Tutorial
Single Output Centralized Power Supplies
As implied, single output centralized supplies are powered by the ac powerline and provide a single dc voltage output. The single output supplies produce an output voltage that may range from 1.0V to 48V. Only the 24V or 48V models are usually used for distributed power. The term, single output supply is used to distinguish these supplies from the front-end supplies that provide 24V or 48V.
For most small, relatively low-power systems centralized power distribution is usually the most cost- and performance-effective. The centralized power distribution system converts the incoming ac power line to a regulated dc output or multiple dc outputs. These outputs then supply power to the specific circuits that require the various voltages. These centralized power systems may have difficulty handling resistive voltage drops and responding to transient loads.
A typical centralized system is the type employed in desktop computers, that is, a single supply provides all the required voltages: +5V, ±12V. However, the centralized approach can suffer from lengthy design times, susceptibility to noise and lack of flexibility.
If the system requires an additional low voltage, the power management subsystem must be redesigned by replacing the entire centralized supply or adding a voltage regulator derived from an existing output. If any existing supply voltage requires a higher current capability, the centralized supply must be replaced.
The centralized power supply offers advantages in applications where it needs to be physically or electrically isolated from the load because the load is sensitive to electrical noise, the heat generated by the power supply or some other aspect. A centralized assembly also provides the user with heat sinking and connectors.
Another advantage for the centralized power supply is the cost associated with powering a small to moderate size system. A single supply with multiple outputs can be more cost effective than a distributed supply with multiple dc-dc converters.
To minimize power distribution losses the centralized supplied should be located near the load. For safety and EMI reasons, it should be located as close as possible to the ac entry point, which often a problematic tradeoff. Although centralized power works well for many applications, it is usually unsuitable for distributing high power at low voltages.
A drawback of the centralized supply is its transient response, which is the ability to react quickly to rapidly changing loads. Another potential problem is its characteristic of concentrating heat in one specific area.