2N3904

The 2N3904 is a widely used NPN bipolar junction transistor (BJT) intended for general-purpose amplification and switching. It is a small-signal transistor typically manufactured in the TO-92 plastic package and is compatible with standard low-voltage circuits.

Electrical characteristics: It is a silicon NPN device suitable for common-emitter or common-collector configurations. The maximum collector-emitter voltage is typically 40 V, the maximum collector-base voltage 60 V, and the maximum emitter-base voltage 5 V. The maximum continuous collector current is about 200 mA, and the total power dissipation is around 350 mW depending on package and mounting, ambient temperature; datasheets give variations. The DC current gain (hFE) is typically in the 100 to 300 range at ~10 mA collector current. The transition frequency fT is around 300 MHz, indicating good high-frequency performance for a small-signal transistor.

Pinout and package: In the TO-92 package, viewed from the flat face with leads pointing downward, the typical pin order is emitter, base, collector (E-B-C). Pin assignments can vary by manufacturer, so consulting the specific datasheet is advised.

Applications: Used as a general-purpose amplifier, switch, buffer, or oscillator in low-power audio, signal processing, and logic circuits. It is commonly paired with the complementary PNP transistor 2N3906 in push-pull stages.

Manufacture and variants: The 2N3904 is a standard part produced by many manufacturers and available in various packaging options and tolerances. Its popularity stems from robust performance, availability, and low cost in the 2N-series family.