Basic electronics MODULE_3_Zener diode.ppt

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2. Department of Electronics and Communication Engineering, MIT, Manipal
Part – I : ANALOG ELECTRONICS
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CHAPTER-1: DIODES AND APPLICATONS
Module – 3: Voltage Regulators
Reference:
Robert L. Boylestad, Louis Nashelsky, Electronic Devices &
Circuit Theory, 11th Edition, PHI, 2012

3. Department of Electronics and Communication Engineering, MIT, Manipal
Module – 3: Voltage Regulators
3
Learning Outcomes:
At the end of this module, students will be able to:
 Describe the working of Zener as voltage regulator
 Discuss the IC based voltage regulator.

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Zener Diode and its characteristics
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Anode Cathode
P N
I-V characteristics of Zener diode
P N
IZK or IZmin
IZM or IZMax
PZM or PZMax
PZM = VZ.IZM

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Equivalent circuit
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Vγ
RF
RR ≈  RZ
VZ
–
+ –
+
N
P
N N N
P P P
 Equivalent circuits of Zener diode
Forward Reverse Breakdown
 Note: RZ is usually very small, can be neglected

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Zener voltage regulation
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7. Department of Electronics and Communication Engineering, MIT, Manipal 7
line regulation and load regulation
R
V
V
I
I
I
I
z
in
L
z




I
V
V
R z
in 

L
Z
z
in
I
I
V
V
R



(i) For Line regulation, RL is constant and
L
Z
L
R
V
I  is also constant and Vin varies bet.
Vin(min) to Vin(max)

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Load regulation
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(ii) For Load Regulation, Vin is constant and RL varies between RLmin and RLmax
and load current is given by and
Lmin
Z
Lmax
R
V
I 
When Vin=Vin(min),and IL is constant
R
V
V
I
z
in(min)
min

 L
z(min)
min I
I
I 

Similarly when Vin=Vin(max) we have
R
V
V
I
z
in(max)
max


L
z(max)
max I
I
I 

Lmax
Z
Lmin
R
V
I 

9. Department of Electronics and Communication Engineering, MIT, Manipal
Zener analysis
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 Step 1:
• Remove the zener diode from the circuit, and calculate the voltage V
across the resulting open circuit
• If V ≥ VZ, the zener is ON, appropriate equivalent model substituted
• If V < VZ, the zener is Off, and open circuit equivalent substituted
 Step 2:
• Substitute the appropriate equivalent model and solve for the desired
unknown
• Suppose that we get V > VZ, then zener is in breakdown region, and
equivalent model is VZ (neglecting RZ)
L
S
L
i
R
R
R
V
V



10. Department of Electronics and Communication Engineering, MIT, Manipal
Zener - problems
1. For the zener network, Vi= 16 V, RS= 1 K, VZ= 10 V and RL= 1.2 K.
Determine Vo, IZ and PZ (Ans: 8.73 V, 0, 0)
1. Repeat with RL= 3 K (Ans: 10V, 2.67mA, 26.7mW)
3. In a zener network, RS = 120Ω, RL = 250Ω and VZ = 5V. Find the minimum and
maximum current flowing through zener when input varies from 9V to 15V.
(Ans: 13.33mA, 63.33mA)
4. For the zener network shown, RS = 10Ω, VZ = 10V, Vi = 25V. Find the minimum and
maximum current through zener when RL is varied between 10Ω and 100Ω
(0.5A, 1.49A)
5. For a zener network, RS = 470Ω, VZ = 12V and Vi = 50V. Find the minimum and
maximum values of RL so that zener diode remains in ON state, given that IZK = 2 mA and
PZM =500mW
(izmax=41.67mA,Rlmax306.6; rlmin=152.2)
6. In a Zener regulator, the input DC is 10 V ± 20%. The output requirements are 5 V, 20 mA.
Given Izmin=5 mA and Izmax=80 mA. Design the Zener regulator.
( Ans: RL=250 Ω, Vinmin=8V , Vinmax=12 V, Rmax=120 Ω , Rmin=70 Ω.) 1

11. Department of Electronics and Communication Engineering, MIT, Manipal
Exercise
1. (a) Consider the circuit shown below.
The Zener Diode regulates at 50V over a range of diode current from 5
mA to 40 mA. Supply voltage V = 200V. Calculate the value of R to
allow voltage regulation from a load current IL = 0 upto Imax; the
maximum possible value of IL. What is Imax?
(Ans: Imax=35 mA)
(b) If R is set as in part (a) and IL = 25mA, what are the limits between
which V may vary without loss of regulation in the circuit?
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(Ans: Vmin=162.5 V, Vmax=293.8 V )

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Self test
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1. If the series resistance increases in an unloaded Zener regulator,
the Zener current
a. Decreases
b. Stays the same
c. Increases
d. Equals the voltage divided by the resistance
2. In a loaded Zener regulator, which is the largest current?
a. Series current
b. Zener current
c. Load current
d. None of these

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IC voltage regulators
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1. Fixed voltage regulator
2. Adjustable voltage regulators

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Fixed voltage regulators
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IC regulator like LM117, LM317, LM338 are adjustable
voltage regulators. IC 78xx and 79xx are positive and
negative voltage regulator.

15. Department of Electronics and Communication Engineering, MIT, Manipal
Part – I : ANALOG ELECTRONICS
1
CHAPTER-1: DIODES AND APPLICATONS
Module – 4: Special Purpose Diodes
Reference:
Robert L. Boylestad, Louis Nashelsky, Electronic Devices &
Circuit Theory, 11th Edition, PHI, 2012

16. Department of Electronics and Communication Engineering, MIT, Manipal
Module – 4: Special purpose diodes
Learning Outcomes:
At the end of this module, students will be able to:
 Explain the working of the LEDs and applications
 Explain the working of the photodiode and applications
 Explain the working of the opto-coupler and applications
 Explain the working of the solar cells and applications
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17. Department of Electronics and Communication Engineering, MIT, Manipal
Diode as capacitor- Varactor diode
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d
A
C




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Light Emitting Diode
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Electrical set-up
of LED

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Photo Diode
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[http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/photdet.html]

20. Department of Electronics and Communication Engineering, MIT, Manipal
Optocoupler
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Schematic of optocoupler
[http://www.ustudy.in/node/7519

21. Department of Electronics and Communication Engineering, MIT, Manipal 21
1. A LED is a diode that gives off ...........when .........biased.
2.LED is manufactured using gallium arsenide gives ........... light.
3. How photo diode differs from rectifier diode?
4. The output voltage of Optoisolator depends upon.........
5.What is dark resistance of photo-diode ?
6. To display the digit 0 in a seven segment display
(a) A must be lighted
(b) F must be off
(c) G must be on
(d) all segments except G should be lighted
Self test

22. Department of Electronics and Communication Engineering, MIT, Manipal
Solar cell
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Structure of solar cell
[www.solarbc.ca]

23. Department of Electronics and Communication Engineering, MIT, Manipal
Solar cell
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Equivalent circuit and I-V characteristic of a solar cell

24. Department of Electronics and Communication Engineering, MIT, Manipal
Solar array
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25. Department of Electronics and Communication Engineering, MIT, Manipal
Summary
In this module we have learnt to:
1

26. Department of Electronics and Communication Engineering, MIT, Manipal
Exercise Problems
1. Light Emitting Diodes (LED) is used in fancy electronic devices such as
toys emit
A. X-rays B. Ultraviolet light C. visible light D. radio waves
2.The maximum wave length of photons that can be detected by a photo
diode made of a semiconductor of band gap 2 eV is
about…………………………
3. List the applications of opto-couplers.
4. What value of series resistor is required to limit the current through a
LED to 20 mA with a forward voltage drop of 1.6 V when connected to a
10V supply? Given VD=1.6 V.
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