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Electronics for dummies - McComb G.

McComb G., Boes E. Electronics for dummies - Wiley publishing, 2005. - 433 p.
ISBN: 0-7645-7660-7
Download (direct link): electronicsfordummies2005.pdf
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^ Base ^ Emitter ^ Collector
A base is wired to a voltage or current and turns the transistor on or off. Emitter and collectors leads connect to a positive or negative voltage source or ground. Which lead goes where varies with the circuit.
You can see this arrangement of connections in Figure 4-11. A few transistors, most notably the field-effect transistor (or FET), include a fourth lead. This lead grounds the case to the chassis of the circuit.
BASE
METAL
TRANSISTOR
BASE
PLASTIC
TRANSISTOR
You absolutely, positively have to make sure that you donít install a transistor the wrong way in your circuit. Switching the connections around can damage the transistor and sometimes other components. You can find yourself even more confused by transistor connections because theyíre often (though not always!) shown from the underside of the case because thatís
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Chapter 4: Getting to Know You: The Most Common Electronic Components
87
where you solder them on. That is, the lead pinouts look as if youíve turned the transistor over and are looking at it from the bottom. This perspective makes soldering the transistor in a circuit board easier.
Transistor types
First, transistors qualify as either NPN or PNP devices. These mysterious abbreviations refer to the sandwiching, or junctions, of the semiconductor materials inside the device. Unless you have x-ray vision, you canít tell the difference between an NPN and PNP transistor just by looking at them. However, the catalog specification sheets, as well as schematics, should tell you the difference, as in Figure 4-12. You select NPN and PNP devices based on how you plan to use the transistor in the circuit. We canít get into the nitty-gritty of choosing an NPN or PNP transistor here because it could fill a whole book. But we can say that you canít mix-and-match NPN and PNP transistors. If a circuit calls for a PNP transistor, you canít substitute an NPN type without expecting to see smoke billowing out of some part of your device.
Figure 4-12:
Schematic symbols for NPNand PNP transistor types. For an NPN, the arrow points out from the center of the symbol. For a PNP, the arrow points in.
NPN TRANSISTOR
PNP TRANSISTOR
As if you didnít have enough stuff to memorize, in addition to the junction type, transistors are categorized by how the junction is created during manufacturing. The two main types of transistors that youíre likely to encounter are bipolar and FET. Hereís how they differ:
Bipolar transistors: These transistors are the most common kind (and theyíre the kind that we cover in the preceding sections). A small input current is applied to the base of the transistor. This in turn, changes the amount of current that flows between the collector and emitter.
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Part II: Aisle 5, Component Shack: Stocking Up
^ FETs (field effect transistors): These transistors also have three connections, but you call those connections gate, source, and drain, rather than base, collector, and emitter. Applying a voltage to the gate controls the current between the source and drain. FETs come in two types: N-chan-nel (similar to NPN) and P-channel (similar to PNP).
Technically, FETs come in two sub types: MOSFET and JFET. For the purposes of your basic electronics education, the differences between these two types donít really matter, but knowing this kind of secret electronics language helps you sound smarter when you talk to your electronics geek friends.
Static discharge can damage FET transistors. At the very least, always store your FETs in anti-static foam. When buying FETs, keep them in their antistatic bag or tube and leave them there until youíre ready to use Ďem.
Packing Parts Together on Integrated Circuits
All the components that we mention in the earlier sections of this chapter come just one to a package. Electronics mavens call them discrete components, meaning separate. (Donít confuse the word with discreet which means minding your own business.)
Enter the integrated circuit, the true marvel of the 20th century. Also called a chip or IC, these amazing creations are miniature circuit boards produced on a single piece of semiconductor. A typical integrated circuit contains hundreds of transistors, resistors, diodes, and capacitors. Because of this circuit efficiency, you can build really complex circuits with just a couple of parts.
ICs are the building blocks of larger circuits. You string them together to form just about any electronic device you can think up.
The way that all the components are wired inside an IC determines what the IC does. You can either solder the IC directly into the circuit board or mount it in a socket.
Integrated circuits most often come enclosed in dual in-line pin (DIP) packages, such as the ones in Figure 4-13. This illustration shows several sizes of DIP ICs, from 8-pin to 40-pin. The most common sizes are 8-, 14-, and 16-pin.
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