JPH1032982A - Inrush-current preventive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inrush-current preventive circuit which can prevent an excessive inrush current from being generated with reference to the momentary interruption of an input AC and which can restrain heat from being generated when the side of a load is short-circuited. SOLUTION: An inrush-current preventive circuit is provided with a resistance 13 which is inserted across a rectifying circuit 30 and a smoothing capacitor 31, with an operational amplifier 14 which outputs a signal according to the difference between a voltage Vr across both ends of the resistance 13 and a reference voltage Vref and with a transistor 11 by which a collector-emitter impedance inserted across the smoothing capacitance 31 and the rectifying circuit 30 is made variable on the basis of a signal from the operational amplifier 14 which is inputted to a base.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inrush current (inrush current) prevention circuit for an AC / DC power supply.

[0002]

2. Description of the Related Art In an AC / DC power supply device, when an input AC is applied, an inrush current (inrush current) is generated by a charging current flowing into a large-capacity smoothing capacitor.
It is not uncommon for this inrush current to show tens to hundreds of amps. As a circuit to prevent this inrush current,
BACKGROUND ART Conventionally, there are a type using a relay and a type using a thyristor. Hereinafter, both will be described.

First, an inrush current prevention circuit using a relay will be described with reference to FIG.

FIG. 8 is a schematic diagram of a rush current prevention circuit using a conventional relay. Here, reference numeral 60 denotes a rectifier circuit for rectifying an AC input waveform, 61 denotes a smoothing capacitor, 62 denotes a transformer constituting a switching regulator, 63 denotes a switching transistor for generating a voltage on the secondary side of the transformer 62, and 64 denotes switching. Transistor 63
Is a drive circuit that drives. The drive circuit 64
It operates with the voltage charged in the smoothing capacitor 61.

[0005] An inrush current prevention circuit 50 shown in FIG. 8 includes a limiting resistor 51 inserted in series to one input AC line,
A switch 52 for short-circuiting both ends of the limiting resistor 51,
And a relay 53 inserted between the two input AC lines to control the ON / OFF operation of the switch 52. The relay 53 turns on the switch 52 when a voltage higher than the operating voltage value is applied to both ends. On the other hand, when the voltage applied to both ends becomes equal to or lower than the reset voltage value, the switch 52
To OFF.

An inrush current prevention circuit 50 using a relay shown in FIG. 8 uses a delay time of a relay to prevent an inrush current. That is, when the input AC is turned on, the relay 5
The switch 52 is turned on by applying a voltage equal to or higher than the operating voltage value to both ends of the switch 3, and the control resistor 51 is short-circuited. However, due to the delay time of the relay 53, the switch 52 is turned on after AC is input. There is a time lag before it becomes. Therefore, when the input AC is turned on, the input AC is supplied to the rectifier circuit 60 via the control resistor 51. Therefore, it is possible to prevent an excessive current from flowing into the smoothing capacitor 61 when the input AC is turned on. it can.

Next, an inrush current prevention circuit using a thyristor will be described with reference to FIG.

FIG. 9 is a schematic diagram of a rush current prevention circuit using a conventional thyristor. Here, components having the same functions as those shown in FIG. 8 are denoted by the same reference numerals.

[0009] An inrush current prevention circuit 70 shown in FIG. 9 includes a limiting resistor 71 inserted in series with the output line of the rectifier circuit 60.
And a thyristor 72 having an anode connected to the terminal of the limiting resistor 71 on the rectifier circuit 60 side and a cathode connected to a terminal of the limiting resistor 71 on the transformer 62 side, and a gate of the thyristor 72 wound around the transformer 62. A coil 73 for applying a voltage between the cathodes, and a resistor 74 inserted between the coil 73 and the gate of the thyristor 72 are provided. The thyristor 72 becomes conductive when a voltage higher than the trigger voltage value is applied between the gate and the cathode.

