Transistor as an Amplifier

[Dineshkumar005]

I wanna know exactly how a Transistor amplifies any signal

 

[klystron]

The collector current is the base current multiplied by the Hfe(Beta) of the transistor

 

[enjunear]

In bipolar transistors (BJTs), a small current across the base-emitter junction causes a larger (proportional) current to flow from the collector to the emitter. In FETs (Field-Effect Transistors), the voltage applied across the gate-source junction controls a large current to flow from drain to source.

BJTs and FETs are all 3-terminal devices, the connections are named differently due to convention. For FET's vs. BJT's.... Drain ~= collector, Gate ~= base, Source ~= emitter.

 

[Ratch]

klystron,

For a bipolar junction transistor (BJT), a little bit of voltage on the base causes a lot of collector current to exist.

Ratch

 

[andre_luis]

...For a bipolar junction transistor (BJT), a little bit of voltage on the base causes a lot of collector current to exist...

This nonlinearity is sometimes usefull in specific circuits, as AGC.

+++

 

[subbuindia]

I wanna know exactly how a Transistor amplifies any signal

Hi friend.......

Transistor act as a amplifier. We know that in a transistor we have three types of regions: EMITTER, COLLECTOR, BASE, and we know that emitter is highly doped, so charge carriers are very high, so resistance is very less, and on the other side collector is moderately doped so charge carriers are less, so resistance is very high. So from the above concept we conclude that in a transistor current is flowing from low resistance to high resistance. for example the 100 electrons are moving from emitter to base, in base only some (4 electrons) of the electrons are neutralized, and remaining 96 electrons are moved to collector terminal through high resistance path. so now same current flowing through high resistance so voltage amplified.

---------- Post added at 04:26 ---------- Previous post was at 04:17 ----------

I wanna know exactly how a Transistor amplifies any signal

Hi friend.........

I want to explain how the transistor work as an amplifier in another way. I take CE configuration. Generally, for CE input resistance is less and output resistance is very high. If we apply input voltage that causes input current Ib. And we Ic=beeta*Hfe, so increases of collector current i.e., for a small increment in the base current causes the large increment in the collector current. Hence Vo=output resistance(It is very high)*output currrent(Ic; It is too very high). So, output voltage increases.

 

[:pH]

Just refer any basic electronics book viz. https://www.google.co.in/url?sa=t&rct=j&q=boylstead&source=web&cd=1&ved=0CDgQFjAA&url=http%3A%2F%2Fbooks.google.com%2Fbooks%2Fabout%2FElectronic_Devices_and_Circuit_Theory_10.html%3Fid%3D32RJvfgkJgwC&ei=aWFwT6LsFYf5rQfYhtGgDg&usg=AFQjCNGa7Y0PEdGY8fnpz7n-UmVVB9zrNg&cad=rja

 

[thannara123]

reffer here
http://www.flashscience.com/electricity/transistor.htm
**broken link removed**

 

[tpetar]

One video like 1000 words.

https://www.youtube.com/watch?v=W8hqr5X5ii0

 

[Dineshkumar005]

Your explanation told about voltage amplification. But how is current amplified using a transistor. Please explain it practically as i find it difficult to interpret the mathematical explanations.

 

[tpetar]

Transistor as current amplifier
**broken link removed**

 

[Ratch]

Dineshkumar005,

I can't blame you for feeling unsatisified with the the video posted in the reply #9. That guy needs to take a course in elementary physics. He says that power is force through a distance, which is wrong. Force through a distance is energy. He says the water from a faucet is measured as force. Wrong, it is measured as pressure. He spends over 12 minutes giving unrelated analogies from mechanics and hydraulics, and then tells you that a transistor is an amplifier bcause it functions as a restrictive valve. An amplifier is more than a valve. There is the valve control mechanism to consider also.

The video in post #11 is wrong also. The current going through the base emitter diode does not control the collector current. There is a lot of literature around saying it does, but that is not true. A BJT operated in the active region is a voltage controlled current amplifier. Any good physics book on transistors will say that the current existing in the collector is controlled exponentially by the Vbe. The current existing in the base is also exponentially related to the Vbe. Dividing the collector by the base current cancels out the exponential relationship and make it appear that the collector current is directly related. That is a false assumption. The base current is a indicator of what the collector current is, not the collector current control. Just as an ammeter does not control the current in a circuit, but only indicates what the value is.

So you asked how does a transistor amplfy, but you didn't specify what amplification you mean. Voltage, current, power? Since a BJT is voltage controlled current source, a little bit of voltage will allow a lot of current to exist. Put a resistor in the path and you have a little bit of voltage controlling a lot of voltage. Optimize the resistor for the largest product of current and voltage and you have a little bit of voltage controlling a lot of power.

Ratch

Look at this thread, especially post #43. https://www.electro-tech-online.com/general-electronics-chat/126200-understanding-transistor-5.html

 

[LvW]

Transistor as current amplifier
**broken link removed**

I would be very cautious with the given link and its "descriptions" how a transistor amplifies.
Example:
•Transistor is equivalent to a variable resistor controlled by the
current through a diode

This is not only a very simplified description - it is simply false.

A correct and reliable description can be found here:
http://amasci.com/amateur/transis.html

 

[s.jayaram88]

Hey friend!! U can try this circuit and check for amplification practically. Try giving ac signal also if required to see how ac amplification takes place. Go to the following site to try it. http://www.docircuits.com

 

[bioda]

helo,

i need to design a CMOS LNA on Multism.please i need a way out.

Thanks

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helo,

i need to design a CMOS LNA on Multism.please i need a way out.

Thanks

 

[Ratch]

s.jayaram88,

Hey friend!! U can try this circuit and check for amplification practically. Try giving ac signal also if required to see how ac amplification takes place. Go to the following site to try it. http://www.docircuits.com

How does this circuit help the OP understand how a transistor amplifies? That is the question he asked. He already knows that there are a zillion amplification circuits that use transistors. So you have not answered his question.


bioda,

Re: Transistor as an Amplifier
helo,

i need to design a CMOS LNA on Multism.please i need a way out.

Thanks

- - - Updated - - -
helo,

i need to design a CMOS LNA on Multism.please i need a way out.

Thanks

So why are you asking that question in this thread which has nothing to do with what you desire. Why not start a new thread on this different topic.

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So why are you asking that question in this thread which has nothing to do with what you desire. Why not start a new thread on this different topic.

Ratch

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Ratch

 

[jeffrey samuel]

based on the bias in the jns of the transistor current amplification takes place

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based on the bias in the jns of the transistor current amplification takes place

 

[s.jayaram88]

Well ya I agree, but he has got all these threads that help him with the theoretical aspects. I thought why not also show him a practical way which may help him in understanding all the points given