Patent ID: 7391631

Claim:
A switching power source device comprising: a rectifier connected to an AC power source; a series circuit connected between positive and negative terminals of said rectifier, said series circuit including a main winding of a boost reactor, a switching element and a current detector for detecting electric current flowing through said series circuit; a rectifying smoother connected between a junction of said main winding of the boost reactor and switching element and negative terminal of said rectifier; and a control circuit for controlling the on-off operation of said switching element in response to voltage induced on an auxiliary winding of the boost reactor to produce a DC output from said rectifying smoother; said control circuit comprising an error amplifier for producing an error voltage between DC voltage from the rectifying smoother and a first reference voltage from a first normal power supply; a multiplier for producing a product of the error voltage from the error amplifier and pulsating voltage generated at the positive terminal of the rectifier; a first comparator for comparing output from the multiplier with a value of electric current flowing through the switching element; and a changeover circuit for turning the switching element off upon receiving an output from the first comparator, and a drive controller connected between the error amplifier and changeover circuit, said drive controller comprising a sweep circuit for producing an increased or decreased voltage; a reset circuit for making the sweep circuit start sweeping the voltage upon producing a drive signal to the switching element; and a second comparator for comparing an output voltage from the error amplifier with the voltage from the sweep circuit and producing an output to changeover circuit to stop the on-operation of the switching element when the voltage exceeds the output voltage from the error amplifier; wherein said drive controller comprises a second normal power supply for producing a second reference voltage, and a level detector having a first input terminal connected to said second normal power supply and a secondinput terminal connected to the sweep circuit for producing the output when the voltage in said sweep circuit reaches the second reference voltage; and; said reset circuit resets the voltage in the sweep circuit in response to an output from said level detector.