Signal and Instrument Transformers
Audio transformers
Audio transformers couple signals, provide isolation, and match impedance. Vacuum-tube output stages rely on them to match high plate-circuit impedance to a low-impedance loudspeaker.
Impedance ratio
Frequency response
At low frequency, magnetizing inductance and core saturation matter. At high frequency, leakage inductance and winding capacitance matter.
RF transformers
RF transformers provide coupling, matching, DC isolation, and balanced/unbalanced conversion using ferrite, powdered iron, air-core, or transmission-line structures.
Current transformers
A current transformer (CT) produces a scaled secondary current for meters, protective relays, and controls. The primary may be only one conductor through the core.
Potential / voltage transformers
A PT or VT scales a high system voltage to a lower measurement voltage. Its secondary is operated differently from a CT and must not be treated like a current-transformer secondary.
Pulse transformers
Pulse transformers provide isolation and level conversion for gate drives, digital interfaces, and switching circuits. Leakage inductance and capacitance determine pulse shape.
Baluns
A balun converts between balanced and unbalanced circuits. Many use transformer action, though transmission-line forms are also common.