DC Motor Control By Using a Chopper Circuit

1. EEE322 Course Project
DC Motor Speed Control By Using
Chopper Circuit

2. Theory
• Dc motors are widely used in robotics for
their small size and high energy output.
• The typical DC motors operate on as few as
1.5 volts on up to 100 volts.
• Roboticists often use motors that operate on
6 12 or 24 volts.
• A low voltage(e.g.12 volts or less ) DC motor
may draw from 100MA to several amps at
stall depending on its design.
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3. • Main characteristics of DC Motors include:
High Speed, Low Torque, Reversibility and
Continuos Motion.
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4. Principle Of Magnet DC Motors
If you were to place a
loop of wire within the
magnetic field of a
horseshoe magnet in
the manner (FİG 14)
and apply current to it
you would experience a
motor action such that
the loop of wire would
try to turn.
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5. • This effect will only occur when the wire lays
adjacent or in line with the magnetic field
(FİG 15).
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6. • Let’s say the loop wire was arranged on a bearing
so that it could freely rotate .What we need is
some way of switching the current through the
wire on each 180 degrees of rotation. We do this
with a simple brush mechanism(FİG 14).In this
case as the loop rotates to a vertical position you
notice that at the end of wire leaves the switch
contact. Under inertia,the loop continues to
rotate until the other side of the loop strikes the
right hand side contact and original loop contact
makes contact with the left hand side brush.
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7. If you examine this concept carefully
you can see that while current is
applied to the brush contacts the loop
of wire will rotate through 180 degrees
where contact will be made again and
the rotor (the revolving thing )will
continue rotation
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8. • The direction of rotation depends on:
The polarity of the battery (Power Source)
• The stator is the stationary outside part of a
motor. The rotor is the inner part which
rotates. The ends of each wire set for a
connecting set is called a commutator. The
torque of a motor is the rotary force produced
on its output shaft.
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9. • When a motor is stalled it is producing the
max. amount of torque that it can produce.
Hence the torque rating is usually taken when
the motor has stalled and is called the stall
torque
• Motors that draw more current will deliver
more power.
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10. Application Side Of the Project
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11. • The speed of the output shaft is directly
proportional with the applied voltage.
• So the voltage drop on load (motor) was the
thing we consider throgh all the design
procedure.
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12. •Voltage drop is controlled by the variable resistance
•Diac – triac compound: Purpose is to reduce loss. Diac simply triggers triac for
frequencies to give output but applications without diac is also possible.
•In fact, the same circuit could easily be done by using simple potentiometer and
capacitor just adjusting the voltage drop on the load.
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13. •H-bridge is used to control direction manually with a digital logic.
•Adapter is used to convert 230 AC into 12 V DC.
•Dimmer (which is shown not by block diagram) is to adjust speed.
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14. • In fact there are ready
integrated circuits for
this purpose but
we made it ourselves for design reasons. (To
reduce the power loss resistance values
decreased. npn – pnp compund used instead
of the same transistor couple which is much
better.)
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16. • Flyback diodes
– Small voltages
– Upside npn downside
pnp
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17. • Specifications of the h-bridge we constructed
– Can handle 2.2 to 9.6 V properly.
– Won’t work with motors with resistance lower
than 5Ω. (Our motor has 20Ω resistance.)
– Dangerous if R1-R2 or R3-R4 connected at the
same time since the battery or source is shorted.
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18. • 5,7 volt ouput is seen
At the output of the
H-bridge.
• Efficiency of the h-bridge we use is about
%48.
• 3V feed is used to handle control of the
bridge.
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19. Where to Use This Circuit &
Suggestions
• This circuit can easily be used for fan
applications and anywhere we need dc motor
to rotate permanently.
• A switch can be used to switch between
“turbo” mode in which we want more power
and torque (overspeeding) from the motor
where we need performance. (Which is
directly connecting to 12V by a switch.)
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20. • For overspeeding there must be calculation done
how much time it will be overspeeded and how
much the motor can handle.
• For fan applications temperature sensors would
be beneficial. (Closed loop control system)
• This circuit can also be used for lighting. Since
there is a net voltage drop of about 6 volts a
group of LED can be directly controlled. Small
light bulbs can be directly handled by this circuit
but for higher ranges need to increase voltage.
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21. • Can be used to drive small conveyor belts in 2
directions and with dimmer would be able to
handle both directional control and speed
control.
• It is also possible to use this circuit for any
robotic application where directional control
is needed with speed control such as RC
helicopters’ or aircrafts’ propellers.
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22. RESOURCES
• Bilgiç, Mustafa Murat. "Single Phase Induction Motor Speed Control Using
PWM AC Chopper Fan Applicaitons” M.Sc. Thesis
Istanbul Technical University, 2007.
• Wikipedia Online Encyclopedia. 2012. Wikipedia. 28.5.2012
< http://en.wikipedia.org/wiki/H_bridge>.
• Which.net 2012 “Speed Controllers” Online Source. 25 May 2012.
<
http://homepages.which.net/~paul.hills/SpeedControl/SpeedControllersB
ody.html>
• Cook, David “h-bridge Motor Driver Using Bipolar Transistors” May 2012
<http://www.robotroom.com/BipolarHBridge.html>
• Datasheets for parts used throughout the project are available at;
• BC307 from Motorola Semiconductor™
• <http://www.datasheetcatalog.org/datasheet/motorola/BC308C.pdf>
• 2N3904 from Fairchild Semiconductor™
• <http://www.datasheetcatalog.org/datasheet/fairchild/2N3904.pdf>
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23. Thanks...
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