JPH06233445A - Overcurrent preventive circuit - Google Patents

Abstract

PURPOSE:To reduce safety costs for the prevention of accidents due to overcurrent and improve the reliability of products by providing first overcurrent detecting means and preventing means and second overcurrent detecting means and preventing means. CONSTITUTION:This overcurrent preventive circuit is for power circuits. It is provided with a first overcurrent detecting means 4 for detecting excessive currents caused by faults inside a circuit; and a first overcurrent preventing means 5 which breaks an excessive current, when the first overcurrent detecting means 4 detects it, and thus prevents accidents, such as firing. The circuit is also provided with a second overcurrent detecting means 6 which detects overcurrents at lower levels than the first detecting means does; and a second overcurrent preventive means 7 which breaks an excessive current when the second detecting means 6 detects it. Implementing these means 4-7 will significantly reduces the rate of returns of products on the market.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the stability of power supply circuits used in information equipment systems and the like.

[0002]

2. Description of the Related Art A conventional overcurrent prevention circuit is shown in FIG. The conventional overcurrent prevention method is the current input to the current generation means,
Alternatively, a method has been adopted in which the current output from the current generation means is monitored, and when an overcurrent is detected, the fuse is cut off or the power supply is cut off.

[0003]

However, in the conventional method, the fuse is blown even for recoverable overcurrent such as a user's careless mistake, and repair work by the manufacturer is required. As a result, the manufacturer's maintenance costs are high, leading to higher product costs.

[0004]

SUMMARY OF THE INVENTION The present invention is intended to solve such a problem, and in an overcurrent prevention circuit used in a power supply circuit or the like, a first aspect of detecting an abnormal current caused by a failure in the circuit or the like. A first overcurrent detection means, a first overcurrent prevention means for interrupting the current to prevent an accident such as ignition when an abnormal current is detected by the first overcurrent detection means, and the first overcurrent detection means. A second overcurrent detecting means for detecting an abnormal current at a level lower than the current level detected by the overcurrent detecting means; and a second interruption of the current when the abnormal current is detected by the second overcurrent detecting means. It is characterized in that it has an overcurrent preventing means of 2.

[0005]

The first overcurrent detecting means operates the first overcurrent preventing means by detecting an overcurrent caused by an unrecoverable failure such as a failure of the electronic component. By this operation, when a fatal defect occurs, the power supply can be cut off permanently to ensure safety.

The second overcurrent detection means detects an overcurrent caused by a recoverable abnormality such as a short circuit of a metal portion exposed to the outside such as a current output terminal, and operates the second overcurrent prevention means. When the abnormal state is resolved and the current returns to the normal state, the operation of the second overcurrent prevention means is stopped. By these operations, when the abnormality of the overcurrent such as the metal contacting the external terminal is eliminated, the operation of the system automatically returns to the normal state.

[0007]

(Embodiment 1) FIG. 1 shows a block diagram for carrying out the present invention. In order to explain the large flow, FIG. 1 is expressed in a block diagram. Reference numeral 1 is a power supply, which supplies necessary power to the entire system including the overcurrent protection circuit of the present invention. Reference numeral 2 is a current generating means, which supplies a current according to the need of the system. A current output unit 3 supplies the current generated by the current generation unit 2 to an external peripheral device. When each element forming the block operates ideally and does not fail, the current flowing into the system does not cause an overcurrent, and the system operates safely only with the block. However, in fact, an overcurrent may flow due to some factor, causing an accident such as smoking or ignition.

There are two main causes for the flow of overcurrent. One is that the elements that make up the circuit break down and become short-circuited. In this case, repair such as replacement of the element is required, and automatic restoration is impossible. Another cause is when the external output terminal is short-circuited. Since the external output terminal is often connected to a peripheral device, a metal part is exposed, and it is often short-circuited due to carelessness of an operator. In that case, it is possible to eliminate the short-circuited state by a simple operation such as removing the foreign matter that caused the short-circuit, and it is possible to automatically restore the normal operating state without repairing such as replacement of parts.

In the present invention, the method of accident prevention differs depending on the cause of overcurrent.

Reference numeral 4 is a first overcurrent detecting means for monitoring the current flowing into the current generating means 2. Reference numeral 5 is a first overcurrent prevention means, which operates to shut off the current flowing from the power source when an abnormality occurs. As soon as the first overcurrent detecting means 4 detects an abnormality in the current flowing into the current generating means 2, the first overcurrent preventing means 5 operates to ensure safety.

Reference numeral 6 is a second overcurrent detecting means, which monitors the output current from the current generating means 2. Reference numeral 7 denotes a second overcurrent prevention unit, which prevents the overcurrent by stopping the operation of the current generation unit 2. When the second overcurrent detection unit 6 detects that an overcurrent is flowing from the current generation unit 2 due to the abnormality of the current output unit 3, the second
The overcurrent prevention means 7 operates to stop the operation of the current generation means 2 to prevent an overcurrent from flowing to the output. When the abnormality of the current output means 3 is canceled and it is confirmed by the second overcurrent detection means 6 that the current returns to normal, the operation of the second overcurrent prevention means 7 is stopped and the operation of the current generation means 2 is stopped. It will be restarted. That is, the second overcurrent detection unit 6 and the second overcurrent prevention unit 7 are configured to be automatically recoverable by removing the abnormal state.

