## Wednesday, October 2, 2013

### Voltage Regulator Calculation

Together with preset R2 it determines the current flowing through the ADJ pin, as follows: Vout = VREF [1+(R2/R1)]+I ADJ R2 If for the sake of convenience we ignore I ADJ, enter the reference voltage (1.2 V) and for R1 select a value of one thousand times that voltage (i.e., 1.2 k?) then the equation is simplified to: R2 = 1000 (Vout – 1.2) In practice, simply determine the voltage drop across R2 (output voltage minus reference voltage) and you get your resistance value directly in kilo-ohms. For example, for 5 V R2 becomes 5–1.2 = 3.8 k? which is easiest made by connecting 3.3k and 470R resistors in series. In the case of relatively low voltages, smaller resistor values are recommended. This is because sufficient current needs to flow to enable the voltage regulator to do its job. A simple solution is to choose, say, 120 ? for R1. R2 then becomes: R2 = 100 (Vout – 1.2)

**Related Posts :**calculation, regulator, voltage