SMD Varistor Specifications

January 5, 2011 Views
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A varistor is an electronic component with a significant non-ohmic current-voltage characteristic. The name is a portmanteau of variable resistor

SMD resistors are manufactured by a number of different companies. Accordingly the specifications vary from one manufacturer to the next. It is therefore necessary to look at the manufacturers rating for a specific SMD resistor before deciding upon exactly what is required. However it is possible to make some generalisations about the ratings that might be anticipated.

Power rating: The power rating needs careful consideration in any design. For designs using SMD’s the levels of power that can be dissipated are smaller than those for circuits using wire ended components. As a guide typical power ratings for some of the more popular SMD resistor sizes are given below. These can only be taken as a guide because they may vary.

  • 1206: 1/8 watt
  • 0805: 1/10 watt
  • 0603: 1/16 watt

Some manufacturers will quote higher power levels than these. The figures given are conservative.

Tolerance: In view of the fact that SMD resistors are manufactured using metal oxide film they available in relative close tolerance values. Normally 5%, 2%, and 1% are widely available. For specialist applications 0.5% and 0.1% values may be obtained.

Temperature coefficient: Again the use of metal oxide film enables these SMD resistors to provide a good temperature coefficient. Values of 25, 50 and 100 ppm / C are available.

Suntan has supply SMD Varistor which called TSVC, TSVC is widely used in Notebook, PDA, Cellular Phone, MP3,Main board, LCM, HUB, Microphone, Wireless LAN, VOIP, Auto electronic and so on. At Suntan website: www.suntan.com.hk ,they have introduced the details about SMD Varistor TSVC by PDF: http://www.suntan.com.hk/pdf/Varistor/TSVC.pdf

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Multilayer Ceramic Capacitor - SMD - TS18

January 5, 2011 Views
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The ceramic SMD capacitors form the majority of SMD capacitors that are used and manufactured. They are normally contained in the same type of packages used for resistors.

  • 1812 - 4.6 mm ~ 3.0 mm (0.18" ~ 0.12")
  • 1206 - 3.0 mm ~ 1.5 mm (0.12" ~ 0.06")
  • 0805 - 2.0 mm ~ 1.3 mm (0.08"~ 0.05")
  • 0603 - 1.5 mm ~ 0.8 mm (0.06"~ 0.03")
  • 0402 - 1.0 mm ~ 0.5 mm (0.04"~ 0.02")
  • 0201 - 0.6 mm ~ 0.3 mm (0.02"~ 0.01")

Suntan Multilayer Ceramic Capacitor - SMD - TS18 has four types of packages used for resistors. In Suntan’s website www.suntan.com.hk there is a Dimensions of Multilayer Ceramic Capacitor - SMD - TS18 as followings:

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Multilayer Ceramic Capacitors constructed

January 5, 2011 Views
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MLCC capacitors are marvels of modern material science. Manufacturing MLCC capacitors is considerably more complicated than manufacturing dipped ceramic capacitors. First, the base ceramic material is mixed with a binder and fashioned into thin sheets. Electrodes are painted onto one side of the sheets using a paint that consists of a liquid binder with fine metal particles in suspension. The metals that are used include gold, palladium, platinum, and silver alloys. The reason for using these metals is that when the base ceramic is fired, oxygen is required for the ceramic proper to form.

Once the ink is dry, the sheets are stacked on top of each other. The painted electrodes are arranged so that alternate electrodes exit from opposite ends. The top- and bottom-most layers do not have painted electrodes. The laminated layers are then compressed and fired, which sinters them into one monolithic structure.

Next, the ends are terminated, often using silver. For leaded capacitors, wires are attached, and finally the capacitor is encapsulated in plastic and marked. In the case of chip capacitors, the silver end terminations are covered with tin to aid soldering. The whole capacitor may be covered with lacquer.

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Capacitors in Series Circuits

December 23, 2010 Views
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Capacitance can be decreased in a circuit by capacitors in series as shown in the following diagram:

We know that capacitance of a capacitor can be decreased by placing the plates further apart. Connecting two or more capacitors in series in effect increases the distance between the plates and thickness of the dielectric, thereby decreasing the amount of capacitance.

The following is the formula for calculating total capacitance in a circuit containing two capacitors in series:
                                                 
CT = (C1 x C2x C3) / (C1 + C2+ C3)

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Notes to uses of Aluminum Electrolytic Capacitors

December 22, 2010 Views
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Aluminum electrolytic capacitors ('capacitors') may cause explosion, fire, or other serious hazard if used outside the specified operating conditions. Please familiarize yourself with the instructions below before using these capacitors.

1.Check the operating and installation environment and use the capacitor within the range of the rated performance specified in the catalog or specifications.

2.Maintain operating temperature and ripple current within the specified ranges. Base your choice of capacitors on the maximum load conditions. A capacitor will overheat under excessive current, potentially resulting in short circuit, fire, or other major failure.

3.A capacitor also generates the self heating. Please bear in mind that the capacitor heats up the interior of the equipment, and take appropriate precautions. Operate the unit under normal conditions and check the temperature of the area surrounding the capacitor.

