Power Electronics Laboratory User Manual by Vishay Dale Datasheet

Power Electronics LaboratorV User Manual SAFETY WARNING

Power Electronics Laboratory

User Manual

Department of Electrical and Computer

Engineering

University of Minnesota

Revised: September 8, 2011

Rev E

SAFETY WARNING

Before using this laboratory, read, understand and follow the Safety Precautions

mentioned inside this manual.

This is an educational laboratory where high-voltage terminals and large current-carrying

components and circuits are exposed for ease of measurements. Therefore, regardless of the

voltage and current levels, these should be treated as high voltages and high currents, and the

safety precautions mentioned in the manual must be followed.

Title Contents

2

Contents

Exp. # Title Page

Safety Precautions 3

1. Laboratory and Power-pole Board Familiarization 6

2. Buck Converter 16

3. Switching Characteristic of MOSFET and Diode 20

4. Boost Converter 23

5. Buck-Boost Converter 26

6. Voltage-Mode Control 30

7. Peak Current Mode Control 36

8. Flyback Converter 41

9. Forward Converter 45

Appendix 49

SAFETY PRECAUTIONS 3.1 General Precautions

3

SAFETY PRECAUTIONS

1. Why is safety important?

Attention and adherence to safety considerations is even more important in a power electronics

laboratory than is required in any other undergraduate electrical engineering laboratories. Power

electronic circuits can involve voltages of several hundred volts and currents of several tens of

amperes. By comparison the voltages in many teaching laboratories rarely exceed 20V and the

currents hardly ever exceed a few hundred milliamps.

In order to minimize the potential hazards, we will use dc power supplies that never exceed

voltages above 40-50V and will have maximum current ratings of 5A or less. However in spite

of this precaution, power electronics circuits on which the student will work may involve

substantially larger voltages (up to hundreds of volts) due to the presence of large inductances in

the circuits and the rapid switching on and off of amperes of current in the inductances. For

example a boost converter can have an output voltage that can theoretically go to infinite values

if it is operating without load. Moreover the currents in portions of some converter circuits may

be many times larger than the currents supplied by the dc supplies powering the converter

circuits. A simple buck converter is an example of a power electronics circuit in which the output

current may be much larger than the input dc supply current

2. Potential problems presented by Power Electronic circuits

• Electrical shock may take a life.

• Exploding components (especially electrolytic capacitors) and arcing circuits can

cause blindness and severe burns.

• Burning components and arcing can lead to fire.

3. Safety precautions to minimize these hazards

3.1 General Precautions

• Be calm and relaxed, while working in Lab.

• When working with voltages over 40V or with currents over 10A, there must be

at least two people in the lab at all times.

• Keep the work area neat and clean.

• No paper lying on table or nearby circuits.

• Always wear safety glasses when working with other than signal-level power.

3.2 Precaut ns to be taken when prepa ng a e cuit 3.3 Precautions 10 be taken before powering the circuit 3.4 Precautions while switching ON the circuit 3.5 Precautions while switching on or shutting down the circuit

4

• Use rubber door mats to insulate yourself from ground, when

working in the Lab.

• Be sure about the locations of fire extinguishers and first aid kits in lab.

• A switch should be included in each supply circuit so that when opened, these

switches will de-energize the entire setup. Place these switches so that you can

reach them quickly in case of emergency, and without reaching across hot or high

voltage components.

3.2 Precautions to be taken when preparing a circuit

• Use only isolated power sources (either isolated power supplies or AC power

through isolation power transformers). This helps in using a grounded

oscilloscope. This reduces the possibility of risk of completing a circuit through

your body. This also reduces the possibility of destroying the test equipment.

3.3 Precautions to be taken before powering the circuit

• Check for all the connections of the circuit and scope connections before

powering the circuit, to avoid shorting or any ground looping, that may lead to

electrical shocks or damage of equipment.

• Check any connections for shorting two different voltage levels.

• Check if you have connected load at the output. This is very important in Boost

and Buck-Boost Converters and converters based on them.

• Double check your wiring and circuit connections. It is a good idea to use a point-

to-point wiring diagram to review when making these checks.

3.4 Precautions while switching ON the circuit

• Apply low voltages or low power to check proper functionality of circuits.

• Once functionality is proven, increase voltages or power, stopping at frequent

levels to check for proper functioning of circuit or for any components is hot or

for any electrical noise that can affect the circuit’s operation.

3.5 Precautions while switching on or shutting down the circuit

• Reduce the voltage or power slowly till it comes to zero.

• Switch of all the power supplies and remove the power supply connections.

3.6 Precautions while mo 1 ymg the circult 3.7 Other Precautions

5

• Let the load be connected at the output for some time, so that it helps to discharge

capacitor or inductor if any, completely.

3.6 Precautions while modifying the circuit

• Switch on the circuit as per the steps in section 3.5.

• Modify the connections as per your requirement.

• Again check the circuit as per steps in section 3.3, and switch ON as per steps in

section 3.4.

3.7 Other Precautions

• No loose wires or metal pieces should be lying on table or near the circuit, to

cause shorts and sparking.

• Avoid using long wires, that may get in your way while making adjustments or

changing leads.

• Keep high voltage parts and connections out of the way from accidental touching

and from any contacts to test equipment or any parts, connected to other voltage

levels.

• When working with inductive circuits, reduce voltages or currents to near zero

before switching open the circuits.

• BE AWARE of bracelets, rings, metal watch bands, and loose necklace (if you are

wearing any of them), they conduct electricity and can cause burns. Do not wear

them near an energized circuit.

• Learn CPR and keep up to date. You can save a life.

• When working with energized circuits (while operating switches, adjusting

controls, adjusting test equipment), use only one hand while keeping the rest of

your body away from conducting surfaces.

Experiment 1

6

Experiment 1

Laboratory and Power-pole Board Familiarization

1.1 Introduction

The power electronics laboratory is built around a reconfigurable circuit board, termed the

Power-pole board, along with accessory daughterboards. The details of the Power-pole board are

discussed in later sections of this experiment. This first experiment will familiarize you with the

laboratory equipment and Power-pole circuit board.

1.2 Laboratory Equipment

Each experiment station has the following equipment.

 Digital Oscilloscope with RS232 interface

 Function generator

 DC power supply 0-60 V - 2 A max

 ±12 V Signal Power Supply (with DIN connector output)

 Differential voltage probe

 Power Pole circuit board and associated plug-in boards with magnetic components and

daughterboards with onboard components for implementing closed loop control.

 Digital Multimeter

 Desktop computer with software for capturing oscilloscope data via RS232 port.

Note: The lab instructor will demonstrate how to use the software to capture oscilloscope

waveforms. Students should bring floppy disks or flash drives to download the captured

waveforms or data for use in their lab reports.

