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Beiträge vom April, 2011

about capacitors

Wednesday, 27. April 2011 2:53

The capacitor or the electrical condenseris a device for storing an electrical charge. In its simplest form a capacitor consists of two metal plates separated by a nonconducting layer called the dielectric.When one plate is charged with electricity from a direct-current or electrostatic source, the other plate will have induced in it a charge of the opposite sign; that is, positive if the original charge is negative and negative if the charge is positive. The Leyden jar is a simple form of capacitor in which the two conducting plates are metal-foil coatings on the inside and outside of a glass bottle or jar that serves as the dielectric.The electrical size of a capacitor is its capacitance, the amount of electric charge it can hold.Capacitors are limited in the amount of electric charge they can absorb; they can conduct direct current for only an instant but function well as conductors in alternating-current circuits. This property makes them useful when direct current must be prevented from entering some part of an electric circuit.Fixed-capacity and variable-capacity capacitors are used in conjunction with coils as resonant circuits in radios and other electronic equipment. Large capacitors are also employed in power lines to resonate the load on the line and make it possible for the line to transmit more power.

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Silver mica capacitors

Tuesday, 26. April 2011 1:38

Silver mica capacitors are high precision high stability high reliability capacitors. They are available in small values, and are mostly used at high frequencies.Mica capacitors, which are now obsolete, were in use in the early 20th century. They consisted of sheets of mica and copper foil sandwiched together and clamped.Silver mica capacitors, also known as silvered mica capacitors, obsoleted mica capacitors. Instead of being clamped with foils these use sheets of mica coated on both sides with deposited metal. The assembly is dipped in epoxy.
The advantages:
greater stability, since there are no capacitive airgaps that can change dimension
airtight enclosure removes the risk of oxidation or corrosion of plates or connections
greater value per volume, since there are no airgaps between plates and mica
the conducting surfaces can be thinner
no clamping mechanism is needed

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Integrated Circuits

Monday, 25. April 2011 5:48

Integrated Circuits play a very important part in electronics. Most are specially made for a specific task and contain up to thousands of transistors, diodes and resistors. Special purposes IC’s such as audio-amplifiers, FM radios, logic blocks, regulators and even a whole micro computers in the form of a micro controller can be fitted inside a tiny package. Depending on the way they are manufactured, integrated circuits can be divided into two groups: hybrid and monolithic. Hybrid circuits have been around longer. If a transistor is opened, the crystal inside is very small. This means a transistor doesn’t take up very much space and many of them can be fitted into a single Integrated Circuit. Most integrated Circuits are in a DIL package – Dual In Line, meaning there are two rows of pins.High power integrated circuits can generate a lot of heat and they have a metal tag that can be connected to a heatsink to dissipate the heat.

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Diode characteristics

Friday, 22. April 2011 6:48

The most important characteristics when using power diodes is the maximum current in the forward direction (IFmax), and maximum voltage in the reverse direction (URmax).The important characteristics for a Zener diode are Zener voltage (UZ),  Zener current (IZ) and maximum dissipation power (PD).When working with capacitive diodes it is important to know their maximum and minimum capacitance, as well as values of DC voltage during which these capacitances occur.With LEDs it is important to know the maximum value of current it is capable of passing. The natural characteristic voltage across a LED depends on the colour and starts at 1.7V for red to more than 2.4v for green and blue. Current starts at 1mA for a very small glow and goes to about 40mA. High brightness LEDs and “power LEDs” require up to 1 amp and more. You must know the exact current required by the LED you are using as the wrong dropper resistor will allow too much current to flow and the LED will be damaged instantly.

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Diodes

Thursday, 21. April 2011 2:24

As with transistors, diodes are fabricated from semi-conducting material. So, the first letter in their identification is A for germanium diode or B for silicon diode. They can be encased in glass, metal or a plastic housing. They have two leads: cathode (k) and an anode (A). The most important property of all diodes is their resistance is very low in one direction and very large in the opposite direction. When a diode is measured with a multimeter and it reads a low value of ohms, this is not really the resistance of the diode. It represents the voltage drop across the junction of the diode. This means a multimeter can only be used to detect if the junction is not damaged. If the reading is low in one direction and very high in the other direction, the diode is operational. When a diode is placed in a circuit and the voltage on the anode is higher than the cathode, it acts like a low value resistor and current will flow.If it is connected in the opposite direction it acts like a large value resistor and current does not flow.

