2. Write a note of photo transistors ? State advantages of photo transistors over photodiodes
Answers
Answer:
a junction transistor, whose base signal is generated by illumination of the base. The emitter current, and hence collector current, increases with the intensity of the light.
Answer:
Phototransistors resemble normal transistor except the fact that the base terminal is not present in case of the phototransistor. Phototransistors convert the incident light into photocurrent. Instead of providing the base current for triggering the transistor, the light rays are used to illuminate the base region.
The base terminal is made up of the material which shows sensitivity towards the light. The circuit symbol of the phototransistor is similar to that of the conventional transistor but the base terminal can be omitted. The two arrows point towards phototransistor indicates that the phototransistor is triggered by the light incident on it.
Advantages of Phototransistor
Higher Efficiency in Comparison to Photodiode: The efficiency of the phototransistor is higher than that of the photodiode. This is because the current gain in case of the phototransistor is more than that of the photodiode, thus, even if the amount of light incident on both is same the phototransistor will generate more photocurrent than the photodiode.
Faster Response: The response time of phototransistor is more than that of the photodiode, this provides the advantage of using the phototransistor in our circuit.
Less Noise interference: The major drawback of photodiodes especially that of avalanche photodiodes is that it is not immune to noise interference. On the contrary, the phototransistors are immune to noise interference.
Economical: Phototransistor is less costly than other light sensitive device, thus it is economical to use phototransistors in light-sensitive applications.
Less Complex: The designing of phototransistors is simple and less complex as compared to LDRs and photodiodes.
Explanation: