Zener diodes

Zener diodes are semiconductor diodes which have been manufactured to have their reverse breakdown occur at a specific, well-defined voltage (its “Zener voltage”), and that are designed such that they can be operated be operated continuously in that breakdown mode. Commonly available Zener diodes are available with breakdown voltages (“Zener voltages”) anywhere from 1.8 to 200 V.

Background: Semiconductor diodes, real and ideal

If we hook up a diode in a simple circuit with a variable voltage source and a current-limiting resistor, we can measure the current I through the diode when a given voltage V is applied across it. For an ideal diode, no current at all passes when the voltage is less than zero: the diode completely prevents reverse current flow. For small positive voltage (“forward bias,” or sometimes “foward voltage”), a tiny amount of current may flow, and a very large amount of current will flow above a given threshold. The amount of current that flows is actually exponential with increasing voltage.

The threshold where an appreciable amount of current flows is typically around 0.7 V for simple semiconductor diodes, but may be as low as 0.15 V for Schottky diodes, or as high as 4 V for certain types of LEDs.Of course, no diode is truly ideal. In real diodes, when the voltage is reversed, a very small amount of current (leakage) may flow. And, more significantly, each diode is rated for a certain maximum amount of reverse voltage. If you apply voltage more negative than that limit, the diode will undergo “reverse breakdown”

and begin to conduct a significant amount of current, but backwards from the normal direction of diode current flow. For a regular diode, we would say that the diode has failed if it begins to conduct current in that direction.

Aside: The actual physics of what happens at breakdown is quite interesting; two separate effects, the Zener effect and Avalanche breakdown both contribute to this behavior.

Background: Semiconductor diodes, real and ideal

To understand how Zener diodes are different from other diodes, let’s first review the properties of regular diodes. And, while there are many different types of diodes– see herefor a long list –we’re going to focus on so-called “normal” semiconductor diodes, most commonly constructed with a p-n silicon junction.Diodes usually come in glass or plastic cylindrical packages, marked with a stripe on one side to indicate polarity. In a perfectly ideal diode, current flows in one direction only, from the anode (positive side) to the cathode (negative side) which is marked with the stripe. The schematic symbol is a triangle pointing towards a bar, where the current flows in the same direction, towards the barred (striped) end. Surface mount versions of diodes tend to follow the same labeling convention, where the cathode end is marked with a broad stripe.

Basics: Introduction to Zener Diodes

Zener diodes are a special type of semiconductor diode– devices that allow current to flow in one direction only –that also allow current to flow in the opposite direction, but only when exposed to enough voltage. And while that sounds a bit esoteric, they’re actually among the handiest components ever to cross an engineer’s bench, providing great solutions to a number of common needs in circuit design.

In what follows, we’ll show you how (and when) to use a Zener, for applications including simple reference voltages, clamping signals to specific voltage ranges, and easing the load on a voltage regulator.

Silicon and Germanium

Solid state electronics arises from the unique properties of silicon and germanium, each of which has four valence electrons and which form crystal lattices in which substituted atoms (dopants) can dramatically change the electrical properties.

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Forward Biased P-N Junction

	Forward biasing the p-n junction drives holes to the junction from the p-type material and electrons to the junction from the n-type material. At the junction the electrons and holes combine so that a continuous current can be maintained.

P-N Energy Bands

To reverse-bias the p-n junction, the p side is made more negative, making it "uphill" for electrons moving across the junction. The conduction direction for electrons in the diagram is right to left, and the upward direction represents increasing electron energy.

Reverse Biased P-N Junction

The application of a reverse voltage to the p-n junction will cause a transient current to flow as both electrons and holes are pulled away from the junction. When the potential formed by the widened depletion layerequals the applied voltage, the current will cease except for the smallthermal current.

The Zener Effect

With the application of sufficient reverse voltage, a p-n junction will experience a rapid avalanche breakdown and conduct current in the reverse direction. Valence electrons which break free under the influence of the applied electric field can be accelerated enough that they can knock loose other electrons and the subsequent collisions quickly become an avalanche. When this process is taking place, very small changes in voltage can cause very large changes in current. The breakdown process depends upon the applied electric field, so by changing the thickness of the layer to which the voltage is applied, zener diodes can be formed which break down at voltages from about 4 volts to several hundred volts.

