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MY EXPERIENCE IN AUTONOMOUS ROBOTICS

Voltage Regulators
Positive Voltage Regulators
Negative Voltage Regulators
Variable Voltage Regulators
Important things to be noted about voltage regulators

VARIABLE VOLTAGE REGULATORS

Most commonly variable voltage regulator is LM317 although other variable voltage regulators are available. The advantage of variable voltage regulator is that you can get a variable voltage supply by just varying the resistance only.

http://focus.ti.com/docs/prod/folders/print/lm317.html

http://www.national.com/pf/LM/LM317.html

http://www.electronics-lab.com/articles/LM317/

3V <= (VIN − VOUT) <= 40V, Vout=1.25 V

Vout=1.25(1+R1/R2)+IadjR2

From the above the equation you can see that output voltage is proportional to R1 and R2. But in the above equation we can neglect Iadj So Vout=1.25(1+R2/R1). If you put R1=R2=1Kohm Vout=2.5V. LM317 can be used to drive motor because it can handle output current up to 1.5A. In some low power devices like image sensor or USB we require 3.3V, in that circuit we use LM317.In a line follower we introduce some speed variations for motor for different bendings, you can do it by either using PWM or using the above circuit.