Patent ID: 8716996

Claim:
A switching control circuit for use in an AC/DC converter that includes a switching device, a noise filter, and a rectifying circuit which rectifies an AC input obtained from an AC source via the noise filter to obtain a rectified input voltage, the switching control circuit comprising: a brownout detector for detecting a brownout state when a maximum instantaneous value of the rectified input voltage has remained below a brownout level longer than a predetermined time period, the brownout detector including a first comparator that receives a first reference voltage and a timer for monitoring whether the maximum instantaneous value of the rectified input voltage has remained below the brownout level longer than the predetermined time period, the timer having an input terminal that receives an output signal from the comparator; and an improper brown-in operation preventing means for monitoring the rectified input voltage with a second comparator that receives a second reference voltage, and for stopping switching operation of the switching device, after the maximum instantaneous value of the rectified input voltage has remained below the brownout level longer than the predetermined period, when a phase angle of the AC input is in a low range, wherein the first reference voltage corresponds to the brownout level.