How Zener Diode works as a Voltage Regulator?
Zener Diode as a Voltage Regulator. Zener diode is a silicon semiconductor with a p-n junction that is specifically designed to work in the reverse biased condition. When forward biased, it behaves like a normal signal diode, but when the reverse voltage is applied to it, the voltage remains constant for a wide range of currents. Oct 09, · A series resistance(R) is placed between a higher voltage(V in) and it is used to limit the current to the load and zener diode. The zener diode compensates for the variation in load current. The diodes used as voltage regulators are called zener diodes. A regular diode will not work effectively as a zener diode,and vice versa.
Zener Diode is a special purpose diode that is used in reverse biased. A Zener diode is manufactured for lower and exact reverse break down voltage. Zener voltage pass regulator is the most common use of Zener diode. An ordinary diode can reach the reverse bias voltage where the diode will be unable to stop the current flow. That voltage is the reverse breakdown voltage. The reverse voltagge voltage is a destructive and permanent damage phenomenon voltagd an ordinary diode.
It must have an adequate power dissipation how does zener diode work as a voltage regulator. Didoes can exhibit two types of roes, Zener breakdown, worm avalanche breakdown. Avalanche breakdown occurs at a comparatively higher negative voltage and uses to occur in Zener and rectifier diode. Where Zener breakdown can occur in Zener diode and at a low negative voltage.
Near Zener breakdown voltage, the electric field is too much intense to pull out the electrons from the valance band toward the conduction band. Zener diode operating below the 5 volts operates on Zener breakdown and above the 5 volts operates upon the avalanche breakdown. The Zener diode is represented by making small modifications to ordinary diode symbols to make it unique.
Both of the symbols are presented here with their direction of current and polarity indicated clearly. Note that the Zener diode is used in reverse bias where an ordinary diode is used in the forward bias for a typical operation.
Reegulator diode operates in reverse bias and its forward characteristics are similar to that of a rectifier diode. In reverse characteristics, the breakdown voltage of the Zener diode comparatively lower than that of an ordinary diode.
As the reverse bias voltage increases a very small amount of the reverse current flows in the reverse direction. The current at this point the breakdown starts, and the impedance at the point is called Zener impedance, and the current called Zener knee current. With a small further increase in reverse voltage, the voltage drop remains constant and the current changes drastically which means that impedance decreases.
The nominal voltage coltage the diode is provided in the datasheet when the current djode I ZT. Once breakdown occurs in the Bow diode voltage zendr, a small amount of increase in voltage makes a huge change in current and the voltage drop across the diode is constant.
A small amount of current I ZK should be maintained to keep the diode in the breakdown region. The current I ZK is the amount reverse current at the keen of the characteristic curve.
A reverse current above aA point I ZM should be avoided for the safe operation of the diode otherwise the diode may be damaged. An ideal Zener diode in reverse breakdown equivalent circuit contains a dc voltage source that has a constant voltage drop across it. For a practical Zener diode regularor reverse breakdown equivalent circuit contains a dc voltage source with a series impedance that voltage drop across the terminal changes with change in current.
What is the voltage across the terminal of the diode when the current is 50mA? The change in voltage due to an increase in the current above the test current causes the Zener terminal voltage to increase. So, hos change in voltage will add up to test voltage and the voltage at 50mA will be.
What is a Zener diode?
Dec 11, · A Zener diode operating in breakdown acts as a voltage regulator because it maintains a nearly constant voltage, which is equal to the Zener voltage, across its terminals over a specified range of reverse-current values. This constant voltage drop across the Zener diode produced by reverse breakdown is represented by a DC voltage symbol. Sep 12, · In practical circuits the simplest form of current source is a resistor. The key in using the zener diode as voltage regulator is that as long as the zener diode is reverse biased, the flow of current greater than a few micro amperes must be accompanied by a voltage . Oct 26, · Let us first comprehend how a Zener diode works before we understand Zener diode as a voltage regulator. When we apply a reverse voltage to a Zener diode, a negligible amount of current flows through the circuit. When a voltage higher than Zener breakdown voltage is applied, Zener breakdown occurs. Zener breakdown is a phenomenon where a significant amount of current flows .
Zener diodes are normal PN junction diodes operating in a reverse-biased condition. These are among the basic types of diodes used frequently, apart from the normal diodes. If you can recall, a simple PN junction diode is formed by a combination of p-type semiconductor material with an n-type semiconductor material.
When one side of a semiconductor crystal is doped with donor impurities and the other side with acceptor impurities, a PN junction is formed. In normal conditions, holes from the p side tend to diffuse to a low concentration region and the same thing happens for electrons from the n-side. Thus the holes diffuse to the n-side and the electrons diffuse to the p-side.
This results in the accumulation of charges around the junction, forming a depletion region. An electric polarity or electric dipole is formed across the junction, causing the flow of flux from n side top side.
This results in varying negative electric field intensity, generating an electric potential across the junction. This electric potential is actually the threshold voltage of the diode and is around 0. This acts as a potential barrier for the flow of majority charge carriers and the device does not conduct.
