power electronics lab manual

POWER ELECTRONICS LAB MANUAL

ASAD NAEEM 2006‐RCET‐EE‐22

LIST OF EXPERIMENTS

EXP# TITLE PAGE# 01

Determination of the Form Factor of Diode

02

02 To demonstrate the use of a semi conductor diode as a half wave rectifier

05

03

To demonstrate the working of full‐wave bridge rectifier

07

04

To demonstrate the waveforms of a thyristor (DIAC) by applying a pulse at its gate

09

05 To study the Triac

13

06

To Study the Pulse Bridge connections of thyristors on resistive/inductive LOAD

16

07

To Study the Pulse Bridge connections of thyristors on

motor load

19

08

To design a simple series VOLTAGE REGULATOR

22

09

Design of an improved variable output series VOLTAGE REGULATOR and plot the graphs between:

• Load current and output voltage • Input voltage and output voltage

26

10 To study IC Regulator LM317 31 11

Power flow control using DIAC and TRIAC

34

12 Power flow control using SCR and DIAC

38

13 To design a variable VOLTAGE REGULATOR using Op‐Amp with over current protection

41

14 To design a variable VOLTAGE REGULATOR using Op‐Amp with fold back current limiter protection

45



Experiment #01

Determination of the Form Factor of Diode

Apparatus:

• Supply • Diode • Resistive Load • Ammeter • Oscilloscope • Connecting Leads • Multimeter

Circuit Diagram:

Theory:

A diode is a specialized electronic component with two electrodes called the anode and the cathode. Most diodes are made with semiconductor materials such as silicon, germanium, or selenium. Some diodes are comprised of metal electrodes in a chamber evacuated or filled with a pure elemental gas at low pressure. Diodes can be used as rectifiers, signal limiters, voltage regulators, switches, signal modulators, signal mixers, signal demodulators, and oscillators.



Form Factor:

Form factor is defined as the ratio of Rms value to the average value and it represents the multiplying factor or scaling factor for a device when its input need to changed from DC to AC.

V-I Characteristics:

A semiconductor diode’s current–voltage characteristic, or I–V curve, is related to the transport of carriers through the so-called depletion layer or depletion region that exists at the p-n junction between differing semiconductors..

Following Figure shows the characteristics of a P-N junction diode (not to scale).



Procedure:

Connect the Circuit Diagram as shown in the figure. With regards to metrology, the arithmetic mean of the diode conducting state current must be distinguish form its root mean square value. Form Factor F Represents the ratio of root mean square value and arithmetic mean value of current.

F = Irms / Iavg

Where

Irms = Root mean square value of the conducting current.

Iavg = Average value of the conducting state current.

Observations and Calculations:

Irms = 0.12 A

Iavg = 0.09 A

Form Factor = 1.34



Experiment #02

To demonstrate the use of a semi conductor diode as a half wave rectifier

Apparatus:

• Bread board • Oscilloscope • Voltage Supply • Resistance • Diode • Connecting wires

Circuit Diagram:

Theory:

Rectifier:

A rectifier is an electrical device that converts alternating current (AC) to direct current (DC), a process known as rectification.

Half-wave rectification: In half wave rectification, either the positive or negative half of the AC wave is passed, while the other half is blocked. Because only one half of the input waveform reaches the output, it is very inefficient if used for power transfer. Half-wave rectification can



be achieved with a single diode in a one-phase supply, or with three diodes in a three-phase supply. Working principle of Half-wave rectifier: When the sinusoidal wave is going positive the diode will conduct but in the negative half of the cycle it will block the current flow so the result wave form will be only the positive half that will be available for half the period of the cycle the other half will be 0 Volt. PROCEDURE:

• Connect the circuit as shown in the diagram. • Calibrate the oscilloscope • Apply the input voltage • observe the input and output waveforms on the screen of

oscilloscope

Observations:



Experiment #03

To demonstrate the working of full-wave bridge rectifier

Apparatus:

• Experimental panel • Oscilloscope • Voltage Supply • Resistors • Diodes • Connecting wires

Circuit Diagram:

Theory:

Rectifier:

A rectifier is an electrical device that converts alternating current (AC) to direct current (DC), a process known as rectification.

