Introduction of NTC:
NTC thermistors, which stand for Negative Temperature Coefficient thermistors, are resistors whose resistance decreases as the temperature increases. They are made of semiconductor materials with a large negative temperature coefficient. These thermistors find widespread applications in switch power supplies, UPS power sources, electronic ballasts, temperature sensors, automatic heating regulators, and more. Below, I'll explain three functions of NTC thermistors: surge current suppression, temperature measurement, and temperature compensation.
These thermistors belong to the power type. Although they are small in size, they can handle high power. Typically, they are connected in series with the mains input line. They have a rated zero-power resistance value, which is usually very small. Zero-power resistance is a fundamental parameter of thermistors provided by manufacturers. When connected in series with the power supply circuit, they effectively suppress the inrush current during startup. Moreover, the power they dissipate is almost negligible.
Characteristics of Power-Type NTC Thermistors:
Specific Circuit Connection for Power-Type NTC Thermistors.
2. Use temperature sensor to measure temperature
As a thermistor that measures temperature, it uses changes in resistance due to changes in external temperature. Because when an NTC resistor is connected to a circuit, a certain amount of current will always pass through it. This current will cause the NTC itself to generate heat, and the NTC resistance will decrease. It has a great impact on the measurement, so it is necessary to control its own heating to avoid excessive current flowing through the thermistor, causing the component to heat itself and produce measurement errors. Write all or part of the resistance value corresponding to the temperature into the CPU, so that when the external temperature changes, the resistance value changes and is reflected as a change in voltage. This kind of packaging includes patch type, epoxy head type, glass seal type, straw hat type, etc.
Thermistor temperature measurement circuit example diagram
Using the resistor voltage dividing principle, when the NTC changes, the voltage also changes. Use the A/D port to detect the voltage change, and write all the data used by the thermistor into the MCU. Different resistance values correspond to different temperatures, and the program Continuously test.
If you have higher temperature accuracy requirements, you can use NTC with higher accuracy, and use a bridge circuit plus an amplifier. The thermistor NT1/NT2 and the resistors R1 and R2 form a bridge circuit. As long as there is a temperature difference in the thermistor, the amplifier will output corresponding signal
3. Temperature compensation
Some electrical appliances have very high precision requirements, especially instruments and meters. Many parts are made of metal wires, such as wire-wound resistors. Metals generally have positive temperature coefficients, so you can use thermal sensors with negative temperature coefficients. The resistors are compensated, one positive and one negative, which can offset errors caused by temperature changes and improve accuracy. For temperature compensation, the alloy copper wire resistor is generally connected in parallel with the NTC thermistor and then in series with the compensated component.
NTC Top 5 brands：muRata、TDK、EPCOS、Thinking and UF capacitors etc. UF capacitors produce both green and black type NTC to replace to replace TDK/Epcs and thinking etc
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Photo |
Description |
UF Capacitors |
TDK/EPCOS |
Thinking-TVR |
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MF72 Power NTC Thermistor |
B57 Series |
SCK*** Series |