Zener Diode – Definition, Circuit Symbol, and Applications

 The Zener diode also permits current to flow the other way once it reaches the Zener voltage. They are the most widely used semiconductor diodes because of their features. 

Zener Diode Definition

A strongly doped semiconductor device created to work oppositely is a Zener diode, sometimes referred to as a breakdown diode. A Zener diode’s junction collapses, and current flows in the opposite direction when the voltage between its terminals is reversed and the potential approaches the Zener voltage (also known as the knee voltage). The Zener Effect is the name of this phenomenon.

Zener Diode Circuit

The Zener voltages used to create Zener diodes might be between a few and hundreds of volts. Similar to conventional carbon-composition resistor values, this Zener voltage varies somewhat with temperature and may deviate between 5% and 10% from the manufacturer’s requirements. It is utilized as a voltage regulator in the standard power supply circuit shown in the diagram below because of its general good stability and precision.

The Zener voltage is 12.6 volts in the regulator circuit.

Operation of a Zener Diode Please note that it is in the circuit above is intentionally biased in the reverse direction. The diode would only drop 0.7 volts if it had been placed in the “standard” orientation or forward-biased, much like a typical rectifying diode.

We must use this diode in reverse-bias mode if we wish to use its reverse breakdown capabilities. The voltage dropping across it will stay at around 12.6 volts as long as the power supply voltage is higher than the Zener voltage (12.6 volts in this case).

It is temperature sensitive, like any semiconductor device. High temperatures will destroy one of them, and because it carries current and reduces voltage, it also generates heat, according to Joule’s Law (P=IE). Because of this, it is essential to build the regulator circuit so that the maximum power dissipation of the diode is not reached.

It’s interesting to note that when Zener diodes malfunction due to high power loss, they often short out rather than open. When biassed either way, like a length of wire, a failing diode drops practically its nominal voltage, making it easy to identify.

Analyzing the Zener Diode Regulating Circuit Mathematically

Let’s do a mathematical analysis of this circuit regulating circuit to ascertain all voltages, currents, and power dissipations. To avoid qualifying all numbers in Figure (a) below as “approximate,” we’ll run calculations using the same kind of circuit shown before and a series resistor with a value of 1000, a Zener voltage of 12.6 volts, and a power supply voltage of 45 volts.

If the power supply voltage is 45 volts and the voltage across the Zener diode is 12.6 volts, then 32.4 volts will be lost across the resistor (45 volts – 12.6 volts = 32.4 volts). 32.4 volts applied across 1000 results in 32.4 mA of circuit current. (Figure b) below)

(a) A 1000 resistor and a Zener voltage regulator. (b) Calculating current and voltage decreases.

 As current times voltage equals power (P=IE), it is simple to determine the power dissipation, of both the resistor and the Zener diode:

Presistor = (32.4mA)(32.4V) Presistor = 1.0498W

P_diode = (324A) (12.6V) P_diode = 4.0824mW

A resistor with a 1.5 or 2-watt dissipation rating and a Zener diode with a power rating of 0.5 would be suitable.

Circuit for a Zener Diode with Greater Resistance

Why not plan the Zener diode circuit to dissipate the least amount of power feasible if excessive power dissipation is harmful? Why not simply size the resistor for a very high resistance value, severely restricting current and maintaining deficient power dissipation figures?

 Consider this circuit, except replace the 1 k resistor with a 100 k resistor. The diode’s Zener voltage and the power supply voltage in the following figure are similar to those in the preceding example.

100 k resistor-equipped Zener regulator.

Presistor = (3244A)(32.4V) Presistor = 10.498mW

P_diode = (324A) (12.6V) P_diode = 4.0824mW

Both power dissipation values should be 100 times less when the current is just 1/100 of what it was before (324 A as opposed to 32.4 mA):

 V-I Features of a Zener Diode

When a reverse-biased voltage is used to the Zener diode, only a very small amount of leakage current may flow until the voltage falls below the Zener voltage.

A Zener diode’s V-I properties may be classified into two categories as follows:

•  Forward Features
• Reverse Features

Zener Diode Forward Characteristics

The forward properties of this are shown in the graph’s top quadrant. We may infer from the chart that its bold properties are identical to those of any other P-N junction diode.

