JPH0549167A - Protective circuit for dc power supply - Google Patents

Abstract

PURPOSE:To protect a DC power supply without using a fuse having limited service life which can not be selected easily. CONSTITUTION:A resistor 3 for limiting surge current to a capacitor 5 for smoothing DC current is connected in series with another resistor 7 and the trip coil 10 of a breaker 6 for interrupting input to a rectifier 1. Furthermore, a capacitor 8 is connected in parallel with the trip coil 10 and when the voltage across the capacitor 8 exceeds a predetermined level, the trip coil 10 is excited to open the breaker 6 thus preventing burning of the limit resistor 3 and protecting a DC power supply.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for a DC power supply device capable of preventing burnout of a rush current limiting resistor to a smoothing capacitor provided in a subsequent stage of a rectifier.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional example of this kind. In the figure, 1 is a rectifier, 2 is a fuse, 3 is a resistor for limiting inrush current, 4 is a contactor, 5 is a smoothing capacitor, 6 is a breaker, and these constitute a DC power supply device. That is, the DC power supply device starts operating by turning on the breaker 6, but at this time, the rush current into the smoothing capacitor 5 is limited by the resistor 3, and the contactor 4 is detected at the time when the rush current becomes a predetermined value or less. Is turned on, DC power is supplied to a load (not shown). At this time,
If power is supplied to the load without the contactor 4 being turned on due to some abnormality, all the load current will flow through the resistor 3. However, since the resistor 3 usually has a short-term rating just after the contactor is turned on, the resistor 3 is burned out when a load current is continuously supplied. Therefore, conventionally, a fuse 2 (a low-voltage current limiting fuse or a temperature fuse is used) is inserted as shown in the figure, and protection is achieved by utilizing the melting action.

[0003]

However, it is necessary to select, as the fuse, one that can be blown in a short-circuit state without being blown by an inrush current, and one that can be continuously used corresponding to the continuous rating of the fuse as the limiting resistance. However, there is a problem that it is difficult to select them, and it is difficult to promote protection and cooperation between them. In addition, the blown fuse must be replaced, which causes a problem of complicated work. Therefore, it is an object of the present invention to provide a protection circuit which does not require such protection coordination and which does not require complicated work.

[0004]

In order to solve such a problem, the present invention comprises a rectifier, a smoothing capacitor for smoothing the output current of the rectifier, and a limiting resistor for limiting an inrush current to the smoothing capacitor. For DC power supply,
The trip coil of the input cutoff breaker of the rectifier is connected to the limiting resistor via another resistor, and a capacitor is connected in parallel with the trip coil, and the trip coil is connected when the capacitor voltage exceeds a predetermined value. Is excited to release the breaker for cutting off the input, thereby preventing the limiting resistor from burning.

[0005]

[Function] By monitoring the voltage across the input current limiting resistor of the smoothing capacitor and operating the trip coil of the input breaker when it exceeds a predetermined value, the fuse can be omitted, and there is no need for protection coordination, which is complicated. It is possible to provide a protection circuit that does not require any work.

[0006]

1 is a block diagram showing an embodiment of the present invention. As is apparent from the figure, this embodiment is different from the conventional example shown in FIG. 4 in that a fuse is omitted and a resistor 7, a capacitor 8, a constant voltage diode 9 and a trip coil 10 are provided instead. is there. The constant voltage diode 9 is provided to protect the trip coil 10 so that an excessive voltage is not applied. Figure 2
Is a timing chart for explaining the normal operation of FIG. 1, where (a) is the input voltage waveform, (b) is the voltage across resistor 3, (c) is the voltage across capacitor 8, and (d) is the contact voltage. The operation waveforms of the container 4 are shown. That is, normally, the voltage across the resistor 3 exceeds the operating voltage of the trip coil 10 of the breaker 6 for a short time at the time of input rush as shown in FIG. Therefore, the actual voltage of the trip coil 10 is shown in the figure (c).
Does not rise to the operating voltage like
Will be input as shown in FIG.

On the other hand, due to the abnormality of the contactor 4, the resistance 3
The voltage across both ends of Fig. 3 (B) is not attenuated as shown in Fig. 2 (B).
In case of
As shown in (c), it rises according to the time constant with the resistor 6 and exceeds the operating voltage of the trip coil 10 at a certain time t. As a result, the trip coil 10 is excited, the breaker 6 is opened as shown in FIG. 3D, the input of the rectifier 1 is cut off, and the resistor 3 is protected. FIG. 3 is a timing chart for explaining the operation at the time of abnormality in FIG. 1, where (a) is the input voltage waveform, (b) is the voltage across resistor 3, (c) is the voltage across capacitor 8, and FIG.
(D) shows the operation waveforms of the breaker.

[0008]

According to the present invention, since the capacitor and the trip relay are used and the fuse having a long life is not used, the troublesome work can be avoided and the safety can be improved. Is obtained.

[Brief description of drawings]

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

FIG. 2 is a timing chart for explaining a normal operation of FIG.

FIG. 3 is a timing chart for explaining an operation at the time of abnormality in FIG.

FIG. 4 is a configuration diagram showing a conventional example.

[Explanation of symbols]

 1 Rectifier 2 Fuse 3 Limiting resistor 4 Contactor 5 Smoothing capacitor 6 Breaker 7 Resistor 8 Capacitor 9 Constant voltage diode 10 Trip relay

Claims (1)

[Claims] 1. A direct current power supply device comprising a rectifier, a smoothing capacitor for smoothing an output current of the rectifier, and a limiting resistor for limiting an inrush current to the smoothing capacitor, wherein another resistor is connected to the limiting resistor. The trip coil of the input cutoff breaker of the rectifier is connected to the trip coil, and a capacitor is connected in parallel with the trip coil. When the voltage of the capacitor exceeds a predetermined value, the trip coil is excited to break the input breaker. A protective circuit for a DC power supply device, characterized in that the limiting resistor is prevented from being burnt out.