JP2017133757A - Burning appliance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To interrupt power supply to an electromagnetic valve 6 even when a pulse period of a watch dog pulse signal becomes shorter than a normal range in a burning appliance which includes a microcomputer 2 for outputting the watch dog pulse signal, and a safety circuit S for electrically conducting the electromagnetic valve 6 with a power source when the watch dog pulse signal is outputted.SOLUTION: When the pulse period becomes shorter than a normal range by outputting the watch dog pulse signal of the microcomputer 2 to a capacitor C1 for control voltage holding through an integration circuit 10 and a coupling capacitor Ca, a current amount to be supplied to the capacitor C1 for control voltage holding is reduced so as to lower the charging voltage thereof.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a combustion device such as a gas stove or a gas water heater provided with an electromagnetic valve such as an electromagnetic safety valve or an original gas electromagnetic valve.

  In combustion equipment such as a gas stove and a gas water heater, it is common to use a microcomputer as a control center of a control controller that performs combustion control. The microcomputer is operated by a clock generated by a built-in microcomputer or an external oscillation circuit, and the clock is also used for timing of various timers and other timers, and detection by dynamic scanning of various operation switches. Since the control based on the above guarantees the stability of combustion and avoids gas leakage and high temperature hot water, the clock frequency is required to have high accuracy and stability.

  For example, when the clock frequency is increased, the flame detection confirmation time is advanced, and there is a concern that the ignition voltage may be determined without sufficiently rising the voltage of the thermocouple, so that misfire errors may occur frequently. On the other hand, when the clock frequency is low, the acceptance sensitivity of the switch for performing the combustion stop operation is deteriorated, and there are cases in which it is difficult to stop the combustion accurately and promptly by the user operation, or it is measured by a timer. For example, it is assumed that the time until the start of the safe operation becomes longer due to the increase in the real time.

  As a method for ensuring the accuracy and stability of the clock frequency, there is a method in which two or more oscillation circuits are mounted and the clocks generated by the respective oscillation circuits are mutually monitored or compensated (for example, see Patent Document 1). This is a factor of cost increase.

  In addition, by adopting a microcomputer with a built-in on-chip oscillator (clock generation circuit) as the control center of the control unit and not providing a crystal oscillation circuit outside the microcomputer using a crystal resonator, it is a component of the control unit of combustion equipment Although it is possible to reduce the size and cost by reducing the number of points and mounting area, frequency abnormalities are found in environments where there are few achievements in use in combustion equipment, and the engine is placed close to a high-heat combustion part and operated daily. It is necessary to take further measures against this.

  On the other hand, as disclosed in, for example, Patent Document 2 below, in a combustion apparatus such as a battery-powered gas stove, a watchdog is connected from a microcomputer so that an electromagnetic valve automatically closes when a microcomputer that performs combustion control runs away. Pulses are output to the solenoid valve drive circuit. The drive circuit outputs the watchdog pulse to the control terminal (base in the case of a bipolar transistor) of the semiconductor switching element via the RC series differentiating circuit, so that only when the watchdog pulse is normally output, The valve is connected to the power supply battery, and when the watchdog pulse is fixed to High or fixed due to runaway of the microcomputer, the solenoid valve is cut off from the power supply.

Japanese Patent No. 5171379 JP-A-8-270822

  Since the watchdog pulse is also generated based on the clock generated by the oscillation circuit, the frequency of the watchdog pulse also varies with the variation of the clock frequency. However, in the circuit configuration of the conventional driving circuit, the frequency of the watchdog pulse The power cannot be shut down even if the battery level is abnormally high.

  SUMMARY OF THE INVENTION An object of the present invention is to automatically cut off power supply even when the frequency of a watchdog pulse is abnormal.

  In order to achieve the above object, the present invention takes the following technical means.

  That is, the present invention relates to a switching circuit provided in a power supply path to an electric load provided for causing the combustion section to perform a combustion operation, and a control voltage holding function capable of holding an on signal voltage for turning on the switching circuit. A capacitor, a pulse signal generator for generating a pulse signal, and a coupling capacitor, and the pulse signal is supplied to the control voltage holding capacitor via the coupling capacitor, whereby the control voltage holding capacitor In the safety stop device for a combustion device in which the switching circuit is turned off by reducing the charging voltage of the control voltage holding capacitor to less than the ON signal voltage when the pulse signal is not supplied. Waveform of the pulse signal between the capacitor and the coupling capacitor A gentle high-frequency cutoff filter is provided, whereby when the pulse period of the pulse signal becomes shorter than the normal range, the amount of current supplied to the control voltage holding capacitor via the coupling capacitor is reduced, and the The charging voltage of the control voltage holding capacitor is configured to decrease to less than the ON signal voltage (claim 1).

