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SUDHARSAN ENGINEERING COLLEGE
ELECTRONIC CIRCUITS I
LAB MANUAL
SUB CODE: EC2208
PREPARED BY
D.RAMESH, Asst. HOD/ECE
M.KARTHIGA, Asst. Prof/ECE
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Circuit Diagram
CE Amplifier with Fixed Bias
Pin Diagram
Bottom view of BC107
B
E
C
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Ex. no: 1. COMMON EMITTER AMPLIFIER WITH FIXED BIAS
Date:
Aim
To design and construct BJT Common Emitter Amplifier using fixed bias .To measure the gain and to plot the frequency response and to determine the GainBandwidth product (GBW).
Apparatus Required
S.No Equipments / Components Range / Details Qty
1. Power Supply (030) V 1
2. Resistor 5.1K, 3M 1
3. Capacitor 1 F 1
4. Transistor BC 107 1
5. AFO (01) MHz 1
6. CRO (020) MHz 1
Fixed Bias with Emitter Resistor
The fixed bias circuit is modified by attaching an external resistor to the emitter. This resistor
introduces negative feedback that stabilizes the Q-point. From Kirchhoff's voltage law, the voltage
across the base resistor is
VRb= VCC- IeRe- Vbe
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Tabulation
VS=
Frequency (Hz) Vo (V) Gain = Vo / Vs Gain = 20log(Vo/Vs)dB
Model Graph
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From Ohm's law, the base current is
Ib= VRb/ Rb.
The way feedback controls the bias point is as follows. If Vbe is held constant and temperature
increases, emitter current increases. However, a larger Ie increases the emitter voltage Ve= IeRe,
which in turn reduces the voltage VRbacross the base resistor. A lower base-resistor voltage dropreduces the base current, which results in less collector current because Ic= IB. Collector current
and emitter current are related by Ic= Iewith 1, so increase in emitter current with temperatureis opposed, and operating point is kept stable.
Similarly, if the transistor is replaced by another, there may be a change in I C (corresponding tochange in -value, for example). By similar process as above, the change is negated and operatingpoint kept stable.
For the given circuit,
IB= (VCC- Vbe)/(RB+ (+1)RE).
Merits:
The circuit has the tendency to stabilize operating point against changes in temperature and -value.
Demerits:
In this circuit, to keep ICindependent of the following condition must be met:
which is approximately the case if ( + 1 )RE>> RB.
As -value is fixed for a given transistor, this relation can be satisfied either by keeping REverylarge, or making RBvery low.
If REis of large value, high VCCis necessary. This increases cost as well as precautionsnecessary while handling.
If RBis low, a separate low voltage supply should be used in the base circuit. Using twosupplies of different voltages is impractical.
In addition to the above, RE causes ac feedback which reduces the voltage gain of theamplifier.
Usage:The feedback also increases the input impedance of the amplifier when seen from thebase,
which can be advantageous. Due to the above disadvantages, this type of biasing circuit is used only
with careful consideration of the trade-offs involved.
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Design
Choose = 250, VCC= 12V, IC= 1 mA
By applying KVL to output side,
VCCICRCVCE= 0
VCC= ICRCVCE
Assume equal drops across RCand VCEVRC= VCE= 6V, ICRC= 6V
RC= 6V/10-3
= 6K
Choosing a standard value for RCas 5.1
By applying KVL to the input side,
VCCIBRBVBE= 0
IB= IC/ = 1mA/250 = 4A
RB = (VCCVBE) / IB
=(12 0.7)/4x10-6=2.825M 3M
Design of input capacitor
F = 1/2hieC
Take F = 100Hz and hie= 1.6 K
C1 = 1/ (2X 1.6 K X 100) = 0.9F 1F
Calculation
Bandwidth = fH- fL
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Procedure
1) Connect the circuit as per the circuit diagram2) Set Vin = 50mV in the signal generator. Keeping input voltage constant, vary thefrequency from 1Hz to 1MHzin regular steps.
3) Note down the corresponding output voltage.4) Plot the graph: Gain in dB Vs Frequency in Hz.5) Calculate the Bandwidth from the Frequency response graph
To plot the Frequency Response
1) The frequency response curve is plotted on a semi-log scale.2) The mid frequency voltage gain is divided by 2 and these points are marked in thefrequency response curve.
