A Project Report Submitted to the
ELECTRICAL ENGINEERING DEPARTMENT AS TERM WORK FOR THE SUBJECT
PROJECT OF SEMESTER VIII OF BE (Electrical) GUIDED BY:
PREPARED BY:
Lect. HITARTH BUCH
Mr. RAHUL PARMAR Mr. SUSHIL RATHOD Mr. HARSHAD PATEL Mr. CHETAN KOTHIYA Mr. VIKRAMSINH MALIVAD
ELECTRICAL ENGINEERING DEPARTMENT L. E. COLLEGE, MORBI-2 SAURASHTRA UNIVERSITY, RAJKOT
i
YEAR 2007.
LUKHDHIRJI ENGINEERING COLLEGE MORBI -363642
CERTIFICATE This is to certify that the project work titled
“SPEED
CONTROL
OF
DC
MOTO MO TOR R USING USING PWM TECH TECHNIQ NIQUE UE” ”
is being submitted by NAME
ROLL NO.
Mr. RAHUL PARMAR Mr. SUSHIL RATHOD Mr. HARSHAD PATEL Mr. CHETAN KOTHIYA Mr. VIKRAMSINH MALIVAD
EXAM. NO.
30 46 33 22 24
for fulfillment of partial requirements of Semester VIII of the degree Bachelor of
Engineering
(Electrical)
of
Saura Saurasht shtra ra Univer Universit sity y for the academ academic ic year 2007. GUIDED BY:
HEAD OF THE DEPARTMENT
ii
LECT. HITARTH BUCH
PROF. S. P. SAPRE
ELECTRICAL ENGINEERING DEPARTMENT L. E. COLLEGE
ELECTRICAL ENGINEERING DEPARTMENT L. E. COLLEGE
Place: MORBI
Date:
ACKNOWLEDGEMENT
We express our deep and sincere thanks to our guide Mr. Hitarth Buch, Lecturer in Electrical Engineering Department, L. E. College, Morbi. Initially he helped us in selecting this project and then guided us throughout the project. He also helped us by taking a lot of pain and sacrificing his personal valuable time in completion of this practical project as well as the project report.
Next, we would like to express our deep gratitude towards Mr. K. B. Rathod, Asst. Prof. in Electrical Engineering Department and Prof. S. P. Sapre, Head of Electrical Engineering Department, who motivated us at one or another stage of the project work.
We express our gratitude to the staff members of Electrical Engineering Department, who directly or indirectly helped us.
iii
Mr. RAHUL PARMAR Mr. SUSHIL RATHOD Mr. HARSHAD PATEL Mr. CHETAN KOTHIYA Mr. VIKRAMSINH MALIVAD
iv
ABSTRACT The The aim aim of deve develo lopm pmen entt of this this proj projec ectt is towa toward rds s prov provid idin ing g efficient and simple method for control speed of DC motor using pulse width modulation technique. The modulation of pulse width is obtained using dual timer IC - NE556.
There are several methods for controlling the speed of DC motors. One simple method is to add series resistance using a rheostat. As considerable power is consumed in the rheostat, this method is not economical. Another method is to use a series switch that can be closed or opened rapidly. This type of cont contro roll is term termed ed as chop choppe perr cont control rol.. The The PWM PWM base based d chop choppe perr circ circui uitt smoothly controls the speed of general purpose DC motors.
To get desired desired modul modulati ation on of pulse pulse width width as output output,, we have have fabricated astable multivibrator and monostable multivibrator circuit using single dual timer IC – NE 556. The width of the pulse is changed by varying the control voltage of the monostable circuit.
