Method and apparatus for input charge control of a power supply

摘要

An example power supply includes an energy transfer element, a switch and a controller. The controller includes a logic circuit and a constant current control circuit. The logic circuit generates a drive signal to control the switch in response to a control signal. The constant current control circuit generates the control signal in response to a received input current sense signal, input voltage sense signal, and output voltage sense signal. An integrator included in the constant current control circuit integrates the input current sense signal to generate an integrated signal representative of a charge taken from the input voltage source. The constant current control circuit is adapted to generate the control signal to provide a constant current at the output of the power supply such that the integrated signal is proportional to a ratio of the output voltage sense signal to the input voltage sense signal.