A Power Efficient LDO-Type Wireless Battery Charger for Biomedical Implants Based on Direct Charging from Regulated Rectifier Current

A LDO-type wireless battery charger that utilizes a rectifier with its output current charging a battery directly is proposed. Since only one rectifier voltage drop is between the peak AC input voltage (V
_ACP
) and the battery voltage (V
_bat
), high power efficiency (PE) can be achieved. Different values of charging current (I
_chg
) required for a given battery charging profile are obtained and regulated through a feedback loop. A constant voltage circuit is also proposed to reduce I
_chg
gradually when V
_bat
is close to the fully charged voltage. For a 13.56MHz input with V
_ACP
= 4.64V, the proposed charger achieved a simulated maximum PE of 86.8% for I
_chg
~ 10mA at V
_bat
= 4.1V.