Lecture 4 ver2 diode_app
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Transcript of Lecture 4 ver2 diode_app
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Chapter 2:Diode Applications (cont.)
Prepared by:Ikhwan Hafiz Muhamad
[email protected] 1, E10-C13
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 1
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Recap Last Lecture
VVPIV
VV
VV
V
outp
outpAVG
poutp
7.02
2
7.02
)(
)(
(sec))(
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 2
VVPIV
VV
VVV
outp
outpAVG
poutp
7.0
2
4.1
)(
)(
(sec))(
(sec)
)(
(sec))( 7.0
p
outpAVG
poutp
VPIV
VV
VVV
HALF-WAVE RECTIFIER CENTER-TAPPED FULLWAVE RECTIFIER
BRIDGE FULL-WAVE RECTIFIER
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Diode Applications
1. Half-wave & full-wave rectification2. Power supply filter & regulators3. Clippers & Clampers
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 3
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Power Supply Filters and Regulators
• Explain and analyze the operation and characteristics of power supply filters and regulators
• Explain the purpose of a filter• Describe the capacitor-input filter• Define ripple voltage & calculate the ripple
factor• Discuss surge current & voltage regulation
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 4
Sub-Chapter Outcomes
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Power Supply Filters
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 5
• Filter is a capacitor in a power supply used to reduce the variation of the output voltage rectifier
ALDifference AC & DC?
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Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 6
Capacitor-Input Filter
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Power Supply Filters
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 7
Capacitor-Input Filter
Ripple Voltage: the small variation (undesirable) inthe capacitor voltage due to the charging &discharging of the filter capacitor
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Power Supply Filters
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 8
Capacitor-Input Filter
Full rectifier easier to filter because of the shorter time between peaks (smaller ripple)
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Power Supply Filters
DC
ppr
V
Vr )(
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 9
Capacitor-Input Filter
Ripple Factor, r, is an indication of filter effectiveness (the lower the ripple factor the better filter)
)(
)()(
2
11
1
rectpL
DC
rectpL
ppr
VCRf
V
VCRf
V
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Power Supply Filters
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 10
Capacitor-Input Filter
Answer: 0.079 @ 7.9%
Eg. Determine the ripple factor for the filtered bridge rectifier with a load as indicated in figure below
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Power Supply Filters
FSM
psurge I
VVR
4.1(sec)
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 11
Surge Current
At the instant the switch is closed, voltage is connected to the bridge and the uncharged capacitor appears as a short. Produce ISurge through D1 & D2
ISurge could destroy the diodes
RSurge used to prevent the diodes from destroy. RSurge < RL;
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Voltage Regulators
78XX OutputInput from
rectifier
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 12
Voltage Regulators Combination of capacitor-
input filter with integrated circuit voltage regulator
Operation:i. the input to the regulator
is first filtered with a capacitor to reduce the ripple to<10%
ii. The regulator reduce the ripple to a negligible amount (acceptable level)
3 terminals: input, output & reference
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Voltage Regulators
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 13
Percent Regulation – present the performance of a voltage regulator
• Line regulation specify how much change occurs in the output voltage for a given change in input voltage
Line regulation
• Load regulation specify how much change occurs in the output voltage over a certain range of load current values.
Load regulation
%100
IN
OUT
V
V
%100
FL
FLNL
V
VV
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1) A certain 7805 regulator has a measured no-load output voltage of 5.18V and a full load output of 5.15V.What is the load regulation expressed as a percentage?
2) If the no-load output voltage of a regulator is 24.8V and the full-load output is 23.9V, what is the load regulation expressed as a percentage?
14
Exercise
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Review section
1) When a 60Hz sinusoidal voltage is applied to the input of a half-wave rectifier, what is the output frequency?
2) When a 60Hz sinusoidal voltage is applied to the input of a full-wave rectifier, what is the output frequency?
3) What cause the ripple voltage on the output of a capacitor-input filter?
4) If the load resistance connected to a filtered power supply is decreased, what happens to the ripple voltage?
15
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5. A certain rectifier filter produce a dc o/p voltage of 75V with peak-to-peak ripple voltage of 0.5V. Calculate the ripple factor?
6. A certain full-wave rectifier has a peak o/p voltage of 30V. A 50uF capacitor-input filter is connected to the rectifier. Calculate the peak-to-peak ripple and the dc o/p voltage developed across a 600ohm resistance.
7. What is the percentage of ripple for the rectifier in question 6?
16
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Diode Applications
1. Half-wave & full-wave rectification2. Power supply filter & regulators3. Clippers & Clampers
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 17
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Clippers and Clampers
• Explain and analyze the operation of diode limiting & clamping circuits
• Explain the operation of diode limiters• Determine the output voltage of a biased
limiter• Explain the operation of diodes clampers
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 18
Sub-Chapter Outcomes
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Diode Limiters (Clippers)
• A diode network that have the ability to “clip” (cut short/crop) off portions of signal voltages above or below certain limits, i.e. the circuits limit the range of the output signal.