v
TABLE OF CONTENTS ACKNOWLEDGEMENT ACKNOWLEDGEME NT....... .............. .............. ............. .......... ........ ........ ........ ........ ........ ........ ........ ........ ....... ... iii ABST AB STRA RACT CT v TABLE OF CONTENTS....... .............. ............... ............... .............. .............. .............. ........... ........ ........ ........ ......vi LIST OF TABLES....... .............. .............. .............. .............. .............. ............... ............... .............. ............ ......... .... viii GLOSSARY OF TERMS....... .............. ............... ............... .............. ............. .......... ........ ........ ........ ........ ........ .... ix 0.1 GOAL ........... ....................... ........................ ....................... ..................... ............... .......... .......... .......... .......... ..... 11 0.2 Pulse Width Modulati Mo dulation on (PWM) Basics Ba sics........... ................... ............. .......... ........ ... 11 2.1 GOAL........... ....................... ........................ ....................... ..................... ............... .......... .......... .......... .......... ..... 17 3.1 GOAL........... ....................... ....................... ....................... ..................... .............. .......... .......... .......... ......... .... 24 3.2 DESIGN OF ASTABLE MULTIVIBRATOR MULTIVIBRATO R............ ...................... ............... ......... .... 24 4.1 GOAL........... ....................... ........................ ....................... ..................... ............... .......... .......... .......... .......... ..... 26
4.3 PULSE WIDTH WI DTH MODULATION MODULATI ON TECHNIQUE: TECHN IQUE:....... ............. .......... ........ ........ ........ ...... ..27 5.1 GOAL........... ....................... ........................ ....................... ..................... ............... .......... .......... .......... .......... ..... 30 5.2 TESTING PROCEDURE PROCED URE AND CALIBRATION CALIBRATIO N........... .................. ............ ........ ... 30 5.2.1 TESTING OF PULSE-WIDTH MODULATION CIRCUIT.. .... .... .... 30 6.1 GOAL........... ....................... ....................... ....................... ..................... .............. .......... .......... .......... ......... .... 32 6.2 WAVE-FO WAVE-FORM RM OBSERVA OBSERVATION TION.......... ...................... ........................ ..................... ........... ..32 7.1 GOAL........... ....................... ........................ ....................... ..................... ............... .......... .......... .......... .......... ..... 34 7.2 COMPONENT COMPONE NT LIST........... ....................... ........................ ................. .......... .......... .......... ........ ... 34 8.1 GOAL........... ....................... ....................... ....................... ..................... .............. .......... .......... .......... ......... .... 36 8.2 TIME ANALYSIS ........... ...................... ....................... .................. ........... .......... .......... .......... ......... .... 36 8.3 COST ANALYSIS ............ ........................ ....................... ................. ........... .......... .......... .......... ....... ..37 9.1 GOAL............ ........................ ....................... ....................... ..................... .............. .......... .......... .......... ......... .... 39 9.2 CONCLUSI CONCLUSION ON........... ....................... ....................... ....................... .................. ........... .......... .......... .......39 10.1 GOAL........... ....................... ....................... ....................... ..................... .............. .......... .......... .......... ......... .... 41 10.2 POSSIBLE MODIFICATIONS MODIFIC ATIONS ........... ....................... ........................ ..................... ........... ..41
APPE AP PEND NDIX IX 42 DATASHEETS DATASHE ETS.......... ...................... ........................ ....................... .................... ............. ......... .......... .......... ....... .. 42
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BIBLIOGRAPHY BIBLIOGRA PHY....... .............. ............... ............... .............. .............. .............. .............. .............. ............ ......... ...... ..45
