From Wikipedia, the free encyclopedia Jump to: navigation, search A switched-mode power supply, switch-mode power supply, or SMPS, is an electronic power supply unit (PSU) that incorporates a switching regulator — an internal control circuit that switches power transistors (such as MOSFETs) rapidly on and off in order to stabilize the output voltage or current. Switching regulators are used as replacements for the linear regulators when higher efficiency, smaller size or lighter weight are required. They are, however, more complicated and their switching currents can cause noise problems if not carefully suppressed. As with any offline electronic systems employing peak-hold AC-DC conversion, simple SMPS designs may have a poor power factor. The power output to cost crossover point between SMPS and linear regulating alternatives has been falling since the early 1980s as SMPS technology was developed and integrated into dedicated silicon chips. In early 2006 even very low power linear regulators became more expensive than SMPS when the cost of copper and iron used in the transformers increased abruptly on world markets. SMPS can also be classified into four types according to the input and output waveforms, as follows. AC in, DC out: rectifier, off-line converter DC in, DC out: voltage converter, or current converter, or DC to DC converter AC in, AC out: frequency changer, cycloconverter DC in, AC out: inverter AC and DC are abbreviations for alternating current and direct current.