1. What's the min voltage a transistor can use?
2. What's the voltage that the transistor will just start to turn on when appliedto its base?
3. can they be used as rf amps
4. what different ampliferrs exist and what are the most common and/or best for various situatins
5. do i need different protection resistors for different operating voltages?
1)There are literaly thousands of transistors available, with operating voltages from several volts to KV.
2)0.6-0.7V for a silicon transistor or 0.3V for a germanium transistor
3) as evandude says, yes
4)there are many amplifiers available, they are all designed around specific operating paramaters such as bandwidth, operating voltage, ouput impedance, input impedance, try searching for amplifiers on google, or use http://www.discovercircuits.com/list.htm
5)as evandude said you do need different protection resistors for different operating voltages.
I don't know about the other partial part numbers you posted but the 2N3904 NPN transistor and 2N3906 PNP transistor are very common and inexpensive in North America.
Look at their datasheets at www.datasheetarchive.com .
I think you need to spend some time reading online information to get an idea for how transistors work, and then spend some time looking at the datasheets for those transistors if you want their specifics.
your question #4 is a very big one; that's the kind of thing you would probably learn over the course of your 3rd year of college. you at least need to be pretty competent about how transistors work in general before you can start to understand the different types of typical transistor amplifiers.
Well, we're just teasing ya.. do you have more specific transistor questions? So you are building a transistor "tester?" There are plenty of reference designs for these. I had one of those once from Radio Shack of all places! It worked for 95% of the parts I ever tried with it. The last time it mis-identified a part, I vowed to never use it again. I hope your design is more reliable than theirs.
Many DVM have build in transistor testers for as little as $10, including shipping. Link; **broken link removed**
So, why build one?
Optikon said:
Well, we're just teasing ya.. do you have more specific transistor questions? So you are building a transistor "tester?" There are plenty of reference designs for these. I had one of those once from Radio Shack of all places! It worked for 95% of the parts I ever tried with it. The last time it mis-identified a part, I vowed to never use it again. I hope your design is more reliable than theirs.
I think your transistor is connected as an emitter-follower. Its base current is nearly the same as its collector and emitter current because the resistors have nearly the same value. Therefore the LED will still light if the transistor has a very low current gain and if the collector is burned out.
Try it like this:
What if you insert a broken npn transistor and because the LED does not illuminate you happily assume it is a working pnp, there are some design flaws with this circuit, definately room for improvement.
There are many schematic drawing programs available, i use livewire by new wave concepts, cost my £15 but it will also simulate circuits so i can test them before i build them (not a very extensive range of components), another program i have started to use is Eagle, it has a wide range of components available, and can do PCB track layouts aswell.