Applications of Photodiode and Phototransistor with Differences

Photodiode symbol, phototransistor symbol

Photodiode and Phototransistor are very useful devices and mostly uses in modern technology. There are huge important applications of Photodiodes in electronic as well as electrical circuits. Here we will discuss also the Phototransistor applications. The working principle of Photodiode and Phototransistor almost the same. There are little differences between the photodiode and Phototransistor which are explained here.

Photodiode and Phototransistor Applications

Photodiode Applications

1. Consumer Electronics: Photodiodes are used consumer electronic devices like Television, Cameras, Radios.

2. Light Detecting Sensor: Photodiodes are also used as a light detecting sensor.

3. Solar System: Photodiodes are used in Solar Cell panels.

4. Measurement System: Photodiodes are used for the measurement of light intensity.

5. Communication System: Photodiodes are used in the optical communication system.

The other applications of Photodiode are,

1. Photomultiplier Tubes
2. Smoke Detectors
3. Pulse Oximeters
4. Charge Coupled Devices
5. Optocoupler or Opto-isolator
6. Medical Devices

Phototransistor Applications

1. Light Detecting Sensor: As the working principle of the Phototransistor is depending upon the Light so it can be used as a Light Detecting Sensor.

2. Security System: Phototransistor can be used in a security system. The basic concept is, a beam of light always falls on the phototransistor, when anyone passing between them and cut the light, the phototransistor will detect.

3. Phototransistor in Counter circuit: Phototransistor can be used in a Counter circuit with the same concept of Security system which is explained above.

4. Optocoupler: Phototransistors are also used in the Optocoupler. Photo-Transistor Optocoupler has phototransistor inside it.

5. Wireless System: Phototransistor is used in the wireless remote control system. The phototransistor is used in Television, Compact Disc Player for wireless remote control system as a receiver.

The other applications of Phototransistor are,

1. Relays
2. Punch Card Readers
3. Level Indication
4. Position Sensing
5. Logic Circuits

Difference between Photodiode and Phototransistor

Photodiode almost same in construction like normal PN Junction Diode. The photodiode is a semiconductor device which can convert light energy into electrical energy. The photodiode can be used as a transducer.

The Photodiode can work in two modes, one is Photovoltaic Mode and another is Photoconductive Mode.

In Photovoltaic mode, the photodiode produces a voltage when the light of sufficient energy falls upon it. The photovoltaic mode of the photodiode used in Solar cells. In Photoconductive Mode, the photodiode is used in reverse bias.

Phototransistor, Phototransistor construction, circuit

The phototransistor is basically an NPN Bipolar Junction Transistor(BJT). The base of the phototransistor is exposed to the external light. When the light falls upon the base of the phototransistor it starts operating.

Let's know the differences between Photodiode and Phototransistor

Photodiode VS Phototransistor

Photodiode basically is a PN Junction Diode which can create an electric current, when the light is falling on this.
Phototransistor basically an NPN transistor which allows the flowing of current when light falls upon its base.
The output response of the photodiode is faster than the phototransistor.
The output response of the phototransistor is lesser than a photodiode.
The sensitivity of the photodiode is lesser than phototransistor.
The sensitivity of the phototransistor is more than the photodiode.
A photodiode can work in the photoconductive mode as well as photovoltaic mode.
Phototransistor cannot work in photovoltaic mode.
Basically, Photodiode has two terminals one is Anode and another is the cathode.
Basically, a phototransistor has two terminals, Emitter, and collector, but some phototransistor has base terminal also for controlling the sensitivity.
The main applications of photodiodes are in solar cell, light sensor, etc.
The main applications of Phototransistors are IR receiver circuit, LASER detector, Counter, etc.

Photodiode Project Idea: Light Sensor Circuit

Here a light level indicator circuit using Photodiode is given below. Here I have tried to give the idea, how we can use the photodiode for indicating light illumination level.

Photodiode Project: Light Sensor Circuit

As you see in the above circuit diagram an Operational Amplifier(OpAmp) is used as a voltage comparator. A predetermined voltage level can be set using the variable resistor or Potentiometer to the pin 3 of the OpAmp.

In normal condition, the voltage will be the same as pin 3 and pin 2. When the light falling on the photodiode decreases the current flowing through the photodiode also decrease. Therefore, a voltage difference will create between the pin 2 and pin 3 of the comparator. When the voltage difference creates the comparator gives HIGH output and the output LED will be glow.
Thus we can indicate light illumination level using Photodiode.

Phototransistor Project Idea: Light Activated Relay

Here a simple circuit diagram of Light Activated Relay using Phototransistor is given below.

Phototransistor Project: Light Activated Relay

The working of this circuit is very simple. When light falls upon the base of the phototransistor it will start conducting current. So a current will through the phototransistor and base of the transistor T2. Therefore the transistor T2 will conduct current and it will energize the relay coil, ultimately the relay becomes NO to NC.

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Applications of Photodiode and Phototransistor with Differences Applications of Photodiode and Phototransistor with Differences Reviewed by ETechnoG on 12:43 Rating: 5
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