DEE3253/6533 – ANALOGUE ELECTRONICS FUNDAMENTAL Diodes
DEE3253/6533 – ANALOGUE ELECTRONICS FUNDAMENTAL
Diodes
Subtopics
1.0 Semiconductor diodes (3 hours)1.1 Introduction to semiconductors materials1.2 Introduction to diode
1.3 Introduction to Zener diode and LED 2.0 Diode applications ( 6 hours)
2.1 Load line analysis and diode approximation 2.2 Series-Parallel Configuration 2.3 Half-wave and Full-wave rectification 2.4 Clippers and Clampers
2.5 Zener diode application
Early Diodes
Thermionic diodes are thermionic valve devices (also known as vacuum tubes)
Electrodes surrounded by a vacuum within a glass envelope, similar in appearance to incandescent light bulbs.
Semiconductor Diodes
Most modern diodes are based on semiconductor p-n junctions In a p-n diode, conventional current can flow from the p-type
side (the anode) to the n-type side (the cathode), but cannot flow in the opposite direction.
Diode symbol
Semiconductor Materials
Semiconductor means the elements having a conductivity between a conductor and an insulator
Commonly used:– Germanium (Ge)– Silicon (Si)– Gallium Arsenide (GaAs)
Single-crystal
Compound
Atomic Structure
Every atom is composed of 3 basic particles: electron, proton & neutron
The outermost orbit are called valence electrons Semiconductor have only 3 – 5 valence electrons
Carbon Silicon Germanium
Atomic Structure
Covalent bonding is the bonding of atoms, strengthened by the sharing of electrons
Ex: covalent bonding of silicon atoms
Energy Levels
There are specific energy levels associated with each orbiting electron
To become a conductor, electron from valence band must absorb energy to across the energy gap and into the conduction band
The energy levels are different for every element
Extrinsic Materials
n-type materials– Extra electrons in the
covalent bond gets from n-type materials such as antimony, arsenic and phosphorus
Extrinsic Materials
p-type materials– Extra holes in the
covalent bond gets from p-type materials such as boron, gallium and indium
Semiconductor Diodes
By simply joining the n-type and p-type material together, a semiconductor diode was born
depletionregion
Semiconductor Diodes
Connect the diode to a source:
The electrons in n-type material will attracts to +ve terminal of the source
The holes in p-type material will attracts to –ve terminal of the source
So, the depletion region becomes bigger and electrons cannot pass, hence no current flows
This is called REVERSE BIAS
Semiconductor Diodes
Connect the diode to a source:
The electrons in n-type material will attracts to +ve terminal of the source and jump into p-type material
The holes in p-type material will attracts to –ve terminal of the source and jump into n-type material
So, the depletion region becomes lesser/gone and electrons can pass, hence current will flows
This is called FORWARD BIAS
Semiconductor Diodes
To conclude, diode can be represented as a switch (but not ideal)
For a forward-bias, 0.7V (knee voltage, VD) have to be applied for the diode (for silicon)
For germanium, VD = 0.2 ~ 0.3V For gallium arsenide, VD = 1.2 ~ 1.4V
Semiconductor Diodes
Comparison of Ge, Si and GaAs diodes
Zener region
Zener Diode
A special type of diode that is supposed to be reversed biased Zener diode works in zener region where the diode start to
breakdown at breakdown avalanche voltage (VZ), and the current is avalanche current (IZ)
It limits a voltage to a certain point to pass through the zener diode
LED (Light-Emitting Diode)
In a forward-biased p-n junction, recombination of the holes and electrons requires energy possessed by the unbound free electrons
In Si and Ge, most of the energy is dissipated in the form of heat and photons
But in other material such as GaAs, the energy generate light but it is invisible for the eye to see (infrared)
