Zener Diode Calculator

A Zener Diode is also known as a breakdown diode, it is an immensely doped semiconductor device that is designed to operate in the reverse direction in which the current is flowing. And hence, when the voltage across the terminals of a Zener diode is reversed and the potential reaches the Zener Voltage (also termed as knee voltage), the junction breaks down and the current flows in the reverse direction. This effect is known as the Zener Effect.

A Zener diode operates just like a normal diode when it is forward-biased in the circuit. When connected in reverse biased mode, a small leakage current flows through the diode in the circuit. As the reverse voltage increases to the predetermined breakdown voltage (Vz), the current starts flowing through the diode. In this case when the current increases to a maximum, which is determined by the series resistor, after which it stabilizes and remains constant over a wide range of applied voltage in the circuit.

There are two types of breakdowns for a Zener Diode:

• Avalanche Breakdown
• Zener Breakdown

Avalanche Breakdown in Zener Diode

Avalanche breakdown in a circuit occurs both in normal diode and Zener Diode at high reverse voltage. When a high value of reverse voltage is applied to the PN junction diode, the free electrons gain sufficient energy and accelerate at high velocities in the avalanche breakdown. 

Zener Breakdown in Zener Diode

The applied reverse bias voltage, when it reaches closer to the Zener voltage, the electric field in the depletion region gets strong enough to pull electrons from their valence band in their electron affinity. The valence electrons gain sufficient energy from the strong electric field of the depletion region of the atom.

There are a few ways in which a Zener diode can be represented in a circuit. A few of these are used for high levels of power dissipation and the others are contained with surface mount formats of the cathode in the circuit. It has a band around one end marking the cathode side of the diode in the circuit.

Zener diode is used as a Shunt voltage regulator for regulating voltage across small loads. The breakdown voltage of Zener diodes will be constant for a wide range of current in the circuit. The voltage across the load will become constant in the reverse biases.

Question 1: Determine the current through Zener diode for the circuit for a current i1 at 17mA and i2 as 7mA in the potential resistor of 800 ohm : (Given: Zener diode break down voltage Vz=5.6V)

Solution: 

The potential difference across 800-ohm resistor will be 5.6V.

Vz=5.6V

I2 = 7mA(by substituting the values)

Then the potential difference between wires is 200 ohm

i1=17-7 mA

i1=10 mA

Hence i1 across this Zener Diode will be 10mA

Question 2: An ideal diode and a 5 Ω resistor are connected in series with a 25 V power supply in the forward bias. Calculate the current that flows through the diode in this biasing.

Solution:

The diode is forward biased and it is an ideal one. Hence, it acts as a closed switch with no barrier voltage. Hence, the current that flows through the diode can be calculated using Ohm’s law in the forward biasing.

V = IR

I =V/R = 25/5 = 5 A

1. How do you define Zener diode?

A Zener diode is a semiconductor device that allows current to flow either in a forward or reverse direction and calculates current in both biasing.

2. Why is Zener Diode used as a regulator?

Zener diode is used as a shunt voltage regulator general. Zener diode is connected parallel to the load to make it reverse bias and once the Zener diode exceeds knee voltage, the voltage across the load becomes constant in the forward biasing.

3. Does Zener Diode exhibit a controlled breakdown?

Yes, Zener Diode does exhibit a controlled breakdown in both biasing.

4. Does Zener Diode work in forwarding biased mode?

Zener diodes act like normal p-n junction diodes under forwarding biased conditions.

5. What is the difference between a Zener diode and a normal diode?

The main difference between a Zener diode and a normal diode lies in the passage of current in the circuit. A normal diode allows current to flow only in one direction while a Zener diode allows current to flow in both directions in this biasing.