Oct 132013
 

The constituent parts of an electronic circuit are called electronic components. Electronic components are the building blocks of electronics. They have two or more terminals and are connected by soldering. Printed circuit boards and electronic components are used for building electronic circuits that perform certain functions. Increasingly, they are integrated into microprocessors, miniaturize and become part of solids and integrated circuits, but in this case we talk about microelectronics. Electronic components are divided into active and passive.

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Passive electronic components have linear volt-ampere characteristic. These are the basic components that can be found in any electronic circuit of radio-electronic equipment. The most typical among them are:
Resistances (resistors)
Resistors are used in electronics as voltage limiters. The determinative parameter is their ohmic resistance. It is indicated on the housing by a color code. The material, from which the resistor is made, is a type of dielectric. Resistors are manufactured with standardized values. The resistance of the resistor can be affected by various external factors, the most powerful of which is the temperature.

Capacitors are electronic components which have the ability to store electrical energy. A capacitor is characterized with polarity – it has a positive and a negative pole. The color code for capacitors gives information about their capacity.
Active electronic components have a non-linear volt-ampere characteristic. Popular among them are:
Transistors, thyristors, varistors, diodes, optocouplers, crystal oscillators, triacs, diacs, etc.
For these and other electronic components we have individual articles in this blog, so in this article we will not discuss their types, principles of operation and application. Here we will pay attention to some electronic components that are widely used in electronics, optoelectronics, radio-engineering and automotive electronics.
Varistors
Varistors are nonlinear semiconductor resistive components with symmetrical volt-ampere characteristic. The resistance of a varistor is changed depending on the applied voltagе. The varistor has as its main characteristic а threshold value of the voltage. When the voltage reaches this value, the varistor increases its resistance to infinity and it doesn’t conduct electric current. Other parameters used for the selection of varistors are the operating current and the power dissipation limit which, if exceeded, can cause burning-out of the varistor. Varistors are connected in parallel in the circuit and serve to protect other electronic components or devices in the circuit, which can arise from peak pulse voltage from lightning, failure in the network, etc. A varistors is denoted as VDR (voltage dependent resistor), and its name is derived from “variable resistor”.

 

Crystal oscillator
A crystal oscillator, as opposed to a quartz resonator which uses the effect of polarization of a dielectric under mechanical pressure, called a piezo-electric effect, uses the opposite piezo-electric effect. When alternating voltage is supplied between the electrodes of a quartz resonator, this causes mechanical vibrations that are proportional to the intensity of the applied electric field. Various kinds of vibrations arise in the plate of the crystal oscillator, and they depend on the shape of the plate. As a result of the oscillations in the plate, which have a certain frequency, sequential resonance can occur, the oscillations will have maximum amplitude, and the electrical resistance between the two electrodes will be minimal. A crystal oscillator consists of a quartz plate SiO₂ two electrodes and a housing.
Triac (symistor)
Symistors, also known as symmetrical thyristors or triacs (triode for alternating current) are semiconductors from the group of thyristors. Triacs are designed using a five layer structure and have bidirectional adjustable conductivity. The five-layer structure with four junctions between the layers can be observed as a grouping of two thyristors. They are triggered by pulses of the control current with the same polarity. The bidirectionality of symistors makes them usable in contactless AC controllers, for controlling inductive loads with low power, in adjustable lighting fixtures, etc.
Optoelectronic components
Optoelectronic components or photo-electronic components are semiconductor photoelectric components, converting light energy into electrical energy or vice versa. They are used in light sensors, cine-machines, automation, electronic circuits, etc. Let us take a look at some photo-electronic components:
– optical couplers are electronic components that are used for transferring electrical signals between two galvanically isolated circuits, using light. An optical coupler protects the system, which receives signals, from the formation of over-voltage. The component most commonly consists of a light source (LED) and a phototransistor, mounted in a common housing.

phototransistors are high-sensitive low-inertia semiconductor converters of light signals into electrical signals. They can amplify the electrical current, generated by light. Phototransistors are preferred over photodiodes when more power at the output is needed. The falling light beam is used as an emitter.
– photodiodes are high-sensitive low inertia semiconductor converters of light signals into electrical current through a photoelectric effect of the PN junction.
– photoresistors are semiconductor componenets, the ohmic resistance of which depends on the degree of illumination. The principle of operation of photoresistors is the phenomenon of photoconductivity of semiconductors. Photoconductivity is the increase of electrical conductivity of semiconductors under the influence of light. The reason for photoconductivity is the increasing of the concentration of charge carriers – electrons in the conductivity area and the holes in the valence zone. The light-sensitive layer of semiconductor material is located between two current-conductive electrodes. Under the influence of the luminous flux the electrical resistance of the layer changes several times (in some types of photoresistors it is reduced two to three times).

