In almost all power supply circuits, magnetic component inductors or transformers are indispensable. For example, inductors are used at the input and output terminals to filter the harmonics of switching waveforms; In the resonant converter, inductance and capacitor are used to generate resonance to obtain sine wave voltage and current; In the buffer circuit, inductors are used to limit the current change rate of power devices; In boost converter, energy is stored and transmitted; Sometimes inductance is used to limit the transient current of the circuit. The transformer is used to electrically isolate two systems, transform voltage or impedance, or generate phase shift (3-phase Δ— Y transformation), storage and transmission of energy (flyback transformer), and voltage and current detection (voltage and current transformer). It can be said that magnetic components are one of the most important components of power electronics technology.