This equipment will be used to set up the circuits and to perform most measurements. The

laboratory will also have several miscellaneous components including power resistors, magnetics

boards, hookup wire, etc. as needed for specific experiments.

1.3 Power-pole Board Familiarization

The main feature of the Power-pole Board is the reconfigurable power-pole consisting of two

MOSFETs and two diodes. The drive circuits for the MOSFETs are incorporated on the board,

and so are the various protection circuits for over current and over voltage. PWM signals to

control the MOSFETs can be generated onboard or supplied from an external source. The power-

pole can be configured to work in various topologies using three magnetics boards (BB board for

1.3.1 Power—polo

7

buck, boost and buck-boost converters, Flyback board for flyback converter, and Forward board

for forward converter) which plug into the Power-pole Board. In addition, there is an option of

doing frequency analysis of each topology by injecting a small-signal sinusoidal control voltage.

The board can also be operated in voltage/current feedback mode using an external control

circuit mounted on a daughter board which plugs into the Power-pole Board.

The basic block diagram of the Power-pole Board is shown in Fig. 1.1 and the actual board is

shown in Fig. 1.2. Please note that the locations of the various components on the board are

indicated in Table 1.1.

1.3.1 Power-pole

The power-pole consists of MOSFETs Q10 and Q15 and diodes D10 and D15. The source of the

upper MOSFET and the drain of the lower MOSFET are connected to screw terminals for

external connection, and so are the anode of upper diode and the cathode of the lower diode. The

voltage and current waveforms at the terminals of the MOSFETs and diodes can be observed.

Table 1.2 shows the locations of test points on the power pole board.

Note:

Take care whenever you are using oscilloscope probes to measure voltage. If the measurement

reference potential is different to the oscilloscope reference potential, you must use differential

probe.

To observe the voltage across the upper MOSFET,

• Connect the positive and negative terminals of a differential probe to the DRAIN and

SOURCE of upper MOSFET.

To observe the upper MOSFET source current,

• Connect the positive and negative terminals of a differential probe to terminals CS2 and

SOURCE (D-2 in Fig. 1.2) of upper MOSFET. The current sense resistor value is 0.05 .

n I! mmﬂlwu 3 .w mm mm . .w mum-w mu mm w w —)m _)m TIE:

8

Figure 1.1: Block diagram of Power-pole Board.

9

Figure 1.2: Power-Pole board.

10

Table 1.1: Location of components on Power-Pole board

No. Component Ref. Des. Location in

Fig. 1.2

1 Terminal V1+ J1 A-1

2 Terminal V2+ J21 L-1

3 Terminal COM (input) J2 A-4

4 Terminal COM (output) J22 L-6

5 DIN connector for

±

12 V signal supply J90 A-5

6 Signal supply switch S90 B-6

7 Signal supply +12 V fuse F90 B-5

8 Signal supply −12 V fuse F95 B-6

9 Signal supply LED D99 B-5

10 Fault LED D32 D-6

11 Over voltage LED D33 D-6

12 Over current LED D34 D-6

13 Upper MOSFET , diode and heat sink assembly Q15, D15 C-2

14 Lower MOSFET , diode and heat sink assembly Q10, D10 C-4

15 Screw terminal for upper MOSFET source J13 D-3

16 Screw terminal for lower diode cathode J11 D-4

17 Screw terminal for upper diode anode J12 E-3

18 Screw terminal for lower MOSFET drain J10 E-4

19 Screw terminal for Mid-point J18 F-3

20 Magnetics Board plug-in space J20 H-3

21 PWM Controller UC3824 U60 I-5

22 Duty ratio pot RV64 RV64 F-5

23 Switching frequency adjustment pot RV60 RV60 I-5

24 External PWM signal input terminal J68 G-6

25 Selector Switch Bank S30 E-5

26 Daughter board connector J60 H-6

27 Switched load R22 K-5

28 Resettable Fuse F21 L-2

29 Control selection jumpers J62, J63 J-5

30 Ramp select jumper J61 H-5

31 Current limit jumper J65 H-6

32 Small-signal ac analysis selection jumper J64 G-5

33 Input current sensor (LEM) CS1 B-1

34 Output current sensor (LEM) CS5 K-2

11

Table 1.2: Test Point Details and Location on Power-pole Board

No. Test Point Description of Test Point Location

in Fig. 1.2

1 V1+ Terminal V1+ C-1

2 V2+ Terminal V2+ K-1

3 CS1 Input current B-4

4 CS2 Upper MOSFET source current D-2

5 CS3 Lower diode or MOSFET source current D-4

6 CS4 Output Capacitor Current K-3

7 CS5 Output current K-4

8 CS LOAD 1 Switched Load Voltage +ve L-5

9 CS LOAD 2 Switched Load Voltage -ve L-5

10 PWM PWM Signal E-6

11 DRAIN (upper MOSFET ) Upper MOSFET drain D-2

11 SOURCE (upper MOSFET ) Upper MOSFET source D-2

12 DRAIN (lower MOSFET ) Lower MOSFET drain E-4

12 SOURCE (lower MOSFET ) Lower MOSFET source E-4

13 ANODE (upper diode) Upper diode anode E-2

13 CATHODE (upper diode) Upper diode cathode E-2

14 ANODE (lower diode) Lower diode anode D-4

14 CATHODE (lower diode) Lower diode cathode D-4

15 GATE (upper MOSFET ) Gate of upper MOSFET C-2

16 GATE (lower MOSFET ) Gate of lower MOSFET C-4

To observe the voltage across the lower MOSFET ,

• Connect an oscilloscope probe to the DRAIN and its ground to the SOURCE (E-4 in Fig.

1.2) of the lower MOSFET.

To observe the lower MOSFET source current,

• Connect an oscilloscope probe to terminal CS3 and its ground to the SOURCE (E-4 in

Fig. 1.2) of the lower MOSFET. The current sense resistor value is 0.05 . The same

test points also measure the lower diode current if that is included in the circuit.

To observe the voltage across the upper diode,

• Connect the positive and negative terminals of a differential probe to terminal CATH and

ANODE (E-2 in Fig. 1.2) of the upper diode.

To observe the voltage across the lower diode,

• Connect an oscilloscope probe to CATHLOW and its ground to the ANODE of the lower

diode (D-4 in Fig. 1.2).

. .2 Magyetics Boards 1.3.3 Sngal Sugglx 1.3.4 Load

12

1.3.2 Magnetics Boards

To build various converters using the Power-pole Board , three plug in boards are provided:

1. BB Board (Fig. 1.3(a)): For buck, boost and buck-boost converters

2. Flyback Board (Fig. 1.3(b)): For flyback converter

3. Forward Board (Fig. 1.3(c)): For forward converter

How to use these boards will be described in the subsequent experiments.

(a) BB Board (b) Flyback Board (c) Forward Board

Figure 1.3: Magnetics boards.

