Class 2 transformers are small line-frequency transformers widely used for control systems requiring 24 VAC signaling, including residential and commercial HVAC systems, industrial controls, and much more. These transformers have large standby losses, low efficiencies, large weights, and high costs. In this work, we propose a power electronics alternative in the form of a low-power solid-state transformer. We design and test two 40 VA 120 VAC to 24 VAC solid state transformers, including a two-stage topology, leveraging an isolated commercial power supply as one of the stages, and a single-stage topology achieving soft-switching during peak voltage conditions, achieving a standby loss less than a sixth of the line-frequency transformers, and improved efficiencies across all load ranges compared to the line-frequency Class 2 transformers.
