JPH0887355A - Microcomputer reset signal generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reset signal generator resetting a microcomputer when power feeding is interrupted momentarily, by using the characteristic of the switching signal of a switching mode power source (SMPS). SOLUTION: The reset signal generator is provided with a switching signal monitor 50 monitoring the switching control signal of SMPS and generating the monitored switching control signal, a comparator 70 comparing the voltage value of the monitored switching control signal and generating a power interrupting time signal when the control signal is not less than a previously fixed value, and a reset signal generation unit 80 generating a reset signal to give a microcomputer 40 in response to this power interruption time signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reset signal generator, and more particularly to a device for resetting a microcomputer using a switching control signal of a switching mode power supply.

[0002]

2. Description of the Related Art As is well known, conventional reset signal generating devices are widely used in various electric / electronic fields. A normal reset signal generation device effectively executes a series of processes by incorporating various electronic devices (for example, a microcomputer (hereinafter referred to as a microcomputer)).

Generally, a microcomputer requires a constant input power supply voltage in order to execute all processes without causing an error or malfunction. A switching mode power supply (SMPS) is used as a device for supplying a constant input voltage to a microcomputer.

This SMPS converts an AC input signal into a constant voltage signal. SMPS generally stores a full-wave rectifier that rectifies an AC input signal, a transformer that lowers the voltage of the AC input signal to supply a desired voltage, and stores the electric energy supplied from the transformer and transfers it to a load. It consists of a large capacity capacitor. In particular, the SMPS has a switch and switching control circuitry connected to it, these elements producing switching control signals. Usually, the role of the switching control signal is to transform the sine wave of the AC input signal into a narrow pulse wave whose peak portion is approximately coincident with that of the sine wave.
Not only does the power factor increase through such waveform transformation, it also reduces the burden on the rectifier and capacitor. Here, the power factor refers to the ratio of effective power to apparent power.

The input power supply voltage of a microcomputer is often unstable or inaccurate, for example due to momentary interruption of power supply, overload of SMPS, etc., resulting in errors or malfunctions in the microcomputer. Therefore,
A reset signal generation device is required to detect an error in the input power supply voltage to the microcomputer and generate a reset signal.

However, it is known that in a system employing a microcomputer and SMPS, the conventional reset device does not have a function capable of resetting the microcomputer.

[0007]

SUMMARY OF THE INVENTION Therefore, the main object of the present invention is to use in a system adopting a microcomputer and SMPS, and to reset the microcomputer by using the switching control signal of SMPS when the power supply is momentarily interrupted. An object of the present invention is to provide a microcomputer reset device that can improve the operation of a microcomputer by giving a signal.

[0008]

To achieve the above object, according to the present invention, a switching mode power supply (SMPS) is adopted together with a microcomputer to process an AC input signal and supply a constant voltage to the microcomputer. When the power supply of the AC input signal is momentarily interrupted, the microcomputer reset device for resetting the microcomputer by using the switching control signal of the switching mode power supply is used for the system. Monitoring means for generating a monitored switching control signal and comparing the voltage value of the monitored switching control signal with a predetermined voltage value, and the monitored switching control signal is determined in advance. If the voltage value is equal to or higher than the specified voltage In accordance with the power interruption time signal, and a reset signal generating means for generating a reset signal to the microcomputer.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will now be described in more detail with reference to the drawings.

Referring to FIG. 1, there is shown a system including a switching mode power supply (SMPS), a microcomputer 40 and a reset signal generator according to the present invention. A
The SMPS that converts the C input into a constant voltage includes a bridge rectifier 22, a filter capacitor, a transformer 24, a rectifying diode 26, a large capacity capacitor 27, a switching transistor 28, and a switching control circuit 30.

As shown in FIG. 1, the AC input current on lines 10 and 12 is rectified through bridge rectifier 22 and applied to filter capacitor 23 and transformer 24. A filter capacitor 23, which is relatively small in capacity compared to the large capacitor 27, is connected to the output of the bridge rectifier 22 and is used to bypass the high frequency riffle that appears on the rectified AC input from the bridge rectifier 22. .

The transformer 24 is connected to the output terminal of the bridge rectifier to reduce the output voltage of the bridge rectifier 22,
The lowered DC output voltage is applied to the rectifying diode 26 and the large-capacity capacitor 27. The transformer 24 includes a primary winding and a secondary winding. One end of the primary winding is connected to the filter capacitor 23 and the bridge rectifier 22, and the other end is connected to the collector of the switching transistor 28. On the other hand, one end of the secondary winding is grounded, and the other end is connected to the anode of the rectifying diode 26. The high frequency component of the down DC output is rectified and smoothed by the rectifier diode 26 and the large capacity capacitor 27, and a constant voltage is supplied to the microcomputer 40.