vii
LIST OF TABLES
TABLE 6-1
WAVE-FORM OBSERVATION
TABLE 6-2
VOLTAGE – SPEED CHARACTERISTICS ON NO-LOAD
TABLE 7-1
PULSE-WIDTH MODULATION
TABLE 7-2
DRIVER CIRCUIT
TABLE 8-1
TIME ANALYSIS
TABLE 8-2
COST ANALYSIS
TABLE 10-1
FUTURE MODIFICATIONS
LIST OF FIGURES
FIG. 1.1
UNMODULATED, SINE MODULATED PULSES
FIG. 1.2
SPECTRA OF PWM
FIG. 1.3
SINE SAWTOOTH PWM
FIG. 1.4
TRAILING EDGE MODULATION
FIG. 1.5
REGULAR SAMPLED PWM
FIG. 1.6
SATURATED PULSE WIDTH MODULATION
FIG. 2.1
PIN DIAGRAM
FIG. 2.2
ASTABLE OPERATION
FIG. 2.3
MONOSTABLE OPERATION
FIG. 4.1
BLOCK DIAGRAM
FIG. 4.2
CIRCUIT DIAGRAM
FIG. 4.3
PWM SIGNAL OF VARYING DUTY-CYCLES
viii
GLOSSARY OF TERMS
AC
- Alternating Current
NPT
- Non – Punch Through
CRO
- Cathode Ray Oscilloscope
DC
- Direct Current
IC
- Integrated Integrated Circuit
PWM
- Pulse Width Modulation
ix
1. INTRODUCTION TO PWM TECHNIQUE
10
0.1 GOAL “To explain PULSE WIDTH MODULATION technique in brief.”
0.2 Pulse Width Modulation (PWM) Basics Ther There e are are many many form forms s of modu modula lati tion on used used for for comm commun unic icat atin ing g information. When a high frequency signal has amplitude varied in response to a lower frequency signal we have AM (amplitude modulation). When the signal frequency is varied in response to the modulating signal we have FM (frequency modula modulatio tion. n. These These signal signals s are used used for radio radio modul modulatio ation n becaus because e the high high frequ frequen ency cy carri carrier er sign signal al is need needs s for for effic efficie ient nt radi radiat atio ion n of the the sign signal. al. When When communication by pulses was introduced, the amplitude, frequency and pulse width become possible modulation options. In many power electronic converters where the output voltage can be one of two values the only option is modulation of average conduction time.
Fig. 1.1 Unmodulated, sine sine modulated modulated pulses 1. Linear Modulation The simplest modulation to interpret is where the average ON time of the pulses varies proportionally with the modulating signal. The advantage of linear linear proces processin sing g for this this applic applicati ation on lies lies in the ease ease of de-mo de-modul dulati ation. on. The modulating signal can be recovered from the PWM by low pass filtering. For a single low frequency sine wave as modulating signal modulating the width of a fixed frequency (fs) pulse train the spectra is as shown in Fig 1.2. Clearly a low pass filter can extract the modulating component fm.
11
Fig. 1.2 Spectra of PWM 2. Sawtooth PWM The simplest analog form of generating fixed frequency PWM is by comparison with a linear slope waveform such as a saw tooth. As seen in Fig 1.2 the output signal goes high when the sine wave is higher than the saw tooth. This is implemented using a comparitor whose output voltage goes to logic HIGH when ne input is greater than the other. Other signals with straight edges can be used for for modu modula lati tion on a risi rising ng ramp ramp carr carrie ierr will will gene genera rate te PWM PWM with with Trai Traili ling ng Edge Edge Modulation.
Fig. 1.3 Sine Sawtooth PWM
It is easier to have an integrator with a reset to generate the ramp in Fig1.4 but the modulation is inferior to double edge modulation.
12
Fig. 1.4 Trailing Edge
Modulation
3. Regular Sampled PWM The scheme illustrated above generates a switching edge at the instant of crossing of the sine wave and the triangle. This is an easy scheme to implement using analog electronics but suffers the imprecision and drift of all analog computation as well as having difficulties of generating multiple edges when when the the sign signal al has has even even a smal smalll adde added d nois noise. e. Many Many modu modula lato tors rs are are now now implemented digitally but there is difficulty is i s computing the precise intercept of the modulating wave and the carrier. Regular sampled PWM makes the width of the pulse proportional to the value of the modulating signal at the beginning of the carrier period. In Fig 1.5 the intercept of the sample values with the triangle determine the edges of the Pulses. For a saw tooth wave of frequency fs the samples are at 2fs.
13
Fig. 1.5 Regular Sampled PWM
There are many ways to generate a Pulse Width Modulated signal other than fixed frequency sine sawtooth. For three phase systems the modulation of a Voltage Source Inverter can generate a PWM signal for each phase leg by comparison of the desired output voltage waveform for each phase with the same sawtooth. One alternative which is easier to implement in a computer and gives a larger modulation depth is using space vector modulation. 4. Modulation Depth
Fig. 1.6 Saturated Pulse Width Modulation For a singl ingle e phase hase inve invert rter er modul odulat ated ed by a sineine-s sawtoo wtooth th comparison, if we compare a sine wave of magnitude from -2 to +2 with a triangle from -1 to +1 the linear relation between the input signal and the average output signal will be lost. Once the sine wave reaches the peak of the transgle the pulses will be of maximum width and the modulation will then saturate. The Modulation depth is the ratio of the current signal to the case when saturation is just starting. Thus sine wave of peak 1.2 compared with a triangle with peak 2.0 will have a modulation depth of m=0.6.
