Q8. The lowest output impedance is obtained in case of BJT amplifiers for ANS. CC Configuration
Q9. Which of the following parameters is used for distinguishing between a small signal and a large-signal amplifier?
ANS. (A) Voltage gain (B) Frequency response (C) Harmonic Distortion (D)Input/output impedances Q10. Removing bypass capacitor across the emitter-leg resistor in a CE amplifier causes
(A) increase in current gain. (B) decrease in current gain. (C) increase in voltage gain. (D) decrease in voltage gain.
M.M.UNIVERSITY, SADOPUR (AMBALA) LABORATORY MANUAL PRACTICAL EXPERIMENT INSTRUCTION SHEET AIM: To study Push - Pull amplifier
EXPERIMENT NO. : ECE-209-07 ISSUE DATE : DEPTT.: ELECTRONICS AND COMMUNICATION ENGINEERING
LABORATORY : SEMESTER : III NO. OF PAGES: 04
Aim: -To study Push - Pull amplifier.
Apparatus required: - Push - Pull amplifier trainer kit and connecting lead.
Theory: -
In a push - pull power amplifier, class B is used to obtain high percentage of efficiency (the relation between taken and given). But these amplifiers suffer from the crossover distortion. It is due to keep the bias nearly cut - off point which cause to flow current in transistor in later cycle.Such class B push - pull output stage is shown in fig. where the voltages at emitters of Q3 and Q2, are pulled to ground through RE while the bias is set for 0.25Vdc just below half of required cut
–
off potential (in these transistor it is 0.6Vdc). Due to it the after zero crossing, part of input wave is not able to perform amplification and cause to produce the crossover distortion, where the cut - off bias cause to flow no current when there is no signal and quiescent current flows according to input–
output signal strength. This enables this mode of configuration to obtain low power dissipation in transistors but high power conversion called the efficiency.Circuit Diagram: -
Fig. 7.1 Circuit Diagram of push-pull amplifier Procedure: -
1. Switch on power. Observe there is no quiescent current flow through the output transistors.
2. Now connect the function generator across the input. Connect CRO as shown in fig. Apply sine wave 1Khz signal of such amplitude to Obtain 3Vpp signal across RL.
3. Observe the current in transistors and the crossover distortion at the zero crossing points.
4. Adjust input amplitude to obtain 6Vpp signal across RL. Note the quiescent current from meter. Measure voltage at collector of Q2 as Vc. Now from the observed values:
The dc power, Pdc = (Vc) x dc current ... watt The ac power, Pac = (Vo rms)2 ÷ RL ... watt Where Vo rms
= (Vo pp / 2) †√2
... V rms
The percent efficiency of amplifier, η% = (Pac / Pdc) x 100Fig. 7.2 Crossover distortion in a push-pull amplifier
Precautions: -
1. Connect the circuit properly as shown in fig7.1.
2. Set the input waveform of correct amplitude and frequency. 3. Connect the CRO to the output terminal.
4. All connection should be tight.
5. Take proper care while taking reading.
Result: -- The class B amplifier has high efficiency (about 70%) but has Crossover distortion which leads to increase in distortion particularly at low input signals.
QUESTION-ANSWER:
Q1. What is feedback in amplifiers?
Ans. The process of combining a fraction of output energy back to the input is called feedback. Q2. What is the application of negative feedback amplifier?
Ans. Negative feedback amplifier makes the circuit stable. Q3. What is voltage series feedback amplifier?
Ans. It is that amplifier in which output voltage feedback in voltage series with input Signal, resulting in an overall gain reduction.
Ans. Shift of an amplifier will change with frequency.
Q6. How does negative feedback increase bandwidth of an amplifier?
Ans. The bandwidth of an amplifier without feedback is equal to separation between 3 db frequencies f1 and f2. If A is the gain, then gain bandwidth product is A* BW. With the negative feedback the amplifier gain is reduced and since gain bandwidth product has to remain constant in both cases, so the bandwidth will increase to compensate for the reduction in gain.
Q7.How do series and shunt feedback differ from each other?
Ans. Series means feedback connecting in series with input signal while shunt means feedback connecting in shunt with input signal.
Q8. Distortion in an amplifier with negative feedback increases or decreases? Ans. Decreases
Q9. Feedback in an amplifier always helps to Ans. Control its output
Q10.When negative feedback is applied to an amplifier, its bandwidth: Ans. Increased.
