voltage amplification!!

[tech_vaibhav_eee]

i am new to electronics ... at present i am reading about various electronic devices and how do they work...i have some doubts over the application of a transistor amplifier(common emitter npn)....
first i would tell u what i know....
there are two circuits , one between base and emitter and other between emitter and collector....the collector emitter circuit is given a large reverse bias voltage and base emitter is given a forward bias voltage...
as the base emitter voltage increase , current in the collector emitter circuit also increase proportionally..(i also know why does it happen...)
how is this circuit used as a voltage amplifier ,i mean on increasing the base emitter voltage only the current in collector emitter increase while the voltage across it remains constant, then how do the voltage gets amplified??

 

[audioguru]

The transistor has a high current gain that is called hFE on its datasheet.
A small increase or decrease in base current creates a current change of up to 800 times in the collector to emitter.
Then select a suitable input signal resistance, suitable base resistors, a suitable collector resistor with suitable power supply voltage and suitable load resistance so that Ohms Law can show you how much the voltage is amplified.

A single transistor can provide a voltage gain of up to 200 but at the higher levels the output is terribly distorted without adding "bootstrapping".

 

[k7elp60]

In the common emitter circuit, there is a resistor from the collector to the supply voltage.
As the collector current increases the collector to emitter voltage decreases. The voltage across the resistor is voltage gain but is opposite polarity of the base voltage increase.
In other words as the base voltage increases the collector current increases but because of the collector load resistor the collector voltage decreases. A small change in base voltage causes a large change in collector voltage and this is voltage gain

 

[Sceadwian]

It is a bit two faced, on a fundamental level the voltage itself isn't actually amplified, neither is the current. But the end result is an output voltage which is some fundamental multiple of the input under a given set of conditions.

Amplify intimates that a low value is raised to a higher value without loss, but in the real world vast quantities of energy are transfered to change the 'window' upon which we look at the original signal. What has occurred is not strictly speaking amplification but carefully controlled transfer of the state of the original signal to some other form of signal which may be 'more' useful than the original signal in a practical sense. The current following ratio of a transistor applied across static impedances is practical voltage amplification. I saw following because it's not actually 'transfered' a current in the base follows the E-C voltage, but the actual current comes from the voltage applied to the E-C junction itself, less physical losses.

I didn't go to school for any of this but I've heard on multiple occasions the best way to teach electronics is to lie and then explain the details of the lie later on because they're too complex to introduce right off the bat. You'll find a lot of differences in the wording used for various devices a far cry from the actual physics involved in the actual effect. The best example I can give is that the positive voltage in practical electrical circuits is actually negatively charged (surplus of electrons) on a physical level. Look up the physics of a basic diode, and then look up the physics of a transistor. Great reading, but it won't teach you any practical circuits, just give you a better idea of what's really going on.

 

[tech_vaibhav_eee]

thanks for your replies!!!
@sceadwian , as you told me , i was reading articles on the working of a transistor...there i ran across this wonderful article by william beaty...please read the article.. i am sending it as an attachment... it is the best article on physics i have read so far...

 

[tech_vaibhav_eee]

not being able to send the attachment..i am sending the link...everybody please read this wonderful article...
SCIENCE HOBBYIST: how transistor works, an alternate viewpoint

 

[k7elp60]

I think is great to understand really how a transistor works, but to dwell on it may hamper learning and understanding for learning about multiple transistor arrays like a integrated circuit. For a integrated circuit it is more beneficial to understand the outputs for inputs and not worry about the nitty gritty of what goes on inside the package. I think going on step further this is true of a transistor also.

 

[Sceadwian]

That's a great web page Tech, found it very informative myself. A whole lot more becomes clear over time when you know the whys of the way things work, especially in real world circuits. ICs are considered 'black boxes' for the most part, you can't really know the exact layout of their semi conductor structure, but a basic knowledge of semi conductors is a good start. Especially given the diversity of the branches of electronics.