Voltage Regulator is very important thing for power supply. Voltage Regulator maintain the output voltage constant as we want. Many ICs can maintain voltage output. For example LM7805 can maintain voltage at 5V. LM7809 can maintain voltage at 9V. LM7812 mantain voltage at 12V and so on. Now we will give you tutorial how to make variable voltage regulator.
The question is, can we regulate voltage at every volt we want? Yes, the answer is LM317. The datasheet says that :
The LM317 device is an adjustable three-terminal positive-voltage regulator capable of supplying more than 1.5 A over an output-voltage range of 1.25 V to
37 V. It requires only two external resistors to set the output voltage. The device features a typical line regulation of 0.01% and typical load regulation of
0.1%. It includes current limiting, thermal overload protection, and safe operating area protection. Overload protection remains functional even if the
ADJUST terminal is disconnected.
How to use LM317 as Variable Voltage Regulator?
Use LM317 as variable voltage regulator is simple, you can use schematic below :
LM317 Vout equation will be : Vout = 1.25V*(1+R2/R1)
So, the key lay on R2. R2 must be variable resistor, so we can change the resistance easily. Changing the resistance will change the output.
If you still thinking that schematic above less simple, you can really make a really simple circuit using only LM317, R1 and R2. But maybe you can get a little noise from this circuit, so you can add capacitor at Vin and Vout.