APPLICATION – MANUAL SPEED CONTROL FOR DC MOTOR Speed is proportional to applied voltage, VM 0 i Potentiometer Arm is movable and allows to change R1 and R2 keeping their sum constant: 2 pot R R Battery Assumption (no load) 0 i speed battery V V Potentiometer is not affected by connection to amplifier Circuit diagram [rpm ] 4 M M M speed KV KV [rpm ] 4 M battery KV
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APPLICATION – MANUAL SPEED CONTROL FOR DC MOTOR Speed is proportional to applied voltage, VM Potentiometer Arm is movable and allows to change R1 and R2.
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APPLICATION – MANUAL SPEED CONTROL FOR DC MOTOR
Speed is proportionalto applied voltage, VM0i
Potentiometer
Arm is movable and allows to change R1 and R2 keeping their sum constant:
2 potR R
Battery
Assumption (no load)0i
speed batteryV V
Potentiometer is not affectedby connection to amplifier
Circuit diagram [rpm] 4M M M speedK V K V
[rpm] 4M batteryK V
Model using node analysis
2 1
0O O S
O
V V VI
R R
1 2
100 , 5 , 8
Find ,O O SI A V V V V
R R
22
2 1
s OOV VV
PR R
Resistors values should be high
Why not use very large values?
13V V
1100I A
1
330
100
VR k
A
2
1
2
2
1
3. . :
5
5:
3
O
O
Re g R
I R
or RI
R
Design equations
Use trial and error. PickHighest possible R1, determineR2 and analyze resulting circuit
1
1
527 450
3/O
R k kR I
2Closest R 430k
Analysis of solution
2 1 2
1 2
S O
O
RV R R IV
R R
4.98
OV V
Are there other factors that weshould consider; e.g., is Ioreally constant?, tolerances?
Standard= Off-the-self – available only in certain values