The Rectifier Diodes There are two approaches for implementing the full-wa...

The Rectifier Diodes There are two approaches for implementing the full-wave bridge: Four individual diodes, as shown in Figure 2–86(a) or a single IC package containing four diodes connected as a bridge rectifier, as shown in part (b).

(Figure 2-86)

Because the rectifier in the single IC package exceeds the specifications and requires less wiring on a board, takes up less space, and requires stocking and handling of only one component versus four, it is the best choice. Another factor to consider is the cost. Requirements for the diodes in the bridge are

? Forward current rating must be equal or greater than 250 mA (maximum load current).

? PIV must be greater than the minimum calculated value of 16.7 V

By reviewing manufacturer’s datasheets on-line, a specific device can be chosen. Figure 2–87 shows a partial datasheet for the rectifier to be used for this power supply. Notice that it exceeds the specified requirements. Four possible websites for rectifiers and diodes are fairchildsemiconductor.com; onsemi.com; semiconductor.phillips.com; and rectron.com.

(Figure 2-87)

The Transformer The transformer must convert the 120 V line voltage to an ac voltage that will result in a rectified voltage that will produce 16V±10% when filtered. A typical power transformer for mounting on a printed circuit board and a portion of a datasheet for the series are shown in Figure 2–88. Notice that transformer power is measured in VA (volt-amps), not watts.

From the partial datasheet in Figure 2–88, select an appropriate transformer based on its secondary voltage (series) and a VA specification that meets the requirement.

(Reference Figure 2-88)