Abstract: A low cost load sensing technique that is suitable for use in sensing batteries in a battery charging circuit is disclosed. The circuit is adapted to be utilized in conjunction with a power supply which may include a primary converter and a voltage feedback circuit. A transformer with a dual secondary winding is connected between the primary converter and the output terminals of the charging circuit. When no load or battery is present, a first feedback loop is utilized with both of the secondary transformer windings in series, which supplies a constant output voltage at the output terminals. When a load is present, a second feedback loop is utilized which includes one of the secondary windings to provide the voltage of the output terminals. A capacitor is connected in parallel with the other secondary winding. When a load is present, a step increase in voltage occurs across the capacitor due to the fact that the both secondary windings are in phase when a load is present.

Abstract: Lithium polymer battery charger apparatus for charging a plurality of equal charge point lithium polymer battery cells prevent overcharging of any cell, whether the cells are arranged in a series stack or are arranged in parallel. When the cells are connected in a series stack, a power supply is connected to the series stack to apply a charge current to the series stack. The state of charge of each cell in the stack is monitored. Information that the state of charge of any cell is approaching full charge is used to control the charge current and to prevent overcharging of any cell.