JP2002100456A - Current-carrying control circuit of heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current-carrying control circuit of a heater which does not cause breakdown of a switching element by output from an AC generator caused by engine rotation, even when operating an engine in a battery removed state and a regulator troubled state. SOLUTION: In this current-carrying control circuit of the heater having the first switching element for controlling current-carrying to the heater from a power source and a comparator for supplying a prescribed control signal to the first switching element, the current-carrying control circuit of the heater has a voltage detecting circuit, connected between the power source and the first switching element and making output on the basis of a voltage component, by detecting the excessive voltage component exceeding prescribed voltage, so as not to impress voltage which exceeds the prescribed voltage on the first switching element and a photocoupler having input terminals connected to the voltage detecting circuit and an output terminal connected to one input terminal of the comparator and the ground.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control circuit for controlling the energization of a heater, and more particularly to an internal combustion engine in which the temperature of an environment is lower than a predetermined temperature and an AC generator generates power with the rotation of the engine. The present invention relates to a heater control circuit for supplying power to a component heater.

[0002]

2. Description of the Related Art Engines (internal combustion engines) of automobiles, motorcycles and the like are equipped with heaters for internal combustion engine parts such as carburetors. The heaters operate under low environmental temperature conditions such as in cold regions. It is provided to ensure its operation when used. For example, a heater provided in the vaporizer prevents moisture in the air in the vaporizer from freezing and hindering the operation of the engine. The heater is normally operated by the current from the battery, but since a large current of several A flows from the battery, if it is used frequently, the power of the battery is significantly consumed. In addition, when the heater is energized when the temperature is high, a vapor lock phenomenon occurs. For this reason, the heater is preferably used only when necessary.

[0003] Since the battery is supplied (charged) by an alternating current generator (generator) that generates power as the engine rotates, the load on the battery by using a heater is small as long as the engine is rotating. However, when a light or a radio is used without operating the engine, the load on the battery is large, which may cause a problem such as a dead battery. That is, since only the main switch is turned on and the engine is not rotating, power is supplied (charged) from the AC generator.
This is because the power of the battery is consumed without power.

As means for solving such a problem, the present inventor has previously described in Japanese Patent Application No. 10-349446.
It has a predetermined environmental temperature determining means (A), a predetermined power generation determining means (B), and a predetermined heater energizing control means (C). ) And a signal from the power generation discriminating means (B) are both supplied to energize the component heater of the internal combustion engine. According to the invention, the circuit for judging the presence or absence of engine rotation by the power generation judging means (B) is not a signal having a pulse-like waveform such as an ignition signal but a signal output from the AC generator with the rotation of the engine. A low-cost energization control device having a simple configuration, excellent reliability, and low cost can be obtained.

[0005]

However, when a car or the like is exported by ship or the like, the battery is usually removed. Therefore, as a loading method of a car or the like, a method of starting the engine with an external power supply and moving the car or the like is adopted. In this case, a battery functioning as a large-capacity capacitor is connected to the energization control device. In other words, a signal having a high peak voltage flows just because the current from the AC generator accompanying the engine rotation is rectified by a simple half-wave rectifier circuit. For this reason, in the power supply control device from which the battery was removed, an excessive voltage was applied to the heater power supply control means (C) having a small withstand voltage, and the heater power supply control means (C) could be damaged.

That is, the entire circuit is configured so that a prescribed voltage of about 12 to 13 V is applied to the battery terminal in a state where the battery is properly connected. Is removed, and a current having a high peak voltage may be supplied. As the heater energization control circuit (C),
Since an FET or the like having a relatively low withstand voltage is used, if the above-described current having a high peak voltage is supplied, there is a great possibility that the heater energization control circuit (C) will be damaged by an excessive voltage higher than the withstand voltage. There was a problem.

Further, even when the battery is mounted, there are factors such as liquid leakage and performance deterioration of the battery, damage and failure of the charging half-wave rectifier circuit or regulator, and the like.
Further, there is a possibility that an excessively high voltage is similarly applied due to the use of an external power supply and the heater energization control means (C) is damaged. This problem also occurs in circuits for controlling various heaters mounted on motorcycles and automobiles. For example, the same problem arises in a control circuit of a heater for preventing fogging of a mirror and a heater of a vehicle-mounted camera for preventing fogging of a lens.

Accordingly, it is an object of the present invention to provide a circuit for controlling current supply to a heater in which a switching element for controlling current supply to the heater is not destroyed by the excessive voltage component.

[0009]

Under such circumstances, the present inventors have conducted intensive studies and as a result, have found that energizing a heater having a first switching element and a comparator for supplying a predetermined control signal to the first switching element. A control circuit connected between a power supply and the first switching element;
A voltage detection circuit for detecting an excessive voltage component exceeding the predetermined voltage so as to prevent a voltage exceeding the predetermined voltage from being applied to the switching element and outputting based on the voltage component; and an input terminal connected to the voltage detection circuit. If the output terminal is provided with a photocoupler connected to one input terminal of the comparator and the ground, even if a high voltage exceeding the withstand voltage is supplied from the power supply to the first switching element, the voltage can be detected. As a result, the present inventors have found that the first switching element can be made conductive and the first switching element can be prevented from being destroyed, and the present invention has been completed.

That is, the present invention provides a heater power supply control circuit, comprising: a first switching element for controlling power supply from a power supply to a heater; and a comparator for supplying a predetermined control signal to the first switching element. A voltage connected between a power supply and the first switching element, for detecting an excessive voltage component exceeding the predetermined voltage and outputting based on the voltage component so that a voltage exceeding the predetermined voltage is not applied to the first switching element; A detection circuit, and an energization control circuit for a heater, wherein an input terminal is connected to the voltage detection circuit, and an output terminal is provided with a photocoupler connected to one input terminal of the comparator and ground. To provide.

According to the invention, even if a signal of an excessive voltage exceeding the withstand voltage of the first switching element is supplied from the power supply, the voltage detection circuit detects this voltage and detects the voltage. Signal from the circuit to the photocoupler,
By operating the photocoupler by this signal, one potential of the input of the comparator is forcibly fixed to the ground potential,
A signal for conducting the first switching element is output from the output of the comparator. This signal causes the first switching element to become conductive. As a result, the excessive voltage component passes through the first switching element and the first switching element is prevented from being destroyed. Further, by employing a photocoupler, an input signal and an output signal are separated, and a stable operation can be obtained. Further, since this circuit has a simple operation and requires only a small number of components, it is excellent in reproducibility, low cost, reliability, and the like.

The present invention also provides a heater power supply control circuit, wherein the voltage detection circuit comprises a Zener diode.

According to the present invention, in addition to the effects of the above invention, the voltage applied to the first switching element can be prevented from exceeding a predetermined value with a simple circuit configuration using a Zener diode.

Further, the present invention provides a heater power supply control circuit, wherein the heater is a carburetor heater for an internal combustion engine.

According to the invention, since the possibility of damage to the first switching element is extremely small, the motorcycle is indispensable for reliable operation of the internal combustion engine when the motorcycle or the automobile is used in a cold environment. And a heater for a carburetor of an automobile or the like can be reliably operated.

[0016]

Embodiments of the present invention will be described below with reference to FIG. Note that the present invention is not limited to the present embodiment.

FIG. 1 is a schematic circuit diagram of a heater control circuit according to an embodiment of the present invention. In FIG. 1, 1 is an engine, 2 is an AC generator, 3 is a half-wave rectifier circuit, 4 is a regulator, 5 is a battery, 6 is a first switching element, 7 is a heater, 8 is an engine rotation detection circuit, and 9 is a 2 switching elements, 10 is a reference voltage generation circuit, 11
Is a temperature sensor, 12 is a comparator, 13 is a hysteresis circuit, 14 is a voltage detection circuit, 15 is a photocoupler, 21
Is a heater control circuit. In addition, a + terminal in FIG. 1 is a power supply terminal of the conduction control circuit 21, and a − terminal is a ground terminal connected to the ground.

In the present invention, the power source includes a power source circuit for generating a DC power source from the AC generator, that is, a power supply circuit, a rectifier circuit, a smoothing circuit, a stabilizing circuit, and the like, in addition to the battery and the AC generator. Used. That is, in FIG. 1, the power supply 20 is a power supply in which an AC generator 2, a half-wave rectifier circuit 3, a regulator 4, and a battery 5 are connected in series in this order.

The first switching element 6 is connected to the battery 5 at the end of the power source 20 including the AC generator 2, the half-wave rectifier circuit 3, the regulator 4, and the battery 5.
The power supply to the heater 7 is controlled by inputting a predetermined control signal between the positive electrode and the heater 7. Examples of the first switching element 6 include an FET, a bipolar transistor, and the like.
Among them, enhancement type P-channel type FET
Is preferable because the circuit configuration can be simplified.

In the present invention, the predetermined control signal is a signal for turning on the first switching element 6 in a non-conducting state. For example, when the first switching element 6 is a P-channel FET, the signal has a potential lower than the threshold value. When the first switching element 6 is an N-channel FET, the signal has a potential exceeding the threshold value. Examples of the heater 7 include a heater using a PTC element.

