Zener diodes are normal pn junction diodes operating in a reversebiased condition. A zener diode is a diode which allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage. An ntype semiconductor has plenty of free electrons and a very few numbers of holes. A diodes working principle depends on the interaction of ntype and ptype semico nductors. Zener diodes are generally employed in multimeters to protect the meter movement against the damage from the accidental overloads. As we have gone through the first part of the article we know what is zener diode and what is the basic principle of operation. The basic purpose of a power supply is to provide one or more fixed voltages to the working circuit, with sufficient current handling capacity to maintain the operating conditions of the circuit. In normal diodes, the breakdown voltage is very high and the diode gets damaged totally if a voltage above the breakdown diode is applied, but in zener diodes, the breakdown voltage is not as high and does not lead to permanent damage of the zener diode if the voltage is applied. Zener diode as a voltage regulator zener diode is a silicon semiconductor with a pn junction that is specifically designed to work in the reverse biased condition. The following are the main application of the zener diode. The zener diode or voltage reference diode is an electronic component that provides a stable and defined voltage. When the voltage across the terminals is reversed and the potential reaches the zener voltage or knee, the junction will break down and current will flow in the reverse direction a desired characteristic.
If, however, the reverse bias is increased until it reaches the breakdown. Definition, symbol, and types of diodes electrical4u. By using an led and a zener diode we can create a circuit which gives turns on the led when a voltage exceeds a certain value. Write down all circuit equations and simplify as much as possible 2. Zener diodes when we first talked about practical diodes, it was mentioned that a parameter associated with the diode in the reverse bias region was the breakdown voltage, v br, also known as the peakinverse voltage piv. In reverse breakdown region high current flow through the diode leading to high power dissipation. Zener effect dominates at reverse voltages less than 5 volt whereas avalanche effect dominates above 5 v. A zener diode is a special type of device designed to operate in the zener breakdown region. At the same time, there will be a constant reverse saturation current due to minority carriers after certain reverse voltage across the junction, the. When the high reverse voltage is applied the width of depletion layer increases. A specific diodes vf depends on what semiconductor material its made out of.
The principle behind zener diode working as stated above the basic principle behind the working of a zener diode lies in the cause of breakdown for a diode in reverse biased condition. Because of its unusual properties it fills a longstanding need in electronic circuitry. Zener diodes acts like normal pn junction diodes under forward biased condition. Zener diode is a special kind of diode which permits the flow of current in the forward direction as well as in reverse direction when the voltage is above a certain voltage known as breakdown or zener voltage what makes them different from other diodes is that zener diodes will also allow current to flow in the reverse direction when the voltage is above a certain value. If the applied reverse voltage across the diode is more than zener voltage, the diode provides a conductive path to the current through it hence, there is no chance of further avalanche breakdown in it. It provides, among other useful functions, a constant voltage reference. When the applied voltage exceeds an specific amount zener breakdown takes place. Typically, a silicon diode will have a vf around 0. Zener diode based integrated filters, an alternative to traditional emi filter devices by lepkowski and johnson power switching, sudden load changes or a short circuit fault in the power distribution system. A zener diode typically suffers a breakdown at a marginally lower voltage than a conventional diode does. When the voltage across the diode is increased, temperature also increases and the crystal ions vibrate with greater amplitude and all these leads to the breakdown of the depletion layer. This voltage regulator is a pn junction diode that has a precisely tailored impurity distribution to provide a welldefined breakdown voltage. The zener diode is mostly used in the commercial and industrial applications.
This was a bad thing before the whole avalanche breakdown, large current. Even at this low voltage, the electric field intensity is strong enough to exert a force on the valence electrons of the atom such that they are separated from the nuclei. A zener diode is similar to conventional pn junction diode except that it is properly doped to achieve sharp breakdown voltage. The zener diode is a form of semiconductor diode that is widely used in electronics circuits as a voltage reference.
