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Electrical Power Supply

Switching Power Supplies

A relatively new development in power-supply technology, the switching power supply, is becoming popular. Switching power supplies are lightweight and very efficient. Almost all personal computers are powered by switching power supplies.

The switching power supply gets its name from the use of transistor switches, which rapidly toggle in and out of conduction. Current travels first in one direction then in the other as it passes through the transformer. Pulsations from the rectified switching signal are much higher frequencies than the power line frequency, therefore the ripple content can be minimized easily with small filter capacitors. Voltage regulation can be accomplished by varying the switching frequency. Changes in the switching frequency alter the efficiency of the power supply transformer enough to stabilize the output voltage.

Switching power supplies are usually not damaged by sudden short circuits. The switching action stops almost immediately, protecting the supply and the circuit load. A switching power supply is said to have stalled when excessive current interrupts its action.

Switching power supplies are light in weight because the components are more efficient at higher frequencies. Transformers need much less iron in their cores at higher frequencies.

Switching power supplies have negligible ripple content at audible frequencies. Variations in the output of the switching power supply are inaudible compared to the hum that is common with power supplies that operate at the 60-Hz AC-power line frequency.

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