JPH10143259A - Rush current preventing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rush current preventing circuit by which the flow of a rush current is prevented even when an input voltage has a hit in a power source circuit or an input voltage switch is quickly turned on/off. SOLUTION: This circuit is composed of a switch 1, limit resistor 2, a 1st relay A, a 2nd relay B and an ON/OFF control circuit C for relay B or the like. When the switch 1 is turned on, the control circuit C operates the relay B through an internal delay circuit after the lapse of time tD (tD>= charging time of capacitor for smoothing in a power source), as a result, the relay A is operated and the limit resistor 2 is short-circuitted. When the switch 1 is turned off, a capacitor 11 inside the control circuit C is discharged through a diode 15 or the like so that the relays B and A are speedily recovered into initial state. Therefore, even when the switch 1 is turned on again without the enough interval, the rush current preventing circuit is normally operated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inrush current prevention circuit used in an apparatus using a power supply.

[0002]

2. Description of the Related Art As a prior art of this kind of inrush current prevention circuit, for example, Japanese Patent Laid-Open Publication No. Hei 8-6650 discloses that an inrush current is re-established even when the resistance value of a limiting resistor or the capacity of a smoothing capacitor inside a power supply is large. As a rush current limiting circuit that can prevent flowing, and can also prevent burnout of the limiting resistor even in the event of a relay failure, a voltage detection unit on the input side of the power supply and a limiting resistor that limits the input current to the power supply The current is supplied to the power supply via the limiting resistor until the voltage on the input side detected by the voltage detecting unit is equal to or higher than the predetermined value. In the inrush current prevention circuit that supplies current to the power supply, the voltage detection unit is connected to the input side of the power supply via the switch unit, and operates when the voltage on the output side of the power supply exceeds a predetermined value. Turn on Structure in which a circuit view have been proposed and used for the purpose of suppressing the peak value of the rush current due to the charging current of the smoothing capacitor in the power supply immediately after the input voltage is turned on in the power supply circuit.

FIG. 3 is a diagram showing a configuration of an example of a conventional inrush current prevention circuit proposed in the above publication. Referring to FIG. 3, the first relay D includes a driving unit (coil unit) 103 connected in parallel to the input voltage Ein between the switch 101 and the limiting resistor 102, and a relay connected in parallel to the limiting resistor 102. And a contact 104. The second relay E includes a driving unit (coil unit) 109 connected in parallel to the output voltage Vout between the power supply 120 and the load 111, and a relay connected in series to the coil unit 103 of the first relay D. And a contact 110.

Next, the operation of the conventional rush current prevention circuit will be described. First, when the switch 101 is turned on, the input-side voltage E is applied between the switch 101 and the input terminal 106.
in is applied. Then, an inrush current for charging the smoothing capacitor 122 inside the power supply 120 starts to flow. In this case, the inrush current is suppressed by flowing through the limiting resistor 102.

The output voltage Vout of the power supply 120 is applied from output terminals 107 and 108 to the drive section 109 of the second relay E. When the relay contact 110 of the second relay E closes, the input side voltage Ein is applied to the drive unit 103 of the first relay D, and the relay contact 104 of the first relay D closes. As a result, both ends of the limiting resistor 102 are short-circuited, and the input voltage Ein is changed to the input terminals 105, 10
6 is applied directly.

After the switch 101 is turned on, the power supply 120
Until the output voltage Vout reaches the operating voltage of the second relay E, a delay occurs due to the charging of the smoothing capacitor inside the power supply. Is suppressed.

[0007]

However, in the above-mentioned conventional rush current prevention circuit, when the input voltage is momentarily interrupted or the input power switch is quickly turned off and on, the rush current prevention circuit is completely incomplete. There is a problem that it does not operate.

The reason is that, in the above-mentioned conventional rush current prevention circuit, the smoothing capacitor inside the power supply has a large capacity in order to satisfy the function as the power supply. The power supply continues to operate due to the charged voltage, and the inrush current prevention circuit has not returned to the initial state when the input voltage is turned on again.

Accordingly, the present invention has been made in view of the above circumstances, and has as its object to provide a rush current that operates normally even when the input voltage is momentarily interrupted or the input voltage switch is quickly turned off and on. It is to provide a prevention circuit.

[0010]

In order to achieve the above object, an inrush current prevention circuit according to the present invention comprises a voltage detection means connected to an input side of a power supply via a switch means, and an input current to the power supply. And a limiting resistor that supplies a current to a power supply via the limiting resistor until the voltage on the input side detected by the voltage detecting means is equal to or higher than a predetermined value. In an inrush current prevention circuit for supplying a current to a power supply without using a resistor, a control means for turning on / off a switch means is provided separately from the power supply.

