Analog subject presentation..

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3. Introduction of Zener diode
A zener diode is a type of diode that permits current not only in the
forward direction like a normal diode but also in the reverse direction
if the voltage is larger than the breakdown voltage known as “Zener
voltage”

4. Introduction of Zener diode
The device was named after Clarence Zener ,who discovered this
electrical property.

5. Introduction of Zener diode
The arrowhead on a zener diode symbol points in the direction of forward
current when the diode is forward biased.
The zener diode is normally operated in reverse breakdown and the current
direction is then from anode to the cathode.

6. Characteristics of Zener diode
The forward characteristics is same as that of ordinary forward
biased junction diode.
On gradually increasing the reverse biasing, the junction breaks
down at a specific well defined voltage known as zener
voltage(Vz ) and current abruptly known as zener current (Iz).
Breakdown condition (Vn-Vp) Vz

7. Basic Zener diode circuit
The most basic zener diode circuit consist of a single zener
diode and a resistor. The zener diode provide the reference
voltage, but a series resistor must be in place to limit the
current into the diode otherwise a large amount of current
would flow through it and it could be destroyed.

8. Application of Zener diode
Zener diodes are widely used as voltage references and as shunt
regulators to regulate the voltage across small circuits. When
connected in parallel with a variable voltage source so that it is
reverse biased, a Zener diode conducts when the voltage reaches
the diode's reverse breakdown voltage.

9. Zener Diode as Voltage Regulator
The term regulator means which regulates or controls.
Zener diode can work as a voltage regulator if it is
introduced in a circuit. The output across the diode will be
constant. It is driven by a current source. As we know if
the voltage across the diode exceeds a certain value it
would draw excessive current from the supply.
To limit the current through the Zener diode series
resistance R is introduced whose value can be chosen
from the following equation
Resistor value (ohms) = (V1 - V2) / (zener current + load
current)

10. Zener limiters
A single Zener diode can limit one side of a sinusoidal
waveform to the zener voltage while clamping the
other side to near zero. With two opposing zeners,
the waveform can be limited to the zener voltage on
both polarities.

11. Zener Comparator
This comparator application makes use
of the properties of the zener diode to
cause the output to switch between
voltages determined by the zener diodes
when the input voltage difference
changes sign. The output circuit amounts
to a zener regulator which switches from
one zener voltage to the other on a
transition.

12. Zener in Power supplies
The voltage from a half-wave power supply is
applied to a resistor R and a Zener diode
connected in series. In normal operation, the
Zener diode operates in the "reverse- breakdown"
mode, in which the reverse voltage is equal to the
nominal Zener voltage and is independent of the
current (as long as the current in non-zero). The
resistor R helps regulate the current through the
Zener diode. As the load current is increased,
some of the current that was flowing through the
Zener diode is bypassed into the load device,
reducing the Zener current, but the voltage
remains constant.

13. Example

14. Solution:
For KVL we get,
-15 + 0.5I + I = 0
or,1.5I = 15
so, I = 10A
Here, Vab = I*RL
= 10*1 = 10V ( Here Vab > Vz Breakdown occur)
IL = Vab / RL =Vz / RL =8 / 1 = 8 A