Hello again,
After copying a drawing to make a THT schematic & PCB, and finding the board size a little too large, I decided to try SMT for the first time.
It’s a simple interface between a FT-8900 and a sound card, for Packet Radio, designed by I6IBE.
The original transistor in the first design was a 2N3019, and not finding one as SMT, I made a ‘best guess’ as a replacement, the BCX56,(SOT-89 package) which according to a datasheet
differs from the Symbol and the Footprint in the V7 Library
There is an old post…
but I’m not sure if it is connected to what I am seeing.
To me, the Datasheet pin labelling looks correct.
You can always check if connection lines suggest you to do connections that agree with schematic and datasheet. Datasheet is the reference always.
I don’t use KiCad libraries. I make a symbol for each element I want to use with right footprint attached and save it in my library. Once checked I then know that I can safely use it not checking anything in datasheet.
I have 8.99 nightly as well as 7.0.11 here, and the pin numbering is in opposite order in the symbol compared to the datasheet SOT89 version. But the footprint seems to match physically anyway; in KiCad 1 is on the left of the footprint and is base, 2 in the middle - collector, 3 on the right - emitter.
…you won’t need an 80V, 1A npn switch to sink probably less than 10mA (I am guessing) to pull the PTT line low.
I use mosfets these days for such applications, but f you want to stay with an npn, maybe try a garden-variety part like the 40V, 200mA, MMBT3904 in a sot-23 package:
Why are you using a big medium power transistor when it looks like you only need a small signal transistor? SOT23 is pretty much the standard size for SMT signal level transistors (Although you can also get MOSfets that can switch a few Amp in SOT23. Dual transistors in a SOT23-6 are also common. You can go to even smaller packages, but those become progressively more difficult to solder. SOT23 is quite easy, while SOT23-6 is already quite difficult because of the small pitch between the pins.
You are discovering that SMD transistor and diode pad numbering is not standardised. Different brands with the same part number can vary which is pad 1.
Check against datasheets VERY carefully.
