A
switched-mode power supply (
switching-mode power supply,
switch-mode power supply,
SMPS, or
switcher) is an electronic
power supply that incorporates a switching regulator to
convert electrical power efficiently. Like other power supplies, an SMPS transfers power from a source, like
mains power, to a load, such as a
personal computer, while converting
voltage and
current characteristics. Unlike a
linear power supply, the pass transistor of a switching-mode supply continually switches between low-
dissipation, full-on and full-off states, and spends very little time in the high dissipation transitions, which minimizes wasted energy. Ideally, a switched-mode power supply dissipates no power.
Voltage regulation is achieved by varying the ratio of on-to-off time. In contrast, a linear power supply regulates the output voltage by continually dissipating power in the pass
transistor. This higher power conversion efficiency is an important advantage of a switched-mode power supply. Switched-mode power supplies may also be substantially smaller and lighter than a linear supply due to the smaller transformer size and weight.