JPS6020930B2 - reset circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION It is an object of the present invention to provide a reset circuit that can apply a correct reset pulse no matter what the ON state of the DC crab source is.

Components that have internal storage elements, such as microcomputers, must clear their internal state by applying a reset pulse when the power is turned on.

The one shown in FIG. 1 shows a conventional simple set circuit, and when a DC voltage is applied to the DC power supply terminal 1,
At this time, since there is no load on the capacitor 3 of the reset pulse generating circuit 2, the DC voltage at the terminal 1 appears as it is at the connection point with the resistor 4. Thereafter, since the capacitor 3 is charged, the potential at the connection point between the capacitor 3 and the resistor 4 decreases. The voltage change (pulse) at this time is applied to the reset terminal 5a of the overlap set circuit 5 as a reset pulse. However, this circuit has a drawback in that when the voltage at terminal 1 rises slowly, when the voltage is applied to terminal 1 at a fast cycle or when it is no longer applied, no reset pulse is applied to reset terminal 5a. Therefore, the present invention aims to provide a reset circuit free from the above-mentioned drawbacks, and one embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 2, the DC power supply terminal 6 is connected to the stabilizing power supply circuit 7.
is connected to the collector of transistor 8.

A Zener diode 9, which is a constant voltage element, is connected between the base of the transistor 8 and a reference potential point. In addition, a resistor 10 is connected between the base and collector of the transistor 8.
is connected.

The emitter of the transistor 8 is connected to a DC power supply terminal of an overlap set circuit 11 having a storage element inside, such as a microcomputer, and further connected to a reference potential point through a series circuit of a resistor 12 and a transistor 13 which is a switching element. There is. A connection point between the resistor 12 and the transistor 13 is connected to a reset terminal 14 of the overlap set circuit 11. Terminal 6 is further connected to the terminal of transistor 15, and the base of this transistor 15 is connected to resistor 1.
6 to the cathode of a Zener diode 9. Resistors 17 and 18 outside the collector of transistor 15
The resistor 17 is connected to the reference potential point through a series circuit with the resistor 17.
The connection point between and 18 is connected to the base of the transistor 13. Transistors 13, 15, resistors 12, 16,
A switch circuit 19 is constituted by circuits 17 and 18. Next, the operation of this circuit will be explained.

It is assumed that a voltage is applied to the DC power supply terminal 6 and rises as shown in a of FIG. Time ratio. Since the voltage of the Zener diode 9 is lower than that of the Zener diode 9 from t to It is in an off state, and the transistor 13 is also cut off. Therefore, a voltage is applied to the reset terminal 14 through the transistor 8 and the resistor 12 during the period from to to t in FIG. 3c. When the time exceeds 0, a current flows through the Jenner diode 9, so that the emitter voltage of the transistor 8 is stabilized.

At this time, the voltage at terminal 6 exceeds the base voltage of transistor 8, so transistor 15 is turned on, and as a result, transistor 13 is also turned on. Therefore, the voltage at the reset terminal 14 drops rapidly as shown in FIG. 3c. This FIG. 3c is a reset pulse. This circuit can obtain a reset pulse even if the rise time of the voltage at the power supply terminal 6 is short or long, and since it does not use a capacitor, the voltage can be applied to the power supply terminal 6 at short intervals. Even if the pulse is not applied, a reset pulse can be generated following this.

The transistor 13 may be another switching element, and the transistor 15 is a switching element that compares the base voltage of the power supply terminal 6 and the transistor 8 and operates when the voltage of the power supply terminal 6 exceeds the base voltage of the transistor 8. Any other circuit such as a field effect transistor that operates by detecting voltage may be used as long as it turns on the transistor 13.

As described above, the present invention can be applied to an emitter follower type constant voltage circuit, and a reset pulse can be obtained regardless of the power-on state without affecting its constant voltage operation. It can be reset at any time.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a reset circuit in a conventional example, FIG. 2 is a circuit diagram of a reset circuit in an embodiment of the present invention, and FIG. 3 is a characteristic diagram for explaining the circuit. 6...DC exposure terminal, 7...Stabilized power supply circuit,
8...transistor, 9...constant voltage element,
10...Resistor, 19...Switch circuit, 13,
15...Transistor, 11...Overlapping set circuit, 12...Resistor. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A reset target circuit is provided which is reset by temporarily applying a voltage when the power is turned on, and a constant voltage element is connected between the base of the transistor whose collector has a DC voltage applied to it and a reference potential point, and A resistor is connected between the collectors of the emitter follower type stabilized power supply circuit, and the emitter of the transistor, that is, the output of the stabilized power supply circuit, is connected to the power supply terminal of the circuit to be reset, and the power supply terminal and the reference potential point are connected to each other. A series circuit of a resistor and a switching element is connected between the two, and the connection point between the resistor and the switching element is connected to the reset terminal of the circuit to be reset, and the voltage difference between the base voltage of the transistor and the DC voltage is applied between the two. Detected by the voltage detection element provided,
A reset circuit comprising a circuit that applies the output signal to the switching element and turns on the switching element when the DC voltage exceeds the base voltage of the transistor.