To Study Zener Diode Characteristics

Aim

To study Zener diode characteristics.

Apparatus Required:

Regulated DC power supply, Voltmeter, Connecting Wires, kit

Specifications:

Breakdown Voltage = 5.1V

Power dissipation = 0.75W

Max. Forward Current = 1A

Theory:

An ideal P-N Junction diode does not conduct in reverse biased condition. A zener diode conducts excellently even in reverse biased condition. These diodes operate at a precise value of voltage called break down voltage. A zener diode when forward biased behaves like an ordinary P-N junction diode. A zener diode when reverse biased can either undergo avalanche break down or zener break down.

Avalanche break down: -If both p-side and n-side of the diode are lightly doped, depletion region at the junction widens. Application of a very large electric field at the junction may rupture covalent bonding between electrons. Such rupture leads to the generation of a large number of charge carriers resulting in avalanche multiplication.

Zener break down: -If both p-side and n-side of the diode are heavily doped, depletion region at the junction reduces. Application of even a small voltage at the junction ruptures covalent bonding and generates large number of charge carriers. Such sudden increase in the number of charge carriers results in zener mechanism.

Circuit Diagram:

Fig (1) – Forward Bias Condition:

Procedure:

Forward biased condition:

1. Connect the circuit as shown in fig (1).
2. Vary Vzf gradually and note down the corresponding readings of Izf.
3. Step Size is not fixed because of non linear curve and vary the X-axis variable (i.e. if output variation is more, decrease input step size and vice versa).
4. Tabulate different forward currents obtained for different forward voltages.

Reverse biased condition:

1. Connect the circuit as shown in fig (2).
2. Vary Vzr gradually and note down the corresponding readings of Izr.
3. Step Size is not fixed because of non linear curve and vary the X-axis variable (i.e. if output variation is more, decrease input step size and vice versa).
4. Tabulate different reverse currents obtained for different reverse voltages.

Observation table:

Zener diode in Forward Zener diode & reverse biased condition should be observed.

Calculations From Graph

Static forward Resistance Rdc = Vf/If

Dynamic forward Resistance rac = ΔVf/ΔIf

Static Reverse Resistance Rdc = Vr/Ir

Dynamic Reverse Resistance rac = ΔVr/ΔIr

Precautions:

1. While doing the experiment do not exceed the ratings of the diode. This may lead to damage the diode.
2. Connect voltmeter and Ammeter in correct polarities as shown in the circuit diagram.
3. Do not switch ON the power supply unless you have checked the circuit connections as Per the circuit diagram.

Result:

1. The zener diode characteristics have been studied.
2. The zener resistance at the breakdown voltage was found to be = ………

Quiz:

Quiz:

Q1:Give applications of Zener diode?

A1:Applications of Zener diode are (a) Voltage regulation (b) Meter protection (c) Zener diode as a peak clipper (d) Zener diode as a reference element

Q2:what is voltage regulation of Zener diode?

A2:Voltage regulation is a measure of circuit’s ability to maintain a constant output voltage even when either input voltage or load current varies.

Q3:what is Zener current?

A3:what is Zener current?

Q4:Give the equation from which series resistance of Zener diode regulator determined?

A4: The equation from which series resistance of Zener diode regulator determined is RS = VS-VOUT / IZMAX Where VS is source voltage, VOUT is output voltage & IZMAX is maximum current through Zener diode.

Q5:Give advantages of Zener diode regulator over other regulators?

A5:Advantages of Zener diode regulator over other regulators are that they are smaller in size, lighter in weight and have longer life.

Q6:What is Zener diode?

A6:Zener diode, also sometimes called the breakdown diode is a P-N junction diode specially designed for operation in the breakdown region in reverse bias condition.

Q7:Give several methods used to manufacture of Zener diodes?

A7:several methods used to manufacture of Zener diodes are diffused structure, diffused and passivated structure and alloy diffused structure.

Q8:In passivated structure of a Zener diode by which layer edges of the junction are covered?

A8:In passivated structure of a Zener diode; Silicon Dioxide layer edges of the junction are covered.

Q9:Give the voltage range availability of Zener diodes?

A9:The voltage range availability of Zener diodes is 2.4v to 200v.

Q10:What is Zener voltage?

A10:The voltage at which the Zener diode breaks down is called the Zener voltage.