M.M.UNIVERSITY, SADOPUR (AMBALA) LABORATORY MANUAL PRACTICAL EXPERIMENT INSTRUCTION SHEET AIM: To study the characteristics of Silicon Controlled Rectifier (SCR) / Thyristor. EXPERIMENT NO. : ECE-209-08 ISSUE DATE :
DEPTT.: ELECTRONICS AND COMMUNICATION ENGINEERING
LABORATORY : SEMESTER : III NO. OF PAGES: 05
Aim: -To study the characteristics of Silicon Controlled Rectifier (SCR) / Thyristor. Apparatus:- NV6530 SCR Characteristic Trainer, 2mm Patch cords
Theory: -
The Silicon Controlled Rectifier (SCR) is a semiconductor device that is a member of a family of control devices known as Thyristors. The SCR has become the work house of the industrial control industry. Its evolution over the year has yielded a device that is less expensive, more reliable and smaller in size than ever before. Typical applications include: DC motor control, generator field regulation, variable frequency drive
(VFD) DC bus voltage control solid state Relays and lighting system control.
The SCR is a three
–
lead device with an anode and a cathode (us with a Standard diode) plus a third control lead or gate. As the name implies, it is a Rectifier which can be controlled–
or more correctly one that can be triggeredto the “ON” state by applyin
g a small positive voltage (VTM) to the gate lead. Once gated ON, the trigger signal may be removed and the SCR will remain conducting as long as current flows through the device. The load to be controlled by the SCR is normally placed in the anode circuit.Commutation:-
For the SCR to turn OFF current flow through the device must be interrupted, or drop below the maximum holding current(IH) , for a short period of time (typically 10-20 microseconds) which is known as the commutated turn
–
off time (tq). When applied to alternating current circuits or pulsating DC system, the deviceWhen used in VFD's or inverters, SCRs are electronically forced OFF using additional Commutating circuitry, Such as smaller SCRs and Capacitors, which momentarily apply an opposing reverse bias voltage across the SCR(This is complicated everything has to be exactly right).
Basic three modes of operation of SCR:
1. Reverse blocking mode
Cathode is positive with respect to anode with gate open.SCR is in reverse bias i.e., junction J1 & J3 in reverse bias J2 is in forward bias. The device act as two PN diode connected in series with reverse voltage applied
across it. Small leakage current of the order of a few mill ampere or microampere flows; this is off state of SCR. If reverse voltage increases, then at critical breakdown level or reverse breakdown voltage (VBR) an avalanche occurs at J1 & J3 & reverse current increase rapidly, so more loss in SCR. This may lead to SCR damage because Junction temperature is increasing. Maximum working reverse voltage across SCR does not exceed
VBR. If applied reverse voltage across SCR < VBR, then the device offers high impedance in reverse direction. SCR is treated as open switch.
2. Forward blocking mode (off state mode)
Anode is positive with respect to cathode with gate open. SCR is forward bias, junction J1 & J3 is forward bias and J2 is reverse bias. Here small forward leakage current flow. If forward voltage increases then J2 junction (rev. bias) will have avalanche breakdown called forward break over voltage (VBO) Maximum working forward voltage across SCR does not exceed VBO. If forward voltage <VBO; SCR offers high impedance. Hence SCR is treated as open switch even though it is forward blocking mode.
3. Forward conduction mode (on state mode)
If we want to bring SCR from forward blocking mode to forward conduction mode there are two modes: By exceeding the forward break over voltage (VBO). By applying gate pulse between gate and cathode. Then SCR is in on state and behave as closed switch.
Procedure:-
1. Connect terminal1 to terminal 4, terminal 2 to terminal 8 and terminal 3 to terminal 12 as shown in figure.
2. Connect Voltmeter across terminal 7 and 8 and Ammeter across terminal and 10 as shown in figure. 3. Make short terminals 5 and 6.
4. Rotate the knob P1 and P2 fully in counter clockwise. 5.
Switch “ON” the power supply.
6. Set the value of Anode Voltage at 35V by using the knob P1.
7. Now Increases gate current Ig gradually by varying knob P2 and observe it.
8. At certain value of gate current, voltmeter reading falls down to almost zero. This action indicates the firing of SCR.
9. Note the gate current value at this position (firing of SCR).
10. Keep the gate current constant by shorting terminal 9 with 10 and connect ammeter to the terminal 5 and 6.
11. Rotate the potentiometer P1 fully in counter clockwise.
12. Rotate knob P1 (from initial position to its maximum limit) gradually and record Anode current for respective value of anode voltages.
