General Purpose Diodes Information

General purpose diodes are two-terminal electronic components that allow current to flow in only one direction, from an anode (+) to a cathode. These simple semiconductors are PN junctions with a positive or P-region with positive ions and a negative or N-region with negative electrons. Applying voltage to the PN junction causes current to flow in only one direction as electrons from the N-region fill “holes” in the P-region. Typically, general purpose diodes are made of semiconductor materials such as silicon, germanium or selenium. General purpose diodes are often used as voltage regulators; in switching applications; and as signal rectifiers, oscillators, and signal modulators / demodulators.

Performance specifications for general purpose diodes include forward voltage, reverse voltage, reverse current, breakdown voltage, and junction operating temperature. Forward voltage (V_F) is the voltage across the diode terminals resulting from the flow of current in the forward direction. Reverse voltage (I_F), the current at which the specified voltage is applied, flows through the diode in the direction of lower resistance. Reverse current (I_R) or leakage current, the current value at which the specified reverse voltage is applied, measures the current that flows when reverse bias is applied to a semiconductor junction. Breakdown voltage (V_BR) is the reverse voltage at which a small increase in voltage results in a sharp rise of reverse current. Junction operating temperature (T_j) is the range of temperatures at which diode are designed to operate.

IC package types for general purpose diodes include transistor outline (TO), diode outline (DO), small outline transistor (SOT), and small outline diode (SOD). Other general purpose diodes are available in a discrete package (DPAK) or in D2PAK, a large surface-mounted package that includes a heat sink. SC-59, SC-74, and SC-76 are plastic, surface-mounted IC packages with three leads. Metal electrode leadless face (MELF) diodes have metallized terminals at each end of a cylindrical body and are designed to fit the same footprints as flat components. QuadroMELF diodes have a square cross section to provide better on board stability and greater "pick and place" accuracy. MiniMELF is a miniature version of MELF and MicroMELF has the same footprint as the SOD110 and SOD323 packages. 

General purpose diodes follow product life style stages that are defined by the Electronic Industries Alliance (EIA) in EIA-724. Numbered stages range from zero to eight and cover product introduction, growth, maturity, market saturation, phase out, last shipment, and removal. The first stage, Life Cycle Stage Code 0, describes general purpose diodes that are in the planning or early design stages.  The last stage, Life Cycle Stage Code 8, describes general purpose diodes that are no longer stocked in inventory or available for sale.

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