PWR_FLAG and Voltage Regulator

I use a voltage regulator LM7812 with my power supply. If I connect the +12V and the PWR_FLAG to the output of the LM7812 then I get the „Error: Pins of type Output and Power output are connected“. If I remove the PWR_FLAG then I get the message that the power input in the schematics is not connected to anything.

One work around this problem is to place a 1 Ohm resistor (R2) between the LM7812 and the PWR_FLAG. In this case the error message goes away, because the LM7812 output is not directly connected to the PWR_FLAG.

Is there some other way to omit this error message, because actually I don‘t need this additional 1 Ohm resistor (R2) in my schematics?

Schematics:

Gawd! I hare that damn PWR_FLAG requirement in Kicad I’ve never under properly understood stood why its needed.
Anyway, what I do is set up the PWR_xxxx flags off to the side of the schematic. So up in the corner I set up PWR_FLAG & PWR_GND to their own designator - VCC, +5V, GND whatever.

This seems to work for me - I do it automatically now
Hope this helps

The pin type of the LM symbol is probably “Output” while it should be “Power output”. Then the power flag isn’t needed.

Can you please show us the pin table of the LM7812CV symbol?

Ha, eelik came to the same conclusion. In addition I think the INPUT pin should be type Power Input, and then there should be a PWR_FLAG on the net it’s on.

There is a LM7812 in the standard library. Did you go off and make your own?

I downloaded the LM7812 symbol from snapeda.com. The INPUT was set to Input, GND to Power input and OUTPUT to output. I changed the OUTPUT to Power output and I could remove the resistor and the PWR_FLAG, without an error.

There is also a LM7812 in the standard Regulator_Linear library, but here I need a PWR_FLAG on the input side and on GND, in order to get it to work.

The PWR-Flagitis of KiCad can be pretty confusing at times.

There is a post in the FAQ about ErrType(3):

I remove the flag if I want to print a hard copy. But, sometimes PCB projects can be expensive and I personally want all the auto-error checking I can get before I throw my money at a new project.

1 Like

That is the correct way to do it. You should have stuck with the standard library. Externally sourced symbols often have wrong pin types.

2 Likes