- A diode is an electrical component acting as a one-way valve for current.
- When voltage is applied across a diode in such a way that the diode allows current, the diode is said to be forward-biased.
- When voltage is applied across a diode in such a way that the diode prohibits current, the diode is said to be reverse-biased.
- The voltage dropped across a conducting, forward-biased diode is called the forward voltage. Forward voltage for a diode varies only slightly for changes in forward current and temperature, and is fixed by the chemical composition of the P-N junction.
- Silicon diodes have a forward voltage of approximately 0.7 volts.
- Germanium diodes have a forward voltage of approximately 0.3 volts.
- The maximum reverse-bias voltage that a diode can withstand without “breaking down” is called the Peak Inverse Voltage, or PIV rating.
Electronics – Electronics is the branch of physics and technology that deals with the emission, behavior, and effects of electrons and with electronic devices.
Most electronic devices use semiconductor components to perform electron control. The study of semiconductor devices and related technology is considered a branch of solid state physics, whereas the design and construction of electronic circuits to solve practical problems come under electronics engineering. This article focuses on engineering aspects of electronics.
Diode – A Diode is the simplest two-terminal unilateral semiconductor device. It allows current to flow only in one direction and blocks the current that flows in the opposite direction. The two terminals of the diode are called as anode and cathode.
The Symbol of Diode
Diodes typically are made from semiconductor materials such as silicon, germanium or selenium and are uses as voltage regulators, signal rectifiers, oscillators and signal modulators/demodulators.
In computer equipment, diodes are commonly used to emit light by passing a current through it, as in light emitting diodes (LEDs).
Properties of a Diode
Zener Diodes- Normally a current does not flow through a diode in the reverse direction. The Zener Diode is specifically designed to begin conducting in the opposite direction when the reverse voltage reaches a voltage threshold. Zener diodes are sometimes used as a voltage sensitive switch.
Triode- The triode was developed two years after Sir John Ambrose Fleming described a Diode as an Oscillation Valve. In 1906 Lee DeForest added a third electrode into the valve between the filament and the plate, this was shaped like a grid iron and he called the electrode the grid.
He was trying to improve the sensitivity of radio detection by trying to control the flow of electrons between a heated (carbon) filament and a positively biased anode or plate and the device produced he called an Audion.
Today we know this configuration as the Triode.
Triode Valve can be used as amplifier, oscillator, transmitter and detector.
Semi-conductors – Semi-conductor is a material whose electrical conductivity lies between insulator and conductor.
Semiconductors are mainly classified into two categories: Intrinsic and Extrinsic.
Intrinsic Semi-conductor - An intrinsic semiconductor material is chemically very pure and possesses poor conductivity. It has equal numbers of negative carriers (electrons) and positive carriers (holes).
Extrinsic Semi-conductor - An extrinsic semiconductor is an improved intrinsic semiconductor with a small amount of impurities added by a process, known as doping, which alters the electrical properties of the semiconductor and improves its conductivity.
Doping – Doping is a process in which small amounts of impurities are added to pure semiconductors causing large changes in the conductivity of the material. Examples include silicon, the basic material used in the integrated circuit, and germanium, the semiconductor used for the first transistors.
Doping process produces two groups of semiconductors: the negative charge conductor (n-type) and the positive charge conductor (p-type).
Semiconductors are available as either elements or compounds.
Silicon and Germanium are the most common elemental semiconductors.
Compound Semiconductors include InSb, InAs, GaP, GaSb, GaAs, SiC, GaN. Si and Ge both have a crystalline structure called the diamond lattice.
P-type semiconductor - A P-type semiconductor is an intrinsic semiconductor (like Si) in which an impurity acting as an acceptor (like e.g. boron B in Si) has been intentionally added. These impurities are called acceptors since once they are inserted in the crystalline lattice; they lack one or several electrons to realize a full bonding with the rest of the crystal.
N-type semiconductor - A N-type semiconductor is an intrinsic semiconductor (e.g. silicon Si) in which a donor impurity (e.g. arsenic As in Si, or Si in GaAs) has been intentionally introduced. The impurities are called donor impurities since they have to give an extra electron to the conduction band in order to make all the bonds with neighboring atoms (As is pentavalent while Si is tetravalent).
The electrical conductivity of a semiconductor increases with increase in temperature.
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