Photodiode and EMITTING

Presentation by JASWANT KUMAR ROLL NO.-12 IT(3rd SEM.) 1 About LEDs (1/2)

• A light emitting diode (LED) is essentially a PN junction opto- that emits a monochromatic (single color) light when operated in a forward biased direction. • LEDs convert electrical energy into light energy.

LED SYMBOL

2 ABOUT LEDS (2/2)

• The most important part of a light emitting diode (LED) is the semi-conductor chip located in the center of the bulb as shown at the right. • The chip has two regions separated by a junction. • The junction acts as a barrier to the flow of between the p and the n regions.

3 LED CIRCUIT • In , the basic LED circuit is an electric power circuit used to power a light-emitting diode or LED. The simplest such circuit consists of a voltage source and two components connect in series: a current-limiting (sometimes called the ballast resistor), and an LED. Optionally, a may be introduced to open and close the circuit. The switch may be replaced with another component or circuit to form a continuity tester.

4 HOW DOES A LED WORK?

• Each time an recombines with a positive charge, electric potential energy is converted into electromagnetic energy. • For each recombination of a negative and a positive charge, a quantum of electromagnetic energy is emitted in the form of a of light with a frequency characteristic of the semi- conductor material.

5 Mechanism behind photon emission in LEDs?

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CB

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holes • When sufficient voltage is applied to the chip across the leads of the LED, electrons can move easily in only one direction across the junction between the p and n regions. • When a voltage is applied and the current starts to flow, electrons in the n region have sufficient energy to move across the junction into the p region.

9 How Much Energy Does an LED Emit?

• The energy (E) of the light emitted by an LED is related to the electric charge (q) of an electron and the voltage (V) required to light the LED by the expression: E = qV Joules. • This expression simply says that the voltage is proportional to the electric energy • The constant q is the electric charge of a single electron, -1.6 x 10-19 Coulomb.

10 Colours of LEDs

• LEDs are made from gallium-based crystals that contain one or more additional materials such as phosphorous to produce a distinct color. • Different LED chip technologies emit light in specific regions of the visible light spectrum and produce different intensity levels.

• LEDs are available in red, orange, amber, yellow, green, blue and white.

11 LED Characteristics & Colours

• One of the major characteristics of an LED is its colour. The different LED characteristics have been brought about by a variety of factors, in the manufacture of the LED. The semiconductor make-up is a factor, but fabrication technology and encapsulation also play major part of the determination of the LED characteristics.

12 Some Types of LEDs

Bargraph 7-segment Starburst Dot matrix

13 LED Performance

LED performance is based on a few primary characteristics:

• Color • White light • Intensity • Eye safety information • Visibility • Operating Life • Voltage/Design Current

14 Applications

• Applications • Mobile Applications • Sign Applications • Automative Uses • LED Signals • Illuminations • Indicators

15 2.

16 What is photodiode

Photodiodes are semiconductor light that generate a current or voltage when the P-N junction in the semiconductor is illuminated by light A photodiode is a type of capable of converting light into either current or voltage, depending upon the mode of operation. The common, traditional Symbol of photodiode used to generate electric is a large area photodiode.

17 Principle of operation

• A photodiode is a p-n junction or PIN structure. When a photon of sufficient energy strikes the diode, it excites an electron, thereby creating a free electron (and a positively charged ). This mechanism is also known as the inner . If the absorption occurs in the junction's , or one diffusion length away from it, these carriers are swept from the junction by the built-in field of the depletion region. Thus PHOTODIODE CROSS SECTION holes move toward the , and electrons toward the , and a is produced. This photocurrent is the sum of both the (without light) and the light current, so the dark current must be minimized to enhance the sensitivity of the device.

18 Photodiode P-N junction state Photodiode types

• PN photodiode • PIN photodiode • Schottky type photodiode • APD () All of these types provide the following features and are widely used for the detection of the intensity, position, colour and presence of light.

19 Features of photodiode

• Excellent linearity with respect to incident light • Low • Wide spectral response • Mechanically rugged • Compact and lightweight • Long life

20 APPLICATION of photodiode

 P-N are used in similar applications to other , such as photoconductors, charge-coupled devices, and photomultiplier tubes. They may be used to generate an output which is dependent upon the illumination (analog; for measurement and the like), or to change the state of circuitry (digital; either for control and switching, or digital signal processing).  Photodiodes are used in devices such as players, smoke detectors, and the receivers for devices used to control equipment from televisions to air conditioners. For many applications either photodiodes or photoconductors may be used. Either type of photosensor may be used for light measurement, as in light meters, or to respond to light levels, as in switching on street lighting after dark.  Photodiodes are often used for accurate measurement of light intensity in science and industry. They generally have a more linear response than photoconductors.  They are also widely used in various medical applications, such as detectors for computed tomography .

21 Photodiode Alarm circuit

This Photodiode based Alarm can be used to give a warning alarm when someone passes through a protected area. The circuit is kept standby through a laser beam or IR beam focused on to the Photodiode. When the beam path breaks, alarm will be gets active.

22 Working of alarm circuit

• The circuit uses a PN Photodiode in the reverse bias mode to detect light intensity. In the presence of Laser / IR rays, the Photodiode conducts and provides base bias to T1. The NPN T1 conducts and takes the reset pin 4 of IC1 to ground potential. IC1 is wired as an Astable oscillator using the components R3, VR1 and C3. The Astable operates only when its resent pin becomes high. When the Laser / IR beam breaks, current thorough the Photodiode ceases and T1 turns off. The collector voltage of T1 then goes high and enables IC1. The output pulses from IC1 drives the speaker and alarm tone will be generated.

A simple IR transmitter circuit is given which uses Continuous IR rays. The transmitter can emit IR rays up to 5 meters if the IR LEDs are enclosed in black tubes.

IR Transmitter Circuit 23 ::The END:: Thank you for your Attention!