What is a MOSFET? I know basically what it is..but what is the exact use in terms of PVs? I get the feeling is it for boosting the signal so you can make a touch switch instead of a manual push switch??
Lol...ok, 'nother stupid question
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A MOSFET, from my limited understanding, allows you to use a low amp switch or make a touch switch.
Here's the touch switch circuit that I've been using (3 x 10Mohm resistors in series between G & S pins)
http://www.e-cigarette-forum.com/forum/battery-mods/181976-1-aa-touch-modbox.html
Those Wiki articles tend to suffer from too much information. Most simply, a MOSFET is a type of transistor that allows you to turn electrical things on and off with a degree of isolation from the thing being powered. It allows you to use low currents to control high currents. Before transistors came along, mechanical relays were used to perform that task. Though, a MOSFET is not limited to switching applications. They can also be used for other types of control like amplification.
That pretty much the basics of it. I like to think of it as a relay. Small current on the gate allows a large current on the drain.
One of the really big advantages of MOSFETs is not only do they allow you to control big currents with little currents, they require a very small amount of current to control big currents. The nature of their construction allows an electric field to control the flow of current through the main body of the transistor. It takes only a tiny amount of current to generate this field, in fractions of millionths (noted as µA). So, the tiny amount of current that flows through your finger is sufficient to generate the required electric field.
The mosfet is used in the modder's world when the switch can't handle the load. examples would be a finger skin switch, a 555 timer control, a microcontroller, or even some of the really cool tactile switches out there that can't handle a couple of amps. A garden hose opening the Hoover Dam is a good analogy.
Nothing really...the mosfet just allows you to use a sigificantly smaller switch, that would be normally underrated, instead of the big fat switch.
The plain old horn switch will work fine and there's nothing wrong with it. However, unless you want to mount it on top or the side, the horn switch isn't that convenient in your pocket. Also a micro switch might be more appealing to you for aesthetic reasons. The problem is a micro switch isn't designed to handle the current required to fire a PV. Lots of people use them anyway but, they can fail spectacularly. The safe way to use a micro switch to fire a mod is to use it to fire a mosfet and have the mosfet carry the current. If you're happy with your horn switch, there's really no reason to use a mosfet.
Another big advantage is getting rid of the inherant resistance of a mechanical switch.
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Could you explain this please? inherent resistance of a mechanical switch?
Everything has some amount of resistance, even a regular wire. Switches have some amount of resistance, although very low. MOSFETs have some amount of resistance, usually higher. However, when switches wear, the carbonization that builds up on the contacts can increase switch resistance significantly. In the longrun, wear on the contacts can render a switch inoperative. This happens much more slowly with a MOSFET because the switch carrys much less current. The switch contacts don't carbonize nearly as fast, if at all. Tactile switches running very low currents usually fail with loss of spring tension before the contacts stop conducting. A properly rated MOSFET will pretty much last forever so the biggest advantage comes with a touch switch which will pretty much never wear out.
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