by which you mean silicon bipolar junction transistors, not jfets, mosfets, or any of the other less common transistor types.
* are electronic switches or amplifiers
can be used as
* amplify current not voltage
more accurately, they use one current to control another
* current flows in the direction which the emitter arrow points
well, actually it flows in exactly the opposite direction since the arrow points in the direction of conventional current which is backwards. But yeah, since we can think about conventional current, the arrow points that way.
* have three legs, emitter (e), base (b), collector (c)
yes, usually, but some have only 2 (typically optical devices)
* like diodes have to be protected with resistors
no
* the base needs about a 1k resistance
no
* the main current flows through the emitter/collector legs
yes (normally)
* a resistance of about 470 ohms must be attached to e or c to limit current
no
* the emitter current (Ie) is the sum of collector (Ic) and base (Ib) currents
normally
that's what you just said, but what about leakage from the collector to the base?
* there are two types of transistor, npn and pnp
with the assumption in my first line above
* In a npn, Ic and Ib flow in, combining to form Ie
more restatements of stuff above
* In a pnp, Ie flows in and splits into Ic and Ib flowing out
more restatement, but "splits", and "combines" are not correct understanding
* In a npn, the base must be "p" positive to switch the transistor on
no. It must be positive wrt the emitter. Both may be -ve, just the base may be less so.
* In a pnp, the base must be "n" negative to switch the transistor on
see above, but backwards
* The positive or negative is relative to Ve or emitter voltage
yes
* A pnp must have Vb = Ve - .6V ("n" means negative or minus) to switch on
no. approximately 0.6V, but it depends on some other factors. Also note that this is specific to silicon transistors (not that you see too many others)
* A npn must have Vb = Ve + .6V ("p" means plus or positive) to switch on
see above
* when switched on completely, transistors are called "saturated"
no (it's not quite that simple)
* when Vb is about .75V above (npn) or below (pnp) the Ve, saturation occurs
no
* when Vb >.6V and Vb <.75V the transistor acts as a current amplifier
Remember that you spoke about transistors being current devices above, and now you're talking voltages.
* the amount which a transistor amplifies the base current by is called its beta value
It's not quite that simple, but this is the definition in one configuration
* the beta value is also known as the Hfe
of course, there's hfe and hFE. They refer to forward current gain in a particular configuration. But yes, that equation holds
* the beta or Hfe is commonly around 100 but varies widely even in supposedly similar resistors
no
* transistors are sometimes called BPJ's or bipolar junctions
no. There are many types of transistors, you've simply picked out BJTs (and silicon ones) for this list.
* transistors have about 20 ohms resistance and drop voltage by 0.7V
not sure what you mean here
* power transistors are bigger (physically) than low power transistors.
often, but not always
* a low power transistor passes <0.5A.
only if you define it as such. I can show you some very small transistors capable of very high currents. What differentiates them is the power they can dissipate (hence why one might call them low or high power). Even there, this is a continuum.
* an example of a general purpose, low power npn transistor is the 2n222 or BC547
OK
* an example of a general purpose, low power pnp transistor is the BC557
OK
* an example of a general purpose, high power npn transistor is the TIP29 or TIP41
no, this is medium power, look at something like the venerable 2N3055 -- especially in TO-3.
* an example of a general purpose, high power pnp transistor is the TIP42 or TIP30
What about the MJ2955? As I said, there is a continuum of values here. Another important one is the various Vce specifications. Can the transistor be used in a 30V circuit, 50V, 80V, 200V, or 1000V circuit?
Any corrections, alterations or additions (even criticisms of this approach) would be welcomed.
Your list represents a set of assumptions and generalizations you (or someone else) has made. Pretty much all of them are wrong in some form (and it would take pages to get some of them close to right).
To gain further understanding you need (many things, but one is) to see an explanation of the physics of a transistor. You don't need to understand it completely or be able to regurgitate it, but the list above tells me you really haven't seen it.
Possibly a quick look at the other types of transistors so you don't think BJT's are the be all and end all of them.
I just flipped through the first 10 or so pages of the introduction to transistors in Horrowitz and Hill. The most advanced mathematics was:
1) simple arithmetic (division and multiplication)
2) the use of the delta symbol meaning "change in"
3) the use of the symbol || meaning "in parallel with (so R1 || R2 means 1/(1/R1 + 1/R2) -- just a bit of shorthand)
I could point you to other books that have pages of calculus describing the same things.