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)
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.