An electric power supply is a device or system that is capable of providing electrical energy to a load-typically by converting electrical energy from one form to another to make the energy compatible with the load's requirements. For example, an electric power supply might convert 120 or 240 volt alternating current (“AC”) energy to lower-voltage, regulated direct current (“DC”) energy appropriate for use by an electronic device such as a computer system. Sometimes power supplies are integrated with the devices for which they supply energy. In other applications, power supplies are discrete components and can be internal or external to the load.
Switching electric power supplies (also known variously as switch-mode power supplies, switched-mode power supplies and other similar terms) are those that make use of active switching circuitry along with inductive elements to accomplish the energy conversion task with a minimum of energy loss. In switching power supplies that take their input from AC mains, a common configuration is to employ rectification circuitry and bulk capacitors to create a DC supply from the available AC input. This DC supply is then provided to one or more switching DC-DC conversion systems that generate desired DC output levels.
An important category of electric power supplies are those that provide electrical isolation. In an isolating power supply, there is no DC circuit between an output of the power supply and the input of the power supply. For example, in an isolating power supply that generates a regulated low-voltage DC output from AC mains, there would be no DC circuit between the low-voltage DC output and the AC mains. A transformer is typically used to provide this electrical isolation. In isolating DC-DC conversion systems, a DC supply voltage is applied with alternating polarities to the primary windings of a transformer with the consequence that power is transferred to the secondary windings of the transformer. Rectification is applied to the voltage at the secondary windings.