Patent ID: 8400120

Claim:
A switching power supply unit comprising: a power converter circuit including a main switching element which is turned on and off; and a control circuit which regulates an output voltage by controlling turning on and off operation of the main switching element, wherein: the control circuit includes calculation means which determines an ON duration and an OFF duration of the main switching element and drive pulse generation means which generates drive pulses with which the main switching element is turned on and off; a control function formula is defined in the calculation means, the control function formula being a continuous function formula which includes, as parameters, an output voltage and an output differential value representing a fluctuation in the output voltage, and has only a single output differential value corresponding to a certain value of the output voltage, the control function formula providing that a corresponding output differential value is positive when an output voltage is below a target value for a regulation of the output voltage, that a corresponding output differential value is negative when an output voltage is above the target value and that a corresponding output differential value is zero when an output voltage is equal to the target value; the calculation means samples an input voltage signal of which input voltage has been detected, an output voltage signal of which output voltage has been detected or estimated and an output differential signal of which a fluctuation in an output voltage has been detected or estimated, at time instants in synchronization with a cycle of switching of the main switching element, performs a predetermined calculation based on the sampled three signals and calculates at least one of the ON and OFF durations of the main switching element in a cycle of switching after the time instant for sampling and, in the ON and OFF durations, an output voltage and an output differential value at the next or after the next time instant for sampling satisfy a relationship provided by the control function formula; and the drive pulse generation means generates the drive pulses such that the main switching element might be turned on and off in a cycle of switching after the time instant for sampling of the three signals based on the ON and OFF durations determined by the calculation means.