Patent ID: 8213200

Claim:
A switching power supply apparatus comprising: a rectifier circuit conducting full-wave-rectification of an AC power supply voltage to obtain a pulsating output; a chopper circuit comprising an inductor, a capacitor, and a switching device, the inductor being connected to the rectifier circuit at a first end and the switching device at a second end, the capacitor smoothing a current fed from the inductor to obtain a DC output, the switching device switching on or off the current fed to the capacitor; an input voltage detector circuit detecting a voltage input to the chopper circuit and outputting an input voltage detection signal; an output voltage error detector circuit detecting an error between the input voltage detection signal and a set voltage, and outputting an output voltage error signal; a first threshold signal generator circuit generating a first threshold signal in-phase with the input voltage detection signal, the first threshold signal comprising a waveform corresponding to a waveform of the input voltage detection signal, and the first threshold signal having an amplitude proportional to the output voltage error signal; a second threshold signal generator circuit dividing a potential difference between the first threshold signal and a reference potential, and generating a second threshold signal; a current detector circuit detecting a current flowing through the inductor, and outputting a current detection signal; a switching control circuit comparing the current detection signal with the first threshold signal and the second threshold signal to turn off the switching device when the current detection signal is equal to or larger than the first threshold signal, and to turn on the switching device when the current detection signal is equal to or less than the second threshold signal; a switching frequency detector circuit detecting a switching frequency of the switching device, and outputting a frequency detection signal; and a frequency error detector circuit comparing the frequency detection signal with a reference frequency signal and outputting a frequency error signal, wherein the second threshold signal generator circuit changes a voltage dividing ratio of the second threshold signal to the first threshold signal based on the frequency error signal to set the frequency detection signal to be substantially constant.