The requirement of fast, steady and safe chargers has become the most important issue for implantable power management. This work proposes a closed-loop control charger consisted of a high efficient rectifier, charging control circuit and PWM signal generators. It makes the charging voltage automatically follow the battery voltage by a feedback loop, which reduces the energy consumption caused by large voltage difference between the constant charging voltage and battery voltage. A prototype was fabricated in 0.8渭m HV CMOS technology, and the measured maximum overall efficiency is 70.67%.