Patent ID: 7180277

Claim:
A circuit for coupling an energy storage device to an output of a first power supply, the circuit comprising: a current-sensing resistor; a switch comprising a pair of outputs coupled in series with the energy storage device and with the current-sensing resistor, and an input receiving a switching signal, the switch assuming a conducting state when the switching signal is at a first level, the switch assuming a non-conducting state when the switching signal is at a second level; a differential high-gain device comprising an output coupled to the input of the switch, a first input biased by a control voltage, and a second input receiving feedback voltage generated by a charging current flowing through the current-sensing resistor; wherein: the output of the differential high-gain device drives the input of the switch with the switching signal at the first level when the control voltage exceeds the feedback voltage by an input offset voltage of the differential high-gain device, and the differential high-gain device drives the input of the switch with the switching signal at the second level when the feedback voltage exceeds the control voltage by the input offset voltage; and the current-sensing resistor, the switch, and the energy storage device are coupled across the output of the first power supply.