JP3862834B2 - Frame rod circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a frame rod circuit that detects the presence or absence of flame using a frame rod.
[0002]
[Prior art]
Conventionally, for example, in a gas combustion apparatus, a flame rod is known as a flame detection element for detecting the presence or absence of a flame of a burner.
[0003]
FIG. 3 is a circuit diagram of a conventional frame rod circuit driven by a dry battery. This frame rod circuit is composed of a primary oscillation boosting unit and a secondary flame detecting unit.
The oscillation booster comprises an oscillation circuit composed of a primary coil T1, a resistor R7, a diode D2 and a transistor Tr3, and a capacitor for eliminating the influence of a dry battery V as a power source and ripple and impedance of the power source. C2. The base of the transistor Tr3 is connected to one end of the primary side coil T1 via the resistor R7, the collector is connected to the other end of the primary side coil T1, and the emitter is grounded. Moreover, the electric power from the dry battery V is supplied to the drawing point of the primary side coil T1.
[0004]
The flame detection unit includes a secondary coil T2 of the step-up transformer T, a frame rod FR, resistors R8, R9, and R10, capacitors C6 and C7, a Zener diode ZD, and an FET. The frame rod FR is connected to one end of the secondary coil T2 via a resistor R8, and is provided with its tip facing the flame forming portion of the burner B which is body-grounded. On the other hand, the negative electrode of the dry battery V is body-grounded, the other end of the secondary coil T2 is electrically connected to the burner B via a resistor R9 to form a loop through which a flame current flows, and via a resistor R10. Connected to the gate of the FET. The FET drain is provided with a flame detection signal output terminal, and the source is body-grounded.
[0005]
With the configuration described above, when power is supplied from the dry battery V, first, the base current flows through the primary side coil T1 and the resistor R7, so that the transistor Tr3 is turned on, and the collector current flows to the primary side coil T1. An induced electromotive force is generated in a direction that increases the base current. When the collector current increases and reaches the saturation current, the direction of the induced electromotive force is reversed to decrease the base current, and the transistor Tr3 is turned off. Thereafter, when the influence of the induced electromotive force disappears, the base current again flows through the transistor Tr3. By repeating such an operation, the transistor Tr3 is periodically turned on / off to generate a periodic voltage in the secondary coil T2. Therefore, in the state where the flame is formed in the burner B, it becomes equal to a circuit in which a diode and a resistor are connected in series by the rectifying action of the flame, and is indicated by an arrow through the secondary coil T2, the resistor R8, the flame and the resistor R9. A flame current that is half-wave rectified in the direction flows, and a negative potential is generated at the point A with respect to the body ground due to a voltage drop at the resistor R9. The voltage of the resistor R9 is smoothed by the capacitor C6, the noise component is further removed by a filter circuit including the resistor R10 and the capacitor C7, and applied between the gate and source of the FET. The FET is normally conducting, but is cut off when the potential difference of the gate with respect to the source falls below a predetermined threshold value. For example, when the threshold value is 0.5 V, conduction occurs when the potential difference of the gate with respect to the source is 0 to −0.5 V, and when the threshold value is lower than −0.5 V, the gate is cut off. Therefore, in a state where a flame is formed in the burner B, the FET is shut off and the output of the flame detection signal becomes Open. On the other hand, when the flame is not formed, there is no potential difference between the gate and the source, the FET is turned on, and the Lo signal is output from the output end of the flame detection signal. Therefore, the presence or absence of flame can be immediately detected based on the signal from the output end of the flame detection signal.
[0006]
[Problems to be solved by the invention]
In this way, the presence or absence of a flame can be detected by allowing the FET to be blocked by a voltage drop at the resistor R9 due to the flow of flame current. However, there is a problem that the accuracy of the determination level is deteriorated because the threshold value of the FET varies greatly from part to part. If the comparison circuit is used, the variation of the determination level can be reduced. However, since the potential generated at the point A is lower than the negative electrode potential of the battery, it is necessary to add a negative power source for driving the comparison circuit in order to input this potential. And the circuit becomes complicated.
Further, since the voltage generated in the secondary coil T2 varies in proportion to the variation of the dry cell voltage, the potential at the point A also varies when the dry cell voltage varies even when the flame resistance is equal. That is, even if they are exactly the same combustion state, they are detected as different combustion states, which is not preferable in terms of detection accuracy. If the stabilized power supply circuit is used to make the voltage constant, the influence due to the fluctuation of the dry cell voltage can be eliminated, but the cost is significantly increased.
The frame rod circuit of the present invention has an object to solve the above problems and improve the determination accuracy with a simple circuit configuration.
