Hello everyone, welcome to the Zimzim DIY channel. Today I have an electronic device to present. We often see it on electronic boards or circuit boards in general. This device is called a thermistor. What is a thermistor? First, let's look at the origin of its name. Thermistor comes from two words combined: Resistor + thermal. Resistor is a resistor, and thermal is heat. Together, they become a thermistor. In Thai, it is a resistor that depends on heat or temperature. The thermistor is actually a resistor that changes its value according to the temperature it receives. So why does the temperature change the resistance value of the thermistor? Let me explain it this way. The materials used to make thermistors are selected from the top quality materials, materials that are sensitive to different temperature ranges, mixed in as little as possible, depending on the desired value. Some of the products that are produced will say that they work well at a certain temperature. For example, if they work quickly at low temperatures, they can be used as air conditioning sensors or ice sensors. Some are sensitive to high temperatures, so they can be used as heat sensors attached to a heat sink. The symbol of a thermistor is similar to a resistor. But there will be a line in the middle or it will be a cylinder like this. It is the same. Now, thermistors have been developed in many forms. But the main ones that can be distinguished are two types: NTC and PTC. NTC stands for Negative Temperature Coefficient. PTC stands for Positive Temperature Coefficient. But most of the ones that I see used in circuits are NTC. Let's look at its working principle. The working principle of NTC is that when the temperature is high, the resistance value will decrease. And if the temperature drops, the resistance value will increase. NTC thermistors are further divided into subtypes, such as 1. Ceramic Bead type, which will be stable. 2. Dis type and Chip type (Disk and Chip) or type will have a slower response. But can manage the flow of current better. 3. Glass type Glass can withstand higher temperatures. We will see NTC applied to general electrical appliances, such as 1. Use as a temperature sensor. We will take NTC to stick on a heat sink. When the sink is hot, the resistance of the NTC thermistor will decrease. Causing the current to flow from difficult to flow to easier. We will then connect it to the op-amp to compare the values. If the op-amp checks that it is really hot, it will take the current and send the power to bias the transistor. The transistor will release the current to make the fan work. 2. Use as a soft start circuit to reduce the surge of current. If you look at the graph, you will see that if we do not put NTC to load something, such as a motor, a large capacitor, it will draw many times more current in the beginning. This will cause the electricity in our house to drop or the light bulb to flicker, causing an unsmoothness. In the old audio equipment, this will be obvious. When we turn on and off the device, there will be a popping sound. But if we connect NTC in series with Line like this, NTC will have a certain resistance value. It will help reduce the current there. It will help slow down the current in the beginning for a short period. But when the current goes in for a while, the device will heat up. The resistance will be low. The current will flow normally again. It's like there is only one wire. If you look at the graph, if the circuit uses NTC, you will notice that NTC has a resistance value. It helps slow down the current in the beginning. When it is hot, it will release the current to flow normally. Therefore, if the NTC used in the circuit is hot, don't be alarmed. The hot one means it works normally. This one has a resistance of 5 ohms when measured at normal room temperature. But most of the datasheets will be specified at 25 degrees. Therefore, if used in our home, the value may not be accurate because our home is hot. The value may change slightly. If we search the DATASHEET, we will find more detailed information. How many amps of current can it supply (5 amps)? How much resistance is reduced when powered (0.125 ohms according to the table, the bottom row to the last row)? We can easily search for the value on the internet. Checking and measuring the initial value NTC always has a resistance value. Connect 2 legs like a general resistance measurement, which is to go to Ohm mode. There will be a value close to the specified value. It may have a slight deviation as I mentioned earlier. If we look at the graph, with the X-axis as the resistance value and the Y-axis as the temperature value, we will see that it will not be a straight line according to the temperature like this. But it will be an exponential curve, which, no matter how you look at it, does not really correspond to the temperature. Because the temperature range The resistance value will change a lot, but let's move on