4/21/2021 0 Comments Photo Transistor Switch Circuit
The input of a sensor can be ay physical quantity like Light, Sound, Temperature etc.
![]() ![]() ![]() Usually, when comparing to a similar photodiode, a phototransistor can provide a current that is 50 to 100 times that of a photodiode. In a two-leaded Phototransistor, the Base terminal electrically unavailable and the device is completely dependent on light. When there is no light falling on the phototransistor, a small amount of leakage current known as Dark Current flows from collector to emitter. The following image shows the collector current characteristics curve. When used, it acts as a regular BJT and when not used, it acts as a Phototransistor. Phototransistor usually have a specific range of wavelengths that they can sense. How linearly the output varies according to the intensity of the light is an important consideration. Also, how quickly the output responds to the changes in the intensity of the light will determine the response time. When it is dark or the intensity of light is less, the phototransistor is OFF and this allows proper biasing of transistor Q2. When the light falls on the photo transistor, which is the usual case, it is turned ON and the gate of the SCR is LOW. As a result, the alarm is activated and it can be reset using the switch.
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