JP3008757U - Temperature control circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] A temperature control circuit for controlling the temperature of an object to be heated by an electric heater does not use an operational amplifier or a microcomputer, has a small number of component parts, is highly reliable, and is inexpensive. Temperature control circuit. [Composition] A temperature sensitive switching circuit (6) consisting of a series circuit of a positive temperature coefficient thermistor (PTH ₁ ) and a resistor (R ₁ ) and a transistor (Q ₁ ), and a dual circuit consisting of _two transistors (Q ₂ and Q ₃ ). Of the load drive circuit for providing current to the load (5) through the stabilizing circuit (3), the set circuit (4) including the starting switch SW for making the bistable circuit (3) conductive, and the transistor (Q ₁ ). It is characterized by having a reset circuit which inverts the bistable circuit (3) to a non-conductive state by conduction.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a temperature control circuit for controlling the temperature of an object to be heated with an electric heater. is there.

[0002]

[Prior art]

FIG. 1 shows a conventional example of a temperature control circuit. The resistors R _A , R _B , R _C and the thermistor NTC constitute the measurement bridge circuit 1, and the reference voltage V _A and the measurement voltage V _B are input to the operational amplifier 2 and the magnitude relation between the two voltages is compared and calculated. Depending on whether the output is H level or L level, the switching transistor Q ₁ is turned on and off, and the on and off output becomes one input of the bistable circuit 3 consisting of the output transistors Q ₂ and Q ₃ and is manually operated at the time of starting. The switching circuit 4 including the heating instruction switch S is another input of the bistable circuit 3, and the current supply to the load 5 such as a relay (relay) is on / off controlled. According to this conventional example, since the bridge circuit 1 and the operational amplifier 2 are required, there is a drawback that the configuration becomes complicated and the cost becomes high.

Conventionally, a positive temperature coefficient thermistor has been known, and it is known to use it for overcurrent protection. FIG. 2 illustrates some of them. Figure (a) shows a positive characteristic thermistor PTH provided in series with the transformer primary side circuit, (b) shows one provided in series with the transformer secondary side circuit, and (c) shows one provided in the motor circuit. (D) shows the one provided in the transistor circuit. This conventional example is an example of use to prevent the transformer and the power transistor of the stabilized power supply from being destroyed when an abnormal current flows in the power supply circuit when an abnormality occurs in the load of the transistor circuit or small motor. If the current flowing through the positive temperature coefficient thermistor PTH increases abnormally, the positive temperature coefficient thermistor PTH itself generates heat, which has the effect of suppressing the load current of the power supply circuit by increasing the resistance. Thus, this conventional example relates to the overcurrent protection technique, not the temperature control technique.

[0004]

[Problems to be solved by the device]

 An object of the present invention is to provide a temperature control circuit having a simple structure that does not use a microcomputer and an operational amplifier by applying a conventionally known positive temperature coefficient thermistor and can be manufactured at a very low cost.

[0005]

[Means for Solving the Problems]

Temperature control circuit of the present invention, the first and positive characteristic thermistor PTH ₁ which is disposed at a position to be the temperature measurement, the first positive characteristic series circuit of a thermistor PTH ₁ and resistor R ₁ between the DC power supply It consists of a temperature sensitive switching circuit which is connected and the emitter-base electrode of the _first transistor Q ₁ is connected in parallel with the first positive temperature coefficient thermistor PTH ₁ and two transistors Q ₂ and Q _3. a current supplied load driving circuit to a load through a bistable circuit FF _1, the a set circuitry to the bistable circuit FF ₁ conductive, conduction of the bistable circuit FF ₁ by the conduction of the first transistor Q ₁ It is characterized by having a reset circuit which reverses the state to a non-conducting state.

The set circuit of the present invention comprises a second positive temperature coefficient thermistor PTH ₂ having an inflection temperature T ₂ lower than the inflection temperature T _{1 of} the first positive temperature coefficient thermistor PTH ₁ and its _second positive temperature coefficient. A second temperature-sensitive device in which the series circuit of the thermistor PTH ₂ and the resistor R ₄ is connected to a DC power source, and the emitter / base electrode of the second transistor Q ₄ is connected in parallel with the second positive temperature coefficient thermistor PTH _2. It can be replaced with a circuit having a switching circuit and a reheat command circuit for reversing the bistable circuit FF ₁ into a conductive state when the second positive temperature coefficient thermistor PTH ₂ becomes below the inflection temperature.

[0007] load driving circuit of the present invention, this was composed of the first bistable circuit FF ₁ and the load and the second series connection of bistable Teikairo FF _2, the bistable circuit FF ₂ of the second A driving start switch SW is provided in the set circuit that is made conductive, and a reset circuit that reverses the conductive state of the second bistable circuit FF ₂ to the non-conductive state is used as an inflection of the _first positive temperature coefficient thermistor PTH ₁ . a third positive characteristic thermistor PTH ₃ with high inflection temperature T ₃ than the temperature T _1, is configured to invert the second bistable circuit FF ₂ when the inflection temperature T ₃ or more be able to.

[0008]

[Action]

 As shown in the resistance-temperature characteristic curve of FIG. 4, the positive temperature coefficient thermistor PTH has a low resistance value in a temperature range below a predetermined inflection temperature T, and a resistance value rapidly increases above the inflection temperature T. It has the following characteristics. For example, the sensor PTH shown in FIG.₁And resistance R ₁ Series circuit is DC power supply V₊, GND when connected between V and GND, the potential V at the connection point (A)₁Is the power supply voltage E, sensor PTH₁The resistance value of R_SThen V₁= ER₁/ (R₁+ R_S). Sensor PTH₁When the temperature is low, the resistance value R_SIs small, the potential is V₁Is high and close to the positive pole V + of the power supply, but the sensor PTH₁If the temperature rises above the inflection temperature T, the resistance value R_SSuddenly increases, and therefore the potential V₁Will fall.

The first transistor Q ₁ is off when the potential of the base B is high, but is switched on when the potential of the base B, that is, the potential V ₁ decreases. The bistable circuit FF ₁ composed of _two transistors Q ₂ and Q ₃ has two transistors, a conductive state in which the _two transistors Q ₂ and Q ₃ are both in an ON state and a non-conductive state in which both transistors are in an OFF state. It can have a steady state and, when conducting, provides current to the load.

When the start switch SW is turned on even for a moment when the first transistor Q ₁ is turned off, the bistable circuit is set (trigger and firing are substantially the same meaning) to be in a conductive state. State is retained. When the first transistor Q ₁ is switched on in this conductive state, the emitter-base electrode of the transistor Q ₂ is short-circuited, and the bistable circuit is reset (turned off) to be in a non-conductive state. .

The invention described in the second item is to replace the set circuit with a circuit that outputs an automatic reheating command in place of the manual start switch SW. The reheating start temperature at this time is determined by the inflection temperature T ₂ of the second positive temperature coefficient thermistor PTH ₂ .

The invention according to the third aspect operates to prevent the dangerous situation by cutting off the power supply when the transistor Q ₆ of the reheat command circuit according to the second aspect has poor connection or disconnection. Mu.

The invention described in the fourth item is a circuit for preventing emptying, in which another bistable circuit FF ₂ is provided in series with a load, and a third positive temperature coefficient thermistor for detecting an emptying state is provided. When PTH ₃ exceeds the inflection temperature T ₃ , the second bistable circuit FF ₂ is reset.

[0014]

【Example】

FIG. 3 shows a circuit diagram of an embodiment of the present invention. In this embodiment, when the heating instruction switch is turned on, energization of the electric heater is started. For example, when the hot water in the pot boils, the positive temperature coefficient thermistor PTH ₁ detects this and the energization of the heater is stopped.

The positive temperature coefficient thermistor PTH ₁ is a sensor having resistance-temperature characteristics as shown in FIG. 4, and it is possible to select a sensor having a predetermined inflection temperature T ₁ . The value of the inflection temperature T ₁ varies depending on the position where the sensor is provided, and for example, when it is provided in a passage through which steam is ejected when boiling, it may be a low temperature of about 60 ° C.

A series circuit of the PTC thermistor PTH ₂ and the resistor R ₁ is connected between the DC power supplies V ₊ and GND, and the emitter / base electrode of the first transistor Q ₁ is connected in parallel with the PTC thermistor PTH _1. Then, these constitute the temperature sensing switching circuit 6. More specifically, the emitter electrode E of the PNP transistor Q ₁ is connected to the direct current power source V _+, and the base electrode B of the transistor Q ₁ is connected to the connection point (A) of both circuit elements PTH ₁ and R _1. ing. The temperature sensing switching circuit 6 is a reset circuit of the bistable circuit 3 described later.

The bistable circuit 3 (also called a flip-flip circuit) is a cross circuit of a PNP type transistor Q ₂ and an NPN type transistor Q ₃ (one connector is connected to the other base and the other collector is one side). It is connected to the base) and maintains two stable states: conductive state (set state or ignition state) and non-conduction state (reset state or extinguished state), and load 5 is connected to output line OUT. It is connected. The load 5 is an electric heater or a relay for controlling the electric heater. The bistable circuit 3 has two input lines, a set input line (S) and a reset input line (R), is set to be conductive when there is a set input, and is non-conductive when there is a reset input. Reset to state.

A set circuit 4 consisting of a series connection of a manually operable start-up switch SW and a resistor R ₂ is connected to a set input line (S) of a bistable circuit 3. This start-up switch SW is called a push switch. It is turned on for a moment when it is pressed, and automatically returns by the force of the spring when the pressing force disappears. Further, the collector electrode C of the transistor Q ₁ of the above temperature / pressure sensing switching circuit 6 is connected to the reset input line (R).

Next, the operation of this embodiment will be described. When the temperature of the positive temperature coefficient thermistor PTH ₁ is low, its resistance value is also small, and therefore the potential at the measuring point (A) is high and the first transistor Q ₁ is in the off state and there is no reset input. In this state, when the switch SW is turned on, the bistable circuit 3 is turned on and current is supplied to the load 5, and when the switch SW is turned off, the bistable circuit 3 is turned off. The current supply to the load 5 is cut off.

When the temperature of the positive temperature coefficient thermistor PTH ₁ rises above the inflection temperature T ₁ , its resistance value rapidly increases, and therefore the potential at the measurement point (A) decreases and the first transistor Q ₁ Turns from the off state to the on state. As a result, the voltage between the emitter and collector electrodes of the transistor Q ₁ decreases, and the bistable circuit 3 is forcibly reset and inverted to the non-conducting state.

FIG. 4 shows a circuit diagram of another embodiment of the present invention. This circuit is different from the embodiment of FIG. 3 in that the start-up switch SW that can be manually operated is replaced with an automatic setting circuit 7. Hereinafter, this difference will be described.

The second PTC thermistor PTH ₂ has a lower inflection temperature than that of the first PTC thermistor PTH ₁ when it is arranged at the same place as the _first PTC thermistor PTH ₁ , as shown in FIG. 5, for example. Thus, when the inflection temperature of the _first PTC thermistor PTH ₁ is, for example, 95 ° C., the inflection temperature of PTH ₂ is, for example, 70 ° C. The series circuit of the second positive temperature coefficient thermistor PTH ₂ and the resistor R ₄ is connected to the DC power source, and the intermediate connection point (B) between these two circuit elements is bistable via the transistor Q ₄ , the transistor Q ₅ and the resistor R _2. It is connected to the set input line of circuit 3.

[0023] Now, when the measured temperature is a first transistor Q ₁ is inverted from OFF to ON which are connected to the first PTC thermistor PTH ₁ is hot, naturally second Seitoku resistance thermistor PTH ₂ Is higher than its inflection temperature T ₂ , therefore the potential at the connection point (B) is high, the transistor Q ₄ is in the ON state, and the transistor Q ₅ is in the OFF state. As a result, the bistable circuit 3 stably holds the reset state, and no current is supplied to the load 5.

When the temperature of the controlled object falls and eventually falls below the inflection temperature T _{2 of} the second positive temperature coefficient thermistor PTH ₂ , the states of the transistors Q ₄ and Q ₅ are inverted, and the bistable circuit 3 Reverses to the set state. By repeating this, heating stop and reheat are repeated between the temperatures determined by the inflection temperatures T ₁ and T ₂ of the first and second positive temperature coefficient thermistors PTH ₁ and PTH ₂ .

FIG. 6 is a circuit diagram of a further improvement of the embodiment shown in FIG. This circuit differs from that shown in FIG. 4 in that a safety circuit 8 is added between the second positive temperature coefficient thermistor PTH ₂ , transistors Q ₄ and Q ₅ and the negative electrode GND of the DC power supply. . The added portion will be described below.

In the safety circuit 8, a resistor R ₅ is additionally connected between the second positive temperature coefficient thermistor PTH ₂ and the negative electrode GND of the DC power source, and the base / emitter electrode of the transistor Q ₆ is connected in parallel with the resistor R _5. B and E are connected, and the collector electrode C of the transistor Q ₆ is connected to the emitters of the transistors Q ₄ and Q ₅ via the diode DX. The diode DX may be omitted.

According to this embodiment, when the second positive temperature coefficient thermistor PTH ₂ is properly connected, the transistor Q ₆ is always in the on state, and the transistors Q ₄ and Q ₅ are normally turned on and off. However, in the unlikely event that the second PTC thermistor PTH ₂ is disconnected or unconnected, the transistor Q ₆ is turned off, and as a result, the transistor Q ₅ cannot be turned on. The effect of preventing a dangerous situation in which the bistable circuit 3 is uncommanded to set and the bistable circuit 3 is unconditionally set is set.

FIG. 7 shows a circuit diagram of still another embodiment of the present invention. In this embodiment, a blank prevention function is added to the embodiment shown in FIG. This additional part will be described below.

The third positive temperature coefficient thermistor PTH ₃ is provided for preventing emptying, and its inflection temperature T ₃ is higher than that of the above-mentioned first sensor PTH ₁ , and the AC power supply circuit It is lower than the temperature corresponding to the melting point of the provided thermal fuse. In other words, if the water heater reaches the boiling point with the first sensor PTH _{1, the} bistable circuit 3 should be reset and the current supply to the load 5 should be cut off, but the reset function should be activated due to some failure. If this is not done, the temperature is set to a temperature at which the current supply to the load 5 is cut off by the operation of this emptying prevention circuit before the thermal fuse blows due to overcurrent or the temperature rise of the equipment.

The series circuit of the third positive temperature coefficient thermistor PTH ₃ and the resistor R ₇ is connected to the DC power source, and the base emitter circuit of the transistor Q ₉ is connected in parallel with the third sensor PTH _3. . A second bistable circuit 9 composed of transistors Q ₇ and Q ₈ is connected between the load 5 and the negative electrode GND of the DC power supply. The input circuit of the bistable circuit 9 has a manual switch SW for heating command and a resistor R ₆ Of the series circuit 10 and the collector / emitter circuit of the transistor Q ₉ are connected. In this embodiment, the load 5 is connected to the DC power supply in series with the first bistable circuit 3 and the second bistable circuit 9, so that the currents of the transistors Q ₇ and Q ₈ of the second bistable circuit 9 are increased. A resistor R ₈ is provided for holding.

In this embodiment, in the normal case of not being empty, the resistance of the third sensor PTH ₃ is sufficiently low that the transistor Q ₉ is off. Therefore, if the heating command manual switch SW is turned on for a moment, the second bistable circuit 9 stably holds the conductive state and the load 5 is driven. However, when the third sensor PTH ₃ exceeds the inflection temperature, it is determined that it is in the empty state, the transistor Q ₉ is turned on, and the second bistable circuit 9 is forced to be in the non-conduction state. To do.

FIG. 8 shows a circuit diagram of an embodiment incorporating all the embodiments described above. The reference numerals in the drawings are the same as those in the above-mentioned drawings. It is obvious to those skilled in the art that details of the circuit may be modified, added, or deleted within the scope of achieving the same purpose in each embodiment of the present invention. It is also apparent to those skilled in the art that in each embodiment, the positive and negative polarities of the DC power supply are reversed and the transistors are replaced by the PNP type and the NPN type to have the same function and effect.

[0033]

[Effect of device]

 According to the present invention, the operational amplifier and the microcomputer are not used and the number of parts is small, so the reliability is very high and the manufacturing cost is significantly reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a conventional example.

FIG. 2 is a circuit diagram showing another conventional example.

FIG. 3 is a circuit diagram showing an embodiment of the device according to claim 1.

FIG. 4 is a circuit diagram showing an embodiment of the device according to claim 2.

FIG. 5 is a characteristic diagram of a positive temperature coefficient thermistor.

FIG. 6 is a circuit diagram showing an embodiment of the device according to claim 3.

FIG. 7 is a circuit diagram showing an embodiment of the device according to claim 4.

FIG. 8 is a circuit diagram of an embodiment in which the embodiments of FIGS. 3, 4, 6, and 7 are integrated.

[Explanation of symbols]

PTH ₁ ... First positive characteristic thermistor PTH ₂ ... Second positive characteristic thermistor PTH ₃ ... Third positive characteristic thermistor 3 ... (First) bistable circuit 4・ ・ ・ Set circuit 5 ・ ・ ・ ・ Load 6 ・ ・ ・ Temperature sensitive switching circuit 7 ・ ・ ・ ・ Automatic set circuit 8 ・ ・ ・ ・ Safety circuit 9 ・ ・ ・ ・ ・ ・ Second bistable circuit

Claims (4)

[Scope of utility model registration request] 1. A DC power supply comprising a first positive temperature coefficient thermistor (PTH ₁ ) arranged at a position where a temperature is to be measured and a series circuit of the first positive temperature coefficient thermistor (PTH ₁ ) and a resistor (R ₁ ). The first positive temperature coefficient thermistor (PTH)
₁ ) in parallel with the emitter of the first transistor (Q ₁ )
A temperature sensitive switching circuit with a base electrode connected,
A load drive circuit for supplying a current to a load through a bistable circuit composed of _two transistors (Q ₂ , Q ₃ ), a set circuit for bringing the bistable circuit (FF ₁ ) into a conductive state, and the first transistor ( A temperature control circuit having a reset circuit for reversing the conduction state of the bistable circuit (FF ₁ ) to the non-conduction state by conduction of Q ₁ ). 2. The second positive temperature coefficient thermistor (PTH), wherein the set circuit has an inflection temperature (T ₂ ) lower than an inflection temperature (T ₁ ) of the first positive temperature coefficient thermistor (PTH ₁ ).
₂ ) and a series circuit of the second positive temperature coefficient thermistor (PTH ₂ ) and the resistor (R ₄ ) are connected to a DC power source, and the second transistor (QH ₂ ) is connected in parallel with the second positive temperature coefficient thermistor (PTH ₂ ). ₂ ) The emitter and base electrodes of ₄ ) are connected
And a reheat command circuit for reversing the bistable circuit (FF ₁ ) to a conductive state when the second positive temperature coefficient thermistor (PTH ₂ ) becomes below the inflection temperature. The temperature control circuit according to claim 1. 3. A parallel circuit of a resistor (R ₅ ) and a transistor (Q ₆ ) is connected in series on the DC power source side common to the second temperature sensitive switching circuit and the reheat command circuit. The temperature control circuit according to 2. 4. The load drive circuit is a first bistable circuit.
(FF₁), The load, and the second bistable circuit (FF₂) In series
This second bistable circuit (FF ₂) Conducted
Manual start switch (SW) is installed in the set circuit
This second bistable circuit (FF₂) Non-conductive
The reset circuit for reversing the conduction state is the first feature
Sex thermistor (PTH₁) Inflection temperature (T₁) Higher than
Inflection temperature (T₃) With a third positive temperature coefficient thermistor (P
TH₃), And the inflection temperature (T₃) When more than the above
Second bistable circuit (FF₂) Is configured to invert
The temperature control circuit according to claim 2, wherein