Apple released the newest model of IPhone on Sept 12^th. The newest model IPhone X is equipped with Apple All processor. It is already known that the typical input voltage to this device is lower than 5.1V. The maximum allowable core voltage of Its central processor is 1.35V. The typically power of this processor is less than 2.5W. Therefore, design a flyback dc-dc converter for powering the Apple All processor.

A. Draw the circuit schematic of the flyback converter with all essential labels marked. What is the function of transformer in a flyback converter?

B. Assume the dc-dc converter's input voltage is 5.1V and its output voltage is 1.35V. The duty ratio should be less than 0.75 to achieve better control resolution. What is the maximum primary to secondary turn's ratio?

C. Based on part B: Assume the transformer is perfectly coupled. If the processor (i.e., load) power is 2.5W, calculate the average current of the transformer primary side winding.

D. Based on part C: Draw the waveforms of v_1 Phi, i_D, i_sl and switch status.