1-31
being a "1," orange a "3," and white "9," the device would be identified as a type 139 semiconductor
diode, or specifically 1N139.
Figure 1-27.—Semiconductor diode color code system.
Keep in mind, whether the diode is a small crystal type or a large power rectifier type, both are still
represented schematically, as explained earlier, by the schematic symbol shown in figure 1-12.
Q33. What does the letter "N" indicate in the semiconductor identification system?
Q34. What type of diode has orange, blue, and gray bands?
DIODE MAINTENANCE
Diodes are rugged and efficient. They are also expected to be relatively trouble free. Protective
encapsulation processes and special coating techniques have even further increased their life
expectancies. In theory, a diode should last indefinitely. However, if diodes are subjected to current
overloads, their junctions will be damaged or destroyed. In addition, the application of excessively high
operating voltages can damage or destroy junctions through arc-over, or excessive reverse currents. One
of the greatest dangers to the diode is heat. Heat causes more electron-hole pairs to be generated, which in
turn increases current flow. This increase in current generates more heat and the cycle repeats itself until
