Phototransistors

December 24, 2023 Post a Comment

Phototransistors

It is used in compact disc players, smoke detectors, lasers, invisible light receivers, etc. The photodiode is used for battery-powered devices that use less power. The phototransistor is used as a solid-state switch, not like a photodiode.

What is a phototransistor and how does it work?

A phototransistor is a bipolar or unipolar transistor where light can reach the base, creating optically generated carriers. This modulates the base-collector junction resulting in an amplified current through transistor action, which can lead to much greater photosensitivity.

What is phototransistor in simple words?

phototransistor. [ fō′tō-trăn-zĭs′tər ] A transistor that regulates current or switches it on and off based on the intensity of the light it is exposed to rather than an external electric signal.

Do phototransistors light up?

Phototransistor advantages These electronic components are relatively cheap as they are effectively a transistor that is open to light.

What type of sensor is a phototransistor?

Products in the phototransistor family are discrete light sensitive components which behave in similar fashion to a bipolar transistor, but use incident light instead of an electrical current applied through a device terminal to cause the device to conduct.

Is phototransistor a light sensor?

A Photo Transistor is a sensor that detects ambient light, a bit like an LDR (and works in a similar way). We prefer these sensors as the package is a little more robust than your traditional LDRs. When light enters the chip on top, it creates a flow of current from the long to the short pin.

How does phototransistor work simple?

The phototransistor effectively converts light energy to an electrical signal. In a phototransistor the base current is produced when light strikes the photosensitive semiconductor base region. The collector-base pn junction is exposed to incident light through a lens opening in the transistor package.

Is phototransistor active or passive?

It is a passive component with no polarity. It represents equal resistance in both the directions and it can be used either with AC or DC.

Is phototransistor analog or digital?

The whiskers are digital sensors and provided two values: 0 (pressed); and 1 (released). Instead of just two values, the phototransistor is an analog sensor that will provide a range of values.

Is phototransistor a photodiode?

The phototransistor is a junction semiconductor device similar to the photodiode in that it generates a current proportional to light intensity. It might be thought of as a photodiode with a built-in current amplifier. The phototransistor is an NPN transistor where the base connection is replaced by an optical source.

What is the output of a phototransistor?

The output is read at the emitter terminal. In both circuits the phototransistor can be used in two modes, an active mode and a switch mode. Operating in the active mode means that the phototransistor generates a response proportional to the light received by the component up to a certain light level.

Is phototransistor a BJT?

A phototransistor is depicted as a BJT with the base terminal removed, and the arrows imply that the base is sensitive to light.

Can a phototransistor get light from an LED?

An LED and a phototransistor are sealed in a light-proof plastic package, so that light from the LED is received by the phototransistor. When the LED is turned on by a current supplied from an external source, the phototransistor is turned on. If the phototransistor is wired as a switch, this can turn on other devices.

Do photocells only work with sunlight?

The photocell can sense when dusk has fallen and automatically turns on the light. On the other hand, it also detects natural lights and turns them off at dawn. If natural light changes, the photocell lights are activated. They are not affected by daylight savings time.

Why does a phototransistor need a resistor?

Any 2-terminal variable resistance can't output a varying voltage on its own, so adding a resistor creates a "wiper" at the phototransistor-resistor junction point.

Can phototransistor detect visible light?

The phototransistor exhibits a responsivity of 26.48 A W−1, a detectivity of 8.42 × 1014 Jones, and an external quantum efficiency of 51% under visible light illumination (635 nm).

What are the characteristics of phototransistor?

Characteristics of Phototransistors

Spectral Response. The output of a phototransistor is dependent upon the wavelength of incident light.
Sensitivity. ...
Linearity. ...
Collector-Emitter Saturation Voltage - V. ...
Dark Current - (I_D) ...
Breakdown Voltages - (V_BR) ...
Speed of Response. ...
Selecting a Photodetector.

Why is photo transistor more efficient than photo diode?

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.

Is phototransistor a LDR?

A light-dependent resistor (LDR) or photoresistor is made of a photosensitive semiconductor that's conductivity changes when exposed to the light. The material's resistance is in several thousand ohms or mega ohms in the dark and falls to a few hundred ohms when subject to light.

Can a phototransistor detect infrared?

The photons coming from the striking light activate the transistor. The phototransistor that we are using in our circuit is an IR phototransistor and it detects infrared light. When infrared light strikes the surface of an IR phototransistor it starts conducting across from collector to emitter.