JP2002010472A - Overcurrent protection circuit and electric apparatus incorporating the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overcurrent protection circuit which maintains the safety of a product, by avoiding abnormalities caused by a current not large enough to blow out the fuse and makes the recovery possible, and an electric apparatus incorporating it. SOLUTION: This circuit has a first transistor Q1, normally kept on to supply input current from a DC power supply to a load, a resistor R1 series connected to the first transistor and the load, and a second transistor Q2 which is turned on, when the potential of the load terminal of the resistor R1 is below a prescribed potential upon detecting it. When the second transistor Q2 is on, the first transistor Q1 is turned off and the input current is turned off. Since the load terminal of the resistor R1 is kept below the prescribed potential after the input current is cut off, the first transistor Q1 is kept off.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent protection circuit and an electric device having the same.

[0002]

2. Description of the Related Art Conventionally, a fuse or the like has been used as a protection circuit for ensuring safety in electric equipment. When a fuse is used as a protection circuit, when an overcurrent flows in the electric device, the fuse is blown to cut off the current, thereby protecting the electric device.

[0003]

However, since the operating point of the fuse is at least 1.5 times the normal operating current, a current large enough for the fuse to operate (blow) even in an abnormal state is obtained. When it does not flow (for example, when a minute abnormal current flows like an open / short test)
May cause smoke or fire. Also, once the fuse is operated, it must be replaced with a new fuse for recovery.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and it is possible to prevent an abnormal state that does not occur until a fuse is blown, maintain the safety of a product, and make it possible to return to a normal state. It is an object to provide an overcurrent protection circuit and an electric device using the same.

[0005]

(1) An overcurrent protection circuit according to one aspect of the present invention is a switching element that constantly turns on and sends an input current from a DC power supply to a load. And a control circuit for detecting a current flowing through the switching element and, when the current is equal to or larger than a predetermined value, turning off the switching element and continuing the off operation. In the present invention, the switching element normally turns on to send the input current from the DC power supply side to the load side (output side). For example, when an excessive current flows due to an abnormality on the load side. The control circuit detects the state, turns off the switching element, and continues the off state, thereby cutting off the current to the load side. For this reason, it is possible to effectively avoid an abnormal state that does not reach the point at which the fuse is blown, thereby maintaining the safety of the product and enabling a resetting operation.

(2) An overcurrent protection circuit according to another aspect of the present invention includes a switching element that normally performs an ON operation and sends an input current from a DC power supply to a load, and a switching element in series with the switching element. And a control circuit that detects a potential of a terminal on the load side of the resistor or a potential related to the potential and turns off the switching element when the potential is equal to or lower than a predetermined potential. It is provided.
In the present invention, the switching element is normally turned on to send the input current from the DC power supply side to the load side, but if an excessive current flows due to an abnormality on the load side,
The voltage at both ends of the resistor increases, and the potential of the load-side terminal of the resistor (or the potential related to the potential) decreases. The control circuit detects the potential, and if the potential is equal to or lower than a predetermined potential, turns off the switching element to cut off the current to the load side. When the current to the load is cut off, the potential of the resistor becomes the ground potential (below a predetermined potential).
The off state of the switching element is also continued.

(3) An overcurrent protection circuit according to another aspect of the present invention comprises: a first transistor which normally performs an ON operation to send an input current from a DC power supply to a load side; A second transistor that is turned on when a potential of a terminal on the load side of the resistor or a potential related to the potential is equal to or lower than a predetermined potential; The first transistor is turned off by turning on the transistor. In the present invention, the first transistor constantly turns on to send the input current from the DC power supply side to the load side. However, if an excessive current flows due to an abnormality on the load side or the like, the first transistor is turned on. , The potential of the load-side terminal of the resistor (or a potential related to the potential) decreases, and when the potential drops below a predetermined potential, the second transistor is turned on.
Then, the first transistor is turned off by the on operation of the second transistor, and the current to the load side is cut off. When the current to the load side is cut off, the potential of the resistor becomes the ground potential, the ON state of the second transistor also continues, and as a result, the first transistor also keeps the OFF state.

