Thermistors

Thermistors are ideal temperature transdusers. A thermistor can be defined as resistor made up of semiconductors having resistance that varies rapidly and predictably with temperature. The word thermistor is a portmanteau of Thermal & Resistors. 

In few cases the resistance of a thermistor may decrease upto 6 percent for 1⁰Celsius in temperature. Due to high sensitivity, thermistors are very useful for precision temperature measurement, control, and compensation. Thermistors are used in the temperature range of 100⁰  Celsius to 300⁰ Celsius. The resistance ranges from 0.552 to 72 Mega Ohms. Thermistors are made up of sintered mixture of metallic oxides such as cobalt, nickel, copper, manganese etc. they are available in the form of beads, rods or discs.Thermistors differ from Resistance Thermo Detectors (RTD) in that the material used in a thermistor is generally a ceramic or polymer, while RTDs use pure metals. The temperature response is also different.The characteristics of a Thermistor can be shown in the picture below:-

Classification of Thermistors:-

 Depending upon the sign of k the Thermistors can be classified into two types. They are:-

1. PTC Thermistors:-

 If k is positive, the resistance increase with the increasing temperature,& the device is called as Positive Temperature Coefficient(PTC) thermistor or Posistor. 

PTC Thermistor

2. NTC Thermistor:-

If k is negative,the resistance decreases with the increasing temperature,& the device is called as Negative Temperature Coefficient(NTC) thermistor.

NTC Thermistor

Thermistors have some advantages. They can be listed as below:-

1. PTC thermistors can be used as current limiting devices for circuit protection, as replacements for fuses.
2. PTC thermistors are used as timers in the degaussing coil circuit of most CRT displays & TVs.
3. NTC thermistors are used as resistance thermometers in low temperature measurements of the order of 10K.
4. NTC thermistors can be used as inrush current limiting devices in power supply.
5. NTC thermistors are regularly used in automotive applications.
6. NTC thermistors can be also used to monitor the temperature of an incubator.
7. Thermistors are commonly used in modern digital thermostats & to monitor the temperature of battery packs while charging.

Electronic Circuits

Electronic circuit is composed of individual electronic components such as resistors, transistors, capacitors, inductors, and diodes connected by conductive wires or traces through which electric current can flow .The combination of components and wires allow various operations such as amplification of signals, computations and transfer of data from one place to another. Circuits can be constructed from discrete components connected by individual pieces of wire, but now the interconnections are created by photolithographic techniques on a laminated substrate (a printed circuit board) and solder components to these interconnections to create a finished circuit.

Bread boards, perfboards or strip boards are common for testing designs. They allow the designer to make quick changes to the circuit.

An electronic circuit can be categorized as follows:-

1.      Analog circuit. 

2.      Digital circuit. and

3.      Mixed-signal circuit.

1.      Analog Electronic Circuit:-

Analog electronic circuits are those in which current or voltage may vary continuously with the time to correspond with the information being represented. Analog circuitry is constructed from two building blocks namely series and parallel circuits. In the series circuit, the current which is passed through all the series components will be same. In the parallel circuit, all the components are connected to the same voltage, and the current divides various components according to their resistance. The basic components of analog circuits are wires, resistors, capacitors, inductors, diodes and transistors (Recently memristors have been added to the list of available components). Analog circuits are very commonly represented in schematic diagrams, in which wires are shown as lines, and each component has unique symbol. When the size is comparable to wavelength of relevant signal frequency, a more sophisticated approach must be used. Wires are treated as transmission lines, with constant characteristic impedance, and the impedances at the beginning and end determine the transmitted and reflected waves on the line.

                                                                           

2. Digital Electronic Circuit:-

In digital electronic circuits, electric signals take on discrete values, to represent the information that is being processed. In the vast majority of cases binary coding is used. Digital circuits make extensive use of Transistors, interconnected to logic gates that provide the functions of Boolean logic. Transistors interconnected so as to provide positive feedback are used as latches and Flip-flops. Digital circuits therefore can provide both logic and memory, enabling them to perform arbitrary computational functions. (Memory based on Flip-flops is known as SRAM (Static Random Access Memory).

