this power loss cannot be eliminated and the power supply circuit 1 becomes large. . In addition to this, power
Since the thermistor 70 'has time to radiate heat, it does not return to the original high resistance at the moment when the AC input to the power supply circuit 1 is cut off, and loses its current limiting ability when turning on / off at short intervals. There is a drawback that it ends up.

Further, in the power supply circuit shown in FIG. 6, the choke coil 4 is used in order to obtain the power for triggering the thyristor 71 from the choke coils 41a and 41b of the power factor correction circuit 4.
1a and 41b are increased in size, workability in manufacturing the choke coils 41a and 41b is deteriorated, and it takes time and labor to increase the cost.

In the power supply circuit shown in FIG. 7, the insulation transformer 5 is complicated and large in size, and there is a drawback in that manufacturing is time-consuming and manufacturing cost is increased. There is a drawback in that the size of 1 itself is also increased.

Further, commercially available hybrid ICs with a built-in inrush current prevention circuit are only for small-capacity power supply circuits, and are not suitable for large-capacity power supplies. Since the hybrid IC has a built-in rectifier for rectifying the supplied AC power into DC, the hybrid IC
C itself becomes large. Moreover, since such a special hybrid IC is expensive, there is a drawback that the manufacturing cost is increased.

The present invention has been made in consideration of the above points, and the structure of magnetic parts such as a coil and a transformer is simplified, and the number of parts is reduced to downsize the power supply circuit itself. At the same time, it is an object of the present invention to provide a power supply circuit having an inrush current prevention circuit that can be manufactured at low cost even if the power supply circuit has a large capacity.

[0021]

According to the present invention, in a power supply circuit including a power factor correction circuit having at least a capacitor, which is connected to a rectification circuit, a current limiting element is provided between the rectification circuit and the power factor correction circuit. And a switching element provided in parallel with the current limiting element to make the switching element conductive when the voltage across the terminals of the capacitor in the power factor correction circuit reaches a set value. It is characterized by having.

Further, the switching element may be made conductive by a voltage obtained by resistance-dividing a voltage between terminals of a capacitor of the power factor correction circuit.

Alternatively, a zener diode may be connected between the capacitor in the power factor correction circuit and the trigger input of the switching element so that the switching element is rendered conductive by the voltage across the terminals of the capacitor.

[0024]

In the above invention, a current limiting element is provided between the rectifying circuit and the power factor improving circuit, and a switching element is provided in parallel with the current limiting element so that a terminal of a capacitor in the power factor improving circuit. By making the switching element conductive when the inter-state voltage reaches the set value, when there is not enough electric charge in the capacitor at the initial stage when the AC power is applied to this power supply circuit, the current limiting element is used. Current flows, the rush current can be effectively prevented, and the switching element is triggered when the voltage between the terminals of the capacitor exceeds a certain value by accumulating the electric charge. Since current flows through the switching element so as to bypass the current, current flows through this switching element, and almost no current flows through the current limiting element. It is never caused loss caused by element.

In addition, it is not necessary to take out the electric power for conducting the switching element from the coil of the power factor correction circuit, the insulating transformer or the like, and the magnetic parts such as the coil and the transformer are simplified in structure, so that the size can be reduced. Also, it can be formed at low cost.

Further, when the switching element is made conductive by a voltage obtained by resistance-dividing the terminal voltage of the capacitor of the power factor correction circuit, the reference terminal voltage of the capacitor for making the switching element conductive is clarified. Can be set to, and surely stable operation can be performed.

Furthermore, when a zener diode is connected between the capacitor in the power factor correction circuit and the trigger input of the switching element and the switching element is made conductive by the voltage across the terminals of this capacitor, the switching element is Since the voltage is made conductive, the reference voltage between the terminals of the capacitor can be clearly determined, and stable operation can be ensured and the circuit can be simplified.

[0028]

EXAMPLES Examples of the present invention will be described below. still,
In the following description, the members denoted by the same reference numerals as those in FIG. 3 are the same or equivalent members, and thus detailed description thereof will be omitted.

FIG. 1 is a circuit diagram showing a main part of a power supply circuit 1 showing a first embodiment of the present invention. The inrush current prevention circuit shown in the figure is provided in the basic circuit of the power supply circuit 1 shown in FIG.

