In electronic equipment, electrical
power transformers with capacities in the
order of 1 kw are largely used ahead of a
rectifier, which in turn supplies direct current
to the equipment. Electrical power transformers
are usually made of stacks of steel alloy
sheets, called laminations, on which copper
wire coils are wound. Electrical powerransformers
in the 1- to 100-W power level are used principally
as step-down electrial power transformers
to couple electronic circuits to loudspeakers
in radios, television sets, and high-fidelity
equipment. Known as audio electrical power
transformers, these devices use only a small
fraction of their power rating to deliver
program material in the audible ranges, with
minimum distortion. The electrical power transformers
are judged on their ability to reproduce sound-wave
frequencies (from 20 Hz to 25 kHz) with minimal
distortion.
At power levels of 1 milliwatt or less, electrical
transformers are primarily used to couple
ultrahigh-frequency (UHF), very-high frequency
(VHF), radio-frequency (RF), and intermediate-frequency
(IF) signals, and to increase their voltage.
These high-frequency electrical power transformers
usually operate in a tuned or resonant circuit
(see Resonance), in which tuning is used to
remove unwanted electrical noise at frequencies
outside the desired transmission range.
