JP2830555B2 - Combustion equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion apparatus having a flame current detection circuit capable of detecting a combustion state of a water heater or the like.

[0002]

2. Description of the Related Art Conventionally, a flame detection circuit of a combustion apparatus has applied an AC voltage to a flame rod and a burner, and has detected the presence or absence of a flame by utilizing a rectifying action by a flame current.

FIG. 3 shows a conventional flame detection circuit, in which an AC voltage is applied between the frame rod 1 and the burner 2 by an AC power supply 3 to change the on / off frequency of an FET (N-channel) 4 to change the voltage. The control unit 7 of a device constituted by a microcomputer that controls the charging voltage of the resistor 5 and the capacitor 6 to be changed.
To determine the presence or absence of a flame. Burner 2
When there is no flame, the battery is charged through the path of the capacitor 8, the resistor 9, and the capacitor 10 and discharged through the same path.
The voltage between the gate and the source of the FET 4 has a waveform of a curve a in FIG. 4 and is repeatedly turned on and off at a frequency of 50%, and the capacitor 6 is charged with the charging current by the resistor 5.
Is discharged only by the on-resistance of the capacitor 6, the charging voltage of the capacitor 6 is small, and the input to the control unit 7 is Lo. Also, in the burner ignition state, when charging due to the rectifying action of the flame,
Current paths such as the capacitor 8, the frame rod 1, the flame A, and the burner 2 are formed, the charging current of the capacitor 10 is reduced, and the gate-source voltage of the FET 4 is represented by a curve b in FIG.
As shown in the figure, the voltage waveform has many negative components, the ON frequency of the FET 4 decreases, the charging current becomes larger than the discharging current of the capacitor 6, and the input to the control unit 7 becomes Hi.

FIG. 5 shows another conventional example. As in the example of FIG. 3, an AC voltage is applied by an AC power supply 3 to a frame rod 1 and a burner 2 connected to a frame ground, and the flame rod flows due to the generation of a flame. The current is converted to a voltage by the resistor 12, and the level is detected by the control unit 7 to determine the combustion state.

[0005]

In such a conventional combustion apparatus, an ignition state of the burner 2 is detected by a flame detection circuit, and ignition or extinguishing is determined based on the detection output signal. Since the combustion is controlled by the control unit 7 that controls the operation of the equipment in response, the flame detection circuit is indispensable for the safe operation of the combustion equipment, and high reliability and performance are required. For example, if a fire extinguishing judgment is made even in an actually ignited state, the combustion operation is stopped, and conversely, if an ignition judgment is made in an actually extinguished state, the fuel supply is continued. Because of the problem of falling into a very dangerous state, the priority is to detect ignition or non-ignition. In the ignition state, an incomplete combustion state in which sufficient air is not sent to the burner 2 continues As for the problem of continuing combustion, there is a problem that individual components of the flame detection circuit vary and the cost is high, and there is a problem that sufficient measures are not taken.

In the conventional example shown in FIG. 5, since the burner 2 connected to the frame ground and the circuit ground of the microcomputer 7 cannot be made the same due to the circuit configuration, sufficient insulation measures must be taken between the circuit ground and the frame ground. It was necessary to apply. Originally, since the flame is generated between the frame rod 1 and the burner 2 and the impedance is high even when the flame current is flowing, a higher dielectric strength is required between the frame ground and the circuit ground.
In such a circuit configuration, when insulation is deteriorated, a minute current flows from the circuit ground to the frame ground, and it may be erroneously determined that a flame current flows. Although there are almost no such problems with equipment such as fan heaters used indoors, in water heaters intended for outdoor installation, a remote control cable with the circuit ground as the negative electrode while the frame ground is grounded to ground is used indoors and outdoors. Therefore, there is a problem that it is extremely difficult to secure insulation including natural phenomena such as rain.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to improve the detection accuracy of a combustion state, reduce the influence of variation between components, and reduce the cost.

[0008]

In order to achieve the above object, the present invention provides a burner for forming a flame and one end of the burner.
DC power supply connected to the frame ground of the equipment including
Provided in the vicinity of the flame, a flame rod which is connected via a current mirror circuit to the other end of the DC power source, said frame
Circuit ground and the circuit ground
Control unit configured on control unit power supply with land as one end
And a resistor connected between the output terminal of the current mirror circuit and the frame ground, wherein a voltage across the resistor is input to the control unit as a flame detection signal. Means to solve the problem.

The current mirror circuit according to the first aspect of the present invention comprises a first transistor connected to a frame rod and having a base and a collector short-circuited, and a first transistor connected between an emitter of the first transistor and a DC power supply. 1, a second transistor having a base connected to the base of the first transistor, and a second resistor connected between the emitter of the second transistor and a DC power supply. A second means for solving the problem is that the collector is connected to a resistor having one end connected to the frame ground.

[0010]

According to the present invention, the frame ground and the circuit ground are made common by the first and second means for solving the above problems.
It is possible to form a flame detection circuit, and a current equal to the flame rod current that changes according to the combustion state of the flame flows as the collector current of the second transistor. Has a correlation with the flame rod current, and by detecting this voltage level, it is possible to determine the ignition state or the combustion state of the burner.

[0011]

An embodiment of the present invention will be described below with reference to FIG. The same components as those in the related art are denoted by the same reference numerals, and description thereof is omitted.

As shown in FIG. 1, a DC power supply 14 has one end connected thereto.
It is connected to the frame ground 14 a of the device including the burner 2, and the other end is connected to the frame rod 1 via the current mirror circuit 15. A resistor 16 is connected between the output terminal of the current mirror circuit 15 and the frame ground 14a, and a voltage between both ends of the resistor 16 is extracted as a flame detection signal and input to the control unit 7. Then, the control of the control unit 7
The circuit ground 7a of the unit power supply (not shown) and the frame
Connect the lands 14a to form a common ground
ing.