Normally there are two types of breakdown zener and avalanche. One is called zener breakdown, and the other, impact or avalanche ionisation. Zener diode definition, vi characteristics, and breakdown. This is an example of a primary application of zener diodes voltage regulation. Zener diode voltage regulators 2 the forward bias region of a zener diode is identical to that of a regular diode. Theoretically, zener breakdown occurs at a lower voltage level then avalanche breakdown in a diode. By using an led and a zener diode we can create a circuit which gives turns on. Maximum current at the rated zener voltage vz200 ua to 200 a.
Zener diode is a junction formed by combining highly doped pn semiconductors. Diode applicationszener diode zener diode zener diode operates in reverse bias rb at the zener voltage v z. There are two effects that can be used in zener diodes. In our previous articles, we explain in detail about diodes, pn junction diode, semiconductors etc. The zener still conducts electricity in the forward direction like any other diode, but also conducts in the reverse direction, if the voltage applied is reversed and larger than the zener breakdown voltage. The diode functions just like any pn diode while forward biased, but its sharp breakdown or its stark indifference, the fact that its voltage remains absolutely constant. Minimum current required for the diode to break down5 ma and 10 ma. In other words, we can say that the concentration of free electrons is high and that of holes is very low in an ntype semiconductor.
It is constructed of a p and an n junction connected together. The drift characteristics are given in many zener diode data sheets. Zener diode operation the zener diode operates just like the normal diode when in the forwardbias mode, and has a turnon voltage of between 0. The reverse breakdown of a pn junction may occur either due to zener effect or avalanche effect. Clarence melvin zener inventor of zener diode only when the need for semi conductor materials exceeded, the urge to develop a device like zener diode spread deeper and wider. The diode the diode is a two terminal semiconductor device that allows current to flow in only one direction. Basics currentvoltage characteristic of a zener diode with a breakdown voltage of. Applications of zener diodes voltage regulator, meter.
The type of diode also has some importance in defining the forward voltage drop. The two effects are totally different, although they produce. Zener diode is a special kind of diode which permits the flow of current in the forward direction as well as in reverse direction when the voltage is above a certain voltage known as breakdown or zener voltage. Use the diode equation for that state to solve the circuit equations and find i d and v d 3. Zener diode theory introduction the zener diode is a semiconductor device unique in its mode of operation and completely unreplaceable by any other electronic device. A heavily doped semiconductor diode which is designed to operate in reverse direction is known as the zener diode. Recipe for solving diode circuits state of diode is unknown before solving the circuit 1. Diode operation no current flows because the holes and electrons are moving in the wrong direction. Zener diode working with circuit diagram and applications. When a zener diode of zener voltage vz is connected in reverse direction parallel to the load, it maintains a constant voltage across the load equal to vz and hence stabilizes the output voltage. Zener diode also known as breakdown diode is made up of silicon pn junction.
When forward biased voltage is applied to the zener diode it allows large amount of electric current and blocks only a. In this article, we are going to explain zener diode and its applications in detail. The limiting voltage depends upon the particular zener diode used. Zener diode as a voltage regulator working principles.
As a result zener diode circuits are often used in power supplies when regulated outputs are needed. When the voltage across the terminals is reversed and the potential reaches the zener voltage or knee, the junction will break down and current will flow in the. Here the question arises where this type of diodes can be useful. The zener diode must have an adequate power rating to avoid the burn out. In the reverse bias condition the zener diode is an open circuit and there is only a small leakage current in the microampere range. As voltage stabilizer the zener diode is used for regulating the voltage. Zener diode is on when it operates on the zener region, i.
It is the disadvantage of this linear power supply. Zener diodes are special silicon diodes which have a relatively low, defined breakdown voltage, called the zener voltage. This type of breakdown occurs for a reverse bias voltage between 2 to 8v. In other words, the diode which is specially designed for optimising the breakdown region is known as the zener diode. Working of the zener diode is similar to a pn junction diode in forwarding biased condition, but the uniqueness lies in the fact that it can also conduct when it is connected in reverse bias above its thresholdbreakdown voltage. A zener diode is a type of diode that allows current to flow in the conventional manner from its anode to its cathode i. As the breakdown voltage is approached the current will begin to avalanche. The zener diode is a semiconductor device unique in its. When forward biased voltage is applied to the zener diode it allows large amount of electric current and blocks only a small amount of electric current. Example zener diode circuit analysis blank ku ittc.
