Let's Make Robots!

Transistor terminal naming conventions.

I am trying to figure out how transistors work and have seen the three terminals on a bipolar transistor labelled base, collector, and emitter.

I am having a hard time understanding the purpose of the three, and would like it if someone could explain why they are named this way. I.e. what is basey about the base and what is the collector collecting?

At the moment they just look like three randomly chosen words.


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I suppose the only thing I would expand on there is the difference between transistors and integrated circuits being on or not. I would point out that the active components in ICs are transistors (with other components there to complete the circuits and keep them working in the proper ranges). Junction transistors are current devices. The only type transistor which is a voltage device (at least on the inputs) are field-effect transistors (which have been used in a few ICs)

Oh you asked about transistors on the lists that were similar to the 2N3904/3906s. It appears the BC109/BC178/BC179 have similar current capabilities, but lower max collector-emitter voltages. If the voltage is not a problem, then any of those might be used for the 2N3904 (since they are all NPNs). The 2N3904 is also a bit faster. (higher frequency).

While not on that list, the BC327 looks like a good one for robot purposes. It is good for 800 mA collector current. 


PNP & NPN transistors are used slightly differently ,

"general convention" constrains NPN and PNP to be wired so:-

Forget the circuit ..... just look at the emitter/collector pins (for general convention)

Q1 is NPN type with its emitter strapped direct to ground......... (so in theory you could call it ...."the ground pin"), however.......

Q2 is PNP type with its emitter connected to supply rail , so it cannot really be called the "ground pin"

C and E are switched around on the symbol for Q2

E(mitter) is always the one with the arrow

U Eagle Eyes U.......how did i miss that....... now corrected thanks.

thing is if you remove the speaker the circuit will be broken despite the grounding of Q1.

Basic electronics explained in cool way (transistor is on top of list)