This paper presents a nonlinear control technique based on feedback Relay systems for photovoltaics applications in converters and inverters. Describes the design of the control law from the state equations of Buck converter, the analysis of limit cycles, stability of the systems to obtain digital control law for further simulation and implementation in programmable logic devices (PLD). We performed the programming of the control technique in hardware description language (VHDL), later we implement in a CPLD and development the prototype of a Buck converter. Finally simulations and tests to the prototype were realized, obtaining optimal results of performance.