JPH05137252A - Power supply circuit - Google Patents

Abstract

PURPOSE:To provide a power supply, producing a predetermined output corresponding to an input voltage, which is protected against surge current occurring after instantaneous interruption of input. CONSTITUTION:At the time of normal operation of a power supply 1, surge current flowing into the power supply 1 is limited by means of a surge current limiting resistor 6 having opposite ends being short-circuited through relay contacts 7. Short circuit of the resistor 6 through the contacts 7 is released by means of a relay 5 in response to instantaneous interruption of input voltage. Since short circuit of the resistor 6 is released upon instantaneous interruption of input even if short circuit of a resistor 3 through contacts 4 has not been released, the power supply 1 can be protected against breakdown due to closing current after instantaneous interruption of input.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a power supply circuit, and more particularly to prevention of inrush current.

[0002]

2. Description of the Related Art Conventionally, in this type of power supply circuit, as shown in FIG. 2, inrush current is prevented by an inrush current limiting resistor 3 when an AC voltage is input, and the AC input is a power source. When applied to 1, the output of power supply 1 causes relay 2
The relay contact 4 connected in parallel with the inrush current limiting resistor 10 is driven to operate to short-circuit the resistor 10. That is, during steady operation of the power supply 1, the operation was performed with both ends of the resistor 3 short-circuited.

However, in this conventional power supply circuit,
AC voltage is input, relay 2 operates, relay contact 4
In the steady state in which the inrush current limiting resistor 3 is short-circuited, when a momentary interruption within the momentary interruption resistance of the power source 1 occurs, the power source 1 holds the output voltage and the relay 2 continues to operate. Therefore, the relay contact 4 remains short-circuiting the inrush current limiting resistor 3. After the momentary interruption, a large inrush current flows, and the power supply 1 may be destroyed.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional drawbacks, and an object of the present invention is to provide a power supply circuit in which the power supply is not destroyed at the time of power recovery even after a momentary interruption occurs. Is to provide.

[0005]

The power supply circuit according to the present invention comprises a power supply which outputs a predetermined output according to an input voltage, and an inrush current limiting element which limits an inrush current to the power supply and short-circuits both ends during steady operation of the power supply. And a means for releasing the short-circuited state of the inrush current limiting element in response to the instantaneous interruption of the input voltage.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of a power supply circuit according to the present invention, and the same portions as those in FIG. 2 are designated by the same reference numerals. In the figure, the power supply circuit of this embodiment is configured to include an inrush current limiting resistor 6, a relay 5 and a relay contact 7 for short-circuiting both ends thereof.

That is, in the power supply circuit of this embodiment, one end of the AC input is connected to one end of the inrush current limiting resistor 3, one end of the relay contact 4 and one end of the relay 5, and the other end of the relay contact 4 is connected to the inrush current. It is connected to the other end of the limiting resistor 3 and the input of the power supply 1. The other end of the AC input is connected to one end of the inrush current limiting resistor 6, one end of the relay contact 7 operated by the relay 5, and the other end of the relay 5, and the other end of the inrush current limiting resistor 6 is the relay contact 7 Of the power source 1 and the other end of the power source 1. A relay 2 for operating a relay contact 4 is provided at the output of the power supply 1.

In such a configuration, the relay 5 is connected to both ends of the AC input, and one end of the AC input is input to the power source 1 through the parallel circuit of the relay contact 4 and the inrush current limiting resistor 3. The other end of the AC input is input to the power supply 1 via a parallel circuit of a relay contact 7 and an inrush current limiting resistor 6. Power supply 1
The relay 2 is connected to the output of and the relay contact 4 connected to the input side is operated.

First, when the input voltage is supplied, the inrush current is limited by the inrush current limiting resistors 3 and 6, and the input voltage is supplied to the power supply 1. At that time, by applying a voltage to the exciting coil in the relay 5, the relay contact 7 operates and both ends of the inrush current limiting resistor 6 are short-circuited.

Next, by applying a voltage to the exciting coil of the relay 2 by the output voltage of the power source 1, the relay contact 4
Is operated and both ends of the inrush current limiting resistor 3 are short-circuited.

Thus, immediately after the input voltage is supplied, the inrush current limiting resistor 3 and the inrush current limiting resistor 6 limit the inrush current. However, after a certain period of time, the inrush current limiting resistor 3 is closed due to the closing operation of the relay contact 7. Limit the inrush current with only.

If a momentary interruption within the momentary interruption resistance of the power source 1 occurs when the power source 1 is operating normally, that is, when the relay contacts 4 and 7 are closed, the relay 5 stops operating. Then, the relay contact 7 is in the open state until the momentary disconnection and another relay contact closing operation.

At this time, the relay contact 4 remains closed, and when the input voltage is restored, the rush current limiting resistor 6 limits the rush current. Therefore, a large amount of current does not flow.

In the above, the case of using a general relay has been shown. However, if a relay having a long relay contact operating time is used, it takes a longer time to short-circuit both ends of the inrush current limiting resistor, which is more effective. is there. Regarding the power supply 1,
Any power source such as a well-known switching power source and series power source may be used, and the present invention can be applied to various power sources.

As described above, by providing the inrush current limiting resistors at both ends of the AC input and short-circuiting one of them by the AC drive relay, even if there is a momentary interruption in the AC input voltage, the relay contact is opened each time. Therefore, even if the AC input power is supplied again, the power can be supplied via the inrush current limiting resistor. In this way, by preventing an abnormal rush current, it is possible to prevent damage or deterioration of reliability.

[0017]

As described above, according to the present invention, by releasing the short-circuited state of the inrush current limiting element in response to the instantaneous interruption of the input voltage, it is possible to prevent the power supply from being destroyed by the inrush current thereafter. is there.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a power supply circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional power supply circuit.

[Explanation of symbols]

 1 power supply 2,5 relay 3,6 resistance 4,7 relay contact

Claims (1)

[Claims] 1. A power source that outputs a predetermined output according to an input voltage, an inrush current limiting element that limits an inrush current to the power source and short-circuits both ends during steady operation of the power source, and a momentary interruption of the input voltage. And a means for releasing the short-circuited state of the inrush current limiting element in response to the power supply circuit.