Optical power supply is usually adopted by the high voltage side of electronic current transformer. To improve the reliability of the system

the power consumption of modulation circuit in high voltage side is demanded as low as possible. Compared with general A/D conversion circuit

the V/F circuit has simple structure and low power consumption

and the conversion speed can meet the requirement of steady-state protection. A kind of modulation method based on the V/F principle is introduced. The test results show that the power consumption of high voltage side circuit is only 23 mW and the system linearity is 0.04% from 5% to 120% within the rated input scope.