How Transistors Work - The Learning Circuit

How to use transistors as a switch - NPN and PNP - Active High and Active Low

How to Use an NPN Transistor to Switch on an LED - Electronics for Absolute Beginners

Transistors Explained Simply: Switches, Amplifiers, Cutoff, Saturation & Q-Point

Transistors as a Switch: Theory & Explanation

A Practical Introduction to Transistors | BJT Transistors as a Switch

Making logic gates from transistors

Digital Logic Gates from Transistors, AND, NAND, OR, NOR, XOR, XNOR, Buffer, and Inverter