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Thyristors
A thyristor is a semiconductor electronic component, a controllable diode. It is used as an electronic switch in circuits with high voltage and large currents. It is used in trigger circuits, rectifiers, regulators, etc.
Transistors
A transistor is a semiconductor component, which is composed of three outlets and three zones, connected in series, with different alloying, which defines the junction of the transistor (NPN or PNP). There is a large variety of different types of transistors but the two basic groups are: bipolar and field-effect transistors (FETs). The most important feature of bipolar transistors is that they have an injection of current carriers through the PN Junction and their operating current is determined simultaneously by two types of current carriers, hence their name bipolar.

FETs don’t have injection of current carriers through the junction and their operating current is determined either by electrons or by holes. That is why field-effect transistors are called unipolar. Transistors can be used for amplification, switching and converting the electronic signal. Transistors are of great practical use and are active components in almost all modern electronic devices. They are often assembled in integrated circuits and chips. In general, the method of operation of a transistor is based on its ability to change voltage or current pulse, which is transmitted through one pair of outlets. The output voltage or current through the other pair of outlets is higher or, respectively, lower.

Main types of transistors:

– IGBT. The name comes from Insulated-Gate Bipolar Transistor. IGBT is three-electrode, bipolar, powerful electronic component used mainly as a powerful electronic switch in switching power supplies, inverters and systems for controlling electric drives. IGBT combines the properties both of bipolar and field-effect transistors – high input resistance at low level of the control power and low residual voltage value in switched-on position.

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– JFET. JFET (Junction Field – Effect Transistor) is a field effect transistor with PN – junction. The control of the output current is carried by the input voltage.

– MOSFET (metal-oxide-semiconductor field-effect transistor) is an electronic version of a switch. MOS switches are widely used in computers, microprocessors, storages, peripheral circuits, etc. Advantages: high input resistance, low power consumption, better temperature stability, low susceptibility to radiation. They are used in power electronics, audio equipment, medical electronics, integrated circuits, computers, aviation, automotive and space industries, in household appliances, etc. They can be of two types: P-channel MOS-P-FET and N-channel MOS-N-FET.
– Bipolar transistors. They are among the most common semiconductor components. They are classified by their power: low-power, medium-power and high-power; by their limiting frequency: low frequency – up to 3 MHz, medium-frequency – 30 to 300 MHz and high- frequency – 300 MHz; by the succession of the junction – PNP and NPN; by the used material: silicon or germanium. They are used for amplification, conversion and generation of electrical signals. Bipolar transistors are components which are operated using electricity.
– One-junction transistors. They have two bases and an emitter. A one-junction transistor is a bipolar three-electrode component with one PN transition.

 Peltier components
A Peltier component is a plate with a large number of thermocouples (over 100). When supplying electric current to the outlets, one side of the component is heated and the other – cooled. The heating side is equipped with a cooling radiator which prevents it from overheating. The degree of cooling of the heated part determines how low will be the temperature of the cold side. Peltier components are used in water dispensers, coolers, etc.
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Capacitors
Capacitors are passive electronic components which can store electrical charge but also admit alternating current go through. A capacitor consists of two or more conductors, with various types of dielectrics, placed between them. A potential difference (voltage) between the two conductors causes the generation of static electric field, which is divided by the dielectric into positive and negative charges. They are kept respectively at the positive and the negative pole of the capacitor.

Capacitors are mostly used in circuits and systems which require the blocking of DC charges and the admission of AC ones. Depending on the construction, the location and the shape of the conductors, as well as the type of the used dielectric, capacitors may be electrolytic, filter, ceramic, polypropylene, paper, stiroflex, tantalum, etc. According to their application, there are start capacitors, operating capacitors, filter capacitors, trimmer capacitors and so on.
Diodes
Diodes are semiconductor components equipped with two terminals – positive and negative (anode and cathode). A diode consists of a semiconductor material that allows current to flow in only one direction, depending on how the diode is designed. A P-N junction is created in the semiconductor material which builds the diode. Each diode has a specific volt- ampere characteristic. There is a great variety of diodes which are divided into several large groups, depending on their structure, function, power, frequency and so on. In general, diodes can be rectifier, Zener, Schottky diodes, photodiodes, varicaps, etc.
Integrated Circuits
An integrated circuit or a chip is a configuration of miniaturized electronic components, placed on a silicon plate. In modern integrated circuits electronic components rarely exist in a discreet manner, they are kind of microprocessors or microcontrollers working with a binary code. Depending on the electronic components, from which integrated circuits are build, they are divided into analog, digital and mixed. Analog ones consist of passive electronic components – resistors and capacitors, rarely transistors. They serve as sensors, supplying circuits, operational amplifiers and they modify analog signals. Digital integrated circuits consist mainly of transistors, logic components, trigger components, microprocessors. They operate with the binary number system. The mixed integrated circuits handle both digital and analog signals.

