how can a transistor work as an amplifier?

Answer 1

With a field-effect transistor, a small voltage at the input is made to control a current at the output. The current is made to flow through a load, which can be a fairly large resistance. As a result, the output voltage can be many times larger than the input.

With the bipolar junction transistor, it is a tiny current at the input that is used to control a much larger current at the output.

The ratio of output voltage to input voltage, or output current to input current is a dimensionless value known as gain, or amplification. In tubes, it was called mu, in transistors it is called hFE.

If you are interested in learning more, I'd suggest that you go to Radio Shack and get some of their beginner's books on learning electronics. They have projects you can build, and Radio Shack has all the parts!

Answer 2

A variable voltage applied to the gate of a field effect transistor controls a current between the source and the drain. In the case of a pnp or npn transistor, the varying voltage to the base controls the current from the emitter to the collector. The gate or base respectively only draws a tiny amount of current. This weak signal controls a much larger current between the other two terminals, so you're amplifying a weak signal. In the days of vacuum tubes, an electrode called the grid, between a hot filament and a cold electrode called the plate controlled the flow of electrons from the filament to the plate. A very weak negative charge on the grid could stop a current flowing, so again it worked as an amplifier.

Answer 3

How Does A Transistor Work

Answer 4

Bipolar Junction Transistor has three terminals namely, base, emitter and collector. To use the transistor as amplifier, depending on what you want to amplify, current or voltage, the configuration of the circuit is decided. Three configurations are normally used. Common Emitter (CE) for voltage amplification, (CB) and (CC) for current amplifications. In CE configuration, the base input current, which is due to the input voltage, controls a wider varying collector(emitter) current due to the change in electric field in the collector base junction.

CE has high input impedance and medium output impedance and provide voltage amplification.

CB has low input impedance and produces no amplification, but provides very low output impedance.

CC provides high input impedance and low output impedance and provides current amplification.


The principle is different for MOS transistors which are of high input impedance type, taking almost nil input current. They work based on the field effect in the channel created between the source and drain. More details can be had from basic electronics book.

Answer 5

A small current applied to the base of a bipolar transistor, or a small voltage applied to the gate of a field effect transistor, controls a much larger current flow through the other two terminals. It's like using a small effort to open a valve controlling a large flow of water.

Answer 6

A transistor is a current controlled current source. That is to say, the amount of electrical current that a transistor outputs depends on the amount of current given to it as input. By varying the input current, you can change the output current.

Here's a pretty good description of how to use transistors in circuits:
http://www.kpsec.freeuk.com/trancirc.htm

Answer 7

Transistor based amplifiers are used for both. An 'operational amplifier' is a common cheap mass produced component, which is a DC coupled amplifier. The applications for these are practically endless.

Answer 8

In digital / analogue circuits this is accomplished by resistance change over the drain side to accomplish gain/loss on the powered circuit. Use a variable resistor and power source in line with the circuit basically. If you throw a transformer in line and 3 more transistors you now have a modulator or mixer depending on what you are working towards and how you set them up.

Answer 9

As BJT is a current controlled device,

Moreover as the current is folw fro the high resistance input circuit to to low resistance output circuit, transistor is functioninig as amplifier..

Above all , As Negative feedback is given it alos makes the BJT workinhg as a amplifier

Answer 10

And the same question pops up again