Transformerlösa

Transformerlösa is a Swedish term that literally translates to "transformerless" and is used to describe electrical and electronic circuits, devices or systems that operate without a mains or output transformer. In practice the label applies to a range of designs including switch-mode power supplies, capacitive dropper power supplies, direct-coupled amplifiers and output-transformerless (OTL) audio amplifiers.

Transformerless designs developed as solid-state components and switching techniques reduced the cost, size and weight of power conversion and audio output stages. Common motivations include space and weight savings, reduced material cost and improved frequency response where transformer characteristics would limit bandwidth.

Advantages of transformerless approaches include compactness, greater efficiency in many switching topologies, and simpler frequency characteristics for audio and high-frequency circuits. Disadvantages and constraints include lack of galvanic isolation from the mains in some topologies, potential safety hazards, increased electromagnetic interference (EMI), and specific grounding requirements. In audio, OTL designs eliminate transformer coloration but demand careful impedance matching and thermal management.

Because transformerless mains-connected devices can present shock or fire risks if improperly designed, many jurisdictions regulate their use and require safety measures such as reinforced insulation, earth connections or isolation barriers to meet standards (for example IEC/EN safety standards). The term is widely used in technical literature and product descriptions to indicate the absence of a transformer and the associated design trade-offs.