mosfets, and fets what are they

[danielsmusic]

what are the propertys or mosfets and fets i know that there types of transistor, but i would like to know what there used for and what they do
eg: a npn transistor lowers the risistance between c and e when there is a voltage at b
a pnp transistor highers the risistance between c and e when there is a valtage at b
both are variable
trasisotrs and act like diodes between b and e, b and c.

 

[Nigel Goodwin]

what are the propertys or mosfets and fets i know that there types of transistor, but i would like to know what there used for and what they do
eg: a npn transistor lowers the risistance between c and e when there is a voltage at b
a pnp transistor highers the risistance between c and e when there is a valtage at b

Sorry, those are both totally incorrect, a bipolar transistor doesn't alter the 'resistance', it changes the amount of current it passes (which is a very different thing!). Funnily enough, FET's DO alter the resistance between drain and source!.

But this isn't really a question that can be answered in a forum, you need to go away and learn basic electronics!.

both are variable
trasisotrs and act like diodes between b and e, b and c.

 

[danielsmusic]

sorry, i assumed that.

 

[Jay.slovak]

danielsmusic, don't feel aggrieved because of Nigel's reply, it sounded a little offensive but he was just trying to help you... :wink:

 

[danielsmusic]

i know i just make mistakes sometimes

 

[zachtheterrible]

They are called Field Effect Transistors. MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor if I remember correctly.

Bipolar transistors are controlled by current.

field effect transistors are controlled by voltage.

Go do a search for a tutorial on them, itll explain much better than I can.

 

[danielsmusic]

do you know what a jfet is then.
i think you right i have seen it somewhere.

 

[zachtheterrible]

It stands for Junction Field effect transistor

 

[mstechca]

what are the propertys or mosfets and fets i know that there types of transistor, but i would like to know what there used for and what they do

FET = Field effect transistor
MOS = Metal Oxide Semiconductor (correct me if I am wrong here)

I only use BJT transistors (both npn and pnp types). I never have used FET's and I don't see a reason to use them as of yet.

eg: a npn transistor lowers the risistance between c and e when there is a voltage at b

not exactly. When b (the base) is positive, a complete circuit exists between collector and emitter. A transistor is NOT a variable resistor.

a pnp transistor highers the risistance between c and e when there is a valtage at b both are variable
trasisotrs and act like diodes between b and e, b and c.

Transistors have nothing to do with valtage, and is valtage supposed to be a new term we don't understand or were you trying to say voltage?

and what you say about a PNP transistor is incorrect. When a negative voltage is injected into the base, the circuit betwen collector and emitter is complete.

You need to look at a book on how transistors work.

 

[danielsmusic]

i mite be able to say on paper but i work with them iv make loads of curcuits with them

 

[eblc1388]

eg: a npn transistor lowers the risistance between c and e when there is a voltage at b

not exactly. When b (the base) is positive, a complete circuit exists between collector and emitter. A transistor is NOT a variable resistor.

Thanks to you I know people were lying to me when they told me the transistor behaves like a variable resistor in my linear voltage regulator circuits.

So linear and switching regulators are all the same. The transistor just conducts completely. :twisted:

 

[checkmate]

i mite be able to say on paper but i work with them iv make loads of curcuits with them

There are lots of circuits on the internet. Just download any and you can make one. But it takes the theoretical background of circuit theory to actually design one. Obviously, your basics are all screwed up. You actually treat every circuit element as a resistor when 90% of electrical circuits aren't resistors at all!

As many others have advised, it's best to get a book and read up on them. It's not something that can be explained in a few paragraphs without diagrams.

 

[danielsmusic]

my own designs

 

[heathtech]

I agree that reading about them is the only way to learn, my friend. But, to break it down to simple terms, BJT's have relatively low impedance at the base, where FET's are very high impedance devices. BJT's are current controlled devices, where FET's are voltage controlled. Certain circuits can be designed with either type and made to work, but the properties of these devices LEND themselves to certain applications. FET's are particularly good in digital circuits, where voltage levels (i.e. 5v,0v) are used as signals. BJT's tend to lend themselves to analog applications. This does not mean, however, that a BJT can't be used in a digital circuit, and that FET's can't be used in analog, so don't be confused. Study more and learn more.