JP2533553B2 - Electric circuit burnout prevention circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a damage prevention circuit for an electric circuit which is supplied with power from the outside, and is particularly suitable for preventing burnout of the circuit due to an abnormality in a circuit load current. The present invention relates to a burnout prevention circuit.

[Conventional technology]

As a method of preventing burnout caused by an overcurrent, a fuse having a function of detecting an overcurrent and opening the conduction path. There are circuit breakers. Further, as a modification of this, there is a fuse which responds to the continuation of an excessive current over time, a fuse which operates by sensing an increase in temperature due to an excessive current, and the like. Incidentally, there is an invention disclosed in, for example, Japanese Patent Application Laid-Open No. 58-165619, as the related art.

[Problems to be solved by the invention]

In the above-mentioned conventional technique, a protection element is used for all normal current paths. The excessive current response type protection element has a problem that the circuit is broken or broken due to an instantaneous excessive load generated on the load circuit or a transient excessive instantaneous current generated when the power is turned on.
Moreover, the accuracy of the operating current value is relatively low. Further, the impedance of the overcurrent path may be high due to the breakdown of the load on the circuit, and the overcurrent may be kept below the operating current value. At this time, heat is generated on the load circuit due to the overcurrent, and in the case of a combustible element, smoking or burning may occur.

In the protection element that responds to the continuation of current over time, malfunction due to momentary excessive current cannot occur. This type of protection element operates when the current continues over time, that is, when the integrated value of the current is constant. This corresponds to the case where the heat generation due to the excessive current exceeds a certain value, and is equivalent to responding to the heat generation. In this case, the accuracy becomes sensitive to heat, and it is difficult to obtain a highly accurate operation. If the abnormal current continues to be a relatively low value as described above, the time until the circuit breaks or breaks becomes long. During this time, heat may be generated in the destructive element due to an excessive current, and the possibility of burning eventually may occur as in the case described above.

Next, in the case of temperature sensitive type, heat is generated due to circuit abnormality,
A temperature sensitive element is installed in the flammable element that causes burnout or the like or the heat generating part (cooling fin, etc.) of the circuit part, and when the temperature rises abnormally, the power supply path is cut off to prevent burnout. Is the way. In this case, it is general that there is a considerable difference between the breaking operation temperature and the normal operation temperature. As in the case described above, if the destruction element or the circuit part has a relatively high impedance, the abnormal current Is a relatively low value. Therefore, the rapid temperature rise necessary for performing the breaking and cutting operation is unlikely to occur, the time until the operation becomes long, and the possibility of burning occurs during that time.

Therefore, if an element that cuts off or cuts off the power supply line is arranged on the power supply line to protect it, if the value of the abnormal current is relatively low or the operating current of the protection circuit is destroyed, the circuit will be destroyed. When the excessive current over time can take various values, especially when it is low with respect to the operating value, the heat generation of the circuit is accumulated over time, and smoke, burnout, or the like can be eventually caused. In order to prevent this problem, it is easy to set the operating current value low. However, when the load current of the circuit fluctuates significantly in the normal operating state, the maximum load current value becomes the lower limit of the setting of the operation current value of the circuit breaker. Then, if the lower limit of the current leading to the burnout at the time of abnormality is lower than this set value and the set value can be taken, the burnout protection is not performed.

Next, it is conceivable that the power supply device side that supplies power has a protection circuit against excessive current. This protection circuit, even if the load circuit side does not have the above protection circuit,
When the load current exceeds the allowable value of the power supply due to temporary overload on the circuit side, artificial power supply short circuit, etc., the power supply side is turned on or off to protect the power supply. Therefore,
As in the above case, if the excessive current due to the abnormality on the load circuit side is within the allowable value of the power supply current, it may not be protected against burnout.

An object of the present invention is to detect an abnormal operation that may result in burnout due to a failure, destruction, short circuit, etc. of an electric circuit, and to disconnect or disconnect the power supply path only when the abnormal operation is caused by an abnormal current. Another object of the present invention is to provide a burnout prevention circuit for an electric circuit that prevents burnout of the circuit.

[Means for solving problems]

The burnout prevention circuit for an electric circuit according to the present invention is connected to an abnormality detecting means for detecting an abnormal operation of the circuit and a power supply end of the circuit, and power is supplied during normal operation of the circuit, and the abnormality detecting means detects an abnormal operation of the circuit Normal power supply means that is cut off when you do,
Power is supplied when the abnormality detecting means detects an operation abnormality of the circuit,
It is characterized in that it is configured by an abnormal power supply line that is opened by overcurrent.

[Action]

According to the present invention, when the power supply starts supplying power to the circuit, when the power supply means at the time of abnormality is not disconnected during the previous power supply, the circuit is in the operation start waiting state and the voltage at the power supply end becomes normal. The normal power supply means is turned on, the power supply is switched to the normal power supply path, and the circuit starts normal operation.

