NTC temperature detection circuit

Abstract

The utility model discloses an NTC (Negative Temperature Coefficient) temperature detection circuit, which belongs to the technical field of temperature measurement and is applied to temperature measurement circuits and related products. The NTC thermistor solves the problem that in the prior art, the linear working temperature interval is small, the total output resistance of the NTC thermistor can keep a good linear relation with the temperature in a wide working temperature range, and the NTC thermistor is characterized in that at least two or more NTC thermistors are connected in series with a common resistor with a fixed resistance value and then connected in parallel; the resistance values of all the NTC thermistors at the normal temperature are different, the resistance values of the common resistors connected with the NTC thermistors with the small resistance values in series at the normal temperature are large, the resistance values of the common resistors connected with the NTC thermistors with the large resistance values at the normal temperature are small, and the resistance values of the common resistors connected with the NTC thermistors with the large resistance values at the normal temperature can be zero.

Description

Technical Field

[0001] The utility model relates to a circuit structure, in particular to the technical field of temperature measurement, and in particular to a linear processing circuit for measuring temperature by adopting an NTC thermistor. Background Art

[0002] Since the birth of NTC (Negative Temperature Coefficient) thermistors, due to their sensitive output signals, good process consistency and low cost, they have been widely used in various electronic and electrical products, such as refrigerators, air conditioners, rice cookers, soybean milk machines and other daily household appliances. They are also widely used as temperature sensors in automobiles, such as coolant temperature sensors, intake temperature sensors, exhaust temperature sensors, fuel temperature sensors, etc. However, due to the serious nonlinear characteristics of their resistance and temperature, the further application of NTC thermistors is hindered. For this reason, a large number of scientific and technical personnel have conducted many related technical research and tests. For example, the literature [1] Wang Yanhui, Zhang Jiao, Wang Qi, et al. Research on the linearization of NTC thermistor temperature measurement using the series-parallel resistance method [J]. Physics and Engineering, 2017, 27 (Z1): 256-259. The series-parallel resistor method achieves the accuracy requirements for engineering applications within a certain temperature range; however, the series-parallel resistor method only performs a certain degree of linear correction within a smaller temperature range. For example, in reference [2] Shi Longzhao, Yang Xiaoling, Wu Shuishun. Design of NTC-thermistor series and parallel temperature compensation circuit [J]. Journal of Fuzhou University (Natural Science Edition), 2003, 31(08): 417-420, the authors pointed out at the end of the article that the linear processing temperature range they used was about 40°C, which could not meet the wide operating temperature requirements in people's living environment.

[0003] The functional relationship between the resistance value and temperature of NTC thermistor can be approximately expressed as:

[0004] Rt = R T0 *e (Bn*（1 / t-1 / T0)）

[0005] Where Rt, R T0 are the resistance values ​​at temperatures t and T0 respectively, Bn is the material constant, and temperatures t and T0 are the absolute temperature values. Summary of the invention

[0006] The present application proposes a circuit structure, the total output resistance of which can maintain a good linear relationship with the temperature within a wide operating temperature range, with low cost and wide adaptability.

[0007] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0008] An NTC temperature detection circuit, characterized in that: it comprises at least two groups of temperature detection circuits, each group of temperature detection circuits is composed of an NTC thermistor connected in series with an ordinary resistor (fixed resistor), and all groups of temperature detection circuits are connected in parallel;

[0009] The NTC thermistors used in each temperature detection circuit have different resistance values ​​at room temperature. The NTC thermistors with larger resistance values ​​at room temperature have smaller resistance values ​​in series with the temperature detection circuits in which they are located; the NTC thermistors with smaller resistance values ​​at room temperature have larger resistance values ​​in series with the temperature detection circuits in which they are located.

[0010] Among the groups of temperature detection circuits, the group of temperature detection circuits in which the NTC thermistor has the largest resistance at room temperature may not be connected in series with an ordinary resistor (fixed resistor), that is, there is only one NTC thermistor. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a circuit diagram of the utility model;

[0012] Figure 2 This is a typical resistance-temperature curve of an NTC thermistor;

[0013] Figure 3 The resistance value and temperature scatter plot of Example 1 and its related linear trend line;

[0014] Figure 4 The resistance and temperature scatter plot of Example 2 and its related linear trend line;

[0015] Figure 5 This circuit is a typical application circuit used in a battery charger. DETAILED DESCRIPTION

[0016] In order to make the technical means and effects of the utility model easier to understand, they are further described below in conjunction with specific embodiments.

