Linear VS Switching Power Supplies

Historically, the linear regulator was the basic technique of producing a regulated output voltage. It controls by cutting a higher input voltage down to a lower output voltage via linearly controlling the conductivity of a series pass power device in response to changes in its load. This results in a large voltage being placed across the pass unit with the load current flowing through it. This headroom loss makes the linear regulator to only be 30 to 50 percent efficient. That means that for each watt delivered to the load, at the least a watt has to be dissolute in heat. The cost of the heatsink actually makes the linear regulator uneconomical above 10 watts for small applications. Below that point, however, they are cost effective in step-down applications.

The switching regulator operates on the power devices in the full-on and cutoff states. This then results in either large currents being passed through the power devices with a low “on” voltage or no current flowing with high voltage across the device. This results in a much lower power being dissipated within the supply. The common switching power supply presents efficiencies of between 70 to 90 percent, no matter the input voltage.

Higher levels of integration have driven the cost of switching power supplies down which makes it an attractive choice for output powers greater than 10 watts or where multiple outputs are desired.

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