| 摘要 |
<p>A controller for a switch mode power supply includes an undervoltage protection circuit (106a) responsive to an input supply voltage indicative signal (VZ1). The input supply voltage indicative signal is also coupled to a foldback point correction circuit (106b). The correction circuit causes a decrease in a maximum duty cycle of a control signal (VOUT) when the input supply voltage increases and is still smaller than a predetermined magnitude. A zener diode (Z1) 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.</p> |
