Hi,
I have had a PCB made and found I made a mistake! I have connected the E of a BCR148 to the C and vice versa, does anyone know off hand of a similar NPN transistor that has these switched around in a SOT-23 package?
Thanks
I've looked up the data sheet for the BCR148, and it has the same layout as just about all SOT-23 transistors, with the collector on its own, with the base and emitter on the other side from the collector.
I am guessing that the layout that you show is what you are looking for not what the BCR148 is?
If so, I have two suggestions. One is mechanically fairly horrible and the other is electrically doubtful, but I think that either would work.
1) Bend the pins of the BCR148 up so that they are level or above the top surface of the package. Now turn the package over, and rotate it so that the base is where is was, and the emitter and collector have been swapped. Solder it by hand and hope no-one looks too closely.
2) As others have mentioned, the base resistors may not be needed. In that case fit a standard transistor like the MMBT3904 in the way that you have laid out. If the collector voltage is small, less than 6 V for that transistor, and you don't need much gain, the transistor will work the wrong way up, just badly, but that might be good enough for your application.
The NPN transistor has N regions for both collector and emitter, with the P region for the base. There are all sorts of clever features in the construction, such as uneven doping of the P base region to improve the gain, which reduces the gain when using it backwards. However, the NPN transistor with the collector and emitter swapped is still an NPN transistor, so it may well work.