JP3171383B2 - Protection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling various electronic circuits that require power supply when an electrical abnormality occurs.
The present invention relates to a protection circuit for shutting off a power supply and protecting an entire electronic circuit.

[0002]

2. Description of the Related Art When an abnormality occurs in an electronic circuit, for example, when an output terminal of a power supply circuit is short-circuited for some reason, an excessive current flows through the power supply circuit and seriously damages circuit components. Sometimes. One of the measures is to increase the reliability of the electronic circuit. Therefore, a test (open / short test) is performed in which the electronic circuit is operated at the allowable power and the terminal of each component used therein is opened or short-circuited to check whether abnormalities such as smoke, heat generation, and ignition occur. ) Is done. However, since this open / short test must be performed for a period comparable to the actual use time, it takes enormous time, man-hours and costs to evaluate the good and bad of the electronic circuit and to properly design the circuit, and the cost is high. It is currently forced to rise.

Another measure to be taken when an abnormality occurs in an electronic circuit is to insert a fuse into the input side of the electronic circuit, melt the fuse by an excessive current, and cut off the supply of power to the electronic circuit. However, the fuse has the inconvenience that once it is blown, the electronic circuit cannot be restarted without replacing it with a new fuse. Also, since the capacity of the fuse is determined by calculating backward from the allowable power of the electronic circuit, in the case of a single-input / multi-output type electronic circuit, if the output powers are significantly different (for example, three output powers of 1 W, 1
If the fuse capacity is adjusted to the minimum output power, the fuse may be blown by a current flowing through a circuit having a large output power. Conversely, the fuse capacity may be reduced to the maximum output power. According to the above, when an abnormality occurs in a small output power, the fuse does not melt, which may damage the circuit, generate heat, smoke, or ignite, so that it is extremely difficult to select a fuse.

Japanese Patent Application Laid-Open No. 63-274363 discloses that when a short circuit occurs between the output terminals of a step-up type switching power supply circuit, the switching operation of the power supply circuit is stopped and a protection circuit provided on the input side thereof. A short-circuit protection circuit that turns off a transistor to cut off power supply to a switching power supply circuit is disclosed.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and when one of an input voltage and an output voltage of an electronic circuit deviates from a set value, an electronic circuit is reliably provided. It is an object of the present invention to provide a protection circuit which protects a circuit, is easy to restart, and has a simple configuration.

[0006]

In order to achieve this object, according to the present invention, a cut-off circuit including a switch element such as an FET in place of a fuse is provided on the input side of the circuit to detect an abnormality in output voltage. A circuit is provided on each output side, and when either the input voltage or the output voltage deviates from the set value, the switch element is opened to cut off the supply of power to the circuit.

In order to realize this, the present invention uses FIG.
A circuit for protecting an electronic circuit, comprising: a cut-off circuit provided between a power supply input terminal to which a power supply voltage is supplied and an input terminal of the electronic circuit; A start-up circuit for applying the power supply voltage to the electronic circuit by bringing the shut-off circuit into a conductive state only for a predetermined period when the output voltage exceeds the predetermined period, and when the output voltage of the electronic circuit reaches a set value within the predetermined period. Thereafter, when the output voltage of the electronic circuit is an abnormal value, the shut-off circuit is kept in a conductive state, and when the output voltage of the electronic circuit is an abnormal value, the shut-off circuit is turned off to cut off between the power input terminal and the electronic circuit. And a protection circuit characterized by comprising:

The starting circuit is configured to operate the time constant circuit for setting the predetermined period and the time constant circuit when the power supply voltage exceeds the reference voltage so that the cutoff circuit is turned on for the predetermined period. And an output of the time constant circuit and an output of the abnormality detection circuit are connected to an input of the cutoff circuit.