3)
The high frequency point is called the upper 3dB point.4) The lower frequency point is called the lower 3dB point.5) The difference between the upper 3dB point and the lower 3dB point in thefrequency scale gives the bandwidth of the amplifier.
6) From the plotted graph the bandwidth is obtained. (i.e) Bandwidth = fH- fL
Result
Thus a BJT Common Emitter Amplifier with fixed bias is designed and implemented and the
frequency response curve is plotted.
The bandwidth is found to be __________________
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Circuit Diagram
CE Amplifier with Self Bias
Design
Drop across RE(VRE) is assumed to be 1V.
Drop across VCEwith the supply of 12V is given by 12V 1V = 11V
Assume equal drops across ICRCand VCE
So ICRC= VRC= 11/2 = 5.5V
Assume IC= 1 mA,
Then RC= VRC/ IC= 5.5V / 1mA = 5.5 K
Instead of using 5.5 K , we can use a standard value of 4.7 K
VRE= 1V, IEIC= 1mA
RE= VRE/IE= 1V/1mA = 1K
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Ex. no: 2. COMMON EMITTER AMPLIFIER WITH SELF BIASDate:
Aim
To design and construct BJT Common Emitter Amplifier using voltage bias (self bias) with
and without bypassed emitter resistor.To measure the gain and to plot the frequency response and to determine the GainBandwidth product (GBW).
Apparatus Required
S.No Equipments / Components Range / Details Qty
1. Power Supply (030) V 1
2. Resistor 1K, 61K, 10K, 4.7K 1
3. Capacitor 1F 1
4. Transistor BC 107 1
5. AFO (01) MHz 1
6. CRO (020) MHz 1
Theory
Voltage divider bias (Self bias)
A combination of fixed and self-bias can be used to improve stability and at the same time
overcome some of the disadvantages of the other two biasing methods. One of the most widely
used combination-bias systems is the voltage-divider type. The voltage divider is formed using
external resistors R1and R2. The voltage across R2forward biases the emitter junction. By proper
selection of resistors R1and R2, the operating point of the transistor can be made independent of
. In this circuit, the voltage divider holds the base voltage fixed independent of base current provided the divider current is large compared to the base current. However, even with a fixed
base voltage, collector current varies with temperature (for example) so an emitter resistor is
added to stabilize the Q-point. However, to provide long-term or dc thermal stability, and at the
same time, allow minimal ac signal degeneration, the bypass capacitor (Cbp) is placed across R3.
If Cbp is large enough, rapid signal variations will not change its charge materially and no
degeneration of the signal will occur.
Merits
Unlike above circuits, only one dc supply is necessary. Operating point is almost independent of variation. Operating point stabilized against shift in temperature.
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Tabulation
Model Graph
Frequency (Hz) Vo (V) Gain = Vo / Vs Gain = 20log(Vo/Vs)dB
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Procedure
To plot the Frequency Response
The frequency response curve is plotted on a semi-log scale.
1) The mid frequency voltage gain is divided by 2 and these points are marked in thefrequency response curve.
2) The high frequency point is called the upper 3dB point.3) The lower frequency point is called the lower 3dB point.4) The difference between the upper 3dB point and the lower 3dB point in the frequency scale
gives the bandwidth of the amplifier.
5) From the plotted graph the bandwidth is obtained. (i.e) Bandwidth = fH- fL
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Design of R1and R2
Drop across VBE = 0.7V
Drop across R2(VR2) = VBE+ VRE= 1.7V
Assume R2= 10 K
VR2= VCC.R2/ (R1+R2)
R1= (12 X 10) / (1.7 10) = 60.5 K
R1is assumed to be 61 K
Design of input capacitor
F = 1/2hieC
Take F = 100Hz and hie= 1.6 K
C1 = 1/ (2X 1.6 K X 100) = 0.9F 1F
Calculation
Bandwidth = fH- fL
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Result
Thus a BJT Common Emitter Amplifier is designed and implemented and the frequency response
curve is plotted.
Bandwidth =
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Circuit diagram:
Design:
Since voltage amplification is done in the transistor amplifier circuit, we assume equal drops
across VCEand Emitter Resistance RE. VRE= 6V. The quiescent current of 1mA is assumed.
We assume a standard supply of Vcc= 12V.