In principle, the predetermined control signal for heating the heater 7 is the first control signal only when it is determined that the engine 1 is rotating and the ambient temperature is lower than the predetermined temperature.
Input to the switching element 6. That is, conduction of the first switching element 6 for a relatively long time to heat the heater 7 for the purpose of preventing freezing of the carburetor (vaporizer) or the like is performed only in principle under the above conditions. Note that, as a rule, the term does not include the case of short-time exceptional conduction other than the purpose of preventing freezing of the carburetor (vaporizer).

In principle, the engine 1 rotates, and
As a circuit configuration that outputs a predetermined control signal to the first switching element 6 only when it is determined that the environmental temperature is equal to or lower than the predetermined temperature, for example, the AC generator 2 An engine rotation detection circuit 8 for detecting that the power is turned off, a second switching element 9 that is turned on by input of a signal from the engine rotation detection circuit 8,
A reference voltage generating circuit 10 for generating a reference voltage by the conduction of the switching element 9, a temperature sensor 11 including a temperature measuring resistor for changing a resistance value according to the environmental temperature and generating a voltage according to the environmental temperature, Voltage and temperature sensor 11
And a comparator 12 that supplies the predetermined control signal to the first switching element 6 when it is determined that the environmental temperature is equal to or lower than the predetermined temperature.

The specific circuit configuration of the circuit for outputting the predetermined control signal to the first switching element 6 is as follows.
When the switching element 6 is, for example, an enhancement-type P-channel FET, the following may be mentioned. That is, as the engine rotation detection circuit 8, for example, a circuit in which a diode, a capacitor, and a resistor are combined to form a circuit that converts an alternating current into a direct current and outputs a signal of a predetermined potential is connected to the alternating current generator 2. Can be As the second switching element 9, for example, FE
One in which an input terminal is connected to an output terminal of the engine rotation detection circuit 8 using T or a bipolar transistor is exemplified. As the reference voltage generating circuit 10, for example, two reference resistors are connected in series via a branch point, one reference resistor is connected to a voltage supply source, and the branch point is connected to a non-inverting input terminal of a comparator. One example is a circuit in which the other reference resistor is connected to the output of the second switching element 9 and grounded when the second switching element 9 is turned on. As the temperature sensor 11, for example, a resistor and a temperature measuring resistor such as a thermistor having a resistance value of a negative temperature coefficient are connected in series via a branch point, and the resistor is connected to a voltage supply source to connect the resistor to a voltage supply source. A circuit configuration in which the temperature measuring resistor is connected to the inverting input terminal of the comparator and grounded is used.

In the specific circuit configuration example, when the second switching element 9 is not turned on, the voltage at the branch point of the reference voltage generating circuit 10 is reduced by the voltage drop of the temperature measuring resistor in the temperature sensor 11. Since the voltage is always higher than the voltage at the branch point of the sensor 11, it is possible to establish a relationship in which the potential of the non-inverting input terminal is always higher than the potential of the inverting input terminal.

As the comparator 12, for example, a comparator IC is used, and a reference voltage generating circuit 1 is connected to a non-inverting input terminal.
0 is connected and the temperature sensor 11 is connected to the inverting input terminal.
Are connected to each other, and the output terminal is connected to the input terminal of the first switching element 6. In this circuit configuration, the temperature sensor 1
When the voltage generated at 1 is higher than the voltage generated at the reference voltage generating circuit 10, a low level signal is output. Therefore, when the signal input to the gate of the first switching element 6 such as a P-channel type FET changes from a high level to a low level, and the potential of the gate becomes lower than the potential of the source by a predetermined value or more. When the temperature sensor 11 includes a thermistor or the like having a negative temperature coefficient and having a higher resistance as the temperature becomes lower, the temperature sensor may be used under a low temperature condition where the environmental temperature is equal to or lower than a predetermined temperature. 11
Is higher than the reference voltage. As a result, a low-level signal is output from the comparator 12, and the first
The operation can be performed such that the switching element 6 is turned on and the heater 7 is heated.

It is preferable that a hysteresis circuit 13 is connected between the output terminal of the comparator 12 and one of the input terminals so that the switching operation of the comparator 12 has a hysteresis characteristic. For example, by using a resistor as the hysteresis circuit 13 and connecting the resistor between the reference voltage generating circuit 10 and the non-inverting input terminal, the comparator 12 outputs a predetermined control signal when the environmental temperature decreases. the temperatures T ₁ to perform the operation, become relationship T ₁ <T ₂ between the temperature T ₂ of comparator 12 performs a switching operation no longer outputs a predetermined control signal when the environmental temperature rises occur In addition, it is possible to prevent the operation from becoming unstable due to chattering at a predetermined temperature.

In the embodiment shown in FIG.
Are connected to the first switching element 6 and the output of the regulator 4. The connection is to supply (charge) the electric power generated by the AC generator 2 with the rotation of the engine 1 to the battery 5.
As shown in the figure, a half-wave rectifier circuit 3 and a regulator 4 are usually connected between the two. In this circuit, since the battery 5 and the AC generator 2 are connected in parallel, for example, when the engine 1 is started with an external power supply with the battery 5 removed when loading or unloading a motorcycle or the like, One switching element 6 is in a state where a signal of a predetermined voltage or more having a high peak voltage generated only by the half-wave rectifier circuit 3 and the regulator 4 and generated by the AC generator 2 can be input. Also, even when the battery 5 is mounted, if the battery 5, the half-wave rectifier circuit 3, the regulator 4 or the like cannot be sufficiently smoothed due to breakage or failure, etc. The switching element 6 enters a state where a signal having a voltage higher than a predetermined voltage having a high peak voltage can be input.

For this reason, in the present invention, a branch point is provided between the battery 5 and the first switching element 6, and a voltage exceeding a predetermined voltage is not applied to the first switching element at the branch point. A voltage detection circuit 14 that detects a signal of an excessive voltage component exceeding a predetermined voltage and performs output based on the voltage component is connected. Examples of the voltage detection circuit 14 include a circuit including a Zener diode, an FET, a bipolar transistor, and the like.
Among them, a circuit composed of a Zener diode is preferable because the configuration can be simplified.

The photocoupler 15 has an input terminal connected to the output terminal of the voltage detection circuit 14 and an output terminal connected to one input terminal of the comparator and the ground. The photocoupler 15 operates according to an input signal from the voltage detection circuit 14 when the voltage detection circuit 14 detects an abnormally high potential, and forcibly drops the non-inverting input terminal of the comparator 12 to the ground potential. Further, since the input signal and the output signal are separated in the photocoupler 15, a stable operation can be obtained.

In the above circuit, the + terminal (power supply terminal) is connected by inserting an engine key. Therefore, when the key is not inserted, the battery 5 and the + terminal are disconnected, and the circuit does not consume any power.

Next, in the schematic circuit shown in FIG.
The switching element 6 is an enhancement-type P-channel FET, the heater 7 is a PTC cab heater, and the engine rotation detection circuit 8 emits a signal of a voltage equal to or higher than the threshold value of the second switching element 9.
The second switching element 9 is an N-channel type FET, a reference voltage generating circuit 10 is connected in series via a branch point of two reference resistances, and one reference resistance is connected to a voltage supply source to compare the branch points. A reference resistor connected to the non-inverting input terminal of the detector 12 and the other reference resistor connected to the output of the second switching element 9, wherein the temperature measuring resistor constituting the temperature sensor 11 is a thermistor having a negative temperature coefficient; The comparator 12 is a comparator IC in which the reference voltage generating circuit 10 is connected to the non-inverting input terminal and the temperature sensor 11 is connected to the inverting input terminal. A specific operation will be described.

First, in a state where a voltage higher than a predetermined voltage is not applied to the first switching element 6, the engine 1
The operation in the case where the rotation of the rotating member and the environmental temperature is equal to or lower than the predetermined temperature will be described in detail. When the engine 1 rotates, the AC generator 2 outputs an AC signal, and the engine rotation detection circuit 8 outputs a signal having a voltage equal to or higher than the threshold value of the second switching element 9. Then, the second switching element 9 is turned on, and the reference resistor that has been non-conductive in the reference voltage generating circuit 10 is grounded via the second switching element 9, and a reference voltage is generated. On the other hand, since the environmental temperature is equal to or lower than the predetermined temperature, a voltage higher than the reference voltage is generated in the temperature sensor 11. In this case, the voltage of the temperature sensor 11 input to the inverting input terminal of the comparator 12 is higher than the reference voltage input to the non-inverting input terminal. Output a low-level signal less than. The first switching element is
When the low level signal is input, the signal is turned on and the heater 7
Is heated by the electric current from the battery 5.

When the engine 1 does not rotate in a state where a voltage equal to or higher than the predetermined voltage is not applied to the first switching element 6, the second switching element 9 does not conduct and the input to the non-inverting input terminal of the comparator 12 is made. Since the reference voltage is higher than the voltage generated by the temperature sensor 11, the comparator 12 outputs a high-level signal exceeding the threshold value of the first switching element from the output terminal. Therefore, the first switching element does not conduct, and the heater 7 is not heated.

