JP2001165783A - Temperature detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve temperature detection that is strong against noise and accurately and stably changes temperature into signals. SOLUTION: A comparator 8 is switched by the resistance value of a thermistor 2 that is changed by temperature change, and a reference voltage 5, and then a signal is sent to a shift register 11. An AND circuit 12 receives input from the shift register 11, and outputs a 'H' signal from an output terminal 7 only when the comparator 8 continues to output the 'H' signal while a clock being inputted from a clock signal input terminal 9 is inputted for three times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature detecting circuit for accurately and stably converting a temperature detected by a thermistor into a signal.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor integrated circuit for detecting temperature, a comparator with hysteresis has been provided in consideration of the influence of noise in order to signal the temperature detected by a thermistor.

Hereinafter, a conventional temperature detecting circuit will be described.

FIG. 3 is a circuit diagram of a conventional temperature detecting circuit. One end of a thermistor 2 is connected to a power supply terminal 1, and the other end of the thermistor 2 is connected to one end of a resistor 3 and an input terminal of a comparator 6 with hysteresis. The other end of the resistor 3 and one end of the reference voltage 5 are connected to the ground terminal 4, and the other end of the reference voltage 5 is connected to the reference input terminal of the comparator 6 with hysteresis. The output is connected to the output terminal 7.

[0005]

However, in the structure of the conventional temperature detecting circuit, the voltage determined by the thermistor 2 and the resistor 3 is close to the same potential as the reference voltage 5 to prevent chattering. Since the detection was performed by the comparator 6, the error was likely to occur.

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a temperature detection circuit which is resistant to noise and can generate a signal with high accuracy and stability.

[0007]

In order to achieve the above object, a temperature detecting circuit according to the present invention comprises a power supply terminal connected to one end of a thermistor, and the other end connected to one end of a resistor and an input of a comparator. Connecting a reference voltage to a reference input of the comparator, connecting the other end of the resistor and the other end of the reference voltage to a ground terminal, connecting a clock signal input terminal to a shift register, and a reset signal input terminal. Is connected to the shift register, each output of the shift register is connected to an input of an AND circuit, and an output of the AND circuit is connected to an output terminal. Since the signal can be detected after a certain period of time using the shift register, it is resistant to noise and can perform highly accurate and stable detection.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram for explaining an embodiment of the present invention. One end of a thermistor 2 is connected to a power supply terminal 1, and the other end of the thermistor 2 is connected to one end of a resistor 3 and a comparator 8 having no hysteresis. , The reference voltage 5 is connected to the reference input of the comparator 8, the other end of the resistor 3 and the other end of the reference voltage 5 are connected to the ground terminal 4, and three clock signal input terminals 9 are provided. , And the reset signal input terminal 10 is connected to the shift register 11, and each output of the shift register 11 is connected to the input of the AND circuit 12.
The output of the ND circuit 12 is connected to the output terminal 7.

In this embodiment having the above-described configuration, the comparator 8 is accurately switched by the resistance value of the thermistor 2 and the reference voltage 5 which change due to a temperature change, and a signal is sent to the shift register 11. In this example, while receiving the input from the clock signal input terminal 9, the clock input from the clock signal input terminal 9 is input three times, and only when the comparator 8 continues to output the "H" signal, the "H" signal is output from the output terminal 7. Is output.

As described above, the signal detected by the comparator 8 is detected by the shift register 11 after a lapse of a certain period of time, so that the temperature can be detected stably against noise and the comparator 8 has no hysteresis. I can do it.

In the circuit example of FIG. 1, the shift register 11 is constituted by three flip-flops. However, as shown in FIG. 2, more (N) flip-flops are provided. By constructing a shift register by connecting a plurality of shift registers or connecting a plurality of shift registers, the signal output from the comparator 8 can be detected more stably.

Further, by making the frequency of the clock output from the clock signal input terminal 9 variable according to the circuit configuration, the signal output from the comparator 8 can be detected more stably. .

[0014]

As described above, according to the present invention,
By detecting the signal detected by the comparator after a certain period of time by the shift register, it is possible to realize a temperature detection circuit that is highly stable against noise as temperature detection and has no hysteresis in the comparator, so that highly accurate temperature detection can be performed. .

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a modification of the embodiment.

FIG. 3 is a circuit diagram of a conventional temperature detection circuit.

[Description of Signs] 1 power supply terminal 2 thermistor 3 resistor 4 ground terminal 5 reference voltage 7 output terminal 8 comparator 9 clock signal input terminal 10 reset signal input terminal 11 shift register 12 AND circuit

Claims (4)

[Claims] 1. An end of a thermistor is connected to a power terminal,
The other end of the thermistor is connected to one end of a resistor and an input of a comparator, a reference voltage is connected to a reference input of the comparator, the other end of the resistor and the other end of the reference voltage are connected to a ground terminal, A clock signal input terminal is connected to the shift register, a reset signal input terminal is connected to the shift register, each output of the shift register is connected to an input of an AND circuit, and an output of the AND circuit is connected to an output terminal. A temperature detection circuit characterized by the above-mentioned. 2. The temperature detection circuit according to claim 1, wherein said comparator is not a comparator with hysteresis. 3. The temperature detection circuit according to claim 1, wherein a plurality of said shift registers are connected. 4. The temperature detection circuit according to claim 1, wherein the frequency of the clock is changeable.