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Unregulated power supplies find very limited use today, since the output dc voltage is proportional to the input ac voltage. Output voltage fluctuates in step with input variations as well as changes in load impedance. Also, ripple voltage can run as high as 10% of the output dc voltage. Even with filter networks on the output, the remaining ripple and load regulation may be insufficient for most modern electronic circuits. But some components -- relays, solenoids, and indicating lamps, for example -- do not usually require a precision and filtered voltage. Thus, an unregulated power supply may be desirable for these circuits because unregulated supplies are simple, reliable, and inexpensive. Additionally, unregulated power supplies are typically more efficient and dissipate less heat than regulated power supplies with the same output voltage and current.
Regulated power supplies are the type most widely used. Two fundamental designs are the linear series-regulated and the switching power supply. Although switching power supplies are considered by many to be the new wave of technology, they have been around for many years. But, because of recent improvements in semiconductor components, capacitors, and transformers, they can be made more reliable, simpler, and less costly than just a few years ago. They are well suited for applications requiring small size, high efficiency, and moderately good regulation. On the down side, however, switching power supplies generate voltage spikes and noise in their outputs and can radiate EMI/RFI because of switching transients. These unwanted signals can seriously interfere with legitimate signals and completely mask others. Thus, carefully designed power supplies should include effective shielding, bypassing, and filtering to prevent propagating noise into sensitive circuits.
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