Correspondingly, is there a way we could determine the type of breakdown action from experimental measurements on a zener diode. Zener breakdown occurs due to high reverse voltage. Jul 17, 2017 unlike normal diodes, which allow only forward current, zener diodes will allow a current to move in reverse when voltage exceeds a specified value, preventing breakdown of the diode. For a silicon diode this voltage is approximately 0. If this reverse biased voltage across the diode is increased continually, the depletion layer becomes more and more wider. Electronic devices are usually small and can be grouped together into packages called integrated circuits. What is a zener diode voltage reference electronics notes. Electronic devices are components for controlling the flow of electrical currents for the purpose of information processing and system control. Zener diode is popularly used as shunt regulator or voltage regulator. Basic electronics notes on vi characteristics of zener. Hbd854 zener theory and design considerations handbook.
These diodes are heavily doped in order to have narrow depletion region. Zener diode article about zener diode by the free dictionary. It can be designed to have a breakdown voltage over a wide range from 0. When forward biased, a small voltage is required to get the diode current flowing. Practical zener diodes may use either the zener effect or the avalanche effect and in some diodes both effects can also occur at the same time, but it is common practice to call all these diodes zener diodes.
Zener diode definition a zener diode is a type of diode that permits current to flow in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger than the breakdown voltage known as zener knee voltage or zener voltage. L is equal to the zener breakdown voltage v zkregardless of the value of load resistor r l or source voltage v s provided, of course, that the zener diode is in breakdown. Diode circuits and applications technology innovation and. The relationship is obtained by applying kvl and it is vs vg r im. It acts as a diode, which can serve in electronics as a rectifier, logic gate, voltage regulator zener diode. It provides the constant voltage from the fluctuating voltage source to the load. For example, a dc motor can produce a surge voltage because it continues to. Zener diode characteristics, working and applications. When reverse voltage vr applied to the zener diode exceeds the break down voltage vb, the process called avalanche breakdown occurs in the depletion layer and starts flow through the device and limits the reverse voltage. Because of this ability to reverse a portion of the current, zener diodes offer several advantages in a circuit that normal diodes dont. Many early inventions were made till 1905, yet a more focused work on semiconductor devices were started only at the time of the second world war.
At low reverse voltages a zener diode behaves in a similar manner to an ordinary silicon diode, that is, it passes only a very small leakage current. Unlike normal diodes, which allow only forward current, zener diodes will allow a current to move in reverse when voltage exceeds a specified value, preventing breakdown of the diode. Both the zener and avalanche effects are also dependant to some degree on the junction temperature of the diode. The zener diode working principles and its various applications.
A specific diode s vf depends on what semiconductor material its made out of. Working principle of zener diode a zener diode is similar to conventional pn junction diode except that it is properly doped to achieve sharp breakdown voltage. When we forward biased the zener diode, it behaves just like a normal signal diode due to 0. Basic diode electronics introduction to diodes the pn junction the pn junction is a homojunction between a ptype and an ntype semiconductor. We call this particular regulator circuit the shunt regulator. There are two types of mechanism by which breakdown can occur at reverse pn junction that are avalanche and zener breakdown. Power is calculated by multiplying current by voltage pie, so we can calculate power dissipations for both the resistor and the zener diode quite easily. When a pn junction diode is reverse biased, the depletion layer becomes wider. The zener diode working principles and its various. Zener diode operation and applications ece tutorials. A zener diode is a special kind of diode which allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, zener knee voltage or zener voltage. However, when connected in the reverse mode, which is usual in most of its applications, a small leakage current may flow. Zener diode is a reversebiased heavilydoped pn junction diode which operates in the breakdown region. The schematic symbol for a zener diode is shown above it is very similar to that of a regular diode, but with bent edges on the bar.
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