![]() ![]() A discrete transistor has three leads for connection to these regions. The regions of a BJT are called emitter, base, and collector. NPN BJT with forward-biased B–E junction and reverse-biased B–C junctionĬharge flow in a BJT is due to diffusion of charge carriers (electrons and holes) across a junction between two regions of different charge carrier concentration. 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. The WIKA pressure switch PSD-30 is available either with PNP or NPN switching output.A bipolar junction transistor ( BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, in North America, the country where the transistor was invented, relay outputs with potential-free contacts for AC 110 V loads are most widely used. In my experience, PNP switching outputs are used mainly in Europe, and NPN outputs almost exclusively in Asia. When a change in signal takes place by reaching a pressure value, the supply voltage (U+) is “switched on”, allowing current to flow from U+ through the load via the transistor and to GND. The load is connected to the switching output with U+ as the reference point. When a change in signal takes place by reaching a pressure value, the supply voltage (U+) is “switched through”, allowing current to flow from U+ through the transistor and through the load to GND. The load is connected to the switching output with GND as the reference point. This is why the load must be connected differently to the transistor outputs. In principle, both are bipolar transistors in which only the internal arrangement of the pn transitions differs. Here is a brief explanation how the two different outputs should be connected. Manufacturers of electronic pressure switches often offer both PNP and NPN switching outputs. ![]()
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