Tony... That was just the sort of constructive feedback I was looking for! :-) Thx, -marc On 10/5/03 18:04, "Tony Harris" wrote: > You really don't need a cap on the middle pin - the middle pin is tied to > ground (for ground reference for the chip), and if you put a cap to it, what > would you put it between, connecting to positive supply is the same as input > pin to ground, and regulated is the same as output to ground... > > The places you need caps are on the input, and on the output. Take a look at > this datasheet... > > http://www.national.com/ds/LM/LM340.pdf > > It has a typical config for a fixed output regulator. > > Personally, I like a decent sized cap on the input to limit input > fluctuations, and a not as big one on the output of the regulator. I'd say > your first cap (100uF) on input, second (10uF) on output, and save the 100nF > for use as a decoupling cap somewhere in what uses the power supply :) I > would also consider a diode for a discharge path (see later in the data > sheet) > > > -Tony > > ----- Original Message ----- > From: "Marc Nicholas" > To: > Sent: Saturday, May 10, 2003 4:43 PM > Subject: [EE]: simple 7805 breadboard power supplies > > >> I must admit I'm a neophyte when it comes to analog electronics...so > please >> bear with me ;-) >> >> I'm building a 7805-based breadboard power supply...to be fed by one of >> those selectable "wall wart" 250mA transformers. >> >> I'm thinking 9vdc in to a 1A 7805, and then a 100uF (35v electro), 10uF > (15v >> electro), and 100nF (100v ceramic -- all I could find) capacitor off pins >> 1-3 respectively. Does this sound reasonable? >> >> Obviously I'll be careful about things like polarity and over heating, and >> the circuit will be semi-permanent (ha! oxy moron!), so I'm not too > worried. >> >> I probably have some 1N4001s kicking around and numerous LEDs if folk > really >> suggest a use 'em. >> >> More importantly, I'm after feedback about what's acceptable in the way of >> capacitor values (and why) and general "gotchas" with power. >> >> TIA :-) >> >> >> -marc >> >> -------------------------------------------------- >> Marc Nicholas Geekythings Inc. C/416.543.4896 >> UNIX, Database, Security and Networking Consulting >> >> -- >> http://www.piclist.com#nomail Going offline? Don't AutoReply us! >> email listserv@mitvma.mit.edu with SET PICList DIGEST in the body >> >> > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > -------------------------------------------------- Marc Nicholas Geekythings Inc. C/416.543.4896 UNIX, Database, Security and Networking Consulting -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body