We introduce a smooth variant of the Hopkins-Singer model of differential K-theory. We prove that our model is naturally isomorphic to the Hopkins-Singer model and also to the Tradler-Wilson-Zeinalian model of differential K-theory.

We gratefully acknowledge a partial support on this work from Mahmoud Zeinalian's NSF grant DMS-1309099. Some part of this work was completed during our attendance at the conference Topology of Manifolds -- A conference in honour of Michael Weiss' 60th birthday. We thank the organizers for financial support and hospitality.