Zener Diode Characteristics(Reverse)

A modest reverse saturation current called Io runs across the diode when a reverse voltage is applied to a Zener voltage. Minority carriers produced thermally are the cause of this current. Depending on the amount of reverse voltage, the reverse current increases dramatically and abruptly as the reverse voltage rises. This is a sign that the breakdown has taken place. This voltage breakdown voltage, also known as the Zener voltage, is denoted by the symbol Vz.

Specifications for a Zener Diode

The following are examples of this application and Its Uses: 

• Zener/Breakdown Voltage – The reverse breakdown voltage has a range of 2.4 V to 200 V and, on rare occasions, 1 kV, with a maximum of 47 V for surface-mounted devices.
• Current Iz (max): This current ranges from 200 A to 200 A at the rated Zener voltage.
• Current Iz (min) is the minimum current needed for a diode to fail.
• Its power rating indicates the highest amount of power it can dissipate. It is determined by dividing the diode’s voltage by its current.
• Diodes at 5 V have the highest temperature stability.
• Zener Resistance (Rz) is the resistance that it shows. The voltage tolerance is generally 5%.

Application of Zener Diode

The following are examples of this application and Its Uses:

• Voltage regulation
• safeguards against overvoltage
• used in circuits that clip
• used to change the voltage

It is appropriate for voltage control because the voltage drop across the diode is constant throughout a wide range of voltages.

The Zener Diode Regulates the Voltage

The series-connected resistors control the current through the diode when there is an excess of voltage when the diode is conducting when the load voltage matches the breakdown voltage. The diode produces some noise in the process, which may be reduced by connecting a decoupling capacitor with a high voltage across the diode.

A Zener Diode Protects Overvoltage

The current flowing through the diode will cause a voltage drop across the resistor when the input voltage rises to the Zener breakdown point. A short circuit to the earth is started as a result.

Utilizing Zener Diodes in Clipping Circuits 

Clipper circuits stop the output signal from exceeding a specific value without affecting the input signal. It can alter and shape trajectories that clip the AC waveform. The clipping circuits restrict a portion of the AC waveform to protect or shape the waveform. These circuits are typically found in TV and FM transmitters to reduce interference.

The Voltage can be Shifted using a Zener Diode

It is to change a signal’s voltage. In the breakdown zone, it can maintain a constant output voltage. Because of its ability to change the voltage, a Zener diode is a perfect element for the operation. Here are several applications for more zen diodes.

Frequently Asked Questions 

1. How does Zener Diode make Voltage Regulation?

By serving as complementary loads and drawing more or less current as needed to maintain a constant voltage drop across the load, Zener diodes as voltage regulators control it. This is equivalent to changing the speed of a vehicle by braking instead of changing the throttle position: not only is it inefficient, but the brakes must be constructed to handle all the engine’s power when the driving circumstances don’t demand it.

Despite this design’s underlying inefficiency, Zener diode regulator circuits are frequently used because they are straightforward. Other voltage-regulating methods are used in high-power situations where the inefficiencies would be unacceptable. Even in those cases, tiny Zener-based circuits are frequently employed to supply a “reference” voltage to power a more effective amplifier circuit that manages the main force.

2. What sets a Zener diode apart from a typical diode?

A Zener diode is an electrical component with two terminals that only conducts electricity in one direction. A steady reference voltage may be produced using a Zener diode. The main application for these diodes is to supply a reference voltage in power supplies. On one end, it has excellent resistance, while on the other, it has low resistance.

3. Why is a regulator made of a Zener diode?

As a voltage regulator Zener Diode shunt voltage regulators, the use of Zener diodes is frequently employed to control the voltage across tiny loads. With Zener Diodes, the breakdown voltage is sharply reversed and remains constant over a wide range of currents.

To ensure that the applied voltage will reverse bias the Zener diode as a voltage regulator, we will thus link it in parallel with the load. Therefore, the voltage across the stream will be constant across the Zener diode if the reverse bias voltage exceeds the knee voltage.

4. Why is Zener Diode used as a regulator?

 It is utilized as a shunt voltage regulator. This is linked in parallel with the load to create reverse bias, and once it reaches knee voltage, the voltage across the load stabilizes. 

5. What distinguishes a Zener diode from a regular diode?

The flow of current is the primary distinction between it and a typical diode. The current can travel in both directions through it but only in one direction through a conventional diode.