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difference between a bipolar transistor and a mosfet?

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jin29_neci

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:lol:

hello guys another stupid question,

What is the difference between a bipolar transistor and a mosfet?

I know that they are physically different but i want to know how they differ in their function and how they are used in a circuits?

I finally how to check a mosfet using an ohmmeter....

thanks :shock:
 
Try searching the INTERNET. There is a whole wealth of information on it for free. If fact these questions have probably already been asked and answered on this forum as well.

For information, a bipolar transistor is basically a current amplifier, and a MOSFET is basically a voltage controlled current amplifier. Both are used in completely different ways. MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor. In Bipolar transistors, the current that flows between the collector and emitter is regulated by (and an amplification of), the current that flows from the base to the emitter. In a FET the voltage present at the gate determines the current that will flow between the drain and source.

There are also two main types of bipolar transistors, Unipolar transistors and many different types of FETs. If you want to know how to use them in circuits buy a book, or search the internet/forum for tutorials, you'll get more information that way. If you have a specific question, that a forum is a good place the ask it. It would take far too long to explain all of them and teach every person, one by one.
 
For such a small package, MOSFETs can handle much larger current and voltages than a same sized bipolar transistor.
 
and thats becose of there much lover resistance over it wich causes the voltage dierence to be smaler and so the heat generated smaler .The max curent of transistors is detemaind how much heat the traistor produces and dispatches (if you drive to much curent trugh it will overheat and burn out).
 
Paul Scherz' book, Practical Electronics for Inventors, has an excellent section that answers the question nicely.
 
Pyroandrew said:
For information, a bipolar transistor is basically a current amplifier, and a MOSFET is basically a voltage controlled current amplifier. Both are used in completely different ways. MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor. In Bipolar transistors, the current that flows between the collector and emitter is regulated by (and an amplification of), the current that flows from the base to the emitter. In a FET the voltage present at the gate determines the current that will flow between the drain and source.
Actually they are both voltage controlled current sources.

The collector current in a bipolar is an expotential function of the B-E voltage.

Ic = beta Ib is more useful in practice but in transistor theory it is a consequence not an absolute.

One advantage of FETs is their very high gate - source resistance.

The attachments are a SwitchCADIII analysis of an NPN transistor. The horizontal axis is Vbe and the vertical is Ic.

Len
Edit, I've just learnt how to convert SwitcherCAD files to .gif
 

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Yeah Len,
You show that a single transistor is very distorted without negative feedback. You also show that a push-pull transistor circuit has crossover distortion without a suitable amount of idle current.

For years I looked at the linear straight line on the datasheet but saw the conflicting distorted waveform on my 'scope. Then I realised that the "straight line" has a nice linear voltage scale on its left side, but a logarithmic scale on its bottom. :lol:
 

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  • vbe.gif
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Audio,
If you mapped your graph on to a linear/linear graph. it would be exponential like mine.

As you implied, for minimal distortion, the transistor has to be biassed correctly and driven correctly.

Len
 
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