1.3.3 Signal Supply

±12 volts signal supply is required for the MOSFET drive circuits and also the measurement and

protection circuits. This is obtained from a wall-mounted isolated power supply, which plugs

into the DIN connector J90 (A-5 in Fig. 1.2). Switch S90 (B-6 in Fig. 1.2) controls the signal

power to the board. Each time a fault occurs, turn off and turn on this switch to reset the board.

The green LED D99 (B-5 in Fig. 1.2) indicates if the +12 V signal supply is available to the

board. Fuses F90 (B-5 in Fig. 1.2) and F95 (B-6 in Fig. 1.2) provide protection for the +12 V and

-12 V supplies respectively.

1.3.4 Load

Any external load is to be connected across terminals V2+ and COM (L-1 and L-6 in Fig. 1.2).

An onboard switched load is provided to facilitate the observation of the transient response of

any converter built using the power-pole. Thus it is possible to periodically switch in and out a

20  load (K-4 to K-6 in Fig. 1.2). The frequency and duty ratio of this load is fixed at 10 Hz

and 10%.

To select the switched load,

1.3.5 Input/Outgut Voltage Measurement 1.3.6 Current Measurement

13

• Put switch 3 of selector switch bank S30 (E-5 in Fig. 1.2) to the top position (Load (SW)

ON).

In order to observe the switched load current,

• Connect the positive and negative terminals of a differential probe to CSLOAD1 and

CSLOAD2 (L-5 in Fig. 1.2). This measures the voltage across the 20  resistor.

• Switched load current is the measured voltage divided by 20.

1.3.5 Input/Output Voltage Measurement

Test points for input/output voltage measurements are provided on the Power-pole Board.

For input voltage measurement,

• Connect the oscilloscope probe to test point V1+(C-1 in Fig. 1.2) and its ground to

COM (D-1 in Fig. 1.2).

For output voltage measurement,

• Connect the oscilloscope probe to test point V2+ (K-1 in Fig. 1.2) and its ground to

COM (L-1 in Fig. 1.2).

1.3.6 Current Measurement

LEM current sensors (B-1, K-2 in Fig. 1.2) are provided to measure the input and output

currents. The input current sensor is located after the input filter capacitor, and the output current

sensor is located before the output filter capacitor. Calibration of the current sensors is such that

for 1A current flowing through each, the output is 0.5 V. These signals are amplified by a factor

of 2 and are brought out to the daughter board connector J60, for use in feedback current control.

Currents through the MOSFETs and output capacitor are measured using current sense resistors.

Refer to Table 1.2 for details of the various current measurement test points.

To measure input current,

• Connect oscilloscope probe to CS1 (B-1 in Fig. 1.2) and its ground to COM (D-1 in Fig.

1.2).

To measure output current,

• Connect oscilloscope probe to CS5 (K-4 in Fig. 1.2) and its ground to COM (L-1 in Fig.

1.2) .

1.3.7 MOSFET Drive Circuit 1.3.8 PWM Signal Generation

14

To measure output capacitor ripple current,

• Connect oscilloscope probe to CS4 (K-3 in Fig. 1.2) and its ground to COM. The current

sense resistor value is 0.1 .

1.3.7 MOSFET Drive Circuit

The power-pole MOSFETs are driven by high side drivers IR2127. These drivers have in-built

overcurrent protection using a current-sense resistor for each MOSFET (see locations C-3 and C-

5 in Fig. 1.2). The voltage across these sense resistors can be observed using test points provided

on the board.

To see the upper MOSFET current,

• Connect the positive and negative terminals of a differential probe to CS2 and SOURCE

of upper MOSFET .

To see the lower MOSFET current,

• Connect an oscilloscope probe to CS3 and its ground to SOURCE of lower MOSFET .

Note: The lower diode current can also be observed using test point CS3. However the

upper diode current cannot be observed.

1.3.8 PWM Signal Generation

PWM signals required for the MOSFETs can be generated using the on-board PWM controller

UC3824 (I-5 in Fig. 1.2). There is also an option to supply PWM signals from an external

source.

To use the onboard PWM,

• Put switch 2 of the selector switch bank S30 (E-5 in Fig. 1.2) to its bottom position

(PWM INT.).

To use external PWM,

• Put switch 2 of the selector switch bank S30 to its top position (PWM EXT.).

• Connect the external PWM signal to the terminal J68 (G-6 in Fig. 1.2).

While using the onboard PWM for operation of the power-pole in open-loop, the duty ratio can

be controlled using pot RV64 (F-5 in Fig. 1.2). The duty ratio can be varied from 4% to 98%.

The frequency of the PWM can be adjusted using the trim pot RV60 (I-5 in Fig. 1.2).

There is a provision for providing an external ramp to the UC3824 IC. This is useful for peak

current mode control. For this, remove jumper J61 (H-5 in Fig. 1.2) and use the RAMP pin on

daughter board connector J60.

1.3.9 Frequency Analy 1.3.10 Power—pole Board in Feedback Control Mode

15

1.3.9 Frequency Analysis

Frequency analysis of any converter built using the power-pole can be done by injecting a low

voltage sinusoidal signal at jumper J64 (G-5 in Fig. 1.2). To do this,

• Remove jumper J64.

• Connect the small signal sinusoidal source at the jumper terminal J64.

Note: J64 is to be shorted in all other modes of operation.

1.3.10 Power-pole Board in Feedback Control Mode

The power-pole board can be operated in either open or closed loop and is selected by jumpers

J62 and J63 (J-5 in Fig. 1.2). For open loop operation,

• Keep J62 and J63 in the righthand positions.

Closed loop operation will be described in the relevant experiment.

Experiment 2

16

Experiment 2

Buck Converter

2.1 Objective

The objective of this experiment is to study the characteristics of a buck converter. The circuit

will be operated under continuous current mode (CCM) and open loop conditions (no feedback).

Our main goal will be to compare the theoretical results with the experimental results.

Simulation results can be obtained by performing Experiment No. 4 in PSpice based Power

Electronics Laboratory User Manual.

2.2 Preparing the Setup

Make the connections on the power-pole board as shown in Fig. 2.1 to use the upper MOSFET

and the lower diode.

• Use the magnetics board BB board for the buck converter circuit. The inductor is 100 µH.

• Use a variable load resistor (RL) as a load.

• Use onboard PWM signals.

• Connect the ±12 signal supply at the DIN connector. Signal supply switch S90 should be

OFF.

2.3 Checks before powering the circuit

• Check the circuit connections as per the schematics.

• Have your circuit checked by your Lab Instructor.

2.4 Powering the Circuit

• Switch ON the signal supply. Check for green LED.

• Adjust the duty ratio to 50%.

• Adjust the switching frequency to 100kHz.

• Apply input voltage Vd of 24 volts at terminals V1+ and COM.