Other materials that emit light during forward-bias operation
Color Construction Forward Voltage
AmberBlueGreenOrangeRed WhiteYellow
AlInGaPGaNGaP
GaAsPGaAsP
GaNAlInGaP
2.15.02.22.01.84.12.1
LED (Light-Emitting Diode)
How an LED works
Diode Approximation
Diode equivalent circuits:– Ideal Equivalent Circuit– Simplified Equivalent Circuit– Piecewise-Linear Equivalent Circuit
Purpose: to represent diode
Piecewise-Linear Equivalent Circuit
Approximation representation of the actual diode Diode have VD and rav for the slope region
Simplified Equivalent Circuit
Assume straight vertical line of ID at VD
No rav
Ideal Equivalent Circuit
Diode as an ideal switch No VD or rav
Load-Line Analysis
A simple analysis which used the diode characteristic to obtain the Q-point (operation point)
A series diode circuit and characteristic:
Load-Line Analysis
For For Connect a line between E / R and E The overlap of the lines becomes the Q-point of the
diode and IDQ and VDQ will be obtained
RDRD IVVVE
REIRIRIEV DDDD ,0 ,0
EVVRVEI DDDD ,)0( ,0
Load-Line Analysis
Problem 2.1a
Determine ID, VD & VR
The circuit:
Problem 2.1a
The diode characteristic:
Problem 2.1a
Solution:– The circuit representation:– For
– For
RIVVVE DDRD
mA 24.2433.080 ,0
kREI
RIEV
D
DD
V 8)0( ,0
EVRVEI
D
DD
Problem 2.1a
The load-line analysis becomes:
RE
E
Q-point
DQI
DQV
Problem 2.1a
From the analysis:– VDQ = VD ≈ 0.9 V– IDQ = ID ≈ 21.5 mA– For VR,
V 095.7)33.0)(5.21(
kmRIV DR
Problem 2.1b
Re-do Problem 2.1a using approximate (simplified) model for diode and compare the result
The diode characteristic becomes:
Problem 2.1b
The solution:
Problem 2.1b
VD is always 0.7 V, so VD = VDQ = 0.7 V From the graph, IDQ = ID ≈ 22 mA So, we get VR = (22m)(0.33k) = 7.26 V ≈ 7.3 V Using Kirchoff’s voltage law, E = VD + VR
The answer are the same
V 3.77.08
R
R
VV
Problem 2.1c
Re-do Problem 2.1a using ideal model for diode and compare the result
The diode characteristic becomes:
Problem 2.1c
The solution
Problem 2.1c
VD is always 0 V, so VD = VDQ = 0 V It acts like an ideal switch From the graph, IDQ = ID ≈ 24.24 mA So, we get VR = (24.24m)(0.33k) = 7.9992 V ≈ 8 V Using Kirchoff’s voltage law, E = VR
The answer are the same
V 8 RV
Series-Parallel Configuration
Diode can be applied to any circuits Usually diode is represented as an
approximated (simplified) model diode To keep the calculation simple, just use the
Kirchoff’s voltage & current law Hint: it is easier to use nodal analysis
technique for circuit representation Important: strong knowledge in CIRCUIT
THEORY!!!!!
Problem 2.5a
Find I The circuit:
Problem 2.5a
For Si, VD = 0.7 V Notice that the diode is in reverse-bias
configuration So, no current will flow, I = 0 A
Problem 2.5b
Find I The circuit:
Problem 2.5b
Solution:– Using nodal analysis, node V is equal to the
voltage supplied, so V = 20
V
Problem 2.5b
Using the simple Ohm’s law:
A 965.020
7.020
RVI
Problem 2.5c
Find I The circuit:
Problem 2.5c
Solution:– One of the diode is in reverse-bias resulting in
open circuit for that part
Problem 2.5c
So, by using the simple Ohm’s law:
A 11010
RVI
Problem 2.7a
Find Vo
The circuit:
Problem 2.7a
Both the diode are in forward-bias, so both are short-circuited For Si, VD = 0.7 V For Ge, VD = 0.3 V The circuit becomes:
0.7 V 0.3 V19 V
SIMPLIFIED
Problem 2.7a
Solution:– Using nodal analysis, voltage at Vo:
V 5.922
19
0
00
VkV
kV
Problem 2.7b
Find Vo
The circuit:
Problem 2.7b
The circuit becomes:
0.7 V
Problem 2.7b
Solution:– The nodal analysis of node Vo:
V 77.4
)2(2.17.010
0
00
Vk
VkV
Problem 2.11a
Find Vo & I: The circuit:
Problem 2.11a
For Si, VD = 0.7 V For Ge, VD = 0.3 V Because of this, current
will flow in the Ge’s diode route
Naturally, current will select the easiest/fastest route
So, the circuit becomes:
0.3 V
