This paper proposes a practical non-linear energy harvesting (EH) model and designs a resource allocation algorithm for simultaneous wireless information and power transfer (SWIPT) systems. The algorithm is formulated as a non-convex optimization problem to maximize the total harvested power at energy harvesting receivers while ensuring minimum required signal-to-interference-plus-noise ratios (SINRs) at multiple information receivers. The non-convex objective function is transformed into an equivalent subtractive form, enabling an efficient iterative resource allocation algorithm. Each iteration involves solving a rank-constrained semidefinite program (SDP) using SDP relaxation. Numerical results show significant performance gains when the resource allocation design is based on the proposed non-linear EH model compared to the traditional linear model. The proposed model captures the non-linear characteristics of EH circuits, which are often overlooked in existing literature. The effectiveness of the proposed model is validated through simulations, demonstrating its ability to achieve higher total harvested power and better resource allocation efficiency.This paper proposes a practical non-linear energy harvesting (EH) model and designs a resource allocation algorithm for simultaneous wireless information and power transfer (SWIPT) systems. The algorithm is formulated as a non-convex optimization problem to maximize the total harvested power at energy harvesting receivers while ensuring minimum required signal-to-interference-plus-noise ratios (SINRs) at multiple information receivers. The non-convex objective function is transformed into an equivalent subtractive form, enabling an efficient iterative resource allocation algorithm. Each iteration involves solving a rank-constrained semidefinite program (SDP) using SDP relaxation. Numerical results show significant performance gains when the resource allocation design is based on the proposed non-linear EH model compared to the traditional linear model. The proposed model captures the non-linear characteristics of EH circuits, which are often overlooked in existing literature. The effectiveness of the proposed model is validated through simulations, demonstrating its ability to achieve higher total harvested power and better resource allocation efficiency.