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What is a transistor and what does it do? For application Answered

Where can I find an explanation of what a transistor is/does, so that afterwards I can actually USE said explanation to apply it to building something. As in not just "its got layers and silicon", or "it's like a switch". I mean seriously, I can read the theory behind charge flow and silicon no-charge wells, but it doesn't help me understand how to use one.

Ex: I have a problem. I want to come up with a circuit to take care of said problem. I start to sit down and think about what I would need to solve said problem with circuitry, and never a transistor crosses my mind. Why? Because I really don't understand their use in terms of creating solutions. I can solder them all day long in kits and projects, but I didn't come up with the solution for that circuit, I'm just soldering-by-the-dots.

I would like to know more about "applied" transistors, not "theoretical" transistors. After all if it "changed the face of electronics as we know it", it's a pretty big hole for me to have in my knowledge base.

Thanks! :)


If you want to design with transistors beyond the simplest kinds of things (oscillators, for example), you're going to have to understand the theory. Maybe not at the level of semiconductor junctions and electron/hole transport, but you'll need to understand where the (pseudo) linear region is and what the saturation characteristics are for the particular transistor you're using and how that affects the circuit you're working with. If you can't read and understand the spec sheet, you can't predict exactly how it's going to behave in your circuit.

These days, it's often preferable to use an IC which combines multiple transistors into something with simpler behavior.

But, at the simplest level: For most basic transistors (ignoring things like SCRs), current from the emitter to the collector will be controlled by current from the base to the collector. When operating in the linear region, the two are fairly close to proportional and the transistor is thus acting as a current amplifier.

The complexities come when you start looking at how accurate that amplifier will be, how much current it actually needs to handle to deliver the amplification your project needs, and so on.

I completely understand your first paragraph, but this is where I think I'm getting hung up. My late uncle had taught me what he knew about electronics awhile back. This included the idea that electrons are "real" matter and have a mass, and that when you're in a DC circuit you are pushing said electrons around the "pipes"/circuit to the positive field of the voltage source. This works because since the positive end of the voltage source is depleted of electrons it takes pushed along electrons in.

Well, whether you use the --electrons race along the circuit-- or the --one electron in pushed all of the electrons over, and the last pops out the other side of the component-- this is opposite of the arrows used in schematics. Long story short, "Negative to Positive" not "Positive to Negative".

Any hints on a Neg-to-Pos explanation of transistors? Or do I just need to throw that thought process away?

The "think of electron flow like water flow" approach will only take you so far. If you really want a water-flow analogy for simple transistors, you can think of them as valves where the water flowing from one input (the base) to the output (the collector) controls how much water is allowed to flow from the other input (the emitter) to the output. When a small input controls a larger one, that's amplification. (This analogy is why vacuum tubes were sometimes referred to as "valves".) The accurate explanation involves the effects of the applied electric field upon the distribution of electrons within and around the semiconductor junctions, and requires some college-level math. (Let's see .. quasineutrality, uniformity, equilibrium, low-level injection, steady-state... OK, I still remember the names of the simplifying assumptions, though I'd have to look up exactly what each of those does to the formulas.) But generally, as a circuit designer, you don't need that level of detail -- all you need is information about how quickly the transistor responds, what the transfer curve is between control and controlled, how much current it can handle before the magic smoke escapes and whether it will need a heat sink to help keep that from happening. As I say: For many applications, it's easier to work with ICs which have already dealt with most of the details for you.

Cool, thanks for the web links.

Because a Bipolar transistor amplifies the current injected/extracted from its base into a much higher current flowing in its collector/emitter, then it acts as an amplifier, and can be used as one.

Transistors are not switches, but if they have a high gain, then they appear to be one, when used in a simple open loop circuit - one without any feedback.

THE best book, bar none, for someone who understands the basics of electronics, but wants to go on, is "The Art of Electronics" by Paul Horowitz and Winfield Hill.

Thanks for the tip on the book. I even found it on Google.

Sorry, but your question and the specifics that you require for an answer make it clear to me that you want it handed to you on a platter. It's a very slacker mentality that says things this way.

Ain't gonna happen. At least not from me.

However, there are plenty of community colleges that can educate you, there are a ton of books, and there is lots of info on the net. Please help yourself.

I'm sorry you feel this way. In fact, my question is for guidance on where to gather better information on the subject, and my "specifics" are to admit my ignorance on the subject. This had no sort of tone about "you want it handed to you on a platter".

Your ignorance is admitted through your final statement, which is only a sign that you cannot read my original post. I specifically asked for guidance through said books, internet, and community colleges due to my lack of finding fitting explanations thus far on my own.

Did I bother someone with personal messages? Am I tYpInG LiKe A mUnChKiN? Did I post my same question 13 times on the Q/A board? No. I asked once, in the area of the website that it is permitted. I gave my request, gave some back story, admitted humility, and was polite enough to say thank you. That is exactly why this site has developed the Q/A section, or am I mistaken?

Now I clearly must not be a fantastic wizard of electronics as you, good sir, but that does not stop me from asking my questions and seeking to learn more for myself. I ask because I wish to learn. Your snide remarks provide nothing but sore feelings from yourself and hope to spread unto others.

As for help? Two members did just that by giving me things to link to and read, and I greatly appreciate their contribution; two other members took their time out to give insight on-topic with what I asked.

Yet you're the only one so far which not only missed the mark, but insisted on extending your apparent unwanted efforts through statements like, "At least not from me." Now, I understand some people like to withhold information for a sense of entitlement or even authority, but this is silly and rude.

If you cannot contribute to the community positively, then do not, and if you must refuse to contribute positively, then you should be so proud to remove yourself from it.

Good day.

Yes, you are correct, I will withhold information from people who ask things and then demand that information needed to use said item be handed to them in a specific siilver-spoon manner without regard to the device/technology background...Sorry, that's just the way it is.

Read diode, tell me if you understood it.


Let's see, I tried to digest that page in order to return a comment for you. Think I'll need to go back over it for some of the newer stuff I hadn't read about before.

But as for things like changing AC -> DC current, taking the absolute value/rectifying an analog signal, using them to prevent reverse flow (or just flow in an unwanted direction), and their ability to be used to form logic circuits... I was familiar with these attributes; however, I have not personally built a solution for anything that utilized diodes.

Built kits and could make sense of why they were where they were, but not used them for myself.

If you get diode valves, you can get triode vales, which work like semiconductor-transistors. The physics of semi-conductors is a bit "quantum", you just want to know how they function, to start there may be understandable (and the triode page links to "transistor")