JPH0223028A - Overcurrent protective circuit - Google Patents

Abstract

PURPOSE:To prevent degradation of elements in an electric part by detecting an output signal from a circuit equivalent to the power source input section of the electric part arranged between the electric part and a regulator for feeding voltage to the part and controlling input voltage for the electric part. CONSTITUTION:Output voltage V from a regulator 5 is fed through a switch 3 to the power source input section 7 of an electrical part 6. A power source input section 1 electrically equivalent to the power source input section 7 of the electrical part 6 is arranged at the output side of the regulator 5 and an output signal S is fed from the power source input section 1 to a current detecting section 2. When the input signal S exceeds over a predetermined level, the current detecting section 2 produces a signal for closing a switch 3, and when the signal S recovers to a normal level the switch 3 is thrown in again. By such arrangement, the elements in the electrical part 6 are protected from breakdown or degradation. It is suitable for protection of a microcomputer.

Description

[Detailed Description of the Invention] [Summary] A current flowing through an equivalent power input section equivalent to a power input section in an electrical component into which the power supply voltage from a regulator is input, and the equivalent power input section connected to the regulator. A current detection part that detects and outputs a detection signal when the detected current exceeds a predetermined value, and a switching part that makes the regulator and electrical components non-conductive or conductive depending on the presence or absence of the detection signal. This overcurrent protection circuit is capable of equivalently detecting the occurrence of an overcurrent in an electrical component and automatically stopping the supply of power supply voltage to the electrical component.

[Industrial application field]

The present invention relates to an overcurrent protection circuit for protecting electrical equipment from excessive current.

More specifically, to prevent internal elements from being destroyed due to burnout due to current exceeding the rating flowing into electrical components,
The above-mentioned overcurrent protection circuit is required.

[Conventional technology]

FIG. 5 is a circuit diagram showing a conventional overcurrent protection means. When a predetermined power supply voltage V (for example, 5V) is supplied from the regulator 5 to the electrical component 6, for example, a microcomputer, the microcomputer operates normally. The elements that make up this microcomputer are:
C with relatively low power consumption! JOS is practically advantageous and tends to be used frequently these days. However, the above C
In the MO3, unlike other semiconductor devices, even if the power supply voltage V increases only momentarily, a type of si-risk phenomenon called a latch-up phenomenon may occur, and the current may rapidly increase. Moreover, once the rough rise phenomenon occurs, it will not stop unless the supply of the power supply voltage V is stopped. As a result, the microcontroller becomes almost short-circuited, and the CMOS is eventually destroyed.

As a countermeasure against this problem, conventionally, a short circuit protection circuit 8 is provided in the regulator 5, and the supply of the power supply voltage V is stopped when the output side (microcomputer side) becomes short-circuited.

[Problems to be Solved by the Invention] As described above, conventionally, the short protection circuit 8 in the regulator 5 was operated to prevent a large current from flowing to the microcomputer. However, since the short circuit protection circuit was originally provided to protect the regulator 5 rather than the microcomputer from short circuits on the output side, it does not operate unless a current flows large enough to cause the microcomputer to be considered short-circuited. Therefore, the following problems occur.

In other words, if a latch-up phenomenon occurs, for example, a fairly large current will continue to flow through the microcontroller until it becomes close to a short circuit, so there is a risk that elements within the microcontroller will be destroyed before the short circuit protection circuit operates. It is a certain thing.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an overcurrent protection circuit that can reliably prevent elements in an electrical component 6 such as a microcomputer from being destroyed. It is something.

[Means to solve the problem]

FIG. 1 is a block diagram showing the basic configuration of the present invention. Note that components similar to those described above are denoted by the same reference numerals.

Here, an equivalent power input section 1 formed to have characteristics equivalent to the power input section 7 in the electrical component 6 to which the power supply voltage V is directly inputted is connected to the regulator 5. Furthermore, a current detection section 5 detects the current flowing through the equivalent power input section 1 and outputs a detection signal S when the detected current exceeds a predetermined value, and a regulator 5 and a regulator 5 depending on the presence or absence of the detection signal S. An overcurrent protection circuit is configured by providing a switching section 3 that makes electrical components 6 non-conductive or conductive, respectively.