13. Plot the graph between anode voltage Va and anode current Ia.
Observations:
Table 8.1 Observation Table S.NO. ANODE VOLTAGE
(Va)
ANODE CURRENT (Ia)
GATE CURRENT CONSTANT (Ig)= ----mA
Precautions:
(1)Always connect the voltmeter in parallel & ammeter in series as shown in fig. (2)Connection should be proper & tight.
(3)Switch „ON‟ the supply after completing the ckt.
(4)DC supply should be increased slowly in steps.
(5)Reading of voltmeter & Ammeter should be accurate.
Fig. 8.1 Static I-V characteristics of a thyristor
Result: -- The graph has been plotted between voltage and current.
QUESTION-ANSWER: Q.1 Define SCR?
ANS. It is a controlled rectifier constructed of a silicon material with third terminal for control purpose. Q.2 Define Forward Break over Voltage?
Q.3 Define reverse Break down Voltage?
ANS. If reverse voltage is increased beyond certain value, SCR will break & this voltage is Called reverse breakdown voltage.
Q.4 Why it is called controlled rectifier?
ANS. Because its operation as rectifier can be con trolled by using gate terminal. Q.5 Define peak forward Voltage?
ANS. It is limiting positive anode voltage above which SCR get damaged. Q.6 Define peak reverse Voltage?
ANS. Max. reverse voltage that can be applied to SCR without conduction in reverse direction. Q.7 Define Holding Current?
ANS. Min. forward current that must be maintained to keep SCR in conducting state. Q.8 Define forward current Rating?
ANS. The max. Value of anode current that SCR con handle safely. Q. 9 Define latching current.
ANS. Min. device current which must be attained by the device before gate drive is removed. Q.10 What do you mean by commutation process?
M.M.UNIVERSITY, SADOPUR (AMBALA) LABORATORY MANUAL PRACTICAL EXPERIMENT INSTRUCTION SHEET AIM: To study Active filter.
EXPERIMENT NO. : ECE-209-09 ISSUE DATE : DEPTT.: ELECTRONICS AND COMMUNICATION ENGINEERING
LABORATORY : SEMESTER : III NO. OF PAGES: 04
Aim: -To study Active filter.
Apparatus:- NV6504 Active filter kit, Oscilloscope, Digital Multimeter. Theory: -
Active Filters: An active filter is a type of analog electronic filter, distinguished by the use of one or more active components i.e. voltage amplifiers or buffer amplifiers. Typically this will be a vacuu m tube, transistor or operational amplifier. There are two principal reasons for the use of active filters. The first is that the Amplifier powering the filter can be used to shape the filter's response, e.g., how quickly and how steeply it moves from
its pass band into its stop band. (To do this passively, one must use inductors, which tend to pick up surrounding. Electromagnetic signals and are often quite physically large.) The second is that The amplifier powering the filter can be used to buffer the filter from the electronic components it drives. This is often
necessary so that they do not affect the filter's actions. Low Pass Filters:
A Low-Pass Filter is a filter that passes low frequency signals but attenuates (Reduces the amplitude of) signals with frequencies higher than the cutoff frequency.
High Pass Filter:
A high-pass filter is a filter that passes high frequencies but attenuates (or reduces) frequencies lower than the cutoff frequency.
Band Pass Filter:
A band-pass filter is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range
Narrow Band-Reject Filter:
The narrow band-reject, often called the notch-filter, The most commonly used notch filter is the twin-T network.
Procedure:
1. Initially rotate potentiometers R1 and R fin fully clockwise direction in order to make R1 = Rf = 10K, so that
according to the formula given below:
Vo = (1+R f /R 1) Vin,
The gain of the output will be twice of the input.
2.Connect an Ohmmeter between TP4 and TP7 (Gnd) Adjust resistance value to 15.9K by varying the potentiometer 22K of High Pass Filter to set the Low
Cutoff frequency (fL) at 1K.
3.Connect Ohmmeter between Vin of Low Pass Filter and TP6. Adjust resistance value to 1.59K by varying the potentiometer 22K of High Pass Filter to set the Low cutoff frequency (fL) at 10K.
4. at their indicated position from
Power Supply section.
5.
Switch „On‟ the Power Supply.
6.Set the output of function generator at 2 Volt, 100 Hz using Oscilloscope with sinusoidal waveform.
7.Connect TP1 with Vin of Filter to give a sinusoidal signal of amplitude 2 Vpp of frequency 100 Hz. 8.Observe output on Oscilloscope.
9.Similarly you can give the triangular and square wave instead of sinusoidal wave, from the function generator section.
