Obtain a lower dc voltage from a higher voltage power supply

摘要

You can use the circuit in Figure 1 to obtain a low regulated voltage, such as 5V dc, from a higher voltage, rectified, sinusoidal voltage source without resorting to an electrically noisy dc/dc converter or wasting watts in a dropping resistor. This application requires a regulated 5V-dc source, but a transformer supplies 18V rms to a fullwave bridge rectifier. During the charging phase, two equal-value electrolytic capacitors, C{sub}1 and C{sub}2, receive charging current when connected in series through forward-biased diodes D{sub}1 and D{sub}2.