JPH0456211B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an energization control circuit for an electric heater used for ignition of combustion equipment, and particularly for use in energizing a ceramic heater that has a short startup time and generates a large amount of heat. Effective.

[Prior art] Ignition devices for combustion equipment ignite in a short time and do not have any effect of noise on microcomputers that control combustion, etc., especially in forced-air combustion equipment where combustion air is supplied by a blower. , so that sufficient heat generation can be obtained for cooling by air flow.
Electric heaters, especially ceramic heaters, which generate high temperatures are used as the ignition means. These heaters, especially those of the so-called rapid temperature rise type that are designed to increase the heat generation temperature, have a low resistance value in order to pass a large current, and the current value is set to a low value in order to prevent the heater from blowing out. is controlled. At this time, since the applied current is controlled by a resistance value that changes based on the temperature of the heater, a direct current whose resistance value can easily be detected is used to supply electricity to the ceramic heater.

[Problems to be Solved by the Invention] However, in order to detect the resistance value and control the current flowing in this way, there is a problem that the circuit for detecting the resistance value becomes complicated and the price increases. .

The present invention provides an inexpensive energization method for heaters used to ignite combustion equipment, which can control the temperature of the heater to prevent melting while maintaining ignition performance that enables prompt and reliable ignition. The purpose is to provide a control circuit.

[Means for Solving the Problems] In the ignition heater energization control circuit of the present invention, the output voltage increases in accordance with the supply time of power, and
The power supply is supplied with a charging/discharging circuit in which the output voltage decreases depending on the elapsed time after the power supply is stopped, and a comparison circuit that outputs an activation signal when the output voltage of the charging/discharging circuit is equal to or lower than a predetermined voltage. a pulse generation circuit that outputs an operating signal of a constant pulse when the pulse generation circuit is activated; an OR circuit that realizes a logical sum of the output of the comparison circuit and the output of the pulse generation circuit; A technical means was adopted consisting of an energizing circuit that conducts electricity.

[Function] In the present invention, the charging/discharging circuit and the comparison circuit perform the following functions.
A timer is formed that operates for a period of time depending on the output voltage of the charging/discharging circuit. When this timer is supplied with power, it outputs an activation signal for a period of time until the output voltage of the charging/discharging circuit reaches a predetermined voltage. This activation signal is transmitted to the energizing circuit via the OR circuit, and the ignition heater is continuously energized. When the output voltage of the charge/discharge circuit becomes higher than the predetermined voltage and the timer operation signal stops, the ignition heater is activated intermittently according to the pulse generation circuit, which outputs a constant pulse operation signal. Power is applied.

When the power supply is stopped, the energization to the ignition heater is stopped, and the output voltage of the charging/discharging circuit decreases according to the elapsed time after the power supply is stopped.

[Effects of the Invention] In the present invention, since the ignition heater is continuously energized at the initial stage of energization, the temperature of the ignition heater rapidly rises to the target temperature. Since the period of continuous energization is limited by a timer formed by the charge/discharge circuit and the comparison circuit, the temperature of the ignition heater does not become too high above the target temperature. After the temperature of the ignition heater rises to the target temperature, the ignition heater is intermittently energized according to the pulse, so the target temperature is maintained and the temperature does not drop. Therefore, ignition can be performed reliably.

In addition, the output voltage of the charging/discharging circuit decreases depending on the elapsed time after the power supply is stopped, so if the ignition operation is stopped once and then restarted, the activation signal will be output depending on the time until re-ignition. The times are different, and the shorter the time until re-ignition, the shorter the output time of the actuation signal. Therefore, the temperature of the ignition heater does not rise excessively, and the ignition heater can be protected.

[Example] Next, a gas water heater 1 showing an example of the present invention in the drawings
The explanation will be based on.

A plurality of slit burners are installed in the lower part of the water heater case 10 of the gas water heater 1, which is schematically shown in FIG.
A double burner group 11 arranged in rows is provided. Combustion air is supplied to the burner group 11 by a blower 12 provided below the water heater case 10. A heat exchanger 13 is provided above the water heater case 10 to heat passing water using the combustion heat of the burner group 11. Further, near the burner group 11 in the water heater case 10, a ceramic heater 14 for ignition and a flame rod 15 for detecting flame are provided.

