Ib, Ibo and should I use the measured forward voltage or Vt in 2n3904 amplifier

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Joined Aug 27, 2020
I've been doing a lot of electrical theory before I build a Class A small signal amp. the Vcc is 14.42 Vdc and I saw some recurring symbols that I couldn't pin down in the datasheet, there bing the difference between Ib and Ibo, how to handle the Forward Voltage drop and which value I should use. I'm kind of new to this field, so any help would be appreciated. Thank you.


Joined Sep 17, 2013
Welcome to AAC!
When designing a practical circuit it is usual to use ball-park or worst-case values for component parameters, because all components have manufacturing tolerances and temperature-dependent properties which have to be allowed for. Going to a second place of decimals would hardly ever be justified., particularly for Vcc. So for a silicon device, for example, the forward voltage drop of a junction would be taken as a nominal 0.6V (or 0.7V). A good amplifier design would incorporate negative feedback to make the gain independent (within reason) of the transistor properties, so that any off-the-shelf sample of a particular transistor type could be used successfully.
As for Ib and Ib0, just keep Ib well below the rated maximum and check it doen't excessively load any preceding stage of the circuit. Ib0 is rarely of interest.
You are doing the right thing and obeying the golden rule in consulting the datasheet of a component you intend to use.