i am trying to design my first pcb, its for a power supply. For the filter caps, I want to provide both a small cap option and big cap option, e.g. C2 supporting both 5mm caps and 10mm caps. How can i do this without redrawing the part.

 

i would enlarge the copper land and add a drill hole. no need to specify a part for just one additional hole.

 

yeah or just add the hole and pull a trace from the main pad over to the new hole..

 

or you can put multiple different caps in the schematic.

 

Slide switch to switch connection between 10 mm and 5 mm cap?If that's what you meant?

 

I meant put both parts into the schematic, place them one over the other on the pcb, and then popualate the one that you want when you assemble the board.

 

Kubeek said what I was thinking. Put two different capacitors connected in parallel, the smaller cap "inside" the footprint of the larger cap. A lot depends on the distance between pins. You may be able to do it like this:



or, if your board house complains that there's overlap, you can turn one of them 90 degrees like this:



EDIT: The first one really didn't work in this example, because the drill of the outer cap is cut off a bit. Like I said, it depends on the pin pitch.

EDIT #2: Or you can do as I have seen professionals do and offset them a bit:

 

Also if you want to do it properly don't forget to make a note in the schematic that these two parts are alternate components.

 

thanks guys, i like the idea of two parts in schematic, will give it a try.

 

the pcb design and the schematic are attached below, could you guys please take a look at it and let me know if anything can be improved. board is approximately 3in x 2in.

Also, is the bridge rectifier wired correctly in the schematic.I have only made the four bridge rectifier diodes with the high current traces, any other diode that might need to handle high current?

 

The schematic is quite hard to read, normally you would draw it like this, so that the highest voltage is on the top and lowest on the bottom. I also makes the design nice and symmetrical and the electrolytic caps oriented the same way.
http://cdn.head-fi.org/a/ab/900x900px-LL-abc0779d_317_337Schematic.png

Second thing is that large capacitors on the output are not necessary and might even ruin the stability of the regulator, so better put them at the input side instead. Also check the datasheet for the recommendations on the blocking caps near the regulators.

 

Hi doors666,

When taking snapshots of schematics/PCB designs drawn in Eagle, it's best to use the "Export" option. Go to "File" --> "Export", browse for where you want to save the image, and set the DPI to 250 or higher, to ensure it is high quality (the higher the DPI, the further it can be zoomed before pixelating). You can do this on both the schematic and PCB designs.

I recommend doing that, then re-uploading the files.

Matt

 

yeah, i realized that about the schematic after i saw some others on the net, but the damage was already done, it will be really hard to redo it now without disturbing the board.

whats generally considered a good value for the output caps for this, I plan to use this as a general purpose bench supply for testing, as well as to power small audio gear.

. not sure if I understand your comment about the blocking caps.

 

As for your circuit, where is the AC input? AC does not have a + or -, so do not label AC inputs with "plus" or "minus".

 

Here are the new exported pics..

 

Again, where is your AC input? If "Vplus" and "Vminus" are supposed to represent your AC source, the circuit will not work. Think you should read up a bit more on how AC works. There are not separate lines for + and -, you have a + and - current on the same wire, with respect to neutral.

 

Try something like this instead:

Connect your regulators to the +25 and -25 volt outputs.

 

I have redone the schematic. Electrically the board was not changed, changed the text on the board. V+ and V- were there as I was initially planning to use an off board rectifier, and later added the diodes here and forgot to change the text on the board to ac power.

question: this should work with dc supply also? Some of the diodes in the BR will never be conducting, but the circuit should work right?

 

Matt, your switch S1 and fuse F1 must be interchanged.
The first component that AC mains LIVE is connected to is the fuse.

A 5A fuse is overkill for an 80VA transformer. I would specify 1A for starters.

 

Matt, your switch S1 and fuse F1 must be interchanged.
The first component that AC mains LIVE is connected to is the fuse.

A 5A fuse is overkill for an 80VA transformer. I would specify 1A for starters.

That's not my circuit, I just pulled it off google

I just used it for illustration of how AC is converted to +/- DC.