14
2. 15
THEORY
16
2.1
GOAL
“To study about Dual timer IC NE556 and its operation as Asteble and Monostable Multivibrator.”
2.2 INTRODUCTION A popular version is the NE555 and this is suitable in most cases where a 555 timer is specified. The 556 is a dual version of the 555 housed in a 14-pin package, the two timers (A and B) share the same power supply pins. The circuit diagrams show a 555, but they could all be adapted to use one half of a 556. The circuit symbol for a 556 is a box with the pins arranged to suit the circuit diagram: for example 555 pin 8 at the top for the +Vs supply, 555 pin 3 output on the right. Usually just the pin numbers are used and they are not labeled with their function. The 556 can be used with a supply voltage (Vs) in the range 4.5 to 15V (18V absolute maximum).
2.3 PIN DESCRIPTION
Fig. 2.1 Pin Diagram The IC 556 is a dual timer 14 pin IC as shown in fig above. There are two sets of six pins (pin no.1 – 6 and pin no. 8 - 13) are same as the pin no. 2 – 7 in IC 555. The brief description of each pin is as follows.
17
Pin 1 & 13: Discharge. Discharge. This pin is connected internally to the collector of transistor Q1. When the output is high Q1 is OFF and acts as an open circuit to external capacitor C connected across it. On the other hand, when the output is
low, Q1 is saturated and acts as a short circuit, shorting out the external capacitor C to ground. Pin 2 & 12: Threshold . This is the non-inverting input of comparator 1, which monitors the voltage across the external capacitor. When the voltage at this pin is greater than or equal to the threshold voltage 2/3 V CC CC , the output of comparator 1 goes high, which inturn switches the output of the timer low. Pin 3 & 11: Control. An external voltage applied to this thi s terminal changes the threshold as well as trigger voltage. Thus by imposing a voltage on this pin or by connecting a pot a pot between between this pin and ground, the pulse width of the output waveform can be varied. When not used, the control pin should be bypassed to ground with a 0.01µF Capacitor to prevent any noise problems. Pin 4 & 10 : Reset . The 555 timer can be reset (disabled (disabled ) by applying a negative pulse to this pin. When the reset function is not in use, the reset terminal should be connected to +V + V CC CC to avoid any possibility of false triggering. Pin 5 & 9: 9: Output . There are two ways by which a load can be connected to the output terminal: either between pin 3 and ground or between pin3 and supply voltage +V +V CC CC . When the output is low the load current flows through the load connected between pin3 and +V + V CC CC into the output terminal and is called sink current. The current through the grounded load is zero when the output is low. For this reason the load connected between pin 3 and +V +V CC CC is load and that connected between pin 3 and ground is called the normally on load and called normally off-load . On the other hand, when the output is high the current through the load connected between pin 3 and +V +V CC CC is zero. The output terminal supplies current to the normally off load. This current is called source current. The maximum value of sink or source current is 200mA. Pin 6 & 8 : Trigger . The output of the timer depends on the amplitude of the external trigger pulse applied to this pin. The output is low i f the voltage at this pin is greater than 2/3 V CC CC . When a negative going pulse of amplitude greater than 1/3 V CC CC is applied to this pin, comparator 2 output goes low, which in turn switches the output of the timer high. The output remains high as long as the trigger terminal is held at a low voltage. Pin 7 : Ground . All voltages are measured with respect to this terminal. Pin 14: 14: +V CC CC . The supply voltage of +5V to + 18V is applied to this pin with respect to ground.
2.4 INPUTS OF 556 18
Trigger input: when < 1/3 Vs ('active low') this makes the output high (+Vs). It monitors the discharging of the timing capacitor in an astable circu circuit. it. It has a high high input input imped impedanc ance e > 2M .
Threshold input: when > 2/3 Vs ('active high') this makes the output low (0V)*. It monitors the charging of the timing capacitor in astable and monostab monostable le circuits circuits.. It has has a high high input input impedan impedance ce > 10M 10M .