Now when a normal diode is biased such that a negative voltage is applied to the n side and positive voltage to the p side, the diode is said to be in forward biasing condition. This applied voltage tends to decrease the potential barrier after it goes beyond the threshold voltage. At this point and afterward, the majority carriers cross the potential barrier and the device starts conducting with the flow of current through it.
When the diode is biased in reverse condition to above, the applied voltage is such that it adds to the potential barrier and hinders the flow of majority carriers. However, it does allow the flow of minority carriers holes in n-type and electrons in p-type.
As this reverse bias voltage increases, the reverse current tends to increase gradually. At a certain point, this voltage is such that it causes the breakdown of the depletion region, causing a massive increase in the flow of current.
This is where the Zener diode working comes into play. 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. Normally there are two types of breakdown- Zener and Avalanche. This type of breakdown occurs for a reverse bias voltage between 2 to 8V. 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.
This results in the formation of mobile electron-hole pairs, increasing the flow of current across the device. This type of break down occurs normally for a highly doped diode with low breakdown voltage and a larger electric field. As temperature increases, the valence electrons gain more energy to disrupt from the covalent bond and less amount of external voltage is required. Thus Zener breakdown voltage decreases with temperature. This type of breakdown occurs at the reverse bias voltage above 8V and higher.
It occurs for a lightly doped diodes with a large breakdown voltage. As minority charge carriers electrons flow across the device, they tend to collide with the electrons in the covalent bond and cause the covalent bond to disrupt. As voltage increases, the kinetic energy velocity of the electrons also increases and the covalent bonds are more easily disrupted, causing an increase in electron-hole pairs.
The avalanche breakdown voltage increases with temperature. In a DC circuit, Zener diode can be used as a voltage regulator or to provide voltage reference. The main use of Zener diode lies in the fact that the voltage across a Zener diode remains constant for a larger change in current. This makes it possible to use a Zener diode as a constant voltage device or a voltage regulator.
In any power supply circuit , a regulator is used to provide a constant output load voltage irrespective of variation in input voltage or variation in load current. The variation in input voltage is called line regulation, whereas the variation in load current is called load regulation. A simple circuit involving Zener diode as a regulator requires a resistor of the low value connected in series with the input voltage source.
The low value is required so as to allow the maximum flow of current through the diode, connected in parallel. However, the only constraint being, the current through Zener diode should not be less than minimum Zener diode current.
Simply put, for a minimum input voltage and a maximum load current, the Zener diode current should always be I zmin. While designing a voltage regulator using a Zener diode, the latter is chosen with respect to its maximum power rating.
In other words, the maximum current through the device should be Since the input voltage and the required output voltage is known, it is easier to choose a Zener diode with a voltage approximately equal to the load voltage, i. Note that for load voltages up to 8V, a single Zener diode can be used.
However for load voltages beyond 8V, requiring Zener voltages of higher voltage value, it is advisable to use a forward-biased diode in series with the Zener diode. This is because the Zener diode at higher voltage follows the avalanche breakdown principle, having a positive temperature of the coefficient. Hence a negative temperature coefficient diode is used for compensation. Of course, these days, practical temperature compensated Zener diodes are used.
In power supplies and many other circuits, Zener diode finds its application as a constant voltage provider or a voltage reference. The only conditions are that the input voltage should be greater than Zener voltage and the series resistor should have a minimum value such that the maximum current flows through the device. In a circuit involving the AC input source, different from the normal PN diode clamping circuit , a Zener diode can also be used.
The diode can be used to limit the peak of the output voltage to Zener voltage at one side and to about 0V at another side of the sinusoidal waveform.
In the above circuit, during positive half cycle, once the input voltage is such that the zener diode is reverse biased, the output voltage is constant for a certain amount of time till the voltage starts decreasing.
Now during the negative half cycle, the Zener diode is in forwarding biased connection. As the negative voltage increases to the forwarding threshold voltage, the diode starts conducting and the negative side of the output voltage is limited to the threshold voltage. Note that to get an output voltage in positive range only, use two oppositely biased Zener diodes in series.
With the growing popularity of smartphones, android based projects are being preferred these days. These projects involve the use of Bluetooth technology-based devices. These Bluetooth devices require about 3V voltage for operation.
In such cases, a Zener diode is used to provide a 3V reference to the Bluetooth device. Another application involves the use of Zener diode as a voltage regulator. Here the AC voltage is rectified by the diode D1 and filtered by the capacitor. This filtered DC voltage is regulated by the diode to provide a constant reference voltage of 15V. This regulated DC voltage is used to drive the control circuit, used to control the switching of light, as in an automated lighting control system.
We hope we have been able to provide precise yet essential information about Zener diode working and its applications. Here is a simple question for the readers — Why are regulator ICs mostly preferred over Zener diode in regulated DC power supply?
Give your answers and of course your feedback in the comment section below. I shall be coming back to your blog for extra soon. What may you suggest about your submit that you just made some days ago? Any sure? Zener Diode Working Semiconductor diode in reverse bias condition If you can recall, a simple PN junction diode is formed by a combination of p-type semiconductor material with an n-type semiconductor material.
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