JPH0865876A - Overcurrent protection device - Google Patents

Abstract

PURPOSE: To provide a device for preventing the burning of an electronic circuit, capable of detecting an abnormal current and cutting it off and at the same time displaying the abnormal condition, which has a small occupied space at low cost and free of maintenance. CONSTITUTION: A current shunted from a sense FET1 of a semiconductor element is converted by a current-to-voltage conversion part 2, and there are provided a comparator 3 for comparing the converted voltage level with a reference voltage 7, a control logic circuit 4 for gating off the sense FET1 when it exceeds the set value of the reference voltage 7, thereby cutting off a current to a board 10 and at the same time outputting an abnormal signal 8 and an abnormal-condition monitoring and abnormal-condition displaying unit 5 for turning off a power supply 12 by a power-off signal 11 at the time of receiving the abnormal signal 8 and at the same time for displaying the abnormal condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent protection device which detects an abnormal current in an electronic circuit, cuts off a current path for supplying a power source, and at the same time displays an abnormal condition.

[0002]

2. Description of the Related Art Abnormal current is one of the causes of burnout of a printed wiring board on which an electronic circuit is formed. This is because a multilayer ceramic capacitor or the like is used as a bypass capacitor for a power supply that supplies current, so that an electrode of the multilayer ceramic capacitor is short-circuited and an abnormal current is generated. In that case, an overcurrent due to a short circuit of the electrodes, that is, an abnormal current is generated, the printed wiring board is heated, and then the printed circuit board is charcoal-fired repeatedly. Finally, an overcurrent of about 6 to 7 A causes ignition. It is empirically known to follow this process.

For example, as shown in FIG. 2, a board 10 forming a plurality of electronic circuits connected to a mother board 6 is one.
If there is ~ n, if there is a possibility of burnout due to overcurrent, that is, abnormal current generated by some cause, the board 10 is provided with a fuse circuit or the like to immediately cut off to prevent ignition. Is normal. However, many of the boards 10 purchased from the outside do not have such a protection circuit. Therefore, as shown in FIG.
For each board 10, a power source 12 having a small current capacity, for example, a current capacity of 6 A or less, which does not ignite as a printed wiring board, may be dispersed, or one power source 12 having a large current capacity may be provided as shown in FIG. On the other hand, in the current path of each board 10, a fuse or a circuit breaker 13 is provided as a protection element as a protection element.

However, (1) the power supply system using the distributed power sources as shown in FIG. 3 requires as many power sources 12 as the number of boards 10, requires a large installation space, and is expensive. (2) Further, in the power supply system using the centralized power source as shown in FIG. 4, when the fuse 13 is used, there is an immediate cutoff fuse for the board 10 having a power consumption of about 2 A, but the consumption of about 5 A is consumed. There is no immediate cut-off fuse capable of supporting the power board 10, and there is a considerable delay in the operation time of the fuse, so it is not possible to reliably prevent the ignition from occurring. (3) If a fuse is used, it is necessary to replace the fuse that has finished operating. (4) Even if a circuit breaker is used, not only does it require a lot of installation space, but it is also necessary to manually operate the circuit breaker. The prior art has a drawback in that it must be restored by the method.

[0005]

SUMMARY OF THE INVENTION It is necessary to prevent burnout of a printed wiring board or the like which constitutes an electronic circuit due to the generation of an abnormal current.
It is extremely important from the standpoint of improving quality and reliability, as well as ensuring safety. Many efforts have been made to increase the nonflammability of the board itself, but there are limits in terms of material selection and cost. In addition, as in recent years, when multifunctional and miniaturized ones and large-scale ones that require a large number of high-density packaging boards are required, conventional fuses and circuit breakers are used. The implementation of burnout prevention measures from abnormal currents has problems that a large installation space is required, cost is high, and maintenance is inefficient.

Therefore, the problem to be solved by the present invention is that an abnormal current may damage an electronic circuit.
For example, in order to prevent the printed wiring board on which the electronic circuit is formed from being burnt out, it detects the occurrence of abnormal current, shuts it off immediately, and at the same time displays the status of abnormality occurrence, in a small space. , And to provide a low-cost, maintenance-free circuit device.

[0007]

According to the present invention, in a protection circuit for preventing burnout of a printed wiring board on which an electronic circuit for generating an abnormal current is formed, a sense FET, which is a semiconductor element among commercially available general-purpose products, is used. (Field-Effect Transisto
r) was used. As shown in FIG. 1, the current shunted from the sense FET is input to a current / voltage conversion unit that converts the current into a voltage,
The converted output voltage is input to the next comparator. The converted voltage is compared with the reference voltage. When an abnormal current occurs, the current shunted by the sense FET also increases abnormally. When the converted voltage level exceeds the value set as the reference voltage, the next control logic circuit outputs the gate OFF signal at the time of abnormality and turns off the gate of the sense FET.

As a result, the current supplied to the board from the power supply through the sense FET is turned off.
At the same time, an abnormality signal is output from the control logic circuit, and the abnormality monitoring and abnormality display unit to which the abnormality signal is input outputs a power OFF signal to turn off the entire power supply. At the same time, the error occurrence status is displayed on the error display unit.