[0007]
[Means for Solving the Problems]
The frame rod circuit according to claim 1 of the present invention for solving the above-mentioned problems is
A transformer for oscillating and boosting battery power,
A detection resistor electrically connected to one end of the secondary coil of the transformer;
A burner that burns fuel gas to form a combustion flame, and a body is electrically connected to the secondary coil via the detection resistor;
A frame rod that is electrically connected to the other end of the secondary coil and is provided with the tip facing the combustion flame;
In the frame rod circuit that determines the presence or absence of flame by generating a voltage in the secondary coil and detecting the current flowing through the combustion flame based on the voltage drop at the detection resistor,
A comparison circuit operated by the battery power supply, and the positive electrode of the power supply of the comparison circuit is electrically connected to the burner body, and a potential obtained by dividing the voltage of the power supply and the potential of the burner body of the detection resistor The gist is to determine the presence or absence of a flame based on the output of a comparison circuit that compares the potential at one end with a low potential.
[0009]
Flame rod circuit according to claim 2 of the present invention for solving the problems is using the battery power source directly in the frame rods circuit according to claim 1 Symbol placement as an operating power supply of the comparison circuit, is generated in the secondary coil The gist is to generate the voltage so as to vary in proportion to the voltage of the battery.
[0010]
The frame rod circuit according to claim 1 of the present invention having the above-described configuration generates a voltage in the secondary side coil of the transformer that oscillates and boosts the battery voltage, and the current flowing through the combustion flame formed in the burner is detected by a detection resistor. The presence or absence of a flame is determined by detecting based on the voltage drop. Further, a comparison circuit operated by a battery power supply compares a potential obtained by dividing the voltage of the power supply with one end potential that is lower than the potential of the burner body of the detection resistor. Since the positive electrode of the power supply for the comparison circuit is electrically connected to the burner body, this one-end potential is lower than the positive potential of this power supply, and the resistance value of the detection resistor is set so that it does not fall below the negative potential of this power supply. By doing so, the power source can be within a range depending on the positive electrode potential and the negative electrode potential. Therefore, it is not necessary to newly provide a power supply for the comparison circuit.
[0012]
Further, in the frame rod circuit according to claim 2 of the present invention having the above-described configuration, the battery power source is directly used as the operation power source of the comparison circuit so that the voltage generated in the secondary coil varies in proportion to the battery voltage. To generate. Therefore, even if the flame resistance is constant, the flame current will fluctuate due to fluctuations in the battery voltage. Does not affect.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
In order to further clarify the configuration and operation of the present invention described above, preferred embodiments of the frame rod circuit of the present invention will be described below.
FIG. 1 is a circuit diagram of a frame rod circuit as an embodiment of the present invention. This flame rod circuit is used in combustion appliances powered by dry batteries such as gas water heaters and gas stoves, and is composed of a primary oscillation boosting unit and a secondary flame detection unit for boosting transformer T Is done.
[0014]
The oscillation booster unit forms an oscillation circuit by the primary side coil T1, the capacitor C1, the resistor R1, and the transistors Tr1 and Tr2 of the boosting transformer T, and also eliminates the influence of the dry battery V as a power source and the ripple and impedance of the power source. Capacitor C2. The electric power from the dry battery V is supplied to the middle point of the primary coil T1 through the choke coil L, from the choke coil L to the base of the transistor Tr1 through the resistor R1, and from the resistor R1 through the base drive coil T3. It is supplied to the base of the transistor Tr2. Transistors Tr1 and Tr2 have the same characteristics, their collectors are connected to both ends of the primary coil T1, and their emitters are grounded and symmetrical.
The capacitor C1 is an oscillation resonance capacitor for stabilizing the oscillation.
[0015]
The flame detection unit includes a secondary coil T2 of the step-up transformer T, a frame rod FR, resistors R2, R3, R4, R5, R6, capacitors C3, C4, C5, a diode D1, and a comparator CP. The frame rod FR is connected to one end of the secondary coil T2 via a resistor R2, and is provided with its tip facing the flame forming portion of the burner B which is body-grounded. On the other hand, the positive electrode of the dry battery V is body-grounded, and the other end of the secondary coil T2 is electrically connected to the burner B via a resistor R3 to form a loop through which a flame current flows, and via a resistor R4. Connected to the non-inverting input side of the comparator CP. A potential value obtained by dividing the battery voltage by the resistors R5 and R6 is input to the inverting input side of the comparator CP as a determination reference potential.