On the other hand, the switching transistor 28 connected to the primary winding of the transformer 24 functions to alternately open and close the circuit of the primary winding of the transformer 24. As is well known in the art, such an operation converts a sine wave of an AC input into a narrow pulse waveform in which a peak portion substantially corresponds to that of the sine wave, and the SMP SMP waveform is converted.
Increase the power factor of S.

The switching control circuit 30 generates a pulse type switching control signal for turning on / off the switching transistor 28. In general, the switching control circuit 30 adjusts the pulse width according to the change in load. More specifically, important characteristics are observed when the switching control circuit 30 operates. That is, each time the power supply to the SMPS is momentarily interrupted, the shape of the switching pulse of the switching control circuit 30 suddenly changes as shown in FIG. Referring to FIG. 2, time t1
In the case where the power supply is momentarily interrupted, the pulse width increases while the voltage decreases over time.
The present invention resets the microcomputer 40 using such characteristics of the switching control signal.

In the preferred embodiment of the present invention, the reset signal generator comprises a switching control signal monitor 50, a photocoupler 60, a comparator 70 and a reset signal generation unit 80. Switching control signal monitor 5
0 monitors the switching control signal from SMPS,
Generate a monitored switching control signal. That is,
The pulse-shaped switching control signal is filtered through the diode 51 and the capacitor 52 to generate the current voltage value of the switching control signal. This current voltage value is compared with a predetermined voltage value by the comparator 70.

The photocoupler 60 converts an electric signal into an optical signal with a diode 61, and a phototransistor 62.
By restoring that optical signal to an electrical signal again,
The comparator 70 and the switching control signal monitor 50 are electrically separated. Therefore, the loads of the comparator 70 and the reset signal generating unit 80 are not affected by the switching control circuit 30. As a result, the switching control circuit 30 is protected from the loads of the comparator 70 and the reset signal generating unit 80. Resistance 6
3 and 65 serve to limit the current flowing to the diode 61 and the phototransistor 62, respectively. The magnitude of the voltage drop across resistor 65 is the same as the voltage of the monitored switching control signal, which is applied to the non-inverting input terminal of comparator 70.

The comparator 70 has an operational amplifier 72 and functions to compare the voltage of the monitored switching control signal with a predetermined voltage applied by the resistor 71 and the Zener diode 73. If the voltage of the monitored switching control signal does not reach the predetermined voltage, the operational amplifier 72 applies the drive signal to the reset signal generating unit 80. The reset signal generation unit 80 has a function of giving a reset signal to the microcomputer 40 in response to the drive signal of the comparator 72.

Although an embodiment of the present invention has been described above, it should be understood that without departing from the spirit and scope of the present invention,
It will be apparent to those skilled in the art that various modifications can be made.

[0019]

Therefore, according to the present invention, the operation of the microcomputer is improved by generating the reset signal for resetting the microcomputer by utilizing the characteristics of the switching control signal of the SMPS when the power supply is momentarily interrupted. can do.

[Brief description of drawings]

FIG. 1 is a switching mode power supply (SMP of the present invention.
S) is a circuit diagram of a system including a microcomputer and a reset signal generator.

FIG. 2 is a waveform diagram showing the characteristics of a switching control signal generated during an instantaneous power failure.

[Explanation of symbols]

 22 bridge rectifier 23 capacitor 24 transformer 26 rectifier diode 27 large capacity capacitor 28 switching transistor 30 switching control circuit 50 switching control signal monitor 60 photocoupler 63, 65 resistance 70 comparator 80 reset signal generation unit

Claims (2)

[Claims] 1. Used together with a microcomputer in a system that employs a switching mode power supply (SMPS) that processes an AC input signal and supplies a constant voltage to the microcomputer,
A microcomputer reset device for resetting the microcomputer using a switching control signal of the switching mode power supply when the power supply of the AC input signal is momentarily interrupted, the switching control signal of the switching mode power supply being monitored, Monitor means for generating a monitored switching control signal, and comparing the voltage value of the monitored switching control signal and a predetermined voltage value, the monitored switching control signal is the predetermined voltage value. In the above case, the microcomputer reset signal generation device is characterized by including a comparison unit that generates a power interruption signal and a reset signal generation unit that generates a reset signal to the microcomputer in response to the power interruption signal. 2. The microcomputer reset signal generator according to claim 1, further comprising a separating unit that electrically separates the monitor unit and the comparing unit.