A nozzle 16 is arranged below the burner group 11 to eject fuel gas supplied from the gas pipe 20. Note that the combustion gas is exhausted from the exhaust port 2 above the water heater case 10.

The ceramic heater 14 has a ceramic substrate 14a molded from silicon nitride as shown in FIG.
The resistor 14b is printed and fired on the surface of the resistor 14b, and then a ceramic substrate 14c is layered and integrated by hot press firing.
is sealed by both ceramic substrates 14a and 14c. The ceramic heater 14 is provided with terminals 14d and 14e for power supply, and each terminal 14
When a voltage is applied between d and 14e, heat is generated depending on the current value.

As shown in FIG. 4, the ceramic heater 14 has a resistance temperature coefficient in which the resistance value increases as the temperature rises. It is a warm type. Since the ceramic heater 14 will melt if its temperature exceeds about 1400°C, in this embodiment, the heater circuit 50, which will be described later,
Ceramic heater 1 to prevent the temperature from exceeding 1200℃
By controlling the current to 4, the temperature of heat generation is suppressed.

The gas pipe 20 that guides the fuel gas to the nozzle 16 includes
A main solenoid valve 21, a main solenoid valve 22, and a governor proportional valve 23 for adjusting the pressure of the supplied fuel gas are provided from upstream, and the gas pipe 20 branches downstream of the governor proportional valve 23 to form a two-bar burner group. One of the branched gas pipes 20a that guides fuel gas to each of the burner groups 11 is provided with an electromagnetic valve 24 that stops the fuel supply in order to burn only the burner group 11.

As shown in FIG. 5, the control device 30 consists of a combustion control circuit 31 that controls the combustion state, which is configured mainly by a microcomputer, and a heater circuit 50 that controls the energization state of the ceramic heater 14. It operates according to the state.

The combustion control circuit 31 controls the start and stop of combustion in a predetermined sequence, and also controls the combustion based on the temperature set by the controller 40, the amount of water inlet, the temperature of the inlet water, and the temperature of the outlet water detected by a water amount sensor and a thermistor (not shown). Perform quantity control.

The heater circuit 50 is a circuit that energizes the ceramic heater 14 for ignition operation when an ignition signal is output from the combustion control circuit 31, and as shown in FIG. The main components are a circuit 53, an OR circuit 54, and a heater energization circuit 55. When a relay (not shown) is driven by an ignition signal, its contact 56 closes and the ceramic heater 14 is energized.

Each circuit of the heater circuit 50 will be explained below.

In the charge/discharge circuit 51, when the contact 56 is closed, the capacitor 61 is connected to the semi-fixed resistor 62 and the diode 63.
When the contact 56 is opened, the capacitor 61 is discharged by the OR circuit terminal 66 through the diode 64 and the semi-fixed resistor 65. Here, the input terminals of the OR circuit element 66 are both connected to the supply line L of the power supply Vcc via a resistor 67, and when the contact 56 closes, the output of the OR circuit element 66 becomes high level, but the diode 64 Since the capacitor 61 is provided in the opposite direction to the capacitor 61, the capacitor 61 is a semi-fixed resistor 6.
2 and diode 63 only. Conversely, when the contact 56 opens, the output of the OR circuit element 66 is inverted to low level, so the capacitor 6
1 can be reliably discharged. The potential of the capacitor 61 is applied to the comparator circuit 52 via the diode 68 as the output voltage of the charging/discharging circuit 51.

The comparison circuit 52 compares the output voltage of the charging/discharging circuit 51 with a reference voltage using a comparator 69, and outputs an output according to the comparison result. Here, the power supply Vcc is connected to resistor 7
The reference voltage obtained by dividing the voltage by 0,71 is applied to the positive input terminal 69a of the comparator 69, and the output voltage of the charging/discharging circuit 51 is applied to the negative input terminal 69b of the comparator 69. An activation signal is output when the output voltage is lower than the reference voltage.

