Transformer: In general, the ac line voltage present in your house wiring is not suitable for electronic circuits. Most circuits require a considerably lower voltage, while a few require higher voltages. The transformer serves to convert the ac line voltage to a voltage level more appropriate to the needs of the circuit to be powered. At the same time, the transformer provides electrical isolation between the ac line and the circuit being powered, which is an important safety consideration. However, a line transformer is generally large and heavy, and is rather expensive. Therefore, some power supplies (notably for PCs) are deliberately designed to operate directly from the ac line without a line transformer. The output of the transformer is still an ac voltage, but now of an appropriate magnitude for the circuit to be powered.

Rectifier: The next step is to force current to flow in one direction only, preventing the alternations that occur in the transformer and the ac line. This process is known as rectification, and the circuit that accomplishes the task is the rectifier. There are many different rectifier configurations that may be used according to the requirements of the circuit. The output of the rectifier is a pulsating dc, which still has some of the variations from the ac line and transformer.

Filter: The pulsating dc from the rectifier is generally still not suitable to power the actual load circuit. The pulsations typically vary from 0 volts to the peak output voltage of the transformer. Therefore, we insert a circuit to store energy during each voltage peak, and then release it to the load when the rectifier output voltage drops. This circuit is called a filter, and its job is to reduce the pulses from the rectifier to a much smaller ripple voltage. No filter configuration can be absolutely perfect, but a properly designed filter will provide a dc output voltage with only a small ac ripple.

Regulator: A regulator is an electronic circuitry which is used to maintain a constant DC o/p in spite of the line voltage variations and the load variations.

Each of the four sections identified above can have a number of variations. Regardless of these variations, each section performs its specific task. To measure the effectiveness of each circuit, we compare the magnitude of the remaining ac component, or ripple, with the dc component of the total voltage appearing at the output of that section. The ratio of ac voltage to dc voltage is known as the ripple factor. The goal of any power supply design is to reduce the ripple factor as much as possible, or at least to the point where the load circuit will not be adversely affected by the remaining ac ripple voltage.