Problem 2.11a
Solution:– Using Kirchoff’s voltage law:
– For I, by using basic Ohm’s law:
V 7.93.0100 V
mA 7.91
7.90 kR
VI
Problem 2.11b
Find Vo & I: The circuit:
Problem 2.11b
For the same type of diode, the circuit will becomes:
Because there is no resistor exist in the parallel route of the diode, current will flow in only one of the diode’s route
0.7 V0.7 V
0.7 V
Problem 2.11b
Solution:– Using Kirchoff’s voltage law:
– For I, by using Ohm’s law:
V 6.147.07.0160 V
mA 553.07.4
126.14
kI
Problem 2.13
Find Vo & ID
The circuit:
Problem 2.13
The circuit becomes:
0.7 V
0.7 V
9.3 V
SIMPLIFIED 9.3 V
SIMPLIFIED
Problem 2.13
The solution:– The nodal analysis for node Vo:
– For ID:
V 2.621
3.9
0
00
VkV
kV
mA 55.12
2.63.9
kID
Rectification
Rectify means improvement, cure healing (pembaikan, penambahbaikan)
For a sinusoidal waveform or any supply that has a variation of input value, diode can be used for rectification
Rectification are used to modified the input value to become only the signal that we want
Half-Wave Rectification
For a full cycle of a sinusoidal or continuous waveform, only half of the waveform is taken to be rectified
Half-Wave Rectification
For the period 0 T/2, the sinusoidal input will give a forward bias supply to the circuit
The diode will “on” and current will pass through Assume that the diode is ideal
Half-Wave Rectification
For the period T/2 T, the sinusoidal input will give a reverse bias supply to the circuit
The diode will “off” and no current can pass through Assume that the diode is ideal
Half-Wave Rectification
For a continuous periodic waveform, the rectified waveform will become:
Where as:
mdc VV 318.0
Problem 2.25
Sketch Vo and determine Vdc:
Problem 2.25
Solution:– To obtain Vm from Vrms:
– The output Vo will be:
– Vdc will be:
V 56.155)110(2
2
rmsm VV
V 47.49)56.155(318.0318.0
mdc VV
Problem 2.26
Sketch Vo
Problem 2.26
Solution:– For the positive input supply:
– The circuit becomes:For Vi < 0.7V: For Vi ≥ 0.7V:
0.7 V
Problem 2.26
– The output for the positive input supply becomes:
– For the negative input supply:
Problem 2.26
– The circuit becomes:
– For maximum Vo: - The output becomes:
+
-
VVkV
kV
o 091.9101
10 00
Problem 2.26
– Combine both the output becomes:
PIV or PRV
Peak Inverse Voltage (PIV) or Peak Reverse Voltage (PRV)
It is a rating to make sure for the reverse-bias operation, the diode didn’t enter the Zener region
PIV is set according to the circuit and the input voltage
mV rating PIV for half-wave rectifier
Full-Wave Rectification
The whole cycle of input signal is used and rectified
Two commonly types of full-wave rectifier:– Bridge Network– Center-Tapped (CT) Transformer
The dc level from a sinusoidal input can be improved 100%. So the Vdc becomes:
mdc VV 636.0
Full-Wave Rectifier: Bridge Network
The most commonly bridge network configuration are build with 4 diodes
Full-Wave Rectifier: Bridge Network
For the positive input supply, the current will take the route as shown below, and the output will becomes:
Full-Wave Rectifier: Bridge Network
For the negative input supply, the current will take the route as shown below, and the output will becomes:
Full-Wave Rectifier: Bridge Network
Combine both of the output becomes:
Full-Wave Rectifier: Bridge Network
Due to the maximum voltage from the input supply is Vm, to keep the diode away from the Zener region, the PIV rating is:
mV rating PIV for full-wave rectifier: bridge network
Full-Wave Rectifier: Center-Tapped (CT) Transformer
It is constructed with 2 diodes and a center-tapped transformer The transformer ratio is 1:2
Full-Wave Rectifier: Center-Tapped (CT) Transformer
For the positive input supply:
Full-Wave Rectifier: Center-Tapped (CT) Transformer
For the negative input supply:
Problem 2.28
The circuit:
1 kΩ120 Vrms
