IC OpAmp dual rail Power connections

Hi All,
I’m new to KiCAD, although I’ve been designing PCB’s for a good while.

I’ve created my full schematic (so much easier than the software I used before :slight_smile: and I’ve designed my power supply with dual rails to supply the Audio OpAmps. The power connections on the schematic selected as +15v and -15V from the Power symbol list.

However, the OpAmp I’m using has the hidden power pins label V+ and V-. There are no V+ and V- symbols in the drop down power connections list, so how you I relate the two?

Many Thanks
Mike

Make a copy of the symbol in your personal library then edit the power pins to make them visible then you can connect to them with wires as normal?

Or edit the instance of the symbol in your schematic.

I have an old IEEE TTL74 symbol in an old v5 project. I noticed that the symbol in the newer library has visible power pins now.

Please tell us your KiCad version and what opamp symbol that you are using. Opamps mostly have the power pins in a separate “Unit” with visible power pins on recent versions

KiCAD 7.0 on a Mac

Thanks Both.

The OpAmp I’m using is the OP275 and yes it does have a third ‘unit’, that’s the one labelled V+ & V-. I’ve put into the schematic a number of OpAmps, but the third unit has never been an insert option. Should it appear on the schematic? From my question I’d assumed connections would be made in the background, hence asking how I can relate the two.

Put that 3rd unit somewhere on the schematic and connect it up to the power rails.

You’ll find that the length of the pins on that power unit match up with the triangle of the op amps on the 50 mil grid, if you wish to include it in the main part of the schematic.

ok but the third unit has never been an insert option?

Place the opamp symbol and then edit the properties to select unit C and you will see the graphics change.

Hidden power pins on an opamp was a terrible idea.
Imagine having two parts on your schematic, one on 12V and 0V, the other on +/-5V rails.
There is no way to avoid shorting rails together

The Unit C approach allows you to do this and also to show the associated decoupling capacitors without cluttering up the analogue function circuits of the opamps.

It all makes a much neater and more informative schematic

OK yes I can see now how you do that as you place the Opamps, but if I select an existing Opamp on the schematic and do that, it changes the ‘unit’ to the power connections, deleting the actual Opamp?

So do I need to go back and delete all the Opamps and replace them?

No, you don’t change the existing opamps. Presumably they are correct in the schematic. You just need to add one instance of a unit C for each IC that you have. Half the number of opamps assuming it’s a dual opamp IC and you have used an even number of opamps.

Look, here’s an example. I was making a ring oscillator with some ancient DTL chips. DTµL846 is the DTL equivalent of the 7400 if you like. You see that I have units A-D for the gates and a unit E for the power.

ring-oscillator

Hmm, and it looks like I have some stray wires in the schematic. It was only to guide the “breadboard” and never turned into a PCB.

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I will often hide the Ref & Value of part C (in properties) and move the power pins to an op amp symbol.
Compare U1 & U2.

ksnip_20230325-005849

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