Su Suntan Tiny Capacitors May Overcome Physical Limits of Hard Drives

February 7, 2009 Views
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Storage—there is never enough of it. I still remember when I thought my 700MB hard drive was huge... until I tried to copy an entire CD onto it for faster access. After that, I spent a period stuck choosing music to stick on my three GB hard drive. Two weeks ago, I ditched six months' worth of simulation data because my 320GB hard drive was full. One TB of new drive later, and I'm wondering how soon it will be before I start feeling the squeeze again. Maybe never, if some of the latest research coming out of Korea and Germany bears fruit.

One of the cool things about hard drive technology is how it has actually kept pace with computer needs. The basic mechanism for hard drive storage, however, does have some fundamental limitations, which manufacturers will have to deal with fairly soon. Bits are currently stored in the orientation of tiny magnets, called ferromagnetic domains, on a hard drive platter. The smaller the domain, the easier it is for that orientation to be scrambled by temperature or stray electromagnetic fields. At a certain size, thermal photons (e.g., heat energy from the surrounding case or the underlying disk) have enough energy to flip a domain's orientation. Manufacturers will have to keep their domain sizes significantly bigger than that threshold size to ensure data integrity, which puts a ceiling on storage density, one we're rapidly approaching.

An alternative is to use ferroelectric domains. Unlike ferromagnetic domains, ferroelectric domains have a natural electric field with an orientation that can be used to represent data. Until recently, these haven't looked that attractive because they have pretty much the same limitations that ferromagnetic domains have, but they lack the cool read-out tricks. Ferroelectric materials, however, do have one big advantage over ferromagnetic materials: they can be used to make really good capacitors. This is exactly what the latest research, published in Nature Nanotechnology, is about.

KEMET Introduces The First 35-Volt Rated Polymer Tantalum Capacitor

February 1, 2009 Views
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Suntan Technology Company Limited
---All kinds of Capacitors

Greenville, SC - KEMET Corporation announced the release of the first ever 35V rated surface mount polymer tantalum chip capacitor.

Since their introduction in the '90s, polymer tantalum capacitors have become a popular choice for capacitance solutions in portable consumer electronics due to their low ESR (Equivalent Series Resistance), high reliability, volumetric efficiency, low profile design and benign failure mode. To date, these devices have been most commonly used in applications at or below 14V and are limited to voltage applications that cannot exceed 20V of continuous duty. These voltage restrictions are driven by limitations in the materials of construction and manufacturing processes that have until today prevented the industry from achieving higher voltage ratings.

"This first-to-market technology represents a significant breakthrough for design engineers," stated Dr. Philip Lessner, KEMET's CTO and Chief Scientist. "Military, aerospace, power supplies and industrial applications will all benefit from this advancement. Our first significant order has been placed by a U.S. military contractor to enhance the performance of a key communications network system that is used by multiple defense agencies around the world," continued Lessner.

By overcoming these voltage limitations through advances in materials and manufacturing processes, KEMET has successfully constructed and qualified the first polymer tantalum capacitors suitable for applications of up to 25V of continuous duty. In addition, these devices have demonstrated surge voltage handling capabilities in excess of 46V. This increase in voltage rating now provides designers working with higher voltage applications, such as 20V to 24V power input rails, with the option of incorporating polymer tantalum technology into new designs as opposed to settling for capacitance technologies that do not offer similar performance advantages.

Designated as the T521 Series, KEMET's initial offering of this new series includes the popular low profile V Case Size (7.3mm x 4.3mm x 1.9mm) with a capacitance rating of 15uF and maximum ESR ratings of 125 milliohms. Future releases will include higher case heights (7.3mm x 4.3mm x 3.0mm) with target capacitance values of 22uF and 33uF as well as smaller footprints (3.5mm x 2.8mm x 2.0mm) targeting application voltages of 6.8uF and less.

Sample quantities are available upon request through your local KEMET Representatives. Mass production quantities are available in increments of 1000 pieces.

Su Suntan Single Turn Trimming Potentiometers

January 31, 2009 Views
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Suntan Technology Company Limited
---All kinds of Capacitors

Trimming potentiometers
perform a variety of circuit adjustments in all types of electronic equipment. The variety of physical configurations available and the ability to withstand today's manufacturing environment offers the designer flexibility in selecting the best trimmer for the application. Around the world, trimmers are used in virtually every electronic market.