[0010] In the inrush current prevention circuit 70 using a thyristor shown in FIG.
The output from 0 flows into the smoothing capacitor 61 through the limiting resistor 71, and charges the smoothing capacitor 61.
Thus, it is possible to prevent an excessive current from flowing into the smoothing capacitor 61 when the input AC is turned on. When the voltage charged in the smoothing capacitor 61 becomes equal to or higher than a predetermined value, the drive circuit 64 operates to cause the switching transistor 63 to perform a switching operation. As a result, electric power is generated in the coil 73, and the electric power is
4 is supplied to the gate of the thyristor 72. When the gate-cathode voltage of the thyristor 72 becomes equal to or higher than the trigger voltage value, the thyristor 72 conducts, thereby short-circuiting the limiting resistor 71.

[0011]

However, in the inrush current prevention circuit using the above-mentioned conventional relay or thyristor, it is sometimes impossible to effectively prevent an excessive inrush current against a momentary interruption of the input AC. There's a problem.

In the inrush current prevention circuit 50 using a conventional relay shown in FIG. 8, since the return voltage of the relay 53 is usually lower than the operating voltage, the instantaneous interruption time (typically several milliseconds to several tens of milliseconds) is required. In some cases, the voltage applied to both ends of the relay 53 does not drop below the reset voltage value. In this case, when the input AC is turned on again, the switch 52 is in the ON state, and the control resistor 51 is short-circuited.
An excessive current flows into the smoothing capacitor 61.

In the inrush current prevention circuit 60 using the conventional thyristor shown in FIG. 9, the smoothing capacitor 61 may not be sufficiently discharged within the instantaneous interruption time. In this case, since the drive circuit 64 continues to operate, the thyristor 7
2 is in the ON state. Therefore, when the input AC is turned on again in this state, the control resistor 71 is short-circuited, and as in the inrush current prevention circuit 50 using the conventional relay shown in FIG. Current flows in.

Further, in the inrush current prevention circuit using the above-mentioned conventional relay or thyristor, there is also a problem that when the load side is short-circuited, an excessive current flows through the limiting resistor and the resistor generates heat.

In the inrush current prevention circuit 50 using a relay shown in FIG. 8, when the load side is short-circuited, the voltage applied to both ends of the relay 53 drops to a value equal to or lower than the reset voltage value, and the switch 52 is turned off. , An excessive current flows into the limiting resistor 51. The limiting resistor 51 is provided to prevent an excessive current from flowing into the smoothing capacitor 61 when the input AC is applied, and therefore needs a certain large resistance value. Therefore, the limiting resistance 5
When an excessive current flows into 1, the limiting resistor 51 generates heat.

In the inrush current prevention circuit 60 using the conventional thyristor shown in FIG. 9, when the load side is short-circuited, a voltage higher than the trigger voltage of the thyristor 72 is not generated at both ends of the coil 73, so that the thyristor 72 is not operated. It becomes conductive. Therefore, as in the case of the inrush current prevention circuit 50 using the conventional relay shown in FIG. 8, an excessive current flows into the limiting resistor 71, and the limiting resistor 71 generates heat.

The inrush current prevention circuit 60 using a thyristor shown in FIG. 9 is provided with a detection circuit for detecting an instantaneous interruption of the input AC. There is a method of forcibly stopping. According to this method, the thyristor 72 simultaneously
Can be turned off, so that even if the input AC is supplied again after the momentary interruption, it is possible to prevent an excessive current from flowing into the smoothing capacitor 61 due to the limiting resistor 71.

However, in this method, the operation of the switching regulator stops at the same time as the instantaneous interruption, so that the output from the switching regulator decreases at the same time as the instantaneous interruption. Therefore, it cannot be used for a precision measuring device or the like that requires a certain output holding time (a time during which an output voltage of approximately 100% can be maintained after a momentary interruption).

Also in this method, when the load side is short-circuited, an excessive current flows into the limiting resistor 71 as in the rush current prevention circuit 60 using a thyristor shown in FIG. There is a problem of generating heat.

The present invention has been made in view of the above circumstances, and can prevent an excessive rush current from being generated in response to an instantaneous interruption of input AC, and suppress heat generation when a short circuit occurs on the load side. It is an object of the present invention to provide an inrush current prevention circuit that can perform the operation.

[0021]

In order to solve the above problems, the present invention provides an AC / D having a rectifier for rectifying an alternating current and a smoothing capacitor for smoothing the output of the rectifier.
A rush current prevention circuit for a C power supply device, comprising: signal output means for outputting a signal corresponding to a current value of a current flowing into the smoothing capacitor; and rush current not flowing into the smoothing capacitor according to the signal. Variable impedance means inserted between the rectifier and the smoothing capacitor to change the impedance as described above.

