Simple 9V voltage regulator circuit

A very quick post here to document a very simple 9V voltage regulator. This is part of my solar switch project. For the final setup, I want to replace the arduino uno with something of a more appropriate size, such as wiring my own arduino-on-a-breadboard, or using an arduino pro mini. In either case, I have to supply my own power from my 12V solar battery source, and seeing as the solar batteries are actually over 13V when fully charged, I need to drop that down a bit to get into the 5 – 12V range accepted by the arduino pro mini.

The circuit laid out on the breadboard with a DC 12V power supply as input.

The circuit laid out on the breadboard with a DC 12V power supply as input.

I researched around and learned that I needed something called a voltage regulator, which is a component that looks much like a common MOSFET transister, but slightly larger. It has three pins which are quite simply voltage in, voltage out, and ground. This couldn’t be easier to understand. I’m using the LM7809 voltage regulator from Fairchild. It takes a maximum of 35 volts as input and outputs 9 volts.

For the most basic voltage regulator circuit, you only need two more components, both capacitors. One sits between voltage in and ground, and the other between voltage out and ground. The former is an electrolytic capacitor of 0.33uF, while the latter is a ceramic capacitor of .1uF. According to various sources, the values do not have to be spot on, and there seems to be an acceptable range, but I took the figures from the LM7809 datasheet to play it safe.

Here is the circuit diagram helpfully provided by the datasheet:

LM78XX voltage regulator circuit diagram

The point is just how simple this is. The next time you need to drop your voltage from a battery or DC plug, just get yourself these three parts and plug them in and save some money.

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