Diode
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A diode is a two-terminal electronic component that conducts electric current primarily in one direction. It has low resistance in one direction and high resistance in the other.
Close-up view of a silicon diode. The anode is on the right side; the cathode is on the left side (where it is marked with a black band). The square silicon crystal can be seen between the two leads.
A high power vacuum tube diode used in radio equipment as a rectifier
Various semiconductor diodes. Left: A four-diode bridge rectifier. Next to it is a 1N4148 signal diode. On the far right is a Zener diode. In most diodes, a white or black painted band identifies the cathode into which electrons will flow when the diode is conducting. Electron flow is the reverse of conventional current flow.
A vacuum tube containing two power diodes
Zener diode
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A Zener diode is a type of diode designed to exploit the Zener effect to affect electric current to flow against the normal direction from anode to cathode, when the voltage across its terminals excee
Diode
…to a low resistance when the reverse voltage across the diode reaches a value called the breakdown voltage. This effect is used to regulate voltage (Zener diodes) or to protect circuits from high voltage surges (avalanche diodes). A semiconductor diode's current–voltage characteristic can be tailored by selecting…
A 1N829 Zener diode