In FIG. 1, reference numeral 80 is a current limiting element provided between the rectifier circuit 3 and the power factor correction circuit 4, and here is a resistor. Reference numeral 81 is a thyristor as a switching element provided in parallel with the resistor 80. Reference numerals 82 and 83 denote voltage dividing resistors provided in series for dividing the voltage between the terminals of the input capacitor 44. An intermediate point P between the voltage dividing resistors 82 and 83 is a diode 86 for protection against reverse current and a protection resistor. It is connected to the trigger terminal of the thyristor 81 via 84.

In the power supply circuit 1 constructed as described above, since no electric charge is stored in the input capacitor 44 at the initial stage when the voltage from the AC power supply 2 is applied, the input capacitor 44 is not charged. Has no potential difference, and the thyristor 81 remains in the off state (non-conduction state).
In this state, the current flows through the input filter 20, the rectifier circuit 3,
It flows into the input capacitor 44 through the choke coil 41 and the diode 43, is current-limited by the resistor 80, and returns to the rectifier circuit 3.

Therefore, the inrush current I _P flowing into the input capacitor 44 is limited by the resistor 80. In addition,
This inrush current I _P is the input voltage from the AC power supply 2 to V
_{Letting IN be} and the size of the resistor 80 be R ₈₀ , it is expressed as shown in the following equation (1). I _P = √2 × V _IN / R ₈₀ …… (1)

Therefore, the larger the resistance value R ₈₀ of the resistor 80, the smaller the inrush current I _P can be made.

When the power factor correction circuit 4 operates and the voltage between the terminals of the input capacitor 44 increases, the voltage at the intermediate point P between the voltage dividing resistors 82 and 83 also increases, which causes the thyristor 81 to pass through the protection resistor 84. Trigger.

When the thyristor 81 is triggered and turned on (conducting state), the current flowing through the resistor 80 until then flows through the thyristor 81, and the power loss due to the resistor 80 is eliminated. be able to.

In this embodiment, the input capacitor 4
In order to supply the trigger signal to the thyristor 81 by using the inter-terminal voltage of 4, the voltage dividing resistors 82 and 83 are provided and the potential of the intermediate point P thereof is used, so that the circuit configuration is simplified.

Further, in this embodiment, the inrush current I _P
The voltage between the terminals of the input capacitor 44, which is the cause of occurrence of the voltage, is divided by the voltage dividing resistors 82 and 83 and used for triggering the thyristor 81. With thyristor 81
Can be triggered, and extremely accurate and reliable control can be performed.

FIG. 2 is a circuit diagram showing a main part of the power supply circuit 1 showing the second embodiment of the present invention. In the figure, the members designated by the same reference numerals as those shown in FIG. 1 are the same or equivalent members, and thus detailed description thereof will be omitted.

In FIG. 2, reference numeral 85 is a Zener diode, which is inserted between the input capacitor 44 and the trigger terminal of the thyristor 81. In this case, for example, when driving the power supply circuit 1, for example, 2 between the terminals of the input capacitor 44.
In the case of a power supply circuit that outputs a voltage of about 00V, the thyristor 81 is triggered by setting the voltage drop by the Zener diode 85 to 120V.

Therefore, in the initial stage when the voltage is started to be applied to the power supply circuit 1, since no charge is stored in the input capacitor 44 as in the first embodiment, a potential difference is generated between the terminals of the input capacitor 44. However, the thyristor 81 is off. Then, charge is stored in the input capacitor 44 through the resistor 80, and the inrush current I _P is limited by the resistor 80.

When the power factor correction circuit 4 operates and the voltage across the terminals of the input capacitor 44 increases, the trigger input of the thyristor 81 connected through the Zener diode 85 and the protection resistor 84 also gradually increases. And
As previously set by the Zener diode 85, the thyristor 81 is triggered and turned on when the voltage between the terminals of the input capacitor 44 exceeds a predetermined voltage.

Then, the current which has passed through the resistor 80 until then flows through the thyristor 81,
The power loss due to the resistor 80 can be eliminated.

In the second embodiment, the thyristor 7
Input capacitor 44 to provide a trigger signal of 1
It is constituted by an extremely simple circuit in which the terminal voltage of (3) is dropped by the Zener diode 85 and connected to the trigger terminal of the thyristor 81. Therefore, the manufacturing cost of the power supply circuit 1 can be minimized, and the circuit mounting area can be reduced as much as possible.

Further, in the second embodiment, the terminal voltage of the input capacitor 44 causing the inrush current is dropped and used for triggering the thyristor 81. Therefore, the thyristor 81 can be triggered at an optimum time, and extremely accurate and reliable control can be performed.

