Switching power supply

A switching power supply, comprising:

• a rectifying circuit for full-wave rectifying an ac input voltage to output pulsating current;
• a chopper circuit comprising a switching device driven with sufficiently higher frequency than that of said ac input voltage, an inductor connected in series with said switching device between output terminals of said rectifying circuit, and a capacitor for smoothing a current fed through said inductor to supply a stabilized dc output voltage;
• means for providing a threshold level signal having a full-wave rectified waveform, in which the phase thereof is the same as that of said ac input voltage, and an amplitude corresponding to an error voltage included in an output voltage of said chopper circuit;
• and
• means for controlling switching timing by repeating the operations of turning off said switching device when current therethrough reaches said threshold level signal and turning on said switching device upon completion of a turn off time,
• wherein a time period of said turn off time is shortened when a duration of the immediately preceding turn on time of said switching means becomes longer and lengthened when a duration of the immediately preceding turn on time of said switching means becomes shorter.

A switching power supply, comprising:

• a rectifying circuit for full-wave rectifying an ac input voltage to output pulsating current;
• a chopper circuit for switching said pulsating current from said rectifying circuit at a high frequency to provide a smoothed dc output voltage at the terminals of an output capacitor;
• a current detection circuit for detecting a switching current of said chopper circuit;
• an operational amplifier for detecting an error voltage of the output voltage of said chopper circuit against reference voltage;
• a multiplier for multiplying an output voltage error signal from said operational amplifier by an input voltage signal of said chopper circuit;
• and
• a switching control circuit for comparing a voltage signal output from said multiplier with a current signal output from said current detection circuit and repeating the operations of turning off said chopper circuit when the current through said switching device in said chopper circuit reaches said voltage signal level and turning on said chopper circuit upon completion of a turn off time,
• wherein a time period of said turn off time is shortened when a duration of the immediately preceding turn on time of said switching device becomes longer and is lengthened when a duration of the immediately preceding turn on time of said switching device becomes shorter.