Here, the signal output means includes a resistor inserted between the rectifier and the smoothing capacitor, and a comparator for outputting the signal in accordance with a difference between a voltage between both ends of the resistor and a reference voltage. And an amplifier circuit.

The variable impedance means may be arranged such that the collector and the emitter are located on a current transmission path between the rectifier and the smoothing capacitor, and the collector is located on the upstream side of the current transmission path with respect to the emitter. It is preferable that the transistor be a transistor that is connected and has the base input with the signal.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of an inrush current prevention circuit according to an embodiment of the present invention. Here, 30 is a rectifier circuit for rectifying the AC input waveform, 31 is a smoothing capacitor, 32 is a transformer constituting a switching regulator, 33 is a switching transistor for generating a voltage on the secondary side of the transformer 31, and 34 is switching. A drive circuit for driving the transistor 33, and 35 is a fuse.
The drive circuit 34 operates with the voltage charged in the smoothing capacitor 31.

The inrush current prevention circuit 10 of the present embodiment shown in FIG. 1 includes a transistor 11, a diode 12, a resistor 13, an operational amplifier 14, and a reference voltage source 15 for generating a reference voltage _Vref. It is configured.

The transistor 11 has a collector connected to the terminal on the return line 36 side of the smoothing capacitor 31 and an emitter connected to the terminal on the return line 36 side of the rectifier circuit 30 via the resistor 13. Therefore,
The terminal on the return line 36 side of the smoothing capacitor 31 and the terminal on the return line 36 side of the rectifier circuit 30 are:
They are connected to each other via the collector-emitter of the transistor 11 and the resistor 13. Diode 12
Has an anode connected to the collector of the transistor 11 and a cathode connected to the emitter of the transistor 11. Thus, the transistor 11 acts as a bypass for a current flowing between the collector and the emitter of the transistor 11 in the reverse direction (from the emitter to the collector).

The operational amplifier 14 outputs a signal corresponding to a difference between the voltage across V _r and the reference voltage V _ref of the resistor 13.
This output signal is input to the base of the transistor 11. As Here, the operational amplifier 14, the voltage across V _r of the resistor 13 approaches the reference voltage V _ref, transistor 1
1 the collector - the impedance between the emitter is increased, the voltage across V _r of the resistor 13 becomes equal to or higher than the reference voltage V _ref, the collector of the transistor 11 - so that the impedance between the emitter to infinity, i.e., the transistor 1
1 is set to OFF. The resistance 13
Is _R , the input current of the resistor 13 for making the voltage _Vr across the resistor 13 equal to the reference voltage _Vref is V
It is represented by _ref / R.

In the rush current prevention circuit 10 of the present embodiment,
As the current flowing into the resistor 13 approaches V _ref / R, the impedance between the collector and the emitter of the transistor 11 increases, and when the current reaches V _ref / R, the transistor 11 is turned off. Here, assuming that the current flowing into the resistor 13 is I ₁ , the current flowing into the smoothing capacitor 31 is I ₂ , and the current flowing into the load side is I ₃ , the current I ₁ flowing into the resistor 13 is I ₁ = I ₂ + I ₃ . Normally, the fluctuation amount of the current I ₃ flowing into the load side is determined by the smoothing capacitor 31 when the input AC is turned on (including a momentary interruption and then turned on again).
Is much smaller than the fluctuation amount of the current I ₂ flowing into the resistor 13, it can be considered that the fluctuation of the current I ₁ flowing into the resistor 13 is due to the current I ₂ flowing into the smoothing capacitor 31. Therefore, according to this embodiment, it is possible to limit the current I ₂ flowing into the smoothing capacitor 31 below V _ref / R-I _3. For this reason, an excessive rush current generated when the input AC is turned on or when the input AC is turned on again after an instantaneous interruption can be suppressed, thereby deteriorating the components of the AC / DC power supply, and in particular, reducing the smoothing capacitor 31. Deterioration can be suppressed.

