Discrete Semiconductor Kit Identification Guide

Contributors: Byron J.
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Biploar Junction Transistors

The ordinary transistor is the Bipolar Junction Transistor. Electrical engineers often abbreviate the name to the initialism "BJT." This kit contains 25 pieces each of the 2n3904 and 2n3906 BJTs. These are ubiquitous "jellybean" parts, usable for many general purpose transistor circuits.

If you look in a book of basic transistor circuits, there's a good chance you will run across the 2N3904 and its complement, the 2N3906. They have been in production for a long time, and are very useful generic transistors.

2N3904 NPN

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The 2N3904 is clearly labeled.

The pinout is fairly straightforward:

  1. Emitter
  2. Base
  3. Collector

2N3904s are easy to use on the breadboard, because the base is in the middle -- the schematic symbol and the part itself correspond.

2N3906 PNP

The 2N3906 is the PNP complement of the 2N3904.

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Also Clearly Marked.

The pin order 2N3904 and 2N3906 is easy to remember because they're the same. Just memorize the letters "EBC."

Even though the pins are in the same order, keep in mind that the emitter flips around between the NPN and PNP variants! You can consider the 2N3906 as the mirror-image of the 2N3904.


The MOSFETs in the kit are smaller than the other transistors - the body is about half the size. Being smaller, there's less room to print on them, so the part numbers are a terse code.

5LN01SP N-Channel MOSFET

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YB is not so obvious

The letters "YB" on the package are the identifier. The other marking on the part in the photo is a lot number or date code, which isn't particularly meaningful if you don't know how to decode it.

The pinout is

  1. Source
  2. Drain
  3. Gate

5LP01SP P-Channel MOSFET

Due to the underlying semiconductor physics involved, P-channel MOSFETs are less common than N-channel. The 5Lx01SP family is somewhat unique in that it includes a P-channel variant, which is a reasonable complement for its N-channel sibling.

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"XB" not XBee

Again, the markings on the part are somewhat cryptic -- the "XB" printed on the body is the identifier.

The pinout matches its N-channel cousin (source, gate, drain). Like the BJTs, these MOSFETs have the same pinout, but the polarity is reversed.

While the 5LP01SP is intended as a complement for the 5LN01SP, its specs aren't a perfect mirror-image. Its transconductance is lower, gate capacitance is higher, and switching time slower. These differences may not be significant in typical applications.