JPH06133444A - Electronic fuse circuit - Google Patents

Abstract

PURPOSE:To eliminate the necessity of application of an overcurrent for the detection of the state of a load and eliminate the delay of the detection time when the recovery of an electronic fuse circuit which cuts off an overcurrent when the overcurrent is applied to the load and, when the load is recovered to a normal state, detects the recovery and recovers automatically is monitored. CONSTITUTION:An electronic fuse circuit is composed of an operation current detecting circuit 12 which detects an operation current io applied when a load 6 is in operation, a protective circuit 11 which cuts off the operation current io when an overcurrent is detected by the operation current detecting circuit 12 and a recovery monitoring circuit 13 which applies a monitoring current im to the load 6 while the operation current io is cut off by the protective circuit 11 and monitors the state of the load 6 and, when the load is recovered to a normal state, releases the cut-off operation of the protective circuit 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic fuse circuit which, when an overcurrent flows through a load, shuts off the overcurrent and, when the load returns to a normal state, detects it and automatically restores it. Regarding

In a private branch exchange or the like, many lines are connected, and there is a possibility that a short circuit accident of a cable connected to the lines may occur. In that case, an electronic fuse circuit is provided in order to shut off the overcurrent and prevent an excessive load from being applied to the power supply device. It is desirable for such an electronic fuse circuit to immediately perform a breaking operation when an overcurrent is detected, and to automatically return to a normal state when the load returns to normal.

[0003]

2. Description of the Related Art Conventionally, an electronic fuse circuit has a detection circuit for detecting a current flowing through a load, a protection circuit for interrupting the current flowing through the load when the detection circuit detects an overcurrent, and a temporary operation due to the overcurrent. It is composed of a recovery circuit for automatically recovering the protection circuit.

In such a recovery circuit, in order to detect whether or not the load has returned to a normal state, the protection circuit is forcibly released from the interruption operation, and at that time, an overcurrent is detected. A method of judging by whether or not there is used (Japanese Patent Laid-Open No. 63-59718).

[0005]

However, in the above-mentioned conventional electronic fuse circuit, an overcurrent is forced to flow to a load that has not returned to the normal state, and this is repeated many times. Therefore, there is a problem that an excessive load is applied to the power supply device and the load is also adversely affected depending on the state of the load.

Moreover, since the load state is detected periodically and intermittently, there is a problem that the detection time is delayed by a maximum of one cycle and the recovery is delayed. In view of the above problems, it is an object of the present invention to provide an electronic fuse circuit that does not pass an overcurrent for detecting a load state and has no delay in detection time.

[0007]

In order to solve the above-mentioned problems, an electronic fuse circuit 1 according to the invention of claim 1 is provided with the structure shown in FIG.
As shown in FIG. 3, an operating current detection circuit 12 for detecting an operating current io flowing when the load 6 operates, and an operating current detection circuit 12 for cutting off the operating current io when an overcurrent is detected by the operating current detection circuit 12. When the operating current is cut off by the protection circuit 11 and the protection circuit 11, a monitoring current im is passed through the load 6 to monitor the state of the load, and when the load returns to the normal state, Protection circuit 1
The recovery monitoring circuit 13 for canceling the interruption operation of No. 1 is configured.

The electronic fuse circuit 2 according to the invention of claim 2
As shown in FIG. 2, the light emitting element 27D of the photocoupler 27 is connected to the operating current detection circuit 12 and the restoration monitoring circuit 13, and the light receiving element 27T of the photocoupler 27 is connected to the light receiving element 27D. When the side element is turned on, the protection circuit 11 is connected so that the protection circuit 11 is shut off.

The electronic fuse circuit 2 according to the invention of claim 3
The protection circuit 11 includes a transistor 26 that performs an interruption operation by turning off the protection circuit 11.
The light receiving side element 27T of No. 7 is connected so as to cut off the base current of the transistor 26 when turned on.

[0010]

The operating current detection circuit 12 detects the operating current io flowing when the load 6 is operating. The protection circuit 11 shuts off the operating current io flowing through the load when an overcurrent is detected. The recovery monitoring circuit 13 loads the load 6 during the interruption operation state.
A monitoring current im is passed to monitor the state, and when the load returns to the normal state, the cutoff operation of the protection circuit 11 is released.

When the transistor 26 is used for the protection circuit 11, the base current is cut off by turning on the light-receiving side element 27T, whereby the cut-off operation state is established. Currents of the operating current detection circuit 12 and the restoration monitoring circuit 13 flow through the light emitting side element 27D, and the photocoupler 27 is turned on or off depending on the magnitude of these currents.

[0012]

FIG. 2 is a diagram showing an embodiment of an electronic fuse circuit 2 according to the present invention. It is assumed that the electronic fuse circuit 2 is connected between the plus side of the power supply device and the frass side of the load, like the electronic fuse circuit 1 of FIG.

Due to the potential difference between the input terminal IN and the output terminal OUT, a base current flows through the transistor 26 through the resistor 22 and the transistor 26 is turned on. When the transistor 26 is turned on, the resistor 21, the transistor 26,
A current (operating current) io flows through the diode 28 and the diode 28. This is the normal operating condition.

At this time, a voltage drop Vd due to the current io occurs across the resistor 21. When the load is in a normal state, the current io is below a certain value (maximum rated value), so the magnitude of the voltage drop Vd is also below a certain value. However, when the current io exceeds a certain value due to a load short circuit or the like, that is, when an overcurrent flows, the voltage drop Vd
Exceeds a certain value.

