This chapter considers some of the more basic applications of diodes treating the diode as a circuit element having a specified current-voltage characteristic. Just as linear passive elements are idealized in order to highlight their salient characteristics and way they affect circuit responses, diodes are idealized for the same reasons. The ideal diode behaves like an ideal switch that is controlled by the direction of current flow, much like a one-way, or no-return, valve that allows fluid to flow in one direction but not in the opposite direction. In practical applications, the presence of the diode can be accounted for in different ways depending on the diode circuit under consideration. A basic voltage-regulating device is the zener diode, which can also be used to provide a reference voltage both in discrete-element circuits and in integrated circuit. The zener diodes are designed to turn on very rapidly and to withstand a fairly large amount of power for a very short time.