Electronic Circuits and Diagram-Electronics Projects and Design

This blog post is continuation to the original post: Fabrication techniques of a P-N junction diode 1. Grown Junction Diode: Diodes of this type are formed during the crystal pulling process. P and N-type impurities can be alternately added to the molten semiconductor material in the crucible, which results in a P-N junction, as shown when crystal is pulled. After slicing, the larger area device can then be cut into a large number (say in thousands) of smaller-area semiconductor diodes. Though such diodes, because of larger area, are capable of handling large currents but larger area also introduces more capacitive…

General Introduction to Fabrication techniques of a P-N junction diode: In practice, the P-N junction is formed from a single mono crystalline structure by adding carefully controlled amounts of donor and acceptor impurities. Here discussion is limited only to acquaintation with the basic techniques and terminology (not expertise in fabrication). The first and foremost requirement is to obtain an extremely pure germanium or silicon. Impurity of less than one part in ten billion (1010) is required for most semiconductor device fabrication to-day. For obtaining pure semiconductor material it is first purified chemically. For reducing the impurities further, and to ensure the…

The photoconductive cell is a two terminal semiconductor device whose terminal resistance will vary (linearly) with the intensity of the inci­dent light. For obvious reasons, it is frequently called a photoresistive device. The photoconductive materials most frequently used include cadmium sulphide (CdS) and cadmium selenide (CdSe). Both materials respond rather slowly to changes in light intensity. The peak spectral response time of CdS units is about 100 ms and 10 ms for CdSe cells. Another im­portant difference between the two materials is their temperature sensitivity. There is large change in the resistance of a cadmium selenide cell with changes in…

An optocoupler (or an optoelectronic coupler) is basically an interface between two circuits which operate at (usually) different voltage levels. The key advantage of an optocoupler is the electrical isolation between the input and output circuits. With an optocoupler, the only contact between the input and the output is a beam of light. Because of this it is possible to have an insulation resistance between the two circuits in the thousands of megohms. Isolation like this is useful in high voltage applications where the potentials of two circuits may differ by several thousand volts.  The most common industrial use of…

What is an LCD/Definition of Liquid Crystal Displays The liquid-crystal display has the distinct advantage of having a low power consumption than the LED. It is typically of the order of microwatts for the display in comparison to the some order of milliwatts for LEDs. Low power consumption requirement has made it compatible with MOS integrated logic circuit. Its other advantages are its low cost, and good contrast. The main drawbacks of LCDs are additional requirement of light source, a limited temperature range of operation (between 0 and 60° C), low reliability, short oper­ating life, poor visibility in low ambient…

Electronic optosensors are devices that al­ter their electrical characteristics, in the presence of visible or invisible light. The best known devices of these types are the light dependent resistor (LDR), the photodiode and the phototransistor. How to make/construction of an LDR Light dependent resistors (LDRs) are made from cadmium sulphide containing no or very few free electrons when not illuminated. Its resistance is then quite high. When it absorbs light, electrons are liberated and the conductivity of the material increases. Cadmium sulphide (CdS) is, therefore, a photoconductor. The approximate relationship between the resistance and illumination is R = AE~a where E is illumination in lux, R is resist­ance…

What is a diode in general? A two electrode device is called a ‘diode‘. Its simply a P-N junction with connecting leads or terminal on the two sides of the P-N junction. Such diodes are also called a “crystal diode” because the junction is grown out of a crystal. A diode allows unidirectional flow of current and it restrains the flow in opposite direction. Its main advantages are cheapness,smaller size,robustness and high efficiency Major application is rectification which is conversion of ac to dc A semiconductor diode can be made of either silicon or Germanium. Both differs in size and…

What is a tunnel diode? Dr.Leo Esaki invented a tunnel diode, which is also known as “Esaki diode” on behalf of its inventor. Its a high conductivity two terminal P-N junction diode doped heavily about 1000 times greater than a conventional junction diode. Because of heavy doping depletion layer width is reduced to an extremely small value of 1/10000 m. Reverse breakdown voltage is also reduced to very small value~0 resulting in appearance of the diode to be broken for any reverse voltage and a negetive resistance section is produced in the volt-ampere characteristics of the diode. What is tunneling…

Vacuum Diodes-Applications and Construction The simplest form of the electron tube for the production and control of free electrons is a Vacuum diode. Two electrodes are there for a vacuum diode known as anode and cathode. Cathode serves as an emitter of electrons where as anode serves as a collector of electrons. Cathode may be a simple filament of tungsten or thoriated tungsten. It can also be a nickel tube coated with barium oxide or strontium oxide. Oxide coated cathode shows greater emission efficiency. Anode is usually a hollow metallic cylinder,it can be of nickel or iron but in case…

Whats is a resistance? The property of a substance, which oppses the flow of an electric current through it is called a resistance. Its is measured in ohms and is represented by letter ‘R’. Each resistor has two main characteristics. 1) Its resistance value in ohms and 2) its power dissipating capacity in watts Resistors are employed for many purposes such as electric heaters,telephone equipments, electric and electronic circuit elements and in current limiting devices. As resistors are used in wide applications there values like power rating,R value, tolerance etc vary. Resistors of resistance value ranging from .1ohms to many…