Transistors are built by stacking three different layers of semiconductor material together. Using the diode (or resistance) test function on a multimeter, you can measure across the BE and BC terminals to check for the presence of those 'diodes'.) Transistor Structure and Operation (This model is useful if you need to test a transistor. There's a whole lot of weird quantum physics level stuff controlling the interactions between the three terminals. Don't base your understanding of a transistor's operation on that model (and definitely don't try to replicate it on a breadboard, it won't work). The diode representation is a good place to start, but it's far from accurate. The diode connecting base to emitter is the important one here it matches the direction of the arrow on the schematic symbol, and shows you which way current is intended to flow through the transistor. By narrowing our focus down - getting a solid understanding of the NPN - it'll be easier to understand the PNP (or MOSFETS, even) by comparing how it differs from the NPN. We'll turn our focus even sharper by limiting our early discussion to the NPN. Digging even deeper into transistor types, there are actually two versions of the BJT: NPN and PNP. In this tutorial we'll focus on the BJT, because it's slightly easier to understand. There are two types of basic transistor out there: bi-polar junction (BJT) and metal-oxide field-effect (MOSFET). Applications II: Amplifiers - More application circuits, this time showing how transistors are used to amplify voltage or current.Applications I: Switches - Application circuits showing how transistors are used as electronically controlled switches.Operation Modes - An overview of the four possible operating modes of a transistor.Extending the Water Analogy - Going back to the water analogy to explain how a transistor acts like a valve.Symbols, Pins, and Construction - Explaining the differences between the transistor's three pins.This tutorial is split into a series of sections, covering: We won't dig too deeply into semiconductor physics or equivalent models, but we'll get deep enough into the subject that you'll understand how a transistor can be used as either a switch or amplifier. Covered In This TutorialĪfter reading through this tutorial, we want you to have a broad understanding of how transistors work. In quantities of thousands, millions, and even billions, transistors are interconnected and embedded into tiny chips to create computer memories, microprocessors, and other complex ICs. If this is the case for all the transistor leads, the transistor is good.In small, discrete quantities, transistors can be used to create simple electronic switches, digital logic, and signal amplifying circuits. Resistance of a few hundred thousand ohms. So in total we'll have six readings, which are shown below:Įach pair should have one side with very high resistance (>1MΩ), and the other side with a much lower Other side should read a much lower resistance, maybe of a few hundred thousand ohms (the cathode-to-anode side). One side of the diode junction should read a very high resistance, above 1MΩ of resistance (the anode-to-cathode side) and the To the reverse position, to switch polarity. To test a transistor, we measure one diode junction with the multimeter leads situated one way and then we flip the leads of the multimeter If you want to learn more about diode testing, check out Of transistors as if they are separate diodes. Knowing that transistors are essentially diodes sandwiched together (placed back-to-back), we can exploit this principle and test the leads

Transistor tester schematic