Technical Drawing Symbols

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What is a Field Effect Transistor?

I am doing a technology project at school using transistors and for my homework I have to find out what an FET (field effect transistor) is and how it differs from a bipolar transistor. I also have to draw an FET symbol.

So. Please could you tell me what both FETs and bipolar transistors are and how they are different and what an FET symbol is.

Thank you :)


*NOTE* please do not use really technical language because I won't understand - it is the first time I have come across transistors.
Umm please don't use this website because i already looked at it and i haven't go a clue what it means... .http://www.pbs.org/transistor/science/info/transmodern.html

The major difference is what controls their operation. bipolar transistors use current flow through them to control a much larger current. FETS have a voltage applied to a gate (with very little current -at least once voltage has stabilized) to control the resistance between two gates. Some FETs need voltage to turn them off, and some need voltage to turn them on

There's lot of different types of FETs, and many of them have their own symbols.

Mosfets are the easiest to draw. Small vertical line with three short horizontal lines coming out to the right. the top most of those horizontal lines (the source) then turns and goes up, and the bottom most of those lines(the drain) turns and goes downwards. the 3rd horizontal line can sometimes be brought straight out (making for a 4 connection transistor- the extra connection is for the substrate- shifts the operating voltages), but it's usually connected to the top most line (the source) via a "diode"pointing towards the source, or a diode pointing to that line from the bottom most line (the drain). The other connection to be drawn is the gate. That is drawn as a short vertical line to the left of the small vertical line you 1st drew. It's connection is a horizontal line, that goes out (usually) from the middle of the vertical representing the gate. Surround all that in a circle to finish the diagram

http://en.wikipedia.org/wiki/MOSFET#Circuit_symbols

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