In each of the above embodiments, the switching element 81 is triggered by using the voltage across the input capacitor 44. Therefore, the switching element 81
The power supply circuit 1 can be used for a magnetic component that does not need to extract electric power from the magnetic component such as the choke coil 41 and the isolation transformer 5 for the trigger of No. 1 and has a relatively large size. It can be miniaturized as much as possible.

Further, according to the present invention, the capacity of the power supply circuit 1 is not limited unlike the commercially available hybrid IC with a built-in inrush current prevention circuit, so that the capacity of the rectifier circuit 3, the input capacitor 44, the insulating transformer 5 and the like can be adjusted. And voltage dividing resistors 82 and 8
3 can be applied to the power supply circuit 1 having an arbitrary capacity by appropriately changing the sizes of the voltage of the Zener diode 85, the voltage of the Zener diode 85, and the allowable current of the switching element 81.

In each of the above embodiments, a thyristor is used as the switching element 81, but the present invention is not limited to this. For example, a triac, a G
A switching element such as a TO thyristor or FET transistor may be used.

In each of the above embodiments, a concrete example of making the switching element 81 conductive by using the voltage between the terminals of the input capacitor 44 is shown, but the present invention is not limited to this. For example, instead of the resistance voltage division, an appropriate method such as voltage division by a capacitor connected in series may be used.

Further, the power supply circuit of the present invention is not applied only to the power factor correction circuit 4 having the above-mentioned configuration, but may be any power factor correction circuit 4 having the input capacitor 44.

[0050]

As described above, according to the present invention, a current limiting element is provided between the rectifier circuit and the power factor correction circuit, and a switching element is provided in parallel with the current limiting element. By configuring the switching element to conduct when the voltage between the terminals of the capacitor in the power factor correction circuit reaches a set value, the capacitor is sufficiently charged at the initial stage when AC power is applied to this power supply circuit. When there is no charge, current flows through the current limiting element, so inrush current can be effectively prevented, and when the charge is stored in the capacitor and the voltage across its terminals exceeds a certain value, the switching element Since it conducts, a current flows thereafter through this switching element, so that there is no loss due to the current limiting element.

In addition, it is not necessary to take out the electric power for conducting the switching element from the coil of the power factor correction circuit, the insulating transformer, etc., and the magnetic parts such as the coil and the transformer are simplified in structure, so that the size can be reduced. Also, it can be formed at low cost.

When the switching element is rendered conductive by a voltage obtained by resistance-dividing the terminal voltage of the capacitor of the power factor correction circuit, the reference terminal voltage of the capacitor for conducting the switching element is clarified. Can be set to, and surely stable operation can be performed.

Furthermore, when a zener diode is connected between the capacitor in the power factor correction circuit and the trigger input of the switching element and the switching element is made conductive by the voltage across the terminals of this capacitor, the switching element is Since the voltage is made conductive, the reference voltage between the terminals of the capacitor can be clearly determined, and stable operation can be ensured, and the circuit can be configured more simply.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a main part of a power supply circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a main part of a power supply circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of a conventional general power supply circuit.

FIG. 4 is a circuit diagram showing a main part of a power supply circuit using a conventional inrush current prevention circuit.

FIG. 5 is a circuit diagram showing a main part of a power supply circuit using another conventional inrush current prevention circuit.

FIG. 6 is a circuit diagram showing a main part of a power supply circuit using another conventional rush current prevention circuit.

FIG. 7 is a circuit diagram showing a main part of a power supply circuit using another conventional inrush current prevention circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... DC stabilized power supply circuit, 3 ... rectification circuit, 4 ... power factor improvement circuit, 80 ... current limiting element, 81 ... switching element, 44
… Capacitor, 85… Zener diode.

Claims (3)

[Claims] 1. In a stabilized DC power supply circuit including a power factor correction circuit having at least a capacitor, which is connected to a rectification circuit, a current limiting element is provided between the rectification circuit and the power factor correction circuit, and A switching element is provided in parallel with the current limiting element, and an inrush current prevention circuit is provided to make the switching element conductive when the voltage across the terminals of the capacitor in the power factor correction circuit reaches a set value. DC stabilized power supply circuit. 2. The stabilized DC power supply circuit according to claim 1, wherein the switching element is made conductive by a voltage obtained by resistance-dividing a voltage between terminals of a capacitor of the power factor correction circuit. 3. A zener diode is connected between a capacitor in the power factor correction circuit and a conduction signal input of the switching element, and the switching element is rendered conductive by the voltage across the terminals of the capacitor. DC stabilized power supply circuit described in.