Rina bears and gold, happy in shelters

Two brown bears, Rina and Ari, yesterday received minikopshti zoo where they were held for years, to be sent to the shelter near Lake Badovc. Even though the owner objected minikopshtit "Eagle", Ministry of Environment, the Environmental Protection Agency in cooperation with the international organization for animal welfare "Four Paws" from Austria, these two bears rescued the purpose of institutional protection of this species Kosovo threatened.
Their release ceremony in open space park bears joined Environment Minister, Dardan Gashi, the U.S. ambassador, Tracy Ann Jacobson and Austrian Ambassador, Johann Brieger.
The decision to withdraw these bears from zoos minikopshtet in Kosovo, operating within the restaurant, is based on the Law on Nature Protection, the Law on the protection of animals as well as international conventions for the protection of endangered species.
Rina and gold are the second bears were rescued with the help of the organization "Four Paws". In March this year, bears, Kassandra, the bear was first placed in shelter bears, near Lake Badovc. By the end of July is expected to be 15 brown bears, which are found in these minikopshte, transported to the shelter.
Such practices are implemented in many countries of the world, where protected species of bears are kept in special shelters serve half-and commercial matters. The case of Kosovo is the first in the region that reaches finalized, although "Four Paws" was like trying to open shelters in Albania and Serbia. This event followed a number of local and international media.

Died in childbirth, postpartum rose

In February, Erica Nigrelli was teaching, as usual, in a Texas high school, when suddenly falling ill and collapsed ground. Three teachers rushed to his aid, using a defibrillator, as expected the ambulance arrived.
The child should be born after three weeks. At a time when 32-year-old arrived at the hospital, doctors were unable to find the pulse, her heart had stopped beating.
The child was born by emergency caesarean and a mistimed births was technically "postmortem", because Erica was pronounced dead.
Then came wonder. Erica went to doctors and to their great surprise, found that her heart had started beating again.
Over the next five days, the 32-year-old was in medical induced coma after being diagnosed with a problem that did not know it had: hipertrofike cardiomyopathy, or heart muscle disease, which hinders blood pumping.
The baby was in intensive care for two weeks. Now, both enjoy good health, although Elayna continues to undergo therapy.
Couple confessed Nigrelli exceptional experience in the show "Early Start" to CNN TCH.
After touching history tracking, spouses joked, saying that if ever Elayna out of control, they will simply recall what took her mother to bring to life.

NASA keeps secret angel year 200,000

NASA and its secret, to 200,000-year-old angel hidden for more than 40 years
One of the best preserved secret for more than four decades, suddenly comes to light to overturn everything we knew and believed until now. An "angel" aged not less than 200,000 years old ... mirëmbuluara reveals secrets of the moon and a thousand doubts arise simultaneously!
And how many things we hide "gene" NASA?
But why did they decided to show us things that threaten to overturn the theory hundreds of "proven" scientifically?
Perhaps we are facing again with another farce, which is targeted to scientists who imagine and believe the arrival of extraterrestrials?
There are dozens of foreign agencies which here refers to a month and a photographer deal with small statue, which has a height of not more than 25cm. Small statue depicts a humanoid (human-specific female) small, with long hair and a gown that covers up and her knees. In the shoulder, it holds a pair of wings, which resemble what everyone imagines naturalists, ie an angel.
But, until there is nothing strange!
What did the most famous photograph in the world, making the rounds of the world in record time, and accompanied by a series of reports that a piece of media is not published or not presented them in front of their readers and viewers and it is true but modified. So, it was an affirmation of the scientist who work for more than 23 years at NASA, saying that this sculpture was unveiled in 1969, attached to the rock, the sampled by Monday and was brought to Earth the spatial mission "Apollo 11"!
Dr.Morris geologist Charles, who was he to reveal the existence of the sculpture, claims he was employed at NASA for more than 23 years, since 1964 until 1987, and even today has close ties with many his colleague.
He also claims that the chemical analysis, which underwent this sculpture, confirmed that it was created by a kind of mixture of iron that exists only on Monday, and it was washed with a glass type material "in hand" which gives the sculpture a gorgeous shiny silver!
According to the professor, geologists consider the situation before 200,000 years, ie 170,000 years before the human being appeared on Earth!
"Metal sample, proving that he is not created on the moon and was transferred there from a ... extraterrestrial beings! This means that once the moon had atmosphere that allowed the development of life there, and he was incredibly intelligent life emerging, with super-abilities and physical beauty, "says the professor.
After exposure to reporters and photographers sculpture, she was transferred and hid in a place without knowing for further study and analysis of laboratory experiments as well ... Maybe one another Christ, or a creature Anunaki?
But as it fell into the hands of Dr.Morris sculpture Charles when she stood for more than 40 years?
"Sculpture was a secret shared among NASA scientists but for" gene "NASA who held secret and kept it as 'rain in the desert' was terror itself, as feared caused global panic! Many personalities who for professional, do not disclose their personal data and prefer to remain anonymous, brought the sculpture, "continues Dr. Charles.
In the report accompanying photographer, a professor from the University of Washington anthropologist, creator of "Angel" considers as being gifted in religious beliefs that resemble the Christian religion!
"There is a possibility that they are being, or that civilization had" Christ "of his, which was to prove that spiritual principles are universal," says Dr. Fredericks Miles from University of New York, and continues giving another version: "Sumer many stories to tell Anunaki in the 18th century BC. Perhaps they are being visited by the Moon and backgrounds are these beings created this wonderful sculpture, by their looks and physical appearance of the exterior. "
Nobody knows if Dr. sculptures and claims. Charles Morris are true.
NASA itself, through its official statement refuted the claim of Dr. Charles. But she had the same thing done on April 20 asked to comment cure claims former astronaut Edgar Mitchell on CNN, which claimed that the collision of a UFO in Roswell, New Mexico was a real event! Edgar, who was a member of the crew of "Apollo 11" in its mission to the Moon, also claimed that American authorities - as well as international ones, know very well that there is extraterrestrial life, but keep it secret from the public!

