JPS60176124A - Reset device of microcomputer - Google Patents

Abstract

PURPOSE:To prevent malfunction of a device by providing a discharge resistor of an electric charge of a capacitor via a diode to a voltage dividing point of a voltage dividing resistor of a transistor (TR) connected to a reset terminal of a microcomputer to ensure the reset operation. CONSTITUTION:When a momentary power failure takes place after power is applied, a voltage of a positive power terminal VDD of a microcomputer 1 is dropped and a TR is turned off at a prescribed time. Then the electric charge charged in a capacitor C1 is discharged via a voltage dividing resistor R3 and most of the charge is discharged rapidly via a discharge resistor R4 and a voltage dividing resistor R6 through a diode D1. On the other hand, since the voltage RST at the reset terminal is decreased according to the power supply Vc since the TR is turned off at a prescribed time. When the voltage of the positive power terminal VDD rises again, the circuit is brought into a similar state when the power is applied from the power interruption, the microcomputer 1 is reset surely and the normal operation is started.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a reset device for a microcomputer that controls devices such as refrigerators and air conditioners.

Conventional configurations and their problems In general, in devices such as refrigerators and air conditioners that are controlled using microcomputers, if an error occurs in the reset operation of the microcomputer when turning on or turning off the power, the device may malfunction. There was a problem that occurred.

Here, an example of a conventional reset point for the microcomputer will be explained with reference to FIG.

In the figure, 1 is a microcomputer that controls the equipment, and has a reset terminal R8T and a positive power supply terminal vD.
D and a negative power supply terminal vss. and,
The plus side power supply terminal vDD is connected to the power supply V, and the minus side power supply terminal vss is grounded. The reset terminal R8T of the microcombi 1 is pulled up to the power supply VC1 through a capacitor CO for resetting, and is grounded through a resistor R8. When the microcomputer 1 is powered on, after the voltage supplied to the positive power supply terminal vDD reaches the operating voltage of the microcomputer 1, the microcomputer 1 maintains the voltage at the reset terminal R8T at H'' level for a certain period of time. , a reset operation is performed, and then normal operation is started by setting the voltage at the reset terminal R8T to the "L" level.

In the above-described conventional reset circuit, when the power is turned on from the power-off state, the voltage supplied to the positive power supply terminal VDD of the microcomputer 1 rises in accordance with the power supply VC, and at time t1 in FIG. In,
The operating voltage v1 of the microcomputer 1 is reached.

At this time, since the capacitor % is in an uncharged state, the voltage at the reset terminal R8T follows the voltage at the positive power supply terminal VDD and reaches the @H'' level as shown in FIG.

When the capacitor co is charged after a certain period of time, the voltage at the reset terminal R8T drops to the "L" level. As a result, the microcomputer 1 performs a reset operation and starts operating normally.

However, if a momentary power outage occurs from a energized state,
Positive side power supply terminal VDD of the microcomputer 1
The voltage drops momentarily and then rises again, reaching the operating voltage V of the microcomputer 1 at time t2 in FIG. 2d. At this time, the charge stored in the capacitor C8 is not discharged in a short period of time, so when the voltage at the positive power supply terminal vDp rises again, the capacitor C8 is charged.

is in a half-charged state, and the voltage at the reset terminal R8T is the second
As shown in the figure, the level goes “L” without rising to “H” level.
Even if it falls to the "H" level, it does not stay at the "H" level for the required fixed period of time and drops to the "L" level. Therefore, there is a problem in that an error occurs in the reset operation of the microcomputer 1, causing a malfunction in the equipment.

OBJECTS OF THE INVENTION It is an object of the present invention to eliminate such conventional drawbacks, ensure the reset operation of a microcomputer, and prevent equipment malfunctions.

Structure of the Invention In order to achieve this object, the present invention uses a voltage dividing resistor and a capacitor in the transistor connected to the reset terminal of the microcomputer, and performs a reset operation when the power supply voltage supplied to the microcomputer reaches a certain voltage or higher. In addition, by providing a resistor for discharging the charge of the capacitor via a diode at the voltage dividing point of the voltage dividing resistor, the microcomputer can be reset reliably even in the event of a momentary power outage, thereby preventing equipment malfunction. It was designed to do so.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 3 and 4. Structures that are the same as those of the prior art will be given the same numbers and symbols, and detailed explanation thereof will be omitted. , R1 is a resistor for supplying voltage to the reset terminal. Tr is a transistor for resetting, and its collector is connected to the reset terminal R3T of the microcomputer 1, and is pulled up to the power supply voltage VC' via a resistor R4, and its emitter is grounded. R2 is the first voltage dividing resistor, R
3 is a second voltage dividing resistor, and the voltage dividing point is the transistor Tr.
The transistor Tr is connected to the base of the transistor Tr, divides the voltage of the power supply voltage VC, and supplies the voltage to the base of the transistor Tr. C1 is a capacitor whose positive terminal is connected to the base of the transistor and pulled down. R4 is the capacitor C
This is the discharge resistance for a charge of 1. R6 is the third voltage dividing resistor, R6
is a fourth voltage dividing resistor, whose voltage dividing point is connected to the discharge resistor, divides the voltage of the power supply voltage VC, and supplies the voltage to one end of the discharge resistor R4. Dl is a diode whose anode side is connected to the positive terminal of the capacitor C1, and whose cathode side is connected to the discharge resistor R4, so that the charge of the capacitor C1 flows to the discharge resistor R4.

