This paper analysis the difficulties to provide a stable DC power supply to sampling and transmitting circuit in the high-voltage side of ECT. According to the storage principle of electromagnetic energy， the technical problems to take energy from magnetic field with self-excitation power supply has been resolved with a ring magnets jacket made by microcrystalline magnetic materials and a special“restricting current funnel” component. The three major indexes of the new ECT（wake-up current， wake-up time， saturation large current） meet the application requirements.