In several previous articles some positive regulators constructed using linear voltage regulator IC that provides fixed output voltage. Now I want to explain how to build a variable voltage regulator that is more flexible because the output voltage can be set as needed.
In this article the regulator IC to be selected is a type LM317 adjustable regulator. The reason this election is already very popular DC voltage regulator IC which is a family of three terminal positive regulator. This IC has a configuration input, adj and output. So this will be easy for the beginner to understand the construction.
LM317 regulator IC is an integrated circuit designed to supply more than 1.5A load current with a voltage range can be set from 1.2V to 37V. So IC LM317 is a voltage regulator IC that can be programmed. Internally it has been installed IC circuit current limiting, short-circuit and over-thermal protection. So this feature would eliminate the worries will be fewer mistakes in construction.
Variable Voltage Regulator Circuit Formula
Here is the basic circuit of a DC voltage regulator circuit IC LM317 (datasheet), where the calculation of the components that will be used to follow the following formula:
VOut = 1.25V (1 + R 2 / R 1) + IadjR2,
in practice negligible IadjR2 is intended for current under 100uA. The Variable voltage regulator circuit below will set the output voltage range of 1.5V to 12V as below.
In the circuit R1 value is 100R (Ohm), while the output voltage changes according to changes in the value of R2 value (Vout) follow the formula above. From the calculation, where the overall R2 using a variable resistor 1K Ohm. Value of the input voltage that can be achieved is at 13.75V (R2 = 1000 Ohm), 12V (R2 = 860 Ohm), 3V (R2 = 140 Ohm), with a minimum value of 1.25V (R2 = 0).
So the value calculation and test circuit obtained results are not much different to the formula, the output voltage increases proportionally with the decrease in the value of resistor R2 in the voltage range of 1.25V-13.75V. Hopefully with practice you are doing you can understand how to build a variable voltage regulator using LM317 (T).