What is a thermistor, its designation on the species and the application of the scheme
In electronics almost always occurs a cascade of different measurements. One of the parameters is monitored constantly, is temperature. With its excellent measuring handle electronic components such as thermistors - Electronic Components made of semiconductors, which changes its resistance value with changes in temperature. In this article I will discuss how denoted look like and what other features have thermistors.
The image on the schemes
So, if you look at the circuit, you will see the following symbols:
Looking where such element is used, the image will be different than one element, namely «t». It is for this letter you will understand correctly that in front of you a thermistor.
The most important characteristic of any RTD is - TCR (temperature coefficient of resistance). It informs you on how many changes the resistor if the temperature is changed by 1 degree.
Where they can be found
Thermistors can be seen in any modern device, here for example, look at the switch mode power supply:
You can hold a simple experiment, take any thermistor and use a multimeter to make resistance measurements in the "cold" state and when heated. You should see that with increasing temperature the resistance value changes.
But do not think that the thermistors are used exclusively for the measurement of temperature, they are also widely used in the protection devices and many other products.
As heating occurs
Thermistors can be heated in two ways, namely:
1. Direct heating. In this case, the thermistor is heated directly to a current flowing through it or its environment. These thermistors have been used in instruments measuring temperature or for temperature compensation.
2. Indirect heating. In this embodiment, the thermistor is heated placed near the heating elements. What is important, in this case the electrical connection is not available. In this embodiment, the thermistor resistance is determined by the function of the current which passes through the heating element, and not through the resistor. Such thermistors - is primarily a combined appliances.
NTC- thermistors and PTC resistors
Just thermistors divided by changes depending on the temperature resistance of the following two types:
1. NTC - thermistors;
2. PTC - thermistors (PTC resistors in other words).
Let's get acquainted with them closer.
NTC - thermistors
Title thermistors such matter from the reduction Negative Temperature Coefficient, which translates as "negative coefficient of resistance." Basic "chip" such thermistors lies in the fact that during heating of the resistance begins to decrease.
Note the arrow on the image have a different direction, it just indicates that the growth of "t" a reduction in "R" and, accordingly, on the contrary.
Such an element can be seen in any pulsed power supply, for example in a conventional computer power supply.
The resistance of NTC - thermistor indicates a temperature of 25 degrees.
Let's look at a simple scheme
Series connection of the load indicates that through this circuit element runs the entire current consumption. In this NTC - thermistor limits the inrush current occurring during charging of the capacitor, which in turn protects the rectifier from breakdown.
At each start BP process begins charging capacitor, and by NTC-thermistor passes a certain current. While the NTC-thermistor is not warmed up his "R" has a pretty big difference. Passing current heats it, which reduces the "R" and subsequently has almost no influence on the flow of current consumed by the instrument.
In other words, the thermistor provides a soft start device and saves the rectifier diodes from being damaged.
Often NTC - thermistors operate additional safety functions, as while some damage Details often amperage rises significantly, which leads to the destruction of the thermistor, thereby de-energizing scheme.
PTC - thermistors (PTC resistors)
Thermistors, whose resistance increases with temperature are called PTC thermistors (Positive Temperature Coefficient - positive coefficient of resistance).
In the diagram, an element designated as follows:
Although an element and received much less common, but before color CRT TV is not I could operate normally without thermistor, and now this element is used in power LED circuits lamps.
In addition, PTC - thermistors are also used as protective devices. For example, a variety PTC resettable fuse.
SMD - thermistors
Widespread use of SMT - assembly was the impetus for the production of SMD - thermistors. By their appearance they are almost identical SMD - capacitors.
Sizes of elements within the series: 0402, 0603, 0805, 1206.
embedded thermistors
The same data elements are actively incorporated into the product, for example, soldering iron with temperature control sting.
conclusion
Thermistors - an essential element of any modern equipment, without which it is impossible to build a comprehensive protection scheme. If the article was useful to you, or are interested in, you will appreciate it Like. Thank you for your valuable attention!