During operation of the circuit, when an operation abnormality occurs in an element or a circuit portion that may cause burnout, the abnormality detection means detects this and switches the power supply path to the power supply means in the abnormality. At this time, the circuit is returned to the operation start waiting state by temporarily turning off or turning off the power supply. Further, at this time, if an abnormal current that is larger than that in the operation start waiting state flows in the circuit side, the abnormal power supply means is turned off or turned off. The circuit is protected from burnout due to an abnormal current because the power supply line during normal and abnormal conditions is cut off.

After that, even if the power is turned on again, the circuit side terminal of the power feeding means at the time of abnormality is in an open state, and a normal voltage is not generated. Therefore, the normal power feeding means does not reach the operating state, the two power feeding paths are opened, and the circuit and the power supply section are disconnected, so that there is a risk of burning even if an abnormality such as a short circuit remains on the circuit side. There is no.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to the embodiments shown in the accompanying drawings.

The accompanying drawings show the present invention applied to a circuit for driving a DC brushless motor 8. Attached in the drawing,
When the power supply 1 is turned on, the motor drive circuit 4 and the power supply voltage detection circuit 2 are energized by the abnormal power supply path 5 composed of fuses and diodes. At this time, the relay contact forming the normal power supply path 6 and the relay contact 7 controlling connection between the motor and the drive circuit 4 thereof are in a disconnected state.

When the output voltage of the power supply 1 is normal, the power supply voltage detection circuit 2
Activates the microcomputer 3. The microcomputer 3 drives the normal power supply path 6 and the relay contacts of the motor connection circuit 7 according to the program, and the drive of the motor 8 by the normal power supply path 6 is started. Up to now, the drive circuit 4 is in a state in which current consumption of only the drive circuit 4 flows in via the power supply path 5 at the time of abnormality. The current in the operation start waiting state is higher than the current when the drive circuit 4 drives the motor 8.
Is small compared to the current in the operating state, and the fuse 51 of the power supply path 5 at the time of abnormality is not broken or cut off.

When the driving of the motor 8 is started, a starting current that causes the motor 8 to start rotating from a stopped state flows, the rotation speed increases, and eventually the motor current decreases as the rotation speed approaches the predetermined rotation speed. When it reaches, the current value of the motor 8 also decreases to a constant value.

The drive circuit 4 controls the rotation detection circuit 9 so that the rotation speed of the motor 8 becomes constant. The microcomputer 3 monitors the rotation speed through the rotation detection circuit 9.

When the rotational speed of the motor becomes abnormal, the microcomputer 3 switches the relay contact 7 for connection and disconnects it, and also disconnects the relay contact of the normal power supply path 6 to switch the power supply path to the power supply path 5 at the time of abnormality. The drive circuit 4 is returned to the operation start waiting state. At this time, if a failure or the like that causes an excessive current occurs in the drive circuit, a current exceeding the operation start waiting state flows in the abnormal power supply path 5, so that the fuse 51 of the abnormal power supply path 5 is also cut off and the power supply is stopped. Stops.

When the abnormal rotation speed is caused by a factor other than the short-circuit destruction of the drive, the fuse 51 is not broken or disconnected, so that the drive circuit 4 maintains the operation start waiting state. When the power source 1 is turned on again by the normal means again, the normal state is restored.

When the fuse 51 of the power supply path 5 is abnormally turned off due to an excessive current, the power supply voltage detection circuit 2 is not supplied with power even if the power supply 1 is turned on again. Since power is not supplied to the short-circuited destruction portion of 4, it is possible to prevent burning and the like.

〔The invention's effect〕

According to the present invention, when the circuit has a failure, a breakdown, a short-circuit breakdown, or the like, the circuit can be turned on or off regardless of the value of the abnormal current, so that the burnout can be accurately prevented by itself. There is.

[Brief description of drawings]

The accompanying drawings are circuit diagrams showing an embodiment in which the present invention is applied to a drive circuit of a DC brushless motor. 1 ... Power supply, 2 ... Power supply voltage detection circuit, 3 ... Microcomputer, 4 ... Drive circuit, 5 ... Abnormal power supply path, 6 ...
Normal power supply line, 7 ... Connection relay, 8 ... Motor, 9 ...
… Rotation detection circuit, 51 …… Hyuse.

Claims (1)

(57) [Claims] 1. An abnormality detecting means for detecting an abnormal operation of a circuit and a power supply terminal of the circuit, which supplies power when the circuit operates normally, and is disconnected when the abnormal detecting means detects an abnormal operation of the circuit. A burnout prevention circuit for an electric circuit, comprising: a normal power supply means, and an abnormality power supply path, which supplies power when the abnormality detection means detects a circuit operation abnormality and is opened by an overcurrent.