Hello friends, in this article I am going to tell you what is a photo transistor?, symbol and structure of a phototransistor use of a photo transistor. so let’s start
What is a photo transistor?
A phototransistor is similar to a normal bipolar transistor, it does not have a base terminal. In place of the base current, light is used to give input to the transistor. The symbol and structure of the phototransistor are shown in the picture.
phototransistor symbol
Structure of PhotoTransistor
The structure of the photo-transistor consists of a light-sensitive collector-base junction. Thus, most of the ed-hole pair generation for base current takes place in the collector-base region. Therefore the area of this region is also more.
There is no electrical connection at the base of the photo-transistor, light is used as an input in this device. When no light falls on its base, a small leakage current flows through the ICFO. This flowing current is called a dark current.
The value of dark current is in nano ampere. When light falls on it, electron-hole pair is generated in its collector-base junction, which produces base current (Ib).
The value of base current (Ib) is directly proportional to Ic. Collector current (IC) is B times the base current. Hence collector current is also directly proportional to the intensity of light.The biasing circuit and characteristic curve of the photo-transistor are shown. This curve shows the relationship between collector to emitter voltage (Vcr) and collector current (Ic) at different light intensities, just like in a normal transistor.
It has been shown in the Characteristics, that when the light intensity at the collector-base junction of the phototransistor increases, the number of electron-hole pairs also increases. Hence the collector current (ic) also increases.
uses of photo transistor?
The maximum use photo-transistor is used in optical switches and solar cells.
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Now you must know what is a phototransistor?, the Symbol and structure of a phototransistor, use of a phototransistor. You must have got a good knowledge of this subject.
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