  According to the safety stop device for a combustion apparatus of the present invention, when a high-frequency cutoff filter is added between the pulse signal generator and the coupling capacitor, the pulse signal is fixed to HIGH or LOW. Not only that, but also when the pulse period is short (when the frequency is high), it is possible to automatically shut off the power supply to the electric load such as a solenoid valve.

  More preferably, the high-frequency cutoff filter can be configured so that the ratio of the direct current component of the output voltage signal of the coupling capacitor increases as the pulse period of the pulse signal becomes shorter than the normal range.

  The high-frequency cutoff filter may be an integration circuit, and more preferably a CR integration circuit. According to this, the above-mentioned function can be realized at low cost.

  The electrical load may be a solenoid valve provided in a fuel supply path to the combustion unit or a control unit for controlling the combustion operation of the combustion unit. According to this, it is possible to automatically shut off the power supply to the electromagnetic valve or the control unit when the pulse signal is abnormal.

  As described above, according to the present invention, it is possible to automatically shut off the power supply when the pulse period of the pulse signal is abnormal.

It is a schematic circuit diagram of the safety stop device of the combustion equipment concerning one embodiment of the present invention. When the pulse period of the watchdog pulse signal of the safety stop device is 10 ms (normal), 8 ms (abnormal), 5 ms (abnormal), 2 ms (abnormal) It is a wave form diagram which shows the voltage waveform of a site | part (a point-d point) and the conduction | electrical_connection current waveform of a backflow prevention diode.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a schematic configuration of a solenoid valve drive circuit 1 such as an original gas solenoid valve and a safety valve in a gas combustion device such as a gas stove and a gas water heater, and a self-power holding circuit 3 of a microcomputer 2 functioning as a control unit. ing. In the present embodiment, both the drive circuit 1 and the self-power holding circuit 3 function as the safety stop device of the present invention.

  More specifically, the combustion device is combusted by controlling a combustion part 4 mainly composed of a gas burner, an electromagnetic valve 6 that opens and closes a fuel supply path 5 to the combustion part 4, and an opening / closing operation of the electromagnetic valve 6. A microcomputer 2 as a control unit that controls the combustion operation of the unit 4, a drive circuit 1 that outputs a drive voltage to the electromagnetic valve 6 when a solenoid valve drive command signal and a watchdog pulse signal output from the microcomputer 2 are input, and a battery 7, a power supply circuit 8 that generates a power supply voltage for the microcomputer 2 and the electromagnetic valve 6 based on the battery voltage, a battery voltage monitoring circuit 9 configured by a voltage dividing circuit, and a pulse signal output from the microcomputer 2 itself. And a self-power holding circuit 3 that holds power supply to the microcomputer 2 itself by a holding output signal.

  The power supply circuit 8 can be configured by a DC / DC converter that outputs a predetermined voltage (for example, 3 V) based on a battery voltage, for example.

  As the microcomputer 2, for example, a built-in on-chip oscillator (clock oscillation circuit) may be employed, or a clock oscillation circuit including an external crystal oscillator may be separately provided. The microcomputer 2 is driven by a clock generated by such an internal or external clock oscillation circuit. In a gas combustion apparatus, a clock frequency of about several MHz to several tens of MHz is generally used.

  The microcomputer 2 (pulse signal generation unit) includes a WD signal output terminal capable of outputting a watchdog pulse signal which is a rectangular wave pulse signal generated based on a drive clock, and an electromagnetic valve capable of outputting an electromagnetic valve drive command. A drive command output terminal and a self-holding output terminal capable of outputting a self-holding output signal composed of a pulse signal similar to the watchdog pulse signal are provided.

  The drive circuit 1 includes first and second switching circuits S1 and S2 that can be turned on to electrically connect the solenoid valve 6 to the power supply circuit 8 and that shut off the solenoid valve 6 from the power supply circuit 8 during the turn-off operation. The first and second switching circuits S1 and S2 are connected in series between the power supply circuit 8 and the solenoid valve 6, and the solenoid valve 6 is connected to the power supply circuit only when both the switching circuits S1 and S2 are turned on. 8, a drive voltage based on the power supply voltage is supplied to the electromagnetic valve 6, and when any of the switching circuits S <b> 1 and S <b> 2 is turned off, the electromagnetic valve 6 is disconnected from the power supply circuit 8 to the electromagnetic valve 6. The drive voltage is not output.

  The first switching circuit S1 is mainly composed of two semiconductor switching elements Q1 and Q2. One switching element Q1 is a pnp transistor provided in the middle of a power supply path from the power supply circuit 8 to the electromagnetic valve 6. It is comprised by. The emitter of the switching element Q1 is connected to the power supply circuit 8 side, and the collector is connected to the solenoid valve 6 side.

