Page 1016 - Basic Electrical Engineering
P. 1016
energy conversion efficiency and to reduce the cost of manufacturing of solar
cells and solar panels.
14.13.7 Phototransistors
A phototransistor is similar to a bipolar junction transistor, generally an n–p–
n type with a bias voltage applied between the collector and the emitter with
the base terminal kept open. No supply is given to the base. The transistor
action is achieved by the light energy falling on its base–emitter junction.
Thus, instead of base current, light energy provides the input to the base.
Figure 14.53 (a) Photodiode with reverse bias; (b) an illuminated photodiode without any bias
voltage; (c) photovoltaic cell
Figure 14.54 (a) Phototransistor working
An n–p–n type BJT with the base terminal open has been shown in Fig.
14.54. The collector base junction, J is reverse biased while the base–emitter
C
