Partlist Wednesday: NPN transistors

Posted on Wednesday, August 3rd, 2011 in partlist, parts by Ian

Every Wednesday we highlight a component from the updated partlist. This week: NPN transistors

Transistors do lots of analog tricks, but we only use them to switch high powered stuff with a weak microcontroller pin. Usually an LED. See the IR Toy, #twatch, PICqueno, or USB POV Toy for the sad truth.

We’ve standardized on the BC818 for most stuff. It’s cheap, always in stock, and it handles a decent load from a small SOT-23 package. The BC81840 has more gain, so it’s our go-to for prototypes, but either part is usually fine.

If you’re choosing a substitute part be sure to check the pinout. The BC818 is “BEC”, pin 1 = base, pin 2 = emitter, pin 3 = collector. This a common package, but there are different parts lurking out there to foul you up. Datasheets always list the pinout differently, so we made this diagram as a quick reference.

Verify your schematic and footprints too. Eagle has every combination of transistor pinout. In our Eagle part library the BEC package is marked with a big note so we don’t repeat past mistakes. Just remember Boys Eat Cheese and you’ll be fine.

For a bigger load, or a continuous load where an SOT-23 package gets hot, we’d go for something similar in SOT-223.

This is meant as a summary of what we use, not an essay on transistors. Please fill in the gaps and share your experience in the comments.

This entry was posted on Wednesday, August 3rd, 2011 at 8:00 pm and is filed under partlist, parts. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

One Response to “Partlist Wednesday: NPN transistors”

  1. tayken says:

    “Boys Eat Cheese” :D That’s good. I had trouble remembering PNP and NPN transistor symbols until I stumbled on some stuff on the good old net a few years ago:
    NPN – Not Pointing iN
    PNP – Pointing iN Proudly

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