Reset input: when less than about 0.7V ('active low') this makes the output low (0V), overriding other inputs. When not required it should be connected connected to +Vs. +Vs. It has has an input impedanc impedance e of about about 10k .
Control input: this can be used to adjust the threshold voltage which is set internally to be 2/3 Vs. Usually this function is not required and the control input is connected to 0V with a 0.01µF capacitor to eliminate electrical noise. It can be left unconnected if noise is not a problem.
The discharge pin is not an input, but it is listed here for convenience. It is connected to 0V when the timer output is low and is used to discharge the timing capacitor in astable and monostable circuits.
2.5 OUTPUT OF 556 The output of a standard 556 can sink and source up to 200mA. This This is more more than than most most chip chips s and and it is suff suffic icie ient nt to supp supply ly many any outp output ut transd transduc ucers ers direct directly, ly, includ including ing LEDs LEDs (with (with a resist resistor or in series series), ), low curren currentt lamps, piezo transducers, loudspeakers (with a capacitor in series), relay coils (with diode protection) and some motors (with diode protection). The output voltage does not quite reach 0V and +Vs, especially if a large current is flowing.
2.6 APPLICATION • •
Astable producing a square wave Monostable - producing a single pulse when triggered
2.7 ASTABLE OPERATION If we rearrange the circuit slightly so that both the trigger and threshold inputs are controlled by the capacitor voltage, we can cause the 555 to trigger itself repeatedly. In this case, we need two resistors in the capacitor
19
charging path so that one of them can also be in the capacitor discharge path. This gives us the circuit shown to the left.
Fig. 2.2 Astable Operation In this mode, the initial pulse when power is first applied is a bit longer than the others, having duration of T=1.1( R + R ) * C . a
b
However, from then on, the capacitor alternately charges and discharges between the two comparator threshold voltages. When charging, C starts at (1/3)Vcc and charges towards VCC. However, it is interrupted exactly halfway there, at (2/3)VCC. Therefore, the charging time, t 1 = 0.693 ( Ra + Rb ) * C
When the capacitor voltage reaches (2/3)VCC, the discharge transistor is enabled (pin 7), and this point in the circuit becomes grounded. grounded. Capacitor C now discharges through Rb alone. Starting at (2/3)VCC, it discharges towards ground, but again is interrupted halfway there, at (1/3)VCC. The discharge time, t 2 = 0.693 Rb
* C
The total period of the pulse train is
t 1 + t 2 = 0.693 ( Ra + 2 Rb ) * C
The output frequency of this circuit is the inverse of the period, f =
1.45 ( Ra
+ 2 Rb ) * C
20
Note that the duty cycle of the 555 timer circuit in astable mode cannot reach 50%. On time must always be longer than off time, because Ra must have a resistance value greater than zero to prevent the discharge transistor from directly shorting VCC to ground. Such an action would immediately destroy the 555 IC.
One interesting and very useful feature of the 555 timer in either mode is that the timing interval for either charge or discharge is independent of the supply voltage, V CC. This is because the same VCC is used both as the charging voltage and as the basis of the reference voltages for the two comparators inside the 555. Thus, the timing equations above depend only on the values for R and C in either operating mode. In addition, since all three of the internal resistors r esistors used to make up the reference voltage divider are manufactured next to each other on the same chip at the same time, they are as nearly identical as can be. Therefore, changes in temperature will also have very little effect on the timing intervals, provided the external components are temperature stable. A typical commercial 555 timer will show a drift of 50 parts per million per Centigrade degree of temperature change (50 ppm/°C) and 0.01%/Volt change in V CC. This is negligible in most practical applications.
2.8 MONOSTABLE OPERATION The 555 timer configured for monostable operation is shown in figure.
Fig. 2.3 Monostable Operation Monostable multivibrator often called a one shot multivibrator In monostable mode, the timing interval, t, is set by a single resistor and capacitor, as shown to the right. Both the threshold input and the discharge transistor (pins
21
6 & 7) are connected directly to the capacitor, while the trigger i nput is held at +VCC through a resistor. In the absence of any input, the output at pin 3 remains low and the discharge transistor prevents capacitor C from charging. When an input pulse arrives, it is capacitively coupled to pin 2, the trigger input. The pulse can be either polarity; its falling edge will trigger the 555. At this point, the output rises to +VCC and the discharge transistor turn off. Capacitor C charges through R towards +VCC. During this interval, additional pulses received at pin 2 will have no effect on circuit operation.
