7. Uncontrolled Diode Rectifier Circuits

For nearly a century, rectifier circuits have been the most common power electronic circuits used to convert ac to dc. The word rectification is used not because these circuits produce dc but rather because the current flows in one direction; only the average output signal (voltage or current) has a dc component. Moreover, since these circuits allow power to flow only from the source to the load, they are often termed unidirectional converters. As will be shown shortly, when rectifier circuits are used solely, their outputs consist of dc along with high-ripple ac components. To significantly reduce or eliminate the output ripple, additional filtering circuitry is added at the output. In the majority of applications, diode rectifier circuits are placed at the front end of the power electronic 60 Hz systems, interfaced with the sine-wave voltage produced by the electric utility. In dc-dc application, at the rectified side or the dc side, a large filter capacitor is added to reduce the rectified voltage ripple. This dc voltage maintained across the output capacitor is known as raw dc or uncontrolled dc.