A switch mode power supply, also known as a switching mode power supply, or sometimes simply as a switcher is an electronic power supply that uses a switching regulator to convert electric power from one form to another. By using a switching regulator, this process is highly efficient. Like other types of power supplies, the main role of a switch mode power supply is to transfer power from a source such as an electrical power grid to a load such as a personal computer. In addition, whilst converting power, other factors such as voltage and current characteristics are also transferred.
A switch mode power supply provides a regulated output voltage which is usually different from the input voltage. It is different compared to a linear power supply, as the pass transistor of a switching mode power supply switches very quickly between full on and full off states. This quick switch minimises wasted energy. Thus switch mode power supplies are regarded as being more efficient compared to linear power supplies – and this is the chief advantage of using switch mode power supplies. Linear power supplies work by dissipating the excess voltage in order to regulate the output, leading to a loss of energy. A linear regulator will regulate its output voltage or current by dissipating the excess electric power in the form of heat. A switch mode power supply regulates output voltage or current by switching ideal storage elements such as inductors and capacitors into and out of different electrical configurations. Switching regulators can be used to replace linear regulators when higher efficiency, smaller size or lighter weights are required.
As stated above, the main advantage of using switch mode power supplies is that this method is more efficient and dissipates less power. Other advantages include that this power supply is a smaller size and has a lighter weight, and generate less heat due to its higher efficiency. By having a smaller sized power supply that weighs less, this means that shipping costs are less and they can be distributed easily. Unfortunately, switch mode power supplies have their disadvantages as well. Switch mode power supplies are more complicated than their linear counterparts and their switching currents can cause electrical noise problems if they are not carefully suppressed. Switch mode power supplies can generate high amplitude, high frequency energy that need to be blocked to avoid electromagnetic interference, ripple voltages and harmonic frequencies.