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Diodes are semiconductor devices that allow electricity to flow through them in only one direction.
Types of diode:
- Electrolytic - obsolete wet chemical diodes used in the 1920s
- Copper oxide - poor efficiency, high leakage current. Obsolete
- Thermionic diode - aka vacuum tube, valve. Obsolete.
- Selenium - ditto. Terrible stink when they fail
- Germanium diode - very low voltage drop, often used as a radio detector
- Silicon diode - by far the most popular type. 0.6v knee, with Vf rising to typically 0.9-1.5v at I_max, but sometimes higher.
- Schottky diode - lower Vf, much used in SMPSUs for greater energy efficiency
- Ultrafast diode - quick recovery diode, maintains high efficiency at high frequency
- Varicap diode - capacitance varies with applied reverse voltage. Mainly used as tuning capacitors
- Zener diode - conduct at a specified Vr, used mainly for voltage regulation
- Light emitting diode - used for lighting