JPS63184075A - Overcurrent detecting circuit - Google Patents

Abstract

PURPOSE:To enable a high speed operation to be performed and overcurrent with a short time span to be detected by producing output signal from a logic element in response to a time when a voltage developed across a resistor by the overcurrent exceeds the threshold voltage of the resistor. CONSTITUTION:A circuit is composed of a resistor R1 for generating a voltage by current 1, a capacitor C1 whose one terminal is connected to the terminal of the resistor R1 wherein higher electric potential is generated, resistors R2 and R3 for supplying the other terminal of the capacitor C1 with a voltage at an arbitrary potential dividing ratio and a logic element 3 whose terminal is connected to the junction of the resistors R2 and R3 and which produces output signal in response to a time when a voltage generated by overcurrent in the resistor R1 exceeds its threshold voltage. By setting the resistance values of the resistors R1, R2 and R3 such that the voltage of the junction of the resistors R2 and R3 exceeds the threshold voltage of the logic element 3 by a prescribed detection current, logic signal is produced and the overcurrent can be detected when a current larger than the prescribed current flows in the resistor R1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an overcurrent detection circuit that protects a circuit by detecting an overcurrent, particularly a short pulse-like current that flows instantaneously.

[Background Art] Fig. 4 shows a conventional example of this type, in which a temporally short pulse-like current ■ flows through the resistor R4, and the terminal ■
A short pulse-like voltage generated at is transmitted to terminal ■ through diode D1, and when that voltage exceeds the reference voltage of comparator 6, the signal at terminal ■ is inverted and it is determined whether the current flowing through resistor R4 is higher than an arbitrary reference. It detects whether In this way, in an overcurrent detection circuit that uses a comparator in the comparison circuit, as the width of the pulse-like voltage generated across resistor R4 becomes shorter, the configuration of the comparator that responds quickly to it and generates the signal becomes more complex and difficult. It's coming. Therefore, as shown in Figure 4, capacitor C8
is connected to terminal ■, and the temporally short pulse-like voltage generated across resistor R4 is stored as a charge in capacitor Cg, and is generated at terminal ■ within the discharge time determined by the time constant of resistor R5 and capacitor C3. It was necessary to supplement the performance of the comparator, which cannot respond.

[Object of the Invention] The present invention has been made in view of the above points, and an object of the present invention is to provide an overcurrent detection circuit that can respond even to a temporally short pulsed current.

[Disclosure of the Invention] Fig. 1 shows the configuration of the present invention, in which a first resistor R generates a voltage by a current ■, and one terminal is connected to the terminal ■ on the side of the resistor R1 that generates a high potential. A connection point between the connected capacitor C1, second and third resistors R1+R3 for supplying voltage to the other terminal of the capacitor C1 according to an arbitrary voltage division ratio, and the second and third resistors Rg and Rs. (2) has an input terminal connected to the logic element 3, which generates an output signal in response when the voltage generated across the first resistor R2 due to an overcurrent exceeds its threshold voltage.

Here, the voltage V at terminal 2 is normally Vt -Rs Vcc/CRt +R,), where VCC is the voltage A. This voltage 2 is set to a value below the threshold voltage of logic element 3. has been done. At this time, an instantaneous current I flows through the first resistor R1.
flows, a pulse-like voltage Vg=I is applied to terminal ■.
R+ is generated, and as a result, the voltage V2' at terminal ■ is Vz'-Rs Vcc/(Rx +Rs) + I
It becomes R1. This voltage v! ' is the threshold voltage V of logic element 3
When the voltage exceeds TH, the logic element 3 generates a logic signal from the terminal ■. In this way, depending on the predetermined detection current, the voltage at terminal ■ is y, and l is the threshold voltage of logic element 3, V? The first, second, and third resistors R+, Rx, Rs
By setting the value of , it is possible to generate a logic signal and detect an overcurrent when a current equal to or greater than a predetermined current value flows through the first resistor R1.

The logic element has a simpler configuration than a comparator, which is an analog circuit, and can easily operate at high speed, so that it is possible to detect overcurrent at a higher speed than in the conventional example.

2 and 3 show embodiments of the present invention; FIG. 2 shows the case where an inverter is used as the logic element 3, and FIG. 3 shows the case where a Schmitt trigger inverter is used. In the embodiment shown in , when the threshold voltage of the inverter 3 is Vt, the voltage v2 of the terminal (2) is set to Vt -R3Vcc/(Rz +R3)<Vt, and the output of the terminal (2) is at a high level.

Due to overcurrent I ■2°=Ri Vcc/(Rs +R,)+IRI
When ≧■7, the output signal is inverted to low level and overcurrent can be detected. Further, in the embodiment shown in FIG. 3, if the higher threshold voltage of the Schmitt trigger inverter 3 is V and the 71% lower threshold voltage is VtL, then the voltage of the normal terminal (■) is Vt -R3Vcc/ (R weight +Rs)
<Vtt, and due to overcurrent I, Vg'-Rs Vcc/(Rt +R3) + IRI
Except that ≧Vy* and an inverted output signal is generated,
Although it is similar to the embodiment described above, a sharp change in the output signal can be obtained by the Schmitt trigger inverter 3. [Effects of the Invention] As described above, the present invention provides a first
a resistor, a capacitor having one terminal connected to the terminal of the resistor that produces a high potential, and a second capacitor for supplying a voltage to the other terminal of the capacitor at an arbitrary voltage division ratio. and a third resistor, and an input terminal is connected to the connection point of the second and third resistors, and an output signal is generated by responding when the voltage generated in the first resistor due to an overcurrent exceeds its threshold voltage. It consists of a logic element that generates
Compared to conventional overcurrent detection circuits that use analog circuit comparators, high-speed operation is easily possible, and overcurrent detection with a short time width can be realized.Also, the logic elements have a smaller configuration than analog circuit comparators. Because of its simplicity, it is particularly effective when formed inside an integrated circuit.

[Brief Description of the Drawings] Figure 1 is a circuit diagram showing the basic configuration of the present invention, Figures 2 and 3 are circuit diagrams each showing an embodiment of the present invention, and Figure 4 is a circuit diagram of a conventional example. be. R1...first resistance, R2...second resistance, R3...
...Third resistor, C8... Capacitor, 3... Logic element. Figure 1 Vcc Vcc Figure 3 Figure 4 Voltage

Claims (1)

[Claims] (1) A first resistor that generates a voltage through current, a capacitor whose one terminal is connected to the terminal on the side that generates a high potential of the resistor, and a voltage that is applied to the other terminal of the capacitor using an arbitrary voltage division ratio. An input terminal is connected to a connection point between the second and third resistors for supplying the voltage and the second and third resistors, and when the voltage generated in the first resistor due to an overcurrent exceeds its threshold voltage. An overcurrent detection circuit consisting of a logic element that generates an output signal in response.