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Manufacturers must ensure that a diode will meet the requirements of its specific end use, so proper diode specifications are essential. Diode specifications are divided into limits and characteristics. It is the limits, which must not be exceeded, that best define the specification. For example, one limit specification called “maximum forward continuous current” refers to the maximum temperature that a diode can operate, which is approximately 248 Fahrenheit (125 Celsius). “Maximum junction temperature” is a limit specification associated with the part of diode construction that is called the diode junction, which is usually limited to operate between 257 Fahrenheit (125 Celsius) and 302 Fahrenheit (150 Celsius).
As with diode specifications, many types of diodes exist, including electronic diodes, high-power diodes, high-voltage diodes and pin diodes. A crystal diode consists of a semiconducting material, such as germanium or silicon, as one electrode and a fine wire “whisker” resting on the semiconductor as the other electrode. A semiconductor diode is a two-electrode semiconductor device having an asymmetrical voltage-current characteristic. A double-base diode is a semiconductor diode in which a potential gradient is produced across the base region by the application of a voltage between two electrodes at either end of the base.
Diode specifications involve diode testing. Precise measurements are taken during testing of diode circuits and other elements. Characteristic specifications are observed during this testing, and they include “forward voltage drop,” which is a small reduction in voltage as the current passes through the diode; “turn-on or turn-off time,” generally given as the maximum number of nanoseconds it takes for the diode to switch between forward and reverse operating conditions; and “thermal resistance,” a specification used for removing heat from the diode.
Other diode specifications that are characteristic include “reverse leakage current,” which measures the capacity of reverse current that may exist under reverse bias conditions. This indicates a measure of imperfections in the manufacturing process. Another characteristic specification is called “junction capacitance” and is a parameter set at a certain operating point. Other limit specifications include “maximum forward surge current,” “maximum forward surge current,” “maximum forward peak current,” “maximum reverse voltage” and “reverse recovery time.”
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