Understanding transistor specification sheets

It is good to know what to look for when reading transistor specification sheets.

Some important things are:

  • NPN vs PNP transistor. – The NPN ones switch on the low side (-) while PNP transistors switch on the high side (+). This is important difference and for example this difference
  • Material (usually Germanium or Silicon) – Forward bias for the base emitter junction is usually 0.2 – 0.3 V for germanium and about 0.6 V for silicon.
    First letter of the transistors name will specify material type where the letters mean:

    • A – Germanium
    • B – Silicon
    • C – Gallium Arsenide
    • R – Compound materials
  • VCEO – Collector to Emitter breakdown voltage. This is the maximum voltage that can be placed from the collector to the emitter.
  • VCBO – Collector to base breakdown voltage. This is the maximum collector base voltage.
  • IC – Collector maximum current
  • VCEsat – The collector emitter saturation voltage
  • Hfe – This is the current gain of the transistor. This is basically the b (beta value).
  • FT – Frequency Transition (this is basically how fast you can switch the transistors state)

Transistor naming:

Note that more than one naming schemes exist so if you get transistor with name like 2N706, then it is not in the naming sceme described above for the materials. 2 here simply means Bipolar transistor.

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