Power Supply Basics

Power supplies, also referred to as electric power converters, include electronic devices utilized to supply electricity to electrical loads. They do not store energy, yet instead obtain electrical energy from an exterior source like the electricity grid, an alternator, a generator, or energy storage device such as a fuel cell or battery.

Power supplies will perform an extremely critical function: they’ll decrease the power supplied to voltage levels which are appropriate for powering loads. The component which performs the function is referred to as a PSU (Power Supply Unit). Also, PSUs may be utilized for converting AC power supply to DC power (using a DC PSU). Lastly, regulated power supply units ensure that power that is supplied to a load is constant, even if AC supply voltages change. It’s crucial for the proper longevity and functioning of electrical load elements.


The most basic PSU form comprises of a smoothing or reservoir capacitor, a diode rectifier circuit, and a transformer. The diode will conduct current — yet only in a single direction. It essentially acts as a gatekeeper, permitting current to pass through a PSU as the AC voltage that leaves the transformer is higher than a load voltage.

A capacitor is charged by applied voltage from a transformer until applied voltage is less than than the load voltage, during which point a diode refuses to permit any more current to a capacitor and the current instead is utilized to power a load.

The PSU will remove the majority of the AC voltage variations, yet not all of them. The rest of the variations are referred to as ripple that rides on top of a DC voltage signal, and certain loads are able to accommodate more ripple than other ones. Power supplies, for more sensitive applications, must be equipped with filters which remove the rest of the ripple.  The quantity of ripple is determined by the capacitor’s value.


Power supplies utilized for a variety of applications have various attributes; however, the same general build. The standard elements discovered in the majority of power supplies include: the input transformer, utilized to step down voltage; the rectifier, utilized to change from AC over to DC voltage; the capacitor, utilized to smooth a signal from a rectifier; and a regulator, utilized to offer a steady output voltage.

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