Om. LEM LEM S aFF m 5mm _ w. LA 3WD MDPO ’7 W9 W0" am 0 WED WW _I WGNE *5 N .m % law-DU" m we WNCHNG BEGUM:v gmm Manama usEEX'E'“ WINE“ U mac Mosm mm Loummv: _).uzv u E H D U In low _) .m/ mm PWMTDBUT %% 5m??? m ER my

17

Figure 2.1: Schematic of Buck Converter

1 Vgﬂing Duty Ratio 2.5.2 Vgﬂing Switching Frcgucncy 2.5.3 Vgﬂing Load

18

2.5 Measurement and Waveforms

Take the following measurements,

2.5.1 Varying Duty Ratio

• Set the duty ratio at 50%, switching frequency at 100 kHz and RL= 10.

• Observe and make a copy of the output voltage and voltage across the diode.

• Vary the duty ratio from 10 % to 90 % (in steps of 10%).

• Measure the average output voltage for the corresponding duty ratio.

• Calculate the theoretical average output voltage for the corresponding duty ratios.

2.5.2 Varying Switching Frequency

• Set the duty ratio to 50 %.

• Measure the peak-peak output ripple voltage and the peak-peak ripple in inductor current.

• Repeat the above procedure for different switching frequencies (40 kHz , 60 kHz, 80

kHz). Make sure that output voltage (V2+) is maintained at 12V.

• Observe and make a copy of the inductor current (CS5) and capacitor current (CS4)

waveforms at 40kHz and at 100kHz

2.5.3 Varying Load

• Set the switching frequency at 100kHz and duty ratio at 50%.

• Set the load resistance RL=10.

• Increase the load resistance and observe the inductor current waveform.

• Keep increasing the load resistance, until the buck converter enters discontinuous current

mode operation. Note down the average inductor current value and make a copy of the

inductor current waveform when the converter starts entering discontinuous current mode

of operation.

2.5 .4 Determining Efﬁciency

19

2.5.4 Determining Efficiency

Determine the efficiency of the buck converter at frequencies of 40 kHz and 100 kHz.

• Set duty ratio at 50%.

• Set load resistance RL=10.

• Measure the average output voltage V2+.

• Measure the average output current Io.

• Measure the average input voltage Vd.

• Measure the average input current Ii.

• Calculate the efficiency of the buck converter for the above two frequencies.

2.6 Lab Report

The lab report should have a brief abstract detailing what has been done in the experiment. The

remaining part of the report should consist of the information asked below along with any

discussion you feel is necessary.

1. Attach a graph output voltage (V2+) versus duty ratio using data obtained in section

2.5.1. Also plot the theoretically calculated results on the same graph. Compare the two

plots and comment about how the buck converter works as a variable dc step down

transformer. Enclose output voltage & voltage across diode waveforms for duty ratio

50%

2. Attach a copy of the inductor current (CS5) and the capacitor current (CS4) waveforms

obtained in section 2.5.2. Explain the relation between the two currents. Comment on the

ripple in the inductor current for the two frequencies.

3. Plot the peak-peak ripple in the output voltage versus switching frequency using data

obtained in section 2.5.2. Plot the theoretical results on the same graph. Compare the two

plots. Comment on why you were asked to maintain the average output voltage constant.

4. Attach a copy of the inductor current waveforms obtained in section 2.5.3. Compare the

theoretically calculated Rcrit with the observed value.

5. Comment on the difference in efficiency results obtained for two switching frequencies.

Experiment 3

20

Experiment 3

Switching Characteristic of MOSFET and Diode using Power-Pole Board

3.1 Objective

The objective of this experiment is to study the switching characteristics of power MOSFETs

and power diodes using a buck converter. The circuit will be operated in open loop conditions

(no feedback). Our main goal is to understand the switching behavior of these two power

devices.

3.2 Preparing the Setup

Construct the buck converter circuit as shown in Fig. 3.1 to use the upper MOSFET and lower

diode.

• Use the BB magnetics board. The inductor is 100 µH.

• Use a variable load resistor as a load.

• Connect ±12V the signal supply to the DIN connector. Signal supply switch S90 should

be OFF.

3.3 Checks Before Powering The Circuit

• Check the circuit connections as per the schematic.

• have your circuit checked by your Lab Instructor

3.4 Powering the Circuit

• Switch ON the signal supply. Check for green LED.

• Adjust the duty ratio to 50%.

• Set the switching frequency of 100kHz.

• Set RL= 12.

• Apply input voltage Vd of 24 volts.

LEM S DFIVE 036“" W. 71 __ 95.4 m ml?" “300°“ M O mmm DRIVE + cs W m"! ‘+ IO$WTV nrw: swam W Mama" mmmm MING" ”SE Wm m MSG“ [MIME H —).12v E a E E I». ‘ 0 WW- 6.qu mm 000 w mmw “55°" E” m m MSG“ LOIDNF 54 mm! Pawn! Runny

21

Figure 3.1: Schematic of Buck Converter

22

3.5 Measurement and Waveforms

1. Observe and make a copy of the Anode-Cathode diode voltage VAK using a differential

probe and the diode current using CS3. Adjust the time base to show the switching details

during turn-ON and turn-OFF.

2. Measure the forward voltage drop across the diode VFM.

3. Observe and make a copy of the Drain-Source Mosfet voltage VDS using a differential

probe and Mosfet current CS1. Adjust the time base to show the switching details during

turn-ON and turn-OFF.

4. Measure the voltage drop across the Mosfet during turn-ON period and estimate the

rds(ON) of the Mosfet. (Note: the differential probe might have an offset, adjust your

measurement based on this offset value.)

5. Measure the average load current Io, and the duty cycle of operation.

3.6 Exercises:

1. Attach the waveforms for turn-ON and turn-OFF of the diode showing the switching

details by expanding the time base.

2. Calculate the conduction loss of the diode using eqn. 2A-1 in the book and the

measurements from step 2 of section 3.5.

3. Attach the waveforms for turn-ON and turn-OFF the Mosfet showing the switching

details by expanding the time base.

4. Estimate the rds(ON) of the Mosfet from step 4 of section 3.5 and compare with the

datasheet of Mosfet IRF640N.

5. Calculate the conduction loss of the Mosfet using eqn. 2-3 in the book and the

measurements from step 4 of section 3.5.

6. Using the values of conduction losses of the Mosfet and the Diode obtained through

measurements, and switching losses of the Mosfet obtained through simulation (Refer to

Experiment No. 2 in the PSpice-based Power Electronics Laboratory User Manual),

estimate the efficiency of the converter. Compare the estimated efficiency with the

efficiency obtained for the buck converter in the “Buck Converter Experiment”.

Experiment 4

23

Experiment 4

Boost Converter

4.1 Objective

The objective of this experiment is to study the characteristics of a boost converter. The circuit

will be operated under CCM and openloop condition. Our main goal is to compare the theoretical

results with the experimental results. For PSpice Simulation refer Exp. No. 5 in PSpice based

power electronics lab manual.