FULL-wave rectification: A full-wave rectifier converts the whole of the input waveform to one of constant polarity (positive or negative) at its output. Full-



wave rectification converts both polarities of the input waveform to DC (direct current), and is more efficient. Working principle of FULL-wave rectifier: During the positive half cycle the diode D1 & D2 are in forward biased condition, they conduct the current. The other diodes are in the reverse biased condition that is why they will not conduct the current. During the negative half cycle the diode D3 & D4 are in forward biased condition, they conduct the current. The other diodes are in the reverse biased condition that is why they will not conduct the current. PROCEDURE:

• Connect the circuit as shown in the diagram. • Calibrate the oscilloscope • Apply the input voltage • observe the input and output waveforms on the screen of

oscilloscope

Observations:



Experiment #04

To demonstrate the waveforms of a thyristor (DIAC) by applying a pulse at its gate

Apparatus:

• Experimental panel • Oscilloscope • Voltage Supply • Resistors • Thyristor • Connecting leads

Circuit Diagram:

Theory:

THYRISTOR:

The thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as bi-stable switches, conducting when their gate receives a current pulse, and continue to conduct for as long as they are forward biased

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Observations:



Experiment#05

To study the Triac Apparatus:

• Trainer • Resistive Load • Triac • Connecting leads • Power Supply • Oscilloscope • Multimeter

Circuit Diagram:

Theory:

SCRs are unidirectional (one-way) current devices, making them useful for controlling DC only. If two SCRs are joined in back-to-back parallel fashion just like two Shockley diodes were joined together to form a DIAC, we have a new device known as the TRIAC:

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Procedure:

Connect the circuit as shown in the figure on the trainer. Pulse is provided to the gate of triac by the triggering circuit of trainer. Change the triggering angle ‘a’ with the help of knob and observe the waveform of output on the oscilloscope.

Observations & Calculations:



EXPERIMENT NO: 06

To Study the Pulse Bridge connections of thyristors on resistive/inductive LOAD

AppAratus:

• Power Supply • Voltmeter • Resistive/Inductive Load • Oscilloscope • Thyristor • Connecting leads

Circuit Diagram:

Theory:

Firing or triggering a thyristor means to apply a positive voltage at the gate (between its gate and cathode).

Firing Angle:

The angle at which the voltage across the gate is applied is called the firing angle.



(a) Resistive Load:

Figure shows a single ideal thyristor supplying a resistive load. The thyristor is being turned ON after a delay of quarter a cycle after the voltage zero. In the case of RESISTIVE load, the load current follows exactly the load voltage.

(b) Inductive Load:

Now the thyristor supplies an INDUCTIVE load and again thyristor is being turned ON after a delay of about a quarter of cycle after the voltage is zero. In this case the load voltage VL is made up of two components, the voltage across the inductor Vi and Vr and the current through the thyristor has an initial value of zero. The conduction period for the fully controlled bridge is π and that of a half controlled bridge is (π-α) as a result of the action of the commutating diode. The effect of commutating diode on the operation of the half controlled bridge is clearly seen from the output voltage and current waveforms. The respective load voltages ignoring diode and thyristor forward voltage drops are:

For Fully controlled bridge,

For half-controlled bridge,



As the direction of the current through the thyristor doesn’t reverse, the effect is to transfer power from DC-system to AC-system in which case the converter is operating in inverting mode.

Procedure:

• Connect the circuit as shown in the circuit diagram • Connect the gate pulse generator and cathode to each

thyristor separately • Vary the firing angle of thyristors from zero to 90 degrees

and observe the variation in the output waveform for both resistive and inductive load individually

• Now vary the firing angle of thyristors from zero to 180 degrees and observe the variation in the output waveform for both resistive and inductive load individually

• Compare the waveforms for resistive and inductive load

WAVEFORMS:



EXPERIMENT NO: 07

To Study the Pulse Bridge connections of thyristors on motor load

AppAratus:

• Power Supply • Resistance • Motor Load • Oscilloscope • Thyristors • Commutating Diode • Connecting leads

Circuit Diagram:

Theory:

Firing or triggering a thyristor means to apply a positive voltage at the gate (between its gate and cathode).



