A transformer is also a kind of inductor. It is made by winding two or more sets of coils on the same coil frame or the same iron core. It uses the mutual induction phenomenon between two inductor coils to transmit AC signals and electrical energy. Transformers can serve roles such as voltage conversion and impedance conversion in circuits. They are very common passive devices in electronic products. There are many types and models of transformers, so when choosing a transformer, you should follow these criteria: 1. Choose different types of transformers according to their specific purposes. 2. Select the performance parameters of the transformer based on the specific requirements of the electronic equipment. 3. Pay attention to the detection of important parameters and the quality assessment of the transformer during selection.