Why is zener diode as voltage regulator

The typical forward voltage at room temperature with a current of around 1 mA is around 0. In the reverse bias condition the Zener diode is an open circuit and only a small leakage current is flowing as shown on the exaggerated plot.

As the breakdown voltage is approached the current will begin to avalanche. The initial transition from leakage to breakdown is soft but then the current rapidly increases as shown on the plot. The voltage across the Zener diode in the breakdown region is very nearly constant with only a small increase in voltage with increasing current. At some high current level the power dissipation of the diode becomes excessive and the part is destroyed. There is a minimum Zener current, I z min , that places the operating point in the desired breakdown.

There is a maximum Zener current, I z max , at which the power dissipation drives the junction temperature to the maximum allowed. Beyond that current the diode can be damaged. Zener diodes are available from about 2. All Zener diodes have a power rating, Pz. Zener diodes are typically available with power ratings of 0. The function of a regulator is to provide a constant output voltage to a load connected in parallel with it in spite of the ripples in the supply voltage or the variation in the load current and the zener diode will continue to regulate the voltage until the diodes current falls below the minimum I Z min value in the reverse breakdown region.

It permits current to flow in the forward direction as normal, but will also allow it to flow in the reverse direction when the voltage is above a certain value - the breakdown voltage known as the Zener voltage. The Zener diode specially made to have a reverse voltage breakdown at a specific voltage.

Its characteristics are otherwise very similar to common diodes. In breakdown the voltage across the Zener diode is close to constant over a wide range of currents thus making it useful as a shunt voltage regulator. The purpose of a voltage regulator is to maintain a constant voltage across a load regardless of variations in the applied input voltage and variations in the load current.

A typical Zener diode shunt regulator is shown in Figure 3. The resistor is selected so that when the input voltage is at V IN min and the load current is at I L max that the current through the Zener diode is at least I z min. Then for all other combinations of input voltage and load current the Zener diode conducts the excess current thus maintaining a constant voltage across the load. The Zener conducts the least current when the load current is the highest and it conducts the most current when the load current is the lowest.

If there is no load resistance, shunt regulators can be used to dissipate total power through the series resistance and the Zener diode. Shunt regulators have an inherent current limiting advantage under load fault conditions because the series resistor limits excess current.

A Zener diode can work as a voltage regulator by functioning as an auxiliary load, pulling more current from the source when the voltage is too high and less current when the voltage is too low. Clarence Melvin Zener was the one who initially described the benefits of this diode.

His research interests were in solid-state physics. He graduated from Stanford University in and obtained his doctorate from the same institution in In , he invented the Zener Diode, which is now used in modern computer circuits.

In , Clarence Zener released a paper on the breakdown of an electrical insulator. You may be experiencing unknown or mysterious failures in your projects when utilizing voltage-sensitive motors or other components in a circuit.

Voltage-sensitive components can sometimes burn because simply they cannot handle the amount of voltage in the current. Circuit 1 has a 12 Volt power supply with a reverse-biased Zener Diode. If we increase the voltage of the power supply to 90 Volts as shown in the circuit 2 diagrams, then the Zener Diode will still allow the current to flow past it. However, the current that goes to the Voltmeter is still about 10 volts. Hence, the Zener diode can be used to create a voltage regulator using this logic in a circuit.

Nominal voltage, power dissipation, forward drive current, forward voltage, packaging type, and maximum reverse current are attributes that are used to classify different Zener diodes.

It is one of the important parameters for Zener Diode selection. The greatest amount of power that the Zener current can discharge is represented by this value. Exceeding this power rating causes the Zener diode to overheat, potentially damaging it and causing the failure of the components connected to it in a circuit. As a result, while choosing a diode for a specific application, this element should be considered.

At the Zener voltage, this is the maximum current that may be passed through the Zener diode without destroying it. This is the minimum current required for the Zener diode to enter the breakdown area and begin working.

Other parameters that act as diode specifications must all be carefully studied before deciding on the type of Zener diode required for any particular design.

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