JPH0624898Y2 - Reset circuit of microcomputer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a reset circuit of a microcomputer used in an electric heating device such as an electric insulation pot.

(Prior Art) For example, an electric heat-insulating pot is provided with a heater, which heats water to bring it to a boil and then keeps it warm. In such an electric heat-insulating pot, if there is no water inside the heater, energizing the heater will result in a so-called empty cooking, which is dangerous. Has become. And such a series of control is performed using a microcomputer.

However, in the microcomputer, the program control may stray due to the influence of noise or the like. In such a case, the heater may be energized irrespective of the input from the sensor, and there is a problem that if there is no water in the pot at this time, it is extremely dangerous.

Further, in the case of using a microcomputer, the program may run out of control even if an instantaneous power failure occurs.

In order to solve such a problem, the present applicant previously developed and applied for a reset circuit shown in FIG.

In this circuit, a smoothing capacitor 3 and a constant voltage diode 4 are connected to a commercial AC power source 1 via a rectifying diode 2, and the constant voltage diode 4 is connected to an NPN type transistor 5.
The constant voltage diode 6 is connected in parallel via the collector and the base of the above, and a constant voltage is output between the emitter of the transistor 5 and the anode of the constant voltage diode 6. The comparator 7 detects the power supply voltage from the collector side of the transistor 5, and when the power supply voltage drops, a reset signal is generated from the comparator 7 and supplied to the reset terminal of the microcomputer 8.

Further, the microcomputer 8 is provided with a watchdog timer output port that outputs a digital signal at a constant cycle when the program control is normally performed, and stops the output of the digital signal when the program control goes astray. The digital signal from the port is supplied to the differentiating circuit 9. The output of the differentiating circuit 9 causes the transistor 10 to perform a switching operation. The transistor 10 is connected in parallel with the capacitor 11, and when the transistor 10 is off, the capacitor 11 is charged through the resistor 12, and when the transistor 10 is turned on, the charge of the capacitor 11 is discharged. It is like this.

The charge level of the capacitor 11 and the reference voltage set by the voltage dividing circuit of the resistors 13 and 14 are compared by the astable multi-circuit 16 having the comparator 15.
Then, when the microcomputer 8 strays and the output of the digital signal disappears, the transistor comes to hold the off state, the charge level of the capacitor 11 reaches the reference voltage, and the astable multi-circuit 16 operates to make the astable state. A reset signal is generated from the multi-circuit 16 and supplied to the reset terminal of the microcomputer 8.

(Problems to be solved by the invention) However, the circuit of this prior application uses two comparators for detecting an instantaneous power failure and for detecting a stray microcomputer, and this comparator has a relatively large mounting area. Therefore, there is a problem that the mounting area of the entire circuit becomes large. Further, since the cost of the comparator is relatively high, there is a problem that the cost of the entire circuit becomes high.

Therefore, the present invention is intended to provide a microcomputer reset circuit that can reliably reset the microcomputer in the event of a momentary power failure of the power supply or stray of the microcomputer, and can reduce the mounting area and cost. Is.

[Means for Solving the Problems] (Means for Solving the Problems) The present invention provides an output port of a microcomputer that outputs a digital signal at a constant cycle during normal program control and stops the output of the digital signal during stray, and this output. Differentiating circuit for differentiating a signal from the port, a first transistor that responds to the output of the differentiating circuit, a second transistor that is turned on by detecting a voltage drop of the power supply, and an off and on operation of the first transistor Is charged and discharged at a relatively slow speed by the capacitor, and is charged at a relatively fast speed by the ON operation of the second transistor, and operates when the charge level of this capacitor reaches a preset predetermined level. It is composed of an astable multi-circuit that supplies a reset signal to a reset terminal of a computer.

(Operation) In the present invention having such a configuration, since the digital signal of a constant cycle is output from the output port when the program control of the microcomputer is normally performed, this digital signal is differentiated by the differentiating circuit, The differential output causes the first transistor to be turned on for a short period of time every digital signal period. In this operation, the charging speed of the capacitor is relatively slow, so that the charging level of the capacitor does not reach the predetermined level in the cycle of the digital signal. Then, the capacitor is discharged before the charge level of the capacitor reaches a predetermined level, and the astable multi-circuit does not operate.

