Zener Diode Voltage Regulator | Explanation and How to Build

A Zener diode voltage regulator is an electrical circuit that maintains a constant DC output voltage using a Zener diode. A perfect regulator would produce a constant voltage regardless of input fluctuations or load current variations.

Zener diode is a popular one in types of diode.

What is Zener Diode

A Zener diode is a type of diode that is specifically engineered to perform under reverse biased situations. They feature a narrower depletion region than typical diodes because they are more highly doped.

zener diode voltage regulator 1

When the voltage across a conventional diode exceeds the reverse breakdown voltage, the diode is broken, but Zener diodes only work in this range. When the reverse voltage is withdrawn from a Zener diode, the depletion zone returns to its original state.

Zener diodes are helpful as voltage regulators because of this feature. Let’s see how this plays out.

Before we can grasp how a Zener diode voltage regulator works, we must first understand how it works.

zener diode voltage regulator 2

When a reverse voltage is applied to a Zener diode, very little current flows through the circuit. Zener breakdown occurs when a voltage greater than the Zener breakdown voltage is applied.

What is Zener Breakdown

The Zener Breakdown principle governs the operation of Zener diodes. A high voltage can allow electrons to tunnel through the depletion zone, to the other side of the junction, when a P-N junction is narrowed.

Because the electron exhibits wave-particle duality, tunneling is a quantum mechanical event. Electrons are treated as wave functions rather than basic ‘particles’ in quantum mechanics.

They are dispersed throughout space, with a chance of meeting at a specific location. Because of this probabilistic character, if a barrier (such as the depletion region) is made tiny enough, the electron has a chance of tunneling through it to the opposite side.

Zener breakdown occurs when a large quantity of current passes through a diode while the voltage drops only little. When the reverse voltage is increased further, the voltage across the diode remains constant at the Zener breakdown voltage, but the current through it continues to rise, as shown in the graph above.

The Zener breakdown voltage is denoted by Vz in the graph. Depending on the application, the breakdown voltage of a zener might range from 1.2 V to 200 V.

The exciting part about this diode is that we can use it as a voltage regulator in our circuit by selecting a Zener diode with a sufficient breakdown voltage.

For example, let’s imagine we want the voltage across a load in our circuit to be less than 12 volts. Then we can connect a Zener diode across the load with a breakdown voltage of 12 volts.

The voltage across the load will never exceed 12 volts, even if the input voltage surpasses that figure.

Let’s look at a circuit diagram to see what we’re talking about.

zener diode voltage regulator 3

The Zener diode is connected across the load RL in this example. The voltage across the load should be regulated and should not exceed Vz.

We select a Zener diode with a Zener breakdown voltage close to the voltage we require across the load based on our needs. The Zener diode is connected in reverse bias mode.

A considerable quantity of current flows through the diode when the voltage across it surpasses the Zener breakdown voltage. The voltage drop across the load is equal to the Zener breakdown voltage since the load is in parallel with the diode.

The Zener diode offers a route for current to travel, protecting the load from excessive currents. As a result, the Zener diode serves two functions: it acts as a voltage regulator and it protects the load from excessive current.

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What is Zener Diode Voltage Regulator

A Zener diode is used in the Zener diode regulator to generate a constant voltage output. It’s simple and inexpensive, which makes it perfect for a variety of applications and for teaching people about voltage regulators.

Zener diodes are a form of semiconductor diode that is unique. They are made up of a doped P-N junction, just as conventional diodes.

While forward biased, all diodes allow current to pass. Zener diodes, unlike other diodes, are intended to allow current to flow even when they are negatively biased.

When reverse biased, Zener diodes have a Zener voltage VZ, which makes them excellent for use as a voltage reference or regulator. Even if the current fluctuates, the Zener voltage VZ remains generally constant.

The current-voltage curve of the Zener diode demonstrates this.

zener diode voltage regulator 4

The actual value of VZ is determined by the semiconductor materials used and the diode’s structure. There are hundreds of Zener diodes available with various VZ values.

This means you can choose the Zener diode based on the needed voltage output when creating a Zener regulator.

How to Build a Zener Diode Voltage Regulator

A Zener diode is a voltage regulator that is particularly useful. It can operate as a voltage regulator by connecting it in the appropriate way in a circuit, regulating the amount of voltage it delivers to a device.

To use a zener diode in a circuit to provide voltage control, it should be reverse biased and linked in parallel to the power source that provides the zener diode’s voltage, with the power source connected to a resistor. A 1KΩ resistor will be used in this project.

How a Zener Diode Voltage Regulator Circuit Works

The circuit below is ideal for creating a zener diode voltage regulator. The 12V power supply is cut off when it passes through the 1KΩ resistor and the zener diode. The zener diode in question has a breakdown voltage of 5.1 volts.

zener diode voltage regulator 5

This results in a 5.1V voltage drop across the zener diode, with the remaining 6.9V falling across the 1KΩ resistor. A steady, consistent voltage of 5.1V will be maintained across the zener diode.

The load that the zener diode powers is then connected in parallel with it. This is due to the fact that voltage in parallel is equal. So, if a zener diode is connected in parallel, the voltage it emits to a device will be 5.1V.

This is how a zener diode works in terms of voltage regulation.

Experiment with alternate settings if you don’t have the exact values above, such as DC voltage or the exact zener diode.

All you need is a voltage that is higher than the zener diode’s breakdown voltage, as well as a resistor to dissipate excess voltage from the zener diode, which is what the 1KΩ resistor is for.

Zener Diode Voltage Regulator Circuit Diagram and Formula

A zener diode voltage regulator is made by connecting a Zener diode to a resistor in series, with the Zener diode in reverse-biased mode. The Zener diode replaces the second resistor, making this equivalent to a voltage divider.

The voltage output is taken across the Zener diode, Vout = VZ:

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Normally, this output is linked across the load, as shown by load resistor RL:

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The Zener diode’s VZ will not change greatly with a change in current, unlike the resistor in a voltage divider, hence Vout should remain constant.

Zener regulators rely on the Zener voltage of the diode, which is based on the quantum mechanical tunneling principle. The voltage across the diode can be thought of as being equivalent to the Zener voltage VZ in general.

The load will encounter a total voltage of VZ since the load voltage is applied across the Zener diode.

The remaining voltage must be decreased across R1 through the resistor. To put it another way,

We can rewrite this using Ohm’s Law as:

The total current through the circuit is equal to the current through the Zener diode plus the current through the load, and it is calculated as follows:

Although all of the current must pass through R1, the Zener diode and load will only see a portion of it.

We can see that load resistance can play a considerable influence in the dynamics of the circuit because the load current is also dependent on the load resistance.

How to Build Zener Diode Voltage Regulator Circuit

Let’s use the same circuit above to fully understand how to build a zener diode voltage regulator circuit.

zener diode voltage regulator 8

When designing and building a zener diode voltage regulator circuit, there are several steps to follow:

Calculate power rating

The maximum power rating of a Zener diode specifies the greatest amount of electric power it can safely dissipate.

Because a Zener diode’s Zener voltage VZ is largely constant, the power rating essentially determines the maximum current that the diode can handle:

Select a zener diode

The Zener diode is the first design option to consider. Zener voltages are available in a wide range of diodes. The method begins with selecting a diode with a Zener voltage (VZ) that corresponds to the output voltage that the regulator will give.

Power and current should also be considered; different Zener diodes with the same VZ can be built for different applications. The data sheet for a diode will usually inform you of the diode’s intended applications as well as technical information.

In order to choose a resistor, you’ll need to know two specifications:

(1) The breakdown current of a diode, often known as the knee current or minimum current (Imin).

(2) The power rating of the diode, which is the maximum power at which it may be operated safely. The maximum current can be calculated using the power rating and the Zener voltage VZ:

Select a Resistor

The two parameters discovered can be utilized to calculate the resistor value required to finish the circuit.

Calculate the Minimum Resistance

Using the highest current and entering it into Ohm’s Law, you can find the minimal value of resistance (Rmin):

Calculate the maximum resistance

Using the minimal current and entering it into Ohm’s Law, you can find the maximum resistance value (Rmax):

Calculate the Ideal Resistance Value with a Load

We can utilize the load resistance to get the optimum resistor now that we know the minimum and maximum resistor values required to properly use the chosen Zener diode.

Kirchhoff’s Current Law (KCL) says that the current exiting any junction must match the current entering the junction. The current flowing through the resistor (I.R) must be equal to the current flowing through the Zener diode plus the current flowing through the load in this case:

Using both the minimum and maximum values for resistor R1 (remember that the voltage across the load is equal to VZ), we calculate the maximum and minimum load currents:

Maximum load current:

Minimum load current:

Zener Diode Voltage Regulator as Power Supply Component

Following the rectifier filter and bleed resistor, zener regulators are often employed in power supply.

A sinusoidal AC signal is converted to a pulsed DC signal by the rectifier.

The rectifier filter smooths the pulsed DC signal, resulting in a ripple-free triangular/sawtooth waveform.

If the circuit is unplugged from the power source, a bleed resistor dissipates any stored charge in the filter capacitors.

Finally, the Zener regulator produces a constant voltage while absorbing voltage and current fluctuations.

Frequently Asked Questions

In order to keep the diode in the breakdown area, what factor is required for voltage regulation?

To keep the diode in the breakdown area, a minimum reverse current is necessary for voltage regulation.

How do you set the breakdown region during diode manufacturing?

The breakdown region can be set during diode production by changing the doping level.

What is a Zener breakdown?

Zener breakdown occurs when a Rectifier and a Zener diode fail at the same time.

When the input varies within the limitations, what happens to the DC output voltage?

When the input varies within the limits of the voltage regulator, the DC output voltage remains constant.

3 thoughts on “Zener Diode Voltage Regulator | Explanation and How to Build”

  1. please advice what to do avoid the heating of series resistor to limit current flow to zener diode. i conformed to the design considerations explained in your tutorials above but still it is a shock to note the heating of a series resistor!

  2. In a situation where the input voltage varies. Say having a 12v input and using with a 1k resistor and a 6v zener diode. Now if the input voltage gets to 9v, will the zener diode still conduct? Let’s say as voltage cutoff


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