JPH074593Y2 - Overcurrent detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION << Industrial Application Field >> The present invention relates to an overcurrent detection circuit for detecting an overcurrent in a conductive line.

<< Prior Art >> FIG. 3 shows a conventional overcurrent detection circuit.

As shown in the figure, this overcurrent detection circuit connects a current detector for detecting a current flowing through the conductive line 1, for example, an anode of a first diode 3 to one end of a current transformer 2, One end of the first resistor 5 and the anode of the second diode 4 are connected to the cathode of the diode 3, and the second resistor 6 is connected to the cathode of the second diode 4.
Also, one end of the capacitor 7 and one input of the comparator 10 are connected, and the other input end of the comparator 10 is connected to the series connection point of the third and fourth resistors 8 and 9, and the current transformer
The other ends of the second, first, second and fourth resistors 5, 6, 9 and the capacitor 7 are connected to the ground line. A DC voltage + V with respect to the ground line is applied to one end of the third resistor 8,
The voltage divided by the third and fourth resistors 8 and 9 is the reference voltage V
It is adapted to be applied to the input terminal of the comparator 10 as ref. The output signal of this comparator 10 is
It is adapted to be taken in by the pulse width control circuit 11 arranged in the subsequent stage. The pulse width control circuit 11 constitutes a part of the power supply side circuit of the conductive line 1, and is designed to perform overcurrent protection when the comparator 10 outputs an overcurrent detection signal.

In the above configuration, the current flowing through the conductive line 1 is detected by the current transformer 2, and the output of the current transformer 2 is smoothed by the capacitor 7 after being rectified by the first and second diodes 3 and 4. And
The terminal voltage of the capacitor 7 is applied to one input terminal of the comparator 10 and compared with the reference voltage Vref determined by the voltage division ratio of the third and fourth resistors 8 and 9. In this comparison, when the terminal voltage of the capacitor 7 becomes higher than the reference voltage Vref, an overcurrent detection signal is output from the comparator 10 and this signal is prevented from being taken into the pulse width control circuit 11 and becoming an overcurrent. .

<< Problems to be Solved by the Invention >> However, according to the above-described conventional overcurrent detection circuit, it takes time to charge the capacitor 7 for the detection output of the current transformer 2 to rise from 0 volt to the reference voltage Vref or higher. Therefore, there is a problem that the reaction of the comparator 10 is delayed and the overcurrent detection speed is slow. On the other hand, it is possible to increase the overcurrent detection speed by reducing the capacitance of the capacitor 7. However, if this is done, the ripple component is applied to the input terminal of the comparator 10 due to a decrease in the smoothing capability, and overcurrent detection malfunctions. May occur.

The present invention has been made in view of the above problems, and an object thereof is to have a high overcurrent detection speed, and
Another object of the present invention is to provide an overcurrent detection circuit having excellent stability of overcurrent detection operation.

<< Means for Solving Problems >> In order to achieve the above-mentioned object, in the overcurrent detection circuit according to the present invention, a current detector for detecting a current flowing in a conductive line and a detection output of the current detector are smoothed. In the overcurrent detection circuit having a capacitor that operates and a comparator that outputs an overcurrent detection signal when the terminal voltage of the capacitor exceeds the reference voltage, always apply a voltage slightly lower than the reference voltage to the capacitor. Then, a charging circuit for charging the capacitor is provided, and the slightly lower voltage is generated by resistance voltage division of a constant voltage.

<Operation> In the present invention, since the charging circuit for charging the capacitor by constantly applying a voltage slightly lower than the reference voltage to the capacitor is provided, the terminal voltage of the capacitor is kept slightly lower than the reference voltage. . Therefore, when the detection output of the current detector rises from 0 volt to the reference voltage or more, the charging time of the capacitor becomes extremely short, and as a result, the overcurrent detection speed increases.

Further, since the electrostatic capacity of the capacitor is not reduced, the smoothing capability of the capacitor is not deteriorated, and therefore the ripple component does not cause the malfunction of the overcurrent detection.

<< Embodiment >> A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

In FIG. 1, components having the same functions as those of the conventional example are designated by the same reference numerals and detailed description thereof will be omitted.