Note: It is important that care must be taken while doing the boost converter experiment

that the load is always connected to the power-pole board. The input and output terminals in

the case of the boost converter are interchanged as compared to that of the buck converter. V2+

& COM is the input and V1+ & COM is the output.

4.2 Preparing the Setup

Make the connections of the power-pole board as shown in Fig. 4.1 to use the lower MOSFET

and the upper diode.

• Use the BB magnetics board for the boost circuit. The inductor is 100 µH.

• Use a variable load resistor as a load.

• Connect the ±12 signal supply to the DIN connector. Signal supply switch S90 should be

OFF.

4.3 Checks before powering the circuit

• Check the circuit connections as per the schematics.

• Confirm that you have connected the input and output terminals correctly to source and

load as shown in Fig. 4.1.

• Have your circuit checked by your Lab Instructor.

4.4 Powering the Circuit

• Switch ON the signal supply. Check for green LED.

• Set the duty ratio to its minimum 10% and RL=20.

• Adjust the switching frequency to 100kHz.

• Apply input voltage Vd of 10 volts at terminals V2+ and COM.

\l Ir ﬁi LEM v" LEM um: anal" Vb Mn P0 " — "WORM" om CC“ 0 Magnum DRIVE _| " WHZ IMWW we smmm “swam AMSTVEW Po'rEN'r'WErER com on mmros- usssxrenm smﬁmn mm max Muslim ”3‘“ IFU m any 5“” m B E E| E E ”9 um. 2mm- MEW om PWM 0W” m o- mmmn H 42v m" m m am “55 D swerED Fa WIM SEN“ Low OF

24

Figure 4.1: Schematic of Boost Converter

4.5.1 Vgﬂing Duty Ratio 4.5.2 Vgﬂing Switching Frcgucncy 4.5 .3 Determining efﬁciency

25

4.5 Measurements

Take the following measurements,

4.5.1 Varying Duty Ratio

• Vary the duty ratio from 10% to 60% (in steps of 10%).

• Measure the average DC load voltage (V1+) for the corresponding values of duty ratio .

• Calculate the theoretical average output voltage for the corresponding duty ratios.

• Compare the observed average output voltage results with the calculated ones.

4.5.2 Varying Switching Frequency

• Set the duty ratio to 50%, switching frequency to 100kHz, RL= 20.

• Observe and make a copy of the input current (CS5) ripple waveform @100kHz.

• Measure the peak-peak input current ripple.

• Repeat the above procedure for different switching frequencies (40 kHz, 60 kHz,

80 kHz).

4.5.3 Determining efficiency

• Set the duty ratio to 50%.

• Adjust the load resistance value to 20.

• Measure the efficiency at switching frequencies of 40kHz and 100 kHz.

4.6 Lab Report

The lab report should consist of the information asked below, along with any discussion you feel

is necessary.

1. Attach a graph of duty ratio versus output voltage using the data obtained in section 4.5.1.

Also plot the theoretically calculated results on the same graph. Compare the two plots.

2. Attach a copy of the inductor current (CS5) waveform obtained in section 4.5.2. Plot the

experimental and theoretically estimated input ripple current on the same graph. Compare

the two graphs and comment.

3. Plot efficiency versus frequency using the data obtained in section 4.5.3. Comment on the

results you obtain.

Experiment 5

26

Experiment 5

Buck-Boost Converter

5.1 Objective

The objective of the experiment is to study the characteristics of the buck-boost converter. The

circuit will be operated under CCM and openloop conditions. Our main goal is to compare the

theoretical results with the experimental results. For PSpice Simulation refer Exp. No. 6 in

PSpice based power electronics lab manual

Note: It is important that care must be taken while doing the buck-boost converter

experiment that the load is always connected to the power-pole board. The input and output

terminals in the case of the buck-boost converter are different as compared to that of the buck or

boost converters.

5.2 Preparing the Setup

Make the connections for the power-pole board as shown in Fig. 5.1

• Use the BB magnetics board for the buck-boost converter circuit. The inductor value is

100 µH.

• Use a variable load resistor as a load.

• Connect the ±12 signal supply to the DIN connector. Signal supply switch S90 should be

OFF.

5.3 Checks before powering the circuit

• Check the circuit connections as shown in Fig. 5.1.

• Confirm that you have connected the input and output terminals correctly to source and

load as shown in Fig. 5.1.

• Have your circuit checked by your Lab Instructor.

5.4 Powering the Circuit

• Switch ON the signal supply. Check for green LED.

• Set the duty ratio to its minimum.

• Set RL= 20.

• Adjust the switching frequency to 100 kHz.

• Apply input voltage Vd of 10 volts at the terminals V1+ and V2+.

LEM v; v“ LEM + ms ._ encurr _ vz. U \m LA more rr mucroa man cm 0 SWITCHED Lou) am: ‘I mm: gonna cucun m n: 5 m 7. nun ._ DRNE _ Myra-AG man Wm POTENTOEIEH ON PWM ro To? use EXTERNAL swrrmsn UNUSED ma WSFEI WM saw. wan IcnvE mm —) uzv H E Fl El El "m M“ O m _) 42v comm O w Pmroao‘r useovmm swrrcHED WWW mesa FWM 515M LOAD 05: ”EM“

27

Figure 5.1: Schematic of Buck-Boost Converter

. .1 Vgﬂing Duty Ratio 5.5.2 Vgﬂing Switching Frequency 5 .5 .3 Determining Efﬁciency 5.5.4 Vgﬂing Load

28

5.5 Measurements

Take the following measurements,

5.5.1 Varying Duty Ratio

• Vary the duty ratio from 10% to 70% (in steps of 10%).

• Measure the average DC load voltage (V2+) for the corresponding values of duty ratio.

• Calculate the average theoretical DC output voltage for the corresponding duty ratios.

• Compare the observed average output voltage results with the calculated ones.

5.5.2 Varying Switching Frequency

• Set the duty ratio to 60%, switching frequency to 100kHz, RL= 15.

• Observe and make the copy of the inductor current (CS5) ripple waveform @100kHz.

• Measure the peak-peak inductor current ripple.

• Repeat the above procedure for different switching frequencies 40 kHz, 60 kHz, 80 kHz.

5.5.3 Determining Efficiency

• Set the duty ratio to 60%.

• Adjust the load resistance to RL=15.

• Measure the efficiency at switching frequencies of 40 kHz and 100 kHz.

5.5.4 Varying Load

• Set the duty ratio to 40%, RL= 20 and switching frequency to 40 kHz.

• Keep increasing the load resistance until the converter enters into the discontinuous

conduction mode and note the value of load resistance.

29

5.6 Lab Report

The lab report should consist of the information asked below along with any discussion you feel

is necessary.

