A simplified power control technique for electronic ballasts of HID lamps is proposed. This power calculator and controller consist of regular operational amplifiers with some passive elements and form simple add operation circuit. From a mathematical model of designed ballast with proposed power controller, the control performance and stability are analyzed by using Matlab and the results show that the stable starting characteristics and steady state characteristics of HID lamp are appropriately guaranteed. The experimental results of the prototype ballast coincide with the simulation results.