All diodes are silicon
Problem 2.28a
Determine DC voltage for output Solution:
– Vm:– Vo:– So, Vdc:
V 71.16912022 rmsm VVV 31.1687.07.071.1690 V
)31.168(636.0.6360 0 VVdc
Problem 2.28b
Determine the required PIV rating for each diode from problem 2.28
Solution:– PIV: V 01.1697.031.168(load) PIV Dm VV
Problem 2.28c
Find the maximum current through each diode
Solution:– ID(max): mA 31.168
131.168(max)0
(max) kR
VI
LD
Problem 2.28d
What is the required power for each diode? Solution:
mW 82.1787.031.168(max) mVIP DD
Problem 2.31
Sketch Vo and determine Vdc
The input and circuit:
Problem 2.31
Solution:– For the positive input supply:– Simplified the circuit:
vi
+
-
vovi
+
-
vo
SIMPLIFIED
1.1 kΩ
Problem 2.31
– Vo(peak):
– The same for negative input supply– So the output will becomes:
V 67.561.12.2
170
0
00
Vk
VkV
56.67 V
Clippers
Configuration that employ diodes to “clip” away a portion of an input signal without distorting the remaining part of the applied waveform
Mainly, there are two types of configuration– Series– Parallel
Clippers
Example of series configuration and the output waveform:
Clippers
Example of parallel configuration and the output waveform:
Clippers
Notice something? Is the configuration similar to something?
Half-wave rectifieris a part ofCLIPPERS
configuration
Example 2.18
Sketch vo
For positive input cycle:
The output will be the sum of vi and +5V
Example 2.18
The output waveform will become:
50 ivv
Example 2.18
For negative input cycle:– For vi ≤ 5: - For vi ≥ 5:
+
-
ivv 50
+
-
00 v
Example 2.18
The output waveform will becomes:
Example 2.18
By comparing the input with the whole output:
Example 2.20
Sketch vo
Example 2.20
For positive input cycle:– For vi ≤ 4 - For vi ≥ 4
ivv 0
+
-
40 v
Example 2.20
The output waveform will become:
Example 2.20
The output for negative input cycle will always +4V due to the external supply of 4V series with the diode
The diode will always be in the “on” mode– The circuit becomes: - The output waveform:
40 v
Example 2.20
By comparing the input with the whole output:
Clampers
Construct of a diode, a resistor and a capacitor
It will shift the waveform to a different level without changing the appearance of the original input signal
The capacitor and resistor ( ) must be large to ensure it doesn’t discharge during the interval that the diode is non-conducting
RC
Clampers
The circuit:
Clampers
Steps for clampers analysis:1. Start the analysis with the condition where the
diode is in forward bias2. The capacitor will charge up instantaneously
during the interval of +ve or –ve input supply where the diode is in forward-bias condition
3. The capacitor will discharge during the next interval of +ve or –ve input supply where the diode is in reverse-bias condition
4. Check that the total swing of the output is the same with the input
Example 2.22
Sketch vo
Example 2.22
Just to check whether the capacitor is appropriate for clamper’s configuration:
For the input given:
For every half interval (+ve or –ve input cycle):
This shows that the capacitor is capable of charging and discharging according to the clamper’s configuration requirement
ms 10)1.0)(100( kRC
ms 11000
1f1T
ms 5.02ms 1
2T
2T
Example 2.22
To start the analysis with the diode in forward-bias mode, the negative input cycle has to be inserted first into the circuit
– The circuit: - The output waveform:
The capacitor will charge up to 25V
Example 2.22
For the next half input cycle that is the +ve cycle:– The circuit: - The output waveform:
The capacitor will discharge thevoltage of 25V
Example 2.22
The whole output waveform will become:
Checking the total swing of the output must match the input:
The total swing of the output is the same with the input that is 30 V
Zener Diodes
The application of Zener diodes have been explained in Subtopic 1.3
