JP2972835B2 - Instantaneous power interruption detection circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an instantaneous power interruption detection circuit, and more particularly, to a microcomputer (CPU) mounted on an electronic device, which protects a microcomputer (CPU) from runaway at the moment of an instantaneous power interruption. The present invention relates to a novel improvement for increasing the detection voltage value so as to operate even with a slight voltage drop at the moment of an instantaneous interruption, achieving high sensitivity, and enabling the microcomputer to be reliably reset.

b. Conventional technology Conventionally used as this kind of instantaneous power interruption detection circuit is a technical magazine "Transistor Technology" published in January 1984.
2 has a circuit configuration shown in FIG. 2 which is a commercially available power supply instantaneous interruption detection circuit.

That is, what is denoted by reference numeral 1 in FIG.
A comparator having a positive terminal 1a and the negative terminal 1b, The positive terminal 1a, the first resistor R ₁ of the end 3 to the other end 2 to the detection circuit for the power supply V _CC is connected is directly connected, the At one end 3, the second resistor R ₂ are connected in series, the other end 4 of the second resistor R ₂ is grounded.

One end 5 of a third resistor R ₃ is connected to the detection circuit power supply V _CC , and the other end 6 of the third resistor R ₃ is connected to the minus terminal 1 b of the comparator 1.

The minus terminal 1b is connected to a first
Capacitor C ₁ and have one ends 7, 8 of the fourth resistor R ₄ is connected with the other ends 9 and 10 are grounded, as the reference power by the first capacitor C ₁ and the fourth resistor R ₄ described above Of the parallel circuit 11.

The conventional instantaneous power interruption detection circuit is configured as described above, and its operation will be described below.

First, when a main power supply (not shown) of 100 V AC provided in the electronic device is turned on, a drive power supply of 5 V is supplied to the detection circuit power supply V _CC .

In this state, the positive terminal 1a of the comparator 1, a power supply voltage is supplied by the resistor R _1, to the negative terminal 1b is
Fourth resistor R and the reference voltage is input by _4, the power supply voltage and the reference voltage are compared. In this state, when the main power supply is momentarily interrupted and the detection circuit power supply V _CC falls below the rated voltage,
The second feedback capacitor C ₂ provided between the positive terminal 1a and the output terminal 1c of the comparator 1, once in the reset state (i.e. output or reset signal 1A of the comparator 1 becomes the L level), the first resistor R time determined by ₁ and the time constant of the second capacitor C _2, the reset state is maintained.

As a result of the experiment, the time constant of the third resistor R ₃ , the fourth resistor R ₄ and the first capacitor C ₁ indicates that the detection circuit power supply V _CC is
Until the voltage dropped to 4.1 V, the microcomputer (not shown) could not be reset.

c. Problems to be Solved by the Invention Since the conventional instantaneous power interruption detection circuit is configured as described above, the following problems exist.

That is, when the detection circuit power supply V _CC is 5 V, as described above, R ₁ is 59 KΩ, R ₃ is 22 KΩ, R ₄ is 33 KΩ, and C ₁ is 1.5 μM.
Since F, C ₂ are set in 1.5MyuF, as the measured value, as shown in FIG. 4, when not lowered to 4.1V, it is not possible to reset the microcomputer, the 4.1V
In the case of the instantaneous interruption described above, the microcomputer may run away without resetting. So, for example,
When the power supply is momentarily interrupted as in a helicopter, a control microcomputer mounted on an important device runs away and may become uncontrollable thereafter.

In addition, it is possible to raise the reset operation point by increasing the values of C ₁ , R ₃ , and R ₄ described above. However, due to various problems such as an increase in the size of each component and the input impedance of the comparator, the limit can be increased. was there.

The present invention has been made in order to solve the above problems, and in particular, protects a microcomputer (CPU) mounted on an electronic device from runaway at the moment of a power interruption,
It is an object of the present invention to provide an instantaneous power interruption detection circuit which increases a detection voltage value so as to operate even when a slight voltage drop occurs during an instantaneous power interruption and has high sensitivity so that a microcomputer can be reliably reset. .

d. Means for Solving the Problems A power supply instantaneous power failure detection circuit according to the present invention is a power supply instantaneous power failure detection circuit configured to output a reset signal from an output terminal by an input connected to a positive terminal and a negative terminal of a comparator. the first resistor R ₁ having one end connected to the positive terminal, the a first resistor R ₁ of the other end connected to the detection circuit for the power supply V _CC, one end of said first resistor R ₁ end a second resistor R ₂ connected to the other end is grounded, a third resistor R ₃ to the other end one end connected to a power supply V _CC for the detection circuit is connected to the negative terminal, the negative terminal a parallel circuit of the first capacitor C ₁ and the fourth resistor R ₄ consists of the configuration and the other ends each having one end connected of which is grounded, the second connected between the positive terminal of the comparator and the output terminal
A capacitor, a third connected in parallel with the first resistor R ₁
A configuration in which a capacitor C _3.

e. Operation In the instantaneous power interruption detection circuit according to the present invention,
The capacitor C _3, because it holds the first voltage across the resistor R _1, becomes higher than the conventional configuration without the detected voltage of the comparator of the third capacitor C _3, the as shown in FIG. 3 Compared to the conventional 4.1V in Fig. 4, the microcomputer is reset at 4.85V.

Therefore, when the main power supply is momentarily interrupted, a reset signal is generated when the voltage drops only 0.15V from the rated power supply 5V, and the microcomputer is reset. Runaway can be prevented.

f. Embodiment Hereinafter, a preferred embodiment of the instantaneous power interruption detection circuit according to the present invention will be described in detail with reference to the drawings.

