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Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
Department of EECE
Diode Applications
Electronic Circuits
Dr. Manar Mohaisen Office: F208
Email: manar.subhi@kut.ac.kr
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Doping ■ It is a controlled addition of impurities to the pure semiconductive
material to increase its conductivity. ►The impurities addition is for target to increase either the holes or the
free electrons.
Review of the Precedent Lecture
Free (conduction) electronfrom Sb atom
SbSi
Si
Si
SiBSi
Si
Si
Si
Hole from B atom
n-type semiconductor. The extra electron from the antimony atom
becomes a free electron. The impurity element is a pentavalent. Impurities: Arsenic (As), antimony (Sb)
p-type semiconductor An extra hole is created because the impurity
element is a trivalent (i.e., it has 3 valence electrons)
Impurities: Boron (B), indium (In), gallium (Ga)
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Diode Approximations
Review of the Precedent Lecture – contd.
VR
IR
VF
IF
0.7 VVR
IR
VF
IF
0.7 VVR
IR
VF
IF
Reverse Current = 0
Ideal Diode Model -Reverse current, barrier potential, and dynamic resistance are neglected. Not accurate model. - Useful for troubleshooting to check whether the diode is working properly or not. - Forward current is given by:
BIASF
LIMIT
VI R=
Practical Diode Model -Reverse current and dynamic resistance are neglected. -Forward current is given by:
Complete Diode Model - Nothing is neglected. - The most accurate model. - Forward current is given by
After VBIAS exceeds the barrier potential, the diode
acts like a short circuit
VB = 0.7V Reverse
Current ≠ 0
BBIASF
LIMIT
V VI R−
= BBIASF '
LIMIT d
V VIR r
−=
+
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Explain the Operation of the Half-wave Rectifier
₪ Explain the Operation of the Full-wave Rectifier
₪ Discussions
₪ Explain the Use of Power Supply Filters and Regulators
₪ Explain Diode Limiting and Clamping Circuits
₪ Explain the Operation of the Voltage Multipliers
₪ Discussions
Class Objectives
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ DC Power Supply
Introduction
can be half-wave or full-wave rectifier
smoothing filter (Low-pass filter)
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Connection 1 ■ Forward Bias
► In the first half cycle, the diode is forward-biased.
► If the diode is ideal, the output voltage equals the input voltage.
■ Reverse Bias ► In the second half cycle, the
diode is reverse-biased.
►There is no output (Vout = 0).
₪ Connection 2 ■ Reverse biasing in the first
half period
■ Forward bias in the second half period.
Half-Wave Rectifier
RL
+ –
+
–
Vout
0 tt 00 tt 11
Vin
0 t t22
I
RL
Vout
tt 00 tt 11
Vin
00
+–
I = 0 A–
+t t22
Connection 1
Connection 2
RL
+–
+
– Vout
0tt 00 tt 11
Vin
0 t t22
I
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Average Value
₪ Peak Inverse Voltage ■ Equivalent to the peak value of the input voltage.
►Diode should be capable of withstanding this repetitive reverse voltage.
Half-Wave Rectifier – contd.
0/2
0/2
0
1 ( )
1 2sin( ) ,
cos( )1
2cos cos(0)22
TAVG
Tp
Tp
p p
V x t dtTV t dtT T
V tT
TTV V
TT
πω ω
ωω
π
ππ
⎡ ⎤⎢ ⎥⎢ ⎥⎣ ⎦
⎡ ⎤⎛ ⎞⎢ ⎥⎜ ⎟⎜ ⎟⎢ ⎥⎝ ⎠⎢ ⎥⎢ ⎥⎢ ⎥⎢ ⎥⎣ ⎦
=
= =
−=
− += =
∫
∫
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Example 2-2
■ Ideal Diode ►The peak output voltage = Vp(in) = 5 V and 100 V, respectively.
►VAVG = Vout / π = 1.59 V and 31.83 V
■ Practical Diode ►The peak output voltage = Vp(in) – 0.7 = 4.3 V and 99.3 V,
respectively.
►Find the average output voltage in this case [Homework: +2points].
