机电专业英语讲义.ppt.Convertor

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一 1.1 Bipolar junction transistors

Today, industrial electronic systems employseveral devices that are described by the term transistor. Each type of transistor has different characteristics and operational conditions that are used to distinguish it from others.

每种晶体管都有区别于其它种类的特征和工作环境。

In the first part of this discussion, we are concerned with the . Structurally, this transistor is described as bipolar because it has two different current-carrier polarities.

首先探讨双极型晶体管。从结构上看，这种晶体管被称为双极是因为它具有两种不同的电流载流子电极。Holes are positive current carriers, whereas electrons are negative current carriers.

空穴是正的载流子，电子是负的电流载流子。

Two distinct kinds of semiconductor crystals are connected together by a common element. 两种截然不同的半导体晶体通过公共元件连接在一起。

The structure of this device is similar to that of two diodes connected back to back, with one crystal being common to both junctions. The center material is usually made thinner than the two outside pieces. 该器件的结构类似于背靠背连接的两个二极管的结构，一个晶体同时属于两个结。其中间的材料通常比两个外边的作得窄些。

In the operation of a single PN diode junction, forward biasing causes conduction and reverse biasing causes nonconduction. 单个PN二结的工作情况是：正向偏置促使其导通，反向偏置导致其截止。

In a transistor, this rule does not apply directly because two junctions are involved. 因为晶体管包含两个结，该规则不能直接应用

For example, when the emitter-base junction is forward biased, it causes a large amount of IE to enter the base region. 例如，其发射-基极处于正向偏置时，它会促使大量的IE 进入基区。

Reverse biasing of the base-collector junction would ordinarily restrict this current. 而基-集电极的反向偏置会限制该电流。

But due to the thin base structure, IE will immediately enter into the collector current IC or output current. 但因基区窄，IE会很快进入集极电流IC或输出电流.

Forward biasing of the emitter-base junction therefore alters or reduces the reverse biasing effect of the base-collector junction in normal transistor operation. 因而，在一般的晶体管工作中，发射-基结的正向偏置会改变或减少基-集结反向偏置的影响。

A transistor is primarily classified as a current-operating device. This means that the output or collector IC will occur only when the emitter-base is forward biased and producing base current. 晶体管被划分为基本电流型器件。这意味着仅仅当发射-基结处于正偏且有基极电流IB时才会有其输出或集电极电流IC

When the base current ceases, collector current stops and the transistor become nonconductive. This condition is called cut off. 当基极电流消失时，集电极电流停止，晶体管处于非导通状态。这种情况就称为截止。

On the other hand, if an excessive amount of base current occurs, the transistor is driven into saturation. When this condition occurs, a further increase in IB will not cause a corresponding change in IC. 相反，如果基极电流过大，晶体管处于饱和状态。在这种情况下，再增加IB不会引起IC的相应变化。

When amplitude control is being achieved, a transistor is rarely operates in the saturation region. When a transistor is used as a switch, it usually operates in the saturation region. 进行幅值控制时晶体管几乎不会处于饱和区。而当它作为开关使用时，经常工作在饱和区。

1.2 UJT Thyristors and SCRS

Thyristors should not be confused with s or field-effect transistors. 不应将晶闸管与双结型晶体管（s，BJTs）或场效应管（field-effect transistors，FETs）混淆起来.

BJTs and FETs are both capable of performing switching operations. As a rule, these devices are not as efficient as thyristor and do not have the power-handling capability. BJTs与FETs都能够完成开关操作。按照惯例，这些器件并没有晶闸管那么有效率且不具备功率（电力）处理能力。Thyristors are used as power control devices, whereas