How does the selenium diode work?

Answer 1

Selenium diodes work much like any other diode. They allow current to flow in a forward direction and block current from flowing in the opposite direction. They have a higher forward bias voltage then silicon and as such generate much more heat then a comparable silicon diode. Most selenium diodes will therefore have an integrated heat sink that helps to dissipate all the heat generated.

As a zener diode, selenium is used in surge suppression where its heat sink helps in survivability during a surge. However, its low alpha (measure of nonlinearity) means that the voltage during a surge is very high and usually unsuitable to be used as protective device without other components in parallel. The reverse voltage is about 26 Volts, so to get higher voltage zener diode, many are placed in series. By connecting them back to back, then a bidirectionial zener diode can be created.

Selenium diode were very common in the 1950s and can be seen in industrial applications of the time. Some model train power supplies were seen to use these components. Since the advent of silicon diodes and their more efficient operation, these part have disappeared from use.

Answer 2

A selenium diode is a type of semiconductor device that allows current to flow in one direction. When forward biased, the selenium diode conducts electricity by allowing electrons to flow through it. When reverse biased, the selenium diode blocks the flow of current by creating a depletion region, similar to other diode types.