Time period,
T
=
1.1 RC
The value of 1.1RC isn't exactly precise, of course, but the round off error error amoun amounts ts to about about 0.126% 0.126%,, which which is much much closer closer than than compon component ent tolerances in practical circuits, and is very easy to use. The values of R and C must must be give given n in Ohms Ohms and and Fara Farads ds,, respe respect ctiv ivel ely, y, and and the the time time will will be in seco second nds. s. You You can can scal scale e the the valu values es as need needed ed and and appr approp opri riat ate e for for your your application, provided you keep proper track of your powers of 10. For example, if you specify R in megohms and C in microfarads, t will still be in seconds. But if you specify R in kilohms and C in microfarads, t will be in milliseconds. It's not difficult to keep track of this, but you must be sure to do it accurately in order to correctly calculate the component values you need for any given time interval. The The timi timing ng inte interv rval al is comp complet leted ed when when the the capa capaci cito torr volta voltage ge reache reaches s the +(2/3) +(2/3)V VCC uppe upperr thre thresh shol old d as moni monito tore red d at pin pin 6. When When this this threshold voltage is reached, the output at pin 3 goes low again, the discharge capacitor (pin 7) is turned on, and the capacitor rapidly discharges back to ground once more. The circuit is now ready to be triggered once again.
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3. CIRCUIT DESIGN
23
3.1 GOAL “To design circuit this gives square pulse of modulated pulse width as output.”
3.2 DESIGN OF ASTABLE MULTIVIBRATOR We have choosen astable frequency as 549 Hz. We have also taken value of capacitor C=0.01μF and R1=10R2. Frequency of output pulse f =
1.45 ( R1
+ 2 R2 ) * C
f , R1 and C Putting the values of of f 549
1.45
=
(10 R2
∴ R2 =
+ 2 R2 ) * 0.00000001
1.45 12 * 549 * 0.00000001
= 22 K Ω
Therefore, R1 = 10 * R2
= 10 * 22 K Ω =
3.3
220 K Ω .
DESIGN OF MONOSTABLE MULTIVIBRATOR
We have taken timing component for monostable multivibrator is 2.42ms. The time period for monostable multivibrator , T = 1.1*R1*C1 Putting the values of T and C1 in above equation R1 =
=
T
1.1 * C 1 0.00242
1.1 * 0.00000001 = 220 K Ω .
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4. CIRCUIT DESCRIPTION AND WORKING
25
4.1
GOAL
“To explain working of the PWM circuit.”
4.2 4.2
BASIC ASIC BLOCK LOCK DIAGR IAGRA AM
As shown in block diagram there are mainly three blocks: Astable Multivibrator, Monostable Multivibrator and Driving Circuit.
