transisters

[catchinit]

Can someone explain in fairly simple terms how transisters work and exactly what this pnp npn thing is all about please? Many thanks in advance.

[mibn2cweus]

A transistor is a three terminal (connections) semi-conductor device, an integration of two diodes. To understand how a transistor works you first need to understand the operation of a diode.

Diodes are essentially a one-way street for electron current flow consisting of two types of semiconductor material that when placed together form a zone where current carriers are depleted. Current carriers move into this zone when the potential differance created in this zone is overcome by applying a small voltage (typically .6 to .7 volts) of the correct polarity (negative to positive) across the junction. Using the opposite polarity will increase the depletion zone so that no current can get through.

In a transistor the amount of current that can pass through a stack of three types of semi-conductor material n-p-n or p-n-p is determined by how much of a much smaller current flows through the first two. This control current creates a conductive path for a larger current to pass through the third.

This (I hope) is a simplification of how a transistor works. To gain a better understanding I recommend further study of the simpler diode junction first.

[mattie]

This should tell you what you want to know - http://www.satcure-focus.com/tutor/page4.htm

[mibn2cweus]

mattie, Good one! I like explanations the follow from things I can relate to from personal experience. An ideal answer for the question posed.

However if anyone desires a more detailed explanation I found this:
Semiconductors

[catchinit]

Absolutely fantastic. Thanks mattie and mib.

[alvin100]

If you want to look at it in even simpler terms, then think of it as a switch with three legs, applying a small voltage(0,6) to one leg allows current to flow through the transister. So basically transistors can be used to switch things on and off (very quickly if need be) The downside of most transistors is that they can only handle tiny amounts of power, so you wouldnt use them to swich devices that need lots of current, heaters, lights, electromagnets etc.