This article deals with resource allocation to maximize the secondary user (SU) throughput in cognitive radio where primary users (PUs) are wirelessly powered by SU signals during the first part of a time-slot, and PUs and SUs share the spectrum during the second part of the time-slot. An optimization problem is formulated to maximize SU throughput under a constraint of minimum PU throughput (due to quality-of-service). As the optimization problem is NP-hard, we decompose the problem into two subproblems by introducing an auxiliary variable, i.e., the consumed energy at PU, and the subproblems are decoupled by minimizing the PU consumed energy. A three-step resource allocation scheme is then proposed to solve the optimization problem with low complexity. Numerical simulations are provided to demonstrate the superiority of the proposed scheme in terms of both performance and computational complexity.