2N2222 NPN Transistor

2N2222A NPN Transistor – The 2N2222A is a popular NPN transistor used for switching and amplification. It has a gain (hFE) of 110–800, allowing it to amplify signals efficiently. The maximum collector current is 800mA, so it is suitable for moderate current loads. To properly bias the transistor, a base current (IB) of up to 5mA should be supplied.

Operation

The transistor operates in two primary regions:

• Saturation Region: Fully biased transistor allows current to flow from collector to emitter, with VCE ≈ 200mV and VBE ≈ 900mV.
• Cut-off Region: No base current is supplied, transistor is off, with VBE ≈ 660mV.

Pin Configuration

• Pin 1 (Emitter): Current exits through the emitter.
• Pin 2 (Base): Controls the transistor’s biasing.
• Pin 3 (Collector): Current enters through the collector.

How to Use 2N2222A

The 2N2222A can function as a switch or amplifier. Applying a voltage across the base-emitter junction induces base current, forward-biasing the transistor and closing the collector-emitter circuit. Always use a base resistor to limit current and prevent damage.

Base resistor formula: RB = VBE / IB

Example: Using a 5V base voltage with a 1KΩ resistor allows a 2N2222A to switch a 500mA motor from a 12V source. This is within the transistor's 800mA collector rating. Using a lower-rated transistor, like a BC547, would risk burning it out.

Applications

• Switching high current loads up to 800mA
• General-purpose switching circuits
• Motor speed control
• Inverter and rectifier circuits
• Darlington pair configurations