  • Multi-turn Trimming Potentiometers
  • Single-turn Trimming Potentiometers
  • Military Qualified Trimming Potentiometers

 

Su Suntan Multi-Turn Trimming Potentiometers

January 31, 2009 Views
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Suntan Technology Company Limited
---All kinds of Capacitors

Trimming potentiometers
perform a variety of circuit adjustments in all types of electronic equipment. The variety of physical configurations available and the ability to withstand today's manufacturing environment offers the designer flexibility in selecting the best trimmer for the application. Around the world, trimmers are used in virtually every electronic market.

Typical applications include measuring linear distance, angles or rotations in production equipment, industrial test and measurement equipment, and medical equipment.

Su Suntan A Bad Capacitor Story Ends Happily

January 31, 2009 Views
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Suntan Technology Company Limited
---All kinds of Capacitors

I worked as a design engineer for an optical-telecom company that had deployed 1000 pieces of equipment worldwide. Having so many modules in the field means a trickle of returns, and it was my job to investigate the failures. One investigation taught me a wonderful lesson.

I received a module whose source of failure was easily identifiable: a charred tantalum capacitor. It failed short, making the whole multithousand-dollar module nonoperational. This surface-mount capacitor—with a 7343 footprint and 20V rating—was sitting on a 12V-dc plane. This failure rate of one capacitor in about 10,000 pieces in this time span was well below the statistical prediction. I took a picture of the fallen capacitor and considered the case closed.

In a few weeks, a customer returned a similar module with a charred and shorted capacitor in the same location. Even including this case, the failure rate was still below statistical prediction. I knew there were five more identical capacitors on the board, sitting in parallel on the same 12V-dc plane. In addition to the module's failure rate, I now had a one-in-six chance with the capacitors. So, I took another picture. I wrote a report to calm upper management, but I had a feeling that I'd better study reliability calculation in general and reliability for tantalum capacitors in particular, and the faster, the better.

In another few weeks, I received another failed module. The same capacitor looked bad. I had by now done my studying and could intimidate other people by saying long and complicated sentences about reliability, but why was it always the same capacitor? Overvoltage? Spikes? No way. The same plane contained plenty of sensitive stuff that would fry well before the capacitor even felt it. Having nothing better, I clung to the theory of excessive ripple current.

The idea of a temperature rise due to ripple current causing the failure gained traction when all three photos of the fallen capacitors revealed a common condition: almost no solder on each negative terminal. The electrical connection was still good, but there was little solder. The capacitor's positive terminal was fine with a fair amount of curvature-profiled solder. I started to promote the idea that the lack of solder had caused impeded thermal contact, but it was only wishful thinking. I calculated the worst ripple current: 10% of the maximum rating. On an operational board, I got less than 5%.

I had already dismissed other ideas—from excessive humidity to airflow turbulence. Suddenly, the picture of the layout popped up in my mind. The layout sections for the five good capacitors were identical: Vias were close to both terminals going down to an internal layer. The bad capacitor had a via at the positive terminal, but, at the negative end, there was a heavy trace going inside the footprint, beneath the capacitor, and only then outside. That's when I knew how to fit together all the pieces of the puzzle.

On the positive terminal, the solder stayed where it was supposed to, clinching the terminal to the PCB (printed-circuit board). On the negative side, however, during assembly, the melted solder drifted under the capacitor and solidified, lifting the negative end and bending the capacitor just enough to create a microcrack—a capacitor's well-known nemesis. I never felt as much excitement writing a technical report as I did the next day.

Su Suntan What is a Varistor?

January 30, 2009 Views
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Suntan Technology Company Limited
---All kinds of Capacitors

A varistor is a type of resistor with a significantly non-ohmic current-voltage characteristic. The name is a portmanteau of variable resistor*, which is misleading since it is not continuously user-variable like a potentiometer or rheostat, and is not a resistor but in fact a capacitor. Varistors are often used to protect circuits against excessive voltage by acting as a spark gap.

