B82805 Push-Pull Transformers EPCOS / TDK B82805 Push-Pull Transformers are constructed with a ferrite core and copper wire for both the primary and secondary winding. The B82805 series features a typical switching frequency of >,250KHz, different turns ratios, and a small SMD package. The transformers are RoHS compatible with applications such as switch-mode power supplies, isolated interface power supplies, industrial automation, and process control.