Question

how will you identify emitter lead In TO5 package​

Answer 1

In a TO-5 package, a notch is present near the emitter lead for identification.

Explanation:

• TO-5 stands for Transistor Outline package with case style : 05
• It is a standard metal can semiconductor device packaging style which is commonly used for three terminal devices such as transistors or for certain less leaded op-amp integrated circuits.
• TO-5 transistors are encased inside a metal case; the transistor chip is mounted on its die-pad.
• To identify between the three terminals of Emitter (E), Base (B) and Collector (C), the metal body, near to the seating plane, has a small metal notch, visible and extending out from the base diameter.
• The terminal right next to the notch is identified as the Emitter, the middle lead is the Base and the remaining lead is the Collector.
• The collector terminal is designed to collect all the majority charge carriers and hence will emit maximum amount of heat. Hence, the collector lead is directly connected to the metal case. A silvery finish is observed at the collector terminal welding with the metal base.
• Both PNP and NPN transistors have notch for lead identification. (e.g. 2N404 Germanium PNP Transistor, 2N5682 NPN Transistor)
• TO-5 packages have characteristic metal cap diameter, metal cap height, base diameter, lead length and lead pitch.

(Refer the below attached diagram)