24-07-2011, 10:12 PM
c8 is required when the regulator is far from the power-supply filter. so normally you would get away with not having it there at all so thats why your circuit works regardless you have stated tha yours is a tl7805 whom which is made by texas instruments whom they sugest a 0.22 uf on the output and a 0.33 uf on the imput. but all that changes when using a diferent brand of 7805 regulator as diferent companies can specify differen values for these 2 capacitors . i have placed a ceramic capacitor of 100 nf (capacitor number is 104) for the value of c8 as the schematic i have for this circuit does have it in place which sugest to me that his c8 capacitor was positioned off board so his wire lengths were longer thus so he actually needed to have the c8 capacitor installed.personally when installing voltage regulators i always install the 2 capacitors 98 percent of all schematics use both capacitors on a regulator and as the second ceramic capacitor cost 0.1 cents you would be silly not to install it anyway all the rest of my caps were ceramic type caps for that reason which are rated at 50 volts and are of a smaller size than what others have used so fit nicely on the prototype board. thers is no advantage of shoving in a larger tantalum capacitor as its package size and shape vary from a ceramic but still achieve the same job as the ceramic cap. if the original circuit designer or anyone else that designs a circuit thinks they need a diferent type of cap it is displayed in that schematic by specifying it in the footnotes the 2 straight lines on schematic means a ceramic capacitor normally unless of course its a audio circuit and then the size and type of capacitors used changes greatly .
