Practical - 29 :- Identify types of transistors based on their physical appearance

Objectives :- 

• The internal structure and function define a transistor's type (e.g., BJT, MOSFET, JFET), the physical appearance is determined by its package type. The package is chosen primarily based on the power dissipation and application (through-hole or surface-mount). 
• the package gives clues about the device's power handling capability and mounting style. You must consult the part number printed on the component and look up its datasheet for confirmation.

Tool/ Equipment / Instruments

1.  Transistor Data Book .... As Required 

Material

1.  Diff. Types Of Transistor Packages .......... 25 Nos.

Procedure 

1.  Pick One of the labeled transistors from given assorted lot , identify the code number and record them in table
2.  Refer below chart to identify the types of Package, all other details as required in table and record them

Package Name	Appearance / Characteristics	Mounting Style
TO-92 (Transistor Outline)	Small, teardrop-shaped plastic body with one flat side and a semicircular back. Three leads protrude from the bottom.	Through-Hole
SOT-23 (Small Outline Transistor)	Very small, rectangular plastic body with three leads on one or both sides.	Surface-Mount (SMD)
SOT-323 / SOT-523	Even smaller versions of the SOT-23, typically used in high-density or miniature circuits.	Surface-Mount (SMD)
Metal Can (e.g., TO-18)	Small, sealed metal cylinder with three or more leads coming out of the bottom. Often used in older or high-reliability/RF circuits.	Through-Hole

The only reliable way to know the type (BJT, MOSFET, IGBT) and polarity (NPN/PNP, N-Channel/P-Channel) of a transistor is to read the part number printed on its body and look up the datasheet.

Example Part Numbers:

• 2N3904 (Commonly found in a TO-92): A Bipolar Junction Transistor (BJT), NPN type.

• IRFZ44N (Commonly found in a TO-220): A power MOSFET, N-Channel type.

• BC547 (Commonly found in a TO-92): A BJT, NPN type.

Lab Procedure for Identification

If the part number is unknown or unreadable, you'll need to use a multimeter or a transistor tester to determine the fundamental type (BJT or FET).

1. Multimeter (Diode Check Mode) Method

A Bipolar Junction Transistor (BJT) behaves like two back-to-back diodes, which can be tested using the multimeter's diode check function.

• For a BJT: You will find two junctions (Base-Emitter and Base-Collector) that conduct electricity in one direction (forward bias, typically 0.6-0.7 V reading) and block in the other (reverse bias, OL or 1reading).

• For a FET (MOSFET/JFET): The Gate is isolated from the Source and Drain (especially in a MOSFET), so you will typically get an Open Loop ($\text{OL}$) reading between the Gate and the other two terminals.

2. Specialized Transistor Tester Method

For a faster and more comprehensive test, a dedicated transistor/component tester (often a small handheld device) will automatically:

1. Identify the component type (BJT, MOSFET, JFET, Diode, etc.).

2. Identify the pin-out (Emitter/Base/Collector or Source/Gate/Drain).

3. Measure key parameters like current gain (h FE) for BJTs or gate capacitance for MOSFETs.

Chart Different types of transistor packages