Transformers having bobbins that are constructed in such a way that pre-formed secondary windings (e.g., resembling springs) may be slipped onto the bobbins after a primary winding has been wound onto the bobbin. Additionally, the secondary windings may also serve as a self-leading device. That is, they may not require terminations on pins of the bobbin, which may reduce cost and complexity. The secondary windings may have circular or non-circular (e.g., flat) cross-sections. The transformer winding techniques provided herein may reduce the number of components, and may promote smaller input filters and/or less filtering stages at a fraction of the cost of conventional transformers.