![]() ![]() Please help improve it to make it understandable to non-experts, without removing the technical details. This section may be too technical for most readers to understand. The arrow on the symbol for bipolar transistors indicates the p–n junction between base and emitter and points in the direction in which conventional current travels. In this article, current arrows are shown in the conventional direction, but labels for the movement of holes and electrons show their actual direction inside the transistor. On the other hand, inside a bipolar transistor, currents can be composed of both positively charged holes and negatively charged electrons. Because electrons carry a negative charge, they move in the direction opposite to conventional current. However, current in metal conductors is generally due to the flow of electrons. Specialized types are used for high voltage switches, for radio-frequency (RF) amplifiers, or for switching high currents.īy convention, the direction of current on diagrams is shown as the direction that a positive charge would move. Bipolar transistors are still used for amplification of signals, switching, and in mixed-signal integrated circuits using BiCMOS. Hundreds of bipolar junction transistors can be made in one circuit at very low cost.īipolar transistor integrated circuits were the main active devices of a generation of mainframe and minicomputers, but most computer systems now use CMOS integrated circuits relying on field-effect transistors. ![]() Diffused transistors, along with other components, are elements of integrated circuits for analog and digital functions. The superior predictability and performance of junction transistors quickly displaced the original point-contact transistor. ![]() The junctions can be made in several different ways, such as changing the doping of the semiconductor material as it is grown, by depositing metal pellets to form alloy junctions, or by such methods as diffusion of n-type and p-type doping substances into the crystal. A bipolar transistor allows a small current injected at one of its terminals to control a much larger current flowing between the terminals, making the device capable of amplification or switching.īJTs use two p–n junctions between two semiconductor types, n-type and p-type, which are regions in a single crystal of material. In contrast, a unipolar transistor, such as a field-effect transistor (FET), uses only one kind of charge carrier. From top to bottom: TO-3, TO-126, TO-92, SOT-23Ī bipolar junction transistor ( BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. These transistors are available in package styles TO-92, SOT23, SOT223 with different prefixes.Typical individual BJT packages. The 2N3904 (NPN) and 2N3906 (PNP) are complementary transistor pairs. Top view or PCB layout view is shown in the lower right corner. Part numbers Pinout of 2N3904 in TO-92 package. The complementary PNP transistor is 2N3906. It is a 200 mA, 40 V, 625 mW transistor with a transition frequency of 300 MHz, with a minimum beta, or current gain, of 100 at a collector current of 10 mA.Įlectrically 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. ![]() Some manufacturers mark "EBC" on the molded part, but all are required to have those connections for a part which is a "2N3904". 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. This transistor is a low-cost device, widely available and sufficiently robust to be of use by experimenters and electronics hobbyists. The construction of the 2N3904 and 2N3906 in the 1960s represented a significant performance and cost improvement, with the plastic TO-92 case replacing metal cans. Both types were registered by Motorola Semiconductor in the mid-1960s.ĭevice packaging and specifications It is complementary to the 2N3906 PNP transistor. It is designed for low current and power, medium voltage, and can operate at moderately high speeds. The 2N3904 is a common NPN bipolar junction transistor used for general-purpose low-power amplifying or switching applications. A 2N3904 in a TO-92 package on a breadboard (lower left) The pinout from left to right is: Emitter, Base, Collector. Common NPN bipolar junction transistor A 2N3904 made by Motorola. ![]()
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