(4) An overcurrent protection circuit according to another aspect of the present invention comprises: a first transistor which normally performs an ON operation to transmit an input current from a DC power supply to a load side; A differential amplifier that obtains and amplifies a difference between a resistor connected to a load side in series with a transistor, a potential related to a power supply voltage, and a potential on the load side of the resistor or a potential related to the potential; And a comparator for comparing the output with the reference potential, and the first transistor is turned off by the output of the comparator. In the present invention, the first transistor constantly turns on to send the input current from the DC power supply side to the load side. However, if an excessive current flows due to an abnormality on the load side or the like, the first transistor is turned on. , The potential at the load-side terminal of the resistor (or the potential related to the potential) decreases. The differential amplifier calculates and outputs the difference between the potential related to the power supply voltage and the potential of the terminal on the load side of the resistor (or the potential related to the potential), and outputs the difference. As the potential (potential related to the potential) decreases, the output of the differential amplifier> the reference potential. Then, an output corresponding to the relationship is obtained from the comparator, and the first transistor is turned off by the output of the comparator to cut off the current to the load side. Also in this case, since the current to the load side is cut off, the potential of the resistor becomes the ground potential, the output of the differential amplifier continues to be large, and as a result, the first transistor also remains off. Will do. In the present invention, the difference between the potential related to the power supply voltage and the potential of the terminal on the load side of the resistor or the potential related to the potential is determined by the differential amplifier.
By doing so, even if there is a fluctuation in the power supply voltage, the influence can be avoided.

(5) The overcurrent protection circuit according to another aspect of the present invention is the overcurrent protection circuit according to the above (4), wherein the constant voltage element, a resistor connected in series to both ends of the constant voltage element, and a variable A resistor is provided, and a connection point between the resistor and the variable resistor is output to the comparator as a reference potential. In the present invention, the voltage across the resistor and the variable resistor is defined by a constant voltage element, and the reference potential is adjusted by adjusting the variable resistor as appropriate to adjust the potential at the connection point between the resistor and the variable resistor. Can be adjusted arbitrarily.

(6) An electric device according to another aspect of the present invention has the overcurrent protection circuit of (1) to (5) built in a power supply circuit. In the present invention, when an overcurrent flows, the current is cut off by the overcurrent protection circuit as described above. Thereby, the power supply circuit is protected, and the device body is also protected.

(7) An electric device according to another aspect of the present invention has a built-in DC-AC conversion circuit in which the overcurrent protection circuit of (1) to (5) is incorporated in a DC power supply. In the present invention, when an overcurrent flows, the current is cut off by the overcurrent protection circuit as described above. Thereby, the conversion circuit main body and the load connected thereto are protected.

(8) An electric apparatus according to another aspect of the present invention has a built-in DC-DC conversion circuit incorporated in the power supply side or the output side of the above (1) to (5). In the present invention, when an overcurrent flows, the current is cut off by the overcurrent protection circuit as described above. Thereby, the conversion circuit main body and the load connected thereto are protected.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. FIG. 1 is a circuit diagram showing a configuration of an overcurrent protection circuit according to Embodiment 1 of the present invention. In this overcurrent protection circuit, a pnp transistor Q1 and a resistor R1 are connected in series between the input terminal 10 and the output terminal 12. A resistor R3 and an npn-type transistor Q4 are connected in series between the base of the transistor Q1 and the ground electrode. A resistor R2 is connected between the base of the transistor Q4 and the input terminal 10. A resistor R4 is connected to the output terminal 12 side of the resistor R1.
Is connected to the other terminal, and the other terminal of the resistor R4 is connected to the base of a pnp transistor Q2. The emitter of the transistor Q2 is the input terminal 1
0, and a resistor R5 and a resistor R6 are connected in series between the collector and the ground electrode. The capacitor C1 and np are connected to the connection point between the resistors R5 and R6.
The bases of the n-type transistors Q3 are connected to each other. The collector of the transistor Q3 is the transistor Q4
And the emitter is connected to the ground potential.

Next, the operation of the overcurrent protection circuit of FIG. 1 will be described. When the DC power is turned on and the positive potential is applied to the input terminal 10, a base current flows through the transistor Q4 via the resistor R2, and the transistor Q4 is turned on.
When the transistor Q4 is turned on, a base current flows through the transistor Q1, and the transistor Q1 is turned on. At this time, if a load is connected to the output terminal 12, the input current from the input terminal 10 flows toward the output terminal 12 via the transistor Q1 and the resistor R1. Then, at this time, the transistors Q2,
Q3 is off.

