Electronic – Regulate 5V to 5V with LM1117


My board will be mostly powered with an already regulated 5V input from USB (or wall charger), but I want it protected for higher supply voltage in case somebody plugs in the wrong voltage.

So I'm putting a voltage regulator on the board after Vin.

Initially I was planning to use the LP2985 but realised I may need to draw higher current, probably around 1A, so I'm considering the LM1117.

I see it is used on the Arduino Nano, which accepts 5V as an input, but after reading the datasheet, I understand Vin needs to be higher than Vout.

Can I use the LM1117 to convert 5V to 5V ?

Best Answer

Adding another regulator is a bad idea since it complicates the power line.

A better solution is to protect your circuit by shutting off the power when the input voltage exceeds some limit. The circuit below will disconnect the source if the voltage goes over 5.5V. You can make it closer to 5V by reducing the Zener voltage from the shown 5.1V device.


simulate this circuit – Schematic created using CircuitLab


When Vin is under 5.5V the zener is off as is Q1. R3 holds the gate of M1 low turning it on as a low resistance. When Vin rises above 5.5V D1 holds the base of Q1 down turning it on which pulls up the voltage on R3 to close to Vin, which turns off M1.