Dictionary of Electrical Engineering Terms
"A" "B" "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M",
"N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"

A Zener Diode: is designed to conduct in the reverse [bias] direction: with a precise breakdown voltage [Vz]. Also refer to the listing of Zener Diode Manufacturers, which includes notations on the types of diodes. Both the government and the military refer to Zener diodes as a Voltage Regulator Diode. So the term Zener may not appear in many documents or specifications that actual reference these types of diodes.
Zener diodes are available in either surface mount or thru-hole components.

Zener Break Down: The reverse break-down voltage of a zener diode. This is the voltage specified in the data sheet as the Zener voltage, and the normal region in which the diode is operated in.

Zener Effect: The reverse breakdown effect in diodes in which breakdown occurs at reverse voltages below 5 volts. The presence of a high energy field at the junction of a semiconductor produces the breakdown. See the curve below.

Diode Voltage Curve
Diode Electrical Characteristics Curve

Zener Clamp: A zener diode used to clamp a voltage at a particular level to protect some other device, rather than being used as a voltage reference. In some cases a diode is also used in series with the zener. This term refers to the manner in which a Zener is used in a circuit and not to any characteristic of a diode.

Zener Impedance: The impedance of a zener diode while at break down voltage. The data sheet might indicate Vz or just 'Z' for impedance.

Zener Knee Current: The reverse current that flows through the zener diode while at the break-down voltage. Zener current shown as Iz in the data sheet.

Zener Voltage: The break-down voltage of a zener diode. The abbreviation Vz is used in a data sheet to indicate Zener voltage. Diodes are normally sorted by the break-down voltage [Vz] and than by the break-down current [Iz].

A diode is a two terminal device using a PN junction [Diode Manufacturers]. Diodes may be made from Silicon, Germanium, Selenium, or Gallium Arsenide. Most diodes will be made of Silicon. Normally a forward voltage drop of 0.7 volts will be seen with Silicon Diodes, and a forward voltage drop of 0.3 volts will be seen with Germanium Diodes.
Diodes are primarily used as switching devices. While zener diode are used as a voltage reference.

Engineering note: Of course a Zener diode will be shown on a schematic with a Zener diode symbol. However a two or three terminal precision voltage reference may also be depicted with the same Zener symbol, and so not be a Zener at all. As an example refer to the definition of Voltage Reference, and the graphic shown for the symbol and the graphic which depicts the actual circuit [not a physical diode at all].

Fabrication note: Although it doesn't matter with axial lead parts, some diode packages may be supplied in two different polarities. That is, a bolt type diode [DO-4 Package] might have the anode connected to the bolt side of the device in one part number, but have the cathode connected to the bolt portion using a slightly different part number. The subtly part number change could be as small as the addition of the letter 'R' to indicate reverse connection.

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