Firing Angle:

The angle at which the voltage across the gate is applied is called the firing angle.

Motor Load:

We have two methods for controlling the speed of a DC motor namely current controlled and voltage controlled method. The speed of motor is inversely proportional to the field current. However speed of motor is directly proportional to the applied voltage. By varying the applied voltage the speed can be varied from a maximum value to rest. If the applied voltage is equal to zero, torque produced in the motor will be equal to zero, thus causing the motor to stop.

By a controlled rectifier, we can vary the voltage input to the motor. The applied voltage will be maximum when the thyristors are triggered at an angle equal to zero degree and it will be zero for a firing angle of 180 degrees. The area under the curve of the rectified voltage reduces with the increasing firing angle thus decreasing the average or DC output.

Procedure:

• Connect the circuit as shown in the circuit diagram • Vary the firing angle of thyristors from zero to 90 degrees

and observe the speed variation for the motor which will be decreasing with increasing firing angle

• Now vary the firing angle of thyristors from zero to 180 degrees and observe the speed variation for the motor which will be decreasing with increasing firing angle



• Observe that the motor will become at rest at a firing angle of 180 degrees

• This is because the average value of input becomes zero at the firing angle of 180 degrees

OBSERVATIONS:

FIRING ANGLE

WAVEFORM SPEED

0

MAXIMUM

90

DECREASING

180

STOP



EXPRIMENT NO: 08

To design a simple series VOLTAGE REGULATOR

AppAratus:

• Transistor D313 • Zener diode • Resistance of 120Ω • Variable resistor • Power Supply

Circuit Diagram:

THEORY:

Simple series voltage regulator:

Adding an emitter follower stage to the simple zener regulator forms a simple series voltage regulator and substantially improves the regulation of the circuit. Here, the load current IR2 is supplied by the transistor whose base is now connected to the zener diode. Thus the transistor's base current (IB) forms the



load current for the zener diode and is much smaller than the current through R2. This regulator is classified as "series" because the regulating element, viz., the transistor, appears in series with the load. R1 sets the zener current (IZ).

Circuit Design:

Given a particular value of VIN, Vout and IL select VZ using equations:

Vout=Vz-VBE

Where

VBE=0.7 V(Si) & 0.3 V(Ge)

Select Q1capable of sustaining a continuous load current of 1A or above.

From the datasheet of selected transistor, get the value of Beta that is hFE and calculate base current IB, using relation:

IB=IE /β=IL / β

Select a suitable power rating for Zener diode (typically commercially available values are 0.25W,0.5W,1W)

Calculate:

Iz.max=PZ / VZ

Calculate value of R1 using the relations:



IZt=Iz.max/2 IR1=Izt+IB

R1= (Vin(min)-Vt2)/IR1

Where

IR1=current flowing through R1 Vin(min)=minimum value of applied input voltage

Calculations for No-Load:

INPUT VOLTAGE NO LOAD OUTPUT VOLTAGE 0 0 5 5.2 12 11.9

12.5 12 13 12.08 14 12.15 15 12.2

17.6 12.7 NO LOAD INPUT OUTPUT RELATION:

0 2 4 6 8 10 12 14 16 18

0

2

4

6

8

10

12

14

INPUT VOLTAGE

NO

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Calculations with Load connected:

OUTPUT CURRENT (mA)

OUTPUT VOLTAGE (Volts)

RL

(KΩ) 4.3 11.5 2.67 7.0 11.5 1.6 10.6 11.46 1.08 13 11.44 0.88

15.7 11.41 0.72 16.9 11.40 0.67

LOAD CURRENT AND VOLTAGE RELATION:

