What is Zener diode? Its principle working and example usage

We often use a Zener diode in a lot of the electronic circuits. For instance, power supplies, voltage detectors, etc.

It is so helpful device in electronics. But…Do you understand good enough?

Today we will learn Zener diode principle working and example applications usage.

Let me explain why we should learn them.

Zener diode principle working example usage

What is Zener diode

Zener diode is a two-pin device. One type of semiconductor type. That has different properties from a general diode.

Look at the image below, showing the Zener Diode (Right) symbol in an electronic circuit. And the shape of the real one looks like a normal diode (left).

Characteristics and symbols of zener diodes

There are many sizes from, according to the wattage. The large size also more watts of power. The picture is only half a watts (1W).

Credit Photo Zener by TeOhk

Basic how Zener diode works

When I was a beginner. I used a long time to understand how it works. You are better than me. I am so happy to see you learn the Zener diode faster.

See a lot of images may help you see.

Look at the block diagram below.

Comparison of bias between Diode and Zener Diode

Both Diode and Zener Diodes have different functions and basic bias.

  • Left: Rectifier Diode requires a forward bias to work.
  • Right: Zener Diode requires a reward bias to work.

What is more?

Internal virtual circuit

Look at the Internal virtual circuit below.

The Zener Diode operates by using breakdown voltage, or Some called Zener diode voltage. When it works during the Reverse bias.

During this breakdown, the voltage drops across the Zener Diode will be constant. From this principle, we can use the Zener diode to maintain a constant voltage.

Then, See the Graph of Zener Diode Properties

The Zener Diode has the same property graph as a general diode. But different at Breakdown voltage. In the diode, the breakdown voltage has a high voltage value.

Graph of Zener Diode Properties

For example, a 1N4001 Diode has a breakdown voltage at 50V, etc. But the Zener diode has this low voltage level, depending on the properties of the Zener Diode.

When considering the reverse bias, in the graph. In the lower range of the breakdown voltage level. It will have a small amount of voltage and current, flows through it.

And, due to the leakage current in the Zener diode. But this current has a very small amount. So, it does not affect the work of Zener Diode.

Are you get a basic idea?

Let’s see the example circuit diagrams that we use this idea. We use it as a voltage detector it is so easy but helpful.

What is the Zener Diode comparable to?

For the first time, I did not understand how it works. But when I saw the image below. I clearly understand. Are you the same as me?

Imagine a Zener diode that looks like the can is punctured. Look at the block diagram below.

Zener diode that looks like the can is punctured

The one who knew said, the picture explaining difficult things easier to understand than text. Is it true?

Let me explain to you.

  • Faucets compare with power supply.
  • Water is like electricity.
  • The water level in the can is comparable to Zener voltage. Which will be at the same level as the hole drilled on the side of the can

Here is a step by step process.

  • When we open the tap. The water will flow from the tap to the can. Which has punctured the side of the can
  • When the water level reaches the hole that is drilled, the water will flow out.
  • The water level is constant, not likely to be higher than the hole level. So it’s the same as Zener Diode operation.

While supplying the current through R1 to Zener diode via K, cathode and pin A, Anode is grounded.

Let’s say it is Zener Diode No. 1N5225 or BZX55C3V0 (3V) 0.5 watts. It has a Zener Diode voltage equal to 3 volts. (See Table 1).

  • BZX55C2V0 (2V)
  • BZX55C2V2 (2.2V)
  • BZX55C2V4 (2.4V)
  • BZX55C2V7 (2.7V)
  • BZX55C3V0 (3V)
  • BZX55C3V3 (3.3V)
  • BZX55C3V6 (3.6V)
  • BZX55C3V9 (3.9V)
  • BZX55C4V3 (4.3V)
  • BZX55C4V7 (4.7V)
  • BZX55C5V1 (5.1V)
  • BZX55C5V6 (5.6V)
  • BZX55C6V2 (6.2V)
  • BZX55C6V8 (6.8V)
  • BZX55C7V5 (7.5V)
  • BZX55C8V2 (8.2V)
  • BZX55C9V1 (9.1V)
  • BZX55C10 (10V)
  • BZX55C11 (11V)
  • BZX55C12 (12V)
  • BZX55C13 (13V)
  • BZX55C15 (15V)
  • BZX55C16 (16V)
  • BZX55C18 (18V)
  • BZX55C20 (20V)
  • BZX55C22 (22V)
  • BZX55C24 (24V)
  • BZX55C27 (27V)
  • BZX55C30 (30V)
  • BZX55C33 (33V)
  • BZX55C36 (36V)
  • BZX55C39 (39V)
  • BZX55C43 (43V)
  • BZX55C47 (47V)

