Question

Explain the term RECTIFIER, HALF-WAVE RECTIFIER, FULL-WAVE RECTIFIER, BRIDGE RECTIFIER, Amplification Thermonic Emission:

The RECTIFIER is the section of the power supply that contains the secondary windings of the power transformer and the rectifier circuit. The rectifier uses the ability of a diode to conduct during one half cycle of ac to convert ac to dc.

HALF-WAVE RECTIFIERS give an output on only one half cycle of the input ac. For this reason, the pulses of dc are separated by a period of one half cycle of zero potential voltage.

FULL-WAVE RECTIFIERS conduct on both halves of the input ac cycles. As a result, the dc pulses are not separated from each other. A characteristic of full-wave rectifiers is the use of a center-tapped, high-voltage secondary.

Because of the center tap, the output of the rectifier is limited to one-half of the input voltage of the high-voltage secondary.

BRIDGE RECTIFIERS are full-wave rectifiers that do not use a center-tapped, high-voltage secondary. Because of this, their dc output voltage is equal to the input voltage from the high-voltage secondary of the power transformer. Bridge rectifiers use four diodes connected in a bridge network. Diodes conduct in diagonal pairs to give a full-wave pulsating dc output.

Amplification

In the descriptions of npn and pnp transistors, the same sort of circuit was used in each with small signal power from a side circuit B controlling the larger power in a circuit A. The transistor enables a signal, too weak in itself to be of direct use, to control a larger power source (battery A in the examples). The control by a small available power over a large usable power is called power gain or amplification. Transistors can be connected in different ways and they can be used for various purposes, including switching.

AMPLIFICATION is the process of increasing the strength of a signal.

An AMPLIFIER is the device that provides amplification without appreciably altering the original signal.

The BASIC TRANSISTOR AMPLIFIER amplifies by producing a large change in collector current for a small change in base current. This action results in voltage amplification because the load resistor placed in series with the collector reacts to these large changes in collector current which, in turn, results in large variations in the output voltage.

The three types of BIAS used to properly bias a transistor are base-current bias (fixed bias), self-bias, and combination bias. Combination bias is the one most widely used because it improves circuit stability and at the same time overcomes some of the disadvantages of base-current bias and self-bias.

Thermonic Emission: The process of electrons emission from a metal surface by supplying thermal energy to it is known as thermonic emission. At ordinary temperatures, the energy possessed by free electrons in the metal is inadequate, to cause them to escape from the surface. When heat is applied to the metal, some of the heat energy is converted into kinetic energy causing accelarated motion of free electrons, which acquire additional energy equal to the work function of the metal. Consequently they overcome the restraining surface barsier and leave the metal surface.