The next series of slides explain how the SEPIC circuit operates. When switch SW1 turns ON, the input voltage is applied to inductor L1-a causing current to ramp up and store energy in the core of L1. The two windings of L1 are coupled to the inductor core, causing the L1 windings to behave like a transformer. Because of the one-to-one turns ratio of the coupled inductor, the input voltage is applied across winding L1-b and the parallel-connected AC coupling capacitor C1. Because of the polarity of L1-b, capacitor C1 is charged to the voltage level of the input voltage. During the ON-time of SW1, energy from the source is stored in the coupled inductor, while the output current is supplied by the output capacitor, Cout. Diode D1 is reverse biased, effectively decoupling all components, except Cout from the load. In summary, when SW1 is turned ON, current flows in winding L1-a causing energy to be stored in the coupled inductor L1. By the transformer action of L1-b, the coupling capacitor C1 is charged to the same level as the input voltage. Because diode D1 is reversed biased, Cout must supply all power to the load.