Half-Wave Rectifier – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Center-Tapped Full-Wave Rectifier
Full-Wave Rectifier
RL
D2
D1F
Vin
+
–
+ –
– +
+
–
–+
0
Vout
0
I
RL
D2
D1F
Vin
+
–
– +
+ –
–
+
+–
0
Vout
0
I
During the first half cycle, the upper diode is forward-biased and the lower diode is reverse-biased.
During the second half cycle, the lower diode is forward- biased and the upper diode is reverse-biased.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Turn Ratio ■ The ratio between the number of turns in the secondary winding
and those in the primary winding. Designated n.
■ Affects the output voltage.
■ Peak Inverse Voltage
Full-Wave Rectifier – contd.
(sec) (sec)(sec)
( )
PIV 0.7V 0.7V2 2
2 0.7 V
p pp
p out
V VV
V
⎛ ⎞ ⎛ ⎞⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠
= − − − = −
= +
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Example 2-5
Full-Wave Rectifier – contd.
(sec) ( ) 0.5(100 V) 50 Vp p priV nV= = =
(sec)( ) 0.7 24.3V2
pp out
VV = − =
( )PIV 2 0.7 2(24.3) 0.7 49.3Vp outV= + = + =
Is this figure correct?
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ The Bridge Full-Wave Rectifier ■ Uses four diodes connected as
shown.
Full-Wave Rectifier – contd.
+
–
+
–
F
Vin
D3
D4
D1
D2RL Vout
+
–0
I
–
+
–
+
F
Vin
D3
D4
D1
D2RL Vout
+
–0
I
( ) (sec) 1.4Vp out pV V= −
(sec)
( )
PIV 0.7V0.7V
p
p out
VV
= −
= +
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ The Bridge Full-Wave Rectifier ■ Vp(sec) = 12 V rms
■ Input is sinusoidal, then
■ Root Mean Square
Full-Wave Rectifier – contd.
(sec) (sec)( )2 17 Vp p rmsV V= =
( ) (sec) 1.4 17 1.4 15.6Vp out pV V= − = − =
( )PIV 0.7 15.6 0.7 16.3 Vp outV= + = + =
2 22
0 0
2
0 0
2
1 1sin( ) cos(2 )2 2
1 cos(2 )2 2
2 2
T Tp p
rms
T Tp
p p
V VV t dt t dtT T
V dt t dtT
V VTT
ω ω
ω
⎡ ⎤⎢ ⎥⎢ ⎥⎣ ⎦
⎡ ⎤⎢ ⎥⎢ ⎥⎣ ⎦
= = −
= −
= =
∫ ∫
∫ ∫
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Explain the Operation of the Half-wave Rectifier
₪ Explain the Operation of the Full-wave Rectifier
₪ Discussions
₪ Explain the Use of Power Supply Filters and Regulators
₪ Explain Diode Limiting and Clamping Circuits
₪ Explain the Operation of the Voltage Multipliers
₪ Discussions
Class Objectives
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Objective ■ Convert the AC power line voltage into a DC voltage.
■ The fluctuation in the filter output voltage is called ripple.
₪ Capacitor-Input Filter ■ Consists of a capacitor connected from the output of the rectifier
to the ground.
Power Supply Filters and Regulators
Vin
0 V Filter 0
VOUTFull-waverectif ier
Rectified output
RL
+
–
Vin+
–VC
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Capacitor-Input Filter – contd. ■ Positive 1st quarter cycle:
►Diode is forward-biased.
►Capacitor charges to within 0.7V of the input voltage.
►Load and capacitor have the same voltage.
■ Remaining part of the cycle ►Diode is reverse-biased.
►Capacitor discharges in the load at a rate determined by RC.
■ 1st quarter of next cycle ►Diode becomes
forward-biased.
Power Supply Filters and Regulators – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Capacitor-Input Filter – contd. ■ Ripple voltage
►The variation in the capacitor voltage due to charging and discharging
►The smaller the ripple, the better the filtering performance.
■ Ripple factor ► It is an indication of the effectiveness of the filter.
► It is defined as
Power Supply Filters and Regulators – contd.
