Although a diode is a sufficent and appropriate device for the switch a MOSFET would also work in this position,as shown in Fig. 1-13 When is on and is off,cur-rent flows upward out of the advantage of using a MOSFET is that it has a much lower voltage drop across it when conducting compared to a diode,resulting in lower power loss and a higher circuit efficiency. The disadvantage is that a more complexcontrol circuit is required to turm no when is turned off. However,several control cir-cuits are available to do this this control scheme is known as synchronous rectification or synchronous switching
In a power electronics application, the current source source in this circuit could represent an inductor that has a nearly constant current in it.