TO-111 Package Data
Transistor Packages Styles TO-111 Case style, Bolt Mounting
 TO-111 Package Drawing | TO-111 Pin Configuration; The TO-111 outline is one of a number of Stud-mount hex packages that bolt to a surface. the difference here is that this component package has 4 terminals. Most of the other components using this general outline only have three terminals. The fourth terminal [4] is connected to the case of the device, which of course is also the metal bolt used to attach the package to another surface. All other pins are isolated from the case. The three other terminals are used for the Base, Emitter and Collector [in regards to a transistor]. A 2N3996 or 2N3997 transistor have the following pin usage. |
The four terminal would be required when the package is mounted on an isolated or a surface not grounded. A metal plate or chassis panel would function to dissipate heat away from the semiconductor within the package. However these surfaces may not always be grounded. Grounding the case helps to block noise from reaching the semiconductor within the TO-111 metal case.
Like many of these pages that carry package related topics, the transistor part numbers are just representative examples. Many other semiconductors may use this package, but are not called out here. The other two transistors in this family, the 2N3998 and the 2N3999 actually use the TO-59 package, which doesn't have the fourth case terminal. All of the transistors listed here have very nearly the same characteristics, but vary in voltage or current just as any transistor might.
The style of the case has nothing to do with the electrical characteristics, and everything to do with mounting options. The different case designations offer different mounting options or connection options. The physical shape or size of the device does effect heat lose or power dissipation. So larger current devices are placed in larger physical devices that have a greater surface area to bleed of heat.
These devices, by design, are completely metal cases with thick metal terminals. Heavy gauge wire should be used when interfacing to the terminals to assist in conducting heat away from the component. Shorter wire conducts heat more efficiently than longer wires. Of course the thicker and shorter the wires, the lower the voltage drop across the wires.
