There are a number of ways in which power supplies may be divided or categorized, including functionally, mechanically, and by power conversion method.
Functionally, power supplies may be divided into regulated power supplies, unregulated power supplies, adjustable power supplies, adjustable regulated power supplies, and isolated power supplies. Regulated power supplies are those that maintain constant power output current or voltage, regardless of variations in load current or input voltage. Unregulated power supplies, on the other hand, will not remain the same, and instead may vary wildly, if and when their load currents or input voltages are altered.
The load current or output voltage of adjustable power supplies may be programmed with mechanical controls, a control input, or both. Similarly, adjustable regulated power supplies are both adjustable and regulated. Finally, unlike most power supplies, whose power input and power output share a common connector, isolated power supplies have a power output that is not dependent on its power input.
In terms of mechanics, power supplies may be classified according to the way they are packaged, or mechanically enclosed. In this area, the categories are bench power supplies, open frame power supplies, rack mount power supplies, and integrated power supplies. First, bench power supplies are standalone desk units used for applications like circuit test and development. Next, open frame power supplies, which are usually built directly into existing equipment or machinery, only have a partial mechanical enclosure. In fact, they sometimes consist only of a mounting base. Rack mount power supplies are made to fit into standard electronic equipment racks. Finally, integrated power supplies are those power supplies that share a printed circuit board with their load.
In a general sense, power supplies can be divided into linear and switching types. Linear power supplies process and convert input power directly, and all of their active conversion components are contained inside their linear operating regions. Switching power supplies, on the other hand, which make up the majority of power supplies, take input power and convert it to alternating current (AC) or direct current (DC) pulses before processing it. The converting components of switching power supplies operate in primarily non-linear regions, which makes for better efficiency.
Since most power supplies are switching types, another major defining factor of power supplies is whether they operate using alternating currents or direct currents. The difference between AC and DC power supplies is quite straightforward: AC power supplies receive their electrical flow from an electrical charge that periodically, but consistently, reverses direction, or alternates. The measure of the alteration of a current is represented by a unit of frequency called Hertz, which is defined as one cycle per second.
So, for example, a 60 Hertz (Hz) current alternates sixty times in one second. DC power supplies, on the other hand, use an electrical charge that flows only in one, linear direction. Usually, they are independent from the electronic device they are powering and housed inside a protective casing. AC and DC power supplies provide power to different types of electrical products, but in general, DC power supplies are more widely used. AC power supplies are often used to power the electrical functions of residential buildings and commercial buildings, as well as electronic adaptors or converters, while DC power supplies usually work inside metal conductors, medical equipment, process control systems, video technology, laptop computers, and cell phones.
Power supplies may be purchased or ordered in a wide variety of configurations and designs. Customers, for example, are offered a number of different ways to present monitored and measured current and voltage information, including analog visual indicators, graphic displays, video displays, and digital numerical displays.
Optional features include computer interface technology, adjustable voltage, fan cooling systems, water cooling, overvoltage protection, overcurrent protection, integral heat sinks, power factor correction, pure sine output, short circuit protection, and backup batteries. Other things to consider when purchasing power supplies include a unit’s output voltage, output power, output frequency, number of outputs, apparent power, operating temperature, and whether the unit runs on direct current, alternating current or both.