JP2755391B2 - Overcurrent protection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] An equivalent power supply input section equivalent to a power supply input section in an electrical component to which a power supply voltage from a regulator is input, and a current flowing through the equivalent power supply input section connected to a regulator are described. A current detection unit that detects and outputs a detection signal when a detection current exceeds a predetermined value, and when there is the detection signal, makes the regulator and the electrical component non-conductive, and there is no detection signal An overcurrent protection circuit comprising: a switching unit that conducts between the regulator and the electrical component, wherein the overcurrent protection circuit equivalently detects that an excessive current has occurred in the electrical component and controls the power supply voltage. It becomes possible to automatically stop the supply to the product.

[Industrial applications]

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

More specifically, the above-mentioned overcurrent protection circuit is required to prevent a current exceeding the rating from flowing into the electrical components and destroying the internal elements due to burning or the like.

[Conventional technology]

FIG. 5 is a circuit diagram showing a conventional overcurrent protection means.
When a predetermined power supply voltage V (for example, 5 V) is supplied from the regulator 5 to the electrical component 6, for example, the microcomputer, the microcomputer operates normally. The elements that make up this microcomputer are:
CMOS with relatively low power consumption is practically advantageous and tends to be used recently. However, in the above-mentioned CMOS, unlike other semiconductor elements, even when the power supply voltage V increases only momentarily, a kind of thyristor phenomenon called a latch-up phenomenon may be caused and the current may increase steadily. Moreover, once the latch-up phenomenon occurs, it does not stop unless the supply of the power supply voltage V is stopped. As a result, the microcomputer is almost short-circuited, and eventually the CMOS is destroyed.

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

[Problems to be solved by the invention]

As described above, conventionally, the short protection circuit 8 in the regulator 5 is operated to prevent a large current from flowing to the microcomputer. However, since the short-circuit protection circuit is originally provided to protect the regulator 5 from a short-circuit on the output side rather than the microcomputer, the short-circuit protection circuit does not operate unless a large current flows so that the microcomputer can be regarded as a short-circuit state. Therefore, the following problem occurs.

That is, for example, when a latch-up phenomenon occurs,
Since a considerably large current continuously flows through the microcomputer until the state becomes close to a short circuit, elements in the microcomputer may be destroyed before the short protection circuit operates.

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

[Means for solving the problem]

FIG. 1 is a block diagram showing the principle configuration of the present invention.
The same components as those described above are denoted by the same reference numerals.

Here, the equivalent power supply input unit 1 formed to have characteristics equivalent to the power supply input unit 7 in the electrical component 6 to which the power supply voltage V is directly input is connected to the regulator 5. Further, a current detection unit 5 that detects a current flowing through the equivalent power supply input unit 1 and outputs a detection signal S when the detection current exceeds a predetermined value, and a regulator 5 when the detection signal S is present. Non-conduction between the electrical component 6;
An overcurrent protection circuit is provided by providing a switching unit 3 that conducts between the regulator 5 and the electrical component 6 when there is no detection signal S.

(Operation)

In FIG. 1, an equivalent power input unit 1 having characteristics equivalent to the power input unit in the electrical component 6, for example, having an equivalent load, is formed outside the electrical component 6. If the current flowing through the equivalent power supply input unit 1 is detected by the current detection unit 2, the electrical component 6
That is, the current flowing into the device is equivalently detected. When the current flowing through the equivalent power supply input unit 1 exceeds a predetermined value set in advance, it is regarded that an abnormality such as a latch-up phenomenon has occurred in the electrical component 6, and the detection signal S is immediately output to the switching unit. 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 stops being output,
The changeover switch 3 is automatically reconnected.

Thus, according to 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 element in the electrical component 6 is destroyed by the excessive current. Can be prevented from occurring. In addition, when the electrical component 6 returns to the normal state, the supply of the power supply voltage V can be automatically restarted, so that there is no need to turn on the power again.

〔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 substantially equal to the input resistance value of the power supply input unit 7 and an equivalent current adjusting resistor 11 for adjusting an equivalent current I flowing through the equivalent input resistor 10 are provided.
And a level setting resistor 12 connected to the equivalent current adjusting resistor 11 for setting the input level of the current detection unit 2 are connected in series, and then arranged between the regulator 5 and the ground to be equivalent. The current input unit 1 is configured. Further, a reference current generating unit 13 including a current source or the like that generates a current during normal operation of the power input unit 7 as a reference current Ir and a reference current adjusting resistor 14 for adjusting the reference current Ir are connected in series. , Similarly arranged between the regulator 5 and the ground. The current detection unit 2 detects a change in the equivalent current I by comparing the potential at the point a with the potential at the point b, and outputs a detection signal S.
And a buffer inverter 22 for inverting the output level of the comparator 21 and converting the output impedance,
A switching control inverter 23 that inverts the output level of the buffer inverter 22 again and inputs the inverted output level to the switching unit 3. Note that, for example, a MOS-type level setting transistor 24 that opens or short-circuits both ends of the level setting resistor 12 according to the level of the output level of the comparator 21,
It is preferable to connect to the output side of the buffer inverter 22 having a low output impedance. Also, as the switching unit 3,
A switching transistor 30 that performs a switching operation according to the output level from the switching control inverter 23 is provided. It is preferable that the input voltage to the switching transistor 30 be supplied from the switching control inverter 23 via the protection resistor 31.

