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Page 323

| Figure 16-11 Cross section of selenium contact rectifier cell (Courtesy, General Electric Co.) |

| between the two materials is called the barrier or blocking layer. Typical dc voltage characteristics are shown in Fig. 16-12. |

| Two common types of these rectifiers are the copper oxide and the selenium rectifiers. Both types are made up of series or series-parallel combinations of blocking layer units. In the copper-oxide unit, the blocking layer is the juncture between a thin film of copper oxide sandwiched between two copper discs. In the selenium unit, the blocking layer is the juncture between a thin layer of selenium sandwiched between the iron disc and a disc of some conducting material. |

| Since such rectifiers transform only a half cycle of ac to dc, combinations can be arranged for rectification of both halves of the ac cycle (Fig. 16-13). Since these units are usually used for only small quantities of dc power, no three-phase and six-phase supply circuits are employed. |

| Figure 16-12 D-C voltage character istics of selenium rectifier cell (Courtesy, General Electric Co.) |

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