| 主权项 |
1. A controller detecting input power and generating a protection signal for a power converter to alarm a load, comprising:
a high voltage start-up pin for connecting with an output terminal of an external start-up circuit, wherein said external start-up circuit has two input terminals coupled to an AC power; a sample-and-hold circuit for periodically sampling a voltage signal at said high voltage start-up pin to generate a detected signal, wherein the detected signal has an envelope proportional to an envelope of a full-wave rectified voltage of the AC power; a brownout detector for generating a first power-fault signal according to said detected signal, wherein said first power-fault signal will be active when said detected signal is below a first threshold voltage for a first time duration, said first time duration being longer than half of a period of said AC power, wherein said brownout detector comprises a comparator having a positive input end, a negative input end, and an output end, said positive input end being coupled with a first threshold voltage, and said negative input end being coupled with said detected signal; and a counter having an input end coupled with said output end of said comparator, and an output end providing said first power-fault signal, wherein said counter will count up when said output end of said comparator is at a high level, and will be reset to an initial state when said output end of said comparator is at a low level, and said first power-fault signal will be active when said counter counts up to a first predetermined number, which is corresponding to said first time duration; an AC-off detector for generating a second power-fault signal according to said detected signal, wherein said second power-fault signal will be active when said detected signal is above a second threshold voltage for a second time duration, said second time duration being longer than half of said period of said AC power; an OR gate having a first input end coupled with said first power-fault signal, a second input end coupled with said second power-fault signal, and an output end providing a third power-fault signal; and a driver, which has an input end coupled with said third power-fault signal, and an output end providing a power-fault driving signal for driving an external photo coupler circuit to generate a power-fault signal. |