When the current level at which the first overcurrent preventing means 5 operates and the current level at which the second overcurrent preventing means 7 operates are converted into the current level flowing into the current generating means 2 and compared, the second overcurrent The current level at which the current prevention means 7 operates is set lower. By doing so, when an overcurrent flows through the current output means 3, the second overcurrent prevention means 7 operates before the first overcurrent prevention means 5 operates, and the entire system automatically recovers. Will be possible.

The cause of the overcurrent flowing through the current output terminal 3 is often an abnormality that can be recovered without replacement of parts, such as an operator's careless mistake. Therefore, when the abnormal condition is canceled, the automatic recovery is performed, so that the repair is unnecessary. When the second overcurrent prevention unit 5 does not operate and the second overcurrent prevention unit 5 operates,
An abnormality has occurred inside the current generating means 2. In that case, repairs such as parts replacement are required,
It cannot be automatically restored. Therefore, the method of interrupting the inflowing current is more effective in ensuring safety.

A concrete circuit diagram for implementing the present invention is shown in FIG. A fuse 8 includes the functions of the first overcurrent detecting means 4 and the first overcurrent preventing means 5. A switching regulator 9 embodies the current generation means 2. An overcurrent detection circuit 10 embodies the second overcurrent detection means 6. 11 is control I
C, which controls the current generation means 2 and has the function of the second overcurrent prevention means 7. The current generated by the switching regulator 9 is supplied from the output terminal 12 to peripheral devices. When a current flows from the output terminal 12, a potential difference according to the magnitude of the flowing current is generated across the current detection resistor 13. The potential difference is amplified by the voltage amplifier 14 and a signal is sent to the voltage comparator 15. Vref is set as the reference voltage of the voltage comparator 15. V
ref is a voltage level that does not occur at the output of the voltage amplifier 14 in the normal operating state, and the output of the voltage comparator 15 becomes high in the normal operating state. When an abnormal current flows through the output terminal 12 and the voltage level generated in the voltage amplifier 14 exceeds Vref, the output of the voltage comparator 15 becomes low, and the control IC 11 stops the operation of the switching regulator. When the current flowing from the output terminal 12 returns to normal, the output of the voltage comparator 15 also returns to High, and the operation of the switching regulator 9 restarts. When an internal element of the switching regulator 9 fails, no current flows through the current detection resistor 13 and an overcurrent flows only through the fuse 8. In that case, the fuse 8 is blown and the power supply terminal 1
The current flowing from 6 to the switching regulator 9 is cut off.

In this embodiment, the level at which the current flowing from the output terminal 12 in the overcurrent detection circuit 10 is judged as an overcurrent is set to 2.5A. When flowing 2.5 A from the output terminal 12, the current flowing from the power supply terminal 16 is 600 mA.
It will be about. Based on the data, the current value at which the fuse 8 blows was set to 800 mA. With this setting, the present invention could be implemented.

(Embodiment 2) FIG. 3 shows another embodiment of the present invention. Elements with the same numbers as in FIG. 2 have the same function. In the example shown in FIG. 3, the position of the current detection resistor is set to the power supply terminal 1
The position where the current flowing from 6 flows is set. The present embodiment is an example in which the overcurrent prevention is basically performed by the second overcurrent prevention means capable of automatically returning. When an overcurrent flows from the output terminal 12, the overcurrent prevention function built in the control IC 11 operates normally, but when an overcurrent occurs due to a failure of an element or the like, the overcurrent prevention function operates normally. It may not work. In such a case, this embodiment is effective. When the overcurrent prevention function built in the control IC does not operate due to a failure of the element, the fuse 8 is blown to ensure safety.

In the embodiments described above, all processing was performed by hardware, but if the system has a CPU and overcurrent detection and overcurrent prevention can be performed by software, the processing is performed using the CPU. be able to. Also,
Since the illustrated circuit is an example for carrying out the present invention, the circuit configuration, signal level, signal polarity, etc. may be optimally configured according to the system to be implemented.

[0018]

By implementing the present invention, the return rate of products on the market is significantly reduced. As a result, the cost of repairing the product was reduced, and the overall manufacturing cost was reduced. In addition, the reliability of the products can be improved, which has led to the improvement of the image of affiliated products.

[Brief description of drawings]

FIG. 1 is a block diagram for implementing the present invention.

FIG. 2 is a circuit diagram showing a specific embodiment of the present invention.

FIG. 3 is a circuit diagram showing a second specific embodiment of the present invention.

FIG. 4 is a block diagram showing a conventional power supply circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, power supply 2, current generation means 3, current output means 4, first overcurrent detection means 5, first overcurrent prevention means 6, second overcurrent detection means 7, second overcurrent prevention means 8 , Fuse 9, switching regulator 10, overcurrent detection circuit 11, control IC 12, output terminal 13, current detection resistor 14, voltage amplifier 15, voltage comparator 16, power supply terminal

Claims (1)

[Claims] 1. In an overcurrent prevention circuit used for a power supply circuit or the like, a first overcurrent detection means for detecting an abnormal current caused by a failure inside the circuit, and an abnormal current by the first overcurrent detection means. A first overcurrent preventing means for preventing an accident such as ignition by interrupting the current when the current is detected,
Second overcurrent detection means for detecting an abnormal current at a level lower than the current level detected by the first overcurrent detection means, and current when an abnormal current is detected by the second overcurrent detection means An overcurrent protection circuit having a second overcurrent protection means for shutting off the current.