Transcript Slide 1
APPLICATION – MANUAL SPEED CONTROL FOR DC MOTOR
Battery
Speed is proportional
to applied voltage, VM
i0
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