Switching power-supply device

摘要

A resonant converter circuit generates an output voltage from an input voltage by switching first and second FETs. A subsequent-stage switching control circuit alternately subjects the first and second FETs in the resonant converter circuit to on/off control with a fixed on-duty ratio and a fixed switching frequency. A boost converter circuit includes an inductor, a smoothing capacitor, and a third FET arranged to switch the energization of the inductor. A previous-stage switching control circuit subjects the third FET in the boost converter circuit to on/off control with a controlled on-duty ratio, and adjusts an output voltage to the resonant converter circuit.

主权项

1. A switching power-supply device comprising:
a non-insulated converter arranged to boost an input power supply voltage, which is input to the non-insulated converter, and output a direct-current voltage; and an insulated bridge converter into which the direct-current voltage output from the non-insulated converter is input and that is arranged to output a direct-current voltage to a load; wherein the insulated bridge converter includes:
a transformer including a primary winding and a secondary winding;an alternating-current voltage generation circuit arranged to be connected to the primary winding, to include a first switch element and a second switch element, and to generate and apply to the primary winding an alternating-current voltage from the input direct-current voltage by switching the first switch element and the second switch element; anda rectifier circuit arranged to be connected to the secondary winding and to rectify and output to the load a voltage induced in the secondary winding by magnetic field coupling with the primary winding; the non-insulated converter includes:
an inductor;a capacitor; anda third switch element arranged to switch energization of the inductor; and the switching power-supply device further includes:
a switching control circuit arranged to alternately subject the first switch element and the second switch element to on/off control with a dead time sandwiched therebetween, using a fixed on-duty ratio and a fixed switching frequency; anda PWM control circuit arranged to subject the third switch element to on/off control, to control an on-duty ratio of the third switch element, and to adjust an output voltage to the insulated bridge converter; when the input power supply voltage is less than a threshold value, which is greater than a voltage at a time of a rated operation and less than a maximum value of an operation input voltage, the PWM control circuit and the switching control circuit performs the rated operation; when the input power supply voltage is equal to the threshold value or greater, the PWM control circuit stops switching control of the third switch element; and the switching control circuit controls at least one of an on-duty ration and a switching frequency of the first switch element and the second switch element.