The present embodiment differs from the conventional one in that a fifth resistor 13 is newly connected between one end of the second resistor 6 and the cathode of the second diode 4. By connecting the resistor 13, the DC voltage + V is divided by the fifth and second resistors 13 and 6, and the divided voltage is always applied to the capacitor 7. The voltage applied to the capacitor is set slightly lower than the reference voltage Vref. The charging circuit 14 of the present invention is formed by the fifth and second resistors 13 and 6.

In the above structure, the capacitor 7 is charged by the divided output of the fifth and second resistors 13 and 6, whereby the terminal voltage of the capacitor 7 is kept slightly lower than the reference voltage Vref.

FIG. 2 is a characteristic diagram for explaining the operation of the circuit of this embodiment in comparison with the conventional one.

When the detection output of the current detector, for example, the current transformer 2 is from 0 volt to the reference voltage Vref or higher, the terminal voltage of the capacitor 7 is shown in FIG. It rises above 0 volts as shown by curve 15, and it takes time t2 before it exceeds the reference voltage Vref.

On the other hand, in the circuit of this embodiment, the fifth and second resistors 13 and 6 are
The terminal voltage of the capacitor 7 becomes the reference voltage by the divided voltage output of
Since it has been charged to a voltage slightly lower than Vref (this is indicated by Vc), energy for charging the capacitor 7 is supplied from the current transformer 2 side until the detection output of the current transformer 2 reaches this voltage Vc. You don't have to.
Therefore, the terminal voltage of the capacitor 7 rises above the voltage Vc slightly lower than the reference voltage Vref as shown by the characteristic curve 16, and the time required for this to exceed the reference voltage Vref is t1. This t1 is much shorter than the conventional t2. This means that the overcurrent detection speed becomes faster than that of the conventional circuit shown in FIG.

As described above, in the circuit of the present embodiment, the detection output of the current transformer 2 is 0 by including the charging circuit 14.
Capacitor 7 when the voltage rises from the volt to the reference voltage Vref or higher
Since the charging time of is extremely shorter than that of the conventional one, the overcurrent detection speed is significantly improved. Further, since the improvement of the overcurrent detection speed is not realized by simply reducing the electrostatic capacity of the capacitor 7, the ripple component included in the detection output of the current transformer 2 is not removed by the capacitor 7. There is no inconvenience of being applied to the input terminal of the comparator 10 and causing a malfunction, and the stability is excellent. Moreover, this stability can be maintained to some extent even if the electrostatic capacity of the capacitor 7 is made slightly smaller than the conventional one. Further, when the capacitance of the capacitor 7 is made equal to that of the conventional one, there is also an advantage that variations in the pulse width in the pulse width control circuit 11 are reduced.

Although one embodiment of the present invention has been described above, it is needless to say that the present invention is not limited to the above embodiment and various modifications can be made. Further, although a current transformer is applied as the current detector in the above embodiment, a minute resistor or the like may be applied instead of this current transformer.

<< Advantages of Device >> As described above, according to the overcurrent detection circuit of the present invention, the overcurrent detection speed is high and the overcurrent detection operation excellent in stability is possible. Also, since a voltage that is slightly lower than the reference voltage is generated by resistance voltage division of a constant voltage, the charging circuit can be constructed at low cost, and by changing the value of one resistance, the above slightly lower voltage can be easily achieved. The voltage value can be adjusted.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an overcurrent detection circuit according to the present invention, FIG. 2 is a characteristic diagram for explaining the operation of this embodiment circuit in comparison with a conventional example circuit, and FIG. It is a circuit diagram which shows the conventional overcurrent detection circuit. 1 ... Conductive line, 2 ... Current detector 7 ... Capacitor, 10 ... Comparator 14 ... Charging circuit

Claims (1)

[Scope of utility model registration request] 1. A current detector for detecting a current flowing through a conductive line, a capacitor for smoothing a detection output of the current detector, and an overcurrent detection signal output when a terminal voltage of the capacitor exceeds a reference voltage. An overcurrent detection circuit having a comparator for charging the capacitor by constantly applying a voltage slightly lower than the reference voltage to the capacitor, the slightly lower voltage being a resistance component of a constant voltage. An overcurrent detection circuit characterized by being generated by pressure.