What is an amplifier?

Can we use transformer as an amplifier? Why or why not?

Wikipedia says:

An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the power of a signal (a time-varying voltage or current). An amplifier uses electric power from a power supply to increase the amplitude of a signal

So, I think a transformer cannot amplify power and thus it cannot be used as an amplifier.

Is the amplifier term only for power gain and not for voltage/current gain? Please clarify this concept.

  • 1
    \$\begingroup\$ yes, you can use a transformer to amplify voltage, or to amplify current, but not both at the same time .... there is a power loss \$\endgroup\$
    – jsotola
    Commented Jun 6, 2018 at 23:03
  • 3
    \$\begingroup\$ Check this out: magnetic amplifier. \$\endgroup\$ Commented Jun 7, 2018 at 0:06

3 Answers 3


An amplifier takes a low power input signal, and a supply of power, and outputs a higher power version of the input signal, with some specified level of fidelity. The output power comes substantially or exclusively from the power supply, and is almost invariably higher power than the input signal, though less than that taken from the power supply. The output can have higher voltage, or higher current capability, usually both.

Although a transformer can increase the voltage or the current of a signal, it can never increase the power. The output power comes exclusively from, and is strictly less than, the input power. I would be very reluctant to describe what a transformer does as amplifying voltage or current, it transforms or changes these values.

There is an unusual active device called a magnetic amplifier, which was very popular before high powered silicon devices were available. It uses magnetic saturation in specially wound transformers. The input signal controls the saturation, which is then able to control the throughput of a much larger supply of power to an output. It is not a simple passive transformer.


Is the amplifier term only for power gain and not for voltage/current gain. Please clarify this concept.

Given that power = voltage x current, if you have power gain then you must have: -

  • Voltage gain or
  • Current gain or
  • Both voltage gain and current gain
  • \$\begingroup\$ That's the opposite of the question asked. Effectively the question asks if something that has voltage gain, but not power gain (due to proportionate current reduction) can be an amplifier. \$\endgroup\$ Commented Jun 12, 2018 at 16:08

In general, an amplifier refers to a circuit whose output is larger than its input with respect to power, voltage and/or current. Thus a transformer, depending on its turns ratio, can either increase voltage or current and thus can be considered an amplifier. Electronic amplifiers are more versatile in terms of being able to amplify voltage, current and/or power over a wider range of gains. They can amplify power because they draw the needed power from their power supply, something a transformer can't do.

  • 1
    \$\begingroup\$ Amplifiers with no voltage gain (generally Av slightly less than 1) are considered amplifiers because their current gain provides power gain. Transformers are not. \$\endgroup\$
    – user16324
    Commented Jun 7, 2018 at 10:23
  • \$\begingroup\$ You say yourself that a transformer can't amplify power. OP gave the definition of an amplifier: "an electronic device that can increase the power of a signal". So how can you still say "a transformer can be considered an amplifier"? It does not make sense, unless you don't agree with the definition OP gave, in which case you should make it clear. \$\endgroup\$
    – dim
    Commented Jun 7, 2018 at 11:30

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