In FIG. 1, an equivalent power input section 1 having characteristics equivalent to, for example, the same load as, the power input section inside the electrical component 6 is formed outside the electrical component 6. If the current flowing into the equivalent power input section 1 is detected by the current detection section 2, the current flowing into the electrical component 6 is equivalently detected. When the current flowing through the equivalent power input section 1 exceeds a preset value, it is assumed that an abnormality such as a latch-up phenomenon has occurred in the electrical component 6, and a detection signal S is immediately output to the switching section. 3 is automatically released. As a result, the connection between the regulator 5 and the switching unit 3 is cut off, and the supply of the power supply voltage V is stopped. Thereafter, when the detection signal S is no longer output, the changeover switch 3 is automatically reconnected.

Thus, in the present invention, the supply of the power supply voltage V to the electrical component 6 can be automatically stopped at the same time when a current exceeding the rating is generated in the electrical component 6, so that the elements in the electrical component 6 are not destroyed due to the excessive current. This makes it possible to prevent this from happening. Moreover, when the electrical component 6 returns to its normal state, the supply of the power supply voltage V can be automatically restarted.
There is no need to turn the power back on.

〔Example〕

FIG. 2 is a circuit diagram showing a first embodiment of the present invention. In this case, an equivalent input resistor 10 having a resistance value approximately equal to the input resistance value of the power input section 7, and an equivalent current adjustment resistor 1 for adjusting the equivalent current I flowing through the equivalent input resistor 10.
1, and a level setting resistor 12 connected to the equivalent current adjustment resistor 11 to set the input level of the current detection section 2.
are connected in series, and then arranged between the regulator 5 and the ground to constitute the equivalent power input section 1.

Further, a reference current generating section 13 consisting of a current source or the like that generates a current during normal operation of the power input section 7 as a reference current Ir, and a reference current adjustment resistor 14 for adjusting the reference current 1r are connected in series. , similarly arranged between the regulator 5 and the ground. In addition, the current detection section 2
consists of a comparator 21 that detects a change in the equivalent current I by comparing the potential at point a and the potential at point a and outputs a detection signal S, and a comparator 21 that inverts the output level of this comparator 21 and outputs an output impedance. A buffer inverter 22 that converts the
and a switching control inverter 23 that inverts the output level of the output signal again and inputs it to the switching section 3. In addition, depending on the level of the output level of the comparator 21, the level setting resistor 1
For example, a MOS type level setting transistor 24 with both ends of the buffer inverter 22 open or short-circuited is preferably connected to the output side of the buffer inverter 22 having a low output impedance. Further, as the switching section 3, a switching transistor 30 is provided which performs a switching operation according to the output level from the switching control inverter 23. Note that the input voltage to the switching transistor 30 is preferably supplied from the switching control inverter 23 via the protective resistor 31.

Next, the operation of the first embodiment will be explained in detail. First, the reference current Ir that flows into the power input section 7 when the electrical component 6, for example, the microcomputer, is operating normally is checked in advance. This reference current Ir is constantly supplied from the reference current generation section 13 to the reference current adjustment resistor 14. Since the reference current Ir may vary somewhat depending on the usage conditions of the microcomputer, etc., adjustment is performed using the reference current adjustment resistor 14. Next, the equivalent current I supplied from the regulator 5 to the equivalent input resistor 10 is adjusted by the equivalent current adjustment resistor 11 to match the reference current Ir.

If the microcomputer is operating normally, the equivalent current and the reference current 1r match, so the potential at point A is equal to the potential at point a, and no detection signal S is output to the comparator 21. Therefore, the output side of the comparator 21 (point C
) remains at “H” (High Level). Therefore, the output side of the buffer inverter 22 remains at “L” (Low Level), so
The level setting transistor 24 does not operate and both ends of the level setting resistor 12 are open.

In addition, the output side (point d) of the switching control inverter 23 is “H”.
”, the switching transistor 30 is in the operating state and the power supply voltage V is supplied to the microcontroller as usual. If a latch-up phenomenon occurs and the current inside the microcontroller increases beyond the rated value, the power supply voltage As V decreases, the potential at point a also decreases.On the other hand, since the potential at point a is constant regardless of changes in the power supply voltage V, a difference occurs between the potential at point a and the potential at point a, which increases the voltage at comparator 21. Detection signal S is output from . Therefore, the output side of the comparator 21 (point C) changes to "L". Therefore, the output side of the buffer inverter 22 becomes "H", so the level setting transistor 24 changes to "L". Resistor 12 for operating and level setting
Both ends of are shorted. As a result, the potential of the switch further decreases, so that the output level of the comparator 21 remains at "L" and becomes stable. That is, the level setting transistor 24 and the level setting resistor 12 enable the comparator 21 to respond sensitively to even the slightest excessive current. Furthermore, since the output side (point d) of the switching control inverter 23 becomes "L", the switching transistor 30 becomes inactive, and the regulator 5 and the microcomputer (DM) are cut off, and the supply voltage V to the microcomputer is cut off. After the regulator 5 is cut off from the microcomputer, the power supply voltage V on the output side of the regulator 5 returns to its normal value, so the switching transistor 3
0 returns to the operating state and resumes supplying the power supply voltage V to the microcomputer.

