Switched-mode power supply control circuit

摘要

A controller for a switch mode power supply includes an undervoltage protection circuit responsive to an input supply voltage indicative signal. The input supply voltage indicative signal is also coupled to a foldback point correction circuit. The correction circuit causes a decrease in a maximum duty cycle of a control signal when the input supply voltage increases and is still smaller than a predetermined magnitude. A zener diode limits the input supply voltage indicative signal in a manner to prevent a further decrease in the duty cycle when the input supply voltage exceeds the predetermined magnitude.