/diy/ - Do It Yourself

>>1538115
there are some canned topologies in which bipolar transistors are often used, e.g. single-transistor common-base, common-emitter, common-collector; multi-transistor long-tailed pair, push-pull, cascode; etc. which have been well-characterized in general (e.g. common-emitter has high input impedance and low output impedance and can voltage gain > 1) and for which there are higher-level design equations
but in general, you can approximate a bipolar transistor in its linear region as a current-controlled current sink: for a pnp, x electrons go from b to e, beta * x electrons go from c to e
if you already understand passive component networks well, check into The Art of Electronics (see OP)

>>1538122
>switches
oh, well, roughly the same idea but you can think digitally: if current is flowing through the b-e junction and the polarity's right, current will be flowing between c and e if the polarity's right
have a look at BJT datasheets, both small-signal (e.g. 2N3904) and power (e.g. 2N3055) to get a sense of the parameters in play in BJTs. some that will probably concern you in non-fault switching cases are: saturation c-e voltage, max power dissipation, Vbe-Ice curve, (sometimes) maximum reverse Vbe. but the cool kids use MOSFETs these days which are a slightly different ball game :^)
>transistor amps
those do get complicated when matters like frequency response come into play, but often they can be broken down into multiple stages of the standard topologies, plus negative feedback around the lot. if you understand Pic related, the common-collector amplifier (high input impedance, low output impedance, voltage gain ~=1, current gain > 1) you have most of the tools necessary to understand other types. when you understand the common-base amplifier (low input impedance, high output impedance, current gain ~=1, voltage gain > 1) you will also understand why not to connect loads to the emitter in switching circuits (hint: Vbe is relative)