1. Attach a graph of duty ratio versus output voltage (CS5) using the data obtained in

section 5.5.1. Also plot the theoretically calculated results on the same graph. Compare

the two plots.

2. Attach a copy of the inductor current (CS5) waveform obtained in section 5.5.2. Plot the

experimental and theoretically estimated ripple current waveforms on the same graph.

Compare the two graphs and comment.

3. Plot the efficiency versus frequency using the data obtained in section 5.5.3. Comment on

the results you obtain.

4. Calculate the critical value of load resistance Rcrit,Buck-Boost at which the converter is in the

border of Continuous-Discontinuous and compare with that obtained in section 5.5.4.

Experiment 6

30

Experiment 6

Voltage-Mode Control

6.1 Objective

The objective of this experiment is to design a controller to operate the buck converter in voltage

control mode. For this experiment, a plug-in daughter board will be used to accomplish the

control objective. The small-signal transfer function () ()

o

vsds



 ( d

is a small-signal perturbation

in the duty cycle and o

v

 is the corresponding variation in the output voltage) must first be

obtained for the buck converter. The plug-in daughter board is used to implement the voltage-

mode control feedback with the required open-loop gain.

6.2 Preparing the Setup and Open-Loop Mode

Construct the buck converter circuit as shown in Fig. 6.1 using the BB magnetics board.

• Connect and turn on the ±12vsignal supply and check for green LED.

• Adjust the duty ratio to 50%.

• Adjust the switching frequency to 100kHz.

• Switch ON the switched load to active position using selector switch bank as shown in

Fig. 6.2.

• Adjust the variable load resistance RL to 10.

• Have your circuit checked by your Lab Instructor.

• Apply DC supply voltage Vd to 30V.

6.3 Measurements in Open-Loop Operation

Observe and make a copy of the output voltage waveform (V2+). Adjust the time base to show

the details of the switching transients as the load is switched.

6.4 Using PSpice to find ()

()

o

vs

ds



Using the schematic file “buck_conv_avg.sch” (Refer to Exp. 10 in PSpice based power

electronics lab manual), perform the following experiment.

5 E LEM \ Ow. w. WORM LEM main mm w. \\ my WE + Manama C'w mm Icy-mm we _ 5%ch mum rmusmw POTENIDMEI'ER m Marmot: usEExrm swuma) wusen m”; mover mm MUNE Scum —).|2v am H E H H H "I“ ' ‘ mm mm 0- open $4” PWMMI'V mm Om LOOP Pwmosot mama mum: mucus W Mom-r mm mow momma m

31

Figure 6.1: Buck Converter using Power-pole board.

\dee‘ "ans ch2 L1 VRT m cm V0 g L PARAMETERS 5 Ncp H vm 30v ‘ v2 R; Va 15v 7, {RC} D (Mo/Mm) {D} ; RLoad W PARAMETERS . v1 , [R] L mow “Mi; (:1 i: (c) c ssmE W V3 R: monms W K; ‘ PARAMETERS “WM 9 R 6 5670mm nucuonvjvg sch PWM TO TOP USE EXTERNAL SWITCHED UNUSED MOSFET PWM SIGNAL LOAD ACTNE BEBE PWM TO BOT. USE ONBOARD SWITCHED MOSFEI' PWM SIGNAL LOAD OFF

32

1. Obtain the Bode plots for the transfer function ()

()



o

vs

ds as shown in Fig. 4-10 of the

textbook for the values given in this simulation.

2. Obtain the gain and the phase of the transfer function ()

()



o

vs

ds in part 1 at the frequency of

1 kHz, which will be chosen as the crossover of the open-loop transfer function ( )

L

Gs.

Figure 6.2: Selector switch position for switched load.

6.5 Type 3 Voltage Controller

EXTERNAL? O O 0 ppm CONTROL 5- “zoop ...................... .- n for Voltage-Mode

33

Once you get the transfer function or the Bode-plot of the buck converter, you can design a

Type-3 voltage controller. The Type-3 voltage control board has the schematic as shown in Fig.

6.3.

The values of the resistors and capacitors of the voltage control board are given in Table. 6.1

• Reference value VREF can be set using the duty ratio pot.

• Reference value VREF can’t be set below 10V.

• For the pin details of terminal strip J60, please refer the schematic of the power-pole

board.

Figure 6.3: Voltage controller plug-in board.

Table 6.1: Voltage control board component values

Component Calculated Value Actual value used

R1 100k 100k

R2

20k

R3

10k

C1

22nF

C2

2.2nF

C3 4.7nF

Figure 6.4: Control selection for Voltage-Mode Control plug-in board

6.6 Preparing the Setup for Voltage-Mode Control Operation

• Set the control selection jumpers J62 and J63 as shown in Fig. 6.4.

• Insert the Voltage-Mode Control plug-in board in the terminal strip 60.

J63

J62

The op-amp in the dotted

region is a part of the IC

UC3824 which is designated

asU60 on the power pole

board. The numbers 9, 12

and 13 are pins of J60 port

on the board

Vref is generated through a

potential divider on the

board

¢Do n7

34

• Keep RL= 10.

• Switch ON the switched load to the active position using the selector switch bank as

shown in Fig. 6.2.

• Turn ON ±12Vsignal supply and check for green LED.

• Have your circuit checked by your Lab Instructor.

• Set Vd to 30V.

• Use the duty cycle pot RV64 to set V2+ to 15V.

6.7 Measurements in Voltage-Mode Control Operation

Observe and make a copy of the output voltage V 2+.

6.8 Lab Report

The lab report should have a brief abstract detailing what has been done in the experiment. The

remaining part of the report should consist of the information asked below along with any

discussion you feel is necessary.

1. Attach the Bode magnitude and phase plot of the small-signal transfer function ()

()

o

vs

ds



from the results obtained in section 6.4

2. Obtain the following quantities from the Bode plot, ()

c

PS f

Gs and ()

c

PS f

Gsfor a

crossover frequency of 1kHz.

3. Calculate the needed phase boost boost



using the values obtained through PSpice above

with a required phase margin of 60 degrees

4. Calculate the controller gain at the crossover frequency given 0.2

FB

k and

() 0.556

c

PWM f

Gs

5. Use the K-factor method described in chapter 4 of the book to design a type 3 voltage

mode controller for the buck converter i.e, determine kc, z



and

p



of the controller Gc(s).

6. Determine the values of the resistors and capacitors used to implement the controller in

Fig. 6.3 and substitute them in Table 6.1.

35

7. The controller is implemented in hardware using the values given in Table 6.1 column

#3. Compare the responses of the output voltage for a step load change with and without

closed loop control. Attach the waveforms obtained in steps 6.3 and 6.7.

