JPH0310516A - Power-on reset circuit - Google Patents

Abstract

PURPOSE:To make a power-on reset signal active even at a low voltage range where an active element cannot be active by adding a relay circuit to a power-on reset circuit comprising the active element. CONSTITUTION:A level of an noninverting input (a) of a comparator 1 depends on a time constant comprising a resistor 4 and a capacitor 2 and an inverting input (b) forms a reference voltage Vr by a resistor 5 and a Zener diode 3. A coil of a relay 6 connects a power supply Vcc and ground, a normally closed contact is adopted for a contact 7 of the relay 6 and connected between an output C of the comparator 1 and ground. At the application of the power supply Vcc and the steady-state is reached, then the contact 7 is opened, since an output of the comparator 1 goes to a low level, the level remains at a low level. After application of the power supply Vcc, the level of the noninverting input (a) is larger than the level of the inverting input (b) after a time constant t3 comprising the resistor 4 and the capacitor 2, the output C of the comparator 1 goes to a high level and a reset signal is released.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a power-on reset circuit.

[Prior art] Conventionally, this type of power-on reset circuit is shown in Figs. 3 and 4.
As shown in the figure, in order to keep the reset signal active until after the voltage is determined, it is comprised of active elements such as a comparator 8 and a transistor 9, as well as a capacitor 11 and a resistor 10 that determine the reset time.

[Problems to be Solved by the Invention] Since the conventional power-on reset circuit described above uses active elements, the power-on reset signal becomes active in a low voltage range in which the active elements do not operate, as shown in FIG. The disadvantage is that it does not.

An object of the present invention is to provide a power-on reset circuit that solves the above problems.

[Means for Solving the Problems] In order to achieve the above object, a power-on reset circuit according to the present invention includes a power-on reset circuit configured with active elements, in which a power source for driving the power-on reset circuit is connected to a relay. A coil driving power source is used, and the output of the power-on reset circuit and the ground potential are connected through the contacts of the relay.

〔Example] Reference will now be made to the drawings for the invention.

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

In the figure, ■ is a comparator, 2 is a capacitor, 3 is a Zener diode, 4.5 is a resistor, 6 is a relay, and 7 is a contact point of the relay 6. The potential of the non-inverting input a of the comparator l is determined by the time constant of the resistor 4 and the capacitor 2, and the inverting input becomes the reference voltage Vr by the resistor 5 and the Zener diode 3. The coil of the relay 6 is connected between the power supply V C (and ground), the contact 7 of the relay 6 is a normally closed contact, and it is connected between the output C of the comparator 1 and the ground. Figure 2 shows the time chart of each signal. Show.Second
C' in the figure is a time chart of the output when only comparator 1 is used. The comparator 1 does not operate until 2 after the power supply Vcc is turned on. Therefore, the output of the comparator l is V as shown by C' in FIG. An attempt is made to output an output that follows C, but since the contact 7 is closed, the output C of the comparator I remains at a low level. Power supply V
When CC reaches vl and enters a steady state, contact 7 becomes open, but since the output of comparator 1 is at low level, it remains at low level. Here, the time constant of resistor 4 and capacitor 2 is the power supply ■. It takes t3 for the potential of non-inverting input a to reach Vr.
Set it to take seconds. Three seconds after the power supply V(() is turned on, the potential of the non-inverting input a becomes higher than the potential of the inverting input A, the output C of the comparator 1 becomes high level, and the reset signal is released.

[Effects of the Invention] As explained above, the present invention adds a relay circuit to the power-on reset circuit composed of active elements, thereby making the power-on reset signal active even in a low voltage range where the active elements do not operate. There is an effect that can be done.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a time chart of the present invention, Figs. 3 and 4 are circuit diagrams showing a conventional example, and Fig. 5 is a power-on diagram in the conventional example. FIG. 3 is a diagram showing a reset signal waveform. l... Comparator 2... Capacitor 3.
...Zena diode 4. Death...Resistor 6...Relay 7...Relay 6 contacts Fig. 2 Fig. 5

Claims (1)

[Claims] (1) In a power-on reset circuit configured with active elements, the power source for driving the power-on reset circuit is a relay coil drive power source, and the output of the power-on reset circuit and the ground potential are connected via the contacts of the relay. A power-on reset circuit characterized by: