JPH0619011U - Temperature control circuit - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain a temperature control circuit that detects a wire breakage abnormality of a thermistor element having a large room temperature resistance value. A heating device, a thermistor element 3 that detects the temperature of the heating device, a voltage comparison element 6 that controls energization to the heating device by a detection voltage C obtained by dividing the power supply voltage A by a resistor 4, and the detection voltage. In the temperature control circuit including the voltage comparator 9 that outputs the disconnection signal G when C is input and the thermistor element 3 is disconnected, the temperature control circuit includes the timed signal generation circuit that outputs the timed signal H until the timed signal is output. Regardless of whether the thermistor element is disconnected for a predetermined time, the heating device is energized, the resistance value of the thermistor element 3 becomes small, the temperature control circuit operates normally, and the disconnection of the thermistor element can be detected. Even with the thermistor element 3 having an extremely large number, the disconnection can be easily detected.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an improvement in a temperature control circuit that detects a wire breakage abnormality of a thermistor element used for temperature control of a heating device and stops energization to the heating device when the element is broken.

[0002]

[Prior art]

 FIG. 2 shows a conventional temperature control circuit using a thermistor element.

Reference numeral 3 is a thermistor element that detects the temperature of a heating device (not shown). Reference numeral 6 is a voltage comparison element, which inputs a detection voltage C obtained by dividing the voltage by the thermistor element 3 and the resistor 4 to a (-) terminal, and a reference voltage B obtained by dividing the power source voltage A by the resistors 1 and 2. The voltage is input to the (+) terminal, both voltages B and C are compared, and a control signal is output. Reference numeral D9 is a voltage comparison element. The reference voltage D obtained by dividing the power supply voltage A by the resistors 7 and 8 is input to the (+) terminal, the detection voltage C is input to the (-) terminal, and both voltage C , D are compared and a disconnection signal G is output. Reference numeral 10 is a transistor for controlling the heating device, and a base terminal thereof is connected with a control signal output of the voltage comparison element 6 and a transistor 11 for bypassing the signal to ground. The disconnection signal G output of the voltage comparison element 9 is connected to the base terminal of the transistor 11. Reference numeral 14 is a power supply that generates a power supply voltage A. Reference numeral 20 is a load driving circuit for driving the heating device.

The operation of the circuit having the above configuration will be described below.

The voltage comparison element 6 stops the control signal when (reference voltage B <detection voltage C), and outputs a control signal otherwise (control signal to the heating device via the transistor 10). To switch. When the resistance value of the thermistor element 3 changes due to the temperature change due to the heat of the heating device, the detection voltage C changes, and the operation of the voltage comparison element 6 controls the heating device to a predetermined control temperature.

The voltage comparison element 9 stops the disconnection signal G when (reference voltage D <detection voltage C), and otherwise outputs the disconnection signal G. When the thermistor element 3 is normal, the sizes of the resistors 7 and 8 are set so that the reference voltage D is slightly lower than the detection voltage C at room temperature. Therefore, when the thermistor element 3 is disconnected, the above-mentioned detection voltage C becomes almost zero, so that the voltage comparison element 9 outputs the disconnection signal G, and the transistor 11 grounds the base input of the transistor 10, and as a result, The transistor 10 keeps the control signal in the stopped state, and the heating device is de-energized.

[0007]

[Problems to be solved by the device]

 When a high operating temperature element is used for the thermistor element 3 such as when the control temperature of the heating device is relatively high, the resistance value at room temperature may become several megohms or more. In that case, the detection voltage C Becomes extremely low, and when the detection voltage C is raised to some extent, the value of the resistor 4 becomes large and does not match the resistance value of the thermistor element 3 at the operating temperature, so the temperature control circuit does not operate normally. There is a problem that the disconnection of the thermistor element 3 cannot be detected.

[0008]

[Means for Solving the Problems]

 The present invention has been made to solve the above problems, and energizes the heating device by a detection voltage obtained by dividing the power supply voltage by a heating device, a thermistor element that detects the temperature of the heating device, and a resistor. In the temperature control circuit, which includes a voltage comparison element to control and a voltage comparison element that outputs a disconnection signal when the detection voltage is input and the thermistor element is disconnected, a timed signal generation circuit that outputs a timed signal, and When the time signal is output from the time signal generation circuit, if the disconnection signal is output, the logic circuit that stops the energization of the heating device is provided.

[0009]

[Action]

 In the above temperature control circuit, the thermistor element is heated by the heating device and its temperature rises during the required time after the start of energization until the time limit signal is output. It is set to the time required for the value to operate normally. When the temperature control circuit and the heating device are connected to the power supply, the heating device is energized for a certain period of time until the timed signal is output, regardless of the disconnection of the thermistor element. Therefore, if the thermistor element is normal, its resistance value decreases to a desired value during this period, and the temperature control circuit operates normally with respect to the heating device. If the thermistor element is disconnected, its resistance value does not decrease to the desired value, and the logic circuit logically judges that the time signal and disconnection signal were output simultaneously, and the temperature control circuit The control signal is held in a stopped state, and the power supply to the heating device remains stopped.