[0009]

[Action]

(1) A sense FET, which is a semiconductor element, was used as an element that immediately cuts off the current supplied from the main power supply and turns it off when an abnormal current occurs, but the shunted current is 1 / 1,000 To a small extent, voltage conversion can be used to perform fine control, and the detection sensitivity is good and there is no operation delay like fuses. (2) Since the detection sensitivity is good, even if an abnormal current occurs for some reason for a short time that does not result in burnout, it will be detected and shut off without fail, and the abnormal situation will be displayed. It is now possible to easily identify the occurrence location. (3) Even if there are many target circuits for which you want to monitor the occurrence of abnormal current, the sense FET is used to save space, and even if an error occurs in one place, the power supply that supplies power to the whole Since it can also be turned off, the safety is improved.

[0010]

1 is a block diagram showing the basic structure of an embodiment of the present invention. (1) In this embodiment, with respect to a plurality of printed wiring boards 10 each having an electronic circuit that may be burnt out due to an abnormal current, the motherboard 6 that supplies current by the centralized power supply system is prevented from burning out. An abnormal current detection and interruption and an abnormal display circuit device provided for the purpose will be described. (2) As shown in FIG. 2, the current supply to each board 10 is
Power is supplied from the power supply 12 connected to the motherboard 6 through the motherboard 6. The abnormal current detection and cutoff circuit of the present invention is provided together on the motherboard 6.

Next, (3) as shown in FIG. 1, each board 10
In the present invention, as a protective element that supplies current from the power source 12 to the
T1 was used. The current of about 1 / 1,000 shunted from the sense FET 1 is input to the next current / voltage conversion unit 2 and converted into a voltage, and the output voltage therefrom is input to the next comparator 3. Then, the comparator 3 compares it with the reference voltage 7.
The reference voltage 7 is a value set by converting a value to be detected as an abnormal current into a voltage. Sense when abnormal current occurs
The current value shunted from FET1 also increases abnormally proportionally. When the level of the voltage converted from the current exceeds the value set as the reference voltage 7, the next control logic circuit 4 outputs the abnormal gate OFF signal 9 to turn off the gate of the sense FET 1.

(4) When the gate of the sense FET 1 is turned off, the current to the board 10 supplied from the power source 12 through the sense FET 1 is turned off. At the same time,
An abnormality signal 8 is output from the control logic circuit 4, and the abnormality monitoring and abnormality display unit 5 to which the abnormality signal 8 is input
Outputs the power OFF signal 11 and turns off the power supply 12. Then, the status of occurrence of the abnormality can be displayed on the abnormality display unit. The abnormality display unit can be provided outside the motherboard 6 at an optimum position.

(5) The overcurrent protection device of the present invention can be used even if only the board 10 is used alone, and the number of the sense FETs 1 can be increased even if there are any number of boards 10 forming an electronic circuit. Furthermore, it is also possible to divide and provide each of the groups of several boards 10. (6) Further, the overcurrent protection device of the present invention is not limited to an electronic circuit formed by a printed wiring board, but can be used as a protection circuit device from burnout due to the generation of an abnormal current in another electronic circuit. it can.

[0014]

Since the present invention is configured as described above, it has the following effects. (1) Compared to fuses and circuit breakers, the use of a sense FET, which is a semiconductor element, as a protection element
The space required for the circuit configuration could be extremely reduced. (2) The sense FET is generally sold in large quantities as a general-purpose product, so it has a low price, and even if the number of uses increases, it hardly becomes a factor of cost increase. (3) Since there is no delay time for operation like a fuse, it has become possible to detect and interrupt the occurrence of abnormal current with high sensitivity and certainty. (4) Therefore, it becomes possible to easily cope with a large number of boards and the like on which the target electronic circuit is formed.

(5) In the case of the prior art in which fuses and circuit breakers are used as protective elements, it was necessary to replace the fuses after operation or restore the circuit breaker settings each time an abnormality occurred. . In the present invention in which the sense FET, which is a semiconductor element, is used as a protection element, the characteristics of the sense FET do not change at all, and therefore it can be repeatedly used as it is. Therefore, "maintenance-free" can be realized for the protection element portion every time an abnormality occurs, and the efficiency is improved, and at the same time, the trouble of having to always prepare a replacement fuse is released.

[Brief description of drawings]

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

FIG. 2 is a conceptual diagram showing a configuration for supplying a current to a board by a centralized power supply system.

FIG. 3 is a block diagram of a conventional distributed power supply system.

FIG. 4 is a block diagram of a conventional centralized power supply system.

[Explanation of symbols]

 1 Sense FET 2 Current / voltage converter 3 Comparator 4 Control logic circuit 5 Abnormality monitoring and abnormality display unit 6 Motherboard 7 Reference voltage 8 Abnormality signal 9 Abnormal gate OFF signal 10 Board 11 Power OFF signal 12 Power supply 13 Fuse or circuit breaker

Claims (2)

[Claims] 1. A protection circuit for preventing a burnout of an electronic circuit due to an overcurrent, comprising: a current / voltage conversion unit (2) for converting a current shunted from a sense FET (1) which is a semiconductor element into a voltage. The comparator (3) that compares whether the voltage level exceeds the reference voltage (7) or the sense FET (1) is turned off when the reference voltage (7) exceeds the set value due to overcurrent. The current to the board (10)
Control logic circuit (4) that outputs an abnormal signal (8) at the same time when it is turned off, and an abnormal condition monitor that displays the abnormal condition while turning off the power supply (12) by the power off signal (11) when the abnormal signal (8) is received An overcurrent protection device comprising: an abnormality display unit (5). 2. A plurality of boards (10) constituting an electronic circuit
Centralized power supply type motherboard to which is connected (6)
The overcurrent protection device according to claim 1, wherein the overcurrent protection device is provided in the.