When the amount of change in the current flowing into the load is large to a non-negligible degree, the line through which the return current flows on the load side is not connected through the resistor 13 as in the rush current prevention circuit 10a shown in FIG. Alternatively, it may be connected directly to the terminal on the return line 36 side of the rectifier circuit 30. In this case, the current flowing into the resistor 13 and the smoothing capacitor 3
1 is equal to the current flowing into the load side, and is not affected by the fluctuation of the current flowing into the load side.
The current flowing into 1 can be limited to _Vref / R or less.

The inrush current prevention circuit 10 according to the present embodiment
Is used to detect the amount of current flowing through the return line 36.
It is smaller than the limiting resistance used in a rush current prevention circuit using a conventional relay or thyristor. Therefore, when the load side is short-circuited, the amount of power consumed by the resistor 13 can be made smaller than that of the limiting resistor, and the amount of heat generated by the resistor 13 can be suppressed. That is, the fuse 35 can be blown before the resistor 13 generates heat.

As in the inrush current prevention circuit 10a shown in FIG. 2, the line through which the return current on the load side flows is directly connected to the return line 3 of the rectifier circuit 30 without the intervention of the resistor 13.
When connected to the terminal on the 6 side, the return current on the load side is
Since the current directly flows into the rectifier circuit 30 without flowing into the resistor 13, it is possible to prevent an excessive current from flowing into the resistor 13 when the load side is short-circuited.

Further, the inrush current prevention circuit 1 of the present embodiment
At 0, if the instantaneous interruption is several milliseconds to several tens of milliseconds, the drive circuit 34 operates with the electric power charged in the smoothing capacitor 34 even during the instantaneous interruption. Therefore, it can be used for a precision measuring instrument or the like that requires a certain output holding time.

The present inventors conducted an experiment in the following manner to confirm the effect of the present embodiment.

A simulation circuit using the inrush current prevention circuit of this embodiment and a simulation circuit not using the inrush current prevention circuit were manufactured. FIG. 3 shows a simulation circuit using the rush current prevention circuit of the present embodiment, and FIG. 4 shows a simulation circuit not using the rush current prevention circuit.

As shown in FIG. 3 and FIG.
Was manufactured using four diodes (model name: 1N5420). Also, as the smoothing capacitor 31, 1000
μF was used. Further, a resistance R _L of 150Ω was used as a load.

As shown in FIG. 3, the inrush current prevention circuit 10 uses a transistor 11 in which two transistors (model name: 2N6834) are Darlington-connected and a diode 12 uses a model name 1N5420.
Further, a resistor having a resistance of 0.5Ω was used. The operational amplifier 14 is a shunt regulator (model name: TL43
It was produced using 1). Figure 5 shows the shunt regulator T
The functional block diagram of L431 is shown. As shown in FIG. 5, the shunt regulator TL431 has a built-in reference voltage source that generates a reference voltage _{Vref of} 2.5 V, and a difference between the reference voltage _Vref and the voltage input to the node R (Reference). , The node C (cathode) and the node A (anod
e) The impedance is changed. The shunt regulator TL431 shown in FIG. 3 is set so that when the current flowing into the resistor 13 becomes _{Vref /} 0.5 = 5 (A) or more, the transistor 11 is turned off.

As shown in FIGS. 3 and 4, an AC power supply 82 of 100 (Vrms) was used as an input AC, and a switch 84 was operated. Current and the output current (FIGS. 3 and current at P ₁ point in FIG. 4) and, current and voltage (P ₂ points 3 and 4 flowing into the load resistor R _L from the rectifying circuit 11 at this time Voltage).

The results are shown in FIGS. FIG. 6 is a diagram for explaining an operation experiment result in the simulation circuit using the inrush current prevention circuit of the present embodiment shown in FIG. 3, and FIG.
5 is a diagram for explaining an operation experiment result in a simulation circuit in which the inrush current prevention circuit shown in FIG. 4 is not used.

In the simulation circuit in which the inrush current prevention circuit shown in FIG. 4 is not used, as shown in FIG.
Immediately after the input AC is turned on, an inrush current of about 50 (A) is generated. Immediately after the input AC is turned on again after a momentary interruption for about 80 milliseconds, an inrush current of about 22 (A) is generated.

