Thread: Amplifier

How an amplifier amplifies the voltage?

It doesn't. It uses an input signal to control a voltage source.

It's like claiming that a car amplifies the driver's force on the gas pedal. It doesn't. The force on the gas pedal controls a much larger power source.

Think of a transistor like a tap or valve. A small voltage applied to the base causes a large change in the effective resistance of the transistor. This allows a large current to be controlled, which can be used to create a large change in output voltage.

http://file.yizimg.com/335677/2009090811191191.pdf

perhaps
"transformer" was meant
instead of "amplifier"?

The power of the signal is the one that is amplified not the voltage.

Actually, it depends on the circuit that is used. With a transistor, 3 basics circuits are used:

• Common base : amplifies voltage (output current is equal to input current).
• Common collector : amplifies current (output voltage is equal to input voltage).
• Common emitter (most classical amplifier circuit) amplifies both voltage and current.

Remark that Merkezcy is right, all these circuits amplify the power of the signal (but the last one gives more power gain). That is a difference with transformers that may increase voltage but decrease current in the same proportion so that the power remains constant.