What is an Adjustable Voltage Regulator?
An Adjustable Voltage Regulator is a regulator that can output adjustable voltages from anywhere in the range that the voltage regulator is designed to output.
A LM317 voltage regulator, for example, can be made to output any voltages from +1.2V-37V. This voltage adjustment is achieved by
placing different resistor values for the resistor R2 below in the schematic.
Here you see we connect two resistors to the voltage regulator. These resistors determine the voltage that the voltage regulator adjusts to and outputs.
The voltage that the adjustable regulator outputs is determined by the equation below:
Therefore, you can see based on this formula, that the more the value of resistor R2 increases, the greater the voltage output. If we put 12 volts into the voltage regulator and want to regulate it down to 5V, based on the formula above, the value of R2 must be 720Ω. Now if we want to output 10 volts, we swap out the R2 resistor and place a 1.5KΩ resistor in its place, and now we will have 10 volts.
This is the advantage of adjustable voltage regulators. You can adjust it to any voltage within the range that the voltage regulator supports.
Note: The capacitors C1 and C2 are used to clean up the power line. C1 is optional and it's used to clean up transient response.
C2 is needed if the device is far from any filter capacitors. This capacitor helps smooth out the power supply line in case of abrupt current spikes.