[0016]
With the above-described configuration, when power is supplied from the dry battery V through the choke coil L, one of the transistors Tr1 and Tr2 is first driven due to h _FE (DC current amplification factor) of the transistor, variations in the primary coil T1, and the like. Turn on. When the collector current of the turned-on transistor increases and reaches a saturation current, the base current of the transistor decreases due to the induced electromotive force generated in the base drive coil T3, and the base of the other transistor Turns on when current flows. When the collector current of this transistor reaches the saturation current, the base current of this transistor decreases due to the induced electromotive force generated in the base drive coil T3, and the base current flows to the other transistor and turns on. Since current flows from the power source to the transistors Tr1 and Tr2 via the choke coil L, the rise of the current that flows when the transistors Tr1 and Tr2 are turned on is moderate, and excessive current is prevented from flowing and power loss due to heat generation is reduced. Reduced. Further, when the transistors Tr1 and Tr2 are alternately turned on and off, a magnetic force in the forward and reverse directions is alternately generated in the primary coil T1, and a sine wave voltage having a magnitude proportional to the battery voltage is generated in the secondary coil T2. appear. Therefore, in the state where the flame is formed in the burner B, it becomes equal to a circuit in which a diode and a resistor are connected in series by the rectifying action of the flame, and is indicated by an arrow through the secondary coil T2, the resistor R2, the flame and the resistor R3. A half-wave rectified flame current flows in the direction, and the potential at point E is lower than the positive potential of the dry cell V by the voltage drop at the resistor R3. The resistance value of the resistor R3 is set so that this potential does not fall below the negative electrode potential of the dry battery V. The potential is smoothed by the capacitor C3 and input to the non-inverting input side of the comparator CP. Then, the output of the comparator CP becomes Lo by falling below the determination reference potential input to the inverting input side. On the other hand, when the flame is no longer formed, the potential at the point E becomes equal to the positive electrode potential of the dry cell V, exceeds the determination reference potential, and the output of the comparator CP becomes Open.
[0017]
When the battery voltage fluctuates, the voltage generated in the secondary coil T2 also fluctuates proportionally, and even if the flame resistance is the same value, the flame current fluctuates and the potential at point E varies. Is obtained by subtracting the voltage drop of the resistor R3 due to the flame current from the positive electrode potential of the dry battery V, and varies in proportion to the variation of the battery voltage. On the other hand, the determination reference potential is also a divided voltage value of the battery voltage and varies in proportion to the variation of the battery voltage, so that the influence on the determination performance due to the variation of the battery voltage is negated.
[0018]
As described above, according to the frame rod circuit of this embodiment, the positive electrode of the dry battery V is body-grounded, and the electric potential obtained by subtracting the voltage drop due to the flame current flowing from the positive electrode potential to the resistor R3 is read. Since it is possible to detect the voltage drop due to the flame current by the comparator CP with a simple configuration without newly adding a negative power supply, it is possible to reduce the variation in the determination level. Moreover, since the voltage fluctuation of the dry battery V does not affect the flame detection determination, the determination accuracy is high and the safety can be increased. Further, it can be used for determination of incomplete combustion based on the magnitude of flame current, that is, flame resistance.
[0019]
In addition, the current that flows through the choke coil L is supplied to the oscillation booster so that the rise of the current when the transistors Tr1 and Tr2 are turned on is gradual, preventing excessive current from flowing and reducing power loss due to heat. It can be very small. Therefore, the life of the dry battery V can be made sufficiently long even if the flame is always detected by the frame rod FR. Furthermore, since the capacity of the capacitor C3 required for smoothing can be reduced by increasing the duty ratio of the signal that is half-wave rectified, the responsiveness to ignition and misfire can be further increased. In addition, since the voltage of the primary side coil T1 vibrates positively and negatively, the output efficiency to the secondary side coil T2 can be increased.
[0023]
Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and it is needless to say that the present invention can be implemented in various modes without departing from the gist of the present invention.
[0024]
【The invention's effect】
As described above in detail, according to the flame rod circuit of claim 1 Symbol placement of the present invention, is possible to reduce the variation determination level by a simple circuit construction because there is no need to provide a new power supply for the comparator circuit it can.
[0025]
Furthermore, according to the frame rod circuit of the second aspect of the present invention, the influence of the battery voltage fluctuation on the determination result can be eliminated with a simple circuit configuration, so that the detection accuracy of the combustion state is increased and safety is improved. improves.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a frame rod circuit as one embodiment of the present invention.
FIG. 2 is a circuit diagram of a frame rod circuit as a conventional example.

Claims (2)

A transformer for oscillating and boosting battery power,
A detection resistor electrically connected to one end of the secondary coil of the transformer;
A burner that burns fuel gas to form a combustion flame, and a body is electrically connected to the secondary coil via the detection resistor;
A frame rod that is electrically connected to the other end of the secondary coil and is provided with the tip facing the combustion flame;
In the frame rod circuit that determines the presence or absence of flame by generating a voltage in the secondary coil and detecting the current flowing through the combustion flame based on the voltage drop at the detection resistor,
A comparison circuit operated by the battery power supply, and the positive electrode of the power supply of the comparison circuit is electrically connected to the burner body, and a potential obtained by dividing the voltage of the power supply and the potential of the burner body of the detection resistor A flame rod circuit that determines the presence or absence of a flame based on an output of a comparison circuit that compares a potential at one end with a low potential. 2. The frame rod according to claim 1, wherein the battery power source is directly used as an operation power source for the comparison circuit, and a voltage generated in the secondary coil is generated so as to fluctuate in proportion to the voltage of the battery. circuit.

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