In this paper, a sliding mode control of LLC resonant dc-dc converter in low voltage and high current application is presented. The proposed controller operates at two fixed switching frequencies to the battery charger of electric vehicles. In resonant converter, because of the soft switching process, switching loss is negligible and converters can be designed at high frequencies to reduce the size, weight and price. To analyze this convertor the harmonic approximation method with state space equation is used. Taking advantage of the approximations used in order to avoid uncertainty, sliding mode control method is used. The mentioned convertor with the proposed controlled is exploited within three switching frequency bands that are lower than resonant frequency, resonant frequency and above resonant frequency. Due to the robustness of the sliding mode control, the output voltage regulation occurs with minimum distortion under a wide variation of input voltage, output voltage and output current. As a result, the battery life increases. In order to verify the results and effectiveness of the proposed converters, the prototype of LLC resonant converters Simulation and experimental results for the input voltage 300-420 V dc, output voltage 36-72 V dc and current output (0-11 A) is presented. The prototype achieves a peak efficiency value of 96%.