KEC Semiconductors' BJTs - Bipolar Transistors

KEC bipolar transistors are current-controlling electronic devices designed to amplify weak signals into signals with large amplitudes. These devices can be used to amplify or drive current. A bipolar junction transistor (BJT) is a three-terminal semiconductor device consisting of two p-n junctions that amplify or magnify a signal. The three terminals of the BJT are the base, the collector, and the emitter. A small amplitude signal applied to the base is amplified and available at the collector, providing the necessary amplification. Note that BJTs require an external DC power supply to carry out the amplification process.

KEC's broad built-in bias resistor transistors (BJT) allow for energy-efficient designs. Various packages are offered for quick switch time and switching conduction loss reduction, and are used for various applications such as automobiles, home appliances, cellular and data communications.

KEC BJTs are designed to amplify signals from audio frequencies up to very high RF frequencies, making them suitable for high-frequency analog circuits, amplifiers, and temperature sensors. Bipolar power transistors are also used in line-operated applications such as low power, line-operated series pass, and switching regulators requiring PNP capability.

KEC's portfolio of bipolar junction transistors (BJTs) meets a wide range of transistor requirements, with voltages spanning from under 30V to over 100V. KEC's BJTs deliver highly efficient performance with low saturation voltage, fast switching speeds, and a compact footprint.

Unlike semiconductor diodes, which consist of two pieces of semiconductor material forming a single pn-junction, bipolar transistors use an additional layer of semiconductor material to produce a device with the properties and characteristics of an amplifier. The basic construction of a bipolar transistor includes two PN-junctions producing three connecting terminals: the Emitter (E), the Base (B), and the Collector (C).

Bipolar transistors are current-regulating devices that control the amount of current flowing from the Emitter to the Collector terminals in proportion to the biasing voltage applied to the base terminal, acting like a current-controlled switch. A small current flowing into the base terminal controls a much larger collector current, forming the basis of transistor action.

The transistor was invented in 1947 by W. Shockley, J. Bardeen, and W. Brattain. The term "transistor" is derived from the words "transfer" and "resistor," describing the operation of a BJT, which transfers an input signal from a low resistance circuit to a high resistance circuit. BJTs were among the first functional transistor devices ever created, emerging from Bell Laboratories in the late 1940s. The inventors were awarded the 1956 Nobel Prize for their efforts in bringing bipolar junction transistors to mass production.

A BJT can be thought of as two PN junctions combined, whereas a diode is just a single PN junction. When viewed externally and measured with a multimeter in diode mode, a BJT transistor appears like two diodes connected together. The key to a bipolar transistor's usefulness lies in the interaction between these two diodes.

Think of a diode as a flap valve that opens when voltage is applied in one direction and closes when voltage is applied in the opposite direction. In a transistor, the two diodes have a linkage between their flap valves in the base, which is closer to both the collector and emitter than to the metal connection. In an NPN transistor, when electrons flow from the emitter to the base, this action opens the valve between them, which in turn opens the valve between the base and the collector, allowing electrons to flow to the collector as well.

If you were to connect two separate PN diodes together by joining the P-doped regions, there wouldn't be any part of the P-doped region closer to both N-doped regions than to the metal attachment point. Consequently, there would be no area where the "valves" created by the PN junctions would be interconnected. Expecting two diodes to behave as a transistor would be like expecting two separate inductors to function as a transformer.

BJTs can increase both analog and digital signals and have the ability to switch DC power supply or function as oscillators. While BJTs are primarily designed to amplify analog current, they can also serve as electronic digital switches in circuitry.