Transcript Slide 1

APPLICATION – MANUAL SPEED CONTROL FOR DC MOTOR
Battery
Speed is proportional
to applied voltage, VM
i0
Potentiometer
Assumption
Arm is movable and allows to
change R1 and R2 keeping
their sum constant: R   R
2
Circuit diagram
pot
i  0 (no
load)
 Vspeed  Vbattery
Potentiometer is not affected
by connection to amplifier
[rpm]  K MVM  4 K MVspeed
[rpm]   4 K MVbattery 
http://www.wiley.com/college/irwin/0470128690/animations/swf/3-23.swf
VO2 Vs  VO 
P

R2
R1
I 1  100  A
Standard= Off-the-self – available only in certain values

V1  3V

R1 
2
Model using node analysis
IO  100 A, VO  5V , VS  8V
VO VO  VS
IO 

0
Find R1 , R2
R2
R1
3V
 30k 
100 A
3 R2
e . g . : R1 
5  I O R2
5
Resistors values should be high
Why not use very large values?
Use trial and error. Pick
Highest possible R1, determine
3
 I O R2 and analyze resulting circuit
R1
5
R1  27k 
 450k
3 / R1  I O
Design equations
Closest R 2  430k 
Analysis of solution
Are there other factors that we
should consider; e.g., is Io
R2VS  R1 R2 I O V  4.98V
O
VO 
really constant?, tolerances?
R1  R2
or : R2 