Therefore, whether the power supply has a higher voltage than the Zener diode voltage.

Basic Zener diode forward bias and the reverse bias

The Zener diode always keeps the voltage drop across it at 3V. The remaining voltage will drop across the resistor.

Not only that, See the next circuit diagrams.

Basic Zener diode circuit in forward bias, reverse bias

See an example of the basic Zener diode between a forward bias (A) and the reverse bias (B).

  • Look at the circuit A.
    When we enter a forward bias voltage. (At the anode pin has more voltage than the cathode). The positive current enters the anode of Zener Diode (ZD1) via Resistor (R1).

    The operation of a Zener diode is like a general diode. It will allow the current to flow through it. And there is the voltage drop across about 0.6V. The rest of the voltage is across the resistor.

    When the voltage of the Zener diode is combined with the resistor, We get the voltage equal to the power supply.
  • Look at the circuit B.
    In contrast, when we enter a reverse bias (The cathode pin has more voltage than the anode pin) to a Zener diode.

    This time, the Zener Diode will have different features than normal diodes.

    The common diodes will not allow currents to flow through them.

    But in this, the Zener diode will allow the current to pass through it. Only when the voltage across the bias reverse is greater than the Zener diode voltage.

    In this, it works. Because the power supply is 6V. And the voltage of the Zener diode is 3V. And, the voltage across the Zener diode is constant. It is the breakdown voltage level as above.

We can change this voltage level(Vz). By changing the number of Zener diode, which the manufacturer has specified, there are many numbers and many sizes as mentioned above.

What is more? We will learn them with many example circuits below.

How to use Zener diode

Normally, Zener diode is used as the regulator circuit. There are many forms, as follows.

Simple current and constant voltage regulator

Look at the basic circuit below.
It is low current regulator circuit. Which is determined by the resistor R1. And the output voltage has a constant value equal to the zener diode voltage in any loads.

We can calculate the appropriate resistance of R1 using the formula:

R1 = (Vin – Vz)/(IL + Iz)

Most in practice. The current-Iz, while the load connected. We usually set it to 5mA. So we get a new formula.

R1 = (Vin -Vz)/(IL + 5mA)

So, Choosing the resistance to depend only on the current flowing through the load. But if wanting to calculate for use in real work.

We have to offset for IZ current. While there is no load as well.

Because while there is no continue loading The current will flow through all Zener Diodes. It should allow for the wattage of Zener Diode to endure while no-load as well.

Want to see real calculate to find R1?

Read Also: 5V Zener regulator low current


Choosing a Zener Diode. We need to look at the watts that the Zener diode can tolerate.

Which is calculated as follows:
  The wattage power lost in the Zener Diode (P) is equal to the Zener diode voltage (Vz) times the current passing through the Zener diode (Iz).

P = Vz x Iz

Note: Iz is obtained from the voltage across the resistor divided by the resistance of that resistor(R).

Do you get an idea?

Basic Higher current Zener and transistor regulator

Look at the circuit below. It is similar to the previous circuit. But it can supply a higher current. Because the transistor is a helper to increase current up.

Basic Higher current Zener and transistor regulator

We connect it in serial before output. Then use a Zener diode voltage as a bias voltage for the Transistor. The output voltage of this circuit is less than Zener diode about 0.6V.

Because the voltage of Zener Diode will drop across between base and emitter of transistor about 0.6 volts.

