The 2N3904 is a common NPN bipolar junction transistor used for general-purpose low-power amplifying or switching applications. The type was registered by Motorola Semiconductor in the mid-1960s, 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 and electronics hobbyists. When looking at the flat side with the leads pointed downward, the three wires emerging from the bottom are connected to, from left to right, the emitter, the base and the collector. Some manufacturers mark "EBC" on the molded part, but all are required to have those connections for a part which is a "2N3904".
It is a 200 mA, 40 V, 625 mW transistor with a transition frequency of 300 MHz, with a minimal beta, or current gain, of 100 at a collector current of 10 mA. It is used in a variety of analog amplification and switching applications.
Electrically similar devices, such as the MMBT3904, are available in a variety of small through-hole and surface-mount packages, including TO-92, SOT-23, and SOT-223, with package-dependent thermal ratings from 625 milliwatts to 1 watt.
The higher-power 2N2222 is a very similar NPN transistor that can safely switch three times as much current as the 2N3904. Nevertheless, in many applications such as variable-frequency oscillators, where lower currents are used to minimize thermal heating and consequent thermal drift of the fundamental frequency, the greater current capacity of the 2N2222 gives it no advantage. Whereas the 2N2222 is optimized to reach its highest gain at currents of around 150 mA, the 2N3904 is optimized for currents of around 10 mA.
The 2N3904 (NPN) and 2N3906 (PNP) are complementary transistor pairs.
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- "2N3904 NPN General Purpose Amplifier Datasheet" (PDF). Fairchild Semiconductor. 2001. Retrieved 2011-04-01.
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- Transistor and Diode Data Book (1973, 1236 pages), Texas Instruments
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