[0010]

【Example】

 An embodiment of the present invention will be described with reference to FIG. However, the parts described in the conventional example are omitted.

Reference numeral 18 denotes a time signal generation circuit, the circuit configuration of which will be described below.

Reference numeral 18a denotes a voltage comparison element that generates a timed signal H. A reference voltage E obtained by dividing the voltage by the resistors 16 and 17 is input to the (+) terminal of the voltage comparison element 18a, and (- The differential voltage F 1 obtained by voltage division by the capacitor 5 and the resistor 15 is input to the terminal). A charge discharge circuit in which a resistor 12 and a diode 13 are connected in series is connected to the capacitor 5 in parallel.

Next, reference numeral 19 is a logic circuit for stopping energization to the heating device when the disconnection signal G is output from the voltage comparison element 9 when the time signal H is output from the time signal generation circuit 18. Is.

Next, the operation of this embodiment will be described.

When power is supplied to the temperature control circuit from the power source 14, initially, the differential voltage F is substantially equal to the power source voltage A, and after a predetermined time (reference voltage E <differential voltage F), the voltage comparison element 18a The time signal H is not output. Therefore, the output of the logic circuit 19 is in a stopped state, the transistor 11 is in a non-conductive state, the control signal output of the voltage comparison element 6 is transmitted to the heating device regardless of the disconnection of the thermistor element 3, and the heating device is kept for a predetermined time. Be charged. During this time, the temperature of the thermistor element 3 rises and its resistance value decreases, so that the temperature control circuit operates normally and detects disconnection of the thermistor element 3.

The differential voltage F gradually decreases as the charging of the capacitor 5 progresses, and eventually (reference voltage E> differential voltage F), the voltage comparison element 18 a outputs the timed signal H. Since the time required until the time signal H is output is set to the initial value as described above, if the disconnection signal G is output when the time signal H is output, the output of the logic circuit 19 is output. Is in an operating state, the transistor 11 is in a conductive state, and the base terminal of the transistor 10 is grounded. Therefore, the control signal output of the voltage comparison element 6 is not transmitted to the heating device, and the heating device is not energized. The discharge circuit consisting of the resistor 12 and the diode 13 outputs the timed signal H immediately when the circuit power supply is turned on and off frequently, so that the electric charge of the capacitor 5 is slowly changed so as not to unnecessarily energize the heating device. It is something to discharge.

By appropriately setting the speed of heating the thermistor element 3 of the heating device, the reference voltage D, and the time required for the time signal generation circuit 18 to output the time signal H, the room temperature resistance of the thermistor element 3 is small. It is possible to reliably detect not only disconnection of the thermistor element 3 but also abnormality such as disconnection of the connection circuit and disconnection of the connection element, from a large one to an extremely large one.

If the power supply voltage applied to the voltage dividing circuit by the capacitor 5 and the resistor 15 is pulsed, the time required to output the time-limited signal H can be lengthened, and a positive temperature coefficient thermistor can be used as the thermistor element 3. When used, part of the positive and negative polarities of the circuit can be changed to operate in the same manner as in this embodiment.

Furthermore, by converting various control signals to the load drive circuit 20, the energy source of the heating device can be selected from a wide variety of different types such as electricity, gas, or liquid fuel.

[0020]

[Effect of device]

 According to the present invention, the heating device is energized for a predetermined time until the time signal generating circuit outputs the time signal, and the heating temperature of the thermistor element is raised to some extent to easily determine whether the resistance value is a disconnection or normal. Since the disconnection is detected after changing the value, the temperature control circuit operates normally and detects the disconnection of the thermistor element.

Therefore, it is possible to provide a temperature control circuit capable of easily detecting disconnection abnormalities of the thermistor element having a small resistance value to an extremely large resistance value at room temperature by using a small amount of inexpensive parts.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of a temperature control circuit according to an embodiment of the present invention.

FIG. 2 is an electric circuit diagram of a temperature control circuit showing a conventional example.

[Explanation of symbols]

 3 Thermistor element 4 Resistance 5 Capacitor 6 Voltage comparison element 9 Voltage comparison element 18 Time limit signal generation circuit 19 Logic circuit A Power supply voltage C Detection voltage G Disconnection signal H Time limit signal

Claims (1)

[Scope of utility model registration request] 1. A heating device, a thermistor element (3) for detecting the temperature of the heating device, and a resistor (4) are used to energize the heating device by a detection voltage (C) obtained by dividing the power supply voltage (A). A temperature control circuit comprising a voltage comparison element (6) to be controlled and a voltage comparison element (9) which inputs the detection voltage (C) and outputs a disconnection signal (G) when the thermistor element (3) is disconnected. A time signal generator (18) for outputting a time signal (H), and the disconnection signal (G) when the time signal (H) is output from the time signal generator (18)
And a logic circuit (19) for stopping the energization of the heating device when is output.