It is generally configured as described above. The operation of the reset circuit will be explained.

When the power is turned on from a power-off state, the voltage applied to the positive power supply terminal vDD of the microcomputer 1 rises in accordance with the power supply Vc as shown in A in FIG. V,
reach. If the capacitor C1 is not connected, then the power supply vc becomes v2 at time t4, and the transistor Tr
The voltage between the base and emitter reaches the ON voltage as shown in B. However, in reality, since the capacitor C1 is in an uncharged state when the power is turned on, charging takes a certain amount of time with a time constant of 01×R2, as shown in C of FIG. )
, at time t6, the voltage between the base and emitter of the transistor Tr reaches the ON voltage, and the transistor Tr is turned ON.

On the other hand, the voltage at the set terminal R3T increases in accordance with the power supply VC, as shown in FIG. 4d, and reaches the H" level at time t6, at which the microcomputer 1 can determine that it is an H" signal. Then, at the above-mentioned time t6, the transistor Tr becomes O.
To do this, the reset terminal R8T falls to the "L" level.

As a result, the microcomputer 1 performs a reset operation and starts normal operation. Here, the time (16-15) is “
This is the required time to maintain the H” level.

In this circuit example, the relationship between the operating voltage v1 of the microcomputer 1 and the power supply voltage v2 when the voltage between the emitter and base of the transistor Tr reaches the ON voltage is v2>v.
The resistance values of the first voltage dividing resistor R2 and the second voltage dividing resistor R3 are set so that the voltage becomes l.

Next, we will discuss the case where a momentary power outage occurs from a energized state. Positive side power supply terminal vDD of microcomputer 1
The voltage decreases, and at time t7 in FIG. 4C, the voltage between the emitter and base of the transistor Tr becomes less than the ON voltage.
Transistor TI is turned off. Therefore, the charge stored in the capacitor C1 is discharged through the second voltage dividing resistor R3, and at the same time, most of the electric charge is rapidly discharged through the diode D1, the discharge resistor R4, and the fourth voltage dividing resistor R6. On the other hand, since the transistor Tr is turned off at time t7, the voltage at the set terminal R8T decreases according to the power supply Vc.3. The resistance value of the fourth voltage dividing resistor is the positive power supply terminal v
It is set so that when the voltage of DD becomes lower than the ON voltage of the emitter-base of the transistor Tr, the charge of the capacitor C19 flows into the discharge resistor via the diode D1.

Then, when the voltage of the positive side power supply terminal VDD rises again, the circuit becomes in the same state as when the power is turned on from the above-mentioned power-off state, and the microcomputer 1 reliably performs the reset operation and starts normal operation.

According to the reset circuit shown in the embodiment, the reset operation of the microcomputer 1 can be reliably performed even when a momentary power outage occurs. Also, the transistor Tr is Q
Since the power supply voltage v2 at the time of N is set higher than the operating voltage v1 of the microcomputer 1, the reset operation of the microcomputer 1 is performed reliably even when the power supply voltage slows up or down, thereby preventing equipment malfunction. Effects of the Invention As is clear from the above explanation, the present invention provides a transistor connected to a reset terminal of a microcomputer, and a first transistor that turns on the transistor when the potential applied to the microcomputer reaches a certain voltage or higher. ．． A second voltage dividing resistor, a capacitor connected between the emitter and base of the transistor, a diode and a discharge resistor for discharging the charge of the capacitor, and a first resistor that starts the above-mentioned discharge when the power supply voltage falls below a certain voltage. ．． Since the second voltage dividing resistor is provided, it is possible to provide a device with a simple configuration that reliably resets the microcomputer even in the event of a momentary power outage and prevents malfunction of the equipment.

[Brief explanation of the drawing]

Figure 1 shows a conventional microcomputer reset device.
FIG. 2 is a voltage waveform diagram thereof, FIG. 3 is a reset device for a microcomputer showing an embodiment of the present invention, and FIG. 4 is a voltage waveform diagram of FIG. 1...Microcomputer, C1...
・Capacitor, Tr...Transistor, R1・
...Resistance, R2...First voltage dividing resistor, R3
......Second voltage dividing resistor, R4...Discharging resistor, R6...Third voltage dividing resistor, R6...Fourth voltage dividing resistor, D, ······diode. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Diagram f Diagram 2 Diagram 4 Diagram 3 Diagram 4 Diagram IIf

Claims (1)

[Claims] A microcomputer having a reset terminal that performs a reset operation at the "H" level, a transistor or a resistor connected to the reset terminal, a resistor that supplies a potential to the reset terminal, and a voltage-divided voltage connected to the base of the transistor. A first voltage dividing resistor and a second voltage dividing resistor that supply voltage, a capacitor connected between the emitter base of the transistor, a diode whose anode side is connected to the voltage dividing point by the voltage dividing resistor, and the diode. A microcomputer reset device comprising a discharge resistor that discharges the charge of the capacitor on the cathode side, a third voltage divider resistor that supplies a divided voltage to the other end of the discharge resistor, and a fourth voltage divider resistor. .