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Lecture 12

1) The document discusses Zener diodes and their use in voltage regulation circuits. It provides examples of Zener diode regulator circuits with either a fixed or variable input voltage or load resistance. 2) The key states of operation for a Zener diode are outlined as either "on" where the voltage is clamped at the Zener voltage, or "off" where it acts as an open circuit. Equivalent circuits for both states are used to analyze the regulator circuits. 3) Examples are provided to calculate voltage, current, and power values for Zener diode regulators under different operating conditions of input voltage and load resistance. Plots of output voltage versus load and input voltage are also

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109 views19 pages

Lecture 12

1) The document discusses Zener diodes and their use in voltage regulation circuits. It provides examples of Zener diode regulator circuits with either a fixed or variable input voltage or load resistance. 2) The key states of operation for a Zener diode are outlined as either "on" where the voltage is clamped at the Zener voltage, or "off" where it acts as an open circuit. Equivalent circuits for both states are used to analyze the regulator circuits. 3) Examples are provided to calculate voltage, current, and power values for Zener diode regulators under different operating conditions of input voltage and load resistance. Plots of output voltage versus load and input voltage are also

Uploaded by

sayed Tamir jan
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Zener Diodes

107

Approximate equivalent circuit for the Zener diode in the three


possible states
Example 2.24 108

Determine the reference voltages provided by the


network, which uses a white LED to indicate that the
power is on. What is the level of current through the
LED and the p
power delivered byy the supply?
pp y How does
the power absorbed by the LED compare to that of the
6-V Zener diode?
Example 2.24 109

C
Current through
h h resister,
i

Power delivered by the supply,

Power absorbed by the LED,

Power delivered by the 66-V


V Zenerdiode,
Zener Diodes
110

Regulator
Example 2.25
111

The network is design to limit the voltage to 20V during the


positive portion of the applied voltage and to 0-V for a negative
excursion of the applied voltage. Check its operation and plot the
waveform of the voltage across the system for the applied signal.
112
Zener Diodes
113

Regulator
The use of the Zener diode as regulator and for analysis point of
view there are three conditions.

1. Vi and RL Fixed

2. Fixed Vi, Variable RL

3. Variable Vi, Fixed RL

Basic Zener regulator.


Vi and RL Fixed 114

 Determine the state of the Zener diode by removing it from the


network and calculating the voltage across the resulting open circuit.

If V≥VZ, the Zener diode is on and the appropriate


pp p equivalent
q model
can be substituted.
If V<VZ, the diode is off, and the open-circuit equivalence is
substituted.
substituted
Vi and RL Fixed 115

 Substitute the appropriate equivalent circuit and solve for the desired
unknowns.

The zener diode current must be determined by an application of


Kirchhoff’s current law,

Power dissipated by the Zener diode is

When the Zener diode is turned on i.e, the voltage across the Zener
diode is VZ volts, it will then “lock in” at this level and never reach the
higher level.
Example 2.26 116

a) Determine VL, VR, IZ, and PZ


b) Repeat (a) with RL=3KΩ

Zener diode regulator


Example 2.26 117

Determining V for the regulator.


Example 2.26 118

Resulting operating point for the network.


Example 2.26 119

Network in the “on” state.


Fixed Vi and Variable RL 120

We have

Solving for RL,

The max IL
Si
Since R is
i constant,
t t so once diode
di d is
i on VR andd IR will
ill be
b constant
t t

Zener current

max. load resistance


Example 2.27 121

Determine the range of RL and IL that will result in VRL being maintained
at 10V.

Voltage regulator.
regulator

VL versus RL and IL for the regulator


122

Fixed RL, Variable Vi


Example 2.28 123

Determine the range of values of Vi that will maintain the zener


diode of fig. below in the “on” state?

Regulator.

VL versus Vi for the


regulator.
Example 2.28 124

Waveform generated by a filtered rectified signal.


Home Work
125

Text Book:

End Problems: P-42,43,44,45,46


, , , ,

Reference Book (Sedra/Smith)

Example: 3.10
Exercises: 3.35

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