2N4403

Classic PNP silicon switching and general-purpose amplification small-signal transistor housed in a plastic TO-92 package, engineered as the exact complementary match to the 2N4401 to handle medium-current push-pull designs. Equivalents: PN4403, 2N3906 (lower current variant), KN4403, NTE159. Real-Life Examples: Complementary audio power output driver pairs, portable radio headphone amplifiers, industrial multi-channel solenoid actuators, and analog sensor signal conditioning blocks.