When the voltage drop Vd exceeds a certain value, a current is flows through the diode 27D, the resistor 25, the Zener diode 30 and the diode 32 of the photocoupler 27, and when it exceeds a certain value, the photocoupler 27 is turned on. Becomes

When the photocoupler 27 is turned on, that is, when the transistor 27T is turned on, the base-emitter of the transistor 26 is short-circuited, the base current becomes zero, the transistor 26 is turned off, and the current io becomes zero. This is the cutoff operation state (or protection operation state) due to overcurrent.

When the transistor 26 is turned off and the cutoff operation is performed, the voltage drop Vd becomes zero, the current is becomes zero, and the current of the diode 27D becomes zero, but at the same time, the input terminal IN and the output terminal OUT are simultaneously output. Since a voltage substantially the same as the power supply voltage is applied between and, a current (monitoring current) im flows through the diode 27D, the resistor 23, the zener diode 29, and the diode 31 by this voltage. Due to this current im, the diode 27D emits light, and the ON state of the photocoupler 27 is maintained. However, the current im decreases depending on the load condition,
The photo coupler 27 is turned off. This is the monitoring state during the breaking operation.

Note that the magnitude of the current im is a minimum amount for turning on the photocoupler 27 and does not adversely affect the load. Resistor 22 and transistor 27T
The current flowing through it is minute and does not adversely affect the load. The resistor 24 is for bypassing the dark current of the photocoupler 27.

When the load returns to the normal state in the monitoring state, the current im flowing in the diode 27D decreases, and therefore the photocoupler 27 is turned off. When the photocoupler 27 is turned off, a base current flows through the transistor 26 to turn it on, the cutoff operation state is released, and the normal operation state is restored.

As described above, when an abnormality occurs in the load and an overcurrent flows, the transistor 26 is immediately detected by detecting it and at the same time, the monitoring of the load state by the current im is started. When the load returns to the normal state and the current im decreases, the cutoff state of the transistor 26 is immediately released, and the normal operation state is restored.

Therefore, since an overcurrent is not passed in order to detect whether or not the load condition is normal,
No excessive load is applied to the power supply device, and the load is not adversely affected. Moreover, since the load state is continuously monitored and the detection time is not delayed, the supply of the current io can be restarted immediately after the load is restored to the normal state.

In the above embodiment, the photocoupler 2
Since the transistor 27T of No. 7 cuts off and releases the transistor 26, the operation speed is fast and the operation is reliable despite the simple circuit. The current is in the diode 27D of the photocoupler 27.
Both the current and the current im flow, thereby performing two operations of detecting an overcurrent and monitoring a load. Therefore, the operation is reliable with a simple circuit.

In the above embodiment, the Zener diodes 29 and 30 are for improving the threshold characteristics of the currents is and im, and the diodes 31 and 32 are for preventing backflow.
In the above embodiment, the resistor 21, the transistor 26,
The protection circuit 11 includes the diode 28 and the transistor 27T, the operating current detection circuit 12 includes the diode 27D, the resistor 25, the Zener diode 30, and the diode 32, and the recovery monitoring circuit includes the diode 27D, the resistor 23, the Zener diode 29, and the diode 31. 13 are respectively configured.

In the above-described embodiment, one photocoupler 27 is used for both overcurrent detection and overcurrent, but two photocouplers may be used so as to perform these separately. In addition, the circuit configurations of the electronic fuse circuits 1 and 2, the types of circuit elements, the values of the circuit elements, and the like can be variously changed in accordance with the gist of the present invention.

[0025]

According to the present invention, it is possible to provide an electronic fuse circuit in which an overcurrent is not passed for detecting the state of a load and the detection time is not delayed.

According to the second aspect of the invention, the circuit is simple and the operation is reliable. According to the invention of claim 3, the circuit is simplified and the operation speed is fast and the operation is reliable.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an electronic fuse circuit according to the present invention.

FIG. 2 is a diagram showing an embodiment of an electronic fuse circuit according to the present invention.

[Explanation of symbols]

 1, 2 Electronic fuse circuit 5 Power supply device 6 Load 11 Protection circuit 12 Operating current detection circuit 13 Recovery monitoring circuit 26 Transistor 27 Photocoupler 27D Diode (light emitting side element) 27T Transistor (light receiving side element) io current (operating current) im current (Monitoring current)

Claims (3)

[Claims] 1. An operating current (i) flowing when a load (6) operates.
and an operating current detection circuit (12) for detecting o), and a protection circuit (11) for cutting off the operating current (io) when an overcurrent is detected by the operation current detection circuit (12). When the operating current is cut off by the protection circuit (11), a monitoring current (im) is passed through the load (6) to monitor the state of the load, and the load returns to a normal state. An electronic fuse circuit, further comprising: a recovery monitoring circuit (13) for releasing the interruption operation of the protection circuit (11). 2. The electronic fuse circuit (2) according to claim 1, wherein the operating current detection circuit (12) and the recovery monitoring circuit (13) include a light emitting side element (2) of a photocoupler (27).
7D) is connected, and the light receiving side element (27T) of the photocoupler (27) is
An electronic fuse circuit, characterized in that the protection circuit (11) is connected so that the protection circuit (11) is turned off when the light-receiving side element is turned on. 3. The electronic fuse circuit (2) according to claim 2, wherein the protection circuit (11) includes a transistor (26) that performs a cutoff operation when turned off, and the protection circuit (11) includes: The light receiving element (27T)
An electronic fuse circuit, which is connected so as to cut off the base current of the transistor (26) when turned on.