The circuit section includes a comparison circuit for comparing the power supply voltage with the reference voltage, and a first transistor which is controlled to be conductive or non-conductive by an output of the comparison circuit and is connected to the time constant circuit. Wherein the interrupting circuit comprises: a second transistor connected between the power input terminal and the electronic circuit; and a control transistor for controlling conduction and non-conduction of the second transistor, wherein the time constant An output of a circuit and an output of the abnormality detection circuit are connected to the control transistor. Preferably, the first transistor and the control transistor are connected by a low-pass filter for preventing chattering.

The electronic circuit is preferably a DC / DC converter circuit of at least one of a step-up type, a step-down type, a step-up / step-down type, and an inverting type. In addition, the DC / D
It is desirable that the C converter circuit has a timer latch function, so that when the output voltage of the DC / DC converter circuit becomes an abnormal value, the operation of the DC / DC converter circuit is stopped.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 schematically shows a configuration of one embodiment of a protection circuit according to the present invention, and is an example in which the present invention is applied to a step-up DC / DC converter circuit. That is, the circuit to be protected is a step-up DC /
There is a DC converter circuit. Since the step-up DC / DC converter circuit 10 is well known and is not the gist of the present invention, a detailed description of the configuration is omitted here.
Only the operation will be briefly described. When the switching transistor Q1 is turned on by the output of the timer latch type control circuit 11, an input voltage is applied to the coil L1 and energy is accumulated. Next, the control circuit 1
1, when the switching transistor Q1 is turned off, the diode D1 is turned on, and the input voltage and the coil L
The voltage summed with the discharge voltage of 1 charges the capacitor C1. This voltage is output from the output terminal Tout to the output voltage Vout.
Is output as On the other hand, the output voltage Vout is equal to the resistance R
1, a voltage which is divided by R2 and is proportional to the output voltage Vout is supplied to the control circuit 11. The control circuit 11
The ratio between the ON period and the OFF period of the switching transistor Q1 is changed in accordance with the fluctuation of the output voltage Vout, thereby keeping the output voltage Vout constant.

In the present invention, the input terminal Ta of the DC / DC converter circuit 10 is connected to the power input terminal Tin via the cutoff circuit 2. Specifically, the input terminal Ta of the DC / DC converter circuit 10 is connected to the drain electrode of the transistor Q2 of the cutoff circuit 2, and the power supply input terminal T
in is connected to the source electrode of the transistor Q2. The gate electrode of transistor Q2 is connected to the collector of NPN transistor Q3, and the emitter of transistor Q3 is grounded.

In the present invention, the power input terminal Tin
Is also connected to the starting circuit 3. That is, the power input terminal Tin
Input voltage Vin is connected in series with resistors R3 and R3.
4 and the voltage between both ends of the resistor R4 is applied to the inverting input of the comparison circuit 5. The reference voltage Vref is applied to the non-inverting input of the comparison circuit 5. The output of comparison circuit 5 is connected to the gate electrode of transistor Q4. The drain electrode of the transistor Q4 is connected to the power input terminal Tin via the resistor R5.
6 is grounded through a series circuit. The resistors R5 and R6 and the capacitor C2 constitute a time constant circuit. The connection point between the capacitor C2 and the resistor R6 is connected to the base electrode of the transistor Q3 via the resistor R7.

Further, the output terminal Tout of the DC / DC converter circuit 10 is connected to the base electrode of the transistor Q3 via the abnormality detection circuit 4. The abnormality detection circuit 4 is a circuit in which a Zener diode D2 and a resistor R8 are connected in series. When the power supply circuit that supplies the power supply input terminal Tin is a circuit having a small capacity of the input voltage (therefore, the current value is small and the output impedance is large), the cutoff circuit 2
Chattering (oscillation) may occur between the starting circuit 3 and the starting circuit 3. In order to prevent this, it is preferable to insert a low-pass filter including the resistor R7 and the capacitor C3 between the connection point between the capacitor C2 and the resistor R6 and the base electrode of the transistor Q3.

