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I know that current is amplified by junction transistor but what about voltage? Is voltage also amplified at same time as current or not? In school professor was explaining me about this and I still don't get it. He was mentioning resistors or something like that.

I hope someone can explain me this more detailed and understandable about transistor gain, whether amplifies current or voltage.

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    \$\begingroup\$ Depends how you are using the transistor. You can get current gain without voltage gain, or voltage gain without current gain, or both voltage and current gain. Any basic introduction to transistors should tell you how. \$\endgroup\$ – user_1818839 Sep 11 '16 at 19:56
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    \$\begingroup\$ I can tell from your question that you are still struggling a lot to follow your teacher. You should take this as a clue that you need to buckle down and spend all of your spare time studying and thinking, for a while, in order to allow the concepts to precipitate in your mind. I don't think a discussion here, short of a couple of long chapters' worth, would be able to help you here. The ideas are several and you need to mentally juggle all of them at one moment. Writing enough here would be very difficult. So just go to the basics and study, then back to the BJT, then apply. Repeat. \$\endgroup\$ – jonk Sep 11 '16 at 20:02
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    \$\begingroup\$ I wish I could have offered more time and effort. If you can, see about getting together with other students. This may help a lot. Or see if there is a tutor available, lab assistant, etc. I could recommend some books, but I suspect you are better off with the books you already have in hand. \$\endgroup\$ – jonk Sep 11 '16 at 20:28
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    \$\begingroup\$ Specifically, maybe take a look at the three common BJT amplifier configurations and their properties: The common emitter amplifier, the emitter follower (common collector), and the common base. Study each of those and how they work and you may be able to answer your own question. You can use your textbooks and Google, and if you have any specific questions about anything you can post back here. \$\endgroup\$ – John D Sep 11 '16 at 21:46
  • \$\begingroup\$ @JohnD : Good point. I already found few of answers to my questions with those three configuration. I found a lot of things about semiconductor and doping, conducting and lot more stuff about properties of transistors on "hyper physics" site (hyperphysics.phy-astr.gsu.edu/hbase/hph.html). I also found some books in pdf format at archive.org. If you have any of yours suggestions about sites or books, I would definitely consider them. Thank both of you :D \$\endgroup\$ – Lu Ka Sep 12 '16 at 14:20
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The fundamental action of a bipolar junction transistor (BJT) is current gain. A small current passed through the base-emitter junction allows a greater current (maybe 100x) to pass between the collector and emitter.

But a BJT is essentially never used by itself, rather it is one component in a circuit, often an amplifier circuit.

By passing the greater collector-emitter current through a resistor, a voltage arises across the resistor. This voltage can be substantially greater in size than the input signal applied to the base of the transistor. So the circuit in which the BJT takes part can exhibit voltage gain.

There are other interpretations of BJTs as a voltage-controlled device (rather than current controlled), but that's for a later chapter.

As a first concept, the BJT is a current amplifier, which deployed in the appropriate circuit, can imbue that circuit with voltage gain, making it a voltage amplifier.

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  • \$\begingroup\$ That was the answer I was looking for! Thank you :) \$\endgroup\$ – Lu Ka Sep 12 '16 at 18:17

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