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1、山东信息职业技术学院电子工程系English for Electronics it might be pulsating, as from an unfiltered rectifier. And these systems are usually called direct current circuit. The first utility systems installed by Edison used dc technology. Not long after Edison installed his direct current system, others realized tha
2、t the use of an alternating current system had advantages over the dc.山东信息职业技术学院电子工程系Every time we turn on a television set, a radio, or any of a other electrical appliances, we are calling on alternating currents to provide the power to operate them. But, what is the alternating current? Different
3、from direct current moving through a conductor or circuit in one direction only, alternating current, abbreviation, ac, is a current that periodically reverses its direction of flow. As fig.1-4 showing, in one cycle, an alternation starts at zero, rises to a maximum positive level at 90 degrees, ret
4、urns to zero at 180 degrees, rises to a maximum negative level at 270 degrees, and again returns to zero at 360 degrees. The number of such cycles completed per second is termed the ac frequency. In the United States and many other areas of the world, the frequency is 60 hertz or cycles per second.
5、And in our country the current used for the transmission of electrical energy and the operation of common machines has a frequency of 50 hertz. 山东信息职业技术学院电子工程系Ac is widely used for the operation of the vast majority of circuits., which can be transmitted over long distances, even without using conne
6、cting wires between source and receiver , provided the change rate of current is fast enough, transformed to various voltages and easily to larger or smaller values using a device known as a transformer ,but dc cannot. However, in many circuit applications such as general purpose lighting and heatin
7、g, either ac or dc can be used. We can convert dc to ac by using a dc-ac converter, a circuit that converts a dc input voltage into an ac output voltage, with or without step-up or step-down, and ac to dc by rectification circuit formed by the diode, resistor and capacitor. 山东信息职业技术学院电子工程系Try to mat
8、ch the following columns: 1. step-up 负载 2. step-down 直流电路 3. dc-ac converter 交流电路 4. regulated power 整流电路 5. load resistance 直流-交流转换器 6. Series circuit 降压 7. Parallel circuit 稳压电源 8. direct circuit 升压 9. alternating circuit 并联电路 10. rectification circuit 串联电路山东信息职业技术学院电子工程系 Reading: Integrated Circu
9、its In 1958, an extremely important device was invented independently by Jack Kilby, working at Texas Instruments, and by Noyce and Moore at Fairchild Semiconductor: the integrated circuit (IC), which combines BJTs, MOSFETs, resistors, and capacitors, as well as their interconnections, into a functi
10、onal circuit on a single chip. 山东信息职业技术学院电子工程系Integrated Circuits are usually called ICs or chips. They are complex circuits which are combination of a few interconnected circuit elements such as transistors, diodes, capacitors and resistors produced in a single manufacturing process on one and the
11、same bearing structure, called the substrate, and intended to perform a definite function involved in converting information.山东信息职业技术学院电子工程系In the early 1960s, ICs contained perhaps 100 devices, and the smallest features were about 25 micrometers (m). Realizing that the cost of complex electronic sy
12、stems could be reduced dramatically by the use of more complex ICs, process engineers have worked diligently to increase the practical dimensions of chips and to reduce the sizes of the devices. Todays most advanced ICs contain in excess of 10 million devices and have features as small as 0.25 m. (A
13、 human hair is about 25 m in diameter.) The trend toward smaller devices is expected to continue. In addition to the increased number of devices, the reduction in the size of features results in higher performance (i.e., faster) digital circuits. Thus, we can anticipate even greater advances in the
14、field of electronics. 山东信息职业技术学院电子工程系The manufacturing techniques used for ICs can be divided into two main types: film technique and monolithic technique. And ICs can be classified by function into two: circuits to be applied in digital systems and those to be applied in linear systems. The digital
15、 ICs are employed mostly in computers, electronic counters, frequency synthesizers and digital instruments. And the analog or linear ICs operate over a continuous range, and include such devices as operational amplifiers. 山东信息职业技术学院电子工程系These advances will result from teamwork by physical electronics scientists, process engineers, circuit designers, and systems designers. Although this book primarily considers circuit design, it provides useful background
