The energy storage inductor is a commonly used original in DC to DC. For example, the external power supply is 9V, but the main chip of the router needs 5V, 9V power supply through the switch tube to the storage inductor and the load in series, because there is 4V voltage on the inductor, so on the load, only 5V, but the opening time can not be too long, too long 9V will pass, the switch tube is controlled by the power management chip, shut down, then 9V is disconnected. Since the inductor is the energy storage element, the magnetic field stored in it is converted into electrical energy and continues to supply power to the load. Maintain load 5V unchanged.