Current-mode control has been used in power supplies since the late 1970s. Although this method of control has been in use for over two decades, its operation and characteristics are not generally well known. Most engineers learn about switching power supplies in terms of the more familiar voltage-mode control, while current-mode control is left for more advanced studies. This is unfortunate because a power supply engineer should know at least the basic differences between voltage-mode and currentmode control to know when to use each control architecture. In this paper, we will go inside current-mode control.