PZTA42 has 3 pins in symbol, 4 pins in footprint
PZTA42 is a SOT-223 NPN BJT (datasheet)
The pin layout of the physical part is BCEC, i.e. 1-Base, 2,4-Collector, 3-Emitter. See screenshot from datasheet:
The current Kicad symbol is basically an NPN-BCE, i.e. 1-Base, 2-Collector, 3-Emitter. The symbol assigns SOT-223 as the default footprint.
The problem is SOT-223 is a 4-pin footprint, but the symbol has only 3 pins. Pin 4 in the footprint should correspond to the collector (pin 2).
I can think of two solutions:
- change the PZTA42 symbol to be essentially Q_NPN_BCEC, which would match the existing SOT-223 footprint
- Keep the PZTA42 symbol as is, but change the default footprint to SOT-223-3_TabPin2. This will effectively connect pins 2 and 4 in the footprint rather than the schematic.
I think 1 is the better solution because then the kicad symbol will match the datasheet. It is a symbol pin change, which will break any schematics currently using this symbol, but is this a big problem if it's already broken?
2 has the advantage of not breaking existing schematics (I think) but then the symbol doesn't match the datasheet, and it will use a non-standard footprint for no real reason.
I'm happy to submit a pull request if I can get some guidance on which solution to go for.