 

Jan 292013
 

Reles

raley_2_400relay universaltime_reley

 

A relay is an electromechanical switch. There are different classifications of relays. The more common ones refer to the controllable quantity: current relays, voltage relays, power relays, pressure relays (pneumatic pressure switch), insulation control relays, etc., according to the principle of operation: electromagnetic relays, magnet electric relays, electrodynamic relays, induction relays. There is also a separate class of semiconductor devices which in case of alternations in certain physical parameters of the environment switch circuits which are also called relays. For example opto relays (optrons) which switch circuits in case of light alternation, reed ampoules, switching in function of the magnetic field, solid state semiconductor contactless relays etc., which we will not discuss in details. Here we will pay special attention to electromagnetic relays.

Electromagnetic relays

Electromagnetic_relay

Electromagnetic relays are composed of an electromagnet (a magnetic core made of ferromagnetic material and a coil wound around the magnetic core), armature of active magnetic material and a switch mechanism. Electromagnetic relays are mainly of two types – current and voltage ones. They can be identified by the structure of the coil. Current relays have coil windings which are made ​​of thick wire and are few in number. They are used in different types of circuit protections. Voltage relays have a coil, whose windings are made of thin wire and they are a lot so that there is high impedance and when there is parallel connection with the consumer, the current that flows through the coil is relatively small.

Operation

Relay-Operation

When we supply voltage to the terminals of the relay winding, the current flowing through the coil induces a magnetic field in the magnetic core. The magnetic field attracts the armature and the armature in turn commutates the switch mechanism. If the relay contacts are normally open (NO), they close and if they are normally closed (NC), they open. Thus there is a change of the state of the electrical circuit at the output. In case of dropping out of the input voltage – the armature resets, being pushed by a spring. These are standard relays with two stable states.

The downside of each relay is the limited electrical life of the contact system. Each commutation arouses micro electric arcs and sparks that accumulate soot on the contact bodies. When the soot increases over thousands of commutations, it begins to impede the passage of electric current through the switch mechanism and the relay cannot operate.

 

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A mercury relay with electrical life 500,000 times.

There are relays incorporating electronic components, manufactured with the purpose of avoiding this disadvantage. For example, a resistor connected to the coil of the relay for better operation or (and) a capacitor connected parallel to the contacts to reduce arcing and interference. Mercury relays, in which the switching element is mercury, are another constructive resolution.

The main difference between a contactor and a relay is that relays have much simpler contact system. A contactor may have a significant number of contacts, some of which close and others open when current flows through the control circuit.

Specifics of operation and usage of relays

Relays have two essential features which determine their application.

1. Relays electrically (galvanically) divide circuits into control and controlled ones, which makes possible their usage as a form of protection.

 

relay

The complete galvanic separation of the two circuits of a relay is clearly demonstrated.

2 . By means of very weak currents in the control circuit, relays can manage much stronger currents in the controlled circuit. In this way they become discrete amplifiers of current, voltage and power in electric circuits. At the input the relay may receive a control signal from various sensors (light, pressure, temperature).

The most common usage of relays is connected with controlling large currents. When currents are too large (hundreds of amps) the entire relay is immersed in engine oil and the contact areas are substantially larger.

Relays are widely used in households for switching refrigerators, washing machines, dishwashers, cookers,

howrelayswork

A demonstration of how a power circuit with significantly stronger current can be managed by small current in the control circuit.

boilers, when starting various electric motors, in cars (automotive relays), etc. Relays are also used when it is necessary to manage multiple circuits by a single control signal. Relays with calibrated operating characteristics and sometimes having multiple operating coils are used to protect electrical circuits from overload or damage; in modern electrical systems these functions are performed by digital tools still called „protective relays“.