Experiment 7 7.2.1 Measurements 7.3.1 Closed Loop Operation Without Slope Compensation

36

Experiment 7

Peak Current Mode Control

7.1 Objective

In this experiment, we will be using a plug-in board to accomplish peak current mode control for

a buck-boost converter. First the aspects of constant frequency peak current mode control will be

explored. Then the plugin board will be used to achieve feedback voltage control of the

converter. The goal is to understand how to design a peak current mode controller with voltage

feedback.

7.2 Preparing setup for Open Loop Operation

• Reconstruct the buck-boost converter used in Expt. 3 as in Fig. 7.1.

• Turn on the signal power supply and set the switching frequency to 100 kHz and duty cycle

such that output voltage Vo=12 V.

• Change the switch positions of the switch bank as shown in Fig. 7.2.

• Set Vd to 20 V and the variable power resistor to 20  .

7.2.1 Measurements

• Observe the output voltage V2+ and inductor current on the oscilloscope.

• Store the waveform.

7.3 Preparing setup for closed loop operation and measurements

7.3.1 Closed Loop Operation Without Slope Compensation

• Setup the control selection as in Fig. 7.3.

• Remove shorting link from J61 and insert the Type 2 Controller plug-in board whose

circuit is shown in Fig. 7.4 into the terminal strip J60 (The pin numbers shown in the

figure correspond to pin numbers on the terminal strip). This board will add the voltage

feedback to the control.

• Set the duty cycle pot to minimum.

• Switch ON the main power supply and set it to 25 V.

LEM W ,EM + DFWE E ; merT _ Vd vat VT. W‘ vauame W W W mm M Remy Mum: I @— TNDUCTOR BOARD cw DOM 0 mm DFWE MPGNEHCS BOMB ZS chmT m Hz m a,“ nun DRNE E swrrcRTNe FREQUENCY musTMENT POTENTKJMETER W W RWM TO TOP nsE EXTERNAL SWTTCRED “ME“ WEN MOSFET NM mm mm mTwE SELEDTDN %.T2v m was“ EXTEHNN. H % 12v E E H E RNMTNRUT EXTERNN. 0 ﬂ uLITv DVCLE — mm“ W RWM TO BOT USEDNBORRD SWTCHED RoTENTmETER O MOSFET RWM sTGNAL LCMD DEE

37

Figure 7.1: Peak Current mode controller schematic.

PWM TO TOP USE EXTERNAL SWITCHED UNUSED MOSFEI PWM SIGNAL LOAD ACTIVE HHBU FWM IO BOT, USE UNBUARD SWITCHED MOSFET PWM SIGNAL LOAD OFF EXTERNAL O O O ()PIL'N ('ONI'ROL LOOP O 11 |\ 1 50pF |\ 482k BZOpF D _ IN 5 186k 12 13 OUT _ 4° o—+ VREF 5 11 o—Ivvv—o 2.0k

38

Figure 7.2: Switch positions for switched load.

Figure 7.3: Switch Position for Closed Loop Operation

Figure 7.4: Type 2 Controller

• Change the switch positions of the switch bank as shown in Fig. 7.1.

• Switch ON the signal power supply. Ensure that main power supply is ON before signal

power supply is switched ON.

• Observe the PWM and the inductor current waveforms.

• Slowly increase the reference voltage by turning the duty cycle pot clockwise. Observe

the point where the inductor current starts displaying oscillatory behavior. Record the

corresponding duty cycle from the scope.

o—Wy—K—o 909k 0.01uF 7.3.2 Closed Loop Operation With Slope Compensation 7.3.3 D namie Performance ofClosed Loop S stem

39

• Plug in the slope compensation jumper on to J61. The slope compensation jumper circuit

is shown in Fig. 7.5. Observe how the inclusion of slope compensation affects the

stability of the converter.

Figure 7.5: Slope Compensation Jumper

7.3.2 Closed Loop Operation With Slope Compensation

• Ensure that the plug-in board and the slope compensation jumper are plugged in.

• Set the duty cycle pot to minimum.

• Switch ON the main power supply and set it to 15 V.

• Switch ON the signal power supply.

• Observe the PWM and the inductor current waveforms.

• Slowly increase the reference voltage by turning the duty cycle pot clockwise. Observe

the point where the inductor current starts displaying oscillatory behavior. Record the

corresponding duty cycle from the scope.

7.3.3 Dynamic Performance of Closed Loop System

• Ensure that the plug-in board and the slope compensation jumper are plugged in.

• Set the duty cycle pot to minimum.

• Switch on the main power supply and set it to 20 V.

• Switch on the signal power supply.

• Slowly increase the reference voltage to 12 V by turning the duty cycle pot clockwise.

• Observe the output voltage V2+ and the inductor current on the oscilloscope. Store the

waveform.

7.4 Lab chort

40

7.4 Lab Report

The lab report should have a brief abstract detailing what has been done in the experiment. The

remaining part of the report should consist of the information asked below along with any

discussion you feel is necessary.

• Plot the output voltage Voand inductor current iL obtained in step 7.2.

• What is the maximum duty ratio stable operation of the converter in step 7.3.1? Plot the

inductor current waveform for stable and unstable operation.

• What is the maximum duty ratio stable operation of the converter in step 7.3.2? Plot the

inductor current waveform for stable and unstable operation.

• Explain how slope compensation affects the range of duty cycle obtainable in constant

frequency peak current mode control.

• Explain why in step 7.3.1, it is important to switch on the signal power supply after

turning on the main power supply.

• Plot the output voltage Vo waveforms and inductor current in closed loop operations with

output voltage feedback (step 7.3.3).

• Comment on the effect of peak current controller on the operation of converter.

Experiment 8 8.5.1 Vgﬂing Duty Ratio

41

Experiment 8

Flyback Converter

8.1 Objective

The objective of this experiment is to study the characteristics of the flyback converter using the

power-pole board in open loop control mode. Our main goal is to compare the theoretical results

with the experimental results.

Note: It is important that care must be taken while doing the Flyback converter experiment

that the load is always connected to the output in the power-pole board.

8.2 Preparing the Setup

Make the connections on the power-pole board as shown in Fig. 8.1 to use the lower MOSFET.

• Use the Flyback magnetics board. The turns ratio N1/N2=2

• Use a variable load resistor as a load.

• Connect the ±12Vsignal supply to the DIN connector. Signal supply switch S90 should

be OFF.

8.3 Checks before Powering the Circuit

• Check the circuit connections as per the schematic.

• Check that the lower MOSFET has been selected.

• Have your circuit checked by your Lab Instructor

8.4 Powering the Circuit

• Switch ON the signal supply. Check for green LED.

• Set the switching frequency to 100kHz and the duty ratio to 50%.

• Set RL= 10.

• Apply input voltage Vd of 15V at terminal V1+ and COM.

8.5 Measurements

Take the following measurement,

8.5.1 Varying Duty Ratio

• Vary the duty ratio from 0% to 50% (in steps of 10%).