FIG. 3A shows the input voltage Vi in FIG.
3 (b) and 3 (c) show the operating state of the transistors Q2 and Q4, respectively.
FIG. 3D is a graph showing a temporal change of the input voltage Va of the DC / DC converter circuit 10 (that is, the voltage on the input side of the coil L1).

The operation of the circuit shown in FIG. 2 will be described below with reference to FIG. When a power switch (not shown) is turned on, a power voltage is supplied to the power input terminal Tin, and the input voltage Vin gradually rises. When the input voltage Vin exceeds the reference voltage Vref, the output of the comparison circuit 5 goes low, and the transistor Q4 is turned off. As a result, the capacitor C2 is charged, and the resistance R5
Since the transistor Q3 is turned on for a period corresponding to the time constant determined by the capacitor C2 and the capacitor C2, the transistor Q2 of the cutoff circuit 2 is also turned on. While the transistors Q3 and Q2 are conducting, the power input terminal Tin
The power supply voltage supplied to the DC / DC converter circuit 10
Supplied to When the output voltage Vout of the DC / DC converter circuit 10 reaches the set value within this period, the abnormality detection circuit 4 keeps the transistor Q3 conductive and keeps the transistor Q2 constantly conductive.

During operation of the DC / DC converter circuit 10,
When an abnormality occurs for some reason and the output voltage Vout greatly exceeds or falls below the set value, the timer latch type control circuit 11 stops generating a drive pulse for driving the switching transistor Q1. Therefore, the output voltage Vout becomes smaller than the set value, and the abnormality detection circuit 4 detects this, and turns off the transistor Q3. As a result, the transistor Q2 is also turned off, so that the power supply to the DC / DC converter circuit 10 is stopped.

When the power supply voltage supplied to the power supply input terminal Tin becomes lower than the reference voltage Vref during the operation of the DC / DC converter circuit 10, the transistor Q4 is turned on, so that the transistor Q3 is turned off. Therefore, transistor Q2 is also turned off, and supply of the power supply voltage to DC / DC converter circuit 10 is stopped.

Thereafter, when the abnormality of the DC / DC converter circuit 10 is repaired, the shut-off circuit 2 is returned to the conductive state by the starting circuit 3 and is supplied to the DC / DC converter circuit 10 via the cut-off circuit 2 in the conductive state. The power supply voltage is supplied.

When the open / short test is performed on the DC / DC converter circuit 10, for example, when the drain electrode and the gate electrode of the switching transistor Q1 are short-circuited, the control circuit 11 performs a timer latch operation to switch the switching transistor Q1. Although the generation of the drive pulse is stopped, a current flows through the coil L1 due to the on-resistance of the switching transistor Q1 because the drain electrode and the gate electrode of the switching transistor Q1 are short-circuited. Therefore, if the DC / DC converter circuit 10 is to be protected by a fuse as in the related art, even if the current flowing through the fuse changes due to a short circuit between the drain electrode and the gate electrode of the switching transistor Q1, the fuse is not melted and the switching is not performed. The transistor Q1 and the coil L1 may burn or burn. To prevent this, conventionally, a coil having a small internal resistance or a switching transistor having a small on-resistance has been selected, or the capacity of the fuse has been reduced. However, in the case of a multi-output type DC / DC converter circuit,
As described above, it is extremely difficult to select a fuse.

On the other hand, in the embodiment shown in FIG. 2, when the control circuit 11 performs a timer latch operation, the power supply and the DC / DC converter circuit 10 are automatically cut off. Can be solved, and the DC / DC converter circuit 10 can be reliably protected when an abnormality occurs.

In the embodiment shown in FIG. 2,
The starting circuit 3 switches the operation state of the transistor Q4 by the output of the comparison circuit 5 that compares the power supply voltage with the reference voltage. Instead, the reference voltage, the comparator, and the open-drain FET are integrated into one chip. A commercially available reset IC may be used.