Next, when the input current exceeds a predetermined current value, the voltage across the transistor Q1 and the resistor R1 increases, and the potential of the resistor R1 on the output terminal 12 side decreases. When this potential falls below a predetermined potential, a base current flows through the transistor Q2, and the transistor Q2 is turned on. By the on operation of the transistor Q2, a voltage is applied to the base of the transistor Q3, and the transistor Q3 is turned on. The on-operation of the transistor Q3 turns off the transistor Q4, and the transistor Q1 turns off because the base current stops flowing. In this way, when the input current exceeds a predetermined current value, the transistor Q1 is turned off, and no current flows to the output terminal 12, so that the transistor Q1 and the load are protected. When the current to the load is cut off, the potential of the output terminal 12 of the resistor R1 becomes the ground potential, and the off state of the transistor Q1 is continued. To return the overcurrent protection circuit to the initial state, the DC power supply may be once turned off and then turned on again.

Embodiment 2 FIG. 2 is a circuit diagram showing a configuration of an overcurrent protection circuit according to Embodiment 2 of the present invention. This overcurrent protection circuit is characterized in that, in relation to the circuit shown in FIG. 1, an operational amplifier is used as a component for detecting an overcurrent. The operational amplifier IC1 constitutes a differential amplifier here. A resistor R4 and a resistor R10 are connected in series between a terminal on the output terminal 12 side of the resistor R1 and the output of the operational amplifier IC1, and the connection point is input to one terminal of the operational amplifier IC1. It constitutes a feedback resistor of the operational amplifier IC1. The resistors R7 and R11 are connected in series between the input terminal 10 and the ground electrode, and the potential at the connection point is input to the other terminal of the operational amplifier IC1. The resistor R8 is connected to the output of the operational amplifier IC1. The periphery of the operational amplifier IC1 is configured as described above, and the potential of the connection point between the resistors R4 and R10 (resistance R
1 potential associated with the potential of the terminal on the output terminal 12 side), and
The difference between the potential at the connection point of the resistors R7 and R11 (potential related to the power supply voltage) is amplified and output. That is, the operational amplifier I
C1 detects the potential associated with the terminal on the output terminal 12 side of the resistor R1. By determining the difference from the potential associated with the power supply voltage, even if the power supply voltage fluctuates, the effect appears on the output. I do not have it. The output of the operational amplifier IC1 is set to be smaller than a reference potential Vref described later in a normal state.

The operational amplifier IC2 forms a comparator here, and the output of the operational amplifier IC1 is input to one terminal. A resistor R9 and a Zener diode ZD1 are connected in series between the input terminal 10 and the ground electrode, and a resistor R13 is connected between the connection point and the ground electrode.
And the resistor R12 are connected in series. Then, the potential at the connection point between the resistors R13 and R12 is input to the other terminal of the operational amplifier IC2 as a reference potential. Therefore, the operational amplifier IC2 compares the reference potential Vref with the output of the operational amplifier IC1, and outputs an output to the base side of the transistor Q3 according to the magnitude of the comparison.

The structures of the transistors Q1, Q3 and Q4 and their peripheral circuits are the same as those in FIG. 1, and a description thereof will be omitted.

Next, the operation of the overcurrent protection circuit of FIG. 2 will be described. When the DC power is turned on and the positive potential is applied to the input terminal 10, a base current flows through the transistor Q4 via the resistor R2, and the transistor Q4 is turned on.
When the transistor Q4 is turned on, a base current flows through the transistor Q1, and the transistor Q1 is turned on. At this time, if a load is connected to the output terminal 12, the input current from the input terminal 10 flows toward the output terminal 12 via the transistor Q1 and the resistor R1. Then, in a normal state, since the decrease in the potential of the terminal on the output terminal 12 side of the resistor R1 is small, the output of the operational amplifier IC1 is smaller than the reference potential Vref, and the output of the operational amplifier IC2 is at the L (low) level. ,
The transistor Q3 is off.

Next, when the input current exceeds a predetermined current value, the decrease in the potential of the terminal on the output terminal 12 side of the resistor R1 increases, and the output of the operational amplifier IC1 also increases. When the output of the operational amplifier IC1 is larger than the reference potential Vref,
The output of the operational amplifier IC2 becomes H (high) level, and the transistor Q3 is supplied with a base current to turn on.
By turning on the transistor Q3, the transistor Q3 is turned on.
4 is turned off and the transistor Q1 is turned off because the base current stops flowing. Then, no current flows to the output terminal 12 side, and the transistor Q1 and the load are protected. Also in this case, since the current to the load side is cut off, the potential of the output terminal 12 side of the resistor R1 becomes the ground potential, and the off state of the transistor Q1 continues. To return this overcurrent protection circuit to the initial state,
The DC power supply may be once turned off and then turned on again.