( )
DC
r ppVr V=
without filter
DC voltage of the filter’s output voltage
( ) ( )1
r pp p rectL
V Vf R C⎛ ⎞⎜ ⎟⎜ ⎟⎜ ⎟⎝ ⎠
≅
DC ( )11 2 p rect
LV Vf R C
⎛ ⎞⎜ ⎟⎜ ⎟⎜ ⎟⎝ ⎠
= −
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Capacitor-Input Filter – contd. ■ Half-wave vs. Full-wave rectifiers
Power Supply Filters and Regulators – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Example 2-7 ■ Vp(pri) = 1.414 Vrms = 1.414(120 V) = 170 V
■ Vp(sec) = n Vp(pri) = 0.1(170 V) = 17 V
■ Vp(rect) = Vp(sec) – 1.4 V = 17.0 V – 1.4 V = 15.6 V
■
■
■
Power Supply Filters and Regulators – contd.
( ) ( )1 1 15.6V 0.591V(120Hz)(220 )(1000 F)r pp p rectL
V Vf R C μ⎛ ⎞ ⎛ ⎞⎜ ⎟ ⎜ ⎟
⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠=≅ =Ω
DC ( )1 11 1 15.6V 15.3V2 2(120Hz)(220 )(1000 F)p rect
LV Vf R C μ
⎛ ⎞ ⎛ ⎞⎜ ⎟ ⎜ ⎟
⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠= − = − =Ω
( )
DC
0.591V 0.03915.3Vr ppV
r V= = =
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Surge Current in the Capacitor-Input Filter ■ Before closing the switch, the capacitor is uncharged
►Uncharged capacitor acts as a short circuit.
■ When the switch is closed ►An initial current, called surge current, passes through the diodes D1
and D2.
■ To avoid defecting the diodes, a fuse is used. ►A fuse is a protection device.
►A slow-blow fuse is generally used.
►Slow-blow indicates a slow melting of the wire inside the fuse.
Power Supply Filters and Regulators – contd.
Fuse (source: wikipedia.org]
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Voltage Regulators ■ A regulator is connected to the output of the capacitor-input filter.
■ It maintains a constant output despite changes in the input.
■ The input of the regulator should have a ripple < 10%.
■ Percent Regulation
►Line regulation .
►Load regulation , where NL and FL refer to no load
and full load (i.e., maximum load)
Power Supply Filters and Regulators – contd.
F1
D2
D3 D1
T1
D4+ +
VoltageregulatorSW1
C2C1
Output capacitor To improve the transient response
Capacitor-input filter
OUT
IN100%V
V⎛ ⎞⎜ ⎟⎜ ⎟⎝ ⎠
Δ= Δ
NL FL
FL100%V V
V⎛ ⎞⎜ ⎟⎜ ⎟⎝ ⎠
−=
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Diode Limiter (Clipper)
■ Clips either positive or negative part
₪ Example 2-9 ■ R1 = 10 kΩ
■ RL = 100 kΩ
■ Vp(in) = 10V
Diode Limiting and Clamping Circuits
( ) ( )1
Lp out p in
L
RV VR R⎛ ⎞⎜ ⎟⎜ ⎟⎝ ⎠
= +
( ) ( )1
100k 10V 9.09V110k
Lp out p in
L
RV VR R⎛ ⎞⎜ ⎟⎜ ⎟⎝ ⎠⎛ ⎞⎜ ⎟⎜ ⎟⎝ ⎠
= +
Ω= =Ω
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Biased Limiters ■ A limiter that has a bias voltage in series with the diode.
■ The diode is forward-biased when Vp(in) exceeds the voltage bias by 0.7 V (i.e., Vp(in) = 0.7 + VBIAS). ►Since the load is connected in parallel with the diode and bias voltage
● V(out) = VBIAS +0.7 V.
■ Otherwise, the diode is reverse-biased. ►The peak output voltage is then given by:
Diode Limiting and Clamping Circuits – contd.
Vin
RL
R1
0+
–
VBIAS + 0.7 V
VBIAS
0
( ) ( )1
Lp out p in
L
RV VR R⎛ ⎞⎜ ⎟⎜ ⎟⎝ ⎠
= +
Positive limiter
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Biased Limiters – contd.