The maximum current that the circuit can supply depends on the capability of the transistor.

If the transistor highly withstands to current. It can supply a lot of currents. And, on the other hand, if there is little resistance. it will supply lower current.

Parts lists

  • Q1: 2N3053, 0.7A 40V NPN Transistor
  • ZD1: 12V 0.5W Zener Diode
  • C1: 10uF 16V Electrolytic Capacitor
  • R1: 1.2K 0.25W 5% Resistor
  • R2: 4.7K 0.25W 5% Resistor

Check out these related circuits, too:

Do you observe? The output is 11.4V only but we want 12V. How do you do?

Then, The solution to the problem is to make the output voltage equal to the Zener diode voltage.

Look at the circuit diagram. Add Diode to offset B-E transistor voltage.

Add Diode to offset B-E transistor voltage
Add Diode to offset B-E transistor voltage

By bringing the Rectifier Diode to a series with a Zener diode. Because of the voltage across the diode, it will just offset the voltage across the pin B-E of the transistor.

The output voltage is therefore equal to the Zener Diode voltage.

Make 3V DC regulator using Zener Diode and transistor

Is it easier? If we use suitable Zener.

Look at the true circuit.

3V DC regulator using Zener Diode transistor

We use the Zener Diode No. 1N5227 or BZX55C3V6. It has a Zener Diode voltage equal to 3.6V.

When the current flows through the base to emitter. There will be the voltage across the base and emitter about 0.6V.

Therefore need to reserve another 0.6V. The output voltage is approximate 3V

For other devices, it has the same principle of DC power supply.

When the transformer reduces the voltage to 9V, it will pass the rectifier diodes D1 and D2 (full-wave rectifier) to be DC voltage.

Then C1 will make the DC current smoother. It passes Resistor R1 to the cathode of Zener Diode.

Next, C2 is a filter capacitor to keep stable Zener voltage. And C3 also is a filter capacitor to reduce a ripple.

This circuit can give output 3V at 800mA max.

See parts list below

  • Q1: 2SC1061, 4A 40V NPN transistor
  • ZD1: 3.6V 0.5W Zener diode ,1N5227 or BZX55C3V6
  • D1,D2: 1N4001, 1A 50V Diode
  • R1: 5K 0.25W 5% Resistor
  • C1,C3: 1,000uF 16V Electrolytic Capacitors
  • C2: 1uF 16V Electrolytic Capacitor
  • T1: 117V/230V AC primary to 9V-0-9V,1A secondary transformer

What is more?

Voltage comparator Zener op-amp regulator

What is a better circuit?

In addition to this method, we also have a way to compare the output voltage with the Zener diode voltage. By using an op-amp as a comparator. As Figure below.

Voltage comparator Zener op-amp regulator circuit
Voltage comparator Zener op-amp regulator circuit

When the power goes into the input, there is a voltage across the 12V Zener diode. Therefore, pin 3 of the op-amp (CA3140) has the voltage is equal to 12V as well.

When the power goes into the input, there is a voltage across the 12V Zener diode. Therefore, pin 3 of op-amp has the voltage is equal to 12V, too.

It causes the output-pin 6 of an op-amp is a positive voltage. To bias Q1 works. So, there is the current flows through pins C-E and R3.

If pin 2 and pin 3 are higher then the voltage will come out pin 6. To bias Q1, has more current flows. Until the voltage pin 2 and 3 are equal.

We will see this circuit has high stability than only one transistor.

Parts you will need

  • IC1: CA3140, 4.5MHz, Bimos Operational Amplifier With MOSFET Input/Bipolar Output
  • Q1: 2N3053, 0.7A 40V NPN Transistor
  • ZD1: 12V 0.5W Zener diode
  • C1: 10uF 25V Electrolytic capacitor
    0.25W Resistors, tolerance: 5%
  • R1, R3: 1.2K
  • R2: 4.7K


We can see that the Zener Diode is used in various circuits.

Here are a few related posts you might want to read:

Related Posts


I always try to make Electronics Learning Easy.

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