Drop across REis assumed to be VRE =6V
Drop across VCEis VCCVRE =6VWe know that ICQ=IE,
Now RE= VRE = 6V = 6K
IE 1X 10-
Design of R1& R2Drop across REis 6VDrop across VBEis 0.6VDrop across the resistance R2is VR2= VBE+ VRE=6.6VAssume R2=10K
VCCR2= 6.6 V
R1+ R2
12 X 10 X 103
= 6.6V
R1+ 10 X 103
120 X 103
= R1+ 10 X 103
6.6
18.18 X 103= R1+ 10 X 10
3R1=
8 K(3.3 K + 4.7 K)
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Ex. no: 3. COMMON COLLECTOR TRANSISTOR AMPLIFIER
Date:
Aim:
1.To design and construct BJT Common Collector Amplifier using voltage divider bias (self-bias).
2. To measure the gain and to plot the frequency response & to determination of GainBandwidth Product
Apparatus required:
1.Transistors - BC107
2.Regulated Power Supply -3.Audio Frequency Oscillator
4.Resistors - 6K,8K,10K5.Capacitors - 47F
6.CRO
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Tabular column
Vs =
Model graph (frequency response)
Frequency VO Gain = VO/ VS Gain = 20 log (VO/VS)(Hz) (Volts) (dB)
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Circuit diagram:
Design:
Such a DC the ICBOof the 1st
stage is multiplied by (+1) times and this will be input Base currentfor the 2
ndstage. Hence the 2
ndstage IEcurrent will be IE= (+1)
2ICO
For silicon transistor ICBOis the order of 10nA at room temperature =100. Now,
IE= (101)2X 10 nA IE
105nA0.1mA
This current will get double with every 100rise in temperature. So to reduce the effect of ICBOthe
1st
stage ICBO
flowing through the emitter of the 1st
stage is not allowing to enter the 2nd
stage by
paralleling a resistor between B & E of the 2ndstage T2.So the ICBO(+1) will flow through thisresistance and a part of this current might flow through hie+ dcRE. This shunting resistance willbe the range of 1 to 4.7 K.
Biasing Design:
Assume R2= 10Kand Ic= 1mA.
Since voltage amplification is done in the Darlington transistor amplifier circuit, we
assume equal drops across VCEand load resistance RC. The ICQ= 1mA is assumed. We assumestandard supply of 12V.
Drop across Reis assumed to be 1V. The drop across VCEwith a supply of 1.2 V is given by
12 1 = 1V.It is equal to VRC& VCE= 5.5V RC=
VRC= 5.5 K(4.7 K)ICDesign of
R1& R2:Drop across REis 1V.Drop across VBE1&VBE2 is 0.6V.Drop across the resistance R2is VRE+ VBE1+ VBE2
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Ex. no: 4. DARLINGTON COMMON EMITTER AMPLIFIER
Date:
Aim:
1. To design a Darlington amplifier using BJT and to measure the gain and input resistance.2. To plot the frequency response and to calculate the Gain Bandwidth Product (GBW).
Apparatus required:
1.Transistors - BC 107
2.Resistors - 1K,4.7K,47K,10K (all are W)3.Capacitors - 47F, 100F4.CRO5.AFO6.RPS7.Connecting wires & Breadboard
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Tabular column:
Vs =
Frequency VO Gain = VO/ VS Gain = 20 log (VO/VS)
(Hz) (Volts) (dB)
Model graph (frequency response):
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Design continuation:
= 1 + 0.6 + 0.6 VR2= 2.2VR2is assumed to be 10 K
VCCR2
= 2.2V R1+
R2
1.2 X 10 X 103= 2.2
R1+ 10 X 103
120 X 103= R1+ 10 X 10
32.2
54.5 X 103= R1+ 10 X 10
3R1=
54.5 X 10310 X 10
3
R1= 44.5 X 103
R1is rounded to be 47 K
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Procedure:
1. Connect the circuit as per the circuit diagram.2. Set VS= 5 mV using AFO.3. Keeping the input voltage constant, vary the frequency from 0 Hz to 1 MHz in regular
steps and note down the corresponding output voltage.
