Indulge Yourself In The Magnificence Of Diamond Jewellery

Such an amazing sight it is to witness an exotic assemblage of diamond jewellery set which is designed with love and crafted with perfection. Indeed, it is! For many, it is a dream to possess beautiful diamond jewellery set. Diamond jewellery possesses fineness and eternity which makes it a perfect gift of love. It represents loyalty, commitment, passion and many other magical words which are just to be felt but far from the reach of human conscience and vocabulary. The diamond jewellery we see today has come to us, crossing several ages. We can see that the jewellery industry has enhanced a lot from all possible fronts.

The jewellery we wear has seen lot of advancement as far as aspects like diamond cleaning, cutting, sculpting and the likes are concerned. The setting with which the diamond sits within the finely moulded gold has also improved a lot. Therefore, the diamond jewellery which we wear today has seen several layers of aesthetic as well as functional enhancements. It represents true craftsmanship and blends well with almost every attire and occasion. It has become quite a common trend to gift diamond jewellery when the occasions like anniversaries and engagements are there. Specially, the diamond engagement rings have become quite common because the very gesture of presenting before your loved one with a magnificent diamond engagement ring makes that person feel elated to the core of the heart.

But, whenever you are on your search for the very best diamond engagement ring for your beloved, it is better to be involved in a rigorous homework. Buying a diamond engagement ring is a great way to invest as well and therefore if you read about the details of the ornament in advance, it is of great assistance to you. So, along with your hot coffee mug, log on to some beautiful diamond jewellery websites and explore as much as you can. Know well about the details and technical aspects of diamond, gold and the making of the diamond jewellery. You must be well aware about the current prices floating in the market. Do not let yourself be fooled for some or the other reason.

True, it is quite obvious that since it is your shopping for diamond jewellery, you will be quite excited about it and if it is diamond engagement ring, you are bound to explode out of enthusiasm. Therefore, be calm and at rest. Search well so that you end up buying a wonderful piece of jewel at the best price. Also, you can select your favourite diamond jewellery online for which you can place order right there. Just fill in your account details and the selected jewellery piece will be there at your threshold on the specified date. You do not need to worry about the confidentiality and security aspects. It is always intact. Such a kind of shopping makes you save lot of time, money and energy. So, now we guess that you have your reason to be happy and to make others happy as well. 

 

Article Source: http://www.articlesnatch.com/Article/Indulge-Yourself-In-The-Magnificence-Of-Diamond-Jewellery/2297741

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Computer Hard Discs

The storage of the data is a very critical task. Different medias are used for the storage of data like Floppy discs,Hard discs,Writable CDs, Writeable DVDS,Tape Drives ,DAT Drives etc. Hard discs or Hard Disc Drives or simply HDD were introduced in IBM Machines in 1956.

Now a Days HDD are also used in Digital Video Recorders , Digital Audio Players and ,Digital Cameras .It was 2005 when SAMSUNG AND Nokia used Hard Discs in Mobile Phones . To secure Data on Networks NAS (Network Attached Storage ) and SAN ( Storage Area Network ) Hard discs are used.

When you talk about form factor of HDD ,it means the size of the hard disc ,there are many sizes like in 1979 the size was 8 Inches ,then in 1980 Seagate introduced 5.25 Inches HDDs .In 1984 3.5 Inch Hard Drive was introduced . 2.5 Inch HDD was introduced by PrairieTek in 1988. Then for Digital Audio Players 1.8 Inch Hard Disc was introduced . Now a Days the smallest form factor is 0.85 Inch used for Mobile Phones.

Switched-mode power supply

Input rectifier stage

AC, half-wave and full wave rectified signals.

If the SMPS has an AC input, then the first stage is to convert the input to DC. This is called rectification. The rectifier circuit can be configured as a voltage doubler by the addition of a switch operated either manually or automatically. This is a feature of larger supplies to permit operation from nominally 120 volt or 240 volt supplies. The rectifier produces an unregulated DC voltage which is then sent to a large filter capacitor. The current drawn from the mains supply by this rectifier circuit occurs in short pulses around the AC voltage peaks. These pulses have significant high frequency energy which reduces the power factor. Special control techniques can be employed by the following SMPS to force the average input current to follow the sinusoidal shape of the AC input voltage thus the designer should try correcting the power factor. An SMPS with a DC input does not require this stage. An SMPS designed for AC input can often be run from a DC supply (for 230V AC this would be 330V DC), as the DC passes through the rectifier stage unchanged. It's however advisable to consult the manual before trying this, though most supplies are quite capable of such operation even though nothing is mentioned in the documentation. However, this type of use may be harmful to the rectifier stage as it will only utilize half of diodes in the rectifier for the full load. This may result in overheating of these components, and cause them to fail prematurely. [3]
If an input range switch is used, the rectifier stage is usually configured to operate as a voltage doubler when operating on the low voltage (~120 VAC) range and as a straight rectifier when operating on the high voltage (~240 VAC) range. If an input range switch is not used, then a full-wave rectifier is usually used and the downstream inverter stage is simply designed to be flexible enough to accept the wide range of dc voltages that will be produced by the rectifier stage. In higher-power SMPSs, some form of automatic range switching may be used.

