I have some questions regarding the proper use of a 7805 Voltage Regulator.. I'm considering make my own standalone Arduino, but I'm still not quite sure how this voltage regulator thing works. I have a 7805(CT?) regulator, and was using it with a breadboard and a volt meter to figure out if it was working or not. I wired up the capacitors, put in 9 volts, grounded the ground pin, and measured the output voltage (a steady 5 volts :)). As a test, I then removed the capacitors and repeated the test, and still received a steady 5 volts output. My question is: What's the point of the capacitors, and how do I know what kind to use? I saw no real difference in the output with or without them! Thanks for the help :-?.
Well, I seem to have found the answer myself :).
Here it is if anyone's interested:
These are all linear regulators. They require input and output capacitors located close to the regulator in order to operate reliably. Without these capacitors or if they are too small or to far away, the regulator can oscillate at high frequencies depending on the load etc. The data sheets make recommendations but I've found that a minimum of 100uF on the input and 10uF on the output always seems to work.
Yes, basically the capacitors are used on the power lines to smooth out any electrical noise.
The faster microcontrollers operate, the more prone they are to noise, which can cause random glitches and resets etc, so capacitors are used to filter this out and provide a cleaner supply.
As that quote says the data sheet should always be consulted but the values don't have to be anything like that high. I use at least 1 to 2.2uF along with a 100nF ceramic.
As was mentioned those values seem too high and you need to review
the datasheet for the component specifications.
A number of linear regulators recommend particular types of capacitors for
stability. A tantalum or electrolytic capacitors with a higher series
resistance (ESR) may be the preferred solution (particular among some
of the older and lower cost parts).
(* jcl *)
A tantalum or electrolytic capacitors
Don't use tantalum capacitors for supply decoupling because when they go they often go short.
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1257464508
heh, i keep telling the people on a vintage mac forum that, but they insist on using tant's cause "they wont leak", which they can
Gumpy Mike,
As that quote says the data sheet should always be consulted but the values don't have to be anything like that high. I use at least 1 to 2.2uF along with a 100nF ceramic.
When you say you use a 2.2uF electrolytic and a 100nF ceramic, do you mean a 2.2uF on the input and a 100nF on the output, or are you using one of each on both sides for a total of four capacitors?
And by the way, depending on the power you supply to it (let's say 9V or 12V), these things can get really hot. Especially if you use an ethernet shield or anything that will considerably increase the power consumption along with your Arduino.
So you may want to consider space for a heat dissipator in your project. This is also within the "proper use" of a 7805...
my two cents.