传感器原理传感器原理 (55).ppt
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1、Principle of Sensors传感器原理光电式传感器Photoelectric Sensors 8.3.3 光敏晶体管 Phototransistors 光敏晶体管光敏晶体管光敏晶体管光敏晶体管 PhototransistorsPhototransistors包括:光敏二极管和光敏三极管。包括:光敏二极管和光敏三极管。包括:光敏二极管和光敏三极管。包括:光敏二极管和光敏三极管。Including:photodiode and phototransistor.Including:photodiode and phototransistor.特点:特点:特点:特点:响应速度快、频率响应好
2、、灵敏度高、可靠性高。Features:Features:Fast response speed,good frequency response,high sensitivity and high reliability.应用:应用:应用:应用:广泛应用于可见光和远红外探测,以及自动控制、自动报警、自动计数等领域和装置。Applications:Applications:Widely used in visible light and far infrared detection,as well as automatic control,automatic alarm,automatic co
3、unting and other fields and devices.光敏二极管光敏二极管光敏二极管光敏二极管 Photosensitive diode Photosensitive diode 结结结结构构构构:光敏二极管的结构与一般二极管相似、它装在透明玻璃外壳中,其PN结装在管顶,可直接受到光照射。Structure:Structure:The structure of photodiode is similar to that of general diode.It is installed in transparent glass shell,and its PN junction
4、 is installed on the top of the tube,which can be directly irradiated by light.注注注注意意意意:光敏二极管在电路中一般处于反向偏置状态。(注注注注意意意意与与与与发发发发光光光光二二二二极极极极管管管管的的的的区区区区别别别别)其原理结构和基本电路如图所示。Note:Note:Photodiodes are generally in reverse bias state in the circuit.(Pay(Pay attention attention to to the the difference diff
5、erence from from light light emitting emitting diodes)diodes)Its principle structure and basic circuit are shown in the figure.工作原理工作原理工作原理工作原理 Working principleWorking principle无光照时:光敏二极管处于载止状态,反向电阻很大,反向电流很小,这时只有少数载流子在反向偏压的作用下,渡越阻挡层形成微小的反向电流即暗电流;有光照时,光敏二极管的工作原理与光电池的工作原理很相似,P-N结处产生光生电子-空穴对;光敏二极管的光电流
6、 I 与照度之间呈线性关系。在电场作用下形成光电流,光照越强光电流越大;光电流方向与反向电流一致。When there is no illumination:the photodiode is in a stop state,the reverse resistance is very large,and the reverse current is very small.At this time,only a few carriers cross the barrier layer to form a tiny reverse current,that is,dark current;Whe
7、n there is illumination,the working principle of photodiode is very similar to that of photocell,and photo-generated electron-hole pairs are generated at P-N junction;There is a linear relationship between photocurrent I and illumination of photodiode.Under the action of electric field,photocurrent
8、is formed,and the stronger the illumination,the greater the photocurrent;The photocurrent direction is consistent with the reverse current.光敏三极管光敏三极管光敏三极管光敏三极管Phototransistor Phototransistor 光敏三极管有PNP型和NPN型两种。光敏三极管是兼有光敏二极管特性的器件,它在把光信号变为电信号的同时又将信号电路放大,因而光敏三极管具有更高的灵敏度。Phototransistor has PNP type and
9、NPN type two.Phototransistor is a device with the characteristics of photodiode,which turns optical signal into electrical signal and amplifies signal circuit at the same time,so phototransistor has higher sensitivity.光敏三极管光敏三极管光敏三极管光敏三极管Phototransistor Phototransistor 结构:结构:结构:结构:与一般三极管相似,具有电流增益,只是
10、它的发射极一边做的很大,以扩大光的照射面积,且其基极不接引线。当集电极加上正电压,基极开路时,集电极处于反向偏置状态。Structure:Structure:Similar to ordinary transistor,it has current gain,except that its emitter side is made very large to expand the illumination area of light,and its base is not connected with leads.When a positive voltage is applied to th
11、e collector and the base is open,the collector is in a reverse bias state.光敏三极管光敏三极管光敏三极管光敏三极管Phototransistor Phototransistor 原理:原理:原理:原理:当光线照射在集电结的基区时,会产生电子-空穴对,在内电场的作用下,光生电子被拉到集电极,基区留下空穴,使基极与发射极间的电压升高,这样便有大量的电子流向集电极,形成输出电流,且集电极电流为光电流的倍。Principle:Principle:When the light irradiates the base region
12、of the collector junction,an electron-hole pair will be generated.Under the action of the internal electric field,the photo-generated electrons will be pulled to the collector,leaving holes in the base region,which will increase the voltage between the base and the emitter,so that a large number of
13、electrons will flow to the collector,forming an output current,and the collector current is times of the photocurrent.光敏三极管光敏三极管光敏三极管光敏三极管Phototransistor Phototransistor 注意:注意:注意:注意:无论NPN、还是PNP型,一般集电结加反偏。Note:Note:No matter NPN or PNP type,the collector junction is generally reverse biased.光敏三极管的光谱特
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