Switching regulator provided with charge-discharge circuit having overcurrent protecting function and soft-start function

Claim 1

A switching regulator comprising: an oscillator circuit for chopping a DC voltage supplied from an input power source to thereby drive a transformer having at least a primary winding, secondary winding and at least one or more additional windings; a rectifier circuit for rectifying an AC output voltage derived from said transformer; an error amplifier circuit for comparing a DC output voltage derived from said rectifier circuit with a first reference voltage to thereby provide an output corresponding to the deviation of said DC output voltage from said first reference voltage; a charge-discharge circuit including a capacitor connected to one of said additional windings, said charge-discharge circuit being arranged so that said capacitor is charged with a voltage induced in said one additional winding in such a manner that the polarity of charges stored in said capacitor when the oscillation of said oscillator is in ON state, becomes opposite to the polarity of the charges stored in said capacitor when the oscillation is in OFF state, the discharge time constant of said charge-discharge circuit being variable with the output of said error amplifier circuit; and a control circuit adapted, when the oscillation is in ON state, for comparing the voltage across said capacitor with a second reference voltage and for applying to the base of a switching transistor a trigger signal for causing the oscillation operation to be switched from the ON state to the OFF state only when the voltage across the capacitor exceeds the second reference voltage.