10. Increase the frequency of input signal step by step and observe the effect on output Vout on Oscilloscope.
Circuit Diagram: -
Observation Table:-
Precautions: -
1. Connect the circuit properly as shown in fig.
2. Set the input waveform of correct amplitude and frequency.
3. Connect the CRO to the output terminal. 4. All connection should be tight.
5. Take proper care while taking reading.
QUESTION-ANSWER: Q.1 Define Low Pass Filter?
ANS. The low pass filter allows all frequencies up to the specified cut-off frequency to pass through it & attenuates all the other frequencies above the cut-off frequencies.
Q.2 Define cut-off frequency?
ANS. It demarcates the pass band & the stop band. Q.3 What is the freq. Range of Pass Band?
ANS. The frequency range of pass band is from 0 to fc. Q.4 What is the freq. Range of Stop Band?
ANS. The frequency range of stop band is from fc to
∞
. Q.5 What are the units of attenuation?ANS. Decibles (dB) & Nepers. Q.6 Define Band Pass Filter?
ANS. It is a combination of two parallel tuned circuits Q.7 Define Attenuators?
ANS. An attenuator is a two-port resistive network & its propagation function is real Q.8 Define Neper .
ANS. t is defined as the natural logarithm of the ratio of input voltage (or current) to the output voltage (or current) provided that the network is terminated in its characteristic impedance Z0.
Q. 9 Is filter a resistive or reactive network ANS. Reactive network
Q.10 Where filter circuits are used?
M.M.UNIVERSITY, SADOPUR (AMBALA) LABORATORY MANUAL PRACTICAL EXPERIMENT INSTRUCTION SHEET AIM: Measurement and Study of Solar cell I-V characteristics.
EXPERIMENT NO. : ECE-209-10 ISSUE DATE : DEPTT.: ELECTRONICS AND COMMUNICATION ENGINEERING
LABORATORY : SEMESTER : III NO. OF PAGES: 04
Aim: -Measurement and Study of Solar cell I-V characteristics.
Equipments Needed:
1. NV6005 Solar cell kit 2. Patch cord
3.Digital Multimeter
Theory: -
Photovoltaic systems convert sunlight directly into electrical energy.
1) Cover glass : The cover glass, made of glass or other clear material such clear plastic, seals the cell from the external environment.
thickness, this layer serves to guide light into the PV Cell. Without this layer, much of the light would bounce off the surface of the cell.
3) Contact Grid : The contact grid is made of a good conductor, such as a metal, and it serves as a collector of electrons.
4) N-Type Silicon : N-type silicon is created by doping (contaminating) the Si with compounds that contain one more valance electrons than Si does, such as with either Phosphorus or Arsenic. Since only four electrons are required to bond with the four adjacent silicon atoms, the fifth valance electron is available for conduction.
5) P-Type Silicon : P-type silicon is created by doping with compounds containing one less valance electrons than Si does, such as with Boron. When silicon (four valance electrons) is doped with atoms that have one less valance electrons (three valance electrons), only three electrons are available for bonding with four adjacent silicon atoms, therefore an incomplete bond (hole) exists which can attract an electron from a nearby atom. Filling one hole creates another hole in a different Si atom. This movement of holes is available for conduction.
F. Back Contact :
The back contact, made out of a metal, covers the entire back surface and acts as a conductor.
Procedure:
1.Take the Solar Energy Trainer NV6005 along with Solar Panel.
2. Place the solar panel in the stand and adjust the panel at an angle of about 45º with the ground. Direct the sunlight straight at the solar panel (angle of 90º).
Note : If sunlight is not properly available then any source of light like lamp can be used.
3. With the DB15 connector connect the Solar Energy Trainer NV6005 with Solar Panel. Then wait for 1 minute to avoid errors due to temperature fluctuations.
b. Connect other end of potentiometer i.e. P2 to positive terminal of ammeter. c. Connect negative terminal of ammeter to negative terminal of solar cell.
d. Now connect the positive terminal of voltmeter to P1 and negative terminal of voltmeter to P2. 6.Record the values of corresponding voltage and current into the Observation Table.
7. Now gradually move the potentiometer in anti- clockwise direction so that the resistance of the potentiometer decreases. Now measure the resistances at successively smaller values and record the corresponding values of voltages and current into the Observation Table below.
8. Plot the I- V characteristics from the measurements recorded in the table, to show how the photoelectric current depends on the photoelectric voltage.
Circuit Diagram: -
Observation Table:-
Precautions:
(1)Always connect the voltmeter in parallel & ammeter in series as shown in fig. (2)Connection should be proper & tight.