What is a phototransistor and how does it work?
A phototransistor is similar to a regular BJT except that the base current is produced and controlled by light instead of a voltage source. The phototransistor effectively converts light energy to an electrical signal.
What is the difference between photodiode and phototransistor?
The photodiode is a semiconductor device which converts the light’s energy into an electrical current. Whereas, the phototransistor uses the transistor for the conversion of light energy into an electrical current. The phototransistor generates current whereas the photodiode produces both the voltage and current.
Is a phototransistor the same as a photoresistor?
No, Photoresistor is sensitive to incident light from anywhere in front of it. Yes, Phototransistor is sensitive to incident light from particular direction and insensitive from other directions. No change in resistance for light intensity regardless of applied voltage i.e. it remains same.
Is LDR a phototransistor?
The most common type of photoconductive cell is a Light Dependent Resistor or LDR. Cadmium Sulphide is used in Photo resistors that are sensitive to near infrared and visible light. The reason it is used is because of its close resemblance of its spectral response curve to that of the human eye.
Is photodiode a phototransistor?
A photodiode consists of a semiconductor diode, that generates current when exposed to light. On the other side, phototransistor consists of a junction transistor that when exposed to light energy generates current. A phototransistor is more efficient as compared to a photodiode.
What makes a phototransistor a photodiode amplifier?
Phototransistors are photodiode-amplifier combinations integrated within a single silicon chip. The phototransistor can be viewed as a photodiode whose output current is fed into the base of a conventional transistor. These photodiode-amplifier combinations are put together to overcome the major limitation of photodiodes: unity gain.
What is the typical gain of a phototransistor?
The phototransistor can be viewed as a photodiode whose output current is fed into the base of a conventional transistor. These photodiode-amplifier combinations are put together to overcome the major limitation of photodiodes: unity gain. The typical gain of a phototransistor can range from 100 to over 1500.
How does a common collector phototransistor circuit work?
The common collector, or emitter follower phototransistor circuit configuration has effectively the same topology as the normal common emitter transistor circuit – the emitter is taken to ground via a load resistor, and the output for the circuit being taken from the emitter connection of the device.
How is the phototransistor used in the switch mode?
The operation of the phototransistor circuit in the switch mode is more widely used in view of the non-linear response of the phototransistor to light. When there is little or no light, virtually no current will flow in the transistor, and it can be said to be in the “off” state. However as the level of light increases, current starts to flow.