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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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R = (6 - 1.2) / 0.040
Do the math in your head, on paper, or with a calculator, and you see that R equals 120 (ohms). So, to pass 40 mA of current through this particular LED when using a 6-volt supply, you use a 120-ohm resistor. Remember to do the calculation again if you change the voltage of the power supply or use an LED with a higher or lower forward voltage drop.
The Transistor: A Modern Marvel
Imagine the world without the simple transistor. Radios would all be the size of a toaster oven. Cell phones would be the size of a washing machine. And todayís super fast computers would be the size of . . . Rhode Island.
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Transistors were developed as an alternative to the vacuum tube. The two main ways that you can use transistors (or vacuum tubes, for that matter) are to amplify a signal or to switch a signal on and off. Besides its small size, a transistor has another advantage ó it uses less power than a vacuum tube to accomplish the same job.
With creative connections in a circuit, you can also use transistors to switch or amplify voltages. This fancy circuit work can confuse you when youíre studying circuits involving transistors. Transistors are very complex little critters, so we just talk about the basic types you encounter when you begin working in the electronics world, what they look like, and other getting-to-know-you details in this book.
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Millions of individual transistors make up the microprocessor at the heart of your home computer. Without transistors, we would live in a world with no PCs. (Hmmm...late at night, slaving away on my computer, I think maybe transistors arenít such a great idea after all... )
Slogging through transistor ratings
Resistors, capacitors, and even diodes have fairly simple and straightforward ratings. But the transistor just has to be difficult. These doohickeys are rated by a number of criteria far too extensive for this book to tackle. Here are just a very few of them:
Collector-to-base voltage Collector-to-emitter voltage Maximum collector current Maximum device dissipation Maximum operating frequency
I am not a number, I'm a free transistor!
At last count, you can find several thousand different transistors currently available from more than two dozen manufacturers. How can you tell them apart? A unique number code, such as 2N2222 or MPS6519, identifies each kind of transistor. If you're rebuilding a circuit that you see in a book or on a Web page, use the transistor number code to find a match.
If you can't find an exact match, you can probably use a close substitute. Transistor manufacturers provide substitution guides that help you find which one of their parts closely matches the transistor that you're looking for. NTE, a major reseller of replacement transistors, provides a popular transistor substitution guide. Visit their Web site at www.nteinc.com for an online cross-reference substitution guide.
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Chapter 4: Getting to Know You: The Most Common Electronic Components
None of these ratings appears anywhere on the transistor ó that would be too easy. To determine these characteristics, you have to look up the transistor in a specifications book, or consult the technical documentation at the manufacturerís Web site. For basic electronics tinkering, you donít need to know ó or even understand ó what these specifications mean. More than likely, you simply use the transistor that your project specifies.
Figure 4-10 shows a grab bag of different kinds of transistors.
The semiconductor material in a transistor is the size of a grain of sand or even smaller. Itís kind of hard to solder wires to something so teensy, so they put semiconductor material in a metal or plastic case. You can find literally dozens and dozens of sizes and styles of transistor cases, and this book definitely canít describe them all. But to help you identify the most common types, hereís what you should look for:
^ Plastic or metal: Signal transistors come in either plastic or metal cases. The plastic variety works for most uses, but some precision applications need the metal variety because transistors that use metal cases (or cans) are less susceptible to stray radio frequency interference. Signal transistors almost always have three lead connections (sometimes four). If the transistor has just two wires, itís probably the light-dependent type, which we talk about in Chapter 5.
^ Size matters: Power transistors come in both plastic and metal cases, and theyíre physically larger than signal transistors.
On the case of transistor cases
Figure 4-10:
A sampler of signal and
power
transistors.
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Figure 4-11:
This is a view of the underside of a package of a three-lead transistor.
Making connections
Transistors typically have three wire leads. The leads in the typical three-lead transistor are
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