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Zener Diode Pdf Free Download

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Zener diodes are semiconductor devices that allow current to flow in both directions but specialize in current flowing in reverse. Also known as breakdown diodes, Zener diodes are the most common electronic components used as stable voltage references for electronic circuits.



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American physicist, Dr. Clarence Melvin Zener, first described the electronic properties of Zener diodes while researching the breakdown mechanisms of semiconductor materials. As a theoretical physicist at Bell Labs in New Jersey, he wrote a research paper later published in 1934, identifying a type of electrical breakdown later known as the Zener effect. These specific processes were named after him in the years afterward in his honor.




Current going across the terminals in reverse bias (backward) is called the Zener effect. When voltage potential is met, this causes the Zener voltage (Vz)/breakdown voltage. Zener diodes uniquely consist of a heavily doped P-N junction that allows current to flow in reverse when reaching Vz. A well-defined Vz can conduct current continuously in reverse bias without getting damaged. Current then increases to a maximum level determined by a series resistor and stabilizes, remaining constant over a range of applied voltages. Therefore, Zener diodes are applicable for use as voltage regulators.


A Zener diode operates within the normal range of forward bias, with a turn-on voltage between 0.3V and 0.7V. When connected in reverse bias, the current flows backward, thus causing a small leakage of current to flow. As the reverse voltage increases to the arranged Vz, current flows throughout the diode. Current increases to a maximum decided by the series resistor and then stabilizes to remain constant over a range of applied voltages.


Zener diodes have two breakdown effects. Knowing these two effects help with understanding their functionality. First is the Zener effect, prevalent in voltages below 5.5V and involves a tunneling effect to cause the breakdown. The second is the avalanche breakdown or impact ionization which occurs in voltages above 5.5V. These breakdowns both result in the same behavior, and they do not require different circuitry, but each does have a different temperature coefficient. The Zener effect has an anode (negative) terminal temperature coefficient, while the avalanche has a cathode (positive) terminal temperature coefficient. Both temperature effects are almost equal to 5.5V. They cancel each other out, making Zener diodes rated at around 5.5V and stable over a wide range of temperature requirements.




Think of a Zener diode like two diodes in parallel, facing opposite directions. The voltage that's forward bias in a Zener diode has a voltage drop of 1V needed for the diode to turn on for the current to flow. The forward voltage is forward biased. The current flowing backward is considered the Zener voltage or reversed biased due to its properties. An example of the Zener voltage is 3.3V. For the current to flow across the diode, the current must maintain at least a minimum of this voltage. Having a predictable voltage drop makes Zener diodes not only useful as voltage regulators, but a correctly set Zener diode may limit the voltage of other devices.


Application examples that utilize Zener diodes are smartphones which contain voltage, voltage reference devices like digital multimeters, and power strips which are surge suppressors. Electronic circuit boards contain Zener diodes and are used to shift voltage, be a waveform clipper, and switch signals in a variety of devices involving Bluetooth technology, televisions, transmitters that produce radio waves, and more.






Some notable manufacturers of Zener diodes include Nexperia, Vishay, ROHM, and Toshiba. These manufacturers produce Zener diodes for use in a variety of electronic components specializing in industries like consumer electronics, automotive, telecommunications, computing, industrial, and more. Zener diodes are small components that play a big role in the devices that serve industry professionals and everyday consumers and they will continue to do so for years to come.


A Zener diode is a special type of diode designed to reliably allow current to flow "backwards" (inverted polarity) when a certain set reverse voltage, known as the Zener voltage, is reached.


The device is named after American physicist Clarence Zener who first described the Zener effect in 1934 in his primarily theoretical studies of breakdown of electrical insulator properties. Later, his work led to the Bell Labs implementation of the effect in form of an electronic device, the Zener diode.[1]


