Lecture 4 ver2 diode_app
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Transcript of Lecture 4 ver2 diode_app
Chapter 2:Diode Applications (cont.)
Prepared by:Ikhwan Hafiz Muhamad
[email protected] 1, E10-C13
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 1
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
Diode Applications
1. Half-wave & full-wave rectification2. Power supply filter & regulators3. Clippers & Clampers
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 3
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
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?
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 6
Capacitor-Input Filter
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
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)
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
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
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;
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
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
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
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
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
Diode Applications
1. Half-wave & full-wave rectification2. Power supply filter & regulators3. Clippers & Clampers
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 17
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
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
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
Diode Limiters (Clippers)
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 21
Parallel Clipper
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
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
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
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.
Diode Limiters (Clippers)
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 26
Parallel Clipper with Biased LimitersAL
Matlab
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
Vin
Vout
Solution
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
Eg: Solution
Diode Limiters (Clippers)
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 31
Voltage-Divider Bias
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
Eg: Solution
33
Diode Limiters (Clippers)
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 34
Series Clipper
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
VON4ViOFF5ViOFF6ViOFF7ViOFF16
VON3VON2VON1VoDiode stateVi
+
V=4 V
Vo
-
+
-Vi
+
V=4 V
Vo
-
+
-Vi
t0 T/2
Vo16
4
Solution:• + ve region
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
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:
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
Diode Limiters (Clippers)
40
Summary of Series Clippers : Refer
Electronic Devices and Circuit Theory: International Edition, 8th
Edition (Robert L. Boylestad) page 87.
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
Diode Clampers
Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 42
Positive Clamper
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.
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
Eg: SolutionAL
Matlab
Sim
ulatio
n
Diode Clampers
46
Summary of clamping circuits : Refer
Electronic Devices and Circuit Theory: International Edition, 8th Edition (Robert L. Boylestad) page 91.
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