• Such a circuit may be used to;– protect the input of a CMOS logic gate against
static– eliminate amplitude noise– fabricate new waveforms from an existing
signal
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 19
Diode Limiters
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Diode Limiters (Clippers)
• 2 general of clippers:a) Series clippersb) Parallel clippers
• Parallel ClippersDiode in a branch parallel to the load.
• Series ClippersDiode is in series with the load.
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 20
Diode Limiters
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Diode Limiters (Clippers)
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 21
Parallel Clipper
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Diode Limiters (Clippers)
• Whenever the input is below 0.7V, the diode is reversed biased and appears as an open.
• The output voltage, VOUT looks like the negative part of the input, but with a magnitude determined by the voltage divider formed by R1 and RL, as follows:
• If R1 is small compared to RL, then VOUT=VIN
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 22
Parallel Clipper
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Diode Limiters (Clippers)
1. Define the input and output port2. Determine the current flow of the circuit3. Determine the applied voltage (transition
voltage) that will result in a change of state for the diode from the “off” to “on” state
4. Draw the output waveform directly below the applied voltage using the same scales
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 23
Analysis Steps for Parallel Clipper
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Example
What should you expect to see displayed on an oscilloscope connected across RL in the limiter shown above? Sketch the waveform for 2 cycles.
Noted: +Vp= +10V; R1 = 100 ohm, RL=1kohm, diode model = 1N4001
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Diode Limiters (Clippers)
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 25
Parallel Clipper with Biased Limiters
By adding a DC source to the circuit, the voltage required to forward bias the diode can be
changed.
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Diode Limiters (Clippers)
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 26
Parallel Clipper with Biased LimitersAL
Matlab
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Diode Limiting Circuits - Example
The diode is forward-biased when the output tries to go above +3.0 V. This causes the output to be limited to voltages less than +3.0 V.
What is the output voltage of positive limiter shown? Sketch the waveform
VinRL
R1
0+
–
VBIAS 0
10 V
2.3 V=
1.0 kW
100 kW3.0 V
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Vin
Vout
Solution
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Diode Limiters (Clippers)
Eg: Determine the output voltage waveform for the circuit below.
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 29
Parallel Clipper with Biased Limiters
Answer: Clipped at ±5.7V
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Eg: Solution
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Diode Limiters (Clippers)
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 31
Voltage-Divider Bias
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Diode Limiters (Clippers)
Eg: Describe the output voltage waveform for the diode limiter in Figure below.
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 32
Voltage-Divider Bias
Answer: Clipped at +8.95V
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Eg: Solution
33
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Diode Limiters (Clippers)
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 34
Series Clipper
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Example : • Determine the Vo and sketch the o/p
waveform for the below network. Assume diode is ideal.
+
V=4 V
RL
Vo
-
+
-
Vit0 T/2 T
Vi
16
-16
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VON4ViOFF5ViOFF6ViOFF7ViOFF16
VON3VON2VON1VoDiode stateVi
+
V=4 V
Vo
-
+
-Vi
+
V=4 V
Vo
-
+
-Vi
t0 T/2
Vo16
4
Solution:• + ve region
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Solution (continued):• - ve region (always ON state)
VON-4
VON-5
VON-6
VON-7
VON-16
VON-3
VON-2
VON-1VoDiode stateVi
t0 T/2
Vo16
4
TV=4 V
Vo
-
+
-Vi
+
t0 T/2
Vo16
4
T
The resulting o/p waveform
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Example : Repeat the previous example using a silicon diode with VD=0.7 V
+
V=4 V
RL
Vo
-
+
-Vi
VD=0.7 V
V
VVVi
VVVi
D
D
3.3
7.04
0
Solution:
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Solution (continued): For i/p voltages greater than 3.3 V the diode open cct and Vo=Vi.
For i/p voltages less than 3.3 V the diode short cct and the network result as;
+
V=4 V
RL
Vo
-
+
-Vi
VD=0.7 V
V
Vo
3.3
7.04
t0 T/2
Vo16
3.3
T
The resulting o/p waveform
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Diode Limiters (Clippers)
40
Summary of Series Clippers : Refer
Electronic Devices and Circuit Theory: International Edition, 8th
Edition (Robert L. Boylestad) page 87.
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Diode Clampers
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 41
• Known as DC-Restorer
• Widely use in analogue television receivers
• A clamper is a network constructed of a diode, resistor, and a capacitor that shifts a waveform to a different dc level without changing the appearance of the applied signal
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Diode Clampers
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 42
Positive Clamper
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Diode Clampers
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 43
Negative Clamper
• Note:• RC time constant should be at least ten times the period
of the input frequency.
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Diode Clampers
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 44
Negative Clamper
Eg: Determine the output voltage waveform. Assume that RC is large enough to prevent significant capacitor discharge
Answer: Vdc = -23.3V
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Eg: SolutionAL
Matlab
Sim
ulatio
n
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Diode Clampers
46
Summary of clamping circuits : Refer
Electronic Devices and Circuit Theory: International Edition, 8th Edition (Robert L. Boylestad) page 91.
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1) What component in a clamping circuit effectively acts as a battery?
2) What is the difference between a +ve limiter and a –ve limiter?
Review section