Patent ID: 8310850

Claim:
A power supply controller, comprising: an input voltage sense input coupled to sense an input voltage sense signal representative of an input voltage of a power supply; an output voltage sense input coupled to sense an output voltage sense signal representative of an output voltage of the power supply; a current limit circuit coupled to generate a current limit signal, wherein the current limit signal is varied relative to a first ratio representative of a ratio of a product of the input voltage and a scaled output voltage of the power supply, to a sum of the input voltage and the scaled output voltage of the power supply, wherein the current limit signal is further varied relative to a second ratio representative of a ratio of the sum of the input voltage and the scaled output voltage of the power supply, to the product of the input voltage and the scaled output voltage of the power supply, wherein the second ratio is substantially equal to a reciprocal of the first ratio, wherein the current limit circuit includes a first variable resistance coupled in parallel with a second variable resistance, wherein the first variable resistance is coupled to be responsive to the input voltage and wherein the second variable resistance is coupled to be responsive to the output voltage; and a drive signal generator coupled to generate a drive signal in response to the current limit signal to drive a power switch of the power supply to limit an output power of the power supply in response to the input voltage.