WEI WMSr-NIL LmDOFr LEM ﬂ“ LEM me m V . W. {N \J mum mfg-53% on W mu com A \J manure mus mermsomn CR1"! WNZ mm DRIVE swmms FFEOUBO Amuswarr summon-man m on Pwmrown USEEXTW swnmeu WUSED Wm: VOSFET mm LDIDKITNE mm any EEC H E D D H ‘“ ‘ mm 0- %.12v no. 0 O 0 OFF mmam usmamu swan) DLIWCICIE mTEmmm Vim: Remy

42

Figure 8.1: Schematic of Flyback Converter

8.5.2 Constant Dut Ratio with varying switching frequency and load

43

• Measure the average output voltage (V2+) for the corresponding values of duty ratios.

• Calculate the theoretical average output voltage value for the corresponding duty ratios.

• Compare the observed average output voltage results with the calculated ones.

8.5.2 Constant Duty Ratio with varying switching frequency and load

• Set the duty ratio to 40%, switching frequency to 100 kHz and RL= 10

• Observe and make a copy of the voltage across the secondary side of the coupling

inductor.

• Observe and make a copy of the input current (CS1) and output current (CS5) in the same

graph

• Repeat the above step (make a copy of the current waveforms and not the voltage

waveform) for RL= 7.5 @ Fs=100 kHz; RL= 10 @ Fs=40 kHz and RL= 7.5 @

Fs=40 kHz

8.6 Lab Report

The lab report should consist of the information asked below along with any discussion you feel

is necessary.

1. Attach a graph of duty ratio versus output voltage (V2+) using data obtained in section

8.5.1. Also plot the theoretically calculated results on the same graph. Compare the two

plots.

2. Attach the copy of the voltage waveform obtained in section 8.5.2. Construct the voltage

across the primary side of the coupled inductor. Label the waveform, both voltage and

time axis appropriately. Note: Ignore the ringing in the waveform

3. Using the voltage waveform obtained in section 8.5.2, construct the voltage across the

primary side switch. Label the waveform, both voltage and time axis appropriately. You

can verify your calculation by observing the waveform on the board. Note: Ignore ringing

and voltage when snubber circuit is on.

M,

44

4. Attach the waveforms obtained in section 8.5.2 and estimate the following: (Need to be

calculated for all the four operating conditions RL= 10 @ Fs=100 kHz; RL= 7.5 @

Fs=100 kHz; RL= 10 @ Fs=40 kHz and RL= 7.5 @ Fs=40 kHz

a. Inductance as seen from the primary side Lm1

b. Peak to peak ripple in the flux

p







given the number of turns in the primary is 42

c. Given the core area Ac=93.9mm2 what is the value of the peak flux density ˆ

B?

Experiment 9

45

Experiment 9

Forward Converter

9.1 Objective

The objective of this experiment is to study the characteristics of the forward converter. The

forward converter will be operated in open loop mode (no feedback). Our main goal is to

compare the theoretical results with the experimental results.

9.2 Preparing the Setup

Make the connections on the power-pole board as shown in Fig. 9.1 to use the lower MOSFET.

• Use the Forward magnetics board. The turns ratio is 1:1:1.

• Use a variable load resistor as a load.

• Connect the ±12Vsignal supply to the DIN connector. Signal supply switch S90 should

be OFF.

9.3 Checks before powering the circuit

• Check the circuit connections as per Fig. 9.1

• Confirm that you have selected the lower MOSFET.

• Have your circuit checked by your Lab Instructor.

9.4 Powering the Circuit

• Switch ON the signal supply. Check for green LED.

• Set the switching to 100 kHz.

• Set the duty ratio to its minimum.

• Set RL= 10.

• Apply input voltage Vd of 20 V at the terminals V1+ and COM.

LEM LEM m ‘l mm v1. W W _ LA Mm P0 rr mm mm m ‘{ macsm mm mm + 1‘17.er um Moms FREQUEMZV Amusww Pwmomp USEEXIEM M0151 UNUSED POIEmDMErER wa: DN on mam mum mm —) w mm NOSE a a E 0“ ‘W‘ EXTERNN. m 0- PWMIFUT mm 0 O O wrvcvuz POTBITIWEV’ER —) 42v WMTO BY ME 0mm: MIXED pm sum mm m: m _:l

46

Figure 9.1: Schematic of Forward Converter

1 Vming Duty Ratio 9.5.2 Constant Dut Ratio with varying switching frequency and load

47

9.5 Measurements

Take following measurements,

9.5.1 Varying Duty Ratio

• Vary duty ratio from minimum to 40% (in steps of 10%).

• Measure the average output voltage (V2+) for the corresponding values of duty ratio.

• Calculate the theoretical average output voltage for the corresponding duty ratios.

• Compare the observed average output voltage results with the calculated ones.

9.5.2 Constant Duty Ratio with varying switching frequency and load

• Set the duty ratio to 40%, switching frequency to 100 kHz and RL= 10

• Observe and make a copy of the voltage across the switch (Mosfet)

• Observe and make a copy of the input current (CS1) and output current (CS5) in the same

graph

• Repeat the above step (make a copy of the current waveforms and not the voltage

waveform) for RL= 7.5 @ Fs=100 kHz; RL= 10 @ Fs=40 kHz and RL= 7.5 @

Fs=40 kHz

9.6 Lab Report

The lab report should consist of the information asked below along with any discussion you feel

is necessary.

1. Attach a graph of duty ratio versus output voltage (V2+) using data obtained in section

9.5.1. Also plot the theoretically estimated results on the same graph. Compare the two

plots.

2. Attach a copy of the voltage waveform across the switch obtained in section 9.5.2.

Estimate theoretically the same waveform and compare. (Ignore the voltage ringing due

to the leakage inductance of the transformer)

3. Attach the waveforms of input current and output current obtained in section 9.5.2. Also

answer the following questions:

48

a. Why is the input current negative for some interval?

b. What is the minimum value of this negative current for all four operating

conditions?

c. Theoretically should the above value change with load? Give reasons for your

answer.

4. Estimate the following: (Need to be calculated for all the four operating conditions RL=

10 @ Fs=100 kHz; RL= 7.5 @ Fs=100 kHz; RL= 10 @ Fs=40 kHz and RL= 7.5

@ Fs=40 kHz.

a. Output inductor value L.

b. Core flux as given in Fig. 8-6 in the book. Number of turns in the primary is 16

and the magnetizing inductance Lm1 is 0.2mH. Hint: Use the minimum value of

the negative current seen at the input.

APPENDIX

49

APPENDIX

The detailed circuit of the power-pole is attached. It consists of two sheets.

50

‘ '1

51

Power Electronics Laboratory User Manual Datasheet by Vishay Dale

INFORMATION

HELP

CONTACT US

FOLLOW US