4.The permissible ripple current declines with the rise in ambient temperature (the temperature of the capacitor's surroundings).Consider the permissible ripple current at the maximum predictable ambient temperature.

5.Electric characteristics change as frequencies change. Check frequency changes in order to choose the right capacitor. Special attention needs to be given to the self heating and short life time both low and high frequency, when equivalent series resistance and inductance change.

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Gold capacitor Description

December 21, 2010 Views
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Gold capacitor 5.5V 1.0 F super capacitor, gold capacitor, ultra capacitor , Electric Double-layer capacitor ,EDLC ,Farad capacitor , super capacitor which have some performance : unlimited charge or discharge cycle ,Small-size, large capacity, excellent voltage holding. Wider temperature range from -25 to70 ,Low ESR ,high energy density. Which nominal capacity range is 0.1F-3000F.operating voltage range is from 2.5V to 5.5V. It used in many fields , Toys, Medical equipment, Bicycle Light, Flashlights, UPS, GPS storing power for Video,Audio,CMOS,RAM,VCR,scanner,Telephone,Computer,LED,Relay,Wireless ,Consumption Electronics, Buzzer

Concerning on TS12S-S (Electric Double Layer Capacitor - Stacked Coin (Small Capacitance)(under develop), miniature size, low leakage, safety and high reliability, the rated capacity is from 0.15F to 8.0F at 2.7~ 5.5V voltage. There are V & H type to be chosen.

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What varistors don't do?

December 20, 2010 Views
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A MOV inside a TVSS device does not provide equipment with complete power protection. In particular, MOV device provide no protection for the connected equipment from sustained over-voltages that may result in damage to that equipment as well as to the protector device.

A varistor provides no equipment protection from inrush current surges (during equipment startup), from over current (created by a short circuit), or from voltage sags (also known as a brownout). A varistor neither senses nor controls such events. Susceptibility of electronic equipment to these other power disturbances is defined by equipment design. Protection from these power disturbances is installed inside that equipment or is provided by other external devices such as an UPS, some voltage regulators and Surge Protectors with built in over voltage protection that make use of a voltage sensing circuit and a relay for disconnecting the AC input when voltage reaches a danger threshold.

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What is a mica capacitor?

December 17, 2010 Views
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Mica, a mineral, is one of the oldest dielectric materials used in capacitor construction. There are several kinds of mica, with differing properties, but mica is in general very stable electrically, mechanically, and chemically. It has a dielectric constant in the range 5–7. Mica has the interesting property that its crystalline structure is asymmetrical. The binding forces in one plane are quite strong, while the binding forces along the perpendicular plane are very weak. Because of this, it has a distinct layered structure, and it is possible to split or cleave mica into very thin, optically flat, sheets. For capacitors, mica sheets in the range 0.025–0.125 mm or even thinner are used.

Mica capacitors are available with values that range from 1–4700 pF and even up to 1 μF, but they are generally thought of as low value capacitors. Rated voltages are in the range 100–1000 V for standard dipped mica capacitors. Rated voltages for RF transmitting capacitors are up to 10 kV. Given the excellent electrical performance of mica capacitors in general, manufacturers typically market them with close tolerances (1% or better).

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About Electrolytic Capacitor

December 17, 2010 Views
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Unlike capacitors that use a bulk dielectric made from an intrinsically insulating material, the dielectric in electrolytic capacitors depends on the formation and maintenance of a microscopic metal oxide layer. Compared to bulk dielectric capacitors, this very thin dielectric allows for much more capacitance in the same unit volume, but maintaining the integrity of the dielectric usually requires the steady application of the correct polarity of direct current else the oxide layer will break down and rupture, causing the capacitor to lose its ability to withstand applied voltage (although it can often be "reformed"). In addition, electrolytic capacitors generally use an internal wet chemistry and they will eventually fail if the water within the capacitor evaporates.

Electrolytic capacitance values are not as tightly-specified as with bulk dielectric capacitors. Especially with aluminum electrolytic, it is quite common to see an electrolytic capacitor specified as having a "guaranteed minimum value" and no upper bound on its value. For most purposes (such as power supply filtering and signal coupling), this type of specification is acceptable.

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What About Capacitance Meters?

December 16, 2010 Views
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Simple capacitance scales on DMMs just measure the capacitance in uF and do not test for leakage, ESR (Equivalent Series Resistance), or breakdown voltage. If the measurement comes up within a reasonable percentage of the marked value (some capacitors have tolerances that may be as much as +100%/-20% or more), then in many cases, this is all you need to know. However, leakage and ESR frequently change on electrolytic as they age and dry out.

Many capacitance meters don't test anything else but are probably more accurate than a cheap DMM for this purpose. A meter of this type will not guarantee that your capacitor meets all specifications but if it tests bad - very low - the capacitor is bad. This assumes that the test was made with the capacitor removed (at least one lead from the circuit - otherwise other components in parallel can affect the readings.

To more completely characterize a capacitor, you need to test capacitance, leakage, ESR, and breakdown voltage. Other parameters like inductance aren't likely to change on you.

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