Laptop Power Supplies: Switch-Mode Vs. Linear

AtBatt Laptop PowerFor years and years, linear power ruled the world of power conversion. However, when switch-mode power became commercially available in the late 1970s, it began to render linear power obsolete. Why is that? And what is the difference between the two? Let us examine both power conversion types and discuss what has made switch-mode the preferred power supply for laptops.

Linear power converters have bulky steel or iron laminated transformers. They provide safety barriers between high voltage AC input and lower voltage DC output. The transformers reduce the AC input from 155V or 230VAC to lower voltage such as 30VAC. The lower AC voltage converts to DC when passed through electrolytic capacitors. That low voltage DC converts into the correct output voltage via a transistor or IC.

Switch-mode power converters take 115V or 230VAC and convert it to high voltage DC. That DC converts to low voltage using small ferrite transformers, FETs or transistors. That voltage converts into the correct DC output voltage by another set of diodes, capacitors and inductors.

When comparing linear and switch-mode power converters, it becomes clear just why laptop manufacturers choose switch-mode converters to charge their laptop batteries. A 50W switch-mode power converter averages a size reduction of……(Read more on Laptop Power Supplies)

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