212Views15Replies

Author Options:

What Do These Mean? Answered

Picture of

I'm trying to construct an entry for the Wicked Lasers contest, however I keep on finding the same letters on several diagrams... 

Can anyone tell me what the G, S and D stand for?

15 Replies

user
steveastroukBest Answer (author)2011-03-20
user
thomas9666 (author)steveastrouk2011-03-20

Thanks.... But what do these mean?


Sorry for being stupid, electronics isn't taught for another 2 years at my school.

Select as Best AnswerUndo Best Answer

user
steveastrouk (author)thomas96662011-03-20

If you're building from an existing diagram, just follow it. Like Sean says, its a MOSFET, a field effect transistor, how it works is tricky to understand.

Select as Best AnswerUndo Best Answer

user
seandogue (author)thomas96662011-03-20

The device is a Field Effect Transistor, a type of transistor that uses an electric field to change the impedance from drain to source from near-infinite to near zero. They can be used as switches and amplifiers, amongst other uses.

A voltage is applied to the Gate terminal to determine the state of the drain/source impedance.

IMO, you should google it or go to wikipedia for a lengthy answer.

Select as Best AnswerUndo Best Answer

user
thomas9666 (author)steveastrouk2011-03-20

And can you explain this very simply....

Select as Best AnswerUndo Best Answer

user
7654321 (author)2011-03-20

A current at the gate makes current flow from the drain to the source (yes the names sound backwards)

Select as Best AnswerUndo Best Answer

user
steveastrouk (author)76543212011-03-21

NO There is no steady gate "current" MosFETs are voltage driven at the control, unlike BJTs.

Steve

Select as Best AnswerUndo Best Answer

user
seandogue (author)steveastrouk2011-03-21

right.

In fact, for all intents and purposes, (and aside from hair-splitting) there isn't any current at the gate, steady or otherwise.

FETs are voltage controlled devices.

A BJT however, can be (in some ways) modeled after a venturi. Flow (literal) from the Base to emitter is necessary to switch the collector/emitter flow. And in fact it is directly proportional to that flow by the Hfe

Select as Best AnswerUndo Best Answer

user
steveastrouk (author)seandogue2011-03-21

Me ? Split hairs ?
I WAS thinking of gate capacitance charging.

Steve

Select as Best AnswerUndo Best Answer

user
seandogue (author)steveastrouk2011-03-21

oops. NO I didn't mean you were splitting hairs. was just trying to imply that yeah...there may be current, but it's tiny and simply a parasitic rather than a causal like in a BJT.

Just trying to keep my comment in the thread rather than making it possibly non-sequitur by posting separately...

Select as Best AnswerUndo Best Answer

user
steveastrouk (author)seandogue2011-03-21

Hehe
Its alright, I am a champion hair-splitter ;-)

Steve

Select as Best AnswerUndo Best Answer

user
seandogue (author)steveastrouk2011-03-21

HA! I was right then. you woulda caught me on it if I hadn't added that qualification. NYAH! ;-)

(as if I'm anyone to talk)

Select as Best AnswerUndo Best Answer

user
seandogue (author)76543212011-03-21

The gate voltage (not current) does not make anything happen other than to reduce the impedance of the semiconductor junction.

Select as Best AnswerUndo Best Answer

user
7654321 (author)76543212011-03-20

Actually I think it can go both ways, nevermind

Select as Best AnswerUndo Best Answer