The analysis of Zener diodes can be divided into 3 categories:– Fixed Vi and RL
– Fixed Vi, variable RL
– Variable Vi, fixed RL
To make the analysis simple, the analysis will be explain directly from the examples
Example 2.26a (Fixed Vi and RL)
Determine VL, VR and IZ
Example 2.26a (Fixed Vi and RL)
To check whether VZ is in the “on” or “off” mode, the value of VL must be determine first
To do that, take out the Zener diode from the diode The circuit become:
Example 2.26a (Fixed Vi and RL)
By doing a nodal analysis for the node VL
As we can see, the value of VL is smaller than VZ, so the Zener diode is in the “off” mode
Which will result in:
And:
V 73.82.11
16
L
LL
Vk
VkV
A 0ZI
V 27.773.816
R
LRi
VVVV
Example 2.26b (Fixed Vi and RL)
Repeat Example 2.26a with RL = 3kΩ
3 kΩ
Example 2.26b (Fixed Vi and RL)
The same analysis is repeated from Example 2.26a where the Zener diode is taken out to examine the value of VL
The circuit becomes:
3 kΩ
Example 2.26b (Fixed Vi and RL)
By doing a nodal analysis for the node VL
As we can see, the value of VL is larger than VZ, so the Zener diode is in the “on” mode
When the Zener diode is in the “on” mode, it will maintain the voltage of 10V. Because of that VL becomes:
And VR becomes:
V 1231
16
L
LL
VkV
kV
V 01 ZL VV
V 61016 RV
Example 2.26b (Fixed Vi and RL)
Using current divider theory:
mA 67.2310
16
kk
RV
RV
III
L
LR
LiZ
Example 2.27 (Fixed Vi, Variable RL)
Determine the range of RL and IL that will result in VL being maintained at 10 V
Example 2.27 (Fixed Vi, Variable RL)
To maintain VL at 10 V, the Zener diode must be in the “on” mode
For IZM = 32 mA, the current at load:
The load would be:
mA 8
321
1050
mk
III ZMRL
k 25.1810mI
VRL
LL
Example 2.27 (Fixed Vi, Variable RL)
For IZ(min), the Zener diode are assume “off” but the voltage VZ are maintained at 10 V
The load current would be:
The load would be:
mA 401
1050
k
II RL
2504010mI
VRL
LL
Example 2.27 (Fixed Vi, Variable RL)
Retrieve back all the IL and RL value:
250mA 40k 25.1mA 8
LL
LL
RIRI
IL (min)
IL (max) RL (min)
RL (max)
Example 2.28 (Variable Vi, Fixed RL)
Determine the range of Vi that will maintain the Zener diode in the “on” mode
Example 2.28 (Variable Vi, Fixed RL)
To maintain Zener diode in “on” mode, VZ must equal to VL:
Taking the maximum current of the Zener diode, input current becomes:
The input voltage will become:
V 20 LZ VV
mA 67.762.1
2060
km
III LZMR
V 87.36)220)(67.76(20
i
Ri
VmRIV
Example 2.28 (Variable Vi, Fixed RL)
For IZ(min), the Zener diode are assume “off” but the voltage VZ are maintained at 20 V
Using nodal analysis at node VL:
Retrieve back all the value of Vi:
V 67.232.1
20220
20
i
i
Vk
V
V 67.23V 87.36 ii VV
Vi (max) Vi (min)
Voltage multiplier circuits use a combination of diodes and capacitors to step up the output voltage of rectifier circuits.
• Voltage Doubler• Voltage Tripler• Voltage Quadrupler
Voltage Multiplier Circuits
Voltage Doubler
This half-wave voltage doubler’s output can be calculated as
Vout = VC2 = 2Vm
Vm = peak secondary voltage of the transformer.
Operation of a Voltage Doubler Circuit
The 1st capacitor charges up to Vm during the positive half of the cycle,then the 2nd capacitor charges up to Vm in the same polarity as the 1st capacitor,finally the output is the sum of the voltages across both capacitors:
Vout = 2Vm
Voltage Tripler and Quadrupler Circuits
By adding more diode-capacitor networks the voltage can be increased.
Practical Applications of Diode Circuits
Rectifier CircuitsConversions of AC to DC for DC operated circuitsBattery Charging Circuits
Simple Diode CircuitsProtective Circuits against OvercurrentPolarity ReversalCurrents caused by an inductive kick in a relay circuit
Zener CircuitsOvervoltage ProtectionSetting Reference Voltages