Ion cyclotron resonance frequency (ICRF) heating is a traditional auxiliary heating method applied to EAST. However, the antenna load will oscillate violently with the change of plasma parameters in the ICRF heating. But fast ferrite branch technology (FFT) can be used to achieve real-time impedance matching by controlling the bias magnetic field of FFT to adjust its equivalent electric length. So an excitation coil power supply is developed to satisfy the requirement of fast and stable change of FFT bias magnetic field. In the power supply design, the method of Pulse Width Modulation is used to achieve rapid real-time conversion of current, and to meet the needs of rapid power conversion. The paper introduces general design of PWM power supply, front DC power supply, energy storage filter circuit and constant current circuit of H bridge sequentially. And an experiment is set on the FFT excitation coil current changing with the control signal, indicating that the rapid real-time current conversion can be achieved.