Classification of The Thermistors

Thermistor is a resistor whose resistance value is very sensitive to temperature. It is also known as semiconductor thermistor. The main characteristics of thermistor is high sensitivity to temperature, small thermal inertia, long service life, small volume, simple structure, and various shapes, which has become the sensitive resistor used very widely.

There are many kinds of thermistor. According to the resistance temperature coefficient, it can be divided in two categories: positive temperature coefficient thermistor (PTC) and negative temperature coefficient thermistor (NTC); In terms of the resistance changes with temperature, there are slow variant (linear) and mutant (nonlinear); On the basis of the heating mode, it can be divided into direct heating and indirect heating; According to its operating temperature range, it can be classified into three categories: normal temperature (-55 to 315 ℃), low temperature (<-55 ℃) and high temperature (>315 ℃); According to the materials used, there are ceramic thermistor, semiconductor (crystal) thermal resistor, metal film thermistor, plastic thermistor, silicon carbide thermistor, glass state thermistor and so on. According to the structure, it can be divided into rod like, spherical, washer, discoid, bead, wire tubular, wafer, square sheet and thin film thermistor etc. The appearances of several thermistors are shown in the following pictures.

                                                                  
Power type thermistor (NTC)               Temperature compensation type thermistor (NTC)             Thermistor with electronic temperature meter (NTC)
                                                                    
Linear thermistor (PTC)                          Time delay starting thermistor (PTC)                                     Overheating protection

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The advantages and characteristics of TEC

TEC have both cooling and heating functions. Its working current is DC current, through changing the polarity of the direct current, the TEC can achieve cooling or heating.
TEC has the following advantages and characteristics in the field of technology.
1. There is no need in using refrigerant, and TEC can work continuously. It doesn’t have gyroscopic effect because there are no rotating parts. And when it works, it has such characteristics as no vibration and noise, long life and easy installation.
2. The TEC has two functions: cooling and heating. The cooling efficiency is generally not high, but its heating efficiency is very high. Therefore, people can fully achieve both heating and cooling functions by using TEC instead of using cooling and heating system respectively.
3. By controlling the input current, TEC can achieve high precision temperature control. Based on the temperature measurement and control means, it is easy to realize remote control, program control and computer control, which is prone to form an automatic control system.

4. The temperature range of the regular temperature TEC is from  -60°C to 200°C; the temperature range of high temperature TEC is from -60°C to 200°C.
In our company, there are many kinds of TECs, such as ATE-127 series, ATE-199 series and ATE-241 series and so on. In these series, there are sealed TECs and non-sealed TECs and there are also high temperature TECs and low temperature TECs. In short, you have many choices to select what you need. Incidentally, we also design and produce TEC controllers based on customers’ requirements and it is very convenient for you to use it to control TECs.

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How to use the NTC

The NTC element is a negative temperature coefficient thermistor, which is widely used in radio production. This paper mainly introduces the applications of the following three aspects.
1. Temperature compensation in instrument circuit
In the instrument circuit, there are a lot of elements with metal wire, which is like wire wound resistance. As metal wire generally has a positive temperature coefficient, using NTC for temperature compensation, errorsproduced bytemperature changes can be offset. Figure 1 is a temperature compensation circuit. NTC is connected in parallel with manganese copper resistance, and then it is in series with the compensating elements, so the function of temperature compensation can be achieved.

Fig. 1 Application of NTC in instrument temperature compensation

2. Steady working point of NTC in the transistor circuit
Figure 2 is a circuit of stable transistor working point of three kinds of NTC.
Figure 2 (a) shows that a simple transistor current amplifier took a big RT in the base loop. When temperature changes in the environment, line output current will change. And after increasing NTC, the collector current can be automatically adjusted and the output gain can be stable.
In the fig 2(b), the NTC is connected in parallel withemitter resistance. When theresistance of transistor emitter junction increases with the temperature increasing, the RT will play the role of compensation.
Figure 2 (C) shows low frequency power amplifier stage of a transistor radio. The under bias resistor of this levelis connected in parallel with on RT.When the temperature rises cause electrode current increasing, the under bias resistance will decrease and the base current will also reduce, so the collector current can be fall, which plays the role of stabilizing operating point.

Fig. 2 Steady working point of NTC in the transistor circuit

3 The temperature measuring device with NTC
What is shown by Figure 3 is a thermistor thermometer. In the figure, the RT is thermistor.As the resistance change of the thermistor is with temperature changes, micro ammeter will change accordingly, which is connected between the bridge diagonal. Thermistor thermometer accuracy can reach 0.1℃, and the temperature sensitivity is under 10s.