4. Plot the graph gain Vs frequency.5. Calculate bandwidth from the graph.
Result:
1. The frequency response curve is plotted on a log scale.2. From the graph the bandwidth isobtained Bandwidth = fH- fL=
Specifications:
1. Transistor - BC107, 50V1A, 3W, 300 MHz
2. Regulated Power Supply (0- 30), 1A
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Circuit diagram:
Pin Details
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Ex. no: 5. COMMON DRAIN AMPLIFIERDate:
Aim:
To design a common drain amplifier and to measure the gain, input resistance and outputresistance with and without Bootstrapping.
Apparatus required:
1. Transistor - BC-107
2. Regulated Power supply - 13. Audio Frequency Oscillator - 14. Resistors - 4.7K, 2.7K, 1M5. Capacitor - 1F6. CRO7. Bread board and connecting wires
Theory:
Here input is applied between gate and source & output between source and Drain. Here Vs = VG+
VGS. When a signal is applied to JFET gate via Cin,VGvaries with the signal. As VGSis fairlyconstant and Vs varies with Vi. Here output voltage follows the change in the signal voltage appliedto the gate, the circuit is also called as Source follower
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Bias design:
VDD= 12 V, IDSS = 9.5mA, ID = 1mA, VP= -4V, Ci= 1F
VGS= IDRS ,ID = IDSS{1-(VGS/VP)}2
RS= 2.7K , Voltage drop across R S= 2.7V
RD DS DD
-RS=12-2.7=9.3V.
Assume equal drops across VRD& VDS
VRD= VDS= 4.65V
RD= VRD/ID= 4.65K
Instead of 4.65K, we can select standard value = 4.7K
FET input is always reverse bias. So choose the value of resistance RGvery large with inThe
range of 1Mto 10M
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Procedure:
1. Connect the circuit as shown in the circuit diagram2. Set Vs= 50 mv in AFO3. Keeping the input voltage constant, vary the frequency from 0 Hz to1MHz in regular
steps and note down the corresponding output voltage.
4. Plot the graph: gain Vs Frequency5. Calculate the bandwidth from the Graph
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Tabulation
VS=
Frequency (Hz) VO(V) Gain = VO/ VS Gain = 20 log(VO/VS)_ dB
Model Graph
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Result:
Thus a common drain amplifier is designed and the gain, input resistance and output resistance
are calculated using the measured parameters.
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Circuit DiagramDifferential Amplifier
Common mode Configuration
Differential mode Configuration
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Ex. no: 6. DIFFERENTIAL AMPLIFIER
Date:
Aim
To construct the Differential Amplifier in
a) Common mode andb) Differential mode, and to find the common mode rejection ratio (CMRR).
Apparatus required
1. Power Supply2. CRO3. Function Generator4.Transistors - BC107 -1 no
5.Resistors - 1K - 2 nos.470 -1 no.
Formula
C.M.R.R = Ad/Ac
C.M.R.R in dB = 20 log Ad/Ac
Ad= Differential mode gainAc = Common mode gain
Theory
The Differential amplifier amplifies the difference between two input voltage signals. Hence it is
called differential amplifier.V1 and V2 are input voltages, Vo is proportional to difference between
two input signals.
If we apply two input voltages equal in all respects then in ideal case output should be zero. But
output voltage depends on the average common level of the inputs. Such an average level of two
input signals is called common mode signal
Higher the value of C.M.R.R, better the performance of the differential amplifier. To improve
C.M.R.R we have to increase differential mode gain and decrease common mode gain
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Model Calculation
For common mode signal
Gain Ac = Vo / Vi
Ac =
For differential mode signal
Gain Ad = Vo / Vi
Ad =
CMRR = 20 log (Ad / Ac)
=
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Procedure
1. Connections are given as per the circuit diagram2. Set Vi=5mV and note down Vo in both differential mode & common mode3. Calculate the gain for both the modes4.
Calculate C.M.R.R
Formulae
For common mode signal: Gain Ac = Vo / Vi
For differential mode signal: Gain Ad = Vo / Vi
Common Mode Rejection Ratio: CMRR = 20 log (Ad / Ac)
Result
Thus a differential amplifier is constructed in both common mode and differential mode and thecorresponding gains are obtained and the CMRR is calculated.
CMRR =
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Circuit diagram:
Bias design:
Since voltage amplification is done in the transistor amplifier circuit, We as equal drops
across VCE& load resistance RE. The quiescent current of 1mA is assumed, we assume a standardsupply of 12V.