Therefore, a timer is formed by the charge/discharge circuit 51 and the comparison circuit 52, and the output time of the activation signal is as follows.
It varies depending on the discharge state of the capacitor 61, and the shorter the time from when the contact 56 opens to the time it closes, the shorter the output time becomes, and the longer the time, the longer the output time becomes. The operating characteristics as a timer are semi-fixed resistors 62,
65, the semi-fixed resistor 62 determines the timer operating time, and the semi-fixed resistor 65 determines the operating time at the time of reactivation.

The pulse generation circuit 53 includes a pulse generation element 72
is used to generate a pulse signal and output it as an operating signal, the frequency is adjusted by a semi-fixed resistor 73, and the duty ratio is adjusted by a semi-fixed resistor 74.

The OR circuit 54 is a circuit that realizes the logical sum of the output of the comparison circuit 52 and the output of the pulse generation circuit 53, and drives the heater energization circuit 55 by the transistor 75 based on the output. Further, in order to inform the user of the energization state of the ceramic heater 14, the light emitting diode 77 is turned on by the transistor 76 using the output.

The heater energization circuit 55 is a circuit that energizes the ceramic heater 14 in accordance with the output of the OR circuit 54.

Here, since the ceramic heater 14 is energized directly by the commercial power source 57, a photocoupler 78 is used for insulation.

The photocoupler 78 includes a light-emitting diode 79 as a light-emitting element and a phototriax 80 as a light-receiving element, and lights the light-emitting diode 79 based on the output of the OR circuit 54. Gate 80a of phototriax 80 and one anode 80
A zero-crossing circuit element 81 is connected between the triac 82 and the anode 80b. Zero cross circuit element 8
1 is a zero voltage switch circuit made into an integrated circuit.

The ceramic heater 14 is connected between the commercial power supply 57 and the anode 82b of the triax 82, and when the phototriax 80 is turned on by the light from the light emitting diode 79, the triax 82
becomes conductive, and the ceramic heater 14 is energized.

Note that a resistor 83 for surge absorption is provided between the anode 82b and the anode 82c of the triax 82.
and a series circuit consisting of a capacitor 84 and a varistor 8
5 are connected in parallel.

Next, the operation of the heater circuit 50 will be explained based on FIG. 6 in accordance with the operation of the gas water heater of this embodiment.

When the user turns on the operation switch using the controller 40, sets the hot water temperature, and opens the hot water tap (not shown), water passes through the heat exchanger 13. When the water flow sensor generates a pulse as the water flows, the combustion control circuit 31 starts ignition control, the blower 12 is driven, and the supply of combustion air into the water heater case 10 is started.

At time t1, when the blower 12 reaches a predetermined rotation speed, a relay (not shown) of the combustion control circuit 31 is driven to close the contact 56, and the current from the power supply Vcc is transferred to the charge/discharge circuit 51, comparison circuit 52, and pulse generation circuit 53. is supplied by a supply line L to. In the charging/discharging circuit 51, current flows from the semi-fixed resistor 62 and the diode 63 to the capacitor 61, and charging of the capacitor 61 is started. Comparison circuit 52
Since the potential of the capacitor 61 is still low with respect to the reference voltage, a high level is output as an activation signal. Further, the pulse generating circuit 53 generates a pulse at the same time as the power supply Vcc is supplied.

At this time, the output of the OR circuit 54 is
The ceramic heater 14 is continuously energized from the heater energization circuit 55, and the output of the ceramic heater 14 becomes high level.
The resistor 14b generates heat due to the supplied current, and the temperature of the ceramic heater 14 quickly rises.

When the capacitor 61 is charged and its potential gradually rises and becomes higher than the reference voltage at time t2, the output of the comparator circuit 52 is inverted and becomes a low level.
Therefore, since only the pulses from the pulse generation circuit 53 are input to the OR circuit 54, the ceramic heater 14 is energized intermittently according to the pulses from the heater energization circuit 55, and the current value is limited. Therefore, the ceramic heater 14 is controlled to a constant temperature, for example, 1200° C., and this temperature is maintained.