  Another switching element Q2 is configured by an npn transistor whose collector is connected to the base of the switching element Q1 via a base resistor R1. The emitter (ground terminal) of the switching element Q2 is grounded to the ground (in the illustrated example, the negative electrode of the battery 7). The base of the switching element Q2 serves as a control terminal for the first switching circuit S1.

  The first switching circuit S1 is turned on only when a watchdog pulse signal having a normal cycle (for example, 9 ms or more) is output from the WD signal output terminal of the microcomputer 2 to the control terminal of the first switching circuit S1. A safety circuit S that outputs an ON operation signal is connected.

  The safety circuit S includes a control voltage holding capacitor C1 capable of holding an ON signal voltage necessary for turning on the switching element Q2, and the capacitor C1 is connected to the base of the switching element Q2 via a base resistor R2. Yes. The negative terminal of the capacitor C1 is grounded.

  The control voltage holding capacitor C1 and the WD signal output terminal of the microcomputer 2 are an RC series circuit (differential circuit) constituted by a high-frequency cutoff filter 10 constituted by a CR integration circuit, a resistor Ra, and a coupling capacitor Ca. 11 and a backflow prevention diode D1. The high-frequency cutoff filter 10, the RC series circuit 11, and the backflow prevention diode D1 are connected in series from the WD signal output terminal side in the order described above. In addition, a clamp circuit (a negative clamp circuit in the present embodiment) including a diode D2 is provided at the output portion of the RC series circuit 11.

  As a result, as shown in the waveform diagram at the time of the pulse cycle of 10 ms in FIG. 2, when a normal watchdog pulse signal is continuously output from the WD signal output terminal, the watchdog pulse signal is first filtered by the high-frequency cutoff filter 10. The high-frequency component is cut and the rising voltage waveform becomes gentle (see the waveform at point a), then passes through the RC series circuit 11 and is supplied to point b shown in FIG. The voltage waveform at the point b is also a gentle AC waveform, and the difference between the charging voltage of the capacitor C1 (the voltage at the point c) and the voltage at the point b becomes larger than the forward voltage of the diode D1 at the apex of the AC waveform. As a result, the diode D2 conducts and charges are supplied to the capacitor C1.

  When the pulse cycle is normal (at 10 ms), the slope near the apex (near the maximum potential) of the voltage waveform at point b is small, so that the conduction time of the diode D1 is relatively long. The height and width of the peak of the conduction current waveform of the capacitor Ca become relatively large, and the charging voltage of the control voltage holding capacitor C1 is stably held to be higher than the ON signal voltage. The output of the drive voltage to is maintained.

  On the other hand, when the pulse period of the watchdog pulse signal is 8 ms, the conduction time of the diode D1 is shortened. As a result, the height and width of the peak of the conduction current waveform of the diode D1 become smaller than normal and supplied to the capacitor C1. As a transient phenomenon, the switching element Q1 is temporarily turned on because the amount of current flowing is smaller than the amount of discharge from the capacitor C1 (mainly the amount of discharge through the resistance component between the base and the emitter of the switching element Q2). However, in the simulation shown in FIG. 2, the switching element Q1 is turned off in about several hundred milliseconds.

  Further, when the pulse period of the watchdog pulse signal is 5 ms, the conduction time of the diode D1 is further shortened. As a result, the height and width of the peak of the conduction current waveform of the diode D1 are further reduced, and the capacitor C1 reaches the ON signal voltage. The switching element Q1 is kept off without being charged.

  In addition, when the pulse period of the watchdog pulse signal is 2 ms, the CR integration circuit so that the output signal of the CR series circuit 11 becomes a DC signal including a high-frequency ripple component having a minimum value of about 0.6 V and a maximum value of about 1.1 V. A time constant of 10 is set, and the capacitor C1 is configured not to be charged although a slight current is conducted through the diode D1 by the AC wave ripple component.

  As described above, according to the solenoid valve drive circuit 1 of the present embodiment, the pulse period of the watchdog pulse signal is in a normal range (for example, 9 ms or more) with a simple configuration in which the CR integration circuit 10 is provided in the conventional safety stop circuit. Even when the time is shorter, the power supply to the solenoid valve 6 can be automatically forcibly cut off by turning off the switching circuit S1.

  The second switching circuit S2 is mainly composed of one semiconductor switching element Q3. The switching element Q3 is composed of a pnp type transistor, and is connected in series with the switching element Q1 between the power supply circuit 8 and the electromagnetic valve 6. The base of the switching element Q3 is connected to the solenoid valve drive command output terminal of the microcomputer 2 via the base resistor R3. In the illustrated example, the solenoid valve drive command output terminal is constituted by an open collector output terminal. At the time of open output, the switching element Q3 is turned off, and when the solenoid valve 6 is opened, a Low signal output is output as the solenoid valve drive command signal. As a result, the switching element Q3 is turned on.

