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Solar cells have a current-voltage (I-V) characteristic which is affected by the radiation and the temperature. To obtain the maximum electricity from solar cells, the power converters for PV (photovoltaic) modules have a function called MPPT (maximum power point tracking). The DC voltage and current are controlled to track the maximum power point (MPP) where the PV modules feed the maximum output power. A module integrated converter (MIC) is individually installed behind of a PV module to seek the MPP. One example is AC module composed of a PV module and a small inverter. In case of AC module, the basic characteristic of the PV module is known by the manufacturer. The domain of MPP can be approximately predicted. The proposed MPPT method takes full advantage of the known I-V characteristic. The I-V plane is divided into two domains by the square root function. One includes MPPs and the other one doesn't. In the previous research, we proposed to use linear functions. However, the linear functions with high slope are effective for high radiation, and those with low slope are suitable for low radiation. The square root functions can cover the both. The operating point can be rapidly approached to the MPP. Around the MPP, the algorithm is switched to the IncCond method. Circuit experiments have been carried out. The measured approaching time to the MPP is reduced from 56.8% to 85.4% compared to the IncCond algorithm. The proposed method can be easily applied to various MPPT algorithms.