We report single-pass difference-frequency generation of mid-infrared femtosecond pulses tunable in the $3.2–4.8\mathrm{\mu }\mathrm{m}$ range from a two-branch mode-locked erbium-doped fiber source. Average power levels of up to $1.1\mathrm{mW}$ at a repetition rate of $82\mathrm{MHz}$ are obtained in the mid infrared. This is achieved via nonlinear mixing of $170\mathrm{mW}$ , $65\mathrm{fs}$ pump pulses at a fixed wavelength of $1.58\mathrm{\mu }\mathrm{m}$ , with $11.5\mathrm{mW}$ , $40\mathrm{fs}$ pulses tunable in the near-infrared range between $1.05$ and $1.18\mathrm{\mu }\mathrm{m}$ . These values indicate that the tunable near-infrared input component is downconverted with a quantum efficiency that exceeds 30%.