Fundamentals of Electronics: A Comprehensive Guide

Transistors - NPN & PNP - Basic Introduction
The Organic Chemistry Tutor

Transistors: NPN and PNP
Transistors are electronic devices used as switches or amplifiers.
In this video, we'll discuss two types of transistors: NPN and PNP.

NPN Transistor
The NPN transistor has two junctions, one between the p-type
and n-type semiconductor materials. It can be thought of as two
diodes connected to each other, with the diode always pointing
towards the n-type material.

PNP Transistor
The PNP transistor is the reverse of the NPN transistor, with two
p-type materials and one n-type material.

Electrical Symbols
The electrical symbols for NPN and PNP transistors are
represented by circles and arrows. The emitter, base, and
collector are indicated by different colors.

Current Flow
In an NPN transistor, current flows into the base, while in a PNP
transistor, current flows out from the base. The direction of
conventional current is from high potential to low potential, while
electrons flow in the opposite direction.

Formulas
Some important formulas to know when dealing with transistors:

 Collector current (IC) = Beta (β) * Base current (IB)
 Emitter current (IE) = IC + IB

Example Problem