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The Working Principle of Thermistor

Thermistor is one of thermal resistors, and the principle is that the resistance change is caused by the change of temperature. But now, the thermal resistor has generally been industrialized, which is basically refers to the PT100, CU50 and other commonly used thermal resistors. The difference between these two kinds of resistance: the thermal resistance is generally refers to the metal thermal resistance (PT100, etc); Thermistor is a semiconductor thermal resistance. The temperature coefficient of semiconductor thermal resistance is more than 10 to 100 times as big as that of metal, and it can detect the temperature change of 10~6℃ and select the resistance value of 0.1 ~ 100kΩ. That is why the semiconductor thermal resistance is called thermistor. The thermistor is generally used in circuit boards. It can be used as a protective device because the resistance changes with the change of temperature. Of course, this is only one aspect. There are many other uses of thermistor. For example, thermistor is used for the temperature compensation of the cold end. However, because of the obvious nonlinear relationship between the resistance and temperature, the consistency of the elements is very poor and it can not have a standard signal as the heat resistance does.

NTC thermistor is the abbreviation of Coefficient Negative Temperature, which is the thermistor with negative temperature coefficient. It is made of the manganese, cobalt, nickel and copper and other metal oxide, which have the properties of the semiconductor. When the temperature is low, the number of oxide material carriers (electron and hole) will decrease, and its resistance value will go high; when the temperature becomes high, the number of carriers will increase, and the resistance will be low. At room temperature, NTC thermistor was varied in the range of 10~1000000Ω and the temperature coefficient is -2%~-6.5%. NTC thermistor can be widely used in temperature measurement, temperature compensation, surge current suppression and other occasions.

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WHAT IS A THERMISTOR?

Thermistors are thermally sensitive resistors whose prime function is to exhibit a large, predictable and precise change in electrical resistance when subjected to a corresponding change in body temperature. Negative Temperature Coefficient (NTC) thermistors exhibit a decrease in electrical resistance when subjected to an increase in body temperature and Positive Temperature Coefficient (PTC) thermistors exhibit an increase in electrical resistance when subjected to an increase in body temperature. U.S. Sensor produces thermistors capable of operating over the temperature range of -100° to over +600° Fahrenheit. Because of their very predictable characteristics and their excellent long term stability, thermistors are generally accepted to be the most advantageous sensor for many applications including temperature measurement and control.

Since the negative temperature coefficient of silver sulphide was first observed by Michael Faraday in 1833, there has been a continual improvement in thermistor technology. The most important characteristic of a thermistor is, without question, its extremely high temperature coefficient of resistance. Modern thermistor technology results in the production of devices with extremely precise resistance versus temperature characteristics, making them the most advantageous sensor for a wide variety of applications.

A thermistor’s change in electrical resistance due to a corresponding temperature change is evident whether the thermistor’s body temperature is changed as a result of conduction or radiation from the surrounding environment or due to “self heating” brought about by power dissipation within the device.

When a thermistor is used in a circuit where the power dissipated within the device is not sufficient to cause “self heating”, the thermistor’s body temperature will follow that of the environment. Thermistors are not “self heated” for use in applications such as temperature measurement, temperature control or temperature compensation.

When a thermistor is used in a circuit where the power dissipated within the device is sufficient to cause “self heating”, the thermistor’s body temperature will be dependent upon the thermal conductivity of its environment as well as its temperature. Thermistors are “self heated” for use in application such as liquid level detection, air flow detection and thermal conductivity measurement.

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Laser Diode Circuit

A laser diode is a diode which outputs a laser beam.

Unlike LED light, a laser’s light output is more concentrated, meaning it has a smaller and more narrow viewing angle. This means it must be directed at its source more directly in order to be picked up. Laser light is also monochromatic, meaning laser light isn’t composed of several lights combined together, but one light of the same wavelength and energy. Normally with LEDs, the different light outputs are based upon different colors combined. One such example is green light. To output green light, blue and yellow lights are combined to give green. Lasers, for the most part, do not follow this. Laser lights have a single spectral color and is almost the purest monochromatic light available.

Laser diodes are used in CD players, CD-ROM drives, and other optical storage drives. They are used in laser printers, laser fax machines, laser pointers, measurement equipment, bar-code and UPC scanners, and in high-performance imagers, as well as various other applications. These are just the most popular and used aspects of them.

To build a laser diode circuit, we must create a driver circuit for the laser diode.

A driver circuit is a circuit which can limit appropriately the amount of current being fed into the laser diode, so that it can function correctly. Too much current and the laser diode will blow. Too little current and the laser diode will not have sufficient power to turn on and operate. Therefore, a driver circuit is needed to give precisely the correct range of current needed so that our diode will operate.

To build the driver circuit, we are going to need a voltage source, a voltage regulator, a diode, an electrolytic capacitor, and a few resistors.

