Transformer is the use of electromagnetic induction principle to change the AC voltage of the device, the main components are primary coil, secondary coil and core (core). The main functions are: voltage conversion, current conversion, impedance conversion, isolation, voltage regulator (magnetic saturation transformer) and so on. According to the purpose can be divided into: power transformers and special transformers (electric furnace change, rectifier, power frequency test transformers, voltage regulators, mine transformers, audio transformers, IF transformers, high-frequency transformers, shock transformers, instrument transformers, electronic transformers , Reactors, transformers, etc.). Circuit symbols commonly used as the beginning of the number. Example: T01, T201 and so on.