Following the energization of the ceramic heater 14, each electromagnetic valve 21, 22 is opened and fuel is supplied to the burner group 11. When the fuel is mixed with air supplied by the blower 12 and ignited.

When ignition is detected by flame rod 15 at time t3, contact 56 is opened and charging/discharging circuit 5
1. Since the comparison circuit 52 and the pulse generation circuit 53 are de-energized, the heater energization circuit 55 de-energizes the ceramic heater 14. At this time, the charge in the capacitor 61 is discharged via the diode 64 and the semi-fixed resistor 65 by the OR circuit element 66 whose output is inverted to a low level.

At time t4, when the flame goes out for some reason or when ignition is not detected by the flame rod 15 within a predetermined time, the combustion control circuit 31
Ignition control is performed again.

At this time, since the amount of discharged charge of the capacitor 61 differs depending on the elapsed time Δt (= t4 - t3) from time t3, it takes until the output voltage of the charging/discharging circuit 51 reaches the reference voltage when being recharged. Time is different. Therefore, since the high level output time of the comparator circuit 52 is changed, the continuous energization time to the ceramic heater 14 is changed. This continuous energization time becomes shorter as the elapsed time Δt becomes shorter, so the ceramic heater 1 whose temperature has not decreased due to the previous energization
4, excessive energization is not performed. Therefore, the ceramic heater 14 will not be damaged or melted down.

After a certain period of time has elapsed after ignition, combustion amount control is performed according to the set temperature of the controller 40 and detection signals from the sensor and thermistor.

Thereafter, once the user closes the hot water tap, water stops flowing into the heat exchanger 13, and combustion stops.

In the above embodiment, a phototriac 80 and a zero cross circuit element 81 were used in the heater energizing circuit 55 shown in FIG. 1, but as shown in FIG. and zero cross circuit element 8
1 may be replaced with a zero-cross circuit 91 having a discrete configuration.

In addition, in order to avoid the effect of temperature changes on the ceramic heater due to burner heating during reuse, within a certain period of time after use is stopped, the timer operation of the charging/discharging circuit and comparison circuit is stopped and pulse generation is performed. It is also possible to energize only by a signal from the circuit, and energize by a signal from a timer only when a certain period of time has elapsed after stopping use.

In the above embodiments, a gas water heater is shown as a combustion device equipped with an ignition device, but a heater or a cooking device may also be used. Furthermore, the fuel is not limited to gas.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a heater circuit in a gas water heater control device according to an embodiment of the present invention, and FIG. 2 is a schematic diagram showing an embodiment of a gas water heater using the ignition heater energization control circuit of the present invention. Fig. 3 is a block diagram showing the structure of the ceramic heater of this embodiment, Fig. 4 is a characteristic diagram showing the resistance value characteristics with respect to temperature changes of the ceramic heater of this embodiment, and Fig. 5 is similar to Fig. 2. FIG. 6 is a time chart for explaining the operation of the gas water heater of this embodiment, and FIG. 7 is a block diagram showing the schematic configuration of the control device in the gas water heater shown in FIG. FIG. In the figure, 14...ceramic heater (ignition heater), 51...charge/discharge circuit, 52...comparison circuit,
53... Pulse generation circuit, 54... OR circuit (logical sum circuit), 55... Heater energization circuit (energization circuit).

Claims (1)

[Scope of Claims] 1. A charging/discharging circuit whose output voltage increases according to the supply time of a power source and decreases according to the elapsed time after the power source is stopped; and an output voltage of the charging/discharging circuit. a comparison circuit that outputs an activation signal when the voltage is below a predetermined voltage; a pulse generation circuit that outputs a constant pulse activation signal when the power is supplied; logic between the output of the comparison circuit and the output of the pulse generation circuit; An energization control circuit for an ignition heater, comprising an OR circuit that realizes a sum, and an energization circuit that energizes an ignition heater according to the output of the OR circuit.