CONTROLLING A SWITCHED MODE POWER SUPPLY WITH MAXIMISED POWER EFFICIENCY

摘要

A control circuit (200) operable to generate a control signal (D) to control the duty cycle of a switched mode power supply (100). The control circuit (200) comprises a reference voltage generator (201) operable in a first mode to generate a predetermined reference signal (VRdes) and operable in a second mode to receive a signal indicative of an input voltage (Vin) of the switched mode power supply (100) and generate a variable reference signal (VRvar) dependent upon the input voltage (Vin), the reference voltage generator (201) being configured to operate in the first mode when the input voltage (Vin) exceeds a threshold value, and to operate in the second mode when the input voltage (Vin) is equal to or smaller than said threshold value. The control circuit (200) further comprises an error signal generator (202) operable to receive a signal indicative of an output voltage (Vout) of the switched mode power supply (100) and operable to generate an error signal (VE) based, on the reference signal (VR; VRvar, VRdes) generated by the reference voltage generator (201) and based on the output voltage (Vout). The control circuit (200) also includes a duty cycle control signal generator (204) operable to generate the control signal (D) to control the duty cycle of the switched mode power supply (100) in dependence upon the error signal (VE).