However, if the program control of the microcomputer sometimes goes astray, the output of the digital signal from the output port is stopped, and the output of the output port is fixed to the high level or the low level. Then, the differential output from the differentiating circuit is stopped and the first transistor continues the off operation. Therefore, the charge level of the capacitor eventually reaches a predetermined level, and as a result, the astable multi-circuit starts operating and supplies a reset signal to the reset terminal of the microcomputer. Thus, the microcomputer is reset in program control and restarts the program from the beginning.

In addition, if the power supply may momentarily lose power, the second transistor is turned on at this time, and the capacitor is charged at a relatively high speed. When the charge level of the capacitor reaches a predetermined level, the astable multi-circuit operates and the reset signal is supplied to the reset terminal of the microcomputer. The microcomputer is also reset when an instantaneous power failure occurs in this way.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 21 is a commercial AC power source, and this power source 21
The power supply circuit 22 is connected to.

In the power supply circuit 22, a smoothing capacitor 24 and a constant voltage diode 25 are connected in parallel to the power supply 21 via a rectifying diode 23 with a polarity shown in the figure. Further, a constant voltage diode 27 having a cathode connected to the base of the rectifying diode 23 and the collector and the base of the NPN transistor 26 is connected to the power source 21. A resistor 28 is connected between the collector and the base of the transistor 26.

The emitter of the transistor 26 and the anode of the constant voltage diode 27 are used as a stabilized constant voltage output terminal.

An astable multi-circuit 29 is connected to the power supply circuit 22.

The astable multi-circuit 29 includes a series voltage dividing circuit including a first resistor 30 and a second resistor 31, and a third resistor 32, a fourth resistor 33, and a capacitor 34 at an output terminal of the power supply circuit 22. Each series circuit is connected. The connection point between the resistors 30 and 31 is connected to the non-inverting input (+) of the comparator 35, and the connection point between the resistor 33 and the capacitor 34 is connected to the inverting input (-) of the comparator 35. .

The comparator 35 has a resistor 36 connected between its non-inverting input (+) and an output terminal, and a series circuit including a resistor 37 and a diode 38 of the polarity shown between its inverting input (-) and an output terminal. Are connected. A resistor 3 having the output terminal of the comparator 35 connected in parallel to the output terminal of the power supply circuit 22.
It is connected to the connection point between the resistor 39 and the capacitor 40 in the series circuit of 9 and the capacitor 40, and the connection point is connected to the reset terminal P ₁ of the microcomputer 41.

An NPN first transistor 42 is connected in parallel to the capacitor 34 via the resistor 33. A diode 43 is connected between the base and the emitter of the first transistor 42 with the polarity shown in the figure.

The microcomputer 41 outputs a digital signal at a constant cycle when the program control is normally performed, and when the program control is straying, the output of the digital signal is stopped and the watchdog is fixed to a high level or a low level. An output port P _{2 of the} timer is provided, and the output port P ₂ is connected to the emitter of the transistor 26 via resistors 44 and 45 in series.

A differentiating circuit 46 is connected between the connection point between the resistors 44 and 45 and the base of the first transistor 42. The differentiating circuit 46 is composed of a capacitor 47 and a resistor 48. The capacitor 47 is connected between the connection point of the resistors 44 and 45 and the base of the first transistor 42, and the resistor 48 is connected to the first transistor 42. It is connected between the base and the emitter of the transistor 42.

Further, an NPN type second transistor 50 is connected in parallel to the series circuit of the third resistor 32 and the fourth resistor 33 via a fifth resistor 49. The base of the second transistor 50 is connected to the cathode of the constant voltage diode 25. The second transistor 5
The diode 51 is connected between the base and emitter of 0 in the polarity shown in the figure.
Are connected.

In this embodiment having such a configuration, when the power supply 21 is turned on, the second transistor 50 is turned on until the positive terminal level of the smoothing capacitor 24 reaches the constant voltage level to be output to the emitter side of the transistor 26. , The capacitor 34 is charged, and the charge level of the capacitor 34 becomes higher than the voltage division level by the resistors 30 and 31, the output of the comparator 35 becomes low level, and the reset terminal P ₁ of the microcomputer 41 becomes low level. Reset signal is supplied. Then, the microcomputer 41 is initially reset.

