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.