Fig. 4.1 Block Diagram The Basic Blocks are explained below: Astable Multivibrator: This This bloc block k prod produc uce e squa square re puls pulses es of same same frequency according to time constant RC. These pulses are fed to next block as triggering pulses. •
Monostable Monostabl e Multivibrator Multivi brator : This block produces square pulses of variable frequencies. The frequency of output pulse can be varied by changing the value of resistor shown in figure. These pulses are fed to the driving circuit. •
Driving Dri ving Circuit Circ uit : This block provides power required to drive the motor. As the frequency of output pulses of Monostable multivibrator changes, the average voltage supplied to motor changes. Hence, the speed of motor changes. •
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4.3 PULSE WIDTH MODULATION TECHNIQUE: Modulation means to vary something. Pulse Width modulation means to vary the width of pulses to obtain desired output voltage. As show shown n in the the diag diagra ram m abov above e we have have used used IC55 IC556 6 for for the the generation of pulses. The left part of IC is used as astable mode to generate square pulses of frequency 549Hz and right part of IC is used as monostable mode. The output of astable mode is fed to the trigger pin (Pin no. 8) of the monostable circuit. This monostable circuit generates pulses of variable width. The Figure shows three different pulse-width modulation signals. Fig. shows a pulse-width modulation output at a 10% duty-cycle i.e. the signal is ON for 10% of period and 90% OFF. Figure also shows Pulse-width modulation output at 50 % and 90 % duty-cycle respectively
4.4 CIRCUIT DIAGRAM
Fig. 4.2 Circuit Diagram
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Fig. 4.3 PWM signal of varying duty-cycles As shown in circuit diagram all the timing components are placed as per the calculation carried out in the portion Circuit Design. A diode D1 is added in parallel with R5 to improve duty cycle in case of Astable multivibrator. This D1 bypasses R2 during the discharging time of the cycle so that TOFF depends only on R2 and C1 only. Hence, discharging time reduces and duty cycle improves. Resistor R4 (22Ω, 2W) serves as current limiter resistor. It avoids overheating of transistor T1 by limiting load current. Transistor T1 drives the motor. T1 turns ON and OFF according to the output pulses of monostable oscillator at pin no. 9. As the transistor gets pulses on its base, it turns ON and motor runs. A diode D2 acts as free wheeling diode. As the T1 turns ON and OFF with high frequency, energy is stored in winding of motor. During OFF period this energy is dissipated in form of circulating current through D2 and winding of motor. If free wheeling diode is not provided, it may damage the transistor T1. The speed can be varied by adjusting VR1, which changes the threshold value to which capacitor C1 in the monostable circuit is charged. This, in turn, determines its output pulse width and hence the average voltage applied to the motor.
28
The position of DPDT switch determines the direction of rotation of motor. By changing the position of switch, we can make the motor to rotate in forward or reverse direction. For effective speed control, ON period of astable should be equal to the maximum pulse width of monostable.
5. TESTING AND CALIBARATION
29
5.1 GOAL “To give details about testing procedure.”
5.2 TESTING PROCEDURE AND CALIBRATION As in any technical project, it is necessary to test the work carried out. Here also we carried out various tests on our project. We assembled the circuit in section by section manner, tested the individual section and if required the section component values were modified depending upon requirements. The overall testing and calibration was divided into following steps. 1) Testing Testing of Pulse-width Pulse-width modulatio modulation n Circuit Circuit 2) Testing Testing of variation variation in speed speed with reference reference to to change change in DC voltage voltage 5.2.1 TESTING OF PULSE-WIDTH MODULATION CIRCUIT 1)
Connect the circu rcuit connection.
2)
Conn Connec ectt the the pow power er supp supply ly to the the ICs ICs from from the the line linear ar regu regula lato torr circ circuit uit
3)
Obse Observ rve e the the wav wave-fo e-form rm at at PINPIN-9 9 of IC 556 556.. Meas Measur ure e eac each outp output ut voltage for each case in observation table shown in table 7.1
4)
Vary Vary the the pot poten enti tiom omet eter er and and obse observ rve e the the eff effec ectt on on the the load load..
5.2.2 TESTING OF VARIATION IN MOTOR SPEED WITH REFERENCE TO CHANGE IN VOLTAGE. 1)
Kee Keep su supply ply volt volta age at its its no nomina inal va value lue.
2)
Obse Observ rve e the the spee speed d vari variat atio ion n of mot motor or and and mea measu sure re the the DC DC volt voltag age e by varying the potentiometer. Observe the speed variation and plot the graphical representation.
3)
Meas Measur ure e each each out outpu putt spee speed d for for each each cas case e and and take take obs obser erva vati tion on in in observation table.
30
6.
RESULTS
31
6.1 GOAL “To give obtained results of the project.”
6.2 WAVE-FORM OBSERVATION
TABLE 6-3 Sr. No. 1.
WAVE-FORM OBSERVATION PIN NO
TYPE OF WAVE-
INFERENCE
AT
FORM Square-wave of
Operation of OP-
PIN NO 9
voltage +12v
AMP in saturation
OF IC 556
TABLE 6-4 Sr. No.
region alternatively
VOLTAGE – SPEED CHARACTERISTICS ON NO-LOAD Output voltage
Speed variation
1. 2. 3. 4. 5.