When the output of the comparator 35 becomes low level, the capacitor 34
Is discharged through the resistor 37 and the diode 38, and its charge level is lowered. When the level of the positive terminal of the smoothing capacitor 24 exceeds the constant voltage level output to the emitter of the transistor 26, the second transistor 50 is turned off, and the voltage dividing level of the resistors 30 and 31 becomes lower than the charging level of the capacitor 34. Higher comparator 35
The output level of becomes high level. In this way, the reset of the microcomputer 41 is released and the program control is started.

When the program control of the microcomputer 41 is normally performed, the output port P ₂ outputs a digital signal of a constant cycle indicated by S in FIG. 2A. This digital signal is created in a program, for example,
If the previous output port P ₂ is “1”, that is, high level, the output port P _{2 is set} to “0”, that is, low level. On the contrary, if the previous output port P ₂ is “0”, that is, low level, the output port P _{2 is set} to “1”, that is, high level. When this process ends, other control is performed, and then the process of the output port P ₂ is performed again. Therefore, if the program operates normally, the high level and the low level are alternately output to the output port P ₂ , and the digital signal is obtained.

When a digital signal is output from the output port P ₂ of the microcomputer 41, this digital signal is output to the differentiation circuit 4
The differential waveform is input to the base of the first transistor 42 after being differentiated by 6. Since this differential waveform has a positive pulse synchronized with the rising edge of the digital signal, the positive pulse causes the first transistor 42 to be turned on for a short time.

On the other hand, the capacitor 34 is charged at a relatively slow rate via the resistors 32 and 33 when the first transistor 42 is off. Then, since the first transistor 42 is turned on before the charge level of the capacitor 34 reaches the voltage division level of the resistors 30 and 31, the astable multi-circuit 29 does not operate, and therefore the reset signal is not generated. For example, as shown in FIG. 2 (b), when the voltage division level L ₁ is about 3V, the charge level of the capacitor 34 is discharged at about 0.5V, and the output of the comparator 35 is shown in FIG. 2 (c). It goes high as shown.

When the program control of the microcomputer 41 becomes stray, the output level of the output port P ₂ is fixed at either the high level or the low level.
For example, it becomes a low level as indicated by T in FIG. Then, the output of the differential waveform from the differentiating circuit 46 disappears and the first transistor 42 continues to be in the off state.

When the first transistor 42 continues to be in the off state, the charging level L ₂ of the capacitor 34 eventually reaches the voltage division level L ₁ by the resistors 30 and 31, as shown in FIG. Then, at that timing, the output of the comparator 35 is inverted to the low level as shown in (c) of FIG. In this way, the low-level reset signal is supplied from the astable multi-circuit 29 to the reset terminal P ₁ of the microcomputer 41, and the microcomputer 41 is reset.

When the output of the comparator 35 becomes low level, the output is fed back to the non-inverting input (+) and the inverting input (-), and the voltage dividing level L ₁ drops to, for example, about 1.3V, but the capacitor 34 and the resistor 37 also. And is discharged through the diode 38.

After that, when a digital signal is generated again from the output port P ₂ , the first transistor 42 is turned on and off, and the capacitor 34 is discharged at a constant cycle. In this way, the output of the comparator 35 is inverted to the high level.

In this way, the microcomputer 41 is reset even when the program goes astray.

If an instantaneous power failure occurs during operation as shown in FIG. 3 (a), the second transistor 50 is turned on when the power supply voltage level drops to a certain level, and the capacitor 3
4 will be charged through the resistor 49 at a relatively fast rate.

Then, as shown in FIG. 3B, the charge level L ₂ of the capacitor 34 reaches the voltage division level L ₁ in a short time,
As shown in (c) of the figure, the output of the comparator 35 becomes low level. In this way, the reset signal is supplied to the reset terminal P ₁ of the microcomputer 41, and the microcomputer 41 is reset.