Embodiment 3 FIG. FIGS. 3 and 4 are circuit diagrams showing another example for generating the reference potential Vref in the overcurrent protection circuit of FIG. FIG. 3 shows an example in which the resistor R12 is replaced with a variable resistor VR12. FIG. 4 shows an example in which the resistor R13 is replaced with a variable resistor VR13. In any case, the reference potential Vref can be finely adjusted.

Embodiment 4 FIG. FIG. 5 is a diagram showing a configuration of a DC-AC conversion circuit (inverter) according to Embodiment 4 of the present invention. In this inverter, an overcurrent protection circuit 22 shown in FIGS. 1 to 4 is inserted between the DC power supply 20 and the inverter unit 24. If an overcurrent flows while a load is connected to the inverter unit 24, the current flowing to the inverter unit 24 is cut off and the inverter unit 2
4 and the load are protected.

Embodiment 5 FIG. 6 is a diagram showing a configuration of a DC-DC converter according to Embodiment 5 of the present invention. In this conversion circuit, an overcurrent protection circuit 22 shown in FIGS. Also in this case, an overcurrent protection circuit 22 may be inserted between the DC power supply 20 and the inverter unit 24 as shown in FIG.

[0024]

As described above, according to the present invention, when the current of the switching element that normally turns on and sends the input current from the DC power supply to the load is equal to or larger than a predetermined value. Since the switching element is turned off and the off operation is continued to interrupt the current, it is possible to effectively avoid an abnormal state that does not occur until the fuse is blown, thereby maintaining product safety. At the same time, it is possible to return again.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a configuration of an overcurrent protection circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram illustrating a configuration of an overcurrent protection circuit according to a second embodiment of the present invention.

FIG. 3 shows a reference potential Vref in the overcurrent protection circuit of FIG. 2;
FIG. 9 is a circuit diagram showing another example (No. 1) for generating the above.

FIG. 4 shows a reference potential Vref in the overcurrent protection circuit of FIG. 2;
FIG. 10 is a circuit diagram showing another example (No. 2) for generating the above.

FIG. 5 is a diagram showing a configuration of a DC-AC conversion circuit (inverter) according to Embodiment 4 of the present invention.

FIG. 6 is a diagram illustrating a configuration of a DC-DC conversion circuit according to a fifth embodiment of the present invention.

Claims (8)

[Claims] 1. A switching element that normally turns on to send an input current from a DC power supply side to a load side, and detects a current flowing through the switching element, and detects that the current is equal to or larger than a predetermined value. A control circuit for turning off the switching element and continuing the off operation. 2. A switching element that normally turns on to send an input current from a DC power supply to a load side, a resistor connected in series with the switching element on the load side, and a load of the resistance. An overcurrent protection circuit, comprising: a control circuit that detects a potential of a terminal on the side or a potential related to the potential and turns off the switching element when the potential becomes equal to or lower than a predetermined potential. 3. A first transistor that normally turns on to send an input current from a DC power supply to a load side; a resistor connected to the load side in series with the first transistor; A second transistor that is turned on when a potential of a terminal on the load side of the resistor or a potential related to the potential is equal to or lower than a predetermined potential, and the first transistor is turned off by the on operation of the second transistor An overcurrent protection circuit. 4. A first transistor that constantly turns on and sends an input current from a DC power supply to a load side; a resistor connected in series with the first transistor to the load side; A differential amplifier that obtains and amplifies a difference between a potential related to a voltage and a potential of a terminal on the load side of the resistor or a potential related to the potential, and a comparator that compares an output of the differential amplifier with a reference potential. An overcurrent protection circuit, comprising: turning off the first transistor by an output of the comparator. 5. A constant voltage element, comprising: a resistor and a variable resistor connected in series at both ends of the constant voltage element, wherein a point of connection between the resistor and the variable resistor is output to the comparator as a reference potential. The overcurrent protection circuit according to claim 4, wherein: 6. An electric device, wherein the overcurrent protection circuit according to claim 1 is incorporated in a power supply circuit. 7. An electric device comprising a DC-AC conversion circuit in which the overcurrent protection circuit according to claim 1 is incorporated in a DC power supply. 8. An electric device comprising a DC-DC conversion circuit incorporating the overcurrent protection circuit according to claim 1 on a DC power supply side or an output side.