Design of Linear Battery Charger with Self-Blocking Reverse Current Path for Biomedical Applications

By charging the implantable medical devices (IMDs) wirelessly, the need for frequent battery replacements on IMDs can be eliminated. With small chip area, linear battery chargers are suitable as charging circuits for IMDs. Due to the connection between the charging circuit and the output of the power receiver, the reverse current may flow out from the battery to the power receiver when the power transmitter stops power transmission, or the coils move apart. Conventionally, some switches were added to block the reverse current path. A new reverse current prevention circuit is proposed in this work for the linear battery charger. During reverse current prevention mode, the reverse current path is automatically blocked without the need of any additional switch. The experimental results from the fabricated silicon chip showed that the charging current during the normal constant current mode is 50.2 mA, with the battery voltage ranging from 3.3 V to 4.21 V. During the reverse current prevention mode, the total battery standby current is reduced to only 7.98 μA.