Drop across REis assumed to be 1V,the drop across VCEwith a supply of 12V is given by 12V-
1V=11V
It is equal to 11/2=5.5V
Now the voltage across the resistance REis 5.5V
VCE= 5.5V
VC= 5.5V IC=1mA
RC= 5.5V/1mA = 5.5K
Instead of using 5.5K, We can use a standard value of 4.7K. It
is assumed that RBB/ (dc+1) = RE/ 10
Hence RBB/ (dc+1) is neglected when compared RE.
Hence VBB= IERE+VBE
Hence VBEis neglected when compared to IERE
Hence IE= VBB/ RE.
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Ex. no: 7. CLASS - A AMPLIFIER
Date:
Aim
To design and construct a ClassA power amplifier.To observe the output waveform and to measure the maximum power output and to determine
the efficiency
Apparatus required:
1. Transistor - BC107 - 1
2. Resistors - 1K, 4.7K, 61K, 10K (all are W)3. Capacitors - 1f,100f(all are electrolytic)
4. CRO - (0-20MHz)
5. AFO - (0-1MHz)6. Regulated Power Supply7. Breadboard & Connecting Wires
Theory:
The Power amplifier is said to be class-A amplifier if the Q-point & the input signal are selected
such that the output signal is obtained for a full input cycle. For this, position of the Q-point is
approximately at the midpoint of the load line.
For all the values of input signal, the transistor remains in the active region &never enters into cut-
off or saturation region. When an a.c input signal is applied, the collector voltage varies
sinusoidally hence the collector current also varies sinusoidally. The collector current flows for
360(full cycle)of the input signal. In other words, the angle of the collector current flow is 360 i.e.
one full cycle.
DESIGN OF R1& R2:
Voltage drop across RE= VRE= 1V
Drop across VBE= 0.7V
Drop across the resistance R2= VBE+VRE= VR2
VR2=1.7V ; R2is assumed to be 10K
VCCR2/ (R1+ R2) = VR2
10*12K/(R1+10K)=1.7V
R1=60.5V61K
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Tabular column:
VI=
Frequency V0 Gain = V0/ Vi Gain (dB) = 20 log V0/ Vi dB(KHz) (mV)
Model graph:
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Procedure:
1. Connect the circuit as per the circuit diagram.2. Set VS=10mV using AFO.
3.Keeping the input voltage constant, vary the frequency from few Hz to 1MHz in regular steps ¬e down the correspondingly output voltage.
4. Plot the graph: gain Vs frequency.5. Calculate bandwidth from the graph.
Result:
The class-A amplifier is designed, constructed and the output waveform is observed. The maximumpower output and the efficiency are determined.
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Circuit diagram
Pin Diagram
Bottom view of BC 107 / BC 178
B
E
C
3-d view
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Ex. no: 8. CLASSB POWER AMPLIFIER
Date:
Aim:
To design and construct a Class B (complementary symmetry) power amplifier.To observe
the output waveform with crossover Distortion and to measure the maximum power output andto determine the efficiency.
Apparatus required:
1.Power Supply - (030) V2. CRO - (020) MHz3.Function Generator - (01) MHz4.Resistor - 47 K - 1No
1 K - 1No5.Transistors - BC 107 - 1No
BC 178 - 1No
Theory:
The figure illustrates a ClassB Power Amplifier, which employs one PNP, and one NPN transistorand require no transformed. This type of amplifier uses complementary symmetry. i.e., the two
transistor have identical characteristics but one is PNP and the other NPN.
Its operation can be explained by referring to the figure. When the signal voltage is positive, T1(the
NPN transistor) conducts, while T2 (the PNP transistor) is cut off. When the signal voltage is
negative, T2conducts while T1is cut off. The load current is
iL= ic1ic2
some advantages of the circuit are that the transformer less operation saves on weight and cost and
balanced pushpull input signals are not required. The disadvantage is obtaining pause of transistormatched closely enough to achieve low distortion.
Procedure:
1. Connect the circuit as per the diagram.2. Set VS= 50mV(say) using the signal generator.3. Keeping the input voltage constant, vary the frequency from 0Hz to 1MHz. Inregular steps. Note down the corresponding output voltage.4. Plot the graph i.e., gain (dB) Vs frequency (on a semilog graph)
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Model graph:
Tabular column:
VI= mV I = mA
Frequency V0 Gain = V0/ Vi Gain (dB) = 20 log V0/ Vi dB(KHz) (mV)
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Formulae
Result
Thus a ClassB (complementary symmetry) power amplifier is constructed and the
output waveforms are observed and the maximum power output and efficiency is calculated.
