What Do These Mean?

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?

Comments

[steveastrouk]

GATE
SOURCE
DRAIN

[thomas9666]

Thanks.... But what do these mean?


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

[thomas9666]

And can you explain this very simply....

[seandogue]

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.

[steveastrouk]

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.

[7654321]

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

[seandogue]

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

[steveastrouk]

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

Steve

[seandogue]

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

[steveastrouk]

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

Steve

[seandogue]

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...

[steveastrouk]

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

Steve

[seandogue]

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)

[steveastrouk]

He he he

[7654321]

Actually I think it can go both ways, nevermind