  When both the first and second switching circuits S1 and S2 are turned on, the electromagnetic valve 6 is connected to the power supply circuit 8 via the switching elements Q1 and Q3, and a drive voltage is output to the electromagnetic valve 6. The In order to cut back electromotive force due to switching of the switching elements Q1, Q3, a negative voltage cut diode D3 is connected to the solenoid valve 6.

  The self-power holding circuit 3 includes a safety circuit S similar to the safety circuit S of the driving circuit 3, and a self-holding output signal composed of a pulse signal similar to the watchdog pulse signal is output at a normal pulse cycle. The power supply to the microcomputer 2 is held only when the power is on, and the power supply to the microcomputer 2 is cut off when the self-holding output signal is HIGH, LOW, or less than a predetermined pulse period. .

  That is, the self-power holding circuit 3 includes a switching element Q4 made of a p-channel FET provided in the middle of a power supply line from the battery 7 to the power circuit 8. The control terminal (gate) of the switching element Q4 is connected to the ground via two switching elements Q5 and Q6 provided in parallel.

  The control terminal of one switching element Q5 is connected to the ON signal voltage output section of the safety circuit S. While the self-holding signal having a normal pulse period is output from the microcomputer 2, the switching element Q5 is turned on. The control terminal of the switching element Q4 is grounded, so that the switching element Q4 keeps the on operation and the power supply voltage continues to be supplied to the microprocessor 100. The safety circuit S is the same as the drive circuit described above, and a detailed description thereof is omitted. Thus, the switching circuit S3 is constituted by the switching elements Q4 and Q5.

  The control terminal of the other switching element Q6 is connected to the positive electrode of the battery 7 via the power switch SW. When the power switch SW is operated and becomes conductive, the switching element Q6 is turned on and the switching element Q4 is turned on. The voltage is supplied to the power supply circuit 8, and the output voltage of the power supply circuit 8 is supplied to the microcomputer 2 as a power supply.

  The microcomputer 2 starts when the power supply voltage is supplied by operating the power switch SW, and maintains the power supply to itself by outputting the self-holding signal immediately after the start, and satisfies a predetermined power-off condition. Thus, the power supply is automatically turned off by stopping the output of the self-holding signal.

  A battery voltage monitoring circuit 9 is connected to the positive electrode of the battery 7 via a switching element Q4, and a battery voltage monitoring signal output from the battery voltage monitoring circuit 9 is supplied to a battery voltage monitoring signal input terminal of the microcomputer 2. Have been entered. The microcomputer 2 is configured to be able to detect the output voltage value of the battery 7 based on the battery voltage monitoring signal input to the battery voltage monitoring signal input terminal during startup.

  The present invention is not limited to the above-described embodiment, and the design can be changed as appropriate. For example, the normal range of the pulse period can be designed as an appropriate range according to the time constant of the CR integration circuit 10.

2 Control unit (pulse signal generator)
4 Combustion section 6 Electric load (solenoid valve)
10 High-frequency cutoff filter (integration circuit)
S1 Switching circuit S3 Switching circuit Ca Coupling capacitor C1 Control voltage holding capacitor

Claims (3)

A switching circuit provided in a power supply path to an electric load provided for causing the combustion section to perform a combustion operation, a control voltage holding capacitor capable of holding an on signal voltage for turning on the switching circuit, and a pulse signal A pulse signal generation unit for generating, and a coupling capacitor; the control signal holding capacitor is charged by supplying the pulse signal to the control voltage holding capacitor via the coupling capacitor; and the pulse In a safety stop device for a combustion device in which the switching circuit is turned off by reducing the charging voltage of the control voltage holding capacitor to less than the ON signal voltage when no signal is supplied,
A high-frequency cutoff filter that smoothens the rising waveform of the pulse signal is provided between the pulse signal generation unit and the coupling capacitor, so that when the pulse period of the pulse signal becomes shorter than the normal range, the cup Combustion characterized in that the amount of current supplied to the control voltage holding capacitor via a ring capacitor is reduced and the charging voltage of the control voltage holding capacitor is reduced to less than the on-signal voltage. Safety stop device for equipment.   The safety stop device for a combustion device according to claim 1, wherein the high-frequency cutoff filter is an integration circuit.   3. The safety stop device for a combustion device according to claim 1, wherein the electric load is an electromagnetic valve provided in a fuel supply path to the combustion unit, or a control for controlling a combustion operation of the combustion unit. A safety stop device for combustion equipment, characterized by being a part.

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