Autocoupling in autotransformer is mainly electromagnetic coupling, which is a transformer with primary winding and secondary winding. Its working principle is mainly that two or more coils are wound on a closed iron core. When alternating current passes through the coil, the coil will generate a magnetic field under the action of the iron core, and then the magnetic field will form its own electromotive force. At the same time, the other coil induces electromotive force with it, thus changing the comparison of coil turns and realizing the purpose of changing the voltage at both ends. In addition, it should be noted that the primary coil and the secondary coil are directly connected, and there is a risk of cross-level leakage, so it cannot be used in the traveling lamp transformer. Autotransformers are small in size, low in loss and high in efficiency, and are usually widely used in electrified railways.
Ring transformer is a kind of electronic transformer, which is divided into three types: standard power transformer, economical power transformer and isolation transformer. The main working principle is that the iron core is made of cold-rolled silicon steel sheet, and the magnetic force is generated by the coil and then induced by the magnetic circuit of the iron core. Ring transformer has strong anti-interference ability, low vibration and noise, and the upper winding of the iron core with low temperature has better heat dissipation, so the iron loss is relatively small. In addition, there is a mounting screw in the center of the ring transformer, which is very convenient for application in electronic equipment. Because of these advantages, it has a wide range of uses, such as computers, medical equipment, instruments, communications, lighting and so on. So far, ring transformers have been produced in China on a considerable scale, which not only meets the domestic demand of rich countries, but also exports in large quantities. In China, it is mainly used for lighting loudspeaker equipment and household appliances.