Inverter stage

The inverter stage converts DC, whether directly from the input or from the rectifier stage described above, to AC by running it through a power oscillator, whose output transformer is very small with few windings at a frequency of tens or hundreds of kilohertz (kHz). The frequency is usually chosen to be above 20 kHz, to make it inaudible to humans. The output voltage is optically coupled to the input and thus very tightly controlled. The switching is implemented as a multistage (to achieve high gain) MOSFET amplifier. MOSFETs are a type of transistor with a low on-resistance and a high current-handling capacity. Since only the last stage has a large duty cycle, previous stages can be implemented by bipolar transistors leading to roughly the same efficiency. The second last stage needs to be of a complementary design, where one transistor charges the last MOSFET and another one discharges the MOSFET. A design using a resistor would run idle most of the time and reduce efficiency. All earlier stages do not weight into efficiency because power decreases by a factor of 10 for every stage (going backwards) and thus the earlier stages are responsible for at most 1% of the efficiency. This section refers to the block marked Chopper in the block diagram.

Voltage converter and output rectifier

If the output is required to be isolated from the input, as is usually the case in mains power supplies, the inverted AC is used to drive the primary winding of a high-frequency transformer. This converts the voltage up or down to the required output level on its secondary winding. The output transformer in the block diagram serves this purpose.
If a DC output is required, the AC output from the transformer is rectified. For output voltages above ten volts or so, ordinary silicon diodes are commonly used. For lower voltages, Schottky diodes are commonly used as the rectifier elements; they have the advantages of faster recovery times than silicon diodes (allowing low-loss operation at higher frequencies) and a lower voltage drop when conducting. For even lower output voltages, MOSFETs may be used as synchronous rectifiers; compared to Schottky diodes, these have even lower conducting state voltage drops.
The rectified output is then smoothed by a filter consisting of inductors and capacitors. For higher switching frequencies, components with lower capacitance and inductance are needed.
Simpler, non-isolated power supplies contain an inductor instead of a transformer. This type includes boost converters, buck converters, and the so called buck-boost converters. These belong to the simplest class of single input, single output converters which utilize one inductor and one active switch. The buck converter reduces the input voltage in direct proportion to the ratio of conductive time to the total switching period, called the duty cycle. For example an ideal buck converter with a 10 V input operating at a 50% duty cycle will produce an average output voltage of 5 V. A feedback control loop is employed to regulate the output voltage by varying the duty cycle to compensate for variations in input voltage. The output voltage of a boost converter is always greater than the input voltage and the buck-boost output voltage is inverted but can be greater than, equal to, or less than the magnitude of its input voltage. There are many variations and extensions to this class of converters but these three form the basis of almost all isolated and non-isolated DC to DC converters. By adding a second inductor the Ćuk and SEPIC converters can be implemented, or, by adding additional active switches, various bridge converters can be realised.
Other types of SMPSs use a capacitor-diode voltage multiplier instead of inductors and transformers. These are mostly used for generating high voltages at low currents (Cockcroft-Walton generator). The low voltage variant is called charge pump.

Regulation

A feedback circuit monitors the output voltage and compares it with a reference voltage, which is set manually or electronically to the desired output. If there is an error in the output voltage, the feedback circuit compensates by adjusting the timing with which the MOSFETs are switched on and off. This part of the power supply is called the switching regulator. The Chopper controller shown in the block diagram serves this purpose. Depending on design/safety requirements, the controller may or may not contain an isolation mechanism (such as opto-couplers) to isolate it from the DC output. Switching supplies in computers, TVs and VCRs have these opto-couplers to tightly control the output voltage.
Open-loop regulators do not have a feedback circuit. Instead, they rely on feeding a constant voltage to the input of the transformer or inductor, and assume that the output will be correct. Regulated designs compensate for the parasitic capacitance of the transformer or coil. Monopolar designs also compensate for the magnetic hysteresis of the core.
The feedback circuit needs power to run before it can generate power, so an additional non-switching power-supply for stand-by is added.

Transformer design
 

SMPS transformers run at high frequency. Most of the cost savings (and space savings) in off-line power supplies come from the fact that a high frequency transformer is much smaller than the 50/60 Hz transformers formerly used.
There are several differences in the design of transformers for 50 Hz vs 500 kHz. Firstly a low frequency transformer usually transfers energy through its core (soft iron), while the (usually ferrite) core of a high frequency transformer limits leakage. Since the waveforms in a SMPS are generally high speed (PWM square waves), the wiring must be capable of supporting high harmonics of the base frequency due to the skin effect, which is a major source of power loss.

Power factor

Simple off-line switched mode power supplies incorporate a simple full wave rectifier connected to a large energy storing capacitor. Such SMPSs draw current from the AC line in short pulses when the mains instantaneous voltage exceeds the voltage across this capacitor. During the remaining portion of the AC cycle the capacitor provides energy to the power supply.
As a result, the input current of such basic switched mode power supplies has high harmonic content and relatively low power factor. This creates extra load on utility lines, increases heating of the utility transformers and standard AC electric motors, and may cause stability problems in some applications such as in emergency generator systems or aircraft generators. Harmonics can be removed through the use of filter banks but the filtering is expensive, and the power utility may require a business with a very low power factor to purchase and install the filtering onsite.
In 2001 the European Union put into effect the standard IEC/EN61000-3-2 to set limits on the harmonics of the AC input current up to the 40th harmonic for equipment above 75 W. The standard defines four classes of equipment depending on its type and current waveform. The most rigorous limits (class D) are established for personal computers, computer monitors, and TV receivers. In order to comply with these requirements modern switched-mode power supplies normally include an additional power factor correction (PFC) stage.
Putting a current regulated boost chopper stage after the off-line rectifier (to charge the storage capacitor) can help correct the power factor, but increases the complexity (and cost).