FIG. 3 is a block diagram showing a second embodiment of the invention. Here, a cut-off time setting section 4 is newly provided between the current detection section 2 and the switching section 3 shown in FIG. .

In FIG. 3, even if the supply of power supply voltage V is immediately stopped after an abnormality occurs in the electrical component 6, it takes a certain amount of time, seconds, for the electrical component 6 to return to its normal state. In consideration of this, the cut-off time setting section 4 sets the non-conduction time of the switching section 3 to T seconds, which is longer than the second. As a result, the electrical component 6 has definitely returned to its normal state after the switching unit 3 is once released and before it is reconnected, so the number of operations of the switching unit 3 is greater than in the case of FIG. less.

FIG. 4 is a circuit diagram showing a specific example of the second embodiment of the present invention. In this case, a cutoff time setting section 4 is further provided between the switching control inverter 23 and the protective resistor 31 in the first embodiment (FIG. 2). This cutoff time setting section 4 is connected to a time setting resistor 41 connected to the output side (point d) of the switching control inverter 23 and the collector of the switching transistor 30, and to the output side (point d) of the switching control inverter 23 and the ground. and a time setting capacitor 42.

In FIG. 4, when the current inside the microcomputer increases beyond the rated value, the output side (point d) of the switching control inverter 23
The operation until it changes to "L" is the same as in the first embodiment. However, the "L" state on the output side (point d) of the switching control inverter 23 is different from that in the first embodiment. Differently, a time setting resistor 41 and a time setting capacitor 42
It lasts for a certain amount of time. As a result, the switching transistor 30 also remains non-conductive for a certain period of time. Here, if the resistance value of the time setting resistor 41 is R1, and the capacitance of the time setting capacitor 42 is C+, then
The non-conducting time T seconds of the switching transistor 30 is T=C,R.

It is expressed as The non-conducting time T seconds is set to be slightly longer than the time required for the microcomputer to return to its normal state.

Although the non-conducting time is set here using only a resistor and a capacitor, it is also possible to set it using a monomultiplier or the like. If this monomulti is used in combination, the transient response time will be faster than when only resistors and capacitors are used, which is advantageous in practice.

〔Effect of the invention〕

As explained above, according to the present invention, an overcurrent protection circuit is realized that automatically stops the supply of power supply voltage at the same time when an excessive current occurs in an electrical component such as a microcomputer. Deterioration and destruction of the element can be prevented. Furthermore, the power supply voltage is automatically resupplied when the electrical components return to their normal state, eliminating the need to turn on the power again.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the principle configuration of the present invention, FIG. 2 is a circuit diagram showing a first embodiment of the invention, FIG. 3 is a block diagram showing a second embodiment of the invention, The figure is a circuit diagram showing a specific example of the second embodiment of the present invention, and FIG. 5 is a block diagram showing a conventional overcurrent protection means. 1... Equivalent power input section, 2... Current detection section, 3
... switching section, 4... cutoff time setting section,
5...Regulator, 6...Electrical equipment, 10.
...Equivalent input resistance, 13...Reference current generation section, 2
1... Comparator, 30... Switching transistor.

Claims (1)

[Claims] 1. In an overcurrent protection circuit comprising a regulator (5) that supplies a power supply voltage (V) to an electrical component (6), the electrical component to which the power supply voltage (V) is input. The detected current is detected by detecting the current flowing through the equivalent power input section (1) equivalent to the power input section (7) in (6) and the equivalent power input section (1) connected to the regulator (5). Current detection unit (2) that outputs a detection signal (S) when a predetermined value is exceeded
and, depending on the presence or absence of the detection signal (S), the regulator (
5) and a switching section (3) that makes the electrical component (6) non-conductive or conductive, respectively.