The most common type of varistor is the metal oxide varistor, or MOV. This contains a mass of zinc oxide grains, in a matrix of other metal oxides, sandwiched between two metal plates (the electrodes). The boundary between each grain and its neighbour forms a diode junction, which allows current to flow in only one direction. The mass of randomly oriented grains is electrically equivalent to a network of back-to-back diode pairs, each pair in parallel with many other pairs. When a small or moderate voltage is applied across the electrodes, only a tiny current flows, causes by reverse leakage through the diode junctions. When a large voltage is applied, the diode junctions break down because of the avalanche effect, and a large current flows. The result of this behaviour is a highly nonlinear current-voltage characteristic, in which the MOV has a high resistance at low voltages and a low resistance at high voltages.

If the size of the transient pulse (often measured in joules) is too high, the device may melt, or otherwise be damaged. For example, a nearby lightning strike may permanently damage a varistor.

Important parameters for varistors are response time (how long it takes the varistor to break down), maximum current and a well-defined breakdown voltage. When used in communications lines (such as phone lines used for modems), high capacitance is undesirable since it absorbs high frequency signals, thereby reducing the available bandwidth of the line being protected.

Su Suntan Electrolytic Capacitor

January 13, 2009 Views
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Suntan Technology Company Limited
---All kinds of Capacitors

Aluminum is used for the electrodes by using a thin oxidization membrane.

Electrolytic Capacitor

Large values of capacitance can be obtained in comparison with the size of the capacitor, because the dielectric used is very thin.

The most important characteristic of electrolytic capacitors is that they have polarity. They have a positive and a negative electrode.

[Polarised] This means that it is very important which way round they are connected. If the capacitor is subjected to voltage exceeding its working voltage, or if it is connected with incorrect polarity, it may burst. It is extremely dangerous, because it can quite literally explode. Make absolutely no mistakes.

Generally, in the circuit diagram, the positive side is indicated by a "+" (plus) symbol.

Electrolytic capacitors range in value from about 1µF to thousands of µF. Mainly this type of capacitor is used as a ripple filter in a power supply circuit, or as a filter to bypass low frequency signals, etc. Because this type of capacitor is comparatively similar to the nature of a coil in construction, it isn't possible to use for high-frequency circuits. (It is said that the frequency characteristic is bad.)

The photograph on the left is an example of the different values of electrolytic capacitors in which the capacitance and voltage differ.

From the left to right:

  • 1µF (50V) [diameter 5 mm, high 12 mm]
  • 47µF (16V) [diameter 6 mm, high 5 mm]
  • 100µF (25V) [diameter 5 mm, high 11 mm]
  • 220µF (25V) [diameter 8 mm, high 12 mm]
  • 1000µF (50V) [diameter 18 mm, high 40 mm]

The size of the capacitor sometimes depends on the manufacturer. So the sizes shown here on this page are just examples.

In the photograph to the right, the mark indicating the negative lead of the component can be seen.

You need to pay attention to the polarity indication so as not to make a mistake when you assemble the circuit.

Su Suntan Capacitor History

January 13, 2009 Views
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Suntan Technology Company Limited
---All Kinds of Capacitors

In October 1745, Ewald Georg von Kleist of Pomerania in Germany found that charge could be stored by connecting a generator by a wire to a volume of water in a hand-held glass jar. Von Kleist's hand and the water acted as conductors and the jar as a dielectric. Von Kleist found that after removing the generator, touching the wire resulted in a spark. In a letter describing the experiment, he said "I would not take a second shock for the kingdom of France." The following year, the Dutch physicist Pieter van Musschenbroek invented a similar capacitor, which was named the Leyden jar, after the University of Leyden where he worked. Daniel Gralath was the first to combine several jars in parallel into a "battery" to increase the charge storage capacity.

Benjamin Franklin investigated the Leyden jar, and proved that the charge was stored on the glass, not in the water as others had assumed Leyden jars began to be made by coating the inside and outside of jars with metal foil, leaving a space at the mouth to prevent arcing between the foils. The earliest unit of capacitance was the 'jar', equivalent to about 1 nanofarad.

Leyden jar or flat glass plate construction was used exclusively up until about 1900, when the invention of wireless (radio) created a demand for standard capacitors, and the steady move to higher frequencies required capacitors with lower inductance. A more compact construction began to be used of a flexible dielectric sheet such as oiled paper sandwiched between sheets of metal foil, rolled or folded into a small package.

Early capacitors were also known as condensers, a term that is still occasionally used today. It was coined by Alessandro Volta in 1782 (derived from the Italian condensatore), with reference to the device's ability to store a higher density of electric charge than a normal isolated conductor. Most non-English European languages still use a word derived from "condensatore".
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