JPS6130116A - Voltage detecting circuit - Google Patents

Abstract

PURPOSE:To stabilize the operation of a voltage detecting circuit with a certain reference voltage and to detect well the state at the power on/off time by transforming temporarily the reference voltage of a reference input terminal in the direction of the change of the output voltage of a comparator when the output voltage of the comparator is changed. CONSTITUTION:An output B of a comparator 10 of the voltage detecting circuit is not only outputted through an inverter 11 but also applied to the input terminal + in a reference voltage side A of the comparator 10 through a capacitor 12. The reference voltage is applied to this input terminal + through a resistance 13, and a voltage at the power source voltage supply or berak time is applied to the input terminal -. The output B at the time when the voltage to be detected to the comparator 10 is changed from the low level or the high level to the high level or the low level is added to the reference voltage temporarily. The reference voltage is reduced or raised temporarily by this temporary application of the output B to stabilize the operation of the comparator 10, thus detecting well the state of the voltage to be detected.

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention is applicable to
The present invention relates to a voltage detection circuit for detecting whether the power supply voltage has risen above a certain reference voltage or fallen below a certain reference voltage.

(b) Conventional technology Can the internal electronic circuit be reset when the power supply voltage is on or is the reset signal/PI when the power supply voltage is off? (
In order to create a (power fail) signal, a voltage detection circuit is used that detects whether an applied voltage is higher than or equal to a specified voltage or lower than a specified voltage and creates a signal.

(c) Problems to be solved by the invention FIG. 2 is a diagram showing an example of a conventional voltage detection circuit. In the figure, 1 is a comparator, 2 is an input terminal, 3 is a reference voltage terminal, 4 is an output terminal. The voltage detection circuit shown in Figure 2 simply inputs the voltage to be detected into a comparator and compares it with the reference voltage. When the voltage to be detected is greater than the reference voltage, the output is set to "H" level. At this time, the output is set to "L" level.

This circuit has an unstable region near the reference voltage, and when the detected voltage and the reference voltage are close to each other, there is a period in which the output repeatedly turns on and off. In particular, when the input voltage changes slowly and the rise and fall times are long, this region becomes long, which is undesirable.

FIG. 3 is a diagram showing an example of waveforms of input and output voltages in the circuit of FIG. 2.

FIG. 4 shows another example of a conventional voltage detection circuit.
In order to eliminate the unstable region that occurs in the circuit shown in the figure, the output voltage of the comparator is returned to the reference input, but in the circuit configuration shown in Fig. 4, the reference level at the off time falls and becomes a different reference level from the reference level at the rise time. Therefore, there is a problem in that it cannot be turned on and off at a constant specified voltage.

FIG. 5 shows a means for solving the (d) problem of input/output voltage in the circuit of FIG. It has a detected input terminal and a reference input terminal into which a reference voltage for setting the detection level is input, and when the detected input terminal voltage is higher than the reference voltage, the output terminal becomes an "L" level voltage. , a comparator whose output terminal becomes an "H" level voltage when the voltage is small, and the output terminal and the reference input terminal are connected through a capacitor, and the change in the output voltage at the output terminal temporarily causes the reference input terminal to rise to the "H" level voltage. The present invention is characterized in that the reference voltage at the input terminal is configured to change in the direction in which the output voltage changes.

(B) Embodiment FIG. 1 is a circuit configuration diagram of an embodiment according to the present invention, in which 10 is a comparator and 11 is an inverter.

12 is a capacitor, 13 is a resistor, and 14 is an input terminal.

15 is a reference voltage terminal, and 16 is an output terminal. In the circuit of FIG. 1, the voltage to be detected is applied to the (-) input terminal of the comparator 10, and the reference voltage is applied to the (+) input terminal of the comparator 10. Therefore, when the detected voltage is greater than the reference voltage, the output of the comparator 10 becomes an "L" level voltage, and when the detected voltage is less than the reference voltage, the output of the comparator 10 becomes an "H" level voltage.

Since the output of the comparator 10 is connected to the (+) input terminal on the reference voltage side through the capacitor, when the detected voltage changes from "L" to "H", the comparator output ■ falls. , (+) input terminals are temporarily lowered, and the voltage difference between the detected voltage and the reference voltage is increased.

As a result, the operation of the comparator is stabilized, and the unstable operation at the time of the rise of the detected voltage in the conventional example time chart shown in FIG. 3 is eliminated.

Conversely, when the detected voltage changes from "H" to "L", the reference voltage at the (+) input terminal is temporarily increased due to the rise of the comparator output The voltage difference between the detection voltages is expanded. As a result, the operation of the comparator is stabilized, and the unstable operation when the detected voltage falls in the conventional time chart shown in FIG. 3 is eliminated.

Here, the change time of the reference voltage based on the change in the comparator output is determined by the time constant τ=
It is only the RC time, and returns to the original level after the time τ, making it possible to keep the reference voltage constant at the time when the detected voltage starts rising/falling.

FIG. 7 is a diagram showing an example of waveforms of input and output voltages in the embodiment shown in FIG.

(f) Effects of the Invention According to the present invention, it is possible to stably operate a voltage detection circuit with a constant reference voltage, and its practical effects are significant.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram of one embodiment according to the present invention. Figure 2 shows an example of a conventional voltage detection circuit;
The figure shows an example of input/output voltage waveforms in the circuit of Fig. 2, Fig. 4 shows another example of a conventional voltage detection circuit, and Fig. 5 shows an example of input/output voltage waveforms in the circuit of Fig. 4. FIG. 6 is a diagram showing a hysteresis characteristic in the circuit of FIG. 4, and FIG. 7 is a diagram showing an example of waveforms of input and output voltages in the embodiment shown in FIG. 1. In Figure F, 10 is a comparator, 12 is a capacitor, 1
3 is a resistor, 14 is an input terminal, and 15 is a reference voltage terminal. vt diagram 2nd bud 5th diagram

Claims (1)

[Claims] It has a detected input terminal into which the voltage to be detected is input and a reference input terminal into which the reference voltage for setting the detection level is input, and when the detected input terminal voltage is higher than the reference voltage, the output terminal has a comparator whose output terminal becomes a "L" level voltage, and when it is small, the output terminal becomes an "H" level voltage, and the output terminal and the reference input terminal are connected through a capacitor, and the change in the output voltage at the output terminal is A voltage detection circuit characterized in that the voltage detection circuit is configured to temporarily change the reference voltage of the reference input terminal in the direction of change of the output voltage.