The small-signal model of a switch-mode power converter is a useful tool in understanding its dynamic behavior and designing a proper compensator. In the power electronics community, people derive small-signal models almost always by perturbation and then extracting the small ac components manually from the whole system equations. This process is not systematic and potentially error prone. This article presents an alternative process to develop small-signal models based on a well-established systematic method that has been used in control system analysis and design for a long period. With this math-centric approach, one just applies standard math operation to linearize a nonlinear system described by its state-space equation, and then uses a well-known formula to derive the transfer functions of the linearized system. This is a precisely defined and systematic process with the advantage of deriving all the transfer functions with a minimum effort.