Next, the operation of the first embodiment will be described in detail.
First, the reference current Ir flowing into the power input unit 7 when the electrical component 6, for example, the microcomputer is operating normally, is checked in advance. The reference current Ir is always supplied from the reference current generator 13 to the reference current adjusting resistor 14. The reference current Ir may vary slightly depending on the conditions of use of the microcomputer, etc.
The adjustment is performed by 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 adjusting resistor 11 to match the reference current Ir. If the microcomputer is operating normally, since the equivalent current I and the reference current Ir match, the potential at the point b becomes equal to the potential at the point a, and the detection signal S is not output to the comparator 21. Therefore, the output side (point c) of the comparator 21 remains “H” (High Level). Therefore, the output side of the buffer inverter 22 is “L” (Lo
w Level), the level setting transistor 24
Does not operate, and both ends of the level setting resistor 12 are opened. Further, since the output side (point d) of the switching control inverter 23 remains "H", the switching transistor 30 is in the operating state, and the power supply voltage V is supplied to the microcomputer as usual.
If the latch-up tower occurs and the current in the microcomputer increases beyond the rating, the power supply voltage V decreases, and the potential at the point b also decreases. On the other hand, since the potential at the point a is constant irrespective of the change in the power supply voltage V, a difference occurs between the potential at the point b and the potential at the point a, and the comparator 21 outputs the detection signal S. Therefore, the output side (point c) of the comparator 21 changes to "L". Therefore, the buffer inverter 22
Since the output side of “H” goes “H”, the level setting transistor
24 operates, and both ends of the level setting resistor 12 are short-circuited.
As a result, the potential at the point b further decreases, so that the output level of the comparator 21 remains stable at "L". That is,
The level setting transistor 24 and the level setting resistor 21 enable the comparator 21 to respond sensitively to a slight overcurrent. Further, the output side (point d) of the switching control inverter 23 becomes “L”,
The switching transistor 30 is brought into a non-operating state, the connection between the regulator 5 and the microcomputer is cut off, and the supply of the power supply voltage V to the microcomputer is stopped. After the regulator 5 is cut off from the microcomputer, the power supply voltage V at the output side of the regulator 5 returns to a normal value again, so that the switching transistor 30 becomes active again and resumes the supply of the power supply voltage V to the microcomputer. .

FIG. 3 is a block diagram showing a second embodiment of the present invention. In this case, a cut-off time setting unit 4 is provided between the current detection unit 2 and the switching unit 2 in FIG. 1 to keep the switching unit 3 non-conductive for a predetermined time after the detection signal S is output. .

In FIG. 3, even if the supply of the power supply voltage V is stopped immediately after the occurrence of an abnormality in the electrical component 6, it takes a certain time t seconds for the electrical component 6 to return to a normal state. In consideration of the above, the non-conduction time of the switching unit 3 is set to T seconds longer than the t seconds by the cut-off time setting unit 4. as a result,
From when the switching unit 3 is released to when it is connected again,
Since the electrical component 6 has definitely returned to the normal state, the first
The number of operations of the switching unit 3 can be reduced as compared with the case of FIG.

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

In FIG. 4, when the current in the microcomputer increases beyond the rating, the operation until the output side (point d) of the switching control inverter 23 changes to "L" is the same as that in the first embodiment. is there. However, the state of “L” on the output side (point d) of the switching control inverter 23 differs from the first embodiment,
A certain time is maintained by the time setting resistor 41 and the time setting capacitor 42. As a result, the switching transistor 30 also remains non-conductive for a certain period of time. here,
Set the resistance value of the time setting resistor 41 to R ₁ and the time setting capacitor.
42 of the capacitance when the C _1, the non-conduction time T seconds of the switching transistor 30 is expressed by T = C ₁ R _1. The non-conduction time T seconds is set slightly longer than the time required for the microcomputer to return to a normal state.

Although the non-conduction time is set using only the resistor and the capacitor here, the non-conduction time can be set using a mono-multi or the like. When this mono-multi is used in combination, the transient response time becomes faster than when only the resistor and the capacitor are used, which is practically advantageous.

〔The invention's effect〕

As described above, according to the present invention, an overcurrent protection circuit that automatically stops the supply of the power supply voltage at the same time that an excessive current occurs in an electrical component such as a microcomputer is realized. Deterioration and destruction of the element can be prevented. Further, when the electrical components return to a normal state, the power supply voltage is automatically re-supplied, so that it is not necessary to restart the power supply.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a principle configuration of the present invention, FIG. 2 is a circuit diagram showing a first embodiment of the present invention, FIG. 3 is a block diagram showing a second embodiment of the present invention, FIG. FIG. 5 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. DESCRIPTION OF SYMBOLS 1 ... Equivalent power input part, 2 ... Current detection part, 3 ... Switching part, 4 ... Shutdown time setting part, 5 ... Regulator, 6 ... Electrical components, 10 ... Equivalent input resistance, 13 ... Reference current generator, 21 ... Comparator, 30 ... Switching transistor.

Claims (1)

(57) [Claims] 1. An overcurrent protection circuit comprising a regulator (5) for supplying a power supply voltage (V) to an electric component (6), wherein the electric component (6) receives the power supply voltage (V). A power supply input section (1) equivalent to the power supply input section (7), and a current flowing through the equivalent power supply input section (1) connected to the regulator (5) to detect a predetermined current. Current detection unit (2) that outputs a detection signal (S) when it exceeds
When there is the detection signal (S), the electrical connection between the regulator (5) and the electrical component (6) is made non-conductive, and when there is no detection signal (S), the regulator (5) and the electrical component are disconnected. An overcurrent protection circuit, comprising: a switching unit (3) that conducts electricity to the product (6).