We present a high-power optical-parametric-oscillator (OPO) based frequency comb in the mid-IR wavelength region. The system employs periodically poled lithium niobate and is singly resonant for the signal. It is synchronously pumped by a $10\mathrm{W}$ femtosecond Yb:fiber laser centered at $1.07\mu \mathrm{m}$ . The idler (signal) wavelength can be continuously tuned from $2.8\text{to}4.8\mu \mathrm{m}$ $\left(1.76\text{to}1.37\mu \mathrm{m}\right)$ with a simultaneous bandwidth as high as $0.3\mu \mathrm{m}$ and a maximum average idler output power of $1.50\mathrm{W}$ . We also demonstrate the performance of the stabilized comb by recording the heterodyne beat with a narrow-linewidth diode laser. This OPO is an ideal source for frequency comb spectroscopy in the mid-IR.