4 6 8 10 12 14 16 1811.4

11.41

11.42

11.43

11.44

11.45

11.46

11.47

11.48

11.49

11.5

OUTPUT CURRENT

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EXPRIMENT NO: 09

Design of an improved variable output series VOLTAGE REGULATOR and plot the graphs between:

• Load current and output voltage • Input voltage and output voltage

AppAratus:

• NPN Transistor D313 • NPN Transistor 2N3904 • Zener diode • Variable Resistance • Resistances • Power Supply • Multimeter

Circuit Diagram:



Circuit Design:

Given a particular value of VIN, Vout and IL select Q1 that is capable of sustaining a continuous load current of 1A or above.

Select Q2 NPN transistor having large value of β.

Select an appropriate Zener diode voltage VZ ranging from 5-12Volts.

Find V2 using the relation:

V2=Vz+VBE2

Where

VBE=0.7V (Si) VBE=0.3V (Ge)

Select an appropriate value of R1 such that IR1 acts as a negligible load to the control element Q1 while IR1 should be such that Iz can be biased easily without affecting the voltage divider network consisting of R1 and R2.

Then calculate R2 by using the relation:

V2=R2*V0/ (R1+R2)

Select IR1>5mA and Iz=1mA

Select VCE2 as 1/2 VIN for linear operation and choose a safe value for IC2. For Q2 mentioned in the suggested components, 5mA to 10mA is a safe value.

Calculate R4 using familiar relation:

VCE2=VCC-ICR4



If designed value for R4 is not standard then round the value of R4 to the next lower standard value and recalculate the collector current IC2.

Using IC2, calculate IB2

IB=IC/β

Calculate value of R3 using the relation:

IR3=IZ-IB2

R3=VBE2/IR3

Decrease R1 and R2 by equal proportion and use a variable resistor of equal to the sum of decrease in R1 and R2.


VIN (VOLTS) VOUT (VOLTS) 10 9.12 12 11.20 14 13.00 15 13.16 16 13.20 17 13.26 18 13.30 19 13.32 20 13.36




IL (mA) VOUT (VOLTS) R2(Ohms) 7.5 15.14 2018 15 15.12 1008 30 15.09 503 45.45 15.09 331.5 75 15.01 200.13 125 14.91 191.28 250 14.93 59.78

LOAD CURRENT AND OUTPUT VOLTAGE RELATION:

0 50 100 150 200 25014.9

14.95

15

15.05

15.1

15.15

LOAD CURRENT

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INPUT OUTPUT VOLTAGE RELATION:

10 11 12 13 14 15 16 17 18 19 209

9.5

10

10.5

11

11.5

12

12.5

13

13.5

INPUT VOLTAGE

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Experiment# 10

To study IC Regulator LM317 Apparatus:

• LM 317 • Resistances(R1=470Ω,R2=5KΩ(variable),R3=2.5KΩ) • Diode • Capacitors(C1=0.12 µF,C2=10 µF,C3=1µF) • Power Supply • Multimeter • Bread board • Connecting wires

Circuit Diagram:

Theory:

LM317 REGULATOR:

The LM317 series of adjustable 3-terminal positive voltage regulators is capable of supplying in excess of 1.5A over a 1.2V to 37V output range. They are exceptionally easy to use and



require only two external resistors to set the output voltage. Further, both line and load regulation is better than standard fixed regulators.

Procedure:

• Connect the circuit as shown in the figure on the bread board • Apply the input voltage through power supply and connect the

multimeter to take output voltage values • Vary the input voltage • Note the respective output voltage • Now, vary the adjustable resistor to get required output

voltage for regulation • Take the output voltage readings by changing the input

voltage keeping adjustable resistor fixed • Verify that the output is regulated at required output voltage

Observations & Calculations:

With Radj=0 (minimum value)

Vin Vout 0 0.1 1 0.5 2 1.4 3 2.3 4 3.3 6 5.2 7 6.1 8 7.1 9 7.5 11 7.5 13 7.5 15 7.5



With Radj=2.84KΩ (required value taking Vout=15Volts)