When the output of the comparator 35 becomes low level, the capacitor 34
Is discharged through the resistor 37 and the diode 38, and its charge level is lowered. In addition, the partial pressure level L ₁ is also the resistance 36
It will be slightly reduced by the return by. After that, the power failure is recovered, and the charge level L ₂ of the capacitor 34 is divided into the voltage division level L ₁
The output level of the comparator 35 is inverted to the high level as shown in FIG. In this way, the reset of the microcomputer 41 is released and the program control is restarted.

In this way, even when the program control of the microcomputer 41 goes astray or when a momentary power failure occurs, the microcomputer 41 is surely reset and the program control starts from the beginning.

Moreover, the comparator used is one in the astable multi-circuit 29.
Since the instantaneous power failure is detected by the second transistor 50 with only one unit, the circuit mounting area can be made smaller than that using two comparators, and the cost can be reduced.

[Advantages of the Invention] As described in detail above, according to the present invention, the charging speed of the capacitor charged and discharged by the turning-on and turning-off of the first transistor is relatively slow. The charge level of the capacitor does not reach the predetermined level, and reaches the predetermined level when the output of the digital signal is stopped. Therefore, the microcomputer is not reset accidentally when the microcomputer is normal, and can be surely reset only when it strays.

Further, since the charging speed of the capacitor charged by the ON operation of the second transistor is relatively high, the charging level of the capacitor reaches the predetermined level in a short time after detecting the voltage drop of the power supply. Therefore, the microcomputer can be reliably reset even in the case of an instantaneous power failure of the power supply.

Moreover, one capacitor and one astable multi-circuit can be used together to reset the microcomputer not only when the microcomputer strays but also when there is a momentary power failure, so that the circuit mounting area can be reduced and the cost can be reduced. You can

[Brief description of drawings]

1 to 3 show an embodiment of the present invention.
FIG. 4 is a circuit diagram, FIG. 2 is a signal waveform diagram for explaining the operation during microcomputer stray, FIG. 3 is a signal waveform diagram for explaining the operation during momentary power failure, and FIG. It is a circuit diagram shown. 29 ... Astable multi-circuit, 30 ... 1st resistance, 31 ... 2nd resistance, 32 ... 3rd resistance, 33 ... 4th resistance, 49
... Fifth resistance, 34 ... Capacitor, 35 ... Comparator, 41
... microcomputer, 42 ... first transistor,
46 ... Differentiation circuit, 50 ... Second transistor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaru Tanaka 2570, Gosuda 1 Kaji, Kamo City, Niigata Prefecture, Toshiba Heat Fixtures Co., Ltd. (72) Hiroaki Kawaguchi 2570 1 Gosuda, Kamo, Niigata Prefecture 1 Toshiba Heaters Incorporated (56) Reference JP-A-58-169219 (JP, A) JP-A-59-225418 (JP, A)

Claims (1)

[Scope of utility model registration request] 1. An output port of a microcomputer that outputs a digital signal of a constant cycle during normal program control and stops output of a digital signal during stray, a differentiation circuit that differentiates a signal from this output port, and the differentiation. A first transistor that responds to the output of the circuit, a power supply circuit that makes the power supply a constant voltage, and a series voltage divider circuit in which a first resistor and a second resistor are connected in series between the output terminals of this power supply circuit. A second transistor that is turned on by detecting a voltage drop of the power supply, and a third resistor and a fourth resistor between the output terminals of the power supply circuit.
Connected through a parallel circuit of a series circuit of a resistor and a series circuit of the second transistor and a fifth resistor and connected in parallel to the first transistor through the fourth resistor, When the first transistor is turned off, the first transistor is charged through the third and fourth resistors at a relatively slow rate, and when the first transistor is turned on, the first transistor is turned on through the fourth resistor and the first transistor. Is discharged by the ON operation of the second transistor and is charged at a relatively high speed through the second transistor and the fifth resistor, the charge level of the capacitor, and the series voltage dividing circuit. A comparator for inverting the output when the charge level reaches the voltage division level, and the inverted output of the comparator is used for the microcomputer. Reset circuit of the microcomputer, characterized by comprising the astable circuit for supplying a reset signal to the reset terminal of.