SelenDioden

SelenDioden, or selenium diodes, are rectifier devices that use elemental selenium as the rectifying medium. They were widely employed in early to mid-20th-century power supplies and radio and television equipment, before silicon-based rectifiers became dominant.

Construction and operation

A selenium rectifier is typically built as a stack of discs or plates in which a layer of selenium is sandwiched between metal electrodes, usually nickel or other conductive plates. Several such cells are connected in series to achieve the desired reverse-voltage rating and current handling. The rectifying action arises from the metal–selenium interfaces and the grain-boundary properties of the selenium layer, which produce a diode-like current–voltage characteristic. When forward biased, the device conducts; when reverse biased, it blocks current, albeit with relatively high leakage compared with modern silicon diodes. Selenium rectifiers require effective heat sinking because power dissipation grows with current.

Characteristics and performance

SelenDioden have a comparatively high forward voltage drop and moderate to high reverse leakage, making them less efficient than silicon diodes. They are relatively slow compared with modern fast-switching diodes and respond poorly to high-frequency signals. Their performance depends on temperature and aging, as selenium can shift characteristics over time. Physical construction makes them bulky, and heat management is a practical consideration in design.

History and legacy

Selenium rectifiers were common from the 1930s through the 1950s and into the early 1960s, used in a wide range of consumer and industrial power supplies. They were gradually replaced by solid-state silicon rectifiers and, later, by more advanced rectifier technologies such as thyristors and diodes in integrated modules. Today, SelenDioden are mostly of historical interest, found in restoration projects and vintage equipment.