The 2N3904 is a common NPN BJT used for general purpose low-power amplifying or switching applications. The type was registered by Motorola Semiconductor in the mid-sixties, together with the complementary PNP type 2N3906, and represented a significant performance/cost improvement, with the plastic TO-92 case replacing metal cans. It is designed for low current and power, medium voltage, and can operate at moderately high speeds. This transistor is low cost, widely available and sufficiently robust to be of use by experimenters When looking at the flat side with the base pointed downward, the three wires emerging from the base are, left to right, the emitter, base and collector leads. What is Transistor? A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Features: 1.This device is designed as a general purpose amplifier and switch. 2.The useful dynamic range extends to 100 mA as a switch and to 100 MHz as an amplifier. 3. NPN silicon epitaxial planar transistor for switching and Amplifier applications. 4. As complementary type, the PNP transistor 2N3906 is recommended. 5. This transistor is also available in the SOT-23 case with the type designation MMBT3904. Application: 1. Small load switch transistor with high gain and low saturation voltage. 2. Well suitable for TV and Home application equipment.