High power-factor control circuit and power supply

A controller for controlling a switched mode power supply (SMPS) that is configured to receive a rectified periodic input voltage, the controller comprising:

• a first input terminal for receiving information about a current flow through a power switch in the SMPS;
• a second input terminal for receiving information about an output of the SMPS;
• and
• an output terminal for providing a control signal to the power switch of the SMPS for turning on/off of the power switch multiple times in a cycle of the rectified periodic input voltage;
• wherein the controller is configured to provide a constant power switch turn-on time in a given cycle of the rectified periodic input voltage, and the controller is configured to determine a maximum value of the envelope of peak currents through the power switch in the given cycle, the envelope of peak currents through the power switch being in phase with the rectified periodic input voltage;
• wherein the controller is configured to maintain a constant output of the SMPS by adjusting the power switch turn-on time for the next cycle of the rectified periodic input voltage based on comparison of a first reference signal with the determined maximum value of the envelope of peak currents through the power switch in the given cycle.