About Transistors

There are many different types of transistors. Take a look at the "Transistor Type / Technology" section on this page from GlobalSpec.

There are a whole bunch of transistor museums that will give you some idea of what there is and what has been abandoned.

http://www.google.ca/search?hl=en&q=%22transistor+museum%22&btnG=Google+Search&meta=

there are different types of transistors

1.pnp

2.npn

2.based on current operated and voltage operated

in ac current the amplitude changes sinosodiually.ac current changes the polarity alternately .in dc the polarity remains the same

electronics deals with the flow of electron in semiconductor.

electrical deals with the flow of electron in conductor

The electrical circuit is composed of L(inductors), R(resistors), C(capacitors), and coductive wirings. The electronic circuits includes at least a semiconductor device.

thanks for your reply.i wanted to know about mosfets

Where are you starting from? The simplest explanation I know of their function is roughly as follows:

There are essentially two types (or flavours) of MOSFETs - called NMOSand PMOS. For both device types, the main current flows along a channel between conducting terminals that are calld the "Source" and the Drain". The difference in use is that to turn an NMOS device on, a control terminal (or "gate") is biased positive. To turn a PMOS device on, the gate is biased negative. All MOSFETs have a further terminal, called the bulk, that is diode connected to the channel, and serves as an additional (usually unwanted) gate; this terminal is often connected to the "Source". {For a very crude approximation, you can think of the device conduction as being like water flowing through a valve, with the valve controlled by the voltage on the gate. Unfortunately, this analogy is of limited value for designing with the devices}

Within these limits, just about everything else can be changed by changing the detail of the design. This is why you will find such a plethora of MOSFET devices. I will describe some of the options for an NMOS transistor (for PMOS simply swap above for below and vice versa). This variety is probably best absorbed piecemeal at first, however, so don't be put off if it's 'too much' as presented here.

For example, NMOS devices can be made so that they are on whenever the potential on the control terminal is near or above the potential of the lower of the conducting terminals. These devices are turned off by biasing the control terminal negative and "depleting" the conduction; such devices mostly described as "depletion" NMOS.

The NMOS devices used for microprocessors, memory and other logic structures are mostly fabricated so that they are turned off when the potential on the gate is near the potential on the lower terminal. These devices conduct when the gate potential becaomes sufficiently positive to enhance the conduction in the channel. They are known as "enhancement" devices.

MOSFETs can be built on the surface of a (relatively-speaking) thick crystal. However, there are some advantages in using a relatively thin film of semiconductor on top of an insulator. The process is known as Silicon On Insulator or SOI. The bulk "connection" of SOI devices is usually effectively left floating - which changes the device characteristics.

Logic devices are generally built so that there is no structural difference between the source and the drain. Power MOS will usually be built so that the drain can be raised to much higher potentials than the source, as this gives relatively easy control at the same time as high output Voltages.

BTW, when I first got involved with electronics (a very long time ago now) the head of the electronics group told me not to bother finding out about MOSFETs, because they were theoretically unsound and so could never be made to work. (Of course he was right, and everything you have heard about since is purely imagination).

Seriously though, he was a well-educated engineer who understood the basic physics - so you should expect detailed understanding of their operation to require a fair grounding in device physics.

transistor is an active device which controls the o/p, by providing proper input...