This is the first and foremost rule in the use of transistors: all currents must be going in the proper directions for the device to work as a current regulator. In other words, two types of charge carriers - electrons and holes - comprise this main current through the transistor.Īs you can see, the controlling current and the controlled current always mesh together through the emitter wire, and their electrons always flow against the direction of the transistor\’s arrow. Small Base-Emitter current controls large Collector-Emitter current flowing against emitter arrow.īipolar transistors are called bipolar because the main flow of electrons through them takes place in two types of semiconductor material: P and N, as the main current goes from emitter to collector (or vice versa). The small current that controls the main current goes from base to emitter, or from emitter to base, once again depending on the kind of transistor it is (PNP or NPN, respectively).Īccording to the standards of semiconductor symbology, the arrow always points against the direction of electron flow. The main current that is controlled goes from collector to emitter, or from emitter to collector, depending on the type of transistor it is (PNP or NPN, respectively). In other words, transistors restrict the amount of current passed according to a smaller, controlling current. Difference between a PNP transistor and an NPN transistorĬapacitor Working Principle - Animation - Tutorials - Explained Working Principleīipolar transistors work as current-controlled current regulators. The schematic symbols are shown in Figure below(a) and (d).īJT transistor: (a) PNP schematic symbol, (b) physical layout (c) NPN symbol, (d) layout. BJT LayersĪ bipolar transistor consists of a three-layer “sandwich” of doped (extrinsic) semiconductor materials, either P-N-P in Figure below(b) or N-P-N at (d).Įach layer forming the transistor has a specific name, and each layer is provided with a wire contact for connection to a circuit. In taking this approach, however, I assume that the reader possesses a certain minimum knowledge of semiconductors: the difference between “P” and “N” doped semiconductors, the functional characteristics of a PN junction (diode), and the meanings of the terms “reverse biased” and “forward biased.” If these concepts are unclear to you, it is best to refer to earlier chapters in this book before proceeding with this one. I don\’t mean to downplay the importance of understanding semiconductor physics, but sometimes an intense focus on solid-state physics detracts from understanding these devices\’ functions on a component level.
#BIPOLAR TRANSISTOR CIRCUIT WITH 2 RESISTORS HOW TO#
Here I want to explore how to use these components, not analyze their intimate internal details. Discussions of holes and electrons are better left to another chapter in my opinion. My intent here is to focus as exclusively as possible on the practical function and application of bipolar transistors, rather than to explore the quantum world of semiconductor theory. Understanding how transistors function is of paramount importance to anyone interested in understanding modern electronics.
This revolution made possible the design and manufacture of lightweight, inexpensive electronic devices that we now take for granted. Technical feats previously requiring relatively large, mechanically fragile, power-hungry vacuum tubes were suddenly achievable with tiny, mechanically rugged, power-thrifty specks of crystalline silicon. The invention of the bipolar transistor in 1948 ushered in a revolution in electronics.
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