As the name implies, a power supply is a component that provides power to an electrical device. The simplest design of power supply is the linear power supply, which uses a transformer and a rectifier to convert voltage from a wall outlet into the type of power the device needs. There are two types of this sort of power supply: regulated and unregulated.
Electricity is distributed to homes and businesses in the form of alternating current (AC) power. It is called alternating current because the electrical charge changes direction periodically. Many electrical devices need direct current (DC) power, which does not change direction, to work correctly. A power supply takes the AC power and converts and smooths it into the kind of power an electrical device can use.
Power supplies come in two basic forms: linear and switching mode. The circuits within a linear power supply use a signal that does not change amplitude over time. A switching mode power supply uses digital circuits that do change amplitude over time.
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A linear power supply works by taking in power from an electrical outlet and putting it through a transformer, where it is turned into a lower voltage of power. So the 120 volts coming in from the wall circuit become 19 volts of AC power. The next step is a process called rectification. During this process, in which the AC power is changed and filtered until it becomes DC power. Finally, the DC power goes through a smoothing step that gets rid of any leftover variations in current.
Both regulated and unregulated linear power supplies are available. An unregulated power supply is the simpler of the two, and it performs the basic transformation and rectification steps but does little or no smoothing. This can result in a supply of power that is not uniform and may vary in voltage. This type is less expensive to make and is usually more durable than the regulated model.
A regulated linear power supply is slightly more complicated. It adds an extra step to the process to keep the output voltage from varying with changes in the incoming AC current. This type of power supply tends to run very hot, and a heat sink and cooling fan are usually needed to keep the unit from overheating. It is better for more sensitive equipment because the output power is more uniform.