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 β (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.