JPH05196511A - Temperature window circuit - Google Patents

Abstract

PURPOSE:To obtain the title circuit which monitors the temperature of electronic equipment, etc., and outputs an abnormal temperature detecting signal as an abnormal temperature when the temperature of the equipment, etc., exceeds a set range by using one thermistor and one transistor against each temperature set as an upper and lower limits, improving the thermistor and transistor from the point of cost and performance, and giving an inexpensive, sure, and highly accurate temperature detecting function to the circuit. CONSTITUTION:The title circuit is constituted of one thermister TH, two comparators A and B, and a plurality of voltage dividing resistors R1-R7 and compares the variation of the voltage across both ends of the thermister TH caused by the ambient temperature with a set voltage range at a preset temperature. When the temperature of electronic equipment, etc., is higher than the preset temperature, the comparator A outputs an abnormal low temperature detecting signal. When the temperature of the equipment, etc., is lower than the preset temperature, the comparator B outputs an abnormal low temperature detecting signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature window circuit used for temperature monitoring of electronic equipment and the like.

[0002]

2. Description of the Related Art Conventionally, a circuit that monitors the temperature of electronic equipment and outputs an abnormal temperature detection signal as an abnormal temperature when the temperature is out of a set range has a temperature limit set to a lower limit and an upper limit. On the other hand, one thermistor and one transistor were used.

A temperature window circuit in the above conventional example will be described with reference to FIG. In the figure, Q1 and Q2 are transistors, TH1 and TH2 are thermistors, and R11 to R
14 is a resistance. When the temperature becomes higher than the selected range, the resistance of the thermistor TH2 becomes low and the transistor Q2
The base potential of becomes high and turns on. That is, the collector current of the transistor Q2 flows through the resistors R12 and R13 and outputs a low abnormal temperature detection signal. Further, when the temperature becomes lower than the selected range, the resistance of the thermistor TH1 becomes high and the base potential of the transistor Q1 also becomes high, so that the transistor Q1 is turned on. That is, the collector current of the transistor Q1 flows through the resistors R12 and R13 and outputs a low abnormal temperature detection signal.

[0004]

However, since the conventional temperature window circuit uses the transistor, there is a problem that the operating temperature depends on the variation of the transistor. In addition, it is not satisfactory in terms of price, such as using two expensive thermistors. At present, there is an increasing demand for devices such as chargers that operate only within a predetermined temperature range, and in order to meet such market demands, inexpensive and reliable temperature window circuits are required. Was there.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a temperature window circuit which is inexpensive, operates reliably, and has a highly accurate detection function.

[0006]

In order to solve the above-mentioned problems, the temperature window circuit according to the present invention includes one temperature window circuit which outputs an abnormal temperature detection signal when an abnormal temperature out of a set temperature range is detected. Comprised of a thermistor, two comparators, and multiple voltage divider resistors, the voltage change across the thermistor caused by ambient temperature is compared with the preset voltage range at the preset temperature It is characterized by outputting an abnormal temperature detection signal.

[0007]

[Operation] One thermistor, two comparators,
It is composed of a plurality of voltage dividing resistors. The voltage change across the thermistor caused by the ambient temperature is compared with a preset voltage range at a preset temperature, and if the temperature is out of that range, the first comparator outputs a low abnormal temperature detection signal. Further, the voltage is compared with a preset voltage range at a preset temperature, and if the temperature is out of the preset range, the second comparator outputs a low abnormal temperature detection signal.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a temperature window circuit of the present invention. In the figure, TH is a thermistor, A is a comparator for high temperature detection, B is a comparator for low temperature detection, and R1.
~ R7 is a resistance. Vcc is a reference voltage, which is a power supply voltage of this circuit. When the temperature is within the set range, the outputs from the comparators A and B are high. When the temperature is outside the set range, the comparator A or the comparator B outputs a low abnormal temperature detection signal.

Next, an operation for detecting a high temperature when the temperature is higher than the set range will be described. Let R1 = R5. If the resistance of the thermistor TH at the detection temperature is RTH, R6 =
Set to RTH + R2. The high temperature detection setting voltage VH is applied to the negative terminal of the comparator A as a comparison voltage. VH = Vcc × R6 / (R5 + R6). The thermistor T applied to the positive terminal of the comparator A
If the voltage on the H side is VTH, VTH = Vcc × (RT
H + R2) / (R1 + RTH + R2). When the temperature becomes high, the resistance RTH of the thermistor TH becomes low. Therefore, VTH applied to the positive side terminal of the comparator A becomes lower than the high temperature detection setting voltage VH applied to the negative side terminal, and the comparator A outputs a low abnormal temperature detection signal. Is output.

Further, the operation for low temperature detection when the temperature is lower than the set range will be described. Let R2 = R4. If the resistance of the thermistor TH at the detection temperature is RTH, R3
= RTH + R1 is set. The low temperature detection setting voltage VL is applied to the negative terminal of the comparator B as a comparison voltage. VL = Vcc × R4 / (R3 + R4).
If the voltage on the thermistor TH side applied to the positive terminal of the comparator B is VTL, then VTL = Vcc × R2
/ (R1 + RTH + R2). When the temperature becomes low, the resistance RTH of the thermistor TH becomes high, so that the VTL applied to the positive terminal of the comparator B becomes lower than the low temperature detection setting voltage VL applied to the negative terminal, and the comparator B outputs a low abnormal temperature detection signal. Is output. Above 2
One circuit can output a low abnormal temperature detection signal outside the set range of high temperature and low temperature, and can be used as a temperature control signal of the device. Further, by changing the input terminal of the comparator, high can be used as the abnormal temperature detection signal.

FIG. 2 shows the voltage applied to the positive terminal of each comparator with respect to temperature. The horizontal axis represents temperature and the vertical axis represents the voltage applied to the positive terminal of each comparator. The thick line H indicates the voltage applied to the positive terminal of the comparator A that detects high temperature, and the broken line L
Indicates the voltage applied to the positive terminal of the comparator B that detects a low temperature. Set the temperature range from 0 ℃ to 40
If it is ℃, abnormal temperature of high temperature is detected at the point Δ on the vertical axis,
An abnormal low temperature is detected at point ○.

[0012]

As described above, the temperature window circuit according to the present invention is composed of one thermistor, two comparators and a plurality of voltage dividing resistors, and changes in voltage across the thermistor caused by ambient temperature. Is compared with the preset voltage range at the preset temperature, and if it is out of that range, an abnormal temperature detection signal is output, so it is inexpensive and reliable in operation, has a highly accurate detection function, and has a charger. It is ideal for monitoring the temperature of equipment that operates only within the set temperature range.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a temperature window circuit of the present invention.

FIG. 2 is a characteristic table showing a voltage applied to a plus side terminal of each comparator with respect to temperature.

FIG. 3 is a circuit diagram of a temperature window circuit in a conventional example.

[Explanation of symbols]

 R1 to R7 resistance TH thermistor A and B comparator R11 to R14 resistance TH1 and TH2 thermistor Q1 and Q2 transistor

Claims (1)

[Claims] 1. A temperature window circuit which outputs an abnormal temperature detection signal when an abnormal temperature out of a set temperature range is detected. The temperature window circuit includes one thermistor, two comparators, and a plurality of voltage dividing resistors. A temperature window circuit characterized in that a voltage change across the thermistor caused by ambient temperature is compared with a preset voltage range at a preset temperature, and an abnormal temperature detection signal is output if the voltage range deviates from the preset voltage range.