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Basic features of transistors

Wednesday, 20. April 2011 2:59

Selecting the correct transistor for a circuit is based on the following characteristics: maximum voltage rating between the collector and the emitter UCEmax, maximum collector current ICmax and the maximum power rating PCmax.If you need to change a faulty transistor, or you feel comfortable enough to build a new circuit, pay attention to these three values. Your circuit must not exceed the maximum rating values of the transistor.Among its other characteristics, this transistor has current amplification coefficient in range between hFE= 100 to 450, and it can be used for frequencies under 300MHz.Current amplification is of importance when used in some circuits, where there is a need for equal amplification of two transistors.For example, 2N3055H transistors have hFE within range between 20 and 70, which means that there is a possibility that one of them has 20 and other 70. This means that in cases when two identical coefficients are needed, they should be measured.

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Electrolytic capacitors

Tuesday, 19. April 2011 4:07

Electrolytic capacitors represent the special type of capacitors with fixed capacity value. Thanks to special construction, they can have exceptionally high capacity, ranging from one to several thousand µF. They are most frequently used in circuits for filtering, however they also have other purposes.Electrolytic capacitors are polarized components, meaning they have positive and negative leads, which is very important when connecting it to a circuit. The positive lead or pin has to be connected to the point with a higher positive voltage than the negative lead. If it is connected in reverse the insulating layer inside the capacitor will be “dissolved” and the capacitor will be permanently damaged. Explosion may also occur if capacitor is connected to voltage that exceeds its working voltage. In order to prevent such instances, one of the capacitor’s connectors is very clearly marked with a + or -, while the working voltage is printed on the case.Tantalum capacitors represent a special type of electrolytic capacitor. Their parasitic inductance is much lower than  standard aluminum electrolytic capacitors so that tantalum capacitors with significantly (even ten times) lower capacity can completely substitute an aluminum electrolytic capacitor.

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about trimming potentiometers

Monday, 18. April 2011 2:27

Trimming Potentiometers are three-terminal resistors that are used to measure or divide voltages, and to protect or control circuits. Potentiometers are variable resistors that are adjusted with a knob or dial.Trimming Potentiometers carry specifications for potentiometer category and actuator configuration. Industrial-grade potentiometers are protected by an enclosure, typically one that is rated by the National Electrical Manufacturers Association (NEMA).  In terms of actuator configuration, choices include single-turn, multi-turn, and slide. With single-turn devices, the shaft rotation is limited to less than or equal to 360 degrees. By contrast, multi-turn Trimming Potentiometers can be rotated multiple times, with as many as 15 or 20 turns from stop to stop. Slide-actuated products require the user to move a handle instead of rotating a knob.Trimming Potentiometers differ in terms of construction, mounting or packaging, performance specifications and features.

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definition of capacitor

Friday, 15. April 2011 5:45

A capacitor is a passive electronic component that storesenergy in theform of an electrostatic field. In its simplest form, a capacitorconsists of twoconducting plates separated by an insulating material called thedielectric. Thecapacitance is directly proportional to the surface areas of the plates, andis inverselyproportional to the separation between the plates. Capacitance alsodepends on thedielectric constant of the substance separating the plates.Capacitors can be fabricated onto integrated circuit (IC)chips. They are commonly used in conjunction with transistors in dynamic random access memory (DRAM). The capacitors helpmaintain thecontents of memory. Because of their tiny physical size, thesecomponents have lowcapacitance. They must be recharged thousands of times per second or theDRAM will lose its data.Large capacitors are used in the power supplies of electronicequipment ofall types, including computers and their peripherals. In these systems,thecapacitors smooth out the rectified utility AC, providing pure, battery-likeDC.

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Passive electronic components

Thursday, 14. April 2011 2:01

Passive electronic components are used in all types of electronic circuitry, but are often overlooked in their importance to the operation of the circuit. The passive electronic component stands ready to perform in a circuit when provided an external voltage or current stimulus. The active component, on the other hand, is often part of the power supply providing the stimulus for the passive circuit. Semiconductors are probably the most commonly used active electronic component.Passive components, like resistors and transformers, are often constructed using resistance wire for resistors and magnet wire for transformers. Various metal foils are often used in wound film capacitor construction.Another construction method used for metal film resistors and tantalum capacitors is to deposit either metal or dielectric film using vacuum thin film sputtering techniques. Vacuum sputtering is a precise and accurate means of construction. No wire or foil windings are necessary with this type of resistor or capacitor construction.

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