The current mirror circuit 15 includes a first transistor 17 connected to the frame rod 1 and having a base and a collector short-circuited, and a first resistor 18 connected between the emitter of the first transistor 17 and the DC power supply 14. A second transistor 19 having a base connected to the base of the first transistor 17, and a second resistor 20 connected between the emitter of the second transistor 19 and the DC power supply 14. The collector of the transistor 19 is connected to the resistor 16
Connected to 21 is a capacitor.

When the burner 2 is ignited, a current flows in the direction of the flame rod 1, the flame A, and the burner 2, and a rectifying action occurs. Frame rod 1
Current flows through the collector current / hF
A base current equal to E will flow. At this time,
The emitter potential of the first transistor 17 is 1 VF (about 0.6 V) higher than the base potential, and the emitter potential of the second transistor 19 whose base potential is equal to the base potential of the first transistor 17 is the first potential. Is equal to the emitter potential of the transistor 17. When the resistance values of the first and second resistors 18 and 20 are made equal, the current flowing through each resistor is as follows: current = (power supply voltage−emitter voltage) / resistance value, and a first transistor in which this current becomes an emitter current 17, the collector current of the second transistor 19 is larger than the collector current of the second transistor 19 by the base current of the second transistor 19, which is equal to the emitter current of the first and second transistors 17, 19. However, the base current in this case is very small and sufficiently negligible in a small-signal transistor having 200 or more.

The flame current flowing through the flame is, as shown in FIG.
There is a correlation with the combustion state (oxygen concentration) during combustion, and when the combustion state is good (oxygen concentration is high), a lot of flame current flows,
Conversely, if the combustion state is poor, the flame current decreases.

The present invention utilizes this phenomenon, in which a collector current equal to the collector current of the first transistor 17 through which a flame current having a correlation with the combustion state flows is passed through the second transistor 19, and the current is passed through a resistor. 16. The voltage is converted by the capacitor 21 and the level is determined by the AD circuit of the microcomputer constituting the control unit 7, and the combustion state such as incomplete combustion as well as ignition or non-ignition is detected. That is, the current mirror circuit 15
Flame current flowing between rod 1 and frame ground 14a
A circuit that allows a current equal to the flame current to flow
And the frame ground 14a and the circuit ground 7a are shared.
I am trying to pass through. In the above description,
The microcomputer incorporates an AD circuit to detect the level, but using a comparator (voltage comparator)
Even if an external AD circuit is configured, the same function can be achieved. Further, the capacitor 21 aims at smoothing the voltage generated at the resistor 16, and there is no particular problem even if the output voltage is not stable.

[0017]

According to the present invention, as is apparent from the above embodiments, a current equal to the flame current flowing in the flame is taken out.
In order to determine the level by converting the voltage to a voltage, highly accurate determination can be made in the detection of the combustion state, and the resistance values of the first and second resistors can be determined by comparing the resistance values of both ends of the resistor generated by the current flowing through the resistor. If the voltage is set to be large enough to satisfy the relationship of (voltage) ≫ (VBE of the second transistor), VB of the second transistor, which is a problem between component elements,
Since the variation in E can be neglected and the collector current flowing through the first and second transistors depends on the accuracy of the first and second resistors, it is not necessary to make hFE equal, and the combustion state can be detected accurately. However, it is not necessary to worry about variations among components, and a circuit can be formed at a low cost. Further, since the frame ground and the circuit ground are common, there is no need to provide protection against insulation between the respective grounds, and the ground is used as the circuit ground, which is effective against noise.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a combustion device according to an embodiment of the present invention.

FIG. 2 is a correlation characteristic diagram of a flame current and a combustion state (oxygen concentration) of the combustion device.

FIG. 3 is a circuit diagram of an example of a flame detection circuit of a conventional combustion device.

FIG. 4 is a main part voltage waveform diagram of the flame detection circuit.

FIG. 5 is a circuit diagram of another example of the flame detection circuit of the conventional combustion device.

[Description of Signs] 1 Flame rod 2 Burner 14 DC power supply 15 Current mirror circuit 16 Resistance

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shinji Miyauchi 1006 Kadoma, Kazuma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-59-145422 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) F23N 5/12

Claims (4)

(57) [Claims] A burner for forming a flame and one end of said burner
DC power supply connected to the frame ground of the equipment including
Provided in the vicinity of the flame, a flame rod which is connected via a current mirror circuit to the other end of the DC power source, said frame
Circuit ground and the circuit ground
Control unit configured on control unit power supply with land as one end
And a resistor connected between the output terminal of the current mirror circuit and the frame ground, wherein a voltage across the resistor is input to the control unit as a flame detection signal. 2. A current mirror circuit comprising: a first transistor connected to a frame rod and having a base and a collector short-circuited; a first resistor connected between an emitter of the first transistor and a DC power supply; A second transistor connected to the base of the first transistor; and a second resistor connected between the emitter of the second transistor and the DC power supply, the collector of the second transistor having one end connected to a frame ground. The combustion device according to claim 1, wherein the combustion device is connected to a resistor connected to the device. 3. The resistance value of the first resistor and the resistance value of the second resistor are such that the voltage generated across the resistor when a normal detection current flows through the frame rod is the base of the first and second transistors. 3. The combustion apparatus according to claim 2, wherein the resistance value is set to be sufficiently higher than the voltage between the emitters. 4. The combustion apparatus according to claim 1, further comprising a control unit that detects a voltage between both ends of a resistor connected between a collector of the second transistor and a frame ground, and determines a combustion state of the burner.