Vin Vout 12 11.03 13 11.94 14 12.95 15 13.90 16 14.87 17 14.96 19 14.96 21 14.96 25 14.96

COMMENTS:

• LM317 is a variable output voltage regulator • We can regulate the output voltage at any required value by

varying the adjustable resistor • Diode is attached to provide the discharging path for C3 • C2 is connected to improve transient response • C1 is also used to improve transient response



EXPRIMENT NO: 11

Power flow control using DIAC and TRIAC

AppAratus:

• DIAC • TRIAC • Capacitor • Variable Resistance • Resistances • Power Supply • Oscilloscope

Circuit Diagram:

THEORY:

The TRIC is triggered by positive gate current when A1 is negative with respect to A2.



A DIAC is connected between the gate and an RC circuit.

When the capacitor voltage rises far enough to overcome the sum of break power voltage of the DIAC and the forward drop of the gate, the DIAC fires, and the capacitor discharges rapidly into the gate, and the TRIAC is triggered into conduction.

Since RP controls the time constant at which the capacitor charges, it is used to control the firing angle θF.

Large values of RP delay the charging and therefore increase the firing angle.

When A1 is negative with respect to A2, the polarities of all voltages are reversed and TRIAC is triggered into conduction during a portion of VE ½ cycles.

The firing angle can be adjusted in practical circuits from 0 to 180.

So load current can be made to flow for nearly an entire cycle of input for a very small portion of input cycle.

The load resistance used must be a power resistor because due to excessive current low power rating resistor may be destroyed. This type of dimmer is best suited for resistive loads only.

There is a spike voltage associated with each TRIAC turn off.

With inductive load connected, the turn on time of the TRIAC increases.

With inductive load connected a full sine wave is achieved even before firing angle becomes zero.

This happens when the firing angle and turn off delay of the TRIAC coincide.



PROCEDURE:

The design procedure of this experiment includes the values of R1, R2 and C1 such that the capacitor voltage during each cycle reaches a point to trigger the DIAC which will then trigger the TRIAC. The commercially available DIAC has a typical break over voltage of 32V. Hence when the DIAC fires in each half cycle it will allow the capacitor to discharge up to 1/3 of the capacitor voltage in this case 32V the DIAC will trigger and then TRIAC will trigger. The same process will repeated in reverse direction.

The capacitor selected must not be of very small value so that the proper triggering may not be possible due to low energy storage and hence low power gate spike for the thyristor. The value of capacitor should be such that the maximum value of current through resistor connected in series with the capacitor is within the safe limits. The power must not exceed the rating of the variable resistor. Typically used values of capacitor are up to 1µF for supply voltages>40V. A lower value than this upper limit results in better design. R2 is used to protect accidental application of full supply voltage across the capacitor which can be damaged due to excessive current.

Connect the circuit as shown in the circuit diagram. Then vary the value of RVAR to change the time constant of the capacitor which in turn will vary the firing angle of TRIAC. Then draw the waveforms.



OBSERVATIONS:



EXPRIMENT NO: 12

Power flow control using SCR and DIAC

AppAratus:

• DIAC • Thyristor(BT-151) • Capacitor(0.1µF) • Diode • Variable Resistance (100KΩ) • Resistance (330Ω) • Power Supply • Oscilloscope

Circuit Diagram:

DESIGN PROCEDURE:

The time constant is given as:



T=RC

Where

T=1/f

And

f=50Hz

Therefore,

T=1/50=20msec

Since only one half cycle is used, so

T=10msec

Taking some suitable value of ‘C’, the value of ‘R’ can be calculated using T=RC.

Assume some value of resistance RL must be used to avoid burning due to high value of current.

A 100 ohms resistance is connected in series with capacitor in its discharging path to limit the gate current.

The diode in series with the DIAC is used to limit the reverse bias voltage at the gate terminals during negative half cycles.

