JPH0417513A - Overcurrent protective circuit - Google Patents

Abstract

PURPOSE:To recover fuse blow-out fault in a short time by connecting a standby fuse in parallel upon elapse of a predetermined time after blow-out of a normal fuse. CONSTITUTION:Upon abrupt DC voltage drop between power source input terminals 1, 2, an excessive input current flows to blow out a main fuse 3. Consequently, a voltage corresponding to the time constant of a resistor 5 and a capacitor 6 is applied through an alarm contact 4 across a relay winding 7 to make a contact 8 of the relay winding 7 upon elapse of a predetermined time after reaching to the sensitive voltage of the relay winding 7. Consequently, power can be fed again to a DC power supply circuit 10 through a standby fuse 9.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an overcurrent protection circuit using a fuse, and more particularly to an overcurrent protection circuit used in a DC power supply circuit that receives a DC power supply as an input.

[Conventional technology]

Conventionally, overcurrent protection circuits using fuses are inserted into the input or output of a power supply circuit, and when an overcurrent exceeding the rated current of the fuse flows, the fuse blows, thereby protecting the own power supply circuit and the power supply destination. Protecting the circuit.

[Problem to be solved by the invention]

The above-mentioned conventional overcurrent protection circuits are susceptible to overcurrent when the DC power supply voltage suddenly drops, or when power is supplied to a signal transmission line, etc., due to the line temporarily falling to the ground due to lightning. Temporary overcurrent, such as overcurrent, can also cause the fuse to blow. In these cases, the overcurrent is caused by an external factor and not a failure of the equipment, so simply replacing the fuse will correct the problem.
Since fuse replacement relies on manual labor, there is a drawback that it takes time to recover from a failure if the fuse rupture occurs in a remote location.

An object of the present invention is to provide an overcurrent protection circuit that can recover from a blown fuse fault in a short time when a fuse is blown due to an overcurrent caused by an external factor such as a sudden change in input power supply voltage.

[Means to solve the problem]

The overcurrent protection circuit of the present invention includes a detection means for detecting that a first fuse connected to a DC power supply circuit is blown, a time limit means that operates after a predetermined time period from the operation of the detection means, and the time limit means. This configuration includes a second fuse that is connected in parallel to the first fuse by the operation of.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In this embodiment, an overcurrent protection circuit is inserted on the input side of a DC power supply circuit 10. As shown in FIG. In FIG. 1, the overcurrent protection circuit added to the DC power supply circuit 10 includes an alarm contact 4 that detects when the normally used main fuse 3 is blown, and a resistor 5. A time limit circuit is constructed of a capacitor 6 and a relay winding 7 and operates after a predetermined time period when the alarm contact 4 operates, and a standby fuse 9 is connected in parallel to the main fuse 3 by a make contact 8 of the relay winding 7. Be prepared.

The operation will be explained below. When the DC voltage supplied between the power supply input terminals 1 and 2 suddenly drops, the input current becomes excessive and the main fuse 3 is blown first. When the main fuse 3 is blown, a voltage is applied to both ends of the relay winding 7 via the alarm contact 4 according to the time constant of the resistor 5 and capacitor 6, and after a certain period of time when the voltage applied to the relay winding 7 is reached, the relay winding is turned off. Make contact 8 of line 7 is closed. Therefore, power can now be supplied to the DC power supply circuit 10 again through the backup fuse 9. Here, the reason why the operation of the relay is delayed for a certain period of time by the resistor 5 and the capacitor 6 so that it is not immediately connected to the other spare fuse 9 is because of external factors such as a sudden drop in the input power supply voltage. This is to ensure the timing until the abnormal phenomenon returns to normal.

〔Effect of the invention〕

As explained above, in the present invention, when a normally used fuse is blown, by connecting another spare fuse in parallel with the blown fuse at a certain time, M t When a fuse blows due to overcurrent, it has the effect of being able to recover from the fuse blowout fault in a short time.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention. 1.2...Power input terminal, 3...Main fuse, 4...Alarm contact, 5...
Resistor, 6... Capacitor, 7... Relay winding, 8... Make contact, 9...
Spare fuse, 10...DC power supply circuit.

Claims (1)

[Claims] a detection means for detecting that a first fuse connected to a DC power supply circuit is blown; a time limit means for operating after a predetermined time period from the operation of the detection means; An overcurrent protection circuit comprising: a second fuse connected in parallel.