The Diode

/ chrisconway1970
  • As mentioned, a diode is made from a small piece of semiconductor material, usually, silicon, in which half is doped as a p region and half is doped as an n region with a pn junction and depletion region in between;
  • The p region is called the anode and is connected to a conductive terminal;
  • The n region is called the cathode and is connected to a second conductive terminal;
  • The basic diode structure and schematic symbol are shown in Figure 2–1;

figure-2-1

Typical Diode Packages

  • Several common physical configurations of through-hole
    mounted diodes are illustrated in Figure 2–2(a);

figure-2-2

  • The anode (A) and cathode (K) are indicated on a diode in several ways, depending on the type of package;
  • The cathode is usually marked by a band, a tab, or some other feature;
  • On those packages where one lead is connected to the case, the case is the cathode;

 

Surface-Mount Diode Packages

  • Figure 2–2(b) shows typical diode packages for surface mounting on a printed circuit board;
  • The SOD and SOT packages have gull-wing shaped leads;
  • The SMA package has L-shaped leads that bend under the package;
  • The SOD and SMA types have a band on one end to indicate the cathode;
  • The SOT type is a three-terminal package in which there are either one or two diodes;
  • In a single-diode SOT package, pin 1 is usually the anode and pin 3 is the cathode;
  • In a dual-diode SOT package, pin 3 is the common terminal and can be either the anode or the cathode;
  • Always check the datasheet for the particular diode to verify the pin configurations;

 

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