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Linear Vs. Regulated DC Power Supply

Almost all electronic equipment, including computers, televisions and stereos, have a circuit -- called a power supply -- that converts 110-volt alternating current to the low-voltage direct current needed to run electronic devices. Most power supplies provide regulation, maintaining a tightly controlled voltage. Some use a traditional linear design, though most now have high-frequency switching designs.

Power Supply Regulation
- In an unregulated power supply, the output voltage changes from fluctuations in the AC line voltage or variations in the current demand. For example, if you have an unregulated power supply plugged into the same household circuit as a refrigerator, and the refrigerator turns on, it causes the voltage in the power supply to sag. Modern electronics need a tightly-regulated voltage, so engineers have developed two main techniques to hold a power supply̵7;s output voltage steady despite changes in either the AC line voltage or the output current.
Linear Design
- A linear power supply has a simple design: A transformer drops the 110 volts from the household outlet to a lower value, such as 10 volts. A set of diodes called a rectifier turns the AC to DC, though this DC has low-frequency electrical noise. Large-value capacitors reduce the noise while a voltage regulator holds the voltage to a steady value within a few percent, removing most of the remaining noise in the process. Most linear supplies also have thermal and short-circuit protection, shutting off the circuit if it overheats or has excessive current demand. Linear supplies are inexpensive and rugged, though the large iron transformer makes them bulky and heavy.
Unregulated Supply
- A few applications don't require regulation of the DC voltage. Battery chargers, lighting circuits and electromagnets do not have the sensitivity to voltage changes that many electronic circuits have. An unregulated supply has most of the components of a linear supply, though it lacks a voltage regulator.
Switching Design
- Since the 1980s, more electronic devices have used a more complex design called a switching power supply. Its basic layout is similar to a linear supply, but instead of the 60-hertz household AC line frequency, it generates an internal frequency of 20 kilohertz or more. The higher frequency means the circuit can use a much smaller transformer.
  
  As with a linear supply, a switching design contains short-circuit and thermal protections. It also has more parts than a linear supply but at a fraction of its size and weight. Mass production reduced the cost of switching supplies, so they are now in wider use than linear supplies.
Uses
- Most new electronic equipment has a switching power supply, including even those with small AC adapters. The switching supply produces a tiny amount of radio interference, however, resulting in high-frequency electrical noise. Nonconsumer electronics, such as scientific and technical equipment, use linear supplies because high-frequency noise causes problems with sensitive circuits.

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