Patent ID: 6954056

Claim:
A switching power supply unit comprising: a switching power supply section for converting an input voltage into a higher output voltage by switching in accordance with a switching control signal, to output the higher output voltage; a soft start section for producing a soft start voltage which gradually increases at start-up; a voltage comparing section for comparing the output voltage with a first reference voltage; a low-voltage circuit section, which compares the soft start voltage with a feedback voltage obtained by feeding back the output voltage, for producing a pulse signal when the soft start voltage is high; and a high-voltage circuit section, which compares either a second reference voltage or the soft start voltage with the feedback voltage according to a relationship of a level of the second reference voltage and a level of the soft start voltage to produce an error signal, for producing a PWM control signal based on a comparison result of the error signal with a triangular wave signal, wherein when the output voltage is lower than the first reference voltage, the pulse signal is output as the switching control signal, and when the output voltage is higher than the first reference voltage, the PWM control signal is output as the switching control signal.