Sensor Technology: Principles, Designs and Applications (Sachan Book 25) by Dr. Vibhav Kumar Sachan

Sensor Technology: Principles, Designs and Applications (Sachan Book 25) by Dr. Vibhav Kumar Sachan

Author:Dr. Vibhav Kumar Sachan [Sachan, Dr. Vibhav Kumar]
Language: eng
Format: azw3, pdf
Publisher: Smt. Jay Devi Sachan Memorial Publication House
Published: 2019-09-27T16:00:00+00:00


Figure 1.32: Characteristics of Photo-transistor

Generally, the sensitivity of a phototransistor is a function of the DC current gain of the transistor. Therefore, the general sensitivity is a function of the collector current and can be controlled by connecting a resistor between the base and the emitter, but for very high sensitivity optocoupler type applications Darlington phototransistors are generally used.

Figure 1.33: Photo-Darlington

Photo Darlington transistors use a second NPN bipolar transistor to provide additional amplification or when higher sensitivity is required from a photodetector due to low light levels or selective sensitivity, but its response is slower than that of a common NPN phototransistor. Photo Darlington devices consist of a normal phototransistor whose emitter output is coupled to the base of a larger NPN bipolar transistor. Because the configuration of a Darlington transistor provides a current gain equal to a product of the current gains of two individual transistors, a Darlington photographic device produces a very sensitive detector.



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