On the other hand, in the simulation circuit using the inrush current prevention circuit of the present embodiment shown in FIG.
As shown in FIG. 6, the rush current is suppressed to about 5 (A) or less both immediately after the input AC is turned on and immediately after the input AC is turned on again after a momentary interruption of about 80 milliseconds. As can be seen from the results, the present inventors have confirmed that it is possible to prevent the occurrence of an excessive rush current immediately after the input AC is turned on or immediately after the input AC is turned on again after a momentary interruption. .

It should be noted that the present invention is not limited to the above embodiment, and various modifications can be made within the scope of the invention. For example, in the above embodiment, the collector-emitter of the transistor 11 is inserted between the rectifier circuit 30 and the smoothing capacitor 31, and the collector-emitter impedance is set based on the signal of the operational amplifier 14 input to the base. By making it variable, the smoothing capacitor 31
Of the present invention has been described. However, the present invention is not limited to this. By changing the impedance inserted between the rectifier circuit 30 and the smoothing capacitor 31 based on the signal of the operational amplifier 14, the inflow current of the smoothing capacitor 31 is reduced. Anything that can be adjusted may be used. For example, the anode-cathode of a three-terminal regulator may be inserted between the rectifier circuit 30 and the smoothing capacitor 31, and the signal of the operational amplifier 14 may be input to the reference.

[0043] In the above embodiments, a signal corresponding to the difference between the voltage across V _r and the reference voltage V _ref of the resistor 13 generates an operational amplifier 14, the one that inputs the signal to the base of the transistor 11 As described above, the present invention may be any device that generates a signal corresponding to a current value flowing into the smoothing capacitor 31 or a characteristic value correlated with the current and inputs the signal to the base of the transistor 11. .

The inrush current prevention circuit of the present invention is not limited to a switching regulator, but may be applied to an AC / DC power supply having a rectifier circuit and a smoothing capacitor.
Can be widely applied.

[0045]

As described above, according to the present invention,
It is possible to prevent an excessive rush current from being generated in response to an instantaneous interruption of the input AC, and to suppress heat generated when the load is short-circuited.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an inrush current prevention circuit according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a modification of the inrush current prevention circuit shown in FIG.

FIG. 3 is a diagram illustrating a simulation circuit using the inrush current prevention circuit illustrated in FIG. 1;

FIG. 4 is a diagram showing a simulation circuit in which an inrush current prevention circuit is not used.

FIG. 5 is a functional block diagram of a shunt regulator TL431.

FIG. 6 is a diagram for describing an operation experiment result in the simulation circuit shown in FIG. 3;

FIG. 7 is a diagram for explaining an operation experiment result in the simulation circuit shown in FIG. 4;

FIG. 8 is a schematic diagram of a rush current prevention circuit using a conventional relay.

FIG. 9 is a schematic diagram of a rush current prevention circuit using a conventional thyristor.

[Explanation of symbols]

 10, 10a Inrush current prevention circuit 11 Transistor 12 Diode 13 Resistor 14 Operational amplifier 15 Reference voltage source 30 Rectifier circuit 31 Smoothing capacitor 32 Transformer 33 Switching transistor 34 Drive circuit 35 Fuse 36 Return line 82 AC power supply 84 Switch

Claims (4)

[Claims] An AC / DC having a rectifier for rectifying an alternating current and a smoothing capacitor for smoothing an output of the rectifier.
A rush current prevention circuit of a power supply device, a signal output unit that outputs a signal corresponding to a current value of a current flowing into the smoothing capacitor, and an inrush current that does not flow into the smoothing capacitor according to the signal. And a variable impedance means interposed between the rectifier and the smoothing capacitor for changing impedance. 2. The signal output means according to claim 1, wherein said signal output means includes a resistor inserted between said rectifier and said smoothing capacitor, and a signal between a voltage between both ends of said resistor and a reference voltage. And a comparison amplifier circuit that outputs a signal. 3. The variable impedance means according to claim 1, wherein the variable impedance means includes a collector and an emitter disposed in a current transmission path between the rectifier and the smoothing capacitor, and the collector disposed in the current transmission path with respect to the emitter. An inrush current prevention circuit, which is a transistor that is connected so as to be located on an upstream side and has the signal input to a base. 4. The inrush current prevention circuit according to claim 3, further comprising a diode having an anode connected to said collector and a cathode connected to said emitter.