Photovoltaic Cells – Efficient, Cheap and Green Renewable Energy

Solar technology is in the market for more than 50 years, but it is still an innovative technology providing cheap, efficient and green electricity to homes, businesses and industries. Large solar energy systems are capable of providing electrical power to remote areas. Therefore, this renewable energy technology is still progressing to meet the power demands.

## What is PV Technology?

Photovoltaic cells, also known as solar cells, convert energy of the sun into electricity. Photovoltaic is a combination of two words, i.e. photo that means light and volt relates to electricity. PV cells combine with electrical configuration to form modules and arrays for providing power to electrical loads, operate motors and charge batteries. A photovoltaic system can produce AC power for appliances with an appropriate power conversion equipment. It can also interconnect or operate in parallel with a utility grid.

Symbol of Photovoltaic Cell

## Operation of a Photovoltaic Cell

A photovoltaic or solar cell is a thin semiconductor wafer, typically silicon, composed of an electric field formed with doped P-type (positive) and N-type (negative) material. The two materials contact to form a PN junction. When the sunrays strikes the PV cell, electrons gain momentum and result in current flow when the PV cell forms an electrical circuit with the electrical load, such as a tool or light. The output power or current of a solar cell is directly proportional to the sunlight intensity striking the cell surface, and depends on the efficiency and surface area of a solar cell.

Diodes – Types and Applications

In semiconductor and electronics industry, a diode is a widely used discrete component. It is a significant element in many electronic circuits and applications ranging from low power signal circuits to power rectification. Based on the functions and ratings, there are different types of diodes. However, all semiconductor diodes contain a PN junction to perform their basic operation.

## Definition of a Diode

A diode is a non-linear semiconductor device with two terminals that allows the flow of current in one direction. The two terminals of a diode are cathode (negative) and anode (positive).

Symbol of a Diode

## Construction of a Diode

The layers of doped semiconductor materials form a PN junction diode. Doping is a process of adding impurities to lower the resistivity of the semiconductor. The N type material has excess electrons as majority carriers, while P type material has holes (positive charge carriers). The P type material and N type material combine to form a PN junction that is a thin layer between the two opposite majority charge carriers.

LEDs – Operation, Types and Drivers

In this tutorial, we will study about the Light Emitting Diode (LED), its different types, operation. This will help in selecting the right type of LED for a particular application.

Light emitting diode (LED) is a solid state device that converts electrical energy into single color light. It is basically a specialized type of PN junction diode that emits either visible light, infrared or laser light at different wavelengths, made from a thin layer of heavily doped semiconductor material.

LED produces ‘cold’ generation light resulting in high efficiency. Unlike LEDs, normal incandescent lamps and bulbs generate large amounts of heat radiating away energy within the visible spectrum. Being a solid state device, LEDs are more durable, small and provide much longer lamp life than other normal light sources.

## Construction of LED

The construction of LED is not similar to a normal signal diode. LED consists of a PN junction surrounded by a hard, transparent plastic epoxy resin hemispherical shaped body. It protects the LED from shock and vibration. The LED junction does not emit much light, so the construction of epoxy resin body helps in reflecting away the emitted photons of light from the surrounding substrate base, thus focusing upwards through the top.

However, some LEDs have cylindrical or rectangular shape construction with a flat top or surface. The cathode and anode terminal of an LED is normally identified by a notch, or by one lead shorter than the other.

## LED Operation

A light emitting diode (LED) is a type of semiconductor diode that emits light when a current flows from anode to cathode across the PN junction of the device. Hence, an LED requires a direct current supply to forward bias the junction with a positive voltage for normal operation. The voltage to current relationship of LED is non-linear as shown in Figure 2, so the LED turns on at a lower voltage and will rapidly draw much higher current as the voltage increases.

Figure 1 – Circuit symbol of an LED and the direction of the conventional current flow

Cabling – Effects and Selecting the Right Cable

In a system design, we often consider cabling as the last step. However, cables play a major role in the performance of a system and an entire system can fail due to improper cabling. For example, a data communication system depends on cabling and in case of inappropriate cables the control could be lost. Also, cabling has different effects depending on a particular application. Therefore, we will discuss about the different effects of cabling on applications and how to select the right type of cable.

## What is a Cable?

Cable, or cabling, consists of two or more insulated conductors wrapped up together. There is a wide variety of multi-conductor cables with different configurations including multiple pairs, twisted pairs, etc. There are also several parallel constructions including woven flat cables and ribbon cables.

## Why Choose Right Type of Cable?

Cable reliability is very important for a long lasting system that is based on signal integrity and durability. The characteristics of cables are imposed on the carrying signals. Ideally, cables should behave as ideal transmission lines with no effect on the signal, but practically it is not possible.

