What Are the Different Types of Power Supplies?

Linear Regulation Power Supply
 

Linear power supplies use standard linear (analog) semiconductor circuits. In a linear power supply, the raw electricity from the power line is first sent through a transformer, which reduces its voltage to a value slightly higher than is required by the computer's circuits. Next, one or several rectifiers, usually semiconductor diodes, convert the now low voltage AC to DC. Finally this DC is sent through the linear voltage regulator, which supplies the carefully controlled DC to your computer's circuits.

Most linear voltage regulators work simply by absorbing the excess voltage made by the transformer, turning it into heat. The regulator adjusts the amount of power it dissipates to constantly supply the same voltage even if the power line voltage varies as much as 10 to 20 percent.

Switching Regulation Power Supply
 

Although more complex, switching power supplies are more efficient and often less expensive than the linear type.

While designs vary, the typical switching supply first converts the incoming 60 Hz utility power to a much higher frequency of pulses, in the range of 20,000 Hz. While the pules are increased in frequency, they are also regulated using a digital technique called pulse width modulation. The duration of each power pulse varies in response depending on the needs of the computer circuitry being supplied. The width of each pulse is controlled by electronically switching the current flow on and off, hence the name of the technique. The pulses are reduced in voltage by a transformer and turned into pure direct current by rectification and filtering.

Switching power supplies earn their efficiency and lower cost in two ways. Switching regulation is more efficient because less power is turned into heat. Instead of dissipating energy, the switching regulator switches all current flow off. In addition, higher frequencies require smaller, less expensive transformers and filtering circuits. Nearly all of today's personal computers use switching power supplies.