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How Does a Switch-Mode Power Supply Work?

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Quick Answer

A switch-mode power supply supplies and converts electricity, usually from alternating to direct current, to electrical equipment through semi-conductors operating in a continuous, high frequency on-and-off mode. The switching function controls the amount of voltage or current produced, based on converted energy stored in inductors or capacitors.

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Whether it is a switch-mode or linear power supply, alternating current electrical energy of a certain voltage passes through the power supply unit and is converted by a transformer to the desired voltage. This energy is then filtered and regulated through a capacitor, where it is transformed into direct current. A sample of the voltage produced acts as a feedback signal in the switch-mode power supply and controls the on-and-off function. Switch-mode power supplies reduce the amount of energy lost or dissipated, as compared with linear supply units, because of this feedback loop. In a linear power supply unit voltage is regulated by dissipating power, a much less efficient approach.

In the switch-mode power supply, the frequency of the voltage coming into the unit is increased before it enters the transformer. Accordingly, its transformer and capacitors are very small. The switch-mode power supply is found in smaller electronics, such as computers and DVD players.

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