Description

The PN2222A are a good general purpose NPN transistor for low to moderate power amplification and switching.

PACKAGE INCLUDES:

• Qty 5 – PN2222A NPN General Purpose Transistors

KEY FEATURES OF PN2222A NPN GENERAL PURPOSE TRANSISTOR:

• NPN Bipolar Silicon construction
• Standard EBC pin-out in TO-92 package
• Up to 40V collector-emitter and 75V collector-base
• Up to 600mA continuous current

The PN2222A are a good inexpensive general purpose NPN transistor for low to moderate power amplification and switching and should be part of every parts bin.

These can be very handy when you need to boost the output of a uC pin to drive something that it can not drive directly.  NPN transistors are generally used in low-side switching applications where they are connected between the load and ground.

Below is an example circuit that uses a PN2222 transistor to create a simple Continuity Checker for testing to see if two points have continuity between them.  This could be a dead short or they could have some resistance between them, but not be open circuit.

When there is continuity between the two probes, the PN2222 transistor base is pulled high and so the transistor switches on and provides the ground path for the LED to light and for the buzzer to sound.

When there is no continuity, the base is left unconnected and the transistor is switched off.  A weak pull-down resistor from the base to the ground could be added to ensure that the transistor stays off when the leads are floating and subject to picking up electrical noise.  That resistor could also be selected so that the base is biased on only when the circuit resistance is less than some value by creating a voltage divider.