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  • Understanding Computer Power Supplies
Technology Articles > Hardware > Power Supplies > Understanding Computer Power Supplies

It seems like every laptop has a different plug or adapter for its power supply. Though it would certainly be convenient to have one universal adapter for every laptop in the world, there are important reasons that companies use unique adapters for their power supplies. And there are even more important reasons why you can’t use just any power supply for any computer. Simply put, different power supplies process electricity differently. The wrong power supply could mean an underperforming computer, or worse—a toasted circuit board.

How do power supplies work? The answer to that question will help explain why it’s important to pair laptops and their individual power supplies correctly.

The Plug
One part of the power supply is universal: the plug that goes into the wall. This plug and its cord bring alternating current (AC) electricity (110 volts in the US, 220 across Europe) from the building’s power supply to the next part of the power supply. Computers run on direct current (DC), not alternating current, so the power supply always has to have a converter in it.

The Converter
For laptop power supplies, the converter is in the heavier box, or “power brick,” usually right at the wall plug or halfway along the cord. For desktop computers, the converter is inside the main box and usually attached to the fan. The converter can generate a good deal of heat as it converts power for the computer or other electronic device. This is why laptops have a cord to keep the brick away from the laptop itself and desktops have the fan to cool the converter down.

The converter receives alternating current power which “alternates” or reverses the flow of electrons back and forth rapidly. It then converts that alternating flow to a single steady uni-directional flow of electrons. There are two different kinds of converters: linear and switching. A linear converter sends direct current output at a very precise level and usually have limiting features that protect the supply and device from overload. Linear converters become large and bulky if they need to handle large operations. A switching converter uses an electronic switch to rapidly turn the current on and off. This removes one half of the “alternation” for alternating current. The output then passes through a smaller transformer or smoothing capacitor to deliver a steady one-way current to the device.

The Output
The final step in the power supply process is delivering output to the device. For laptops, phones, electric shavers, and other rechargeable battery devices, this is simple. A single low-voltage direct current is passed to the device through the remaining cord and unique adapter. Different devices require different voltages, so each power brick is specifically built to deliver the correct voltage to its device. Unique adapter size helps prevent confusion and damage. Manufacturers also typically print the output voltage on the brick.

Output on the power supply in a desktop computer is considerably more complex. It delivers individual currents to different parts of the computer, so it has multiple transformers and output cables. Each one takes the correct voltage to its component (hard drive, motherboard, other drives).