Battery charger

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS In the following, if a voltage is stated at a particular point in a circuit, it is to be understood that such voltage is measured relative to ground.
In each of FIGS.
1 through 4, the grounds are terminals G1, G2, G3, and G4, respectively.
FIG.
1 illustrates a conventional lithium-ion cell charging circuit whose elements are interconnected in accordance with known technology.
An alternating-current source 101, which may typically be a mains power source at standard mains voltage (110-120 volts in North America), provides power to the input winding 103 of a transformer 105 whose secondary winding 107 delivers an AC output that is rectified by a bridge rectifier circuit 109 and is smoothed by smoothing capacitor 111.
If desired, more elaborate smoothing may be provided in this conventional circuit and in the charge circuit according to the invention, to be described below.
If the resulting unregulated DC current applied at a voltage V.
sub.
W1 between terminals W1 and G1 in the circuit were applied directly to lithium-ion cell 135 to be charged, there would be a serious risk of applying too high a charging current or too high a charging voltage, or both, to the lithium-ion cell 135, risking damage to the cell 135 and other hazards (including serious internal gas expansion within cell 135 and potentially an explosion).
Accordingly, it is conventional to provide in such charging circuit regulator subcircuits to control the current and voltage applied to the cell 135.
If the lithium-ion cell 135 is nearly fully discharged to rated minimum discharge voltage when it is connected to the circuit of FIG.
1 at terminals Z1 and G1 for recharging, there is no immediate risk or applying too high a charging voltage (the fully discharged condition of cell 135 precludes too high an initial charge voltage rise); the immediate risk is that too high a charging current might be applied.
Accordingly, the linear current regulator subcircuit comprising charge control integrated circuit (IC) device 113 and resistor 119 ensures that charging current is kept within an acceptable range