When the ambient temperature exceeds a predetermined temperature in a state where a voltage equal to or higher than the predetermined voltage is not applied to the first switching element 6, the reference voltage input to the non-inverting input terminal of the comparator 12 is applied to the temperature sensor 11. , The comparator 12 outputs a high-level signal from the output terminal, the first switching element does not conduct, and the heater 7 is not heated, as in the case where the engine 1 does not rotate.

Second, the operation in a state where a voltage higher than a predetermined voltage can be applied to the first switching element 6 for some reason will be described in detail. In addition, only when the engine 1 is rotating and the environmental temperature is equal to or lower than the predetermined temperature, the first
Since the switching element 6 is turned on and the heater 7 is heated, the operation is the same as the operation in a state in which a voltage equal to or higher than the predetermined voltage is not applied to the first switching element 6, and therefore the description is omitted.
Only the differences will be described.

That is, in a state where a voltage equal to or higher than a predetermined voltage can be applied to the first switching element 6 for some reason, the Zener diode (voltage detection circuit 14) outputs a signal of an excessive voltage component exceeding a predetermined voltage. Upon detection, the photocoupler 15 receiving the input of the signal conducts, and the input to the non-inverting input terminal of the comparator 12 is set to the ground potential. Therefore, the potential of the inverting input terminal of the comparator 12 becomes higher than the potential of the non-inverting input terminal by the voltage generated in the temperature sensor 11, and the comparator 12 outputs a low-level signal. As a result, the first switching element 6, the gate / source voltage becomes equal to or higher than a predetermined value, the first switching element 6 is turned on, the heater 7 is heated, and excessive power is consumed. At this time, the first switching element 6 is in a conductive state, and a high voltage is not applied between the source and the drain, so that damage is avoided.

The heater control circuit of the present invention can be widely used in a circuit having a switching element for controlling a heater. For example, an internal combustion engine component such as a carburetor for an engine (internal combustion engine) of an automobile, a motorcycle or the like. It can be used to control heaters for vehicles and to control heaters for defogging on-vehicle camera lenses and mirrors.

[0038]

According to the power supply control circuit of the first aspect of the present invention, even if a signal of an excessive voltage exceeding the withstand voltage of the first switching element is supplied from the power supply, voltage detection is performed. The circuit detects this voltage, and the photocoupler changes the input of the comparator based on the input signal from the voltage detection circuit, so that the comparator outputs a predetermined control signal for conducting the first switching element. 1
It is possible to prevent the first switching element from being destroyed by an excessive voltage when the switching element is turned on. Also,
Since the input signal and the output signal are separated by employing the photocoupler, a stable operation can be obtained.

According to the power supply control circuit of the second aspect of the present invention, in addition to the effects of the first aspect, the voltage applied to the first switching element can be controlled by a simple circuit configuration using a Zener diode. Value can not be exceeded.

According to the power supply control circuit of the third aspect of the present invention, the carburetor heater can be reliably operated. In particular, even when there is a problem in the power supply system, the carburetor heater can be reliably operated, so that the engine of a motorcycle or an automobile can be reliably operated particularly in a cold environment.

[Brief description of the drawings]

FIG. 1 is a schematic circuit diagram showing a first embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 engine 2 AC generator 3 half-wave rectifier circuit 4 regulator 5 battery 6 first switching element 7 heater 8 engine rotation detection circuit 9 second switching element 10 reference voltage generation circuit 11 temperature sensor 12 comparator 13 hysteresis circuit 14 voltage detection circuit 15 Photocoupler 20 Power supply 21 Heater energization control circuit

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Atsushi Mitsu 1-8-1 Shintoda, Hamamatsu-shi, Shizuoka Nichias F-term in Hamamatsu Laboratory (reference) 3K058 AA23 AA30 BA00 CA03 CD01

Claims (3)

[Claims] An electric power supply control circuit for a heater, comprising: a first switching element for controlling energization from a power supply to a heater; and a comparator for supplying a predetermined control signal to the first switching element. A voltage detection circuit connected between the first switching element and the first switching element for detecting an excessive voltage component exceeding the predetermined voltage so as to prevent a voltage exceeding the predetermined voltage from being applied to the first switching element, and performing an output based on the voltage component; A heater conduction control circuit, wherein an input terminal is connected to the voltage detection circuit and an output terminal has a photocoupler connected to one input terminal of the comparator and ground. 2. The heater conduction control circuit according to claim 1, wherein said voltage detection circuit is constituted by a Zener diode. 3. The heater control circuit according to claim 1, wherein the heater is a carburetor heater for an internal combustion engine.