| 摘要 |
<p>According to one embodiment, there is provided a switching power-supply device including a switching element (Q1), a constant current element (Q2), a rectifying element (D1), first and second inductors (L1 and L2), and constant voltage circuits (V1 to V5). The switching element (Q1) supplies, when the switching element (Q1) is on, a power-supply voltage of a direct-current power supply to and feeds an electric current to the first inductor (L1). The constant current element (Q2) is connected to the switching element (Q1) in series and turns off the switching element (Q1) when the electric current of the switching element (Q1) exceeds a predetermined current value. The rectifying element (D1) is connected to any one of the switching element (Q1) and the constant current element (Q2) in series and feeds the electric current of the first inductor (L1) when the switching element (Q1) is turned off. The second inductor (L2) is magnetically coupled to the first inductor (L1) and supplies induced potential to a control terminal of the switching element (Q1). The constant voltage circuits (V1 to V5) apply control potential to a control terminal of the constant current element (Q2).</p> |
