電子信息專業(yè)英語(yǔ)ppt課件-資料下載頁(yè)
2025-05-01 18:02本頁(yè)面
【正文】 子工程系 The symbol and standard labeling for the operational amplifier are shown in Fig 24(a). The two required external power supplies have been explicitly shown in the diagram, although showing them is not the usual practice. All five currents have been labeled, in addition to appropriate node voltages, referred to the indicated mon ground terminal. In this primitive circuit, the voltage vi is used to control the output voltage vo. Let us examine this control function in detail to find out both the extent of the control, and the cost of the control。 that is, how much power must be applied from source vi to control a given amount of power at the vo terminal. To address the first problem, we set up the circuit exactly as in Fig 25(a), and measure the output voltage vo, both as a function of time and as a function of vi, assuming vi is some lowfrequency sinusoid. The results are shown in Fig 25(b) and 25(c). Note the difference in scale of the voltage axes, indicating that the output voltage is perhaps 300,000 times as large as the input voltage. The plot of vo versus vi shows a region around the origin where vo is fairly linearly related to vi, but much beyond this range the control bees ineffective, and vo stays at a fixed voltage, or saturates, at roughly either +12 volts or ?12 volts, depending on the polarity of vi. The curves will also differ for different samples of the same Op Amp type. 山東信息職業(yè)技術(shù)學(xué)院電子工程系 Different devices of the same type might have different characteristics. The characteristics might also depend on temperature. One key to the usefulness of these little circuits is in the engineering principle of feedback, particularly negative feedback, in which a portion of the output signal of the Op Amp is fed back to the v? input of the Op Amp. And it constitutes the foundation of almost all automatic control processes. Examples of Op Amp circuits built this way include inverting and noninverting amplifiers, buffers, adders, integrators, and differentiators. Op Amp circuits are sometimes built using the positive feedback connection, in which a portion of the output signal of the Op Amp is fed back to the v+ input of the Op Amp. Examples of such Op Amp circuits include oscillators and parators. 山東信息職業(yè)技術(shù)學(xué)院電子工程系 Homework 翻譯 ? A practical energy source may take one of many forms, for example, depending on electrochemical, electromagic, thermoelectric and photoelectric etc., in principle, but for the purpose of circuit analysis only two idealized forms are recognized, to one of which all practical sources approximate. There are the voltage source and the current source. ? The voltage source maintains a constant terminal voltage irrespective of the current supplied to the load. It is important to appreciate that the voltage may be a function of, for example, time, temperature, pressure etc. It is constant only with respect to variations of load. ? The current source maintains a constant current in the load irrespective of the terminal voltage which, in this case, is determined by the magnitude of the load. As with the voltage source, the generated current may depend on many other factors, but its one essential attributes is its independence of load.
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