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Circuit diagram:
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Ex. no: 9. HALF WAVE RECTIFIER
Date:
Aim
1. To design a Half wave rectifier with simple capacitor filter.2. To measure the DC voltage under load and ripple factor and to compare with calculatedvalues.
Apparatus Required
1. CRO - (0-20 MHz)
2.Multimeter
3.Diode - 1N4007
4.Transformer - 230V / 120- 12v, 200 mA
5.Resistor - 500-1/4W(carbon film resistors)
6.Capacitor - 100F /25V
7.Connecting Wires and Bread Board
Procedure
Half wave rectifier
(i) Without Capacitor1.Test your transformer: Give 230v, 50Hz source to the primary coil of the transformer and
observe the AC waveform of rated value without any distortion at the secondary of the
transformer.
2.Connect the half wave rectifier as shown in figure.3.Measure the Vdc&Vacusing DC and AC Voltmeters.
4. Calculate the Ripple factor r = Vac/Vdc
Note:The rectifier output consists of both AC & DC components. To block DC component100f
(Electrolytic) Condenser is used.
5. Compare the theoretical ripple factor with the practical ripple factor.
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Model Graph
VI(v)
T(m sec)
Input Wave Form
Vo(V) With filter
Without filter
T(m sec)
Half Wave Rectifier Output
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(ii) With Capacitor1. Connect the half wave rectifier with filter circuit as shown in fig.2. Assume r= 10% of ripple peak-to-peak voltage for R= 500. Calculate C using theformula r = 1/23fRC3. Connect CRO across load.4. Keep the CRO switch in ground mode and observe the horizontal line and adjust it tothe X-axis.
5. Switch the CRO into DC mode and observe the waveform.
Result
Thus the Full wave rectifier is designed with and without capacitor filter and the
corresponding dc output voltages and the ripple factors are measured and verified with the
theoretical values.
Ripple Factor
Theoretical Practical
Specifications:
1. Diode 1N4007 (700V- PIV, Idc= 1A)
2. RPS (0-30),1A
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Circuit diagram:
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Ex. no: 10. FULL WAVE RECTIFIER
Date:
Aim
1. To design a Full wave rectifier with and without simple capacitor filter.2. To measure the DC voltage under load and ripple factor and to compare withcalculated
Apparatus Required
1. CRO - (0-20 MHz)
2.Multimeter -
3.Diode - 1N4007
4.Transformer - 230V / 120- 12v, 200 mA
5.Resistor - 500-1/4W(carbon film resistors)
6.Capacitor - 100F /25V
7.Connecting Wires and Bread Board
Procedure
Full wave rectifier
(i) Without Capacitor1. Test your transformer: Give 230v, 50Hz source to the primary coil of the transformerand observe the AC waveform of rated value without any distortion at the secondary of the
transformer.
2. Connect the full wave rectifier as shown in figure.3. Measure the Vdc&Vacusing DC and AC Voltmeters.4. Calculate the Ripple factorr = Vac/Vdc
Note:The rectifier output consists of both AC&DC components. To block DC component
100f (Electrolytic) Condenser is used.
5. Compare the theoretical ripple factor with the practical ripple factor.
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Model graph:
VI(v)
t (m sec)
Input Wave Form
VO(V)With filter
Without filter
t (m sec)
Full Wave Rectifier Output
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(ii) With capacitor:1. To plot ripple peak-to-peak voltage Vs. Idc to choose C a ripple factor of 0.15 isassumed.
2. To get a variable load resistance a number of 500, 5W of resistance are to beconnected in parallel. Hence Idc= Vdc/( N X 500). Where N is number of 500resistances
connected in parallel.
3. Plot the graph IdcVs ripple peak to peak.4. The above steps are repeated for the various values of capacitance.
Result
Thus the Full wave rectifier is designed with and without capacitor filter and the corresponding dc
output voltages and the ripple factors are measured and verified with the theoretical values.
Ripple Factor
Theoretical Practical
Specifications:
1. Diode 1N4007 (700V- PIV, Idc= 1A)
2 RPS (0-30) 1A