[0017] Example 1

[0018] The NTC thermistor devices produced by Murata Manufacturing Co., Ltd. (referred to as Murata) are large in batches and have stable production processes. This embodiment uses the NTC thermistor of Murata. The electrical parameters and descriptions in the circuit are as follows:

[0019] Rntca and Rntcb are NTC thermistors, where Rntca is an NTC with a resistance of 1.0 kΩ at a B value of 3500K at room temperature, and Rntcb is an NTC with a resistance of 100 kΩ at a B value of 4250K at room temperature; the remaining resistors are ordinary resistors, Rpa is 47.0 kΩ, and Rpb is 8.2 kΩ;

[0020] Rntca and Rpa are connected in series to form the first temperature detection circuit, Rntcb and Rpb are connected in series to form the second temperature detection circuit. AB It refers to the total resistance between points A and B. The relevant data table of resistance and temperature in this embodiment is as follows (the unit of resistance is kΩ):

[0021]

[0022] As shown in the table above, the temperature-resistance data is analyzed by the univariate linear regression analysis method in the literature [3] Li Jiulong, Li Ling, Liu Ruimin, et al. Application of univariate linear regression analysis method in pressure sensor data fitting [J]. Measurement Technology, 2022, 42 (2): 40-49. The total resistance R AB The relationship between resistance and temperature is analyzed, and the characteristic curve of resistance and temperature of this embodiment is as follows: Figure 3 As shown, the horizontal axis unit is ℃, the vertical axis unit is kΩ, and the total resistance is highly linearly related to the temperature, and the relationship is:

[0023] y = - 0.4299x + 43.83, where x is the temperature in degrees Celsius and y is the total resistance.

[0024] Example 2

[0025] This embodiment uses Murata's NTC thermistor, and the electrical parameters and descriptions in the circuit are as follows:

[0026] Rntca and Rntcb are NTC thermistors, where Rntca has a B value of 4250K and a resistance value of 470 kΩ at room temperature, and Rntcb has a B value of 3500K and a resistance value of 4.7 kΩ at room temperature; the remaining resistors are ordinary resistors, Rpa is 0 kΩ, and Rpb is 68 kΩ;

[0027] Rntca and Rpa are connected in series to form the first temperature detection circuit, Rntcb and Rpb are connected in series to form the second temperature detection circuit. AB It refers to the total resistance between points A and B. The relevant data table of resistance and temperature in this embodiment is as follows (the unit of resistance is kΩ):

[0028]

[0029] Similarly, analyze the total resistance R AB The relationship between resistance and temperature is shown in the following figure. Figure 4 As shown, the horizontal axis unit is ℃, the vertical axis unit is kΩ, and the total resistance is highly linearly related to the temperature, and the relationship is:

[0030] y = - 0.6065x + 77.95, where x is the temperature in degrees Celsius and y is the total resistance.

[0031] The above embodiments clearly describe the technical solution features of this circuit structure; it is obvious that the total resistance of this circuit structure changes linearly with the temperature change. In the actual application circuit, only a constant total DC working current needs to be provided to generate a DC voltage that changes linearly with the temperature in the circuit;

[0032] like Figure 5 The figure shows a typical application circuit of this circuit structure in a battery charger. The reference terminal in the figure is also called the reference input terminal. It is obvious to the technicians in this industry that exchanging the electrical positions of some components in this circuit or connecting the resistors Ra, Rb in parallel or in series are all completely equivalent circuits of this circuit. When applied to a battery charger, Figure 5 Compared with the prior art such as the circuit in patent application 202021206114.9, the circuit shown can obtain a more ideal linear compensation voltage output within a wider temperature range, and can better meet the requirements for chargers in Appendix B lead-acid battery charger temperature compensation of GB / T36944-2018.

[0033] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and the description in the specification are only to illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected, such as using a thick film (integrated) circuit manufacturing method to package the present circuit structure into a separate electronic component. The scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. An NTC temperature detection circuit, characterized in that: The invention comprises at least two groups of temperature detection circuits, each group of temperature detection circuits is composed of an NTC thermistor connected in series with an ordinary resistor with a fixed resistance; all the temperature detection circuits are connected in parallel; in each group of temperature detection circuits, the resistance values ​​of the NTC thermistors at normal temperature are different, the NTC thermistor with a smaller resistance value at normal temperature and the ordinary resistor connected in series with the temperature detection circuit where it is located has a larger resistance value; the NTC thermistor with a larger resistance value at normal temperature and the ordinary resistor connected in series with the temperature detection circuit where it is located has a smaller resistance value.

2. The NTC temperature detection circuit according to claim 1, characterized in that: In each temperature detection circuit, the NTC thermistor with the largest resistance at room temperature has a resistance of 0, that is, the temperature detection circuit has only one NTC thermistor.

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