What is the use of photo transistor?

What is the use of photo transistor?

Phototransistors are used extensively to detect light pulses and convert them into digital electrical signals. These are operated by light rather than electric current. Providing a large amount of gain, low cost and these phototransistors might be used in numerous applications.

How does a photo transistor work?

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.

How do I connect Arduino to phototransistor?

3. Connect a phototransistor to Arduino

  1. int val; void setup()
  2. { Serial.begin(9600); // sets the serial port to 9600.
  3. } void loop()
  4. { val = analogRead(0); // read analog input pin 0.
  5. Serial.print(val); // prints the value read. Serial.print(” “); // prints a space between the numbers.
  6. delay(10); // wait 10ms for next reading.

How many types of photo transistor has?

The phototransistors can be configured in two different configurations viz., common collector and common emitter, depending on the terminal which is common between the input and output terminals, similar to normal transistors.

What is photodiode and its application?

A photodiode is a semiconductor p-n junction device that converts light into an electrical current. The current is generated when photons are absorbed in the photodiode. Photodiodes may contain optical filters, built-in lenses, and may have large or small surface areas.

What is the difference between LDR and phototransistor?

LDR varies the light depending on certain factors. Photodiode has a quicker response time as opposed to LDR which is analog. LDR is a bidirectional resistor whereas photo diode is a unidirectional resistor. Both LDR and photo diode have low costs.

What is the symbol of photodiode?


One Ge (top) and three Si (bottom) photodiodes
Type Passive
Working principle Converts light into current
Pin configuration anode and cathode
Electronic symbol

What is the difference between phototransistor and photodiode?

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.

What is photodiode and its working?

A photodiode is a semiconductor p-n junction device that converts light into an electrical current. The current is generated when photons are absorbed in the photodiode. A photodiode is designed to operate in reverse bias.

Which is the combination of photo transistor?

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.

Why it is called photo transistor?

Although ordinary bipolar transistors exhibit the photosensitive effects if they are exposed to light, the structure of the phototransistor is specifically optimised for photo applications. The photo transistor has much larger base and collector areas than would be used for a normal transistor.

Can a photo transistor be considered as a photodiode?

In other words, a photo transistor can be considered as a Photodiode with current amplifier. A phototransistor converts photons to charge directly, just like a photodiode, and in addition to this, a phototransistor also provides a current gain. The symbol of phototransistor is shown below.

How does a phototransistor turn on a transistor?

There are two other things to consider which has nothing to do with the characteristics of the phototransistor i.e. its size and cost. When there is enough light falling on the phototransistor Q1, it turns ON and provides a base current to transistor Q2. As a result, Q2 is turned ON and the Relay is energized.

Why are phototransistors used in opto-isolators?

As a result of their ease of use and their applications, phototransistors are used in many applications. Opto-isolators – here the phototransistor is used as the light sensor, the light emitter being relatively close, but at a different potential.

Why is the base connection of a photo transistor left open?

The photo-transistor operates because light striking the semiconductor frees electronics / holes and causes current to flow in the base region. Photo-transistors are operated in their active regime, although the base connection is generally left open circuit or disconnected because it is often not required.