Zener Diode, Symbols and Basic Circuits

Zener Diode, Symbols and Basic Circuits

Zener Diode Definition

Understanding Zener Diode, Functions, Symbols and Circuits – Zener diodes are silicon diodes that can work well in the breakdown region.

The name Zener comes from the American scientist Clarence Melvin Zene who discovered the Zener effect.

In general, zener diodes have clear, glass-like physical characteristics with an orange-red interior. But there are also signal diodes (not zener) which are also physically similar to zener like 1N4148.

In addition to the clear physical form, there is also a physical shape similar to a 1n4007 rectifier diode, but the physical color is gray.

Every Zener company has a different physique.

To see more about the physical diode, please go to component sales providers such as DigiKey, Mouser, LCSC, Arrow, Future Electronics, Avnet, TTI Inc, and others.

Zener Diode, Symbols and Basic Circuits

Before going any further, let’s get back to the characteristics or properties of diodes, by which we can understand how Zener diodes work.

In rectifier diodes we know the terms Forwared Bias, Reverse Bias, Knee Voltage, and Breakdown Voltage.

Likewise for Zener Diodes, this term is also used.

What does it mean?

Forward Bias is a condition where the anode of the diode is connected to a positive voltage source and the cathode is connected to ground, so that current can flow through the diode.

Reverse Bias is a condition where the cathode of the diode is connected to a positive voltage source and the anode is connected to ground, so that current cannot flow through the diode.

Knee Voltage or Knee Voltage is a voltage where at this voltage the current flows very very quickly.

This Knee Voltage is the same as the potential barrier voltage, where the silicon diode has a barrier voltage of 0.7V while the germanium voltage is 0.3V.

In addition to knee tension, another term is also used, namely offset.

If you don’t understand what Knee Voltage means, I’ll give you a real example like this:

There is a pipe where the water in the pipe cannot flow, because in the middle of the pipe there is a closed water faucet.

To turn the water faucet, it takes energy, say the power is 0.7.

If the power used to rotate the water faucet is below 0.7, then the water faucet does not rotate, causing the water to not flow.

If the power used to turn the faucet is 0.7, then the faucet will rotate slightly and flow a little water current.

The higher the power to turn the faucet, the wider the faucet, the more water flows.

well, just like the diode, the initial power to push the silicon diode valve is 0.7V, so there will be current flowing.

The higher the knee, the more current can flow.

Breakdown voltage is the working voltage limit of a diode. which can damage a diode.

When does the diode breakdown voltage occur?

breakdown voltage occurs when the diode is reverse biased and the voltage applied to the diode is very large.

If the silicon diode is an ordinary rectifier, working in the breakdown region will cause the diode to be damaged.

But this is where the advantage of the zener diode, the zener diode will work very well at the breakdown voltage.

If the zener diode is forward-biased, the zener diode works like a rectifier diode.

However, if the zener diode is reverse biased, no current will flow, just like a rectifier diode.

Except when it reaches the breakdown voltage.

Zener Diode, Symbols and Basic Circuits

How Can Zener Diode Maintain Voltage?

For example, in fact like this, there is a zener diode circuit connected to a voltage source.

The source is 8V, while the breakdown voltage on the zener is 10V.

When the voltage source is connected to the zener in the reverse biased position, there is no change in the output voltage of the zener diode remains 8V.

When the voltage is increased to 12V, the zener diode will decrease the voltage from 12V to 10V.

How did it happen?

breakdown voltage or hereinafter we say the zener voltage is exactly how it works like knee voltage, it’s just that the knee voltage works on forward bias, while the zener voltage works on reverse bias.

For example in a silicon rectifier diode the knee voltage is 0.7V. With this voltage, this new diode can flow current.

A zener diode with a zener voltage specification of 10V, can only flow when a voltage is given above 10V in the reverse biased area.

This means that when 10V is over voltage on the zener, the zener will “discharge” to ground in proportion to the high voltage.

The higher the voltage, the more current is dissipated.

It is from this effect that the zener diode can maintain voltage.

Zener diodes have different zener voltages. Each zener voltage value is usually written on the physical zener diode.

Zener voltage varies. As of this writing, zener voltages are available from 1V to 240V.

The zener power (power dissipation) also varies, including 1.5mW to 1.5 kW.

For more details on the voltage and power of a zener diode, you can visit the website of an electronic component distributor such as Digikey. Mouser, AVnet, TTI Component, Future, LCSC and so on.

So, if we buy an ordinary diode at an electronics component store, we will usually be asked how many amperes the diode is?

but if we buy a zener diode, usually what is asked is what is the voltage? and how much power?

Zener Diode Function

Zener diodes are widely used in electronic circuits because of their ability to maintain voltage. Among the functions of the zener diode are:

  • Zener diode can function as a voltage stabilizer.
  • As a voltage reference.
  • shunt voltage regulator.
  • safety overvoltage.

Example for safety overvoltage, let’s make a voltmeter. The maximum limit for reading our homemade voltmeter is 12V.

If 50V is applied to the voltmeter, the inner circuit of the voltmeter can be damaged.

From that, we put a zener diode with a zener voltage of 12V at the input of the voltmeter.

If the voltmeter is connected to a 50V voltage source, the voltmeter will read a fixed voltage of 12V, so the voltmeter circuit remains safe.

With a variable input voltage, this zener diode can adjust itself and provide a fixed output voltage.

For example, a zener diode has a 5V specification, so regardless of the input voltage, the output voltage remains 5V with a little voltage tolerance.

How to use Zener Diode?

To be able to use a zener diode there are several things that we must understand, namely, the zener diode must be reverse biased (Figure 3).

For example, we have a zener diode with a zener voltage specification of 5V and a power capability of 10W. The source voltage (Vs) is 12V. The current for the load is 3A.

How to determine Shunt Resistance (Rs) to ensure Zener stability?


Look for aris zener of known specs.

Iz-max = Pz / Vz = 10W / 5V = 2A.

Iz-min = 0A

Then find the current through the shunt resistor, say the shunt current (Is).

Is-min = Load – (Iz-max) = 3A – 2A = 1A

Is-max = Load – (Iz-min) = 3A – 0A = 3A

When viewed from the circuit, the source voltage (Vs) is the sum of the shunt voltage (Vrs) plus the zener voltage (Vz)

Vs = Vrs + Vz = (Is . Rs) + Vz

Rs = (Vs – Vz ) / I s

Since Is there are two minimum and maximum, then later the value of Rs also has two, minimum and maximum Rs.

Rs-min = (Vs – Vz) / Is-min = (12V – 5V) / 1A = 7V / 1A = 7 Ohms

Rs-max = (Vs – Vz) / Is-max = (12V – 5V) / 3A = 7V / 3A = 2.33 Ohms

So the value of Rs to ensure the stability of the zener is between 2.33 Ohm to 7 Ohm

For simple circuits with small voltages, a zener diode can be useful. However, the zener diode is very influential with the current and temperature.

So its use is not very efficient. To be more efficient we can use a voltage regulator.

I hope this article is useful.

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