A conventional solid-state diode allows significant current if it is reverse-biased above its reverse breakdown voltage. When the reverse bias breakdown voltage is exceeded, a conventional diode will conduct a high current due to avalanche breakdown. Unless this current is limited by external circuits, the diode may be permanently damaged due to overheating. A Zener diode exhibits almost the same properties, except the device is specially designed so as to have a reduced breakdown voltage, the so-called Zener voltage. By contrast with the conventional device, a reverse-biased Zener diode exhibits a controlled breakdown and allows the current to keep the voltage across the Zener diode close to the Zener breakdown voltage. For example, a diode with a Zener breakdown voltage of 3.2 V exhibits a voltage drop of very nearly 3.2 V across a wide range of reverse currents. The Zener diode is therefore well suited for applications such as the generation of a reference voltage (e.g. for an amplifier stage), or as a voltage stabilizer for low-current applications.[2]


Another mechanism that produces a similar effect is the avalanche effect as in the avalanche diode.[2] The two types of diode are in fact constructed in a similar way and both effects are present in diodes of this type. In silicon diodes up to about 5.6 volts, the Zener effect is the predominant effect and shows a marked negative temperature coefficient. Above 5.6 volts, the avalanche effect dominates and exhibits a positive temperature coefficient.[3]


It is also worth noting that the temperature coefficient of a 4.7 V Zener diode is close to that of the emitter-base junction of a silicon transistor at around -2 mV/C, so in a simple regulating circuit where the 4.7 V diode sets the voltage at the base of an NPN transistor (i.e. their coefficients are acting in parallel), the emitter will be at around 4 V and quite stable with temperature.


Modern designs have produced devices with voltages lower than 5.6 V with negligible temperature coefficients,[citation needed]. Higher voltage devices have a temperature coefficient that is approximately proportional to the amount by which the breakdown voltage exceeds 5 V. Thus a 75 V diode has 10 times the coefficient of a 12 V diode.[citation needed]


At the atomic scale, this tunneling corresponds to the transport of valence band electrons into the empty conduction band states; as a result of the reduced barrier between these bands and high electric fields that are induced due to the high levels of doping on both sides.[3] The breakdown voltage can be controlled quite accurately by the doping process. While tolerances within 0.07% are available, commonly available tolerances are 5% and 10%. Breakdown voltage for commonly available Zener diodes can vary from 1.2 V to 200 V.


The emitter-base junction of a bipolar NPN transistor behaves as a Zener diode, with breakdown voltage at about 6.8 V for common bipolar processes and about 10 V for lightly doped base regions in BiCMOS processes. Older processes with poor control of doping characteristics had the variation of Zener voltage up to 1 V, newer processes using ion implantation can achieve no more than 0.25 V. The NPN transistor structure can be employed as a surface Zener diode, with collector and emitter connected together as its cathode and base region as anode. In this approach the base doping profile usually narrows towards the surface, creating a region with intensified electric field where the avalanche breakdown occurs. Hot carriers produced by acceleration in the intense field can inject into the oxide layer above the junction and become trapped there. The accumulation of trapped charges can then cause 'Zener walkout', a corresponding change of the Zener voltage of the junction. The same effect can be achieved by radiation damage.


The emitter-base Zener diodes can handle only low currents as the energy is dissipated in the base depletion region which is very small. Higher amounts of dissipated energy (higher current for longer time, or a short very high current spike) causes thermal damage to the junction and/or its contacts. Partial damage of the junction can shift its Zener voltage. Total destruction of the Zener junction by overheating it and causing migration of metallization across the junction ("spiking") can be used intentionally as a 'Zener zap' antifuse.[6]


Zener diodes are widely used as voltage references and as shunt regulators to regulate the voltage across small circuits. When connected in parallel with a variable voltage source so that it is reverse biased, a Zener diode conducts when the voltage reaches the diode's reverse breakdown voltage. From that point on, the low impedance of the diode keeps the voltage across the diode at that value.[8]


In this circuit, a typical voltage reference or regulator, an input voltage, Uin (with + on the top), is regulated down to a stable output voltage Uout. The breakdown voltage of diode D is stable over a wide current range and holds Uout approximately constant even though the input voltage may fluctuate over a wide range. Because of the low impedance of the diode when operated like this, resistor R is used to limit current through the circuit.


A load may be placed across the diode in this reference circuit, and as long as the Zener stays in reverse breakdown, the diode provides a stable voltage source to the load. Zener diodes in this configuration are often used as stable references for more advanced voltage regulator circuits.

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