The tragic past of the stars of Hollywood!

The tragic past of the stars of Hollywood!Many people may think that Hollywood stars have had a smooth go smoothly, and that they are prodigies fate. But in fact is not true, because many of them come from an often tragic past, poor or problematic. Here some of the world-famous who have had a go that would not have envied man.Charlize Theron - American actress and model has had a tragic past. Her father repeatedly abused with alcohol.During a family row, Charlize father, icili was drunk, hit his mother and physically threatened both mother and daughter.While trying to defend himself and her daughter, Charlize's mother shot her husband with a gun, killing him in front of his daughter.Oprah Winfrey - star of television, Oprah Winfrey, has had a hard life when it was small. It was born from two poor parenting teens, from Mississippi. Oprah was separated from parents at a very young age, being moved to Wisconsin.Since I was 9 years old she had had sexual harassment from males. Because of the trauma, Oprah found support to alcohol, and drugs. She gave birth prematurely to a son when he was only 14-years old, who died a short time later.Things started to go better when Oprah began work in as a reporter on local television.Shania Twain - Canadian singer, Shania Twain, we can not say that there was an easy life. She grew up in poverty, so that often in her house there was no bread to eat. She lost her mother and stepfather when he was only 21-years as a result of a car accident and had to care for her three sisters smaller.Demi Moore - Demi Moore's mother was just a teenage alcoholic with bipolar problems when brought to life the famous actress. In the absence of a biological father, her stepfather brought no less a problem in the family, due to alcohol abuse and works not stable. Moore's parents were both addicted to alcohol and physically abusing each other. In the 1980s, her stepfather killed himself. Moore found peace when high school ended, while the first had the role in "General Hospital".

Revealed the mystery of Lady Diana!

