JPH04341006A - Power-on reset circuit - Google Patents

Abstract

PURPOSE:To surely implement power-on reset without malfunction due to the effect of other signal. CONSTITUTION:The circuit is provided with a fixed resistor 13 whose one terminal is connected to a power supply line 11 receiving power only at power-on reset and whose other terminal is connected to an output terminal 12 connecting to a reset terminal of the element to be reset, a diode 14 connected in parallel with the fixed resistor 13 to block a reverse current, a capacitor 15 whose one terminal connects to the output terminal 12 and whose other terminal connects to ground, and a variable resistor 21 whose one terminal connects similarly to the output terminal 12 and whose other terminal connects to ground. The fixed resistor 13 and the variable resistor 21 form a voltage division circuit to the output terminal 12, and the variable resistor 21 is adjusted to give a potential of the output terminal 12 so that it does not exceed a threshold level except at resetting.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power-on reset circuit that is connected to a power-on reset terminal of an element such as an IC (integrated circuit) and performs reset upon power-on.

0002

2. Description of the Related Art FIG. 2 shows a conventionally used power-on reset circuit. This circuit 10 has one end connected to a +5V (volt) power supply line 11 that is energized only at the time of power-on reset, and the other end connected to an output terminal 12.
A fixed resistor 13 connected to the fixed resistor 13, a reverse current blocking diode 14 connected in parallel with the fixed resistor 13, and a capacitor 15 connected at one end to the output terminal and grounded at the other end. ing.

In this conventional power-on reset circuit, a fixed resistor 13 and a capacitor 15 constitute a differential circuit. The diode 14 serves to prevent the charge stored in the capacitor 15 of this differential circuit from returning to the power supply line 11 side. Therefore, this power-on reset circuit 10
When the power is turned on to the unit in which the
A reset pulse is output from 2. This reset pulse is input to a reset terminal (not shown) of an IC (not shown) or the like to reset it.

0004

By the way, such a power-on reset circuit 10 may receive signals from other units even before the power is turned on to the unit including the power-on reset circuit 10. As a result, there have been cases in which the potential appearing at the output terminal 12 has already exceeded the threshold level of the IC or the like before the unit is powered on. In this case, the IC
There was a problem in that the unit remained reset and the unit did not operate properly.

SUMMARY OF THE INVENTION An object of the present invention is to provide a power-on reset circuit that can reliably perform a power-on reset without malfunctioning due to the influence of other signals.

[0006]

[Means for Solving the Problems] In the present invention, (a) one end is connected to a power supply supplied only at power-on reset, and the other end is connected to an output terminal connected to a reset terminal of an element to be reset; a resistor, (b) a diode connected in parallel with this fixed resistor to block reverse current, (c) a capacitor whose one end is connected to the aforementioned output terminal and whose other end is grounded, and (d) the aforementioned The power-on reset circuit is provided with a variable resistor having one end connected to the same output terminal and the other end grounded.

That is, in the power-on reset circuit of the present invention, a voltage dividing circuit is configured by a fixed resistor and a variable resistor, and a voltage dividing point is connected to an output terminal. Therefore, by appropriately adjusting the resistance value of the variable resistor, it is possible to set the resistance value to be below the threshold level of an IC or the like except at the time of reset, and malfunction can be prevented.

[0008]

EXAMPLES The present invention will be explained in detail with reference to Examples below.

FIG. 1 shows the configuration of a power-on reset circuit in one embodiment of the present invention. This circuit 20 is energized only at power-on reset.
A fixed resistor 13 whose one end is connected to a V (volt) power supply line 11 and whose other end is connected to an output terminal 12, a diode 14 for blocking reverse current connected in parallel with this fixed resistor 13, and an output terminal. 12, and a variable resistor 21, which has one end connected to the output terminal 12 and the other end grounded.

In this power-on reset circuit 20 as well, the fixed resistor 13 and capacitor 15 constitute a differentiating circuit with a predetermined time constant. The diode 14 serves to prevent the charge stored in the capacitor 15 of this differential circuit from returning to the power supply line 11 side. In the power-on reset circuit 20 of this embodiment, the fixed resistor 13 and the newly provided variable resistor 21 constitute a voltage dividing circuit. The potential at the voltage dividing point of this voltage dividing circuit is the potential at the output terminal 12. Therefore, by appropriately adjusting the value of the variable resistor 21, the voltage level appearing on the output terminal 12 side can be changed.

[0011] That is, by adjusting the value of the variable resistor 21, even if a signal from another unit is routed to the power supply of this power-on reset circuit 20, the power-on reset circuit will operate before and after the power-on reset circuit 20 operates. The output terminal 12 can be adjusted so as not to exceed a threshold level.

0012

[Effects of the Invention] As explained above, in the present invention, malfunction of the circuit due to signals from other units can be prevented with a simple configuration of connecting a variable resistor to a conventional circuit.
This has the effect that power-on reset can be performed reliably.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a power-on reset circuit in one embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional power-on reset circuit.

[Explanation of symbols]

11 Power line 12 Output terminal 13 Fixed resistance 14 Diode 15 Capacitor 20 Power-on reset circuit 21 Variable resistance

Claims (1)

[Claims] 1. A fixed resistor having one end connected to a power supply that is supplied only at the time of power-on reset, and the other end connected to an output terminal connected to a reset terminal of an element to be reset;
A diode connected in parallel with this fixed resistor to block reverse current; a capacitor connected at one end to the output terminal and grounded at the other; and a capacitor connected at one end to the output terminal and grounded at the other end. A power-on reset circuit characterized by comprising a variable resistor.