32
7. BILL OF MATERIAL
33
7.1
GOAL
“To give details of components used in project.”
7.2
COMPONENT LIST
TABLE 7-1
PULSE-WIDTH MODULATION
Sr.
Component
Reference
No. 1 2 3 4 5 6 7
Type IC 556 RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR VARIABLE
8 9
RESISTOR CAPACITOR CAPACITOR
TABLE 7-2 Sr. No. 1 2 3
Value
Remark
Number IC 556 R1 R2 R3 R4 R5 VR1
220KΩ 220KΩ 330Ω 22Ω,2W 22KΩ 10KΩ
TIMER IC FIXED RESISTOR FIXED RESISTOR BISING RESISTOR CURRENT LIMITOR FIXED RESISTOR VARIATION OF PULSE WIDTH
C1 C2
0.01µF 0.01µF
RC TIME CONSTANT RC TIME CONSTANT
DRIVER CIRCUIT
Component Type TRANSISTOR DIODE DPDT SWITCH
Reference Number SL100 1N4001
Remark DRIVING TRANSISTOR FREE WHEELING DIODE MOTOR DIRECTION REVERSAL
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8. TIME & COST ANALYSIS
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8.1 GOAL “To give time and cost analysis of the project”
8.2 TIME ANALYSIS TABLE 8-1 SR.
TIME ANALYSIS TASK
TIME
NO.
REQUIRED
1 2 3
Selection of project Study of fundamental theory Desi Design gn of of over overal alll circ circuit uitry ry and and com compo pone nent nt sel selec ecti tion on and and
(IN WEEKS) 1 2 1
4
purchasing components Test Testin ing g of of ind indiv ivid idua uall sec secti tion ons s (on (on GP Boar Board) d) and and mak making ing
2
5
necessary modifications Inte Integr grat ated ed test testing ing of the the pro projec jectt (on (on GP Boar Board) d) and and
1
making necessary modifications Assembling and testing of the project on final GP Board Writing Project report Computerization of o f the report ( including figures) Total Time Required in Weeks
1 1 1 10
6 7 8
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8.3 COST ANALYSIS TABLE 8-2 SR.
COST ANALYSIS WORK / COMPONENT
NO.
COST
IC 556 RESISTORS CAPACITORS TRANSISTOR GENERAL PURPOSE PRINTED CIRCUIT BOARD PROJECT REPORT REPORT DATA ENTRY, PRINTING , XEROXING
Rs. 30 30 5 15 20 600
AND BINDING CHARGES TOTAL COST OF THE PROJECT
700
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9. CONCLUSION
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9.1 GOAL “To conclude the work carried out.”
9.2 CONCLUSION From the project work, following points can be concluded.
1. It fulfils all the requirements for its application. 2. The The moto motorr resp respon onds ds to the the aver averag age e valu value e of the the puls pulses es and and not not to the the individual pulses as the chopper works at high frequency. 3. Changing the duty-cycle of the pulse by changing the potentiometer changes the average voltage level. 4. It is possible to improve overall performance of the chopper drive
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10. FUTURE MODIFICATIONS
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10.1
GOAL
“To highlight possible modifications that can be made in the project for improving performance”.
10.2
POSSIBLE MODIFICATIONS
Following are the possible future modifications in our project work.
TABLE 10 10-1 Sr. No. 1
FUTURE MO MODIFICATIONS Modification
Purpose
Use of micro-
Constant speed variation
controller/micro-processor 2
for closed loop operation Use of MOSFET or IGBT
Higher voltage and power requirement
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APPENDIX DATASHEETS
42
43
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BIBLIOGRAPHY 1) Electronics For You – EFY Enterprises Pvt. Ltd. 2) OPAMP OPAMP and and Linear Linear Integra Integrated ted Circui Circuitt – R. A. A. Gayakwa Gayakwad. d.
3) Power Electronics Circuits, Devices and Applications - Rashid M. H. 4) Power Electronics - P. S. Bhimbara. 5) Texas Texas Inst Instrum rument ents s Linear Linear IC IC Data Data Book Book
6) WEB SITE SUPPORT - www.kpsec.freeuk.com - www.datasheetcatelog.com
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