The same or equivalent parts as those in the conventional example will be described using the same reference numerals.

FIGS. 1, 3, and 5 are a circuit diagram and an operation characteristic diagram showing a power supply instantaneous interruption detection circuit according to the present invention.

In FIG. 1, reference numeral 1 denotes a comparator having a plus terminal 1a and a minus terminal 1b,
The other end 2 of the positive terminal 1a has a power supply V for a detection circuit.
_CC is connected at one end 3 is a direct first resistor R ₁ connected to the one end 3 is connected to the second resistor R ₂ directly, the other end 4 of the second resistor R ₂ is grounded I have.

One end 5 of a third resistor R ₃ is connected to the detection circuit power supply V _CC , and the other end 6 of the third resistor R ₃ is connected to the minus terminal 1 b of the comparator 1.

The minus terminal 1b is connected to a first
Capacitor C ₁ and have one ends 7, 8 of the fourth resistor R ₄ is connected with the other ends 9 and 10 are grounded, as the reference power by the first capacitor C ₁ and the fourth resistor R ₄ described above Of the parallel circuit 11.

Furthermore, said between positive terminal 1a and the output terminal 1c, together with the second capacitor C ₂ for feedback are provided, between both ends 2 and 3 of the first resistor R _1, the third capacitor C
₃ are connected in parallel.

The instantaneous power interruption detection circuit according to the present invention is configured as described above, and its operation will be described below.

First, when a main power supply (not shown) of AC100V provided in the electronic device is turned on, a driving power supply of 5V which is stepped down in advance is supplied to the detection circuit power supply _VCC .

In this state, the positive terminal 1a of the comparator 1, a power supply voltage is supplied by the resistor R _1, to the negative terminal 1b is
Fourth resistor R and the reference voltage is input by _4, the power supply voltage and the reference voltage are compared.

In this state, when the main power supply is momentarily interrupted and the detection circuit power supply V _CC falls below the rated voltage, the voltage across the first resistor R ₁ becomes the third voltage.
Because it is held by the capacitor C _3, the operating point of the comparator 1 (i.e. detection voltage value reset is)
(That is, the same effect as increasing C ₁ , R ₃ , and R ₄ occurs).

That is, as shown in FIG. 5, when the power supply V _CC is momentarily interrupted and the voltage drops, the state of the drop is as shown in FIG. 5 (3) in the conventional state without the third capacitor C ₃ . (B)
Although the voltage at the point is proportional to the drop of the power supply V _CC , since the voltage across the first resistor R ₁ is maintained by the presence of the third capacitor C ₃ as in the present invention, the drop of the power supply voltage V _CC there it first voltage at one end 3 of the resistor R _1, ie becomes a voltage drop of the positive terminal 1a of the comparator 1, drop of voltage of the third positive terminal 1a of the comparator) from the conventional case where the capacitor C ₃ is absent Becomes larger, and as a result, the comparator 1 operates only by a slight drop in the power supply voltage V _CC , and the voltage at the point (B) in FIG.
As shown in (4), the descending speed becomes faster than in the state of (3), and as a result, the detected voltage value of the comparator 1 becomes higher than in the prior art. Therefore, as shown in (5) and (6) of FIG. 5, the timing at which the output 1A from the comparator 1 changes from “H” to “L” level and the reset signal 1A is output is earlier than in the related art.

According to the results of the experiment, in the circuit configuration having the same time constant as that of FIG. 2, as shown in FIG. 3, the comparator 1 operates and resets when the voltage drops to about 4.85 V, which is higher than the conventional voltage. To prevent runaway when the computer voltage drops.

g. Effects of the Invention Since the instantaneous power interruption detection circuit according to the present invention is configured as described above, the following effects can be obtained.

That is, by the third capacitor provided in the first resistor,
By holding the voltage across the first resistor, the comparator outputs a reset signal, so that the detected voltage value of the comparator becomes higher than when there is no third capacitor. Reset can be performed, and malfunctions of electronic devices due to runaway of the microcomputer and accidents such as helicopters can be prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an instantaneous power interruption detecting circuit according to the present invention, FIG. 2 is a circuit diagram showing a conventional configuration, FIG. 3 is a characteristic diagram showing an instantaneous power interruption state in the present invention, and FIG. FIG. 5 is a characteristic diagram showing the instantaneous power interruption state according to the configuration. FIG. 1 is a comparator, 1a is a plus terminal, 1b is a minus terminal, R ₁ is a first resistor, V _CC is a power supply for a detection circuit, R ₂ is a second resistor, R ₃ is a third resistor, C ₁ is a first capacitor, R ₄ represents a fourth resistor, C ₂ is the second capacitor, C ₃ third capacitor, 11 is a parallel circuit.

Claims (1)

(57) [Claims] 1. An instantaneous power interruption detection circuit for outputting a reset signal (1A) from an output terminal (1c) by an input connected to a plus terminal (1a) and a minus terminal (1b) of a comparator (1). , A first resistor having one end connected to the positive terminal (1a).
R ₁ and, wherein a first resistor R ₁ of the detection circuit for the power supply V _CC connected to the other end, a second resistor R ₂ to the other end one end connected to the first end of the resistor R ₁ is grounded And one end thereof is connected to the detection circuit power supply V _CC and the other end thereof is the minus terminal (1).
a third resistor R ₃ connected to b), the negative terminal (1
b) A parallel circuit of the first capacitor C ₁ and the fourth resistor R ₄ (11) having one end connected to each other and the other end grounded
When the comparator (1) the positive terminal of the (1a) and a second capacitor connected between the output terminal (1c) (C _2), third capacitor C ₃ connected in parallel with the first resistor R ₁ And an instantaneous power interruption detection circuit.