Patent ID: 6100664
Filing Date: 2000-08-08
Classification: H02J,Y02B

Abstract:
A battery charger comprising:input terminals for a connection to a wall transformer power supply to receive a supply of current;output terminals for connection to a battery to be charged;a switch coupled to the input terminals that controls flow of current from the transformer either to the output terminals for charging the battery or to ground;a resistor connected in series with the switch and the input terminals;a diode connected between the input terminals and output terminals so as to permit current flow to the input terminals when the voltage at the input terminals is greater than the voltage at the output terminals;a controller coupled to the switch to control whether the switch is open or closed, coupled to the resistor to monitor current flow through the resistor and coupled to the output terminals to monitor voltage in the battery, the controller determining when there is sufficient residual charge in the battery to initiate a charging mode comprising oscillation between first and second intervals, during the first interval the controller closing the switch and creating a short-circuit current path through the switch wherein current flows through the switch and increases at a rate dependent on a secondary leakage inductance of the transformer until the current through the resistor reaches a first threshold, and during the second interval the controller opening the switch so that the current from the transformer flows through the diode into the battery and through the resistor and decreases at rate dependent on the secondary leakage inductance of the transformer until it reaches a second threshold which is less than the first threshold.