电子技术专业英语教学课件作者何茗unit1.ppt

Unit 1 Basis of Electric Circuits,Electric circuits The elements that comprise the circuit model are called ideal circuit components. An ideal circuit component is a mathematical model of an actual electrical component, like a battery or a light bulb. It is important for the ideal circuit component used in a circuit model to represent the behavior of the actual electrical component to an acceptable degree of accuracy. The tools of circuit analysis, the focus of this unit, are then applied to the circuit.,下一页,返回,Unit 1 Basis of Electric Circuits,Circuit analysis is based on mathematical techniques and is used to predict the behavior of the circuit model and its ideal circuit components. A comparison between the desired behavior, from the design specifications, and the predicted behavior, from circuit analysis, may lead to refinements in the circuit model and its ideal circuit elements. Once the desired and predicted behaviors are in agreement, a physical prototype can be constructed.,下一页,上一页,返回,Unit 1 Basis of Electric Circuits,The physical prototype is an actual electrical system, constructed from actual electrical components. Measurement techniques are used to determine the actual, quantitative behavior of the physical system. This actual behavior is compared with the desired behavior from the design specifications and the predicted behavior from circuit analysis. The comparisons may result in refinements to the physical prototype, the circuit model, or both. Eventually, this iterative process, in which models, components, and systems are continually refined, may produce a design that accurately matches the design specifications and thus meets the need.,下一页,上一页,返回,Unit 1 Basis of Electric Circuits,From this description, it is clear that circuit analysis plays a very important role in the design process. Because circuit analysis is applied to circuit models, practicing engineers try to use mature ciruit models so that the resulting designs will meet the design specifications in the first iteration. In this unit, we use models that have been tested for between 20 and 100 years; you can assume that they are mature. The ability to model actual electrical systems with ideal circuit elements makes circuit theory extremely useful to engineers.,下一页,上一页,返回,Unit 1 Basis of Electric Circuits,Saying that the interconnection of ideal circuit elements can be used to quantitatively predict the behavior of a system implies that we can describe the interconnection with mathematical equations. For the mathematical equations to be useful, we must write them in terms of measurable quantities. In the case of circuits, these quantities are voltage and current. The study of circuit analysis involves understanding the behavior of each ideal circuit element in terms of its voltage and current and understanding the constraints imposed on the voltage and current as a result of interconnecting the ideal elements.,下一页,上一页,返回,Unit 1 Basis of Electric Circuits,Circuit analysis is based on the variables of voltage and current. Voltage is the energy per unit charge created by charge separation and has the SI unit of volt v=dw/dq. Current is the rate of charge flow and has the SI unit of ampere (i=dq/dt).The ideal basic circuit element is a twoterminal component that cannot be subdivided; it can be described mathematically in terms of its terminal voltage and current. The passive sign convention uses a positive sign in the expression that relates the voltage and current at the terminals of an element when the reference direction for the current through the element is the direction of the reference voltage drop across the element,下一页,上一页,返回,Unit 1 Basis of Electric Circuits,Power is energy per unit of time and is equal to the product of the terminal voltage and current; it has the SI unit of watt. The algebraic sign of power is interpreted as follows: If p0, power is being delivered to the circuit or circuit component. If p0, power is being extracted from the circuit or circuit component.,下一页,上一页,返回,Unit 1 Basis of Electric Circuits,The circuit elements introduced in this chapter are voltage sources, current sources, and resistors. An ideal voltage source maintains a prescribed voltage regardless of the current in the device. An ideal current source maintains a prescribed current regardless of the voltage across the device. Voltage and current sources are either independent, that is, not influenced by any other current or voltage in the circuit; or dependent, that is, determined by some other current or voltage in the circuit. ,下一页,上一页,返回,Unit 1 Basis of Electric Circuits,A resistor constrains its voltage and current to be proportional to each other. The value of the proportional constant relating voltage and current in a resistor is called its resistance and is measured in ohms. Ohm’s Law establishes the proportionality of voltage and current in a resistor. Specifically V=IR if the current flow in the resistor is in the direc。