Memory based on storage of charge in a capacitor, DRAM (Dynamic Random Access Memory) is also widely used).

Digital circuits are very easy to design when compared to analog circuits for the same level of complexity, because each logic gate regenerates the binary signal, so the designer need not account for distortion, gain control, offset voltages, and other concerns faced in an analog design. As a consequence, extremely complex digital circuits, with billions of logic elements integrated on a single silicon chip, can be fabricated at low cost. Such digital integrated circuits are ubiquitous such as calculators, mobiles, computers...

Digital circuitry is used to create general purpose computing chips, such as microprocessors, & custom designed logic circuits, known as Application Specific Integrated circuits (APSIC’s). Field Programmable Gate Arrays (FPGA’s), chips with logic circuitry, whose configuration can be modified after fabrication, are also widely used in prototyping & development.

                               

3.      Mixed Signal Circuits:

Mixed signal or hybrid circuits contain both analog & digital circuits. Examples include comparators timers, PLLs, ADCs (analog to digital converters), & DACs (digital to analog converters).

Most modern Radio & Communication circuitry uses mixed signal circuits. For example in a receiver analog circuitry is used to amplify the frequency so that they reach the suitable state to be converted into digital values, after which further signal processing can be performed in digital domain.   

Electronics

Hi friends, in this post I want to tell that how did electronics originate and it’s development.

Electronics is a branch of engineering which deals with the development of electronic devices and their utilization. Electronics can also be defined as the study of behaviour of electrons, their control and use.

Development of Electronics:-

The discovery of propagation of electromagnetic energy by Hertz may be the beginning of the electronics era. This experiment demonstrated the radio communication. Radio is based on the experiments in electricity and magnetism. In 1820, a Danish Physicist, Hans Christian Oersted found a relation between electricity and magnetism. He found that an electric in a wire deflects the magnetic needle.

diode vacuum tube

Later in 1830 a British physicist, Michael Faraday discovered that a moving magnet can generate electricity but he did not put his ideas into mathematical equation. A British physicist, James clerk Maxwell put Faraday’s ideas into mathematic form, later he discovered electromagnetic waves.  In 1887 German physicist, Henrich Hertz   demonstrated the effect of electro-magnetic radiation through space this experiment demonstrated the wireless transmission for radio communications using radio waves. Guglielmo Marconi (1895) used a long wire as an antenna to develop a practical radio system for long distances. Fleming in 1904 invented a vacuum tube that allowed the current only in one direction which was later named as diode vacuum 

triode vacuum tube

tube and was used to detect electromagnetic waves. In 1906 Dr.Lee Defrost, an American scientist invented a triode vacuum tube, which could amplify weak electrical AC signals. Because of the advancement in the design of vacuum tubes, radio communication progressed rapidly. Around 1915, triode (with few improvements) was used in oscillator circuit and also in telephone system. In 1920, 

Transistor

radio broadcasting with regularly scheduled programs was started by station KDKA using standard AM (Amplitude modulation) radio band. Several types of microwave tubes were developed, during the Second World War these tubes made possible the modern RADAR and other communication systems. The era of solid electronics began with the invention of transistor in 1947 at Bell Telephone laboratories by Walter Brattain, John Bardeen and William Shockley. 

Solid state devices have replaced tubes for most uses in the field of electronics. The transistor is an application of controlled electron flow in solid semiconductor materials such as silicon (Si) and germanium (Ge). In 1958,it was thought that silicon and germanium can be used to build an entire circuit, called monolithic circuit. It was named an integrated circuit(IC). In 1959 Noyce gave an idea for making multiple devices on a single piece of silicon. In 1961 IC’s were produced commercially by Fairchild and Texas instruments. This development was a great achievement in the field of electronics. Thus electronics originate and got developed