The hottest tmp01 temperature controller and its a

Tmp01 temperature controller and its application

Abstract: This paper introduces the working principle of tmp01 programmable temperature controller and the setting method of control points, and analyzes the typical application circuit of tmp01 in temperature control and transmission

key words: temperature controller; AD654VFC； Introduction to Darlington transistor

1

tmp01 temperature controller is a low-power programmable temperature controller produced by American ad company. It has two degradable packages: 8-pin dual in-line and surface mount, which are convenient for both buyers and sellers to package. The working temperature range is - 55 ℃. The speed of the motor is changed to + 85 ℃, and the single voltage of 4.5V ~ 13.2v works. The chip can generate a DC voltage signal proportional to the temperature. When the measured temperature is higher or lower than the set temperature trigger point, a control signal is generated from one of the two output terminals respectively. The setting of the temperature point can be achieved by selecting an external resistance. The temperature control accuracy of the controller can reach ± 1 ℃, and the control signal output load capacity can reach 20mA, which can be used to control a variety of devices

2 working principle

tmp01 is a temperature sensor with linear voltage output. Its composition principle is shown in Figure 1. The voltage reference terminal VREF can output a low drift 2.5V reference voltage, and the voltage signal proportional to the absolute temperature is output at the vptat terminal. The temperature coefficient is 5mv/K and 1.49v at 25 ℃. The two comparators can compare the external high and low temperature set point voltage (sethigh, Setlow) with the internal temperature sensor voltage respectively; When the temperature measured by the internal sensor is higher or lower than the temperature trigger point set by the external resistance, an open circuit output signal is generated at the over or under end to start the external heating or cooling device to work, so as to realize the dual temperature automatic control function

tmp01 temperature controller is internally equipped with temperature hysteresis module. A 1K Ω resistor is used at the input end of the comparator to generate a hysteresis offset voltage to realize temperature hysteresis. An appropriate external resistor is selected to control the internal hysteresis current (ihys) and set the degree of hysteresis temperature. After setting the hysteresis temperature, the output of the comparator can be started or reset only when the input of the internal comparator is equal to the sum of the temperature sensor voltage and the hysteresis offset voltage

the relationship between internal hysteresis current (ihys) and external temperature setting reference terminal current (ivref) is as follows:

ihys = ivref = 5 μ A／℃＋7 μ A

because VREF = 2.5V, when the reference load resistance is 357k Ω or greater (the output current is 7 μ A or less), with a temperature lag of 0 ℃. If the load resistance value is larger, it will only further reduce the output current and internal hysteresis current, and will not affect the temperature setting

tmp01 the 2.5V low drift reference output of the temperature controller is easy to divide the voltage with resistance or potential externally, so as to accurately set the heating/cooling point not affected by temperature. In addition, other voltage sources can also be used to replace the reference voltage

3 setting method of temperature control point

set the temperature control point of tmp01, using the following steps: (1) select the hysteresis temperature. (2) Calculate the hysteresis current ihys. (3) Select the temperature control point. (4) Calculate the distribution value of each resistance

the calculation method of temperature setting is illustrated by an example below, and the parameters are shown in Figure 2

design requirements: set the hysteresis temperature to 2 ℃. When the temperature is higher than 25 ℃ or lower than 0 ℃, tmp01 outputs control signals respectively

4 application example analysis and precautions

when tmp01 is used to directly drive the relay, the current should not exceed 20mA (the current can be determined by dividing the resistance by the relay coil voltage). Driving high-power equipment should achieve the purpose of control by driving relays, high-power FET, thyristor and Darlington tube. In order to avoid voltage sparks induced by the coil of the relay, a diode should be connected at both ends of the relay coil. In DC circuits, high-power thyristors are usually used to replace relays. When tmp01 is used as a high current switch, the self heating caused by the large load at the output end will bring temperature error. External transistors can be used to remove the load at the output end to avoid self heating. By selecting external transistors to divert most of the current, tmp01 can be used to control many high-voltage devices. Figure 3 shows a Darlington transistor circuit using tmp01 to control a high current switch

tmp01 is not only used to automatically control the heating/cooling device, but also can output voltage signals proportional to the temperature. If the voltage is converted into digital frequency signal, the long-distance transmission of temperature measurement value can be realized. Figure 4 is a circuit that converts the temperature signal measured by tmp01 into a frequency signal for long-distance transmission. The analog voltage proportional to temperature (vptat) is input to the in-phase end of ad654. The input stage composed of input amplifier and NPN tube follower converts the analog input voltage into a driving current proportional to it. The driving current charges the timing capacitor CT at the same time, and the oscillation frequency (output frequency) of the multivibrator is proportional to the charging current. The output of ad654 is a square wave signal in positive proportion to the input analog voltage signal. The output formula is as follows:

tmp01 voltage temperature coefficient 5mv/℃ corresponds to the output end of 25Hz/℃, which is 7.5khz at 25 ℃. At the signal receiving end, AD650 can be used to convert the frequency signal into DC voltage signal, so as to realize the long-distance transmission of temperature

the error sources that affect the temperature control accuracy of tmp01 include internal error sources and external error sources. Internal error sources include initial tolerance, reference voltage temperature drift, set point comparator input offset voltage and bias current, and hysteresis current scale factor. External error sources mainly come from resistance accuracy and grounding error voltage. In practical use, it is mainly considered to reduce the impact of external error sources. The external resistance error will directly affect the accuracy of the set point. Especially when fixing the temperature setting, the resistance with appropriate temperature coefficient should be selected, and the temperature drift of the resistance should be fully considered. At the same time, the layout of the circuit board, the placement of components and the influence of leakage current should be paid less attention to, so as to reduce the common thermal error source. The bottom end of the resistance voltage divider shall be as close to the ground as possible to reduce the coupling between voltage drop and external noise sources. When the chip is powered by an external power supply, it is best to connect 0.1 μ Bypass capacitance of F

references

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[2] song Jiayou. Integrated electronic circuit design manual [M]. Fujian: Fujian science and Technology Press, 2002.

[3] Li Hua. MCS-51 Series MCU practical interface technology [M]. Beijing: University of Aeronautics and Astronautics Press, 1993