JPH02133808A - Rush current preventing circuit - Google Patents

Abstract

PURPOSE:To prevent a rush current by switching a power supply route to a relay by charging previously the power to be supplied to a capacitive load into a load via a semiconductor switch element and a resistance. CONSTITUTION:A power supply 1 supplies the power to a capacitive load 2 via a relay 4. An excessive rush current is produced when the relay 4 is closed. In this respect, a semiconductor switch element 5 is previously turned on, and a capacitor 3 is charged while a current is limited by a resistance 6. Then the relay 4 is closed when the capacitor 3 is charged up to a certain level. In this case, the element 5 and the realy 4 are controlled by a control circuit 7. Thus it is possible to prevent the rush current that is caused when the relay 4 is opened and closed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current switching method, and particularly to an inrush current prevention circuit when power is supplied to a capacitive load.

[Conventional technology]

Traditionally, switching current to and from capacitive loads has been through transistors or relays.

[Problem to be solved by the invention]

Although the above-described conventional switching of current using transistors can suppress inrush current, there is a problem in that power loss is large. Furthermore, when switching using conventional relays, an excessive inrush current is generated, which causes the contacts of the relay to weld.

[Means to solve the problem]

The inrush current prevention circuit of the present invention includes a relay that opens and closes a power line that supplies power to a capacitive load, a circuit in which a semiconductor switch confectionery connected in parallel with the relay and a resistor are connected in series.
It has a control circuit that performs time-series control of opening and closing of the relay and on/off of the semiconductor switch element.

[Effect]

In the present invention, power is supplied to a capacitive load by charging the load in advance using a semiconductor switch element and a resistor, and then switching the power supply path to a relay.

〔Example〕

Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In the figure, 1 is a power supply, 2 is a capacitive load, and 3 is a capacitor, and this capacitor 3 isometrically represents the capacitance of the capacitive load 2. 4 is a relay that opens and closes the power line that supplies power to the capacitive load 2; 5 is a semiconductor switch such as a transistor or thyristor; 6 is a resistor connected in series with the semiconductor switch element 5; and a resistor 6 are connected in parallel with the relay 4. T is a control circuit that performs time-series control of opening and closing of the relay 4 and turning on and off of the semiconductor switch element 5. 8
Control signal lines m, 8b, and 8c are control signal lines.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

A power supply 1 supplies power to a capacitive load 2 via a relay 4 . Here, since an excessive rush current occurs when closing the relay 4, the semiconductor switch element 5 is turned on in advance.
The capacitor 3 is charged while the resistor 6 limits the stain current. Then, by closing the relay 4 while the capacitor 3 is charged to some extent, inrush current to the load side is prevented.

At this time, the semiconductor switch element 5 and the relay 4 are controlled by the control circuit 7.

FIG. 2 is a block diagram showing an example of a specific configuration based on FIG. 1, and shows a case where a thyristor is used as the semiconductor switching element.

In FIG. 2, the same reference numerals as in FIG. 1 indicate corresponding parts, 4m is a relay, 4b is a relay contact of this relay 4a, and these constitute the relay 4 shown in FIG. 5a is a thyristor.

7m is a resistor, Tb is a capacitor, 7c is a diode, 7
d is a transformer, 7@ is a resistor, 7f is a capacitor, and 7g is a resistor, and these constitute the control circuit 7. and,
The resistor 7e and capacitor 7f constitute a time constant circuit. 9 is a diode for absorbing back electromotive force.

Next, the operation of the embodiment shown in FIG. 2 will be explained.

First, the power supply 1 supplies power to the capacitive load 2 via the relay contact 4b. ζNow, in order to prevent an excessive rush current when closing the relay contact 4b, when a control signal is applied to the control signal line 8a, the transformer 7d first generates a gate voltage for the thyristor 5a, and the thyristor 5a Turn on.

(At this time, relay contact 4b is open.) And,
The current flowing through the thyristor 51 is limited by the resistor 6,
Charge the capacitor 3 of the capacitive load 2. A time constant circuit consisting of a resistor 7e and a capacitor 7f sets the time during which the capacitor 3 is charged to a certain extent, and when the capacitor 3 is charged, a voltage is applied to the relay 4a which is the drive part of the relay contact 4b, and the relay contact 4b Close. At this time,
Since the capacitor 3 is not charged, the inrush current is suppressed.

Next, when the relay contact 4b closes, no current flows through the thyristor 5a, the thyristor 5& is turned off, and the only path through which the current flows is through the relay contact 4b. therefore,
In order to stop the power supply to the capacitive load 2, it is sufficient to turn off only the relay contact 4b.

In this way, inrush current can be prevented when the current is switched on and off by the relay.

〔Effect of the invention〕

As explained above, the present invention prevents inrush current by supplying power to a capacitive load through a semiconductor switch element and a resistor, charging the load in advance, and then switching the power supply route to a relay. There is an effect that can be done. In addition, since the current flows only through the relay during steady state, the loss in the power line can be reduced, and since one semiconductor switch element is used only for initial charging, it can be small and small capacity, and the loss at this time can be reduced. has the effect of being small.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an embodiment of a specific configuration based on FIG. 1...Power source, 2...Capacitive load, 4...Relay, 511...Semiconductor switch element, 6...Resistor, 7...Fist/control circuit.

Claims (1)

[Claims] A relay that opens and closes a power line that supplies power to a capacitive load, a circuit in which a semiconductor switch element and a resistor are connected in parallel with the relay, and a circuit that opens and closes the relay and turns the semiconductor switch element on and off. An inrush current prevention circuit characterized by having a control circuit that performs time-series control.