an the September edition of "Vanity Fair" article on the Princess of Wales gives details of the history of love between her and Pakistani surgeon, Hasna Khan, with whom she had a two-year relationship, before her death in 1997 . Talked to prestigious American Yameenah Khan, former wife Hasna Khan and close friend of the princess. Their relationship began in 1995, after meeting at the hospital "Royal Brompton" when Diana was visiting a friend of her hospitalized for heart problems. "He was madly in love Hasna and wanted to marry him, even though it meant that he would have to be moved and lived in Pakistan," said Yameenah.She recalled that Diana met twice in Pakistan, when fundraising for a hospital to be built there, but also to discuss the secret marriage with Hasna. "He wanted to know how hard I would have to live in Pakistan and sought advice on how to adapt the Pakistani men and their cultural baggage," says Yameenah. In May of 1996-s, the Princess visited his family in Lahore. Wanted to spend time with family Hasnatit, in order to be recognized by and received approval of his mother on the link. "Marriage to a British girl is the worst nightmare for any mother conservative" explains Yameenah. "Hasna, which Diana described as" Mister Miracle "was a very reserved man who came from a conservative Pakistani family. He was very concerned about how will their relationship work. Hated the thought that would end below the target of cameras throughout his life, "she adds. According Princess servant, Paul Burrell, their relationship ended in June 1997 by the Diana's. At the end of the report, she began meeting with Dodi al Fayed, are probably an attempt to make jealous Hasna, which so far has never spoken publicly about their relationship, nor has collaborated with directors of films on the life of Princess . However, the "secret romance" Their focus is on the film "Diana" which opens in theaters in September. Diana and Al Fayed died in a car crash in Paris in attempt to escape paparazzi. In March 2008, Hasna said in connection with the death of Diana, their relationship began in the summer of 1995 and, although they had talked about getting married, he had said that he could not afford media attention. Also said he believed the car crash that killed Princess was a "tragic accident". The surgeon had told police in 2004 he doubted that she would be pregnant at the time of death because always using birth control pills.

Now can persuade through GPS-it!

The test, conducted last month off the Italian coast, is one of the most highly sophisticated GPS is realized and is the fruit of several years of work group from the University of Texas.American researchers have managed to modify the signalsGPS (Global Positioning System) by sending a hundredmeters from the yacht's itinerary being "cheated" crew thathe adhere to the right path. "We all imitate GPS-s group. Toconfuse the yacht GPS system, researchers must generatefalse signals that were different from those truths.Theoretically, the navigation system will accept signals, but the location was not that accurate. When met with realsignals on the receiver, they were stronger ours. "A commonGPS receivers based on signals from at least four satellites,but accuracy improves by increasing the number of satellites.In the ocean can be achieved signals from 10 satellitessimultaneously. Knowing the location of each satellite andthe exact time when the signal arrives, it is possible to determine the location of the receiver with an accuracy measured in meters. GPS works by measuring the signals received from satellites that are in orbit 20 000 km above the Earth. If asatellite signal will only be false, then the system can not exclude being consistent with the signals coming from other satellites. If half of them are not accurate, then the system starts "doubt".

The secret of a happy life feminine!

A woman can be happy, regardless of the circumstances and the fact that it is married, rich or poor, is with or without children, work or home. This means that happiness is an internal matter and that men and money, are 'as other'. But is it really that simple, People read what he writes. During a seminar for couples, a woman becomes the question: "Your husband makes you happy? Makes you really happy? ". At that time, her husband responds by raising his head, which meant confidence. He knew that his wife would say Yes, because she never complained during the marriage. However woman answered with resounding: No! "No, my husband did not feel happy!" At this point, the man was looking for the nearest exit look of the room. "My husband has not made me happy, makes me happy, I feel happy!" And continued:* The fact that I am not happy or not depend on him but on me! My happiness just puts me! I decided to be happy! In every moment, in every situation of my life, if my happiness will depend on someone else, then I had big trouble! "* I decided to be happy! If my house is empty or full, I'm happy!* If we come together, or stand alone when I'm happy!* If the job pay well or not, I'm happy!* I am married, but I was happy when I was alone! I'm happy for myself!* Other Things, people, situations, or I call moments: Experience can give me moments of joy or sorrow!* When someone close dies, I am a happy person, in a moment of inevitable sadness.* I've learned from experience that transitional and live are endless: To love, to forgive, to help, to accept, to understand ...* There are people who say: now I can not feel happy, because I am sorry, because I have no money, because it is very hot, because I was offended because someone does not love me anymore, because most fail to appreciate, because my husband is not one that I expected because my kids make me happy, because I work in a common profession, and so endless ...* I love life, not because my life is easier than the others. It's because I decided to be a happy person and I am responsible for my happiness! When I made the decision I made for the sole reason: To remove a burden from my shoulders husband and others ...* In this way my work happy marriage of many vitesh.Mos allow anyone to be responsible for your happiness!* Being happy is hot though, even if you are sick, even if someone has hurt you, even if you do not want and do not appreciate!* Just to have peace to accept the things we can not change, courage to change the things we can and the wisdom to distinguish between them!