Verified answer

The emitter is the input, the collector is the output, and the base is what controls the amount of current that flows between the emitter and collector kind of like a switch. In other words the base is what turns the transistor "on" making current flow through the emitter and collector.

The difference between an NPN and a PNP transistor is how you hook the wire that hooks up to the base to make it turn on. To make an NPN transistor turn on connect the wire from the base to the collector. On a PNP hook it to the collector. The wire that hooks to the base generally has a resister connected to it in series because the base doesn't need full current in order for it to fully turn on in it's full capacity, only a little bit is needed. As a matter of fact, no resister can make the transistor overheat and burn out.

I hope this is helpful.

I can't explain transistor physics in this small space, I'll cover the highlights only.

In a junction transistor, NPN, in the common emitter connection, the most common, the input is the base, the output is the collector, and the emitter is the common, usually grounded.

If you apply a small current to the base, it causes a larger collector current to flow. With resistors to convert that to voltage, a small voltage at the base can cause a larger voltage at the collector, and therefore the transistor has gain and can amplify signals.

For switching purposes, a + voltage at the base causes the collector to go to ground, zero volts, a low. Thus the transistor functions as a digital inverter.

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Transistors is commenly used as electric switches, it has no movable parts so it behaves as an insulater.

Transistors can be regarded as a type of switch, as can many electronic components. They are used in a variety of circuits and you will find that it is rare that a circuit built in a school Technology Department does not contain at least one transistor. They are central to electronics and there are two main types; NPN and PNP. Most circuits tend to use NPN. There are hundreds of transistors which work at different voltages but all of them fall into these two categories.

Transistors are manufactured in different shapes but they have three leads (legs).

The BASE - which is the lead responsible for activating the transistor.

The COLLECTOR - which is the positive lead.

The EMITTER - which is the negative lead.

The diagram below shows the symbol of an NPN transistor. They are not always set out as shown in the diagrams to the left and right, although the ‘tab’ on the type shown to the left

Hope this help :)

First, you need to know there are (essentially) two types of common transistors FETs and BJTs.

Since you mention the "base" then you are refering to a BJT (bipolar junction transistor). There are two flavors of this transistor: PNP and NPN.

If you use an NPN transistor, you can connect the emmiter to ground and connect the collector to +V through a load. The base, when you apply a sufficient current (i.e. connect it to +V through a current-limiting resistor) will cause current to flow through your load. This is how to configure a NPN BJT as a low-side switch. So, there are really no "inputs" or "outputs". It all has to do with current through a load.

Transistor Leads use to amplify current, for example they can be used to amplify the small output current from a logic Integrated Circuit so that it can operate a lamp, relay or other high current device. In many circuits a resistor is used to convert the changing current to a changing voltage, so the transistor is being used to amplify voltage. The three Leads when you put in a circuit board has a respective function.

http://en.wikipedia.org/wiki/Bipolar_junction_tran...