Until now, the protected circuit 1 has been a boost type DC /
Although the embodiment which is a DC converter circuit has been described, the circuit protected by the present invention is not limited to this, and includes a power supply circuit such as a step-down or step-up / step-down DC / DC converter circuit and an inverting circuit. , Any electronic circuit to which power is supplied. Note that FIG. 4 illustrates an example of a configuration of the inverting circuit. A transistor Q5 and a diode D3 are connected in series between a power input terminal Tin to which an input voltage Vin is applied and a power output terminal Tout from which an output voltage Vout is obtained, and a cathode of the diode D3 is grounded via a coil L2; The anode of the diode D2 is grounded via the capacitor 4. A switching pulse is applied to the gate electrode of the transistor Q5.

[0024]

As apparent from the detailed description of the present invention with reference to some embodiments, the present invention eliminates the necessity of the conventional open / short test, so that the design and evaluation of an electronic circuit are possible. Can be greatly reduced. In addition, the present invention is not limited to a single-input / single-output electronic circuit, and even if a single-input / multi-output electronic circuit is used, when an abnormality occurs in the circuit, the electronic circuit can be reliably disconnected from a power supply. As a result, there is a special effect of improving reliability without damaging electronic circuit components in the event of an abnormality.

Moreover, enormous time and cost for selecting an optimum fuse can be eliminated, and the degree of freedom in circuit design can be increased accordingly. Further, since no fuse is used, it is not necessary to replace the fuse, and it is not necessary to store the fuse.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically illustrating the configuration of the present invention.

FIG. 2 is a circuit diagram showing one embodiment of a protection circuit according to the present invention.

FIG. 3 is a diagram for explaining an operation of the protection circuit of FIG. 2;

FIG. 4 is a diagram illustrating an example of an inversion circuit.

[Explanation of symbols]

1: electronic circuit, 2: shutoff circuit, 3: start circuit,
4: Abnormality detection circuit, Tin: power supply input terminal, Tou
t: output terminal

Claims (6)

(57) [Claims] 1. A circuit for protecting an electronic circuit, comprising: a cut-off circuit provided between a power supply input terminal to which a power supply voltage is supplied and an input terminal of the electronic circuit; A starter circuit for applying the power supply voltage to the electronic circuit by bringing the cutoff circuit into a conductive state for a predetermined period when the output voltage of the electronic circuit has reached a set value within the predetermined period. Thereafter, when the output voltage of the electronic circuit is an abnormal value, the shut-off circuit is kept in a conductive state, and when the output voltage of the electronic circuit is an abnormal value, the shut-off circuit is turned off to cut off between the power input terminal and the electronic circuit. And a protection circuit comprising: 2. The protection circuit according to claim 1, wherein said activation circuit includes a time constant circuit for setting said predetermined period, and said time constant circuit when said power supply voltage exceeds said reference voltage. And a circuit unit that operates to make the cutoff circuit conductive only for the predetermined period, wherein an output of the time constant circuit and an output of the abnormality detection circuit are connected to an input of the cutoff circuit. Protection circuit. 3. The protection circuit according to claim 2, wherein the circuit section is configured to compare the power supply voltage with the reference voltage, and that conduction and non-conduction are controlled by an output of the comparison circuit, and A first transistor connected to a time constant circuit, wherein the cutoff circuit includes a second transistor connected between the power input terminal and the electronic circuit, and a conduction / non-conduction state of the second transistor. A protection circuit, comprising: a control transistor for controlling conduction, wherein an output of the time constant circuit and an output of the abnormality detection circuit are connected to the control transistor. 4. The protection circuit according to claim 1, wherein the electronic circuit is at least one of a boost type, a step-down type, a step-up / step-down type, and an inverting type.
A protection circuit, which is a converter circuit. 5. The protection circuit according to claim 4, wherein the DC / DC converter circuit has a timer latch function, whereby an output voltage of the DC / DC converter circuit becomes an abnormal value. A protection circuit for stopping the operation of the DC / DC converter circuit. 6. The protection circuit according to claim 3, wherein the first transistor and the control transistor are connected by a low-pass filter for preventing chattering. And protection circuit.