## Effects of Cabling

### Skin Effect

The alternating current flowing through the cable has magnetic field associated with it that becomes a source of self inductance of the cable. The self inductance is inversely proportional to the conductor radius and results in lower impedance in the outer rings of the conductor;

$X_L = 2\pi fL$

Where, f is AC frequency in hertz.

For a cable composed of one or more concentric circular elements in a conductor, a greater magnetic flux is enveloped at the conductor’s center portion compared to the outside part. Consequently, the center of the conductor has greater self-induced back emf, causing the current density to be greater on the conductor surface. The greater concentration at the surface is commonly known as “Skin Effect”. This effect results in incremental increase in the effective resistance of the conductor. Skin effect becomes more apparent with increasing frequency.

Skin effect in a current carrying conductor

Bypass Capacitors – Why and How to Use Them?

You may have heard about the phenomenon of bypassing in circuits, however, we may not have sufficient knowledge of how to apply this technique in real circuits. In this tutorial, we will discuss about the bypass capacitors, why we need to use and how to use these capacitors in circuits.

## What is a Bypass Capacitor?

A capacitor that filters out the AC signal removing the noise and provides a DC signal is known as a bypass capacitor. The capacitor connected in the figure below is a bypass capacitor bypassing AC noise and allowing pure DC signal to pass through the component.

Operation of a Bypass Capacitor

## Why Use Bypass Capacitors?

In electronics, most of the circuits are digital in nature using direct current (DC). It has been observed that variations in voltage can cause problems to the circuit operation. A circuit may operate incorrectly due to voltage swing. In practical circuits, the voltage fluctuation is usually caused by the AC component that may ride over DC signal causing noise. Therefore, a bypass capacitor is needed to dampen the AC or noise present at all frequencies. Also, it prevents the unwanted communication between devices sharing the same power source.

Rotary Encoders – Understanding for Practical Implementation
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In this tutorial, we will study about one of the commonly used and accurate sensors used for position and speed measurement or control known as Rotary encoders.

Rotary Encoder is a sensor that generates an electrical (either analog or digital) signal in response to a rotational movement. This signal helps in determining or controlling the position or speed of a mechanical device. It is also known as a shaft encoder since it is mounted on a cylindrical shaft. A rotary encoder is often used to measure linear movement by combining with mechanical conversion devices. They are used in a variety of applications for precision and control of speed or position, including assembly machines, robotics, medical devices, testing equipment, etc.

A rotary encoder used for turn right, turn left and push to select functions in electronics devices

## Types of Rotary Encoders

Rotary encoders are available in different types that are classified by output signal and sensing technology. Other types would also include single turn and multiple turn encoders. The classification of rotary encoders is as follows:

Proximity Sensors and Their Applications
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In today’s fast growing world, the most innovative and attention seeking technology is definitely Sensors. The word sensor itself defines why this technology has been developed i.e. sensing the target or signal. The formal definition goes like “A device that detects the presence or absence of an object, or certain properties of that object, and provides feedback without getting in contact with them.”

Sensors measure the physical quantity and convert it into signal which can be easily read by user or a simple electronic instrument. There are several sensors working in the field of science nowadays. Some sensors are made to be used in daily life while there are many sensors that have been facilitating humans in research and engineering field.

## Proximity Sensor

The basic purpose of a proximity sensor is to perceive occurrence of any object without being in contact with it. A proximity sensor makes a field around it by emitting electromagnetic radiations. The beam of electromagnetic radiations traces any object or hurdle in its way. The term ‘target’ is used for the object that a proximity sensor intuits in its path. The sensor looks for any alteration made in its field. Target usually replaces a certain beam of the field or hurdles its projection. Different fields or sensors are used to detect different targets.

The lack of physical contact with the target usually makes an increment in the life of a proximity sensor. The absence of mechanical parts fakes it more reliable and grants it a long life.

Nominal Range is maximum range of the field in which a sensor can detect the presence of any object. It is the utmost distance through which it map outs the target. Most of these sensors have an adjustable Nominal range. Its level can be adjusted according to the presence of object.

This sensor has one transmitter and one receiver. The transmitter emits infrared rays which, when bounces off after hitting some object, are captured by the receiver. On the basis of the time taken by the rays to come back to sensor, one can determine how far or close is the object from the sensor. These sensors are mostly used in applications where short range detection is required.

## Types of Proximity Sensor

Following are the major types of proximity sensors.

### Capacitive proximity sensors

Figure 1 – Capacitive Proximity Sensors