Diode Limiting and Clamping Circuits – contd.
What is the input at this point?
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Biased Limiters – contd. ■ Example 2-10
■ When VA exceeds 5.7 V ►D1 becomes forward-biased.
►V(out) equals 5.7 V.
►D2 is still reverse-biased.
■ When VA goes below -5.7V ►D2 becomes forward-biased.
►V(out) equals -5.7 V.
►D1 is still reverse-biased
■ For values between 5.7V and -5.7V ►Both diodes are reverse-biased.
►Depending on the load value, the input voltage is partitioned between R1 and the load.
Diode Limiting and Clamping Circuits – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Voltage-Divider Bias
■ VBIAS is simply given by
Diode Limiting and Clamping Circuits – contd.
VBIAS is the voltage applied to R3
3BIAS SUPPLY
3 2
RV VR R⎛ ⎞⎜ ⎟⎜ ⎟⎜ ⎟⎝ ⎠
= +
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Example 2-11
Diode Limiting and Clamping Circuits – contd.
Vin
RL
R1
0+
–
VBIAS + 0.7 V
VBIAS
0
3BIAS SUPPLY
3 2
220 12 8.25 V220 100RV VR R
⎛ ⎞⎜ ⎟⎜ ⎟⎜ ⎟⎝ ⎠
= =+= +
8.25 V
= 8.95 V
Note that there is a power supply of 12V and R2
parallel to the bias voltage. These two elements are not shown in the figure.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Diode Clampers ■ A clamper is a circuit that adds a DC level to an AC signal.
►Clampers are also referred to as DC restorers.
■ The capacitor charges and acts as a DC voltage source. ►RC time constant should be large enough to avoid discharging of the
capacitor. RC = 100 for excellent clamping action.
Diode Limiting and Clamping Circuits – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Diode Clampers ■ Example 2-12
►When the input reaches about +0.7V, the diode is forward-biased.
►The capacitor is charged up to (-(24V – 0.7) = -23.3 V)
● Consider the polarity of the capacitor!
►The diode is then reverse-biased.
►The capacitor acts as a DC voltage source (consider a negligible discharging)
►The circuit can be analyzed as if it includes an AC voltage source and a DC voltage source (The later one replaces the capacitor).
Diode Limiting and Clamping Circuits – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Voltage Doubler ■ Half-wave Doubler
►During the positive half cycle
● D1 is forward-biased, and C1 is charged to Vp less the diode drop.
● D2 is reverse-biased.
►During the negative half cycle
● D2 is forward-biased and C2 is charged by both the input and C1 which acts as a DC voltage source. C2 is charged to (2Vp –1.4 V )
● D1 is reverse-biased.
►The output is a half-wave filtered voltage.
Voltage Multipliers
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Voltage Doubler ■ Full-wave Doubler
►Class discussion
● Groups of students analyze the full-wave doubler based on the following Figures.
Voltage Multipliers
0
Vp
C1
–
++
–Vp
C2
Reverse-biased
D2
D1
0–Vp
+
–+
–
2Vp
Reverse-biased
D2
D1
+
–
+
–Vp
+
–
Vp
I
I+
–
C1
C2
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Voltage Tripler ■ 1st positive half cycle
►D1 is forward-biased.
►C1 charges to Vp – 0.7 V.
■ 1st negative half cycle ►D2 is forward-biased.
►C1 acts as a DC voltage source.
►C2 charges to 2(Vp – 0.7).
■ 2nd positive half cycle ►D3 is forward-biased.
►C1 and C2 acts as DC voltage sources.
►C3 charges to 2(Vp – 0.7).
Voltage Tripler & Quadrupler
Voltage Tripler
Voltage Quadrupler
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Explain the Operation of the Half-wave Rectifier
₪ Explain the Operation of the Full-wave Rectifier
₪ Discussions
₪ Explain the Use of Power Supply Filters and Regulators
₪ Explain Diode Limiting and Clamping Circuits
₪ Explain the Operation of the Voltage Multipliers
₪ Discussions
Summary and Discussion
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
Discussion & Notes
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