The outline of the present invention will be described below. In the present invention, a power supply (1 in FIG.
Voltage detection means (3 in FIG. 1) connected to the input side of 6)
And a limiting resistor for limiting the input current to the power supply (2 in FIG. 1)
And supplying a current to the power supply via the limiting resistor until the voltage on the input side detected by the voltage detection means is equal to or more than a predetermined value, and supplying a current to the power supply when the voltage is equal to or more than the predetermined value. The inrush current prevention circuit includes control means (C in FIG. 1) for controlling ON / OFF of the switch means separately from the power supply. The circuit means for controlling ON / OFF of the switch means inputs the input voltage. In this case, the ON control is performed after a certain period of time determined by the time constant in the control means (C in FIG. 1). When the input voltage is cut off, the OFF control is performed immediately.

Therefore, even if the input voltage is momentarily interrupted or the input voltage switch is quickly turned off and on, the inrush current prevention circuit operates normally and the inrush current can be reliably prevented from flowing.

[0013]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

Referring to FIG. 1, an inrush current prevention circuit according to an embodiment of the present invention includes a switch 1, a limiting resistor 2, a first relay A, a second relay B, and an ON / OF for relay B.
An F control circuit C and the like are provided. In FIG. 1, 3
Is a drive unit of the first relay A, 4 and 14 are relay contacts, 1
6 is a power supply, 17 and 18 are power supply input terminals, 19 and 20 are power supply output terminals, and 21 is a load.

The first relay A is composed of a drive unit 3 connected in parallel to the input side voltage Ein and a relay contact 4 connected in parallel to the limiting resistor 2.

The second relay B is a relay B ON / OF.
It is composed of a drive unit 13 connected to the output of the F control circuit C and a relay contact 14 connected in series to the drive unit 3 of the first relay A.

The ON / OFF control circuit C for the relay B includes a transformer 5, a rectifier 6, and a smoothing capacitor 7 connected in parallel to the input side voltage Ein to supply a drive voltage for the drive unit 13 of the relay B; It comprises a field effect transistor 12 for controlling the operation of the relay B, and a delay circuit composed of resistors 8, 9, 10, a capacitor 11, and a diode 15. More specifically, resistors 8 and 9 are connected in series between the output terminals of the rectifier 6 in parallel with the smoothing capacitor 7, and one end of the resistor 10 and a cathode terminal of the diode 15 are connected to a connection point of the resistors 8 and 9. , The other end of the resistor 10 and the anode terminal of the diode 15 are connected to one end of the capacitor 11 and connected to the control terminal (gate terminal) of the field effect transistor 12, and the field effect transistor 12 It is inserted between the resistor 9 and the other common connection point of the capacitor 11.

The capacity of the smoothing capacitor 7 is reduced as long as the driving of the driving section 13 of the second relay B is not hindered.

Next, the operation of the embodiment of the present invention shown in FIG. 1 will be described with reference to the timing waveform chart of FIG.

First, when the switch 1 is turned on (closed), an input voltage Ein is applied between the switch 1 and the power input terminal 18. Then, an inrush current for charging the smoothing capacitor 22 inside the power supply 16 starts to flow. The inrush current is supplied to the smoothing capacitor 2 inside the power supply 16.
2 has been charged and continues to flow until the voltage Vc across the capacitor 22 has stabilized, but since it flows through the limiting resistor 2, its maximum value is suppressed.

In the ON / OFF control circuit C for the relay B,
After the switch 1 is turned ON by an internal delay circuit, the field effect transistor 12 becomes conductive after a certain period of time (the delay time tD is determined by, for example, the time constant of the CR delay circuit of the resistor 10 and the capacitor 11), and the drive is performed. The part 13 is the second
Is operated.

By setting the delay time tD to the charging time of the smoothing capacitor 22 inside the power supply 16,
After the switch 1 is turned on and the smoothing capacitor 22 inside the power supply 16 is sufficiently charged, the second relay B can be operated.

When the second relay B is operated, the relay contact 14 is turned on (closed), the first relay A is operated, and both ends of the limiting resistor 2 are short-circuited. Is applied directly between the input terminals 17, 18.

Next, when the switch 1 is turned off (open), in the ON / OFF control circuit C for the relay B, since the smoothing capacitor 7 has a small capacity, it is quickly discharged by the resistors 8 and 9.

The capacitor 11 includes a diode 15
Through the resistor 9. Therefore, the second relay B returns immediately.

The first relay A is connected to the relay contact 14 of the first relay B when the drive voltage to the drive unit 3 is lost.
Is turned off, so that the operation is immediately restored similarly to the second relay B.

Next, the operation and effect of the embodiment of the present invention will be described.

