<p>This paper proposes a method for estimating the output voltage and current of a large-capacity capacitor charger for driving a magnetron, based on an LCC resonant converter. The proposed estimation method enables the high-voltage output to be estimated using only voltage and current measurements on the low-voltage side of the transformer, thereby enhancing the reliability of the sensing circuit. In addition, since there are no limitations on the estimable output voltage and current, the proposed method can be applied to high-voltage applications with specifications in the hundreds of kilovolts range. The resonant current waveform of LCC resonant converter exhibits diverse shapes depending on the input-to-output voltage ratio. To address this issue, the operating principle of the converter was analyzed by approximating the resonant current waveform as a trapezoidal shape. Based on this analysis, simplified equations for estimating output voltage and current were derived, and an output estimation algorithm was developed accordingly. To validate the proposed algorithm, an LCC resonant converter with a rated output of 20&#xa0;kV and 30&#xa0;kW was designed, and simulations were conducted. The simulation results under the various output conditions were within 1% for output voltage and 3% for output current, respectively, demonstrating the validity of the algorithm.</p>