 

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TEC Controller

TEC controller is a kind of semiconductor device, which realize the refrigerating and heatingprocess according to the current trend through the TEC.And our TEC controllers are also based on TEC current direction and strength to realize temperature control. By using the TEC controller, we can precisely adjust the temperature of the object. And it has the advantages of high efficiency, high stability, high reliability and small size.

Our TEC controller is used to drive low cost TEC with the high stability, high response speed and high efficiency. Because of small volume,it does not require the heat radiation in the process of operation. Our products are 100% lead-free, and conform to the RoHS standard. It is widely used in EDFA laser module, temperature controllers in the sensor instrumentations and some other fields. The following detailed description of one type of our products.

TECA1-XV-XV-D

TECA1-XV-XV-D is designed to drive the TEC with high efficiency, zero interference, small package and high stability when regulating the temperature of an object. This module provides interface portfor the customers to set the desired temperature of the object (That is the set point temperature), the maximum output voltageand the compensation network. It is divided into two categories (with compensation network and without compensation network), and there aretwo kinds of packagingforms (DIP and SMT).

According to the different voltage and current,this type of TEC controllercan be divided into many kinds, and customers can choose the TEC controller based on their need.

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Laser Driving Power Supply

In recent years, high precision semiconductor laser with continuous adjustable high stability is more and more widely used in military and civilian fields. And the demand of driving power supply used with laser is also becoming more and more. The semiconductor laser driving power supply with excellent quality and high stability and high precision should ensure the laser work safely, anti-interference ability is strong and the laser has the normal service life.
The work current of semiconductor laser with high power can reach more than dozens of ampere, and the node voltage is more than 1V. So the driving power supply of this laser should be a constant current power supply with high current stability. And the power supply must have protection circuit, anti-electric shock measures and no high voltage. The transient current, voltage spikes and many other factors are easy to damage the laser, and the current and temperature fluctuations will cause changes of light power, which can influence the output accuracy and stabilization. From here we see that semiconductor lasers have very high demand on driving power.
Next I will introduce the laser driver of our company, which can drive diode lasers with high current and high stability. AAS30A5V is an electronic power supply designed for laser diode with 0~30A. The output current of 0-30A can be set by setting the 0-2.5V analog voltage. There are over temperature and short circuit protection device in power supply. The modulation frequency can be as high as 5 KHz, resulting to an approximately 56μS rise/fall time at the output current.

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ATE1-127 TEC Modules

ATE1-127 TEC Modules have 127 pairs of Peltier elements. The maximum voltage is 15.4V, and there are 17 kinds of maximum current to choose from. The TEC module is used to accurately adjust the object temperature, when working with TEC controller, a highly stable and efficient temperature control system is constituted. ATE1-127 TEC is composed of two pieces of bare ceramic plate with very smooth surface. The ceramic plates can be installed to the flat surface of the metal, and there are a few layers of thermal conductivity of filler material (thermal conduction silicon or conductive grease) between them. When installing, please ensure uniform force so that thermal contact between TEC ceramic and metal will be good, and thermal resistance will be reduced to the minimum.

TEC can withstand the vertical force but can’t withstand the tangential force, especially the vibration. Even a tiny vibration tangential force will cause internal cracks ofPeltier elements.Althoughthe early damage can’t cause the operational problems, with time going by, the further problems will come out, namely, the resistance of the TEC will increase slowly until it stops working.
The TEC can rapidly adjust object temperature and make temperature stable in a wide range with high accuracy.This module is widely applied in many fields, such as solid state laser, optical components, CCD, IR camera, biological technology test, etc.ATE1-127 TEC Modules have 62 types, and you can choose what you need.

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Laser Driver

In optical fiber communication, optical module function is very important, and laser driver is used for light emission front, which can realize laser bias and modulation. The laser controller converts the voltage signal into current signal with high speed to modulatelaser and generate high-speed light signal. And then the light signal is coupled to the optical fiber transmission.
In order to meet the different requirements of design, our company has various types of laser controller, such asultra-low noise laser driver, high efficiency laser driver, dual channel mode laser driver, etc. These laser drivers are described below.
(1) Ultra-low noise laser driver
The ATLSXA103 series is designed for driving integrated chips of diode laser. This laser driver has low noise, no heat sink, small volume, etc. According to the difference of the maximumoutput current, it can be divided into 100mA, 200mA, 250mA, 500mA, 1A and other different types.Because of low power consumption, heat sink isn’t generally needed in the use process.

(2) High efficiency laser driver
High efficiency laser driver mainly includes three series: CWD-01-V2-D, ATLS201D and ATLS202. The efficiency of this product can be up to more than 90%, the volume is small, and the current haslarge span: the minimum output current is 1A; the maximum can reach as high as 10A. And the same models can also be used in parallel.

(3) Dual channel mode laser driver
Dual channel mode laser driver is divided into LDA1-CP1 and LDA1-CP2. The former is used to drive the P laser, and the latter is used to drive the N laser.

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