Single phase transformers are designed to supply electric power to single-phase systems. These electrical devices transfer energy from one circuit to another via electromagnetic induction. Single phase power usually includes one hot lead and a grounded return line or neutral. Single phase electrical distribution is used mainly in residential and commercial applications, typically for lighting and heating. Single phase transformers carry many product specifications, including transformer type, winding turns, cooling method, core type, output voltage, and mounting or form factor. Performance specifications, approvals, and features are also important parameters to consider. 

Types of Single Phase Transformers

There are many types of single phase transformers. Products include audio, balun, buck-boost, constant voltage (CVT), constant current, distribution, flyback (FBT), generator step-up (GSU), harmonic mitigating, high frequency, high voltage, impedance matching, and industrial control transformers. Categories of single phase transformers also include interface, inverter, isolation, leakage, lighting, medical, multi-ratio, neutral grounding, power, rectifier, resonant, solar power, and substation transformers. Autotransformers and variac or variable autotransformers are also available from single phase transformer suppliers. 


Like other types of transformers, single phase transformers may be used to increase or decrease the voltage from one side of the transformer to the other. The turn ratio or number of windings on the primary and secondary sides of the device determines the change in voltage. Step-up transformers produce a secondary voltage that is larger than the primary voltage. Step-down transformers have a secondary voltage that is smaller than the primary voltage. Variable single phase transformers are devices with a setting for changing the turn ratio as needed. One-to-one transformers are single phase transformers with a turn ratio of 1:1 or near 1:1.  

Product Specifications

Cooling method, core type, output voltage, and mounting or form factor are additional product specifications to consider when selecting single phase transformers. There are four choices for cooling method: dry-type or air cooled, oil filled, water cooled, and other. Core types are listed as laminated, split, toroidal, and other. The output voltage is either alternating current (AC) or direct current (DC). There are many mounting or form factor styles for single phase transformers. Choices include chassis mount, chip transformer, dish or disk, H-frame, modular jack, pad mounted, printed circuit board (PCB), and pole mounted.  

Selecting Single Phase Transformers

Selecting single phase transformers requires an analysis of performance specifications (including the single-phase primary configuration) as well as compliance with regulatory standards. Performance specifications include operating frequency range, maximum primary voltage rating, maximum secondary voltage rating, maximum secondary current rating, power rating and operating temperature. The single-phase primary configuration is listed as single, dual, quad (2+2) 5-lead, ladder, or other. In terms of regulatory standards, single phase transformers that are sold in Europe must be RoHS and WEEE compliant.