In modern electronic systems, voltage regulation is a basic function required by the system for optimal performance. The regulator provides a constant output voltage irrespective of changes in line voltage, load requirements, or ambient temperature. For years, monolithic regulators have simplified power-supply design by reducing design complexity, improving reliability, and increasing the ease of maintenance. In the past, monolithic regulator systems have been dominated by linear regulators because of relatively low cost, low external component count, excellent performance, and high reliability. However, limitations to applicability and performance of linear regulators can force the user to other more complex regulator systems, such as the switching regulator. Because of improvements in components made especially for them, switching-regulated power supplies have proliferated during the past few years. The emergence of inexpensive, high-speed switching power transistors, low-loss ferrites for inductor cores, and low-cost LSI circuits containing all necessary control circuitry has significantly expanded the range of switching regulator application. This application note describes a new integrated subsystem that contains the control circuitry, as well as the switching elements, required for constructing switching regulator systems (Figure 1). The principle of operation is discussed, a complete system description provided, and the analysis and design of the basic configurations developed. Additional information concerning selection of external switching elements and design of the inductor is provided.