In the embodiment of the present invention, when the input voltage is cut off, the rush current prevention circuit immediately returns to the initial state. Therefore, even if the input voltage is momentarily interrupted or the input voltage switch is quickly turned OFF-ON, The inrush current prevention circuit operates normally and can prevent the inrush current from flowing.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to explain the above-mentioned embodiment of the present invention further with specific examples, an embodiment of the present invention will be described with reference to the drawings.

Referring to FIG. 1, an inrush current prevention circuit according to one embodiment of the present invention includes a circuit breaker 1, a limiting resistor 2 (resistance value 15Ω), a power relay A for driving 100 VAC, an optical MOSFET relay B, and a relay B. ON / OFF
It comprises a control circuit C and the like.

The ON / OFF control circuit C for the relay B is
Secondary side 100V: Secondary side 12V transformer 5, rectifier 6,
From the smoothing capacitor 7 (capacitance 10 μF), the field effect transistor 12 driven by 4 V, and the resistors 8 and 9 (both resistance values are 2 kΩ), the resistance 10 (resistance value 80 kΩ), the capacitor 11 (capacity 10 μF), and the diode 15 Be composed.

Next, the operation of the embodiment of the present invention will be described in detail.

First, when the circuit breaker 1 is turned on, the relay B ON / OFF control circuit C activates the relay B about 0.2 seconds after the circuit breaker 1 is turned on by an internal delay circuit, Activate A.

The relay B is an optical MOSFET relay,
Since the current driving range is wide, the capacitance of the smoothing capacitor 7 is small, and the operation is stable even when the voltage after smoothing has ripples.

When the circuit breaker 1 is turned off, the smoothing capacitors 7 and 11
By discharging for m seconds, the relay B is immediately returned and the relay A is returned.

[0036]

As described above, according to the present invention,
If the input voltage is momentarily interrupted or the input voltage switch is
This has the effect of preventing the inrush current from flowing even when FF-ON is performed.

The reason is that, in the present invention, when the input voltage is momentarily interrupted, the state of the rush current prevention circuit is immediately returned to the initial state.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a time chart for explaining the operation of the embodiment of the present invention.

FIG. 3 is a diagram showing a configuration example of a conventional inrush current prevention circuit.

[Explanation of symbols]

 1, 101 switch 2, 102 limiting resistor 3, 13, 103, 109 relay driving unit 4, 14, 104, 110 relay contact 5 transformer 6 rectifier 7, 11 capacitor 8, 9, 10 resistor 12 field effect transistor 15 diode 16, 120 Power supply 17, 18, 105, 106 Power input terminal 19, 20, 107, 108 Power output terminal 21, 111 Load

Claims (5)

[Claims] 1. A voltage detecting means connected to an input side of a power supply via a switch section, and a limiting resistor for limiting an input current to the power supply, wherein a voltage on the input side detected by the voltage detecting means is provided. In the rush current prevention circuit that supplies a current to the power supply via the limiting resistor until the value becomes equal to or more than a predetermined value, and supplies a current to the power source without using the limiting resistance when the value exceeds the predetermined value. A rush current prevention circuit comprising control means for turning on / off the switch unit separately from the power supply. 2. ON / OF of supply of input side voltage (Ein)
An input voltage switch for switching F; a first switch connected in parallel to a limiting resistor for controlling an input current to a power supply; and a parallel connection to the input side voltage between the input voltage switch and the limiting resistor. A driving unit connected to the driving unit and driving the first switch; a second switch connected in series to the driving unit; and a control unit for controlling ON / OFF of the second switch. Current is supplied to the power supply through the limiting resistor until the voltage of the power supply reaches or exceeds a predetermined value. In the circuit, when the input voltage switch is ON, the control unit that receives the input-side voltage as an input turns on the second switch after a predetermined delay time, and as a result, the first switch Is ON and the limiting resistor is short-circuited, and when the input voltage switch is OFF, the control means:
And controlling the second switch to turn off immediately and return to the initial state. 3. The control circuit according to claim 2, wherein
At time N, after a delay time set to be approximately equal to or greater than the charging time of the smoothing capacitor in the power supply,
3. The inrush current prevention circuit according to claim 2, wherein the second switch is turned on. 4. The control means includes a delay circuit comprising a resistor and a capacitor, and a switch element for controlling activation of a drive circuit of the second switch, and is determined by a time constant of the delay circuit. 3. The rush current prevention circuit according to claim 2, wherein the delay time is set to be substantially equal to or longer than the charging time of the smoothing capacitor in the power supply. 5. The control circuit according to claim 1, wherein
5. The rush current prevention circuit according to claim 4, further comprising: means for discharging the electric charge stored in the capacitor of the delay circuit at the time of FF.