PROCEDURE:

• Connect the circuit as shown in the circuit diagram • Apply the input voltage source • Observe the output waveform • Vary the firing angle • Draw the output waveforms for different values of firing

angle



OBSERVATIONS:

For resistive load:

For inductive load:



EXPRIMENT NO: 13

To design a variable VOLTAGE REGULATOR using Op-Amp with over current protection

AppAratus:

• NPN Transistor D313 • NPN Transistor 3904 • Zener diode • Op-Amp 741 • Variable Resistance • Resistances

(R1=83KΩ,R2=130KΩ,R3=47KΩ,R4=820Ω,RL=24Ω, RSC=1.4Ω)

• Power Supply • Multimeter

Circuit Diagram:



Circuit Design:

Given a particular value of VIN, Vout and IL, select Q1 that is capable of sustaining a continuous load current of 1A or above.

Select Q2 NPN transistor having large value of β.

Select an appropriate Zener diode voltage VZ ranging from 5-12Volts.

Calculate:

Iz, max=PZ/VZ

Calculate value of R4 using the relation:

IZt=IZ, max/2 IR4=IZt +IB

R4= (VIN(min)-VZ)/IR4

Where:

VIN(min)=Minimum value of applied input voltage

IB =Bias current of Op-Amp (500nA for 741)

IR4=Current flowing through resistor R4

Select an appropriate value of R1 such that IR1 acts as a negligible load to the control element Q1.

Then calculate R2 by using the relation:

VO= (1+R1/R2)/VZ

Decrease R1 and R2 by equal proportion and use a variable resistor of equal to the sum of decrease in R1 and R2.

Given a maximum safe value of IL, calculate RSC using relation:



RSC=VBE2/IL(max)

Design for RL:

RL=VL/IL

Power rating for RL=VL*IL


VIN (VOLTS) VOUT (VOLTS) 15 11.5 16 11 17 11 18 11.3 19 11.3 20 11.1


IL (mA) VOUT (VOLTS) R2(Ohms) 0.288 11.1 38.4 0.48 11.2 23.5 0.69 11.6 16.1 0.67 10.0 14.5 0.75 8.5 11.4 0.66 6.5 10.3 0.64 3.0 5.2 0.60 2.0 3.3 0.60 0.60 1.0




0 2 4 6 8 10 12 14 16 18 200

2

4

6

8

10

12

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EXPRIMENT NO: 14

To design a variable VOLTAGE REGULATOR using Op-Amp with fold back current limiter protection

AppAratus:

• NPN Transistor D313 • NPN Transistor 3904 • Zener diode • Op-Amp 741 • Resistances

(R1=100KΩ,R2=130KΩ,R3=470Ω,R4=820Ω,R5=1KΩ, RSC=38Ω)

• Power Supply • Multimeter

Circuit Diagram:

Circuit Design:

Given a particular value of VIN, Vout and IL, select an appropriate RSC using:



VBE=VRSC-VR5

Assume suitable values of R5 and R6, then

VR5= (R5/(R5+R6))*VOUT

VRSC=VBE+VR5

RSC=VRSC/IL(max)

Design for R1 and R2:

Assume suitable value of R1 and then

VZ=VOUT(R2/(R1+R2)

R2= VZ(R1+R2)/ VOUT

Design for R4:

IR4=IZ+IOP-AMP

But as IOP-AMP =500nA, so

IR4=IZ

R4= (VIN(min)-VZ)/IR4

Where:

Design for RL:

RL=VL/IL

Power rating for RL=VL*IL


VIN (VOLTS) VOUT (VOLTS) 15 11.03 16 11.05



17 11.06 18 11.08 19 11.10 20 11.10


IL (mA) VOUT (VOLTS) RL(Ohms) 0.254 11.85 47.0 0.465 11.03 24.0 0.480 10.96 23.0 0.498 10.90 22.0 0.586 10.50 17.7 0.209 3.29 6.8 0.137 1.75 4.3 0.090 0.69 2.0 0.079 0.32 1.0 0.069 